Department of Mechanical Engineering

Transcription

1 Department of Mechanical Engineering I/ II SEMESTER 10MEL48B MACHINE SHOP Workshop Practice Lab (15WSL16 / 26) Laboratory Manual NAME OF THE STUDENT : BRANCH : UNIVERSITY SEAT NO. : SEMESTER & SECTION : BATCH : Academic year:

2 INDEX S L. NO WORKSHOP PARACTICE LAB PAGE NO. FROM TO VTU SYLLABUS 3 3 About Safety precautions 4 4 Introduction to fitting 5 5 About Engineering material 6 6 About Fitting tools 7 18 About Fitting operations Rectangular model Rectangular model Triangular model Introduction to Welding Lap- Joint Butt -Joint T- Joint L- Joint PART A: FITTING PRACTICE I. II. III. IV. V. VI. 4. Triangular model 5. Semicircular model 6. Semicircular model 7. Dove-tail mode 8. Dove-tail mode 9. Model for practice PART B: Welding Practice I PART C : Sheet Metal Fabrication I Introduction to sheet metal fabrication 14 Rectangular Tray Cylinder Pentagon cylinder 17 Hexagon cylinder Frustum of a cone

3 I-VTU SYLLABUS WORKSHOP PRACTICE (CBCS) Sub Code Hrs/ Week Total Hrs. : 15WSL16/26 : : IA Marks Exam Hours Exam Marks : 20 : : Fitting: a. Study of fitting tools b. Study of fitting operations & joints c. Minimum 5 models involving rectangular, triangular, semi circular and dovetail joints. 2. Welding: d. Study of electric arc welding tools & equipments e. Minimum 4 Models- electric arc welding-butt joint, Lap joint, T-joint & L-joint. 3. Study and demonstration of Sheet metal and soldering work. 4. Study & demonstration of power Tools in Mechanical Engineering Scheme of Examination: Fitting / Sheet metal Welding Viva Voce Total 3 30 Marks 10 Marks 10 Marks Marks

4 II- ABOUT SAFETY PRECAUTIONS DO S & DONT S 1. Wear shoes to protect your feet. 2. Do not wear wrist watch while working. 3. Beware of the live electrical wires don t attempt or try to touch them. 4. Use hand glows / Welding shield. 5. Handle the tools / machines as per the instruction given by the Faculty. 6. Use proper/ right tools. 7. Keep the tools in the right place else that may hurt you. 8. Use fire extinguisher to put off the flame. 9. Do not touch or pour water on burning live electric wire. 10. Use first aid box or inform the faculty for need of medical assistance. *Strictly follow the above instructions. 4

5 III- INTRODUCTION TO FITTING Even in the most mechanized industry, although majority of the work can be finished with the help of machines, there are certain operations, which have to be carried out manually using hand tools. For example, i) In production shops, when two or more parts are to be assembled ii) Sometimes it necessary to replace or repair a component, which must fit accurately with another component on re-assembly. Ex-Fitting FITTING Fitting is the process of assembling two or more metal parts together by removing excess material so as to obtain a required fit. OR It is the process of removing unwanted material with the help of hand tools/ power tools, from a given stock (work piece) for making a component or fitting one in the other to form a matting or fitting pair. Ex:- 1) key and key hole 2) A Bush and a shaft. Fitting requires the use of various hand tools and considerable manual effort. Fitting work involves a large number of hand operations to finish the work to desired shape, size and accuracy. The hand operations in Fitting shop include 1. Marking. 2. Sawing. 3. Chipping. 4. Filing. 5. Scraping. 6. Drilling. 7. Tapping. 8. Dieing. 9. Fitting etc. 5

6 IV-About Engineering Materials Materials that are used in the engineering Practice are called Engineering Materials. These have physical, mechanical and chemical properties. Classification of Engineering Materials Metals Ferrous Metals Iron Non-Metals Non-Ferrous Metals Steel Metals A metal is a solid (Exception: Mercury) having weight. It is opaque and a good conductor of heat and electricity. Non-Metals These are available in the form of liquids, gases or solids such as wood, stone, Rubber, plastic, ceramic, concrete, asbestos etc. Ferrous Metals Iron containing metals such as pig iron, cast iron, wrought iron, carbon steel, Alloy steel, Nickel steel etc., are called ferrous metals. These can be attracted by magnets and are susceptable to rusting. Non-Ferrous Metals Non-Ferrous metals are those, which do not contain iron. Metals like Gold, Silver, Copper, Aluminium, Tin, Platinum, and Nickel, Bronze etc, and its alloys are Non-Ferrous metals. These can neither rust nor can be attracted by magnets. Cast iron It is an Iron based material containing 91-94% iron and other elements such as Carbon (2-4%), Silicon ( %), Manganese ( %), Sulfur (0.2%max) and Phosphorous (0.6%max). Types of Cast iron: - Gray cast iron, malleable iron, white cast iron. Steel: May be defined as an alloy of iron and carbon. Besides this, it also contains Silicon, Manganese, Sulfur and Phosphorous.One of the differences between Cast iron and steel is the amount of carbon percentage.based on the carbon content, steel is divided into a) Low Carbon Steels- the carbon content ranges from %. Low carbon steels are also called as soft or Mild steel (M.S). b) Medium Carbon Steels-the carbon content ranges from %. c) High Carbon Steels-The carbon content ranges from % Mild steel (MS) Mild steel may be defined as an alloy of iron (91-94%), and carbon ( %). Besides this, it also contains Silicon, Manganese, Sulfur and Phosphorous. Low carbon steels are also called as soft or mild steel. These steels are used for bolts and nuts, structural work, axles, shafts etc Alloy Steel In alloy steel in addition to carbon and iron, alloying elements such as chromium, Nickel, Vanadium etc. are mixed. Ex: - Stainless steel, High Speed steel (H.S.S) (Tool steel). Tool steel is widely used in the manufacturing of cutting tools. 6

7 V- FITTING TOOLS The Tools used in Fitting practice may be classified into the following categories. a) Holding Tools b) Marking and Measuring Tools c) Cutting tools d) Finishing Tools e) Striking Tools f) Miscellaneous Tools Holding Tools Vice: A Vice is a tool used to hold the wok piece (job) in position while various operations are being carried out. 1) Bench vice 2) Machine vice 3) Leg vice 4) pipe vice and 5) Hand vice Bench vice The vice used for bench work is called bench vice. The bench work includes filing, sawing, and threading operations. It consists of a cast iron body carrying a fixed jaw and movable jaw. Both the jaws are made of cast steel and are brought together by means of hand operated Screw.Seperate cast steel plates known as jaw plates are fixed to the jaws my means of set screws which can be replaced when worn out. The face of the jaw plates have teeth (serrations), which helps in gripping the work firmly. Specification: - the width of the jaws determines the size of the vice. Machine vice Machine vice is used to hold work piece in Machine tools. Machine vice is able to tilt and swivel. It is mounted on the table of a Machine. Ex:-Drilling Machine, Milling Machine and Shaping Machine. Leg vice or Black smith s vice It is used for holding work piece that has to be cut, chipped or hammered. It consists of a fixed jaw with long leg and movable jaw that can be moved by means of a hand operated screw. Pipe vice It is used for holding round section parts such as pipes, tubes. Hand vice It is used for carrying work on small jobs, such as screws, keys, rivets etc., which cannot be held in the Bench vice. It consists of two jaws that can be operated by means of a wing nut. V-block with Clamp V-block is a rectangular or square block with v-groves on one or both the sides, opposite to each other. The angle V is usually 90 degrees. V-blocks are used for checking the roundness of cylindrical work piece and for marking centers accurately. Material- Hardened Steel or Cast Iron. 7

8 Marking and Measuring tools Surface plate Surface plate is a plain surface. The surface is machined to very fine limits. The plate is constructed in such a way that it will not wrap or twist. It is used for testing the flatness of finished work piece. Providing a base support for marking gauges or scribing block. Testing the accuracy of Try square. Material- Cast iron or hardened steel or granite stone. Specification: - It is specified by length x width x height x grade. Angle plate It consists of two faces machined at right angles (90 degrees) to each other. A number of slots are cut on both the horizontal and vertical faces as shown in figure. These slots enable the work piece to be held firmly by means of bolts and nuts. It is also used to support work piece, when you are using the surface gauge for marking out. Material- Gray Cast iron Scribing block or Surface gauge A scribing block has three parts-base, spindle and scriber. The base of the scribing block is machined to have a flat surface. A Vertical spindle fitted on the base carries a scriber and 8

9 by adjusting the screw, the scriber can be fixed to any inclination and height along the spindle. It is used for scribing lines on work pieces and also used for checking parallel surfaces. The Scribing block can be used to locate accurately the centers of round bars in conjunction with the Vee-block. Specification- Height of the Vertical spindle Scriber A Scriber is a thin steel rod with a pointed end or ends, one of the ends may be bent at right angles to allow access to holes. It is used to scribe (or) mark lines on the metal work pieces. Scribers are available in several sizes and types. The point should be ground to a 30 degrees angle and kept sharp for accuracy. Material- High carbon steel (Hardened &Tempered). Specification-It is specified by its length and diameter. Try Square or Engineers Square Try square also called Engineering Square is one of the basic tool used in fitting work. It consists of a steel blade riveted exactly at 90 degrees into a hard steel stock of rectangular cross section as shown in figure. The stock acts as a fence and the blade as guide for marking. It is used for 1) Checking squareness or perpendicularity of work piece. 2) Testing for Straightness and 3) Marking straight lines (at right angles) on work piece. Material-Steel (hardened and tempered). Specification-the Size of Try-square is specified by the length of the blade (100mm, 150mm, and 200mm). 9

10 Steel rule or Steel scale It is used for measuring and marking the required dimensions on the work piece. The scale is graduated in millimeters, centimeters and inches. Least count of normal steel rule is1mm. Spring Divider It is used for scribing (marking) circles, arcs, bisecting lines and perpendicular lines on metal work piece. It also used for transferring dimensions from scales to objects. Material- Tool steel (Hardened &Tempered). Specification-Max length /radius which can be scribed Spring caliper: Caliper are devices used for measuring and transferring the inside \outside dimensions of components. Calipers are of two types, viz, outside spring caliper and inside spring caliper. Material- Tool steel 10

11 Outside spring caliper-it is used for measuring the outer diameter of shafts (rods) and thickness of parts. Inside spring caliper- It is used to measure the inner diameter/dimensions of parts. Center Punch It is used for marking round indentations on metal surfaces. This provides a center for locating the sharp end of the divider point and center for holes that are to be drilled. It is also used for marking points along a line, which enables to cut the work piece easily. The point angle should be ground to 90 degrees Material- High carbon steel. Specification-By length and angle. Dot punch ` It is used for marking points along a line which enables to cut the work piece easily. The point angle should be ground to 60 degrees Letter punch It has square body with a tapered end. At this end, a projection, corresponding to the replica of the letter to be marked is made. It is used to punch Alphabetic letters (A to Z) on metal work piece 11

12 Number punch It is similar to letters punch in construction but has numbers at its end. The numbers used are from 0 to 8 (six used as nine also). It is used to punch numbers on metal work piece. Vernier caliper These are used for measuring outside as well as inside dimensions accurately. It may also be used as a depth gauge. Example: to measure outer diameter of shafts and cylinders, to measure inner diameter of holes and depth of holes. The main scale is divided into millimeters. In this case 49 main scale divisions ie 49 mm is divided into 50 vernier scale divisions. One vernier scale division equal to (49/50) 0.98 mm Hence, Least count of the vernier caliper (LC) = 1 main scale division 1 vernier scale division = 1MSD - 1 VSD = 1mm- (49/50) mm =0.02 mm Total reading =Main scale reading (MSR) + Least count (LC) X Vernier Coinciding Division Vernier height Gauge The vernier height gauge, clamped with a scriber, is shown in Fig.Vernier height gauges are particularly suitable for marking off accurate distances and center locations. It is also used in inspection of work pieces. The accuracy and working principle of this gauge are the same as those of the vernier caliper. 12

13 Vernier Height Gauge Micrometer: External micrometer is used to measure external diameters and lengths. The degree of accuracy is high. Pitch = distance moved on barrel No. of rotations given to thimble = 0.5 mm 1 = 0.5 mm Least count of micrometer = pitch/ No of divisions on the thimble. = 0.5 mm / 50 = 0.01 mm. Total reading =Barrel scale reading (MSR) + Least count X Thimble scale reading (TSR) MICRO METER Cutting tools Hack saw frame with blade. 13

14 The hacksaw is used for cutting metal by hand. The hacksaw blade has a number of teeth ranging from 5 to 15 per centimeter. Lesser number of teeth is used for cutting materials like Aluminium, brass and Bronze and large number of teeth is used for cutting hard materials like steel, C.I etc. Hack saw blades are fitted either in a solid frame or adjustable frame to accommodate different lengths of blade. It is made of high-speed steel. The hacksaw blades are specified byits material, length, width, thickness and pitch of the teeth. The common dimensions are length mm, width 13 mm-16 mm, thickness 0.6 to 0.8 mm, pitch 1 to 1.8 mm. The blades are fixed with teeth facing forward and the teeth are staggered, which are known as set of teeth. These make slots wider than blade thickness, preventing the blade from jamming Twist drill The twist drills are used for making holes. The drills are made of HSS (high speed steel) with a straight or taper shank. The straight shank drills are held in drill chuck and fitted to the spindle of drilling machine and the taper shank is directly fitted to the spindle. The drills are manufactured to standard sizes in specified steps. A bench-drilling machine is commonly used in workshops Twist drill. 14

15 Taps and Tap wrenches A tap is a hardened steel tool, used for cutting internal threads in a drilled hole. Hand taps are usually supplied in sets of three for each diameter and thread size. Each set consists of a i) Taper or first tap ii) Intermediate or second tap and iii) plug or bottoming or third tap. In hand tapping, the tap is rotated with the help of a tap wrench. These taps are identical in all features except in the taper lead. For identifying the type taps quickly the taps are either numbered as 1, 2, and 3 or rings are marked on the shank. Dies and die holder Dies are the cutting tools used for marking external threads. Dies are made either solid or split type. They are fixed in a die holder for holding an adjusting the die gap. They are made of tool steel or high carbon steel. Finishing tools Files A file is a cutting tool used to remove small amount of material from the surface of the work piece and also helps in giving a smooth surface finish. A number of teeth, parallel and 15

16 inclined at suitable angle are cut on the flat surface of the file. The various parts of a file are shown in figure the main parts of the file include, Tang-It is the pointed part that fits into the wooden handle. Heel It is end of the tang that forms a curved edge. Face -It is the portion of the file on which cutting teeth are formed. Point It is the end opposite the tang Files are often tapered along their length but they may also be parallel. Material -tool steel (hardened) Specification- length, single cut /double cut, shape and pitch. Example Length (say 400 mm) Single cut /Double cut Shape (say square cross section) Pitch or grade (say smooth) Files are classified and named according to a) Size/length b) cut c) shape and d) pitch /grade. (a) Size: the size of the file is identified by its length. It is the distance from the point to the heel excluding tang. The selection of the length of the file varies depending on the size of the job. Sl.no Size(length) mm mm mm Application Used for fine work and small sized jobs Used for medium sized work For general and large sized work (b) Cut: Based on the cutting teeth, files are classified as single cut files and double cut files Single cut file Double cut file Single cut file: In single cut file, the teeth are cut in parallel rows across the faces of the file and normally inclined at an angle of 60 degrees with the centerline of the face. Double cut file: A double cut file has two sets of teeth crossing each other as shown fig. one set of teeth are cut similar to a single cut file and the other set runs diagonally across the first set and are normally inclined at an angle of 10 degree to the center line of the face. 16

17 Single cut files gives better finish when compared to double cut files but at the same time removes material at a comparatively slower rate. (C)Shape of files -Files is classified based on the shape of their cross-section. Various types of files. Flat files are used for general work or finishing flat surfaces. 1) Squares files are used for filing square corners, rectangular slots, keyways, enlarging a square or a rectangular holes etc. 2) Triangular file or three-square files are used mainly for filing corners with angles less than 90 degrees. 3) Round files are used for filing concave surface and also for enlarging round holes. 4) Half-round file the curved face of the half-round file is used for filing concave surfaces and the flat face is used for filing convex surfaces. 5) Knife edge file is used for filing narrow slots and corners having angles less than 90 degrees (D) Pitch of teeth /grade Pitch refers to the spacing between two consecutive teeth. Table shows the classification of files based on their pitch. The files are listed in descending order of their roughness. Description Rough. 8 teeth/cm Single cut Double cut Bastard 12 teeth/cm Second cut. 16 teeth/cm Uses For rapid removal of Large amounts of material from softer materials. Rapid removal of Small amounts of material. Used for filing on harder materials. Gives good surface finish 17

18 Smooth teeth/cm Used for smooth surface finish. Removes small amounts of material. Dead Smooth. >40 teeth/cm Used for accurate and smooth surface finish. Striking Tools Hammers: The hammer is defined as a device used to deliver blows to an object or strike another object, in the sense that it is used for driving nails, fitting parts and breaking up objects. It is also used for striking purposes while punching, bending, chipping, and riveting. Available in various shapes and structures, hammers are designed for specific purpose. The hammer consists of a handle to which a heavy head, usually made of metal is attached, with one or more striking surfaces. The hammer is specified by its weight (125 grams to 1500 grams) and the shape of the pein. Different types of hammers are straight pein hammer, ball pein hammer, cross pein hammer Material Cast steel or carbon steel. Ball pein hammer:-this is the most common type of hammer which has a ball-shaped end of the head opposite to the striking face. It is used for all kinds of engineering works. The ball end being useful for sheet metal forming and it is made in weights from 1000gm to 1.5kg. It is used for riveting and chipping. Cross pein and straight pein hammer:-these have blunt, chisel-shaped ends on the head opposite to the face. It is used for bending, stretching, hammering into shoulders, curves. Miscellaneous Tools Anvil : It provides the necessary support during punching and chipping by resisting the heavy blows given to the work piece by hammer.the beak is used in sheet metal work for bending the sheet metal to round shapes. Material-The body is made of mild steel or cast steel with a hardened top face. 18

19 File card: It is a metal brush used for cleaning the files. FITTING OPERATIONS Marking and Measuring The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. Generally one end of work piece is filed flat and the measurements are taken from this reference end. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot puntch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts; clean the face of cuts and to give the final shape to a work piece. The flatness and square ness of the surfaces finished by filing are checked with try square. Methods of filing- a) Cross-filing b) Draw filing Cross-filing- this method is used for efficient removal of maximum amount of metal in the shortest possible time. It may be noted that the file must remain horizontal throughout the stroke (long, slow and steady) with pressure only applied on the forward motion. Draw filing-this method is used to remove file marks and for finishing operations. Here, the file is Griped as close to the work as possible between two hands. In this method of filing, a fine cut file with a flat face should be used. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. The surfaces are to be finish filed after sawing Chipping-It is the process of removing unnecessary thick layers of metal using cold chisel and hammer. 19

20 Drilling It is the operation of producing circular holes in a metal piece with the help of bench drilling machine and drilling tools. Tapping- It is the process of generating internal threads in a ready hole using a set of three hand taps. Dieing-It is a manual operation of generating external threads on a round rod or pipe using a die and die holder. Fitting /Assembly: After finishing the individual pieces as per dimensions they are joined /fitted for an assembly. Safe and correct practices: 1) All the tools and measuring instruments are to be cleaned and kept in the respective places when not in use. 2) The sliding parts and pins are to be properly lubricated. 3) The vice should not be over tightened; otherwise it may damage the spindle. 4) The sharp edges of a chisel or scriber are to be covered with a cap to avoid getting damaged and to prevent accidents. 5) The handles of hammers are to be checked for cracks etc. 6) The surface plate has to be covered and kept when not in use and tools and jobs should not be thrown on the surface plate to avoid damage to the surfaces 20

21 21

22 Use of Different Types of Files 22

23 . How to hold the Hacksaw 23

24 Date: Model No: 1./ /. Rectangular model-1 AIM: To fabricate the fitting model as per the drawing given below. 17, MATERIAL: Mild Steel ( L x B x t ) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular rough file. Rectangular smooth file. L- Square. Theory : The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 24

25 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of X mm in L1, Y mm in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. 25

26 Post Viva question: 1) What do you mean by fitting? (or) Define fitting? Give practical example. Fitting is the process of assembling two or more metal parts together by removing excess material so as to obtain a required fit. Ex: - 1) key and key hole 2) A Bush and a shaft 2) Name the tools, which are used in fitting? a) Work holding tools b) Marking and Measuring tools c) Finishing and cutting tools 3) Name work holding devices used in Fitting. (or) What are the types of vices? a) Bench vice b) Machine vice c) leg vice d) pipe vice e) hand vice 4) Name Marking and measuring tools used in Fitting a) Surface plate b) Angle plate c) Scribing block/surface gauge d) Scriber e) Try square f) Divider g) Center punch h) Steel rule or Scale i) caliper (Inside caliper and Outside caliper) 5) What is the purpose of Marking? a) To Transfer measurements and Dimensions from drawing to workpice for further operations. b) To obtain shape on work piece to the design given in the drawing. c) To check Dimensional suitability of raw material for a given Job. 6) What are the tools required for Marking.(or) Name Marking tools used in Fitting a) Surface plate b) Angle plate c) V block d) Divider e) Scriber f) Punches g) Marking Hammer h) Try Square i) Steel Rule j) Scribing Block or Surface gauge 7) What is meant by Measurement? Determining the Size of a job in terms of Standard unit is called measurement. 8) Name measuring tools used in Fitting. a) Steel rule b) Vernier Caliper c) Micrometer d) Depth gauge e) caliper (Inside caliper and Outside caliper) 9) Name Finishing and cutting tools used in Fitting. a) Files b) Hack saw c) Chisel 10) What is the classification of materials? Metals and Non-Metals. 26

27 Date: / /. Model No: 2 Rectangular model-2 AIM: To fabricate the fitting model as per the drawing given below , MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular rough file. Rectangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 27

28 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. 8. Then male and female work pieces are assembled (joined) in order to make firm joint. Pre Viva Questions: 1. What is the difference between Metal and Non metal give example? 2. What is the difference between ferrous and nonferrous metal. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. Post Viva question: 28 X mm in L1, Y mm

29 1) What is the classification of metals? a) Ferrous metals b) non-ferrous metals. 2) Differentiate between the ferrous and non-ferrous metals. Ferrous Metals: Iron containing metals such as pig iron, cast iron, wrought iron, Mild Steel, carbon steel, Alloy steel, Nickel steel etc., are called ferrous metals. These can be attracted by magnets and are susceptible to rusting. Non-Ferrous Metals: Non-Ferrous metals are those which do not contain iron. Metals like Gold, Silver, Copper, Aluminum, Tin, Platinum, and Nickel, Bronze etc, and its alloys are Non-Ferrous metals. These can neither rust nor can be attracted by magnets. 3) What s the composition of CI Material? CI-Cast Iron a) Iron (91-94%), Carbon (2-4%), Silicon ( %), Less percentage of, Manganese, Sulfur and phosphorous 4) What s the composition of MS Material? 5) What is the classification of steels based on carbon content? Based on the carbon content, steel is divided into a) Low Carbon Steels- The carbon content ranges from %. -Mild steel (MS) b) Medium Carbon Steels-the carbon content a range from c) High Carbon Steels-The carbon content ranges from % 6) Name the commonly used material for preparing fitting models. Mild Steel (MS). 7) What is the use of Alloy steels? In alloy steel in addition to carbon and iron, alloying elements such as chromium, Nickel etc. are mixed. Ex: - Stainless steel, High speed steel, Tool steel (0.8 to 1.5% carbon).etc. Alloy steels are widely used in the manufacturing of Cutting tools. 8) Name the parts of the bench vice? a) Body with Fixed Jaw b) Movable jaw c) Jaw Plate d) Screw spindle e) Handle f) Base 9) How will you specify a bench vice? Width of the jaws determines the size of the vice 10) Which material is used to make the vices? Cast iron Date :./../.. Model No: 3 29

30 Triangular model-1 17, ,5 AIM: To fabricate the fitting model as per the drawing given below. 15 MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular and triangular rough file. Rectangular and triangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 30

31 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of X mm in L1, Y mm in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. Post Viva question: 31

32 1) What do you mean by leg vice? It is used for holding work piece that has to be cut, chipped or hammered 2) What is the use of Pipe vice? It is used for holding round section parts such as pipes, tubes. 3) Why is it named as V-block? V-block is a rectangular or square block with V-groves on one or both the sides, opposite to each other. The angle V is usually 90 degrees. 4) What is the use of V-block? V-blocks are used for checking the roundness of cylindrical work pieces and for marking centers accurately. 5) What is a surface plate? Why it is used? Surface plate:-surface plate is a plain surface. It is used for testing the flatness of finished work piece. Providing a base support for marking gauges or scribing block. Testing the accuracy of Try square. Material- Cast iron or hardened steel or granite stone. Specification: - It is specified by length x width x height x grade. 6) What is the use of try square? It is used for 1) checking squareness or perpendicularity of work piece.2) Testing for Straightness and 3) marking straight lines (at right angles) on work piece. 7) How will you specify a try square? The Size of Try-square is specified by the length of the blade (100mm, 150mm, and 200mm). 8) Define least count? A smallest measurement that can be obtained from measuring instrument. Or. A smallest measurement that can be measured by using measuring instrument. 9) What is the use of Vernier caliper? It is used for measuring outside as well as inside dimensions accurately. It may also be used as a depth gauge (to measure depth of holes). Hence, Least count of the vernier = 1 main scale division 1 vernier scale division. 10) What is the use of micrometer? Micro meter: External micrometer is used to measure external diameters and lengths. The degree of accuracy is high. Date : /../. Model No: 4 32

33 Triangular model-2 AIM: To fabricate the fitting model as per the drawing given below. 17, , MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular and triangular rough file. Rectangular and triangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 33

34 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. 8. Then male and female work pieces are assembled (joined) in order to make firm joint. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. 34 X mm in L1, Y mm

35 Post Viva question: 1) What is the use of steel rule? It is used for measuring and marking the required dimensions on the work piece. 2) What are the types of spring calipers? a) Outside spring caliper b) inside spring caliper 3) What is the use of outside spring caliper? It is used for measuring the outer diameter of shafts (rods) and thickness of parts. 4) What is the use of inside spring caliper? It is used to measure the inner diameter/dimensions of parts 5) What is the use of angle plate? It consists of two faces machined at right angles (90 degrees) to each other. A number of slots are cut on both the horizontal and vertical faces as shown in figure. These slots enable the work piece to be held firmly by means of bolts and nuts. It is also used to support work piece, when you are using the surface gauge for marking out. 6) What is the use of Dot punch? It is used for marking points along a line which enables to cut the work piece easily. 7) What is the point angle of Dot punch? 60 degrees Material- High carbon steel. Specification-By length and angle. 8) What is the use of center punch? 1) It is used for marking round indentations on metal surfaces. 2) This provides a center for locating the sharp end of the divider point and center for holes that are to be drilled. 3) It is also used for marking points along a line which enables to cut the work piece easily. 9) What is the point angle of Center punch? 90 degrees 10) What is the use of number punch? It is used to punch numbers (0 to9) on Metal work piece. Model No: 5 /./. Date Semicircular model :

36 AIM: To fabricate the fitting model as per the sketch given below R MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular rough file. Rectangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 36

37 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of X mm in L1, Y mm in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. Post Viva question: 1) What is the use of letter punch? 37

38 It is used to punch Alphabetic letters (A to Z) on Metal work piece. 2) What is the use of Universal Scribing block or surface gauge? It is used for scribing lines on work pieces and also used for checking parallel surfaces. The Scribing block can be used to locate accurately the centers of round bars in conjunction with the Vee-block 3) What is the use of scriber? It is used to scribe (or) mark lines on the metal work pieces. 4) What is the use of spring divider? It is used for scribing (marking) circles, arcs, bisecting lines and perpendicular lines on metal work pieces It also used for transferring dimensions from scales to objects. 5) What is the difference between divider and Caliper? A divider is a marking device used to mark dimensions, But a caliper is a measuring device used to measure dimensions. 6) Name finishing tools used in Fitting. a) Files b) Sand Paper 7) What is a file? A file is a cutting tool used to remove small amount of material from the surface of the work piece and also helps in giving a smooth surface finish 8) Name the parts of the files? Tang-It is the pointed part that fits into the wooden handle. Heel It is end of the tang that forms a curved edge. Face -It is the portion of the file on which cutting teeth are formed. Point It is the end opposite the tang 9) Classification of files. Files are classified according to a) Size or length b) Shape c) Grade d) Cut 10) Name the different types of files and their uses? Round files are used for filing concave surface and also for enlarging round holes. Half-round file the curved face of the half-round file is used for filing concave surfaces and the flat face is used for filing convex surfaces. Knife edge file is used for filing narrow slots and corners having angles less than 90 degrees Date :./ / Model No: 6 38

39 Semicircular model -2 AIM: To fabricate the fitting model as per the drawing given below R 15 MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular and semicircular rough file. Rectangular and semicircular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 39

40 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. 8. Then male and female work pieces are assembled (joined) in order to make firm joint. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. Post Viva question: 1) What are the methods of filing? 40 X mm in L1, Y mm

41 a) Cross Filing b) Draw Filing 2) Name the materials used in the manufacture of files? Files are made of Hardened and Tempered Steel 3) Show me single cut file and double cut file. 4) What do you mean by single cut and double cut files? A single cut file has rows of teeth in one direction across the face, which is useful for filing soft materials like Aluminium, Brass, and Bronze. A double cut file has 2 rows of teeth cut diagonal to each other.the double cut file is useful in removing materials at faster rate in Harder Material. Single cut files gives better finish when compared to double cut files but at the same time removes material at a comparatively slower rate. 5) Differentiate between rough and smooth file? A rough cut file has very coarse spaced teeth.it is used for rough work. It removes more material. A smooth cut file has more closely spaced teeth.it is used to get smooth surface. 6) What is the use of flat file? Flat files are used for general work or finishing flat surfaces. 7) What is the cross-section of flat file? Rectangle 8) What is the use of square file? Squares files are used for filing square corners, rectangular slots, keyways, enlarging a s quare or a rectangular hole etc. 9) A file removes the metal during Stroke. Forward stroke. The file removes metal during the forward stokes. No pressure is applied on the Return Stroke, but the file is allowed to remain on the work piece. 10) What is the cross-section of Square file? Square cross-section. Date : / /.. Model No: 7 Dove tail model -1 41

42 AIM: To fabricate the fitting model as per the drawing given below , MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular and triangular rough file. Rectangular and triangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 42

43 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. Post Viva question: 1) What is the use of triangular file? 43 X mm in L1, Y mm

44 Triangular file or three-square files are used mainly for filing corners with angles less than 90 degrees. 2) How will you specify a file? Specification- length, single cut /double cut, shape and pitch. Example Length (say 400 mm) Single cut /Double cut Shape (say square cross section) Pitch or grade (say smooth) 3) The edge of a file that does not have teeth on it is called a Safe edge. 4) What is the material used to make a chisel Material - High carbon steel or tool steel having octagonal or hexagonal crosssection. 5) What are the types of hammers? What is the material used to make a hammers. Different types of hammers are a) straight pein hammer, b) ball pein hammer, c) cross pein hammer. Material Cast steel or carbon steel 6) What type of hammer mostly used in fitting operations? Ball pein hammer 7) What is a twist drill? The twist drills are used for making holes. The drills are made of HSS (high speed steel).a bench drilling machine is commonly used in workshops. 8) What is a hacksaw? The hacksaw is used for cutting metal by hand. The hacksaw blade has a number of teeth ranging from 5 to 15 per centimeter. Hack saw blades are fitted either in a solid frame or adjustable frame to accommodate different lengths of blade 9)Hacksaw blades having lesser number of teeth per cm are used for cutting materials. soft materials Ex:-Aliminium.brass and Bronze. 10) Hacksaw blades having larger number of teeth per cm are used for cutting materials. Hard materials like steel, C.I etc. Date:././. Model No: 8 44

45 Dove tail model-2 AIM: To fabricate the fitting model as per the drawing given below , MATERIAL: Mild Steel (M.S) TOOLS REQUIRED Scriber. Steel rule. Dot Punch Hacksaw frame with hacksaw blade. Bench vice Rectangular and triangular rough file. Rectangular and triangular smooth file. L- Square. Theory : Marking: The marking is the first step in fitting. Marking on the work can be done by setting out dimensions with the help of a working drawing. The measuring instruments used in fitting are scale, Calipers, vernier caliper, micrometer, height gauge etc. Marking tools used in fitting are Scriber, Dot punch, Scribing gauge etc.. Filing: Filling is the process of removing burrs from cuts, clean the face of cuts and to give the final shape to a work piece. The flatness and squareness of the surfaces finished by filing are checked with try square. Sawing: It is the method of removing excess material quickly with the help of hand hack saw. PROCEDURE 1. Check the dimensions of the given work piece with respect to the given model. 2. File the one edge of the given work piece to straightness and checked with Try square. 45

46 3. File the adjacent edge so that it is square with first edge filed and checked with Try square. File the upper and bottom surfaces of work piece. 4. Paste white color on the upper surface of the work piece (with chalk powder and water). 5. By marking gauges (Scale, Try square, Scriber, Divider), mark the dimensions on the given work pieces. 6. Using Dot punch and Hammer, make the punch marks (dots) on the marked dimensions on the given work piece. 7. By using hacksaw remove the extra material from the work piece and use cold chisel, if necessary to remove the material.. Removing small amount (1 mm to 2mm) of material Files can be used. 8. Then male and female work pieces are assembled (joined) in order to make firm joint. Pre Viva Questions: 1. What is the difference between Metal and Non metal.? 2. What is the difference between Iron and Steel. 3. What is the difference between MKS system and SI system? 4. What is safety? SKETCH OF THE FINISHED MODEL Result: The model is prepared as per the drawing given. Verification: The measurement of the model reveals that there is a deviation of in L2 and Z mm in L3 & L4. Conclusion: The model prepared is within / beyond the tolerance. 46 X mm in L1, Y mm

47 Post Viva question: 1) Name the materials of hacksaw blade? It is made of high speed steel. The hacksaw blades are measured by its length, width, thickness and pitch of the teeth. 2) How hacksaw blades are specified? The hacksaw blades are specified by its material, length, width, thickness and pitch of the teeth. 3) What is the specification of try square? Specification-the Size of Try-square is specified by the length of the blade (100mm, 150mm, and 200mm). 4) What is the use of Taps? Name the tap types in an each set? A tap is a hardened steel tool, used for cutting internal threads in a drilled hole. Hand taps are usually supplied in sets of three for each diameter and thread size. Each set consists of a 1) taper tap 2) Intermediate tap and 3) Plug or bottoming tap. 5) With what tool internal threads are cut. Taps 6) What is the use of Dies in fitting? Dies are used for cutting external threads. They are made of tool steel or high carbon steel. 7) With what tool external threads are cut. Dies. 8) What are the steps to be carried out in fitting job? 1) Filing 2) Marking &Measuring c) Sawing d) Filing e)fitting/assembly. 9) What is the use of file-card? It is a metal brush used for cleaning the files. 10) What is the use of Flat chisel? Chisels are used for removing surplus metal from the work piece. They can be used as a substitute when files and hacksaw blades are impossible to use. Specification- Length and width of the edge. The process of removing metal using a chisel is called chipping. 47

48 MODELS FOR PRACTICE 48

49 49

50 WELDING PRACTICE INTRODUCTION Process of joining two or more parts to make a single part termed as a Fabrication process. A fairly large number of industrial components are made by fabrication processes. Common examples are aircraft and ship bodies, building trusses, welded machine frames, sheet metal parts etc. The fabrication is often the most economical method and relies on raw material obtained from one of the primary manufacturing process such as rolling and extrusion. Hence, it may be called a secondary manufacturing process. Classification Fabrication process The Various fabrication processes can be classified according to Method of Joining as follows. 1) Mechanical Joining by means of bolts and nuts, screws,rivets. 2) Adhesive joining by employing synthetic glues such as epoxy resins. 3) Metallurgical fusion process like Welding, Soldering and Brazing The Various fabrication processes can be classified according to Type of assembly...1) Temporary joining process 2) Permanent. Joining process Temporary joining process: The joints obtained by these processes will be such that the connected parts can be separated easily with out any damage. Example: - Joints obtained by brazing, soldering, bolts and nuts. Studs and nuts, screws etc Permanent Joining process: The joints obtained by these processes will be such that the connected parts have to be broken in order to separate them. Example: - Joints obtained by riveting, welding etc. Welding: Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. Applications of welding It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, pressure vessels, furnaces, tanks, refrigerators, furniture, boilers, and shipbuilding. Repair and maintenance work. Example: joining broken parts, rebuilding worn out components etc. Classification of welding process. Plastic welding: In plastic welding, the metal parts to be joined are heated to the plastic state (or above) and then fused together by applying external pressure. No filler metal is used in this process plastic welding is also called pressure welding processes. Example: -Forge welding, resistance welding. Fusion welding In fusion welding process, the parts to be joined are heated above their melting temperature and then allowed to solidify without application of pressure. A filler material is used during welding process. Example: - arc welding and gas welding 50

51 Types of Arc welding process 1) Carbon arc welding 2) Metal arc welding 3) Metal inert gas welding 4) Tungsten inert gas welding 5) Plasma arc welding 6) Submerged arc welding Electric Arc Welding (Metal Arc Welding):Arc welding is a fusion method of welding that utilizes the high intensity of the arc (generated by current flow) to melt the work pieces. A solid continuous joint is formed upon cooling. In arc welding process makes use of filler material to supply additional material to fill the gap between the workspaces. The filler material used in welding process is called Electrode. It is made of a metallic wire called core wire, which is of the same material or nearly the same chemical composition as that of the work piece metal or base metal. The core wire is uniformly coated with flux. Principle of Arc Welding: The source of heat for arc welding process is an electric arc.the arc is produced by striking the electrode on the work piece. The electrode is momentarily separated from the work piece by a small gap such that the arc is still maintained between the work piece and the electrode.the electrical energy is thus converted into heat energy. The high heat at the tip of the electrode is sufficient to melt the work piece. The tip of the electrode melts and combines with the molten metal of the work piece there by forming a homogeneous joint. Welding process In arc welding process the electrode holder holding the electrode forms one pole of the circuit and the parts to be welded forms the other pole. The electrode serves both to carry the arc and also acts as a filler rod to deposit the molten metal into the joint. An arc is struck by touching the tip of the electrode with the work piece and instantaneously the electrode is separated from the work piece by a small distance of 2-4 mm such that the arc is still maintained between the electrode and the work piece. The temperature of the arc ranges from C. The high heat of the arc melts the work piece metal forming a small molten metal pool. At the same time, the tip of the electrode also melts and the molten metal of the electrode is transferred into the molten metal of the work piece in the form of globules of molten metal. The deposited metal fills the joint and bonds the joint to form a single piece of metal. Applications: Arc welding process is used for fabrication work, repair and maintenance work. The process finds applications in boiler and pressure vessel fabrication. Shipbuilding. Joining of large pipes and penstock, building and bridge construction, automotive and aircraft industries etc. Arc Welding Machine The source of heat for arc welding process is an electric arc. To supply the current for welding, two types of power sources are 51

52 available, viz; alternating current (A.C) and direct current (D.C). Current requirements: amperes for thin materials amperes for general work amperes for heavy work. Welding using A.C current: Fig shows the schematic representation of an A.C welding circuit. The welding circuit consists of Step down transformer-to reduce the usual supply voltage ( V) to that required for welding (15-90V) Two cables one cable, to the electrode holder holding the electrode and other, the ground cable Ground clamp used to connect one end of the ground cable to the work piece or to the table carrying the work piece Electrode holder and Electrode Welding using D.C current: The schematic representation of a D.C welding circuit is shown in fig In D.C welding, the electrode acts as one terminal and the work piece as the other terminal (either +ve or -ve) with D.C generator, greater heat is generated at the positive pole. Hence. The work piece should be connected to the positive pole of the D.C generator and the electrode to the negative pole in order to melt greater mass of metal in the work piece material. In A.C, the melting rate cannot be controlled, because equal heat is generated at the electrode and the work piece. Comparison between A.C and D.C in Welding Alternating Current (from Transformer) More efficiency Power consumption less Cost of equipment is less Higher voltage hence not safe Not suitable for welding non ferrous metals Not preferred for welding thin sections Any terminal can be connected to the work or electrode Direct Current (from Generator) Less efficiency Power consumption more Cost of equipment is more Low voltage safer operation 52

53 suitable for both ferrous and Non ferrous metals preferred for welding thin sections Positive terminal connected to the work Negative terminal connected to the electrode Electrodes used in Arc welding: Welding electrodes used in arc welding are of two types. 1) Consumable electrodes 2) Non-consumable electrodes. Consumable electrodes: These are made of metallic wire and are consumed during the welding process. The selection of a particular metal for the electrode depends upon their purpose and the chemical composition of the work piece metal to be welded. Consumable electrodes are further classified as coated electrodes and plain/bare electrodes. Coated electrodes In these electrodes, the metallic wire is coated with flux.during welding, the work piece melts and at the same time, the tip of the electrode also melts. As the globules of molten metal pass from the electrode to the work piece, they absorb oxygen and nitrogen from the atmospheric air. This causes the formation of some non- metallic constituents that are trapped in the solidifying weld metal and thereby decrease the strength of the joint. In order to avoid this, a flux is coated on the metallic wire. Flux A flux is a material used to prevent, dissolve, or facilitate removal of oxides and other undesirable surface substances. Various constituents like titanium oxide, cellulose, manganese oxide, calcium carbonates, mica, iron oxide etc. are used as flux materials for coating. The flux coated on the electrode performs the following functions. prevents oxidation of molten metal helps in the removal of oxides and other undesirable substances present on the surface of the work piece Chemically reacts with the oxides and forms a slag. The slag floats and covers the top portion of the molten metal thereby preventing it from rapid cooling. To remove any oxide formed. To stabilize the arc To make welding easy. To avoid difficulties in welding. Plain / Bare electrode: The metallic wire (core wire) is left plain or uncoated with flux. These electrodes do not prevent oxidation of the weld and hence the joint obtained is weak. Non consumable electrode: Non-consumable Electrodes are made of carbon, graphite or tungsten that does not get consumed during welding. Oxidation Metals in molten condition absorb oxygen from atmosphere and form metallic oxides. This process is known as oxidation. The formation of metallic oxides must be prevented. To prevent oxidation, we use coated electrodes. Advantages of Arc welding: 53

54 Most efficient way to join metals Lowest-cost joining method Affords lighter weight through better utilization of materials Joins all commercial metals Provides design flexibility Limitations of Arc welding: Manually applied, therefore high labor cost. Need high energy causing danger Not convenient for disassembly. Defects are hard to detect at joints. Gas Welding Process: Principle: Gas welding is a fusion type of welding that utilizes a strong flame, generated by the combustion of gases to melt the work piece. The gases are mixed in proper proportions in a welding blow pipe called welding torch. A solid continuous joint is formed upon cooling. The combination of gases used in this process is Mixture of oxygen and acetylene Mixture of oxygen and hydrogen. Oxy-Acetylene welding Oxygen and acetylene mixture are most commonly used in gas welding and the process is widely called oxy-acetylene process. It consists of supply of oxygen and acetylene under pressure in cylinders, pressure regulators, a torch, hoses and accessories like goggles and lighter. The oxygen and acetylene cylinders are connected to the torch through pressure regulators and hoses. The regulator consists of two pressure gauges. One for indicating the pressure with in the cylinder and the other shows the pressure of the gas fed into torch, which may be regulated. The torch mixes the two gases and the flame may me controlled by adjusting the oxygen and acetylene supply. Gas Welding Equipment. 1. Gas Cylinders Pressure Oxygen 125 kg/cm2 Acetylene 16 kg/cm2 2. Regulators Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depends upon the thickness of the work pieces welded. 3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve Some of the Important points related to Gas Welding. Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch The temperature generated during the process is 33000C When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld 54

55 Fluxes are added to the welded metal to remove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. Solid coating or gas. Types of flames produced in gas welding Three types of flames can be produced at the torch tip by regulating the ratio of oxygen to acetylene. (a) Neutral flame. (b) oxidizing flame. (c) carburizing or reducing flame. Neutral flame (Oxygen and Acetylene are mixed in equal proportions) A neutral flame is produced when approximately equal volumes of oxygen and acetylene are burnt at the torch tip (I has a balance of fuel gas and oxygen). The flame has a nicely defined inner whitish cone surrounded by sharp blue flame. The temperature of the neutral flame is around 32000C.. Used for welding steels, aluminium, copper and cast iron etc and can also be used for metal cutting. Oxidizing flame (Excess of Oxygen) If more oxygen is added to the Neutral flame, the cone becomes darker and more pointed, while the envelope becomes shorter and fiercer is called Oxidizing flame. Has the highest temperature about 34000C.Used for welding brass and brazing operation. Carburizing flame (Excess of Acetylene):If the volume of oxygen supplied to the Neutral flame is reduced, the resulting flame will be a Carburizing or reducing flame i.e., rich in acetylene. A reducing flame can be recognized acetylene feather that exists between the inner cone and the outer envelope. Has the highest temperature about 30000C.The outer flame envelope is longer than that of the neutral flame and is usually much brighter in colour. This type of flame is used for welding non- ferrous metals. Soldering Soldering is a method of joining similar or dissimilar metals by means of filler metal whose melting temperature is below 450 0C. The filler metal usually called solder is an alloy of tin and lead in various proportions. Soldering is commonly used for joining circuits in electronic components. In sheet metal work and in sealing of metal containers Brazing Brazing is a method of joining similar or dissimilar metals by means of a filler metal whose melting temperature is above 450 0C, but below the melting point of the base metal. 55

56 The filler metal called spelter is a non ferrous metal or alloy. Copper and copper alloys Silver and silver alloys and aluminum alloys are the most commonly used filler metals for brazing. Welding Tools and Safety Equipments Electrode holder:- It is used to hold the electrode during welding refer fig it consists of a handle and a pair of jaws operated by means of spring. The electrode holder forms one element of the welding circuit. One cable (wire) from the transformer is connected to the electrode. Due to this reason, the electrode holder should be well insulated. Chipping Hammer:-During welding, the flux coated on the electrode reacts with the oxides and other impurities and forms a slag. The slag being lighter floats over the surface of the molten metal and on solidification forms a thin layer over the weld bead. A chipping hammer is used for removing the slag formed on the weld bead. One end of the chipping hammer is sharpened like a cold chisel and the other end to a blunt, round point. Material- Tool steel Wire brush: - The wire brush usually made up of steel wire is used for cleaning the work piece before and after welding. Tong:-A tong is used for holding the work piece during/after welding. Ground clamp: - Ground clamp is connected to the end of the ground cable. Ground cable forms one pole of A.C. Goggles and Hand shields:-the sparks produced during welding are harmful and should not be seen with naked eyes. Goggles are used to protect the eyes of the welder form the rays of the arc and flying particles of hot metal. Hand shields and helmet type shields are used to protect the eyes and also the face of the welder. Hand gloves:-hand gloves are used to protect the hands from the sparks produced during welding and also from the heat of the electrode holder. C- Clamp The C-Clamp shown in fig is used for holding the job firmly on the work table during welding. Common welding terms Base metal: - The metal to be joined or cut is termed as the base metal. Bead or weld bead:-bead is the metal added during single pass of welding. The bead appears as a separate material from the base metal. Striking voltage: - The minimum voltage at which the arc may be struck. Fillet weld:- The metal fused into the corner of a joint made of two pieces placed at approximately 90 degrees to each other. Tack weld- A small weld, generally used to temporarily hold the two work pieces together during actual welding, is the tack weld. 56

57 . Safe and correct practices. 1) Welding should be carried out in a well ventilated place and the place should be free of inflammable materials. 2) All the safety gadgets are to be used strictly. 3) Care should be taken to avoid dragging the welding cable and checked periodically for any open insulation. 4) The cables should be prevented from coming into contact with hot metal, water, oil etc. 5) Always keeps fire fighting equipment like water, sand, gas fire extinguisher, for any fire hazard emergency. 6) Before welding, the parts to be welded are thoroughly cleaned from dust, foreign matter, oil grease, rust etc. 7) The instructions given in the manufacture s catalogue are to be strictly followed. 57

58 Model practice Model No 1 Date:./../. Lap Joint AIM: To do lap joint by welding as shown in the sketch MATERIAL: Mild Steel (M.S) TOOLS REQUIRED: 1. Rectangular file. 2. Steel rule. 3. Scriber. 4. Welding Electrode. 5. AC Welding Machine. 6. Metal brush. 7. Welding shield. 8. Hand glows. 9. Tong. 10. Bench vice. 11. Chipping hammer. Theory: Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. In arc welding process the electrode holder holding the electrode forms one pole of the circuit and the parts to be welded forms the other pole. The electrode serves both to carry the arc and also acts as a filler rod to deposit the molten metal into the joint. An arc is struck by touching the tip of the electrode with the work piece and instantaneously the electrode is separated from the work piece by a small distance of 2-4 mm such that the arc is still maintained between the electrode and the work piece. The temperature of the arc ranges from C. The high heat of the arc melts the work piece metal forming a small molten metal pool. At the same time, the tip of the electrode also melts and the molten metal of the electrode is transferred into the molten metal of the work piece in the form of globules of molten metal. The deposited metal fills the joint and bonds the joint to form a single piece of metal. Current requirements: amperes for thin materials amperes for general work 58

59 amperes for heavy work. PROCEDURE 1. The given M.S work pieces are thoroughly cleaned of rust,scale and other foreign materials 2. Two work pieces are positioned on the work table (welding table) as shown in the figure. 3. Connect the earth clamp of the welding machine to work table or base metal. 4. Select the proper size of the Electrode according to the thickness of the metal piece and amperage. Thickness of metal piece Current Range Size of the Electrode 5. Use hand shields, hand gloves and apron etc 6. After Selecting Proper size of the Electrode, place it in the Electrode holder. 7. Switch on the main and then the starter of the machine. 8. Bring the electrode near the weld joint and complete the circuit to maintain the correct arc length. Move the electrode on the weld joint until the molten metal fills the parent metal. 9. Cool the joint for few minutes and remove the slag by chipping hammer 10. Brush the weld joint by the wire brush. Pre viva questions: 1. What is welding? 2. Difference between current and voltage. 3. Difference between temporary joint and permanent joint. 4. Difference between rod, plate and sheet. 5. What is meant melting point? SKETCH OF THE FINISHED MODEL 59

60 Result: Verification: Conclusion: POST VIVA QUESTIONS 1) Define Fabricating process. Joining two or more elements to make a single part termed as a Fabrication process. Example: aircraft and ship bodies, building trusses, welded machine frames, sheet metal parts etc. 4) Define Temporary joining process and give Example. Temporary joining process: - The joints obtained by these processes will be separated easily with out any damage to the connected parts. Example: - Joints obtained by brazing, soldering, bolts and nuts. Studs and nuts, screws etc 5) Define Permanent Joining process and give Example. Permanent Joining process: -. The joints obtained by these processes will be such that the connected parts have to be broken in order to separate them. Example: - Joints obtained by riveting, welding etc 6) What is welding? Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. 8) Classification of welding. Or. Mention different types of welding process. 1) Plastic welding 2) Fusion welding 9) Is welding a permanent or temporary fastening method. Permanent fastening method. 12) Define pressure welding or plastic welding. Name some pressure welding process. In plastic welding, the metal parts to be joined are heated to the plastic state (or above) and then fused together by applying external pressure. No filler metal is used in this process. Plastic welding is also called pressure welding processes. Example: -Forge welding, resistance welding. 13) Define fusion welding, name some fusion welding process. In fusion welding process, the parts to be joined are heated above their melting temperature and then allowed to solidify without application of pressure. A filler material is used during welding process. Example: - arc welding and gas welding 14) Differentiate between gas welding and arc welding. In gas welding process combustion of oxy-acetylene (oxygen-hydrogen) gases in different proportions is used for heating the work pieces. In gas welding filler rod is used for joining work pieces. In case of Arc welding Electrical Arc (AC OR DC) is used for heating the work pieces. In arc welding electrode is used for joining work pieces. 60

61 Model No 2 Date:././ Butt Joint AIM: To do butt joint by welding as given in the drawing MATERIAL: Mild Steel (M.S) TOOLS REQUIRED: 1. Rectangular file. 2. Steel rule. 3. Scriber. 4. Welding Electrode. 5. AC Welding Machine. 6. Metal brush. 7. Welding shield. 8. Hand glows. 9. Tong. 10. Bench vice. 11. Chipping hammer. Theory: Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. In arc welding process the electrode holder holding the electrode forms one pole of the circuit and the parts to be welded forms the other pole. The electrode serves both to carry the arc and also acts as a filler rod to deposit the molten metal into the joint. An arc is struck by touching the tip of the electrode with the work piece and instantaneously the electrode is separated from the work piece by a small distance of 2-4 mm such that the arc is still maintained between the electrode and the work piece. The temperature of the arc ranges from C. The high heat of the arc melts the work piece metal forming a small molten metal pool. At the same time, the tip of the electrode also melts and the molten metal of the electrode is transferred into the molten metal of the work piece in the form of globules of molten metal. The deposited metal fills the joint and bonds the joint to form a single piece of metal. Current requirements: amperes for thin materials amperes for general work 61

62 amperes for heavy work. PROCEDURE 1. The given M.S work pieces are thoroughly cleaned of rust,scale and other foreign materials 2. Two work pieces are positioned on the work table (welding table) as shown in the figure. 3. Connect the earth clamp of the welding machine to work table or base metal. 4. Select the proper size of the Electrode according to the thickness of the metal piece and amperage. Thickness of metal piece Current Range Size of the Electrode 5. Use hand shields, hand gloves and apron etc 6. After Selecting Proper size of the Electrode, place it in the Electrode holder. 7. Switch on the main and then the starter of the machine. 8. Bring the electrode near the weld joint and complete the circuit to maintain the correct arc length. Move the electrode on the weld joint until the molten metal fills the parent metal. 9. Cool the joint for few minutes and remove the slag by chipping hammer 10. Brush the weld joint by the wire brush. SKETCH OF THE FINISHED MODEL Result: Verification: Conclusion: 62

63 POST VIVA QUESTIONS 1) List the different types of arc welding process? 1) Carbon arc welding 2) Metal arc welding 3) Metal inert gas welding4) Tungsten inert gas welding 5) Plasma arc welding6) Submerged arc welding 2) Name some of the sources available for heating in arc-welding process. 1) Transformer (A.C) 2) Motor Generator (D.C) 3) Rectifiers (converts AC into DC). 3) What is the minimum Arc-gap should be maintained between electrode and work piece for existence of arc. 2mm to 4mm. 4) Draw an A.C arc-welding circuit. (OR) Name the components used in welding ac-circuit 5) The amount of current required for arc welding circuit. 50 to 500 Appears 6) The amount of voltage required for arc welding circuit. 20Volts 40 Volts 7) What type of Transformer used in Ac arc welding process. Step down Transformer 8) What is the function of Step down Transformer? Decrease the voltage to from 230V to50v-90v. Increase the current to 50Amps-400 Amps. 9) The temperature developed in the arc welding process degrees-6000 degrees. 10) Draw a DC circuit for arc welding process. 11) What is DCSP? OR DCEN-Direct current Electrode Negative. Direct current straight polarity. In this case work piece is connected to the positive terminal of the welding Machine. Electrode holder is connected to the negative terminal of the welding machine. DCSP gives greater depth of penetration, more heat at job, used for weld thicker plates. Or Electrode is cathode, work piece is cathode. 12) How many number cables required in arc-welding process. Three cables are required in arc-welding. 1) Cable for connecting Main supply to Transformer. 2) Cable for connecting Transformer to electrode Holder. 3) Cable for connecting Transformer to work piece Table (for Farthing). 63

64 Model No 3 Date: / /.. T- Joint AIM: To do T joint by welding as given in the drawing MATERIAL: Mild Steel (M.S) TOOLS REQUIRED: 1. Rectangular file. 2. Steel rule. 3. Scriber. 4. Welding Electrode. 5. AC Welding Machine. 6. Metal brush. 7. Welding shield. 8. Hand glows. 9. Tong. 10. Bench vice. 11. Chipping hammer. Theory: Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. In arc welding process the electrode holder holding the electrode forms one pole of the circuit and the parts to be welded forms the other pole. The electrode serves both to carry the arc and also acts as a filler rod to deposit the molten metal into the joint. An arc is struck by touching the tip of the electrode with the work piece and instantaneously the electrode is separated from the work piece by a small distance of 2-4 mm such that the arc is still maintained between the electrode and the work piece. The temperature of the arc ranges from C. The high heat of the arc melts the work piece metal forming a small molten metal pool. At the same time, the tip of the electrode also melts and the molten metal of the electrode is transferred into the molten metal of the work piece in the form of globules of molten metal. The deposited metal fills the joint and bonds the joint to form a single piece of metal. 64

65 Current requirements: amperes for thin materials amperes for general work amperes for heavy work. PROCEDURE 1. The given M.S work pieces are thoroughly cleaned of rust,scale and other foreign materials 2. Two work pieces are positioned on the work table (welding table) as shown in the figure. 3. Connect the earth clamp of the welding machine to work table or base metal. 4. Select the proper size of the Electrode according to the thickness of the metal piece and amperage. Thickness of metal piece Current Range Size of the Electrode 5. Use hand shields, hand gloves and apron etc 6. After Selecting Proper size of the Electrode, place it in the Electrode holder. 7. Switch on the main and then the starter of the machine. 8. Bring the electrode near the weld joint and complete the circuit to maintain the correct arc length. Move the electrode on the weld joint until the molten metal fills the parent metal. 9. Cool the joint for few minutes and remove the slag by chipping hammer 10. Brush the weld joint by the wire brush. SKETCH OF THE FINISHED MODEL Result: The model is welded as per the drawing. Verification: The welding is poor/ discontinuous/ good Conclusion: The reason is.. 65

66 POST VIVA QUESTIONS 1) What is oxidation? Metals in molten condition absorb oxygen from atmosphere and form metallic oxides. This process is known as oxidation. The formation of metallic oxides must be prevented. To prevent oxidation, we use coated electrodes. 2) Mention the current requirements for thin and thick materials amperes for thin materials amperes for general work amperes for heavy work (thick materials). 3) What is an electrode? A welding electrode is defined as a component of the welding circuit through which current is conducted. OR. Electrode forms one pole of the electric circuit, while work piece forms the other pole. Electrode is used in Arc welding process. 4) What is Filler rod? Filler metal supplies additional material to fill the gap between work pieces. Material of the filler rod is same as the base metal. Filler rod is used in gas welding process. 5) What is the difference between electrode and filler metal. Electrode forms one pole of the electric circuit, while work piece forms the other pole. Filler metal supplies additional material to fill the gap between work pieces. In case of arc welding process, the filler metal apart from supplying additional metal also acts as an electrode by forming a component of the electric circuit. 6) Name parts of electrode. 7) specify a welding electrode, you have used. Electrodes are specified by its diameter (diameter of core wire) and length. The size of the electrode is measured in Standard wire gauge (SWG). 8) Classification of electrodes. 1) Consumable electrodes a) Coated electrodes b) plain/bare electrodes 2) Non-consumable electrodes 9) Amount of arc length required between electrode work pieces. The distance through the center of the arc from the lip of electrode to the bottom of arc crater is termed as arc length. It ranges from 3mm to 4mm. 66

67 Model No 4 Date : / /.. L- Joint AIM: To fabricate L joint by welding as per given drawing MATERIAL: Mild Steel (M.S) TOOLS REQUIRED: 1. Rectangular file. 2. Steel rule. 3. Scriber. 4. Welding Electrode. 5. AC Welding Machine. 6. Metal brush. 7. Welding shield. 8. Hand glows. 9. Tong. 10. Bench vice. 11. Chipping hammer. Theory: Welding is the process of joining similar metals by application of heat, with or without application of pressure or filler material. In arc welding process the electrode holder holding the electrode forms one pole of the circuit and the parts to be welded forms the other pole. The electrode serves both to carry the arc and also acts as a filler rod to deposit the molten metal into the joint. An arc is struck by touching the tip of the electrode with the work piece and instantaneously the electrode is separated from the work piece by a small distance of 2-4 mm such that the arc is still maintained between the electrode and the work piece. The temperature of the arc ranges from C. The high heat of the arc melts the work piece metal forming a small molten metal pool. At the same time, the tip of the electrode also melts and the molten metal of the electrode is transferred into the molten metal of the work piece in the form of globules of molten metal. The deposited metal fills the joint and bonds the joint to form a single piece of metal. Current requirements: amperes for thin materials amperes for general work amperes for heavy work. 67

68 PROCEDURE 1. The given M.S work pieces are thoroughly cleaned of rust,scale and other foreign materials 2. Two work pieces are positioned on the work table (welding table) as shown in the figure. 3. Connect the earth clamp of the welding machine to work table or base metal. 4. Select the proper size of the Electrode according to the thickness of the metal piece and amperage. Thickness of metal piece Current Range Size of the Electrode 5. Use hand shields, hand gloves and apron etc 6. After Selecting Proper size of the Electrode, place it in the Electrode holder. 7. Switch on the main and then the starter of the machine. 8. Bring the electrode near the weld joint and complete the circuit to maintain the correct arc length. Move the electrode on the weld joint until the molten metal fills the parent metal. 9. Cool the joint for few minutes and remove the slag by chipping hammer 10. Brush the weld joint by the wire brush. SKETCH OF THE FINISHED MODEL Result: Verification: Conclusion: POST VIVA QUESTIONS 68

69 1) What are the sizes of electrodes? Core wire diameter-3.15, 4.0, 5.0, 6.3,10 mm and 12.5 mm. Core wire length-350mm and 450 mm as per Indian standard. 2) Differentiate between consumable electrode and non-consumable electrode. Consumable electrode-these are made of metallic wire and are consumed during the welding process. Non-consumable electrode- Non-consumable Electrodes are made of carbon, graphite or tungsten that does not get consumed during welding. 3) Why electrodes are not coated fully. One end of the electrode is left bare (uncoated with flux) which is usually held in the electrode holder. The uncoated part helps in transmitting full current from the electrode holder to the front end of the electrode coating. The flux coating acts as an insulator ofelectricity.hence, electrodes are not coated fully. 4) What are the functions of flux on flux coated electrode? prevents oxidation of molten metal helps in the removal of oxides and other undesirable substances present on the surface of the work piece Chemically reacts with the oxides and forms a slag. The slag floats and covers the top portion of the molten metal thereby preventing it from rapid cooling. To stabilize the arc To avoid difficulties in welding. 5) Name the material of core wire of electrode. Material of the core wire is same as the work pieces to be welded. 6) What is the material of flux used in the electrode? Titanium oxide, cellulose, manganese oxide, calcium carbonates, mica, iron oxide etc. are used as flux materials for coating. 7) What is a flux? Why is it used? A flux is a material used to prevent, dissolve, or facilitate removal of oxides and other undesirable surface substances. prevents oxidation of molten metal 8) What are the defects that will result if flux is not used in welding? a) Reduce the Strength of the joint. b) Oxidation of molten metal will take place. 9) Define base metal. The metal to be joined or cut is termed as the base metal. 10) What is the use of chipping hammer? A chipping hammer is used for removing the slag formed on the weld bead 11) What is the use of electrode holder? It is used to hold the electrode during welding 12) What is the use of wire brush? The wire brush usually made up of steel wire is used for cleaning the work piece before and after welding. 13) What is the use of goggles? Goggles are used to protect the eyes of the welder from the rays of the arc and flying particles of hot metal. 14) What is the use of hand shields? Hand shields and helmet type shields are used to protect the eyes and also the face of the welder 69

70 SHEET METAL FABRICATION PRACTICE INTRODUCTION: When the thickness of a material is much smaller than length and width, it is known as sheet or plate. When the thickness is less than 6mm it is categorized as sheet and when thickness is greater than 6mm it is categorized as plate. Sheet metal work is the shaping or forming operations of mostly sheet. These sheet metal processes are very much different from the processes for shaping thick bars, rods, blooms, billets etc. THEORY OF SHEET METAL WORK: When an elastic material is subjected to increasing force, it deforms and stress within the material keeps on increasing. A typical stress strain diagram of an elastic material is as shown in the figure. Material follows Hooke s law up to point A called yield stress. When stress in the material exceeds yield stress, material deformation becomes permanent and when the stress reaches ultimate or fracture stress, the material fails. These materials are known as ductile materials which on increasing stress then yield and deform and then only fail. But there are materials which do not yield much but fail prematurely and they are called brittle materials. In sheet metal forming in some operations, forces are applied such that stress in the metal exceeds just the yield stress but well below ultimate stress called plastic state, so that metal is deformed to the required shape but does not fracture. These processes are : Bending,drawing,coining,embossing,stretch forming,spinning,deep drawing, roll bending and super plastic forming and all these processes takes place in plastic state. But in some processes, so heavy forces are applied that the stress in the material exceeds ultimate stress and the material fractures. These processes are shearing, punching and piercing. SHEET METAL WORK: The metal forming processes such as cutting, shearing, punching, piercing, embossing, drawing, coining, deep drawing, stretches forming, spinning, roll bending, super plastic forming are all sheet metal operations. Compared to machining or forging or extruding processes, the sheet metal processes are much cheaper as the machines required are much cheaper or they are suitable for large scale production. The machines used for sheet 70

71 metal forming are: Shearing machine, 3 roll/4roll bending machine, arbor press, hydraulic press, fly press, stretch forming machine, flow forming machine etc. THE MATERIALS: Used in sheet metal forming are: M.S, Aluminium alloys, copper alloys, zinc alloys, Magnesium alloys, Tin alloys, G.I, Stainless steel (SS) etc. Material should have good ductility for sheet metal forming. Galvanized iron is steel coated with zinc to protect it from rusting an also can be soldered. Stainless steel is highly ductile material specially in an annealed state it has 40% elongation. Steel sheet coated with tin is called tin plate and rust proof and also used in making food containers, cans, pans and dairy equipments. Several industrial, household and consumer products are made by sheet metal forming. Storage tanks, pressure vessels, oil tankers, cooking utensils such as pressure cookers, instrumentation boxes, containers, small as well as big packing boxes, trunks, suit cases, boiler parts, heating ducts, air ducts, gutters etc all are sheet metal products. DEVELOPMENTS: Most of the sheet metal parts are formed by flat sheets. All the 3 dimensional bodies(hollow) can be formed by correctly making corresponding shape in flat condition and then it is folded and made to yield and final 3 dimensional body is made. After folding, the joints are of standard joint configurations as shown in the figures. 71

72 SHEET METAL ALLOWANCES: If a sheet metal of thickness t is bent to 90 with radius R from a flat sheet as shown in the fig., the total length in flat condition and after bending are not same. Length of the flat sheet=l Length after bending=x1+x2+x3 and x1,x2 are straight distances and x3 the length at bend and this varies for outer layer, inner layer and central/neutral layer. Hence to calculate correct length l to be taken to get final bend as shown in the fig, Mid layer length is taken as L=x1+x2+ (R+t/2) 2 The difference of l and L is called bend or sheet metal allowance. The sheet metal allowance varies based on the bend radius, the thickness of sheet, bend angle, material condition etc. there are empirical estimations available for sheet metal allowances and are tabulated and are readily available. SHEET METAL TOOLS AND FITTING TOOLS: 1) Marking tools: Steel rule, vernier calipers, scriber, divider, try square, universal scribing block, surface plate, vernier height gauge, bench vice, bevel protractor, punches, wire gauge. 2) Cutting tools: snips/shears, chisel, files. 3) Bending tools: mallet, stakes: beak horn stake, hatchet stake, half moon stake, creasing stake, funnel stake, pipe stake, horse stake, pliers etc. Steel rule, vernier calipers, vernier height gauge: These are measuring instruments used for various measurements. The accuracy of scale being 1mm and that of vernier caliper and vernier height gauge being 0.02 mm. They are made of steel. Bevel protractor: it is made out of steel and is used for measuring and marking angles in drawing developments. Try square: it is made by hardened steel and used for marking perpendicular lines and checking perpendicularity. Wire gauge: it is made of steel hardened and used for checking the thickness of sheet metal and wires. Most commonly used gauge is called imperial standard wire gauge(swg) and the markings vary from 4 to 24. Higher the gauge no. lesser is the thickness and standard wire sizes are as given in the table. 72

73 SWG No Size in mm SWG No Size in mm SWG No Size in mm Surface plate: it is a flat base of granite (or cast iron). It has high surface finish, flatness and hard and used for placing sheet etc for marking and measurement. Bench vice: it is a holding device made of C.I and M.S. it is used to hold jobs, sheet and also pressing at bend line to form a bend. Scriber, caliper and divider: These are marking tools made of iron tool steel material. Universal scribing block or surface gauge: it consists of casting from base and M.S spindle, clamp etc. it is very convenient marking tool. The base with v-groove is useful to take reference dimensions on round bodies. Snips/shears: it is similar to scissors but stronger and heavier and straight as well as contoured. Cuts can be made along the already marked profiles and cut in to pieces. It is made of carbon steel or tool steel. Chisels: When there is no approach or access to line to be cut by snips/shears from an edge the material can be cut using chisel. Chisels are made of high carbon steel, tool steel or alloy steel. There are varieties of chisels for different applications. Files: these are cutting tools to remove metal from surfaces. Mallet: a wooden or plastic or hyde hammer is generally known as mallet. Thin sheet metal bending and shaping is done by softer hammer such as wood or plastic to avoid or minimize deep dents, marks pr scratches. Mallets are of different shapes to suit sheet metal forming. Stakes: in the absence of sheet metal forming machines such as fly press, bending, folding, rolling machines, for hand forming, stakes are the tools used. These are tools made of steel and are of anvil shape. They are for forming the shapes by bending, forming, riveting, seaming. Using mallet, the sheet to be shaped are placed over the stakes of appropriate shape and hammered by mallet to permanently deform the sheet to the required shape. Stakes act as supporting tools or mandrel for the sheet to be formed. Stakes are made in different shapes and sizes. A stake consists of a shank, a horn and head. The formation of sheet metal items requires forming a corner with radius and contours of circular,conical,tapered etc and different types of stakes are available to form all the types of corners, profiles etc. The various types of stakes are : blow horn stake, beak horn stake, candle mould stake, creasing stake, hollow mandrel stake, solid mandrel stake, double seaming stoke, conductor stake, hatchet stake, bevel edge stake, common square stake, copper smith stake, bottom stake, hand dolly stake. Pliers: Pliers are used in sheet metal work for holding, cutting and bending work. Various types of pliers are: 73

74 (a) Flat nose pliers: It has flat jaws rounded on the outside. It is used for holding and forming work. (b) Round nose plier: It has long jaws rounded on the outside. It is used for holding and forming various shapes and patterns. (c) Slip joint combination plier: It has an adjustable jaw. It is general purpose tool. 74

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