Cutting Tools and Cutting materials
Cutting Tools One of most important components in machining process Performance will determine efficiency of operation Two basic types (excluding abrasives) Single point and multiple point Must have rake and clearance angles ground or formed on them
Cutting-Tool Materials Toolbits generally made of seven materials High-speed steel Cast alloys (such as stellite) Cemented carbides Ceramics Cermets Cubic Boron Nitride Polycrystalline Diamond
Cutting Tool Properties Hardness Cutting tool material must be 1 1/2 times harder than the material it is being used to machine. Capable of maintaining a red hardness during machining operation Red hardness: ability of cutting tool to maintain sharp cutting edge Also referred to as hot hardness or hot strength
Cutting Tool Properties Wear Resistance Able to maintain sharpened edge throughout the cutting operation Same as abrasive resistance Shock Resistance Able to take the cutting loads and forces Shape and Configuration Must be available for use in different sizes and shapes.
High-Speed Steel May contain combinations of tungsten, chromium, vanadium, molybdenum, cobalt Can take heavy cuts, withstand shock and maintain sharp cutting edge under red heat Generally two types (general purpose) Molybdenum-base (Group M) Tungsten-base (Group T) Cobalt added if more red hardness desired
Cast Alloy Usually contain 25% to 35% chromium, 4% to 25% tungsten and 1% to 3% carbon Remainder cobalt Qualities High hardness High resistance to wear Excellent red-hardness Operate 2 ½ times speed of high-speed steel Weaker and more brittle than high-speed steel
Carbide Cutting Tools First used in Germany during WW II as substitute for diamonds Various types of cemented (sintered) carbides developed to suit different materials and machining operations Good wear resistance Operate at speeds ranging 150 to 1200 sf/min Can machine metals at speeds that cause cutting edge to become red hot without loosing harness
Manufacture of Cemented Carbides Products of powder metallurgy process Tantalum, titanium, niobium Operations Blending Compaction Presintering Sintering
Types of Carbide Lathe Cutting Tools Blazed-tip type Cemented-carbide tips brazed to steel shanks Wide variety of styles and sizes Indexable insert type Throwaway inserts Wide variety of shapes: triangular, square, diamond, and round Triangular: has three cutting edges Inserts held mechanically in special holder
Tool Geometry Terms adopted by ASME SIDE RELIEF SIDE CLEARANCE Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cutting-Tool Terms Front, End, Relief (Clearance) Allows end of cutting tool to enter work Side Relief (Side) Permits side of tool to advance into work Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cutting-Tool Terms Side Cutting Edge Angle Angle cutting edge meets work Positive Negative - protects point at start and end of cut Nose Radius Strengthens finishing point of tool Improves surface finish on work Should be twice amount of feed per revolution Too large chatter; too small weakens point
Side Rake Large as possible to allow chips to escape Amount determined Type and grade of cutting tool Type of material being cut Feed per revolution Angle of keenness Formed by side rake and side clearance Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Back Rake Angle formed between top face of tool and top of tool shank Positive Top face slopes downward away from point Negative Top face slopes upward away from point Neutral Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cutting Speeds and Feeds Important factors that influence speeds, feeds, and depth of cut Type and hardness of work material Grade and shape of cutting tool Rigidity of cutting tool Rigidity of work and machine Power rating of machine
Lathe is one of the oldest important machine tools in the metal working industry. A lathe operates on the principle of a rotating work piece and a fixed cutting tool. A rope wound round the work with its own end attached to a flexible branch of tree and other end being pulled by man caused job to rotate intermittently. With its further development a strip of wood called lath was used to support the rope and that is how the machine came to be known as lathe. The cutting tool is feed into the workpiece, which rotates about its own axis, causing the workpiece to be formed to the desired shape. Lathe machine is also known as the mother/father of the entire tool family.
The Lathe Machine is one of the oldest and most important machine tools. As early as 1569, wood lathes were in use in France. The lathe machine was adapted to metal cutting in England during the Industrial Revolution. Lathe machine also called Engine Lathe because the first type of lathe was driven by a steam engine.
Henry Maudsley was born on an isolated farm near Gigghleswick in North Yorkshire and educated at University Collage London. He was an outstandingly brilliant medical student, collecting ten Gold Medals and graduating with an M.D. degree in 1857.
This term engine is associated with the lathe owing to the fact that early lathes were driven by steam engine. It is also called centre lathe. The most common form of lathe, motor driven and comes in large variety of sizes and shapes.
Engine lathes are classified according to the various designs of headstock and methods of transmitting power to the machine. 1. Belt Driven Lathe 2. Motor Driven Lathe 3. Gear Head Lathe The power to the engine lathe spindle may be given with the help of a belt drive from an overhead line shaft but most modern machines have a captive motor with either a cone pulley driven or an geared headstock arrangement.
A bench top model usually of low power used to make precision machine small work pieces. It is used for small w/p having a maximum swing of 250 mm at the face plate. Practically it consists of all the parts of engine lathe or speed lathe.
A lathe that has the ability to follow a template to copy a shape or contour.
A tool room lathe having features similar to an engine lathe is much more accurately built and has a wide range of spindle speeds ranging from a very low to a quite high speed up to 2500 rpm. This lathe is mainly used for precision work on a tools, dies, gauges, and in machining work where accuracy is needed. This lathe machine is costlier than an engine lathe of the same size.
A lathe in which the work piece is automatically fed and removed without use of an operator. It requires very less attention after the setup has been made and the machine loaded.
Turret lathe is the adaptation of the engine lathe where the tail stock is replaced by a turret slide(cylindrical or hexagonal). Tool post of the engine lathe is replaced by a square cross slide which can hold four tools.
It has heavier construction and provides wider range of speeds. The saddle carrying the turret head moves along the whole length of the bed. Much longer jobs can be machined. Turret head directly mounted on the saddle. The front tool post can carry 4 tools and rear tool post may have 1 or 2 tools. Turret may have4 to 6 tools. More than one tool may be set to operate simultaneously. There is no lead screw.
A highly automated lathe, where both cutting, loading, tool changing, and part unloading are automatically controlled by computer coding. E.g. CNC Lathe M/C.(Computer Numerical Control Machine)
This is heavy rugged casting made to support the working parts of lathe and also guide and align major parts of lathe. Made to support working parts of lathe. On top section are machined ways. Guide and align major parts of lathe.
The headstock houses the main spindle,speed change mechanism, and change gears. The headstock is required to be made as robust as possible due to the cutting forces involved,which can distort a lightly built housing.
Induce harmonic vibrations that will transfer through the work piece, reducing the quality of the finished work piece.
Contains number of different-size gears. Provides feed rod and lead-screw with various speeds for turning and thread-cutting operations TOP VIEW
The arrangement which are employed in feed gear boxes to obtain multispindle speeds and different rates of feeds are: I. Sliding Gear Mechanism II. III. Sliding Clutch Mechanism Gear Cone And Tumbler Gear Mechanism IV. Sliding Key Mechanism V. Combination of any two or more of the above Usually two or three levers must be moved to obtain the desired combination within a given range.
Used to move cutting tool along lathe bed. Consists of three main partsi. Saddle ii. Cross-slide iii. Apron
Movement of entire carriage assembly along the bed provides feed for the tool parallel to the lathe axis. The compound rest can be swivelled on the cross slide in the horizontal plane about vertical axis. To the front of the carriage is attached the apron. It is fastened to the saddle and hangs over the front of the bed. The apron houses the automatic feed mechanism for longitudinal and cross feeds and the split nut for thread cutting.
Mounted on top of saddle. Provides manual or automatic cross movement for cutting tool.
Fastened to saddle. Houses gears and mechanism required to move carriage or crossslide automatically. Locking-off lever inside apron prevents engaging split-nut lever and automatic feed lever at same time. Apron hand wheel turned manually to move carriage along lathe bed
Upper and lower tailstock castings. Adjusted for taper or parallel turning by two screws set in base. Tailstock clamp locks tailstock in any position along bed of lathe. Tailstock spindle has internal taper to receive dead center. Provides support for right-hand end of work.
In tail stock jobs of different lengths are provided with quill which can be moved in and out by means of a screw and then locked in position. The movement of the quill is parallel to the lathe axis. The quill has a tapered bore into which is fitted a hardened centre which locates and holds the w/p when turning between centre. This bore may also be used for supporting tools for operations like drilling and reaming.
Engages clutch that provides automatic feed to carriage. Feed-change lever can be set for longitudinal feed or for cross-feed. In neutral position, permits split-nut lever to be engaged for thread cutting. Carriage moved automatically when split-nut lever engaged
Distance carriage will travel in one revolution of spindle. Depends on speed of feed rod or lead screw. Controlled by change gears in quick-change gearbox. Obtains drive from headstock spindle through end gear train. Chart mounted on front of quick-change gearbox indicates various feeds.
(a) and (b) Schematic illustrations of a draw-in-type collets. (c) A push-out type collet. (d) Workholding of a part on a face plate.
- Forholding cylindrical stock centered. - For facing/center drilling etc. - This is independent chuck generally has four jaws, which are adjusted individually on the chuck face by means of adjusting screws.
-Collet chuck is used to hold small work pieces. -Thin jobs can be held by means of magnetic chucks.
Don t touch cutter or chips while machine is running. Make sure work is clamped tightly in chuck or collet. Be careful to stay clear of chuck jaws.
All lathe operators must be constantly aware of the safety. Handle sharp cutters, centres, and drills with care. Remove chuck keys and wrenches before operating. Always wear protective eye protection. Always stop the lathe before making adjustments. Know where the emergency stop is before operating the lathe. Correct dress is important, remove rings and watches. Do not change spindle speeds until the lathe comes to a complete stop.
Lathes are highly accurate machine tools designed to operate around the clock if properly operated and maintained. Lathes must be lubricated and checked for adjustment before operation. Improper lubrication or loose nuts and bolts can cause excessive wear and dangerous operating conditions.
Drilling machine
Introduction Drilling is a metal cutting process carried out by a rotating cutting tool to make circular holes in solid materials. Tool which makes hole is called as drill bit or twist drill.
Drilling machine A power operated machine tool which holds the drill in its spindle rotating at high speeds and when actuated move linearly against the work piece produces a hole.
Types of drilling machine. Portable drilling machine Bench drilling machine Radial drilling machine Pillar drilling machine Gang drilling machine Multiple drilling machine
Portable drilling machine
Bench drilling machine These are light duty machines used in small workshops. Also called Sensitive drilling machines because of its accurate and well balanced spindle. Holes of diameter 1 mm to 15 mm.
Bench drilling machine
parts Vertical main column Base Moving drill head Work table Electric motor Variable speed gear box and spindle feed mechanism.
working Work piece with the exact location marked on it with the centre punch is clamped rigidly on the work table. spindle axis and center punch indentation are in same line. Machine is started and drill bit is lowered by rotating feed handle. Drill bit touches the work and starts removing material.
Bench drilling machine
Radial drilling machine These are heavy duty and versatile drilling machine used to perform drilling operate on large and heavy work piece. Holes up to 7.5 cm.
Radial drilling machine
parts Heavy base Vertical column Horizontal arm Drilling head
working Work piece is marked for exact location and mounted on the work table. Drill bit is then located by moving the radial arm and drill to the marked location. By starting drill spindle motor holes are drilled.
Drilling machine operation Reaming Boring Counter boring Counter sinking Spot facing Tapping
Reaming It is a process of smoothing the surface of drilled holes with a tool. Tool is called as reamer. Initially a hole is drilled slightly smaller in size. Drill is replaced by reamer. Speed is reduced to half that of the drilling.
Reaming
Boring It is process carried on a drilling machine to increase the size of an already drilled hole. Initially a hole is drilled to the nearest size and using a boring tool the size of the hole is increased.
This process involves increasing the size of a hole at only one end. Cutting tool will have a small cylindrical portion called pilot. Cutting speed = twothirds of the drilling speed for the same hole. Counter boring
Counter sinking This is an operation of making the end of a hole into a conical shape. Cutting speed = half of the cutting speed of drilling for same hole.
Spot facing It is a finishing operation to produce flat round surface usually around a drilled hole, for proper seating of bolt head or nut. It is done using a special spot facing tool.
Tapping Process of cutting internal threads with a thread tool called as tap. Tap is a fluted threaded tool used for cutting internal thread Cutting speed is very slow.
Specification of a radial drilling Power capacity eg: 1.5 hp for drilling motor and 0.5 hp for elevating motor. The range of speed of spindle eg: 50 to 2800 rpm. machine
Length of arm on which drill head can traverse. eg: 600 mm. Vertical movement of the arm eg: 500 mm. Angular swing of arm eg: 360
Boring Machine In machining, boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a cannon barrel. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole.
Boring machine
TYPES OF BORING There are various types of boring. The boring bar may be supported on both ends (which only works if the existing hole is a through hole), or it may be supported at one end. Lineboring (line boring, line-boring) implies the former. Backboring (back boring, backboring) is the process of reaching through an existing hole and then boring on the "back" side of the workpiece (relative to the machine headstock).
The two types of the boring machine, each of which has several varieties, are the horizontal boring and drilling machine, and the vertical boring and turning mill.
HORIZONTAL BORING MACHINE
VERTICAL BORING MACHINE
JIG BORING MACHINE
Floor Type Horizontal Boring Machine
Vertical boring machine
METHODS OF LOCATING HOLES IN JIG BORING M/CS Lead Screw Method Mechanical and electrical gauging Optical Measuring Method
Jigs and Fixtures
Definitions Jig: A device that holds the work and locates the path of the tool. Fixture: A device fixed to the worktable of a machine and locates the work in an exact position relative to the cutting tool. Superior Jig Flexible Fixturing Systems
What are Jigs and Fixtures Anything used to hold a work piece in a desired location Locate parts for precision Repeating process on a series of parts Holding parts for machining, painting, assembly
Two main types of jigs: For machining purposes Locates the component, holds it firmly in place, and guides the cutting tool. For assembly purposes Locates separate component parts and holds them rigidly in their correct positions while they are being connected. Northwestern Tools
Drill jig terms Open jig (also called plate jig or drill template) The simplest type of drill jig Consists of a plate with holes to guide the drills, and may have locating pins that locate the workpiece on the jig
Drill jig terms Drill bushings Precision tools that guide cutting tools such as drill and reamers into precise locations in a workpiece. Accurate Bushing Co.
Drill jig components Jig body Holds the various parts of a jig assembly. Cap screws and dowel pins Hold fabricated parts together
Drill jig components Locating devices Pins, pads, and recesses used to locate the workpiece on the jig.
Drill jig components Clamping devices
Drill jig components Locking pins Inserted to lock or hold the work piece securely to the jig plate while subsequent holes are being drilled.
Uses of Jig and fixture Reduce cost of production. Increase the production. To assure high accuracy of parts Provide for interchangeability Enable heavy and complex parts to machine Reduced quality control expenses. Increased versatility of machine tool. Less skilled labour. Saving labour. Partially automates the machine tools Use improve the safety, accidents low
Elements of Jig and fixture Sufficiently rigid bodies (plate, box or frame structure Locating elements. Clamping elements. Tool guiding elements. Elements for positioning or fastening the jig or fixture.
Dimensioning Jig Drawings
Designing jigs Jigs can also be designed as per requirement of the workpiece for holding and other machining operations. Northwestern Tools
Type of Fixtures Milling fixtures Fixture components Fixture design considerations Sequence in laying out a fixture Standard Parts Co.
Fixture components Fixture base Standard Parts Co. Fixture components and the workpiece are usually located on a base, which is securely fastened to the milling machine table.
Fixture components Clamps American Drill Bushing Co. Clamps counteract forces from the feed of the table and rotation of the cutter.
Fixture components Set blocks Cutter set blocks are mounted on the fixture to properly position the milling cutter in relation to the workpiece.
Basic Categories of Jigs Clamps Chucks Vises Bushings Modular Fixtures
Clamps
Chucks
Vises
Bushings
Modular Fixturing
Application
Resources Catalogs Websites Journal Articles
Jigs and Fixtures
V-location In V-location, work pieces having circular or semicircular profile are located by means of a Vee block. The block should be used accurately so that the variation in the work piece size are not detrimental to location.
Vee can be used for both locating and clamping purpose for this two Vee can be used, one fixed other sliding one. Fixed Vee is used for locating and sliding one for clamping.
The sliding Vee block may be actuated by means of a hand operated screw.
Bush location Shaft type work pieces can be easily locate in a hardened steel bushes. The bushes can be plain or flanged type. A flange straighten the bush and also prevent it from being driven into the jig body if it is left unlocked.
Design principles of location purpose The following principles should be followed while locating surfaces. 1.At least one datum or reference surface should be established at the first opportunity. 2. For ease of cleaning, locating surfaces should be as small as possible. 3. The locating surfaces should not hold swarf and thereby misalign the workpiece
4.Locating surfaces should be raised above surrounding surfaces of the jigs or fixture. 5. Sharp corners in the locating surfaces must be avoided. 6. Adjustable type of locaters should be used for the location on rough surfaces.
7. Locating pins should be easily accessible and visible to the operator. 8. To avoid distortion of the work, it should be supported as shown in fig.