0DQXIDFWXULQJ 7HFKQRORJ\,,

Transcription

1 0DQXIDFWXULQJ 7HFKQRORJ\,, (For B.E. Mechanical Engineering Students) Dr. S.Ramachandran, M.E., Ph.D., Professor and Head R. Thamarai Kannan, M.Tech., Assistant Professor Department of Mechanical Engineering Sathyabama University Jeppiaar Nagar, Chennai Dr. S. Ramesh, B.E., M.Tech (IIT-M), Ph.D., Principal Annai Mathammal Sheela Engineering College, Erumapatty, Namakkal (DT) AIR WALK PUBLICATIONS (Near All India Radio) 80, Karneeshwarar Koil Street, Mylapore, Chennai Ph.: , aishram2006@gmail.com

2 First Edition: Second Edition: All Rights Reserved by the Publisher This book or part thereof should not be reproduced in any form without the written permission of the publisher. Dedicated to Copies can be had from : Our Parents AIR WALK PUBLICATIONS (Near All India Radio) 80, Karneeshwarar Koil Street, Mylapore, Chennai Ph.: , Books available in all book stalls with attractive discounts Books will be door delivered after payment into AIR WALK PUBLICATIONS A/c No (IFSC: BKID ) Bank of India, Santhome branch, Mylapore, Chennai - 4 (or) S.Ramachandran, A/c.No (IFSC:IDIB000S201), Indian Bank, Sathyabama University Branch, Chennai ISBN : Typeset by: aksharaa muthra aalayam, Chennai Ph.: Printed at: Abinayaram Printers, Chennai - 4. Ph.: ,

3 Anna University Syllabus MANUFACTURING TECHNOLOGY II Unit I Theory of Metal Cutting 9 Introduction: Material removal processes, types of machine tools - theory of metal cutting: chip formation, orthogonal cutting, cutting tool materials, tool wear, tool life, surface finish, cutting fluids. Unit II Centre Lathe and Special Purpose Lathes 9 Centre lathe, constructional features, cutting tool geometry, various operations, taper turning methods, thread cutting methods, special attachments, machining time and power estimation. Capstan and turret lathes - automats - single spindle, Swiss type, automatic screw type, multi spindle - Turret Indexing mechanism, Bar feed mechanism. Unit III Other Machine Tools 9 Reciprocating machine tools: shaper, planer, slotter - Milling: types, milling cutters, operations - Hole making: drilling - Quill mechanism, Reaming, Boring, Tapping - Sawing machine: hack saw, band saw, circular saw; broaching machines; broach construction -push, pull, surface and continuous broaching machines. Unit IV Abrasive Processes and Gear Cutting 9 Abrasive processes: grinding wheel - specifications and selection, types of grinding process - cylindrical grinding, surface grinding, centreless grinding - honing, lapping, super finishing, polishing and buffing, abrasive jet machining - Gear cutting, forming, generation, shaping, hobbing. Unit V CNC Machine Tools and Part Programming 9 Numerical control (NC) machine tools - CNC: types, constructional details, special features - design considerations of CNC machines for improving machining accuracy - structural members - slide ways - linear bearings - ball screws - spindle drives and feed drives. Part programming fundamentals - manual programming - computer assisted part programming. Total Number of Periods: 45 Periods

4 JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY III Year B.Tech. M.E.I-Sem MACHINE TOOLS (PRODUCTION TECHNOLOGY II) UNIT I T P C 4+1* 0 4 Elementary treatement of metal cutting theory Element of cutting process Geometry of single point tool and angles chip formation and types of chips built up edge and its effects chip breakers. Mechanics of orthogonal cutting Merchant s Force diagram, cutting forces cutting speeds, feed, depth of cut, tool life, coolants, machinability Tool materials. Kinematic schemes of machine tools Constructional features of speed gear box and feed gear box. UNIT II Engine lathe Principle of working, specification of lathe types of lathe work holders tool holders Box tools Taper turning thread turning for Lathes and attachments. Turret and capstan lathes collet chucks other work holders tool holding devices box and tool layout. Principal features of automatic lathes classification Single spindle and multi-spindle automatic lathes tool layout and cam design. UNIT III Shaping slotting and planing machines Principles of working Principal parts specification classification, operations performed. Kinematic scheme of the shaping slotting and planning machines, machining time calculations. UNIT IV Drilling and Boring Machines Principles of working, specifications, types, operations performed tool holding devices twist drill Boring machines Fine boring machines Jig Boring machine. Deep hole drilling machine. Kinematics scheme of the drilling and boring machines

5 UNIT V Milling machine Principles of working specifications classifications of milling machines Principal features of horizontal, vertical and universal milling machines machining operations Types geometry of milling cutters milling cutters methods of indexing Accessories to milling machines, kinematic scheme of milling cutters milling cutters methods of indexing. UNIT VI Grinding machine Fundamentals Theory of grinding classification of grinding machine cylindrical and surface grinding machine Tool and cutter grinding machine special types of grinding machines Different types of abrasives bonds specification of a grinding wheel and selection of a grinding wheel Kinematic scheme of grinding machines. UNIT - VII Lapping, honing and broaching machines comparison to grinding lapping and honing. Kinematics scheme of Lapping, Honing and Broaching machines. Constructional features of speed and feed Units, machining time calculations UNIT - VIII Principles of design of Jigs and fixtures and uses. Classification of Jigs & Fixtures Principles of location and clamping Types of clamping & work holding devices. Typical examples of jigs and fixtures.

6 Contents 1 CONTENTS Chapter 1 THEORY OF METAL CUTTING 1.1 Introduction Types of motion in machining Metal Removal Processes Classification of Metal Removal Processes Chip forming Processes Turning, Boring and other Lathe Operations Machining parameters and related terms in turning operation Shaping, Planing and Slotting Machining Parameters in Shaping, Planing Drilling and Reaming Machining Parameters for Drilling Milling Machining Parameters in Milling Broaching Thread Cutting Machining Parameters in thread cutting Grinding Honing and Lapping Gear Cutting (a) Formed Cutter method (b) Generating Method Types of Machine / Cutting Tools Parts and Nomenclature of Single Point Cutting Tool

7 2 Manufacturing Technology - II Tool Signature Influence of Tool angles in machining Theory of Metal Cutting Mechanics of Metal Cutting and Chip formation Chip Formation Methods of Metal Cutting Processes Differences between orthogonal and oblique cutting Types of Chips Variables affecting type of chip Continuous Chips Continuous Chips with Built up Edges Discontinuous Chips Chip Breakers Geometry of Chip Formation Cutting Tool Materials Desirable Properties of Cutting Tools (i) Hot Hardness (ii) Wear Resistance (iii) Toughness (iv) Mechanical and Thermal Shock Resistance 1.69 (v) Friction (vi) Chemical reaction/affinity between the Tool and Workpiece (vii) Availability and Manufacture (viii) High Thermal Conductivity (ix) Coefficient of Thermal expansion (x) Tool Cost Types of Cutting Tool Materials (i) Carbon Tool Steels or Carbon Steels (ii) Medium Alloy Steels

8 Contents 3 (iii) High Speed Steels (HSS) (iv) Cast Alloys (or) Stellites (v) Cemented Carbide Tools (vi) Ceramic Tools (vii) Diamond Cutting Tools Tool Wear Tool Wear Mechanisms Types of Tool Damage in Cutting Flank Wear Crater Wear Tool Failure Measurement of Wear Tool Life Tool failure Criterion Factors affecting Tool Life Machining Cost Machinability Factors affecting machinability Surface Finish Cutting Fluids Solved Problems in Cutting Forces CHAPTER - 2 Centre Lathe and Special Purpose Lathe 2.1 Introduction Principle of working of Lathe Types of Lathes Speed lathe Engine lathe or Centre lathe

9 4 Manufacturing Technology - II Bench Lathe Tool room lathe Special purpose lathe Capstan and Turret lathes Automatic lathes Numerically controlled lathes Size and Specification of a Centre Lathe Centre Lathe Constructional features of centre lathe Bed Head stock Tail stock Carriage Tool post Apron Feed mechanisms End Gear Train Tumbler Gear mechanism Feed gear box Feed rod and Lead screw Drive Mechanism Feed rod or Feed shaft Lead screw Apron mechanism Half nut mechanism (Thread cutting mechanism) Head stock mechanisms Lathe Accessories and Attachments Lathe Accessories (a) Lathe centres (b) Chucks (i) Three jaw or Universal chuck

10 Contents 5 (ii) Four Jaw chuck (iii) Collet chuck (iv) Magnetic chuck (c) Face plate (d) Angle plates (e) Catch plate and carriers (dogs) (f) Mandrels (g) Steady Rest (h) Follower rest Cutting Tools Classification of cutting tools (single point cutting tool) Factors affecting cutting Tool efficiency Types of tools (i) Forged tool (solid tool) (ii) Brazed tip tool (iii) Fastened tip tool (Mechanical fastening) (iv) Tool bit and Tool holders (v) Tools for method of operation (a) Turning Tool (b) Chamfer Tool (c) Boring Tool (d) External Thread Cutting Tool (e) Internal Thread Cutting Tool (f) Facing Tool (g) Grooving tool (h) Parting Tool (i) Right Hand Tool (j) Left Hand Tool (k) Round Nose Tool Cutting Tool Geometry

11 6 Manufacturing Technology - II Single Point Cutting Tool terms and Gemoetry (a) Back rake angle (b) Side Rake Angles (c) End Relief Angle (Clearance Angle) (d) Side Relief Angle (e) End cutting Edge Angle (f) Side cutting edge Angle (Lead Angle) (g) Lip Angle Chip Breaker Lathe Operations Centering Plain or Straight Turning (i) Rough turning (ii) Finish Turning Shoulder Turning (or) Step turning Taper Turning Eccentric Turning Cam Turning Chamfering Facing Knurling Filing Polishing Grooving or Necking Parting-Off Spinning Spring Winding Forming Drilling Reaming

12 Contents Boring Counter boring, counter sinking and spotfacing Tapping Under cutting Taper boring Milling Grinding Taper Turning Methods Taper turning by using a form tool Compound rest swiveling method Set over or tailstock offset Method Taper turning attachment method Template and tracer attachment Combination of longitudinal and cross feed Thread Cutting Change Gear Calculations Types of Gear connections Metric Thread on English Lead Screw Procedure for cutting external thread Cutting Internal thread procedure Cutting Left hand threads Cutting Tapererd threads Square thread cutting Cutting Multiple Start threads Special Attachments Milling Attachment Grinding Attachment Gear cutting on Lathe Machining Time and Power Calculation

13 8 Manufacturing Technology - II 2.12 Capstan and Turret Lathe Introduction Capstan and Turret lathe Principle parts of Capstan and Turret lathe Types of Turret Lathes Difference between Capstan - Turret lathe and Engine Lathe Difference between Capstan and Turret lathe Size and specification of Turret Lathe Work holding devices Tool holding devices Turret Tools Tooling layout for Capstan and Turret Lathes Automats Automation Mechanisms on Capstan and Turret Lathes Turret Indexing Mechanism or Geneva Mechanism Bar Feeding Mechanism CHAPTER - 3 Other Machine Tools 3.1 Reciprocating Machine Tools Shaper Parts of a shaper Shaper drive mechanisms Feed Mechanism

14 Contents Work holding devices in shaper Shaper Operations Shaper tools (Shaper cutting tools) Shaper Cutting Speed, Feed and Depth of Cut Planing Machine Planer Size and Specifications Main parts of a planer Driving mechanism Electrical drive: (Table drive by reversible Electric motor) Types of tool Planer operations Slotter Specification of slotter Drives Feed mechanism Work holding devices Slotter tools Slotter operations Milling Milling Machine Size and specification of milling machine Comparison between plain and universal milling machine Work holding devices Cutter holding device (or) Tool holding device Milling Machine Attachments Milling Cutters Plain milling cutter Side milling cutter

15 10 Manufacturing Technology - II 3. End Mill Cutters Angle milling cutter Form milling cutters Metal slitting saw cutters T-slot milling cutters Fly cutter Nomenclature of plain milling cutter Cutter Angle Fundamentals of the milling process Peripheral milling (i) Up milling (ii) Down milling Face milling Milling Operations (i) Plain (or) Slab milling (ii) Face milling (iii) Angular milling (iv) Straddle Milling (v) Gang Milling (vi) End Milling (vii) Form Milling (viii) Gear Cutting (ix) T-slot milling (x) Side Milling Indexing (or) Dividing Heads Indexing Method Hole Making Drilling Machine Classification of drilling machine Specification of drilling machine Feed mechanism

16 Contents Drilling operations (i) Drilling (ii) Reaming (iii) Boring (iv) Counter boring (v) Counter sinking (vi) Spot facing (vii) Tapping (viii) Grinding (ix) Lapping (x) Trepanning Drill Tool Nomenclature Drill holding devices Reaming tools Types of Reamers Tapping Tool Drilling parameters calculations Solved Problems Boring Types of boring machines Horizontal boring machine Vertical Boring Machine: (VBM) Horizontal boring machine operations Vertical boring machine operations Boring cutting tools Precision boring machine Jig boring machine Sawing Machines Selection of Blade for Sawing Machine Broaching Types of broaching machines

17 12 Manufacturing Technology - II 3.58 Size and specification of broaching machines Tool Nomenclature Broaching Operations CHAPTER - 4 Abrasive Processes and Gear Cutting 4.1 Introduction Abrasives Natural Abrasives (i) Sandstone or solid quartz (ii) Emery (iii) Corundum (iv) Diamonds (v) Garnet Artificial Abrasives (i) Silicon Carbide (SiC) (ii) Aluminium oxide Al 2O (iii) Boron carbide (iv) Cubic Boron Nitride (CBN) Abrasive grain size or Grit Number and Geometry Grinding Principle of Grinding Mechanics of Grinding Grinding Wheel Characteristics of Grinding wheel Type of abrasive used Grain size or Grit size Wheel Grade and Hardness Grain spacing or structure Type of Bond

18 Contents 13 (a) Vitrified bond (b) Silicate bond (c) Shellac bond (d) Rubber bonding (e) Bakelite or Resinoid bond (f) Oxychloride bond Size and shape Mounted wheels Specification and selection of Grinding wheel Standard marking system of Grinding wheel Selection of Grinding wheels Glazing, Loading and Gumming of Grinding wheels (i) Glazing (ii) Loading (iii) Gumming Dressing and Truing of Grinding wheel (i) Dressing (ii) Truing Balancing of Grinding Wheel Mounting of Grinding Wheels Parameters In Grinding Types of Grinding Machines and Processes Rough grinders (a) Floor stand grinder and bench grinder (b) Portable and Flexible shaft grinder (c) Swing frame grinder (d) Abrasive belt grinders Precision grinding machines Cylindrical grinding (centre type) machines

19 14 Manufacturing Technology - II (i) Traverse grinding (ii) Plunger type grinding Plain centre type grinder Parts of plain centre type grinder Universal centre type grinder Plunge-centre type grinding machine Centre-less type grinding machines (i) Through feed (ii) In-feed centreless grinding (plunge cut grinding) (iii) End-feed centreless grinding Internal Grinders (i) Work rotating type or chucking type (ii) Planetary type (iii) Centreless internal grinding Surface grinding machines (i) Planar or reciprocating table type (ii) Rotary table type Tool and cutter grinder Special grinding machines Microfinishing Processes Honing Honing tool Lapping Methods of lapping (i) Individual piece lapping (ii) Matched piece lapping (iii) Hand lapping (iv) Machine lapping Types of lapping operations Super finishing Buffing and polishing

20 Contents Polishing Buffing Abrasive Jet Machining (AJM) Gear Cutting and Manufacture Gear manufacturing methods (i) Non machining process (forming process) (ii) Machining process Form cutting processes Gear cutting using End cutter/end mill in milling machine Procedure for spur gear cutting in milling machine by formed cutter Indexing and dividing heads Indexing methods Simple Indexing Compound Indexing Differential Indexing Helical gear milling by form disc cutter Gear cutting by a single point cutting tool (Formed tool) Gear cutting by formed end mill Gear cutting by shear speed process Gear cutting by template method Gear generating processes Gear planing process (Rack cutter generating process) Gear shaping process (pinion cutter generating method) Gear hobbing process Gear hobbing machines Gear forming (Non machining methods) Casting

21 16 Manufacturing Technology - II Hot rolling Stamping Powder-metallurgy Extruding Coining Chapter 5 CNC Machine Tools and Part Programming 5.1 Numerical Control (NC) Machine Tools CNC CNC System Basic components of CNC system Standard Axes of Machine Tool Feed Back Device Classification of CNC Systems Classification of CNC Based on Feed Back Control Open Loop Control System Closed loop control system Classification of CNC based on motion control system Point to Point (Positional) control system (PTP) Straight line Paraxial Motion control system (or) Straight Cut control system: Contouring control system (Continuous path control system): Interpolators Absolute Positioning System Incremental coordinate system CNC controllers Functions of CNC Controllers Direct Numerical Control (DNC system)

22 Contents Components of DNC system Advantages of DNC Design consideration of CNC machines for improving machining accuracy Factors affecting CNC machine s accuracy Factors to be considered for testing the performance of a CNC machine Control System Design Analog Control System Digital Control System Punched tape (or) Magnetic Tape (or) Pendrive (USB) (or) CD Open loop vs Closed loop system Linear vs Rotary Transducers Mechanical System Design Main Structural Members of CNC Machine Tools Slides and Slideways (or) Guide Ways Friction Slideways (Wear resistant slideways) V-slideways Flat and Dovetail Slideways Cylindrical guideways Anti Friction Linear Motion (LM) Guideways Recirculating linear ball bearings (for slide ways) Recirculating Ball Bush (for slide ways) Recirculating Ball Screw and nut (for slideways) Hydrostatic Type Slideways Aerostatic Slideways

23 18 Manufacturing Technology - II 5.28 Spindle Drives and Feed Drives Work Holding Devices Requirements of work holding devices Linear Pallet shuttle Rotary Pallet Tool Holding Devices Spindle Tooling Automatic Tool Changers Tool Magazine - Turret Chain Type Tool Magazine Tool changing Feed Back Devices Linear Transducers Glass scales with line grating Ferranti system (using Moire Fringe effect) Binary Coded Scale Inducto syn Rotary transducer (Angular position measuring transducer) (a) Absolute Encoder (b) Incremental encoder Resolver Machining Centers Vertical Machining Centre: (VMC) Horizontal Machining Centre: (HMC) Universal Machining Centre Tooling for CNC Machines Part Programming Fundamentals for CNC Machines Types of Words (or) Codes in CNC Standard Formats in Programming:

24 Contents Word Address Format Tab sequential Format Fixed Block Format Manual Part Programming Part programming for PTP (Point to Point) machining: Part programming for machining along curved surface (Turning Operation) Part programming for Milling operations: Subroutines (Macros) (L code) Canned Cycles: [(or) Fixed cycle (or) Standardised cycle] Non-standarised Fixed cycles Do-Loops Parametric Subroutines Macros Mirroring Computer Assisted Part Programming (CAP) APT [Automatically Programmed Tools] ADAPT EXAPT APT Language Four Types of Apt Statements Geometry Statement Motion Statements Postprocessor Statements Auxiliary Statement: Macro Statement in APT to 194

25 Theory of Metal Cutting 1.1 Chapter 1 THEORY OF METAL CUTTING 1.1 INTRODUCTION Machining is a manufacturing process which involves forcing of a cutting tool through the excess material of the work piece thereby removing the unwanted material in the form of chips, so as to obtain the final desired shape and size to the work piece. It may be emphasized that the cutting tool never peels off chips or the excess material from the work piece, but the chips are generated because of plastic deformation of metal just ahead of the cutting edge of the tool. Machining is normally the most expensive manufacturing process because more energy is consumed and a lot of waste material is generated in the process. Still, machining is widely used because, It delivers very good dimensional accuracy and good surface finish. Machine tools does not require elaborate tooling. Machining can be employed to all engineering materials. It can also generate accurate contours with high tolerances. The wear of tool is not costly, if it is kept within limit. Large number of parameters can be suitably controlled during machining.

26 1.2 Manufacturing Technology - II Types of motion in machining For machining, it is necessary to have relative motions between the work piece and tool. Two types of relative motions are necessary. For example, to drill a hole, we have to rotate the drill or work piece and besides this, we have to press the drill against the work piece. The first motion (i.e rotation of drill or work piece) is called the primary or cutting motion and the second motion (pressing of drill) is called feed motion. In turning a circular cylinder on lathe, the cutting motion is obtained by rotation of the workpiece, and feed motion forms the motion of tool parallel or perpendicular to work piece axis and normal to the cutting motion. The cutting speed is the rate of primary cutting motion and it determines the rate at which the material is being removed. In all machine tools, the primary cutting motion is powered. Apart from small machines with hand feeds, feed motions on most of the machine tools are also powered. Auxiliary or handling motion helps to handling and clamping of the work piece in the machine, advancing the cutting tool to engage the work piece, positioning the tool in desired orientation with respect to workpiece, disengaging tool, withdrawing tool, removing machined work piece. On manually operated machine tools, auxiliary motions are performed manually by operator. In automatic machine tools, the auxiliary motions are carried out in the required sequence by the machine itself.

27 Theory of Metal Cutting METAL REMOVAL PROCESSES Metal removal process is a manufacturing process by which a work piece is given (i) a desired shape (ii) a desired size and (iii) a desired surface finish. To achieve one or all of these, the excess material from the work piece is removed in the form of chips with the help of some properly shaped and sized tools. The metal removal processes are chip forming processes Classification of Metal Removal Processes Metal removal processes are broadly classified into two categories. (i) Chip forming (Metal Cutting / Removal) Processes: Examples are Turning, Boring, Shaping, Planing, Slotting, Drilling, Reaming, Milling, Broaching, Thread Cutting, Grinding, Honing, Gear cutting etc., (ii) Chipless Forming Processes: Examples are Rolling, Spinning, Forging, Extrusion, Stamping etc., Chip forming Processes Chip forming processes are manufacturing processes in which the desired shape, size and surface finish of work piece is obtained by separating layer from parent workpiece in the form of chips, whereas in chipless forming processes no chips are formed Turning, Boring and other Lathe Operations Traditional machining operations like turning, boring, facing, grooving, thread cutting, drilling, chamfering etc are carried out on a machine tool called

28 1.4 Manufacturing Technology - II Lathe. Lathe is one of the most important machine in any workshop. Its main objective is to remove material from outside by rotating the work against a cutting tool. The various Lathe Operations are discussed as below. Turning: Turning is a machining operation for generating external surfaces of revolution (cone-shaped or cylindrical shaped) on the workpiece. In turning, work is rotated where as tool has a linear motion, parallel to the axis of the work. In this operation, the work is held either in the chuck or between centers and the longitudinal feed is given to the tool either by hand or power. Turning operation is shown in Fig The turning operation in which there are steps on the work is called step turning as shown in Fig 1.2 Work Chuck Chuck Work Chuck Work Fig 1.1 Plain turning Fig 1.2 Step turning Fig 1.3 Facing Facing: When the feed motion of the tool is axial i.e parallel to the work piece axis, a cylindrical surface is generated. If on the other hand, feed motion is radial (normal to the axis of rotation), an end face or shoulder is produced. This operation is called facing as shown in Fig. 1.3.

29 Theory of Metal Cutting 1.5 Boring: Boring is a machining operation for generating internal surface of revolution i.e., it is an operation of enlarging of a hole already made in workpiece with the help of a single point tool called boring tool. Boring tool is held in the tool post and fed into the work by hand or power by movement of carriage. Boring is shown in Fig. 1.4 Chuck Work Chuck Work Boring tool Drill Fig 1.4 Boring Fig 1.5 Drilling Drilling: Drilling is an operation of making a hole in a workpiece with the help of a drill. In this operation, the work piece is held in the chuck and drill is held in the tail stock. The drill is fed manually into the rotating workpiece by rotating the tailstock hand wheel. Drilling is shown in Fig Reaming: Reaming is an operation of finishing the previously drilled hole. In this operation as shown in Fig. 1.6, a reamer tool is held in tail stock and it is fed into the hole in the similar way as for drilling. Undercutting or Grooving: It is an operation of making a groove on the body of work, by feeding the tool perpendicular to the axis of the workpiece. In this

30 1.6 Manufacturing Technology - II Chuck Work Reamer Chuck Work Tool Fig 1.6 Reaming Fig 1.7 Under cutting operation as shown in Fig 1.7, a tool of appropriate shape is fed into the rotating work piece upto the desired depth at right angles to the centre line of the work piece. Threading: It is an operation of cutting helical grooves (threads) on the external cylindrical surface of workpiece as shown in Fig The work is held in a chuck or between centers and the threading tool (V-tool) is fed longitudinally to the rotating workpiece. The longitudinal feed is equal to the pitch of the thread to be cut. Work Work Threading V-Tool Fig 1.8 Threading KnurlingTool Fig 1.9 Knurling

31 Theory of Metal Cutting 1.7 Knurling: Knurling is a process of impressing diamond shaped or straight line pattern on to the surface of a work piece. The diamond shaped pattern or impressions are called knurls. In this operation, a knurled tool is moved longitudinally to a rotating workpiece. The projection on the knurled tool reproduces depressions on the work surface as shown in Fig Machining parameters and related terms in turning operation The different machining parameters or variables in turning are discussed below (Refer Fig. 1.10) Work piece Direction of rotation b d Position of Tool at start Position of Tool after one revolution f s Tool Fig 1.10 Geometry of Cut in Turning Cutting speed (V): Cutting speed is the relative velocity between work piece and cutting edge of tool responsible for cutting action. It is given by relationship V DN 1000 in m/min

32 1.8 Manufacturing Technology - II where D Diameter of work at engagement N Rotational speed of work in RPM Uncut chip thickness: It is the thickness of the layer of material being removed by the cutting tool in the direction of the feed motion. The feed in turning is normally expressed in mm per revolution. Uncut chip thickness t f cos s where f Feed per revolution. s Side cutting edge angle of turning tool. Depth of cut: It is the normal distance between the machined and unmachined surfaces measured along a normal to the machined surface. In turning, it is the radial distance between machined and unmachined surface. From the Fig. 1.10, the cutting edge engagement is b while the depth of cut is d, hence, Depth of Cut d b cos s Area of Uncut Chip: It is the cross sectional area A c of the layer of the work being machined. Area of Uncut chip A c f d. Metal removal rate (R w : It is the volume of material being removed per unit time from the work piece. R w 1000 f d V in mm 3 /min Here, f, d are in mm, V is in m/min Machining time: If L is the length of workpiece to be turned, then the time of cutting T c per pass is given by

33 Theory of Metal Cutting 1.9 Time T c L/f N In machining, however tool is not positioned in direct contact with the work piece at the start of cut. It is kept at a small distance away from the job. This is called approach allowance or approach length l a. Then, The Machining Time T m L l a f N Problem 1.1 Evaluate the machining time for turning of a 100 mm diameter rod to 92 mm diameter over a length of 60 mm at a spindle speed of 500 RPM. The maximum depth of cut is limited to 3 mm and the feed f is 0.5 mm per rev. The side cutting edge angle of the tool is 30. Approach allowance 5 mm. Also calculate cutting speed for each pass. Given: Initial diameter D i 100 mm, Final diameter D f 92 mm, Length L 60 mm, Speed N 500 RPM, d 3 mm, f 0.5 mm/rev, s 30, l a 5 mm Solution Total diameter to be reduced D i D f mm Diameter reduced in one pass d mm No. of pass required to reduce 8 mm 2 pass. One Rough pass of 3 mm depth of cut and one finish pass of 1 mm depth of cut mm

34 1.10 Manufacturing Technology - II Cutting Speed for 1 st rough pass V 1 D i N m/min Cutting Speed for 2 nd finish pass V 2 D i 6 N m/min Since for both the passes, the spindle speed and feed are common Machining time T m No. of passes L l a f N T m mins Shaping, Planing and Slotting Shaping is a machining operation for generating flat surface by means of single point cutting tool reciprocating over a stationary work piece. The feed motion is intermittent i.e. imparted to the work piece at the end of each stroke. The reciprocating motion of the tool is obtained either by the crank and slotted lever quick return motion mechanism or whitworth quick return motion mechanism. The shaping action is shown in the Fig The surfaces produced in shaping may be horizontal, vertical or inclined. Shaping is performed on the machine tool called shaper. In general, shaper can produce any surface composed of straight line elements. Some of examples of the parts produced by shaping operation are shown in Fig. 1.12

35 Theory of Metal Cutting 1.11 Tool Tool motion d f Work Piece Fig 1.11 Shaping Action (a) Grooved block (b) Dovetail slide (c) Guide grib (d) V-block 1.12 Parts produced on a shaper

36 1.12 Manufacturing Technology - II Planing is a machining operation similar to shaping operation primarily intended to produce plane and flat surfaces by a single point cutting tool. The fundamental difference between a shaping and planing is that in planing the work which is supported on the table reciprocates past the stationary cutting tool and the feed is supplied by the lateral movement of the tool, whereas in shaping the tool which is mounted upon the ram reciprocates and the feed is given by the crosswise movement of the table. Planing operations are carried on machine tool called planer. Slotting operation falls into the category of shaping and planing. The major difference between a slotting and shaping is that in a slotting, the ram holding the tool reciprocates in a vertical axis, whereas in shaping the ram holding the tool reciprocates in a horizontal axis. A vertical shaper and slotter are almost similar to each other as regards their construction, operation and use. Slotting operation is used for cutting grooves, keyways, slots of various shapes, for cutting internal and external gears etc Machining Parameters in Shaping, Planing In shaping or planing, the cutting speed V varies even in a single stroke. Cutting speed V is calculated as follows. Cutting Speed V N L in m/min where N : No. of Complete Strokes per minute (one working stroke return stroke) L : Length of stroke in mm;

37 Theory of Metal Cutting 1.13 : Ratio of time taken in return stroke to time taken in cutting stroke. Depth of Cut d: Depth of cut is equal to the normal distance between the unmachined and machined surface measured along a normal to the machined surface. Nominal feed rate f is equal to the movement given to the workpiece in a shaper (or to the tool in planer) in a direction normal to other cutting velocity direction. Area of uncut chip A c f d Metal removal rate R w f d L w N Machining time T m B w For Shaping f N where L w : Length of workpiece along stroke B w : Width of the workpiece Machining Time for Planer T m B w l s 1 B w t f s V c f r. s where l s Length of stroke f s V c t r Feed per stroke Average cutting speed in m/min Average cutting speed to average return speed ratio Time for reversal of work table.

38 1.14 Manufacturing Technology - II Drilling and Reaming Drilling is a machining operation in which a hole is produced or enlarged by use of a cutting tool called drill, usually having more than one cutting edge. The primary cutting motion is a rotary motion given to either work piece or to drill and the feed motion is a translation motion given to drill as shown in Fig The cutting action is done by the cutting edges on the end face. Drill Work piece f t b b Fig 1.13 Drilling Action Reaming is a hole finishing process. The motion of tool is similar as in case of drilling. Cutting edges of a reamer are on its periphery. These cutting edges are either straight or helical.

39 Theory of Metal Cutting Machining Parameters for Drilling Cutting Speed V D N in m/min 1000 where D Drill diameter in mm N Speed of drill in RPM d Depth of Cut d D/2 Feed f Feed per revolution of drill (or) movement of drill along its axis in one revolution. Uncut chip thickness t c f cos 90 where 2 is point angle of drill. Area of Uncut chip A c f D/n 2 where n No. of cutting edges. Metal removal rate R w D2 f N 4 in mm 3 /min Machining time T m L f N where L Length of hole Milling Milling is a machining process in which flat as well as curved surfaces are produced by rotating multi-edges cutting tools called milling cutters and the work is fed past it. The work piece is rigidly mounted on the machine table and the cutter is on the spindle or arbor. The work is fed slowly past the cutter while the cutter revolves at fairly high speed. The main milling operations are Slab milling, Face milling,