SECOND EDITION Fundamentals of Machining Processes Conventional and Nonconventional Processes Hassan Abdel-Gawad El-Hofy Tai ngay!!! Ban co the xoa dong chu nay!!! SECOND EDITION Fundamentals of Machining Processes Conventional and Nonconventional Processes SECOND EDITION Fundamentals of Machining Processes Conventional and Nonconventional Processes Hassan Abdel-Gawad El-Hofy Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2014 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S Government works Version Date: 20130620 International Standard Book Number-13: 978-1-4665-7703-9 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint Except as permitted under U.S Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers For permission to photocopy or use material electronically from this work, please access www.copyright com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400 CCC is a not-for-profit organization that provides licenses and registration for a variety of users For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com I dedicate this edition of the book to Omer, Youssef, Zaina, Hassan, and Hana Contents Foreword xvii Preface xix Acknowledgments xxiii Author xxv List of Symbols xxvii List of Abbreviations xli Machining Processes 1.1 Introduction 1.2 Historical Background 1.3 Classification of Machining Processes 1.3.1 Machining by Cutting 1.3.1.1 Form Cutting 1.3.1.2 Generation Cutting 1.3.1.3 Form and Generation Cutting .6 1.3.2 Machining by Abrasion 1.3.3 Machining by Erosion 11 1.3.3.1 Chemical and Electrochemical Erosion 11 1.3.3.2 Thermal Erosion 11 1.3.4 Combined Machining 12 1.3.5 Micromachining 13 1.4 Variables of Machining Processes 14 1.5 Machining Process Selection 15 Review Questions 16 Cutting Tools 17 2.1 Introduction 17 2.2 Tool Geometry 19 2.2.1 American (ASA) (Tool-in-Hand) (Coordinate) System 21 2.2.2 Tool Angles in Orthogonal System of Planes 22 2.2.3 Relationship between the ASA and Orthogonal Systems 26 2.2.4 Effect of Tool Setting 27 2.2.5 Effect of Tool Feed Motion 28 2.2.6 Solved Example 29 2.3 Tool Materials 29 2.3.1 Requirements of Tool Materials 29 vii viii Contents 2.3.2 Classification of Tool Materials 31 2.3.2.1 Ferrous Tool Materials 31 2.3.2.2 Nonferrous Tool Materials 33 2.3.2.3 Nanocoated Tools 42 Problems 45 Review Questions 46 Mechanics of Orthogonal Cutting 47 3.1 Introduction 47 3.2 Chip Formation 47 3.2.1 Discontinuous Chip 48 3.2.2 Continuous Chip 49 3.2.3 Continuous Chip with a Built-Up Edge 51 3.3 Orthogonal Cutting 52 3.3.1 Force Diagram .54 3.3.2 Shear Angle 56 3.3.3 Shear Stress 58 3.3.4 Velocity Relations 58 3.3.5 Shear Strain 59 3.3.6 Rate of Strain 60 3.3.7 Theory of Ernst–Merchant 60 3.3.8 Theory of Lee and Shaffer 62 3.3.9 Experimental Verification 63 3.3.10 Energy Consideration 64 3.3.11 Solved Example .64 3.4 Heat Generation in Metal Cutting 66 3.4.1 Cutting Tool Temperature 68 3.4.2 Temperature at Shear Plane 70 3.4.3 Factors Affecting the Tool Temperature 71 3.4.3.1 Machining Conditions 72 3.4.3.2 Cutting Tool 72 3.4.3.3 Cutting Fluids 72 3.4.4 Temperature Measurement 77 3.4.5 Solved Example 78 Problems 80 Review Questions 84 Tool Wear, Tool Life, and Economics of Metal Cutting 87 4.1 Tool Wear 87 4.1.1 Introduction 87 4.1.2 Forms of Tool Wear 88 4.1.2.1 Crater Wear 89 4.1.2.2 Flank Wear .90 4.1.3 Impact of Tool Wear 92 Contents ix 4.2 Tool Life 93 4.2.1 Formulation of Tool-Life Equation 93 4.2.2 Criteria for Judging the End of Tool Life 95 4.2.3 Factors Affecting the Tool Life 96 4.2.3.1 Cutting Conditions 96 4.2.3.2 Tool Geometry 96 4.2.3.3 Built-Up Edge Formation 97 4.2.3.4 Tool Material 97 4.2.3.5 Workpiece Material 97 4.2.3.6 Rigidity of the Machine Tool 98 4.2.3.7 Coolant 98 4.2.4 Solved Example 98 4.3 Economics of Metal Cutting 99 4.3.1 Cutting Speed for Minimum Cost 100 4.3.2 Cutting Speed for Minimum Time 104 4.3.3 Cutting Speed for Maximum Profit Rate 106 4.3.4 Solved Example 108 Problems 109 Review Questions 110 Cutting Cylindrical Surfaces 113 5.1 Introduction 113 5.2 Turning 113 5.2.1 Cutting Tools 114 5.2.2 Cutting Speed, Feed, and Machining Time 114 5.2.3 Elements of Undeformed Chip 117 5.2.4 Cutting Forces, Power, and Removal Rate 118 5.2.5 Factors Affecting the Turning Forces 120 5.2.5.1 Factors Related to Tool 120 5.2.5.2 Factors Related to Workpiece 121 5.2.5.3 Factors Related to Cutting Conditions 121 5.2.6 Surface Finish 122 5.2.7 Assigning the Cutting Variables 125 5.2.8 Solved Example 125 5.3 Drilling 128 5.3.1 Drill Tool 129 5.3.2 Elements of Undeformed Chip 130 5.3.3 Cutting Forces, Torque, and Power 133 5.3.4 Factors Affecting the Drilling Forces 135 5.3.4.1 Factors Related to the Workpiece 136 5.3.4.2 Factors Related to the Drill Geometry 136 5.3.4.3 Factors Related to Drilling Conditions 137 5.3.5 Drilling Time 137 5.3.6 Dimensional Accuracy 138 493 Machining Process Selection Roughness average (Ra), µm (min) 50 Process 25 12.5 6.3 3.2 1.6 0.80 (2000) (1000) (500) (250) (125) (63) (32) Flame cutting Snagging Sawing Planing, shaping Drilling Chemical milling Electrical discharge machining Milling 0.40 0.20 0.10 0.05 0.025 0.012 (16) (4) (2) (8) (1) (0.5) Average application Less frequent application Broaching Reaming Electron beam Laser Electrochemical Boring, turning Barrel finishing Electrolytic grinding Roller burnishing Grinding Honing Electropolishing Polishing Lapping Superfinishing Sand casting Hot rolling Forging Permanent mold casting Investment casting Extruding Cold rolling, drawing Die casting FIGURE 16.3 Surface roughness produced by common production methods 1-Surface texture (From Surface Roughness, Waviness, and Lay, ANSI/ASME B 46.1-1985, American Society of Mechanical Engineers With permission.) The principal causes of surface alterations produced by the machining processes are High temperatures and high temperature gradients Plastic deformation (PD) Chemical reactions and subsequent absorption into the machined surface Excessive machining current densities Excessive energy densities Table 16.7 summarizes the possible surface effects by different machining processes of some engineering metals and alloys 494 Fundamentals of Machining Processes TABLE 16.7 Summary of Possible Surface Alterations Resulting from Various Material Removal Processes Conventional Material Nonhardenable 1018 steel Hardenable 4340 and D6ac steel D2Tool steel Type 410 stainless steel (martensitic) Type 302 stainless (austenitic) 17-4 PH steel 350-grade maraging (18% Ni) steel Nickel- and cobalt-base alloys Inconel alloy 718 Rene 41 HS 31 IN 100 Ti-6Al-4V Milling, Drilling, and Turning Grinding R PD L&T R PD L&T MCK UTM OTM R PD L&T MCK UTM OTM R PD L&T MCK UTM OTM R PD L&T R PD L&T OA R PD L&T RS OA HAZ R PD L&T MCK HAZ R PD L&T Nontraditional EDM ECM CHM R PD MCK UTM OTM R MCK RC R MCK RC UTM OTM R SE IGA R SE IGA R SE IGA R SE IGA R PD MCK UTM OTM R MCK RC UTM OTM R SE IGA R SE IGA R PD MCK UTM OTM R MCK RC UTM OTM R SE IGA R SE IGA R PD R SE IGA R SE IGA R SE IGA R SE IGA R PD RS OA R MCK RC R MCK RC OA R RC RS OA R SE IGA R SE IGA HAZ R PD MCK R MCK RC R SE IGA R SE IGA HAZ R PD MCK R MCK RC R SE IGA R SE IGA R PD R PD OA 495 Machining Process Selection TABLE 16.7 (continued) Summary of Possible Surface Alterations Resulting from Various Material Removal Processes Conventional Material Refractory alloy molybdenum TZM Tungsten (pressed and sintered) Milling, Drilling, and Turning Grinding R L&T MCK R L&T MCK Nontraditional EDM R MCK R MCK R MCK R MCK ECM R SE IGA R SE MCK IGA CHM R SE IGA R SE MCK IGA Source: Field, M et al., Ann CIRP, 21(2), 219 With permission Notes: R, roughness of surface; PD, plastic deformation; L & T, laps and tears; MCK, microcracks; HAZ, heat-affected zone; SE, selective etch; IGA, intergranular attack; UTM, untempered martensite; OTM, overtempered martensite; OA, overaging; RS, resolution or austenite reversion; RC, recast, respattered, vapor-deposited metal 16.2.6 Production Quantity The production quantity plays an important role in the selection of the machining process Methods of raising productivity include the use of the following: • • • • • • • High machining speeds High feed rates Multiple cutting tools Staking multiple parts Minimization of secondary (noncutting) time Automatic feeding and tool-changing mechanisms High power densities Production quantity is crucial in determining the type of automation required to produce parts economically The related equipment is selected from the knowledge of inherent capabilities and limitations dictated by the production rate and quantity The choice depends on cost factors and breakeven charts constructed for this purpose Depending on the number of parts to be machined, one of the following scenarios will be adopted: Jobbing production (1–20 pieces): Stand-alone general-purpose machines with manual control, requiring the smallest capital outlay, are used for this purpose Their operation is labor intensive Labor 496 Fundamentals of Machining Processes costs not drop significantly with increasing batch size (Figure 16.4); thus, such machines are best suited to one-off and small batch or jobbing production The operator may be a highly skilled artisan or, in case of repetitive production, may be semiskilled operator These equipment provide high part flexibility (variety) Turret and capstan lathes are preferred than manually controlled machines for batch sizes greater than those indicated by point A (Figure 16.4) Batch production (10–5000 pieces): Stand-alone numerical-controlled (NC), CNC, or machining centers are most suitable for small batch production, although, with the trend toward increasing use of friendly programming devices and with the application of GT, batch sizes involving 100–5000 may be economically machined Once the workpiece is clamped on the CNC-machine tool and the reference point is established, machining proceeds with great accuracy and repeatability Nonproductive setup time is particularly nil Therefore, CNC can become economical even for small lots that are widely separated in time (Figure 16.4) The operator may again be highly skilled, this time with some programming knowledge; alternatively, the programs may be provided to the Manual Unit manufacturing A Turret B NC, CNC FMS General purpose automatics Special purpose automatics and flowlines Material cost 10 102 103 Jobbing production Batch production 104 105 Batch size 106 Mass production FIGURE 16.4 Economical approach and batch size Machining Process Selection 497 machine by a part programmer who may be working from the database of a CAD/CAM system In this case, a semiskilled operator performs machine supervision and service functions FMS may be economically adapted for batch sizes exceeding those indicated by point B (Figure 16.4) Mass production (3,000–1,000,000 pieces): In large batch and mass production, flexible lines or automatics (programmable) are most economical, while special-purpose (hard programmed) transfer lines or automatics are limited to the mass production of standard parts (Figure 16.4) In both cases, special-purpose machinery (dedicated machines) is equipped for transferring materials and parts (flow lines) Although machines and specialized tooling are expensive, both labor skills required and labor costs are relatively low However, these equipment and manufacturing systems are generally adapted for a specific type of product, and hence, they lack flexibility The change over from product to another is very costly 16.2.7 Production Cost The economic aspects of machining processes consider the total cost of a product including the cost of material and tooling and fixed, direct, and indirect labor costs Small batches are commonly made on general-purpose machines that are versatile and capable of producing different shapes and sizes Under such conditions, the direct labor costs are higher For large quantities (medium batches), CNC machines or jigs and fixtures are used, which lead to the reduction of labor cost For larger volumes, the labor costs can further be reduced by using machining centers, flexible machining systems (FMS), or special-purpose machine tools Design for manufacturing (DFM) is one method of achieving high product quality while minimizing the manufacturing cost The following principles aid the designers in specifying components and products that can be produced at minimum cost: Simplicity of the product Standard material and components Standard design of the product Specify liberal tolerances This concept is very important to produce parts accurately and economically Product design recommendations for each operation should be strictly followed by the part designer Design complications should be avoided so that the machining time is reduced, and consequently, the production rate is increased Machine tool and operation capability in terms of possible accuracy and surface integrity should also be considered, so that the best 498 Fundamentals of Machining Processes technology, machine tool, and operation are selected To that end, it is recommended to consider the following: Use the most machinable materials available Avoidance of secondary operations such as deburring, inspection, plating, painting, and heat treatment Design should be suitable for the production method that is economical for the quantity required Utilizing special process capabilities to eliminate many operations and the need for separate costly components Avoiding process restrictiveness and allowing manufacturing engineers the possibility of choosing a process that produces the required dimensions, surface finish, and other characteristics 16.2.8 Environmental Impacts The possible hazards of the selected machining technology may affect the operator’s health, the machine tool, and the surrounding environment (Figure 16.5) Reduction of such hazards requires careful monitoring, analysis, understanding, and control toward environmentally clean machining technology The hazards generated by the cutting fluids have led to the introduction of the minimum quantity lubrication (MQL), cryogenic machining, and dry machining techniques Noise/vibrations: During machining, vibrations and noise components are generated Noise levels of 85 dB are the maximum noise level regarded as safe and tolerable for an h exposure When noise levels exceed 90 dB, hearing damage is liable to occur, and therefore earplugs must be worn Flying chips Traditional machining Cutting fluid Hazard effect on labor Noise Hazard effect on machines FIGURE 16.5 Traditional machining hazards Hazard effect on soil Vibrations Hazard effect on air Machining Process Selection 499 Flying chips: Flying chips form a major hazard and risk on operator as they fly from the machine during the cutting process Flying particles such as metal chips may result in eye or skin injuries or irritation Grinding, cutting, and drilling of metal and wood generate airborne particles that affect the respiratory system Under such circumstances, it is always recommended to wear safety glasses, goggles, or shields and use of proper ventilation Cutting fluids: Cutting fluids contain many chemical additives that can lead to skin and respiratory diseases and increased danger of cancer This is mainly caused by the constituents and additives of the cutting fluids as well as the reaction products and particles generated during the machining process Unfortunately, spoiled or contaminated cutting fluids are the most common wastes from the machining process that are considered hazardous wastes to the environment due to their oil content, chemical additives, chips, and dust During machining, at high cutting speeds (>3500 m/min), high temperature is generated in the machining zone that vaporizes fluids and metal particles These emissions enter the atmosphere thus forming a complex mixture of vapors and fumes containing elements of the workpiece, cutting tool, and cutting fluids Cutting fluids have negative health effects on the operators that appear as dermatological, respiratory, and pulmonary effects Exposure to mists caused by the cutting fluids raises worker’s susceptibility to respiratory problems that depends on the level of chemicals and particles contained in generated mists Table 16.8 shows the various sources of hazards and risk associated with a variety of conventional and nonconventional machining operations 16.2.9 Process and Machine Capability A measure of the process capability is attained when meeting customer requirements by comparing the machining process limits to the required tolerance limits The process capability index Cpk measures the variability of a process 6σ and compares it with a proposed upper tolerance limit (UTL) and a lower tolerance limit (LTL) as shown in Figure 16.6: (X − LTL) ( UTL − X ) or CPk = 3σ 3σ where ‾ is the mean of the process X σ is the standard deviation of the process If Cpk is greater than 1.00, then the process is capable of meeting design specifications If it is less than 1.00, then the process will generate defects Metal cutting ECM CHM EDM LBM USM AJM Risk Hazard Type Machining Process Hazard Source X X X X X X X X X X X X X X X X X Environmental Water pollution Air pollution Soil pollution X X X X X X X X Noise X X X X X Physical X X Hazards Associated by Different Machining Processes Hearing loss Vibration Radiation Dust Magnetic field Musculoskeletal TABLE 16.8 Ill health Cancer Flora/fauna Exhaustion Fatigue Lung disease Exhaustion Fatigue Electric shock X X X X X X X Death Slurry X Allergy X X X X X X X X X X Lung cancer X X X X X X X X X X X X X X X X Lung disease X X X X X X X X Injury Gasses Chemical Lung cancer Skin burns Lung disease Injury X X X Vapors Liquids Explosions X Equipment failure Sharp edges X X X X X X X X Injury Mists Fume Flying chips Mechanical/ manual handling Safety Burns Injury Fire X X X X Burns Fundamentals of Machining Processes 500 501 Machining Process Selection Upper tolerance limit (UTL) Distribution of individual values Process spread Lower tolerance limit (LTL) FIGURE 16.6 Process capability chart The process capability ratio (Cp) measures the capability of a process to meet design specifications It is defined as the ratio of the range of the tolerance to the range of process spread, which is typically ±3σ (Figure 16.6): CP = (UTL − LTL) 6σ Therefore, if Cp is less than 1.0, the process range 6σ is greater than the tolerance range (UTL–LTL) A process capability ratio Cp greater than 1.0 indicates that the process is capable of meeting specifications In such a case, no defective parts will be produced Machine Capability: Since a dispersion of ±3σ is expected in manufacturing, it is usual to compare 6σ to the tolerance to express the machine capability (MC) as MC = 6σ × 100% (UTL − LTL) If MC is greater than 100%, the MC is poor and defective parts will be produced At MC = 100%, the machine is just capable, and when MC