Manufacturing design and technology  drills  science and technology of advanced operations

M a n u f a c t u r i n g D e s i g n a n d Te c h n o l o g y Science and Technology of Advanced Operations V I K T O R P A S T A K H O V Tai ngay!!! Ban co the xoa dong chu nay!!! Science and Technology of Advanced Operations Manufacturing Design and Technology Series Series Editor J Paulo Davim   Drills: Science and Technology of Advanced Operations (2014) Viktor P Astakhov Diamond Tools in Abrasive Machining (2014) Mark Jackson M a n u f a c t u r i n g D e s i g n a n d Te c h n o l o g y Science and Technology of Advanced Operations V I K T O R P A S T A K H O V 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: 20130923 International Standard Book Number-13: 978-1-4665-8435-8 (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 Contents Preface xv Acknowledgments xxv Author xxvii Chapter Drilling System 1.1 Fundamentals 1.1.1 Basic Drilling Operations 1.1.2 Machining Regime in Drilling Operations 1.1.2.1 Cutting Speed 1.1.2.2 Feed, Feed per Tooth, and Feed Rate 1.1.3 Depth of Cut and Material Removal Rate 1.1.4 Cut and Its Dimensions .8 1.1.5 Selecting Machining Regime: General Idea 10 1.1.6 Cutting Force and Power 13 1.1.6.1 Definition of Terms According to ISO Standard 13 1.1.6.2 Basis of the Cutting Force and Power Calculations 13 1.2 Drilling System for HP Drills: Structure, Properties, Components, and Failure Analysis 15 1.2.1 System Concept 15 1.2.2 Drilling System 20 1.2.2.1 Structure of the Drilling System .20 1.2.2.2 Coherency Law 21 1.2.2.3 System Objective 22 1.2.3 Case for HP Drills 22 1.2.4 Design of Drilling Systems .25 1.2.4.1 Part Drawing Analysis and Design of the Tool Layout 27 1.2.4.2 Drill Selection/Design .28 1.2.4.3 Drill Material Selection 32 1.2.4.4 HP Drill Design/Geometry Selection 33 1.2.4.5 Part-Holding Fixture Design/Selection .34 1.2.4.6 Metal Working Fluid 35 1.2.4.7 Controller 35 1.2.4.8 Machine Tools 37 1.2.4.9 Tool Holders .40 1.2.5 Summary: Checklist of Requirements for the Drilling System for HP Drilling 49 References 52 Chapter Tool Failure as a System Problem: Investigation, Assessment, and Recommendations 55 2.1 2.2 2.3 Traditional Notions and Approaches 57 Failure: A System-Related Definition 58 Tool Failure Prime Sources 58 v vi Contents 2.4 2.5 2.6 Preparation Stage: Collecting Information 59 2.4.1 Knowing That a Failure Occurs 59 2.4.2 Tool Tracking: The Tag System 59 2.4.3 Automated Tool Tracking with RFID .60 2.4.4 Collecting Other Supporting Information and Evidences 63 2.4.5 Assessment of the Collected Evidences: Obvious Root Causes 64 2.4.6 Additional Information Needed for Normal Tool Failure Analysis 68 2.4.6.1 Tool Drawing 69 2.4.6.2 Tool Layout 69 2.4.6.3 Tool Inspection Report 70 2.4.6.4 Part Inspection Report 70 2.4.6.5 Drilling System Background Information 70 2.4.6.6 Additional Information if the Problem Was Solved 73 2.4.6.7 Tool History 73 2.4.6.8 Inventory Count and Delivery Schedule for the Next Supply 73 Part Autopsy and Tool Reconstruction Surgery 73 2.5.1 Example: Step 1—Failure Information 74 2.5.2 Example: Step 2—Analysis of the Collected Failure Information .75 2.5.3 Example: Step 3—Sectioning the Autopsy Specimen 75 2.5.4 Example: Step 4—First Microscopic Examination of the Sectioned Part 78 2.5.5 Example: Step 5—Breaking the Precut Section and Separating Debris/Tool Fragments 78 2.5.6 Example: Step 6—Examining the Surface of the Machined Hole .80 2.5.7 Example: Step 7—Reconstruction of the Bottom of the Hole Being Drilled 81 2.5.8 Example: Step 8—Reconstruction of the Drill and Root Cause Determination 82 2.5.9 Example: Step 9—Archiving the Evidence and Writing a Report 84 Tool Wear 85 2.6.1 Background Information 85 2.6.2 Standard Wear Assessment 88 2.6.3 Statistical Analysis of Tool Wear Curves 91 2.6.4 Common Wear Regions of Drills 99 2.6.5 Assessment of Tool Wear of HP Drills 103 2.6.6 Correlations of Drill Wear with Force Factors 104 2.6.7 Assessment of Wear Resistance of Tool Materials 105 2.6.8 Real Mechanisms of Tool Wear: Pure Abrasion, Adhesion, and Abrasion–Adhesive Wear 107 2.6.9 Special Wear Mechanisms: Reaction of the Cutting Tool on Increased Cutting Speed and the Optimal Cutting Temperature 111 2.6.9.1 Prevailing Concept 111 2.6.9.2 Optimal Cutting Temperature: Makarow’s Law 115 2.6.10 Special Wear Mechanisms: PCD 116 2.6.11 Casting Defects and Tool Wear/Failure 126 2.6.12 Special Wear Mechanisms: Cobalt Leaching 130 vii Contents 2.6.13 Facts and Physics of the Wear of Tool Materials 133 2.6.13.1 Need for a New Theory of Tool Wear 133 2.6.13.2 Diffusion Self-Healing of Microcracks 137 References 139 Chapter Tool Materials 143 3.1 3.2 3.3 3.4 Words of Wisdom 143 Basic Properties 144 3.2.1 Wear Resistance 145 3.2.2 Toughness 145 High Speed Steels 147 3.3.1 Why HSSs? 147 3.3.2 Brief History 148 3.3.3 Common Grades of HSS 149 3.3.3.1 Group I: General-Purpose HSSs 150 3.3.3.2 Group II: Abrasion-Resistant HSSs 150 3.3.3.3 Group III: High Red Hardness HSSs 150 3.3.3.4 Group IV: Super HSSs 151 3.3.4 Factors Affecting Intelligent Grade Selection of HSS 151 3.3.5 Formation of Properties 154 3.3.5.1 Casting of HSS 156 3.3.5.2 Dealing with Cast Structure 158 3.3.6 Components in HSS 167 3.3.6.1 Tungsten and Molybdenum 167 3.3.6.2 Chromium 167 3.3.6.3 Vanadium 168 3.3.6.4 Cobalt 168 3.3.6.5 Carbon 168 3.3.6.6 Sulfur 168 3.3.7 Heat Treatment of HSS 170 3.3.7.1 Soft Annealing and Stress Relieving 170 3.3.7.2 Hardening and Tempering 171 3.3.7.3 Cryogenic Treatment of HSSs 173 3.3.8 Coating of HSS 175 Cemented Carbides 179 3.4.1 What Is Cemented Carbide? 180 3.4.2 Brief History 180 3.4.3 Grade Classification 182 3.4.3.1 Earlier Standards 182 3.4.3.2 Current Standard 183 3.4.4 Problem 186 3.4.5 Properties of Cemented Carbides 187 3.4.5.1 Introduction Notes 187 3.4.5.2 Groups of Properties 188 3.4.5.3 Formation of Properties: Basics 189 3.4.5.4 Some Important Properties 190 3.4.5.5 Nondestructive Testing of Carbide Properties Using Magnetic Measurements 197 3.4.5.6 Nanoparticle Carbides: Research and Expectations 206 viii Contents 3.4.6 Carbide Blanks 207 3.4.6.1 Blanks for Carbide-Tipped Drilling Tools .208 3.4.6.2 Round Carbide Blanks 210 3.4.6.3 Round Carbide Blanks Made of Advanced Carbides 214 3.4.7 Coating 216 3.4.7.1 Methods of Application 216 3.4.7.2 Coating Strategies 220 3.4.7.3 Quality Control 222 3.4.8 Cryogenic Treatment of Cemented Carbides 226 3.4.9 Considerations in Proper Grade Selection 228 3.5 Diamond 230 3.5.1 Introduction 230 3.5.2 Blanks for Drilling Tools: PDC and PCD Disks 231 3.5.3 Manufacturing of PCD Disks 234 3.5.3.1 Process 234 3.5.3.2 Powder Mix 238 3.5.4 Grain Size 241 3.5.5 Interfaces 244 3.5.6 Thermal Stability 245 3.5.7 PCD Grade Selection and Quality Inspection 250 3.5.7.1 Grade Selection Considerations 250 3.5.7.2 Quality Assessment of PCD Products 253 References 255 Chapter Twist and Straight-Flute Drills: Geometry and Design Components 259 4.1 Classification 260 4.2 Basic Terms 265 4.3 Constraints on the Drill Penetration Rate: Drill 268 4.4 Force Balance as the Major Prerequisite Feature in HP Drill Design/Manufacturing 269 4.4.1 Theoretical (Intended) Force Balance 269 4.4.2 Additional Force Factors in Real Tools 271 4.4.3 Resistance of a Drill to the Force Factors 272 4.4.3.1 Resistance to the Drilling Torque 273 4.4.3.2 Resistance to the Axial Force 276 4.4.3.3 Drill-Design/Process-Related Generalizations/ Considerations Related to Resistance to the Force Factors .284 4.4.3.4 Improving Drill Rigidity 287 4.4.3.5 Axial Force (Thrust)–Torque Coupling 290 4.5 Drill Geometry 291 4.5.1 Importance of the Drill Geometry 291 4.5.2 Tool Geometry Measures to Increase the Allowable Penetration Rate 292 4.5.3 Straight-Flute and Twist Drills Particularities 292 4.5.4 Systems of Consideration 295 4.5.5 Drilling Tool Geometry in T-hand-S: Rake and Clearance Angles 296 4.5.6 Drilling Tool Geometry in T-mach-S and T-use-S: Clearance Angles 307 4.5.7 Drilling Tool Geometry in T-mach-S and T-use-S: Rake Angles 314 4.5.7.1 Rake Angle in T-mach-S/T-use-S γcf Determination According to the First Approach 315 ix Contents 4.5.7.2 Rake Angle in T-mach-S/T-use-S γne Determination According to the Second Approach 318 4.5.7.3 Comparison of the First and Second Approaches 323 4.5.7.4 Chip Breakage 328 4.5.8 Chisel Edge 336 4.5.8.1 General 336 4.5.8.2 Case 1: The Primary Flank Is Planar and Its Width Is Equal to or Greater than 2ao 337 4.5.8.3 Case 2: The Primary Flank Is Planar and the Width of the Primary Flank Is Equal to ao 346 4.5.8.4 Drill Flank Is Formed by Two Surfaces (Generalization: Tertiary Flank Plane and Split Point) 350 4.5.8.5 Modifications of the Chisel Edge 359 4.5.9 Point Angle and Margin 366 4.5.9.1 Axial/Radial Force Ratio 368 4.5.9.2 Uncut Chip Thickness (Chip Load) and Chip Flow 368 4.5.9.3 Exit Burr and Delamination 369 4.5.9.4 Cycle Time 372 4.5.9.5 Back Taper 372 4.5.9.6 Margin and Minor Cutting Edge 377 4.6 Drill Design Optimization Based on the Load over the Drill Cutting Edge 384 4.6.1 Uncut Chip Thickness in Drilling 385 4.6.2 Load Distribution over the Cutting Edge 386 4.6.3 Drills with Curved Cutting Edges 387 4.6.4 Generalization 393 References 394 Chapter PCD and Deep-Hole Drills 397 5.1 5.2 PCD Drilling Tools 397 5.1.1 Challenges of Work Materials 397 5.1.1.1 Metal-Matrix Composites 397 5.1.1.2 Polymer-Based Composite Materials 399 5.1.1.3 Similarity and Differences 401 5.1.2 PCD-Tipped Drilling Tools 401 5.1.3 Full-Face (Cross) PCD Drills 407 5.1.3.1 First Approach: PCD Is Sintered in a Part of the Drill Body 407 5.1.3.2 Second Approach: PCD Segment(s) Is Brazed into the Drill Body 416 Deep-Hole Drills 427 5.2.1 Introduction 427 5.2.2 Common Classification of Deep-Hole Machining Operations 428 5.2.2.1 Force Balance and the Meaning of the Term Self-Piloting Tool 430 5.2.3 Additional Force Factors in Real Tools 432 5.2.4 Common Feature of SPTs: Supporting Pads 434 5.2.4.1 Locating Principle of SPTs 434 5.2.4.2 Optimal Location of the Supporting Pads .440 5.2.4.3 Location Accuracy of the Supporting Pads .444 832 Appendix C: Basics of the Tool Geometry Using the earlier considerations and the model shown in Figure C.46, one can obtain expressions for h1 and her as  h1 = Rce  − + Br  her = (    (C.43) ) Rce − 1 + Br Br cos γ + Br sin γ (C.44) According to Poletica (1969), the stress distribution at the flank contact surface is as follows:   x 2  τcf ( x ) = τ y exp  −3      ∆   (C.45) where τy is the yield shear strength of the work material x is the distance from the cutting edge Integrating Equation C.45, one can obtain the mean shear stress at the tool flank interface τcf = 0.505τ y (C.46) which is in excellent agreement with experimental results obtained by Zorev (1966) and Chen and Pun (1988) The foregoing analysis allows obtaining the expression to calculate the friction force at the tool– workpiece interface as FfF = 0.625τ y Rceb1 Br sin α (C.47) where b1 is the true uncut chip width, which calculates depending on the tool geometry (Astakhov 2010) In a simple case of turning, it is equal to the width of the chip (Figure C.37) It directly follows from Equation C.47 that the friction force at the tool flank is directly proportional to the radius of the cutting edge Moreover, a simple comparison of the model shown in Figures C.43a and C.45 clearly shows that a sharp cutting edge is always better than a honed/ chamfered one in terms of metal cutting as its performance results in a lower cutting force and temperature If one has any doubt about this statement, let him hone the edges of his razor (e.g., Gillette Fusion) and then try to shave C.4.2 Edge Preparation C.4.2.1 Idea Cutting edge preparation (hereafter, CEP) is a modification of the cutting edge (considered as a theoretical line) into a transitional surface between tool rake and flank surfaces (planes) In other words, CEP is a technology of applying a defined radius to the cutting edge to improve quality of the transitional surface between the rake and the flank faces and thus improve cutting edge quality 833 Appendix C: Basics of the Tool Geometry Although as suggested by the current analysis and confirmed by experimental results (Thiele et al 2000; Tugrul Özel et al 2005), a sharp cutting edge is better than a honed one in terms of cutting forces and temperatures; multiple experimental studies and author’s experience reveal the following: • Tool life of high-speed steel, carbide, PCD, and PCBN tools (single point, twist and straight-flute drills, reamers, milling tools, etc.) increases when the proper (optimal hone radius) EP is used (Agnew 1973; Mayer and Stauffer 1973; Rech 2006; Biermann and Terwey 2008; Cheung et al 2008) • The size and surface finish and the process stability (spiraling, chatter marks) in machining of aluminum alloys are much better when a suitable EP is used Even small hand honing by a diamond file can improve these parameters noticeably These well-known results are explained as follows As mentioned previously, defects of the cutting edge are present in nearly all cutting tools (Rodriguez 2009) They are mainly the result of finish EDMing and grinding Considered by many as microscopic, these defects are not small as many practitioners believe Figure C.44 exemplifies this statement These defects include microcracks, burrs, burns, and serrated cutting edges that lead to great variations in tool performance particularly in demanding applications In the author’s opinion, increased adhesion of the work and tool materials is the major damaging factor Adhesion between tool and work materials always results in the formation of the BUE, which grows in each cycle of chip formation (Astakhov 1998/1999) The problem is in its size and strength of adhesion bonds The poorer the topology of the cutting edge, the greater these two factors When BUE reaches a certain height (depending on the strength of adhesion bonds), it is periodically removed by the moving chip Such a removal does the damage as BUE takes away pieces of the tool material Figure C.47 shows a graphical example of the damaged cutting edge due to this process This issue is discussed in Chapter where adhesion tool wear is considered in detail and a fairy tale about the so-called protective action of BUE is completely dismantled BUE Damaged cutting edge FIGURE C.47  BUE on the drill cutting major edge 834 Appendix C: Basics of the Tool Geometry The available information and author’s personal experience show that EP works because it Significantly improves the microfinish on the tool–chip and tool–workpiece contact interfaces that reduces adhesion forces over these interfaces (Astakhov 2006) Heals surface microdefects such as cracks and voids in the vicinity of the cutting edge left by the grinding wheel as shown in Figure C.48 and C.49 These defects are critical because they cause micro- and then macrochipping of the cutting edge EP just heals these defects (Komarovsky and Astakhov 2002) as ductile micro-cutting takes place even on superhard tool materials (Jahanmir et al 1999; Zhong 2003; Kang et al 2006) (Figures C.48 and C.49) Reduces tool vibration (Astakhov 2011) Improves coatability of the cutting tools As well known (e.g., Bouzakis et al [2009]), the application of PVD coating on a sharp edge results in a very high internal stress As a result, such a coating breaks away and peels off very shortly after starting cutting For this reason, EP is mandatory for tools to be coated Figure C.50 shows an example of coating properly applied on a rounded cutting edge Edge preparation Rce Final geometry—smooth transition surface “Sharp” cutting edge FIGURE C.48  Essence of the CEP technology Before EP After EP 20 μm (a) 20 μm (b) FIGURE C.49  Example of EP results: the cutting edge (a) before EP and (b) after EP by a drag finishing machine by Otec Co 835 Appendix C: Basics of the Tool Geometry FIGURE C.50  Tool carbide cutting edge coated by layers of CVD diamond coating The next logical question is when EP works The foregoing analysis suggests that EP is always a trade-off between the factors that cause an increase in tool life as better microfinish of the contact surfaces (less adhesion between the tool and work materials) and better coating and strength of the cutting wedge and those that cause a decrease in tool life as higher friction forces and temperatures on the contact surfaces As a result, there should be the optimal solution, in terms of tool life, radius of the cutting edge The foregoing analysis and the model shown in Figure C.45 suggest that the radius of the cutting edge Rce should be judged against the uncut chip thickness hD For characterization of cutting tool sharpness, the relative tool sharpness (hereafter, RTS) of the cutting edge was introduced as RTS = hD /Rce (Outeiro and Astakhov 2005) The minimum value of this ratio that corresponds to negligibly small influence of the cutting edge radius on the cutting process is referred to as the critical relative tool sharpness RTScr Zorev (1966) suggested the following empirical rule: the radius of the cutting edge does not affect the cutting process if RTS is equal to or more than 10 In many practical machining operations, however, RTS is less than 10 As a result, the radius of the cutting edge should be considered as a significant factor in the modeling of the cutting process For example, if one tries to evaluate the influence of the cutting feed and the parameters of the cutting tool geometry, the discussed RTScr should be always kept in mind The radius of the cutting edge and thus RTS affect both the contact stresses (force) on the tool flank and tool geometry as discussed by the author earlier (Astakhov 2010) For example, RTS affects heat partition in the cutting system Figure C.51 shows an example of energy partition in the cutting system As seen, the amount of thermal energy transported by the chip (Qc), conducted into the workpiece (Qw), and conducted into the tool (Qt ) directly depends on RTS (Outeiro and Astakhov 2005) As RTS decreases, more heat goes into the workpiece causing machining residual stresses and into the tool causing lower tool life Moreover, when machining with shallow uncut chip thicknesses, a small RTS causes a shift of the region of maximum tool temperatures from the rake face into the flank face that causes excessive flank wear (Astakhov 2010) The radius of the cutting edge may also affect the rake angle As shown by the author earlier, this angle is calculated as   hD  − 1 arcsin  γ n1 =   Rce   γn  if hD < Rce ⋅ (1 + sin γ n ) if hD ≥ Rce ⋅ (1 + sin γ n ) (C.48) 836 Appendix C: Basics of the Tool Geometry 100 Qt Q (%) 80 Qw 60 Qc 40 AISI 1045 Uncoated tool v = 75 m/min dw = 2.5 mm 20 RTS FIGURE C.51  Influence of RTS on energy balance when machining AISI 1045 steel Available information on the theory and application of EP allows drawing the following important conclusions: ISO 1832: 2004/2005 and ANSI B212-4 both define various types of EP to be included in the cutting insert designations The detailed information was presented by the author earlier (Astakhov 2010) Among multiple available forms of EP, more than 80% of honed cutting tools receive a radius hone (Figure C.52a), which is centrally located on the cutting corner of the tool, that is, the extent of EP Lep = Rce Tools with this type of hone are used for general applications A half-parabolic shape is known as a waterfall or reverse waterfall, depending on its orientation to the rake and flank surfaces With a waterfall-shaped hone, the EP is skewed toward the top side of the tool as shown in Figure C.52b where normally for the waterfall EP, its size along the rake face is twice greater (2Lep) than that along the flank face (Lep) The main benefit of a waterfall-shaped hone is that the honing process leaves more tool material directly under the cutting edge, which further strengthens the corner (Shaffer 2000) Although the optimal RTS of equal to or greater than 10 is most desirable for cutting tools, practical RTS for drilling tools is selected from the range of 6–10 Note that the optimal RTS is very sensitive to the parameters of the drilling system, so it varies significantly depending upon a particular machining system, cutting tool, tool and work materials, etc What is the most important, however, is that this optimum lies within a rather narrow range An example is shown in Figure C.53a (Cheung et al 2008) for steel drilling In drilling of aluminum alloys with PCD drills, the window of opportunity is even smaller as shown in Figure C.53b As can be clearly seen, even small deviation from the optimal cutting edge radius to either side results in steep reduction in tool life This explains a great Lep Rce (a) 2Lep Lep Lep (b) FIGURE C.52  Common shape of EP: (a) radius hone shape and (b) waterfall-shaped hone 837 Appendix C: Basics of the Tool Geometry 750 14,000 600 Number of holes Number of holes 450 300 150 7,000 PCD drill 8.75 mm dia 14,600 rpm 0.45 mm/rev Alum alloy A390 100 (a) 10 20 30 Cutting edge radius (μm) 40 50 (b) 12 16 20 Cutting edge radius (μm) FIGURE C.53  Influence of the cutting edge radius on the tool life in drilling: (a) twist drills in steel drilling and (b) PCD drills in high-silicon aluminum alloy A390 drilling scatter in EP application results as the optimal radius and its allowable deviation range (tolerance) are not normally established and thus are not a part of the tool drawing Therefore, the optimum radius of CEP should be determined for critical applications EP should be kept at minimum in machining of high-strength work material of low thermoconductivity and great strain hardening, for example, titanium alloys C.4.2.2  Technology and Cost There are three basic methods of EP: mechanical, thermal, and chemical Each method includes a number of technologies developed Figure C.54 lists these methods and associated technologies The basic description and details of these technologies are discussed by Rodriguez (2009) Each technology developer/EP machine manufacturer shows various sales presentations proving that a particular technology/machine is the best These presentations/brochures/catalogs are generously supported by high-quality SEM images before and after, showing significant improvement in the quality of the transition surface and rake and flank contact areas A rather great variety of available technologies makes it not simple for a cutting tool engineer/ manufacturing/application specialist to pick up one that seems to be the right choice for a given application or for a product line of a particular tool company To the first approximation, a comparison presented by Platit Co (shown in Table C.1) can be used Figure C.55 shows a typical manufacturing cost structure for common drilling tools (Rodriguez 2009) C.4.2.3  Metrology of EP The proper metrology has to be an inherent part of any application of EP technology although this is not nearly the case in reality Such a metrology allows one to Compare the results of EP, that is, compare the quality of the cutting edge before and after EP application Assure that the optimized parameters of EP are actually applied Assure the consistency of EP technology or, alternatively, compare different EP technologies in order to select the most suitable for a given application The rule of thumb is as follows: if a proper metrology of EP is not available, it is better not to apply EP at all 838 Appendix C: Basics of the Tool Geometry Edge preparation methods Edge preparation technologies Honing by hand Micro-abrasive jet machining (blasting) Mechanical Brushing Drag finishing (polishing) Initial edge condition—sharp Magnetic finishing Final edge condition—honed Slip grinding Rce EDMing Laser beam EP Thermal Plasma beam EP Electron beam EP Chemical FIGURE C.54  Basic methods and technologies of EP TABLE C.1 Qualitative Comparison of Various EP Technologies Criteria/ Features Quality Repeatability Flexibility Productivity Cost Availability of standard machine Flute polishing Coating droplet removal Special features Honing by Hand (with Diamond File) Best Depending on operator Very high Low Salary only Brushing Drag Finishing MicroBlasting (Dry) MicroBlasting (Wet) Water Jet Magnetic Finishing Good Good Good Good Medium Medium Good Good Good Good Good Good High Medium High Yes Medium Medium Medium Yes Medium Medium Low Yes High High Medium Yes Medium Very high Very high High Medium High Yes Yes Yes Yes Yes Limited in depth Yes Yes Yes Yes Yes Problems with small tool diameter Residual abrasive material on tool surfaces High compressed air consumption Typical for very small batch of tools Source: Platit Co., Selzach, Switzerland Large-scale production, corrosion problems Demagnetizing needed 839 Appendix C: Basics of the Tool Geometry EP: 10%–14% Coating pre-treatment: 6%–10% Coating: 16%–20% Grinding: 46%–60% Coating pre-treatment: 8%–10% FIGURE C.55  Manufacturing cost structure for common drilling tools A comparison of the quality of the cutting edge before and after EP application can be carried out using SEM to obtain images similar to images shown in Figure C.49 Being useful for the research purposes, this way is totally not feasible as an inspection procedure in toolmaking for obvious reasons The use of universal optical microscopes at high magnification results in unclear images not suitable for the proper assessment Therefore, specially designed and calibrated microscopes, optical and ultrasonic, should normally be used According to the author’s experience, the portable inspection machine promSkpGo by Zoller Co (Figure C.56) intended for a process-oriented measurement of the cutting edge rounding can be used for fast and accurate assessment of EP A specially designed universal drill holding fixture shown in Figure C.57 allows fast and proper orientation of the drill’s cutting edge to be investigated with respect to the microscope optical axis As can be seen, the drill shank as its datum (see Chapter 7) is positioned in a V-block and held tightly by a spring lever A spherical joint and graduated dials allow final adjustment of the drill position Using this fixture, any desirable edge of the drill can be properly oriented and inspected At the first stage of the quality assessment, the drill cutting edge and the adjacent rake and flank faces are observed in the manner shown in Figure C.58 The following can be seen in this figure: • EP did not improve the surface roughness of the rake and flank faces in the manner as intended (see Figure C.49) • The width of EP is not uniform As such, the maximum material removal by EP took place at the drill corner FIGURE C.56  Portable inspection machine promSkpGo by Zoller Co for the assessment of the quality of the cutting edge 840 Appendix C: Basics of the Tool Geometry FIGURE C.57  Universal drill holding fixture FIGURE C.58  Qualitative assessment of the cutting edge and the adjacent rake and flank faces The black shadow lines indicate the boundaries, and the middle of the region of the cutting edge is scanned for quantitative assessment The next step is digitizing of the selected region of the cutting edge and assessment of its radius distribution as shown in Figure C.59 As was expected from the earlier analysis of visual appearance of the cutting edge (Figure C.58), the variation of its radius is great Figure C.60 shows the summary report of the quality of EP It includes the maximum radius of the cutting edge approximated digitally, the distribution of this radius over the length of the selected region, and the roughness of the cutting edge (termed as chipping) Using this report, one may conclude that the quality of EP is very low so that the application of such an EP to the drill will result in lower tool life than that for the same drill with no EP Figure C.61 shows an example of improved EP As can be seen, the waterfall-type (see Figure C.52b) EP is applied The desirable range of the cutting edge radius (the tolerance on this radius) Appendix C: Basics of the Tool Geometry 841 FIGURE C.59  Digitizing of the selected region of the cutting edge and assessment of its radius distribution FIGURE C.60  Summary report of the quality of EP is set as its lower and upper boundaries The variation of this radius over the cutting edge is small and just below the mean value preset in the evaluation program Being much better than that shown in Figure C.60, the roughness of the cutting edge is still too high that clearly indicates that the roughness of the flute and flank grinding should be improved to obtain the maximum advantage of EP in HP drilling Figure C.62 shows a more detailed evaluation of the quality of EP The parameters of EP in any selected section over the inspection region can be evaluated individually Moreover, the rake, 842 Appendix C: Basics of the Tool Geometry FIGURE C.61  Example of improved EP FIGURE C.62  Parameters of EP and tool geometry in the selected section of the region 843 Appendix C: Basics of the Tool Geometry –0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 FIGURE C.63  Topography of the whole cutting edge clearance, and wedge angles can also be measured as shown in the figure Figure C.63 shows topography of the whole cutting edge in 3D This image can be rotated in 3D, so a detailed examination of any region of the cutting edge can be accomplished Note that when the drill corner is included into consideration, its rounding is the greatest It is clearly seen in Figure C.63 In the author’s opinion, this is the weakest point of EP for HP drills as sharp drill corners are of prime importance in HP drilling Honing by hand (with diamond file) is listed as the best EP technology in Table C.1 simply because an experienced EP operator never touches drill corners No other EP technology available today can provide protection for drill corners C.4.2.4  Final Recommendation on EP Some application recommendations are as follows: As with coating, EP should not be attempted to use to solve tooling or other drillingsystem-related problems Optimization of the drilling tool geometry, 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