MACHINABILITY OF ENGINEERING MATERIALS

Transcription

1 MACHINABILITY OF ENGINEERING MATERIALS

2 Machinability of Engineering Materials B. MILLS B.SC., M.Sc., Ph.D., C.Eng., F.LM., M.Inst.P. and A. H. REDFORD B.Sc., Ph.D., A.R.T.C.S. Department of Aeronautical and Mechanical Engineering, University of Salford, UK APPLIED SCIENCE PUBLISHERS LONDON and NEW YORK

3 APPLIED SCIENCE PUBLISHERS LTD Ripple Road, Barking, Essex, England Sole Distributor in the USA and Canada ELSEVIER SCIENCE PUBLISHING CO" INC. 52 Vanderbilt Avenue, New York, NY 10017, USA British Library Cataloguing iu Publication Data Mills, R Machinability of engineering materials, L Manufacturing processes I, Title II, Redford, A,H, TJ 1185 ISBN-13: e-isbn-13: DOl: 10,1007/ WITH 96 ILLUSTRATIONS AND 22 TABLES APPLIED SCIENCE PUBLISHERS LTD 1983 Softcover reprint of the hardcover 1st edition 1983 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner, Applied Science Publishers Ltd, Ripple Road, B"arking, Essex, England Photoset in Malta by Interprint Ltd

4 PREFACE In the manufacturing industries, despite the development and improvement of metal forming processes, a great deal of reliance is still placed on metal cutting processes and this will continue into the foreseeable future. Thus, there will continue to be a requirement for the development of improved cutting tool materials, workpiece materials, cutting fluids and testing methods; collectively this activity can be described as improving machinability. Machinability is a parameter which in many ways is vague, sometimes qualitative and very often misunderstood. The purpose of this text is to give a broad understanding of the concept, methods of assessment and ways of improving machinability to the manufacturing engineer, the metallurgist and the materials scientist. The text should also be of interest to those engaged in research in manufacturing engineering and metal cutting. The text, of necessity, does not attempt to give detailed information about the machining characteristics of a wide range of tool and workpiece materials. It is felt that this is beyond the scope of the book and is best left to other sources, such as machinability data banks and the Machining Handbook*, whose main objective is to present this kind of information. It is hoped that the reader will be able to progress logically from the fundamental aspects of the metal cutting process to the sections on the more specific topics of machinability including machinability testing and the properties of tool and workpiece materials which affect their machining performance. Finally, a section is devoted to the use of machinability data as an aid to 'optimising' the performance of metal cutting machines. * Metals handbook of machining, Vol. 3, American Society for Metals (1967). v

5 vi PREFACE The major portion of the text is concerned with describing the work of other researchers. Whilst the present text cannot possibly reference all the work that has gone into metal cutting research we hope that the material presented is broadly representative of the work done. During the last decad'e the authors have been fortunate in working and associating with many workers in the metal cutting field, in the United Kingdom, Europe, the United States of America and the Soviet Union. The number of such associates is too numerous to list; this would in any case be unwise for reasons of possible omissions. Our association with such colleagues and research students is greatly valued and appreciated. B. MILLS AND A. H. REDFORD

6 CONTENTS Preface Chapter Chapter The Concept of Machinability.... Introduction.... Definition of Machinability.... Fundamental Aspects of the Machining Process.... Mechanics of Metal Cutting.... Chip formation.... The effect of changes in cutting parameters on cutting forces.... The effect of changes in cutting parameters on cutting temperatures.... Tool Wear.... Mechanisms of wear..... Types of wear.... Relationship between tool wear and time.... Relationship between tool wear and cutting conditions Relationship between tool life and temperature Tool life criteria Surface Finish..., Introduction Mechanism of surface finish production Factors which influence surface finish production Chip Formers Mechanics of chip formers.... v vii

7 viii CONTENTS Chapter ~ Effect of cutting conditions on chip forming.... Effect of chip formers on cutting forces.... Effect of chip formers on tool wear..... The Action of Cutting Fluids.... References.... The Assessment of Machinability.... Types of Machinability Test..... Short Machinability Tests.... Non-Machining Tests.... Chemical composition tests.... Microstructure tests.... Physical properties tests.... Machining Tests.... The constant pressure test.... The rapid facing test.... Tapping tests.... Degraded tool tests.... Accelerated wear tests.... High-speed-steel tool wear rate test.... Taper turning test.... Variable-rate machining test..... Step turning test..... Combination of Machining Parameters.... Machinability Assessment for Processes Other than Single Point Turning.... Introduction.... Machinability assessment in drilling.... Machinability assessment in milling.... Machinability Assessment Relating One Process to Another.... On-Line Assessment of Tool Wear.... References Chapter 4 Tool Materials Historical Background Requirements of Tool Materials High-Speed Steels Introduction Structure of high-speed steels

8 CONTENTS IX Heat treatment of high-speed steels Applications of high-speed steels Cemented Carbides Introduction Classification of cemented carbides Structure and properties of cemented carbides Mixed cemented carbides bonded with cobalt Coated cemented carbides Titanium carbide cemented carbides Cast Cobalt Alloys Ceramic Cutting Tool Materials Diamond References Chapter 5 Workpiece Materials Introduction Ferrous Materials... 'j Carbon steels Free-machining steels Stainless steels Cast irons Titanium Alloys Nickel-Based Alloys Aluminium Alloys Magnesium and its Alloys Copper and its Alloys.... References.... Chapter The ISO Machinability Test Introduction.... Reference Workpieces.... Reference Tool Materials and Tool Geometries.... Reference Cutting Fluids.... Cutting Conditions.... Tool Life Criteria and Tool Wear Measurements.... Tool Wear Measurement.... Equipment.... Tool Life Test Procedure.... Evaluation of Tool Life Data

9 x CONTENTS Chapter 7 The Effect of Machinability Data on Metal Removal Performance and Economics Introduction Criteria of Performance Economics of Turning Operations Machining for Minimum Cost Machining for Maximum Production Machining for Maximum Profit Machinability Data Applied to Milling Reliability of Machinability Data Reference Appendix 1 Analysis to Determine Cutting Temperatures in Single Point Metal Cutting Appendix 2 Analyses for Two Short Absolute Machinability Tests A2.l The Variable-Rate Machining Test A2.2 The Step Turning Test Index