Micro-Cutting E-Book

Dehong Huo

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Microsystem and Nanotechnology Series
• Sprache: Englisch

Seitenzahl: 553

Veröffentlichungsjahr: 2013

Beschreibung

Micro-Cutting: Fundamentals and Applications comprehensively covers the state of the art research and engineering practice in micro/nano cutting: an area which is becoming increasingly important, especially in modern micro-manufacturing, ultraprecision manufacturing and high value manufacturing.

This book provides basic theory, design and analysis of micro-toolings and machines, modelling methods and techniques, and integrated approaches for micro-cutting. The fundamental characteristics, modelling, simulation and optimization of micro/nano cutting processes are emphasized with particular reference to the predictabilty, producibility, repeatability and productivity of manufacturing at micro and nano scales.

The fundamentals of micro/nano cutting are applied to a variety of machining processes including diamond turning, micromilling, micro/nano grinding/polishing, ultraprecision machining, and the design and implementation of micro/nano cutting process chains and micromachining systems.

Key features
• Contains contributions from leading global experts
• Covers the fundamental theory of micro-cutting
• Presents applications in a variety of machining processes
• Includes examples of how to implement and apply micro-cutting for precision and micro-manufacturing

Micro-Cutting: Fundamentals and Applications is an ideal reference for manufacturing engineers, production supervisors, tooling engineers, planning and application engineers, as well as machine tool designers. It is also a suitable textbook for postgraduate students in the areas of micro-manufacturing, micro-engineering and advanced manufacturing methods.

Leseprobe

Contents

List of Contributors

Series Preface

Preface

Part One: Fundamentals

1 Overview of Micro Cutting

1.1 Background and Scope

1.2 Materials in Micro Cutting

1.3 Micro Cutting Processes

1.4 Micro Cutting Framework

References

2 Micro Cutting Mechanics

2.1 Introduction

2.2 Characterization of Micro Cutting

2.3 Micro Cutting Mechanics

2.4 Micro Machinability Issues and the Scientific Approaches

2.5 Summary

References

3 Micro Tooling Design and Manufacturing

3.1 Tool Size and Machining Scale

3.2 Manufacturing Methods for Solid Shank Micro Tools

3.3 Coatings and Coated Solid Shank Micro Tools

3.4 Importance of Coated Micro Tools

3.5 Diamond Micro Cutting Tools

3.6 Micro Cutting Tool Wear

3.7 Smart Cutting Tools

References

4 Ultraprecision and Micro Machine Tools for Micro Cutting

4.1 Introduction

4.2 Components of High Precision Machine Tools

4.3 Diamond Turning Machines and Components

4.4 Precision Milling Machines

References

5 Engineering Materials for Micro Cutting

5.1 Introduction

5.2 ‘Size’ Effects

5.3 Strain and Stress in Cutting

5.4 Elastic and Plastic Behaviours at the Micro-scale

5.5 Fracture

5.6 Metals, Brittle Materials and Others

5.7 Summary

References

6 Modelling and Simulation of Micro Cutting

6.1 FE Modelling and Analysis

6.2 Molecular Dynamics (MD) Modelling and Analysis

6.3 Multiscale Modelling and Analysis

6.4 Summary

References

Part Two: Applications

7 Diamond Turning and Micro Turning

7.1 Introduction

7.2 Ultra-precision Diamond Turning

7.3 Micro Turning

7.4 Challenges Arising from Micro Turning

References

8 Micro Milling: The State-of-the-art Approach Towards Applications

8.1 Introduction

8.2 Fundamental Elements in Micro Milling

8.3 Micro Milling Mechanics

8.4 Modelling of the Micro Milling Process

8.5 Metrology and Instrumentation

8.6 Scientific and Technological Challenges

8.7 Application Perspectives

8.8 Concluding Remarks

References

9 Micro Drilling Applications

9.1 Chapter Overview

9.2 Investigation of Chatter in Mesoscale Drilling

9.3 Investigation of Chatter in Micro Drilling

9.4 Case Study: Micro Drilling Medical Polymer Materials and Composites

9.5 Conclusions

Acknowledgements

References

10 Micro Grinding Applications

10.1 Introduction

10.2 Principles and Methodologies

10.3 Implementation Perspectives

10.4 Application Cases

Acknowledgements

References

11 In-Process Micro/Nano Measurement for Micro Cutting

11.1 Introduction

11.2 The Hybrid Instrument for Micro Cutting and In-process Measurement

11.3 In-process Measurement of Micro Cutting Force

11.4 In-process Measurement of Micro Wear of Cutting Tool

11.5 In-process Measurement of Micro Surface Form

11.6 Summary

References

Index

Microsystem and Nanotechnology Series

Series Editors – Ron Pethig and Horacio Dante EspinosaMicro-Cutting: Fundamentals and ApplicationsCheng, Huo, August 2013Nanoimprint Technology: Nanotransfer for Thermoplastic and Photocurable PolymerTaniguchi, Ito, Mizuno and Saito, August 2013Nano and Cell Mechanics: Fundamentals and FrontiersEspinosa and Bao, January 2013Digital Holography for MEMS and Microsystem MetrologyAsundi, July 2011Multiscale Analysis of Deformation and Failure of MaterialsFan, December 2010Fluid Properties at Nano/Meso ScaleDyson et al., September 2008Introduction to Microsystem TechnologyGerlach, March 2008AC Electrokinetics: Colloids and NanoparticlesMorgan and Green, January 2003Microfluidic Technology and ApplicationsKoch et al., November 2000

This edition first published 2013 © 2013 John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Micro cutting : fundamentals and applications / edited by Kai Cheng, Dehong Huo. pages cm Includes bibliographical references and index.

ISBN 978-0-470-97287-8 (cloth)1. Micromachining. I. Cheng, K. (Kai), editor of compilation. II. Huo, Dehong, editor of compilation. III. Title: Microcutting. TJ1191.5.M4983 2013 671.3′5–dc23

2013015108

A catalogue record for this book is available from the British Library.

ISBN: 978-0-470-97287-8

List of Contributors

Dr Yoshikazu AraiDepartment of NanomechanicsTohoku UniversitySendai, JapanDr Ampara AramcharoenSingapore Institute of Manufacturing Technology (SIMTech), A*STARSingaporeDr Qingshun BaiSchool of Mechanical and Electrical EngineeringHarbin Institute of TechnologyHarbin, P R ChinaProfessor Dr.-Ing Christian BrecherFraunhofer-Institut fuer Produktionstechnologie IPTWerkzeugmaschinenlabor WZLder RWTH Aachen, GermanyDr Jiaxuan ChenSchool of Mechanical and Electrical EngineeringHarbin Institute of TechnologyHarbin, P R ChinaProfessor Kai ChengSchool of Engineering and Design,Brunel UniversityUxbridge, Middlesex, UKProfessor Wei GaoDepartment of NanomechanicsTohoku UniversitySendai, JapanProfessor Han HuangSchool of Mechanical & Mining EngineeringThe University of QueenslandQueensland, AustraliaDr Dehong HuoSchool of Mechanical and Systems Engineering,Newcastle UniversityNewcastle Upon Tyne, UKProfessor Mark J. JacksonDepartment of Mechanical EngineeringTechnologyCollege of TechnologyPurdue UniversityWest Lafayette, USAKang-Won LeeDepartment of NanomechanicsTohoku UniversitySendai, JapanProfessor Yingchun LiangSchool of Mechanical and Electrical EngineeringHarbin Institute of TechnologyHarbin, P R ChinaDr Paul T. MativengaSchool of Mechanical, Aerospace and Civil Engineering (MACE)The University of ManchesterManchester, UKProfessor Shreyes N. MelkoteGeorge W. Woodruff School of Mechanical EngineeringGeorgia Institute of TechnologyAtlanta, USAK. MosimanDepartment of MechanicalEngineering TechnologyCollege of TechnologyPurdue UniversityWest Lafayette, USADr Young-Jin NohDepartment of NanomechanicsTohoku UniversityAramaki Aoba 6-6-01, Aoba-kuSendai, JapanT. NovakovDepartment of Mechanical EngineeringTechnologyCollege of TechnologyPurdue UniversityWest Lafayette, USADr Yuki ShimizuDepartment of NanomechanicsTohoku UniversitySendai, JapanDr Sathyan SubbiahSchool of Mechanical and Aerospace EngineeringNanyang Technological UniversitySingaporeDr Ing Christian WenzelOberingenieurFraunhofer-Institut fuer Produktionstechnologie IPTSteinbachstrasse, GermanyDr Tao WuSchool of Engineering and Design,Brunel UniversityUxbridge, Middlesex, UK

Series Preface

This book series provides a thorough summary of the methods used in micro- and nano-technology research and shows how these advances are currently influencing many scientific fields of study and practical application. This contextual presentation ensures that the books are appropriate for readers with varied backgrounds, while being useful for self-study or as classroom materials. Readers of these books will learn the fundamental principles necessary to understand the topic and then explore examples that are representative of the application of these fundamental principles.

Micro- and nano-scale materials created by novel fabrication techniques and metrology methods are the basis for many modern technologies. Several books in this series provide a resource for building a thorough scientific understanding of the field. These includeIntroduction to Microsystem Technology by Gerlach and Dotzel,Microfluidic Technology and Applications edited by Koch, Evans, and Brunnschweiler,Fluid Properties at Nano/Meso Scale by Dyson, Ransing, P. Williams and R. Williams, andNanoimprint Technology: Nanotransfer for Thermoplastic and Photocurable Polymer edited by Jan Taniguchi. Multiscale modeling, an important aspect of microsystem design, is extensively reviewed inMultiscale Analysis of Deformation and Failure of Materials by Jinghong Fan. Specificimplementations and applications are presented inAC Electrokinetics: Colloids and Nanoparticles by Morgan and Green,Digital Holography for MEMS and Microsystem Metrology edited by Asundi. Topics of biological mechanics are discussed inNano and Cell Mechanics: Fundamentals and Frontiers edited by Espinosa and Bao.

This book on micro-cutting, edited by Kai Cheng and Dehong Hou, presents technology that has been developed over the last two decades to bridge the manufacturing size-scale between precision and nanoscale manufacturing, i.e. feature sizes from a few millimeters to tens of micrometers. Featured here are the micro-cutting tool fundamentals, principalprocesses, and design-guiding modeling that have led to new applications for micro-cutting manufacturing. New micro-cutting tools, often developed via miniaturization of conventional machining tools, retain many of the advantages of conventional machining, not least of which is the capability to process many different materials such as metals, polymers, and ceramics. This flexibility establishes micro-cutting as an important manufacturing advancement and guarantees that the technology will find use in a wide array of practical applications.

Horacio D. EspinosaRonald Pethig

Preface

The motivation for manufacturing the smaller and smaller workpieces has been essentially the same since manufacturing was first established as an art/science – new applications, easily fabricated, less expensive, better performance and higher quality. The emergence of miniature and micro products in the last one or two decades is increasingly demanding the production of components and products with dimensions in the range of a few tens of nanometres to some few millimetres. Mechanical micro cutting is one of the key technologies to enable the realization of high accuracy complex micro products made from a variety of engineering materials including silicon, while a great many micro manufacturing processes have been developed.

Kinematically similar to conventional macro cutting, micro cutting is a mechanical material removal process to fabricate micro and miniature components using geometrically defined cutter edges, but the uncut chip thickness is normally a micrometer or less. As the unit removal size decreases, issues of cutting tool edge geometry, grain size and material micro structure, and so on, considered to have little or no influence at macro scale, become dominant factors with strong influences on the cutting mechanics and dynamics, and eventually result in machining accuracy, surface integrity and the quality of the machined component or product.

Micro cutting raises a great number of issues, mainly due to the size or scale associated with the process. When either the ratio of part size to be produced or size of the micro structure of the work material to the cutting tool dimension or cutting parameters becomes smaller, the size effects can change the whole aspect of the machining. Furthermore, scientific understanding of fundamentals and applications in micro machining is essential and much needed so as to address the underlying necessities for predictability, producibility, repeatability and productivity of manufacturing at micro and nano scales.

There are numerous books on MEMS and MEMS based micro manufacturing, which focus on lithography-based micro manufacturing processes. There are also several excellent books in non-MEMS micro manufacturing published in the last few years. But these books only briefly discussed certain aspects of mechanical micro machining normally within a single book chapter. Micro cutting as a new subject area in its own right with emerging cutting edge technologies is attracting international interest especially in the micro manufacturing community. This book is concerned with the state of the art research and engineering practices in micro cutting, including its concept and scope, enabling technologies, underlying theory, research methods, latest development and applications, and so on. It is the first book dedicated solely to the topic of micro cutting.

The book comprises two parts, Part One addresses fundamental aspects of micro cutting processes and Part Two, their applications. The first chapter overviews the micro cutting processes. The history and development process of micro cutting is presented, followed by conception and scope of micro cutting. It is difficult to give a single definition of micro cutting as it is a fast developing and timely subject area. Therefore, Chapter 1 attempts to characterize and define micro cutting by using a number of key features, namely, uncut chip thickness, micro part/feature dimensions and cutting tool geometry, underlying mechanics and application areas. Micro cutting mechanics are central to the progress of this subject area. Micro cutting mechanics aspects are therefore discussed in Chapter 2. Size effects related to micro cutting mechanics are categorized into three groups – cutting edge radius, grain size and material properties size effect. Influences of these size effects on cutting force, surface generation and burr formation in particular are reviewed. There are increasing demands on an industrially applicable micro cutting process for hard materials, scientific approaches to tackling micro-machinability are therefore discussed. Chapter 3 focuses on the enabling technology for micro cutting – micro tooling design and fabrication – which is the key to the interface between micromachining machine tools and processes. The latest developments on micro tooling design, tool materials, coating and tool wear are presented and the chapter concludes with the smart micro tooling as a future trend. In addition to the process and material size effects, micro cutting process performance is strongly dependent on the development of machine tools which is another enabling technology for micro cutting. Ultra-precision and micro machine tools for micro cutting are the subject of Chapter 4. The state of the art machine tools suitable for micro cutting and characteristic machine components for both industrial and in-house research machine tools have been studied. Micro cutting is capable of processing a full range of materials; however micro cutting some engineering materials efficiently and effectively still remains a challenge. Chapter 5 investigates engineering material behaviours at the micro scale and provides an overview of machinability of various engineering materials that have been processed using micro cutting processes. It is usually difficult and expensive to conduct micro cutting experiments in particular to make in-process observations for condition monitoring and quality control purposes. Micro cutting mechanics research relies heavily on accurate modelling and simulation. Key modelling methods, including FE (Finite Elements), MD (Molecular Dynamics) and newly developed multi-scale simulation, are discussed in Chapter 6. The modelling and simulation are critically important for undertaking the investigation on micro cutting chip and surface generation, cutting temperature, defects and burrs formation, cutting optimization strategies, and so on, in a scientific and interactive manner.

The chapters in Part Two of the book are devoted to applying the fundamentals of micro cutting (presented in Part One) in a variety of machining processes including diamond turning and micro turning (Chapter 7), micro milling (Chapter 8), micro drilling (Chapter 9) and micro grinding (Chapter 10). Operation principles, machine equipment and micro tooling used material removal mechanisms specific to individual micro cutting processes, and application perspectives are discussed in these respective chapters. In-process micro/nano measurement is essential to the success of micro cutting research development and applications. In-process precise measurement of micro cutting force, cutting temperature, micro tool wear and micro surfaces are desirable for process monitoring, quality control and inspection purposes. This topic is fully explored in the final chapter (Chapter 11) of the book. The application chapters above are intended to reveal micro manufacturing researchers and practitioners with good exemplars of how to implement and apply micro cutting in precision and micro manufacturing routine practices, although more concrete detailed application examples may need to be provided.

The international interest in the subject is evident, with more than 20 esteemed authors coming from 11 institutions in seven countries on four continents. We are grateful to them all, for the benefit of their advice and expertise, and their patience in supplying us with their specialist chapters.

This book can be used as a textbook for a final year elective subject on manufacturing engineering, or as an introductory subject on advanced manufacturing methods at the postgraduate level. It can also be used as a textbook for teaching advanced manufacturing technology in general. The book can also serve as a useful reference for manufacturing engineers, production supervisors, tooling engineers, planning and application engineers, as well as machine tool designers.

At Brunel University and Newcastle University, we are indebted to colleagues Dr Richard Bateman, Dr Robin C. Wang, Dr Tim Minton, Dr Sarah Sun, Dr Khalid Nor, Dr Lei Zhou, Dr Najmil Aris, Dr Ibrahim Shidi, Mr Paul Yates, Dr Atanas Ivanov and Professor Kenneth Dalgarno for their assistance in checking many of the details of the chapters and for stimulating discussions. We have been appreciative of the support from Tom Carter, Anne Hunt, Debbie Cox and many others at the publisher, John Wiley and Sons Ltd., as the book has developed from its draft outline form through various stages of production.

Finally and most importantly, our greatest thanks have to be reserved for our respective darling wives, Lucy Lu and Jun Tian, for their steadfast support and interest throughout the preparation of the book.

Kai Cheng and Dehong HuoLondon, UKNovember 2012

Part One

Fundamentals

1

Overview of Micro Cutting

Dehong Huo1 and Kai Cheng2

1 School of Mechanical and Systems Engineering, Newcastle University

2 School of Engineering and Design, Brunel University

1.1 Background and Scope

1.1.1 Micro Manufacturing

The increasing demands on micro and miniature parts, components and systems have led to the development of micro and nanotechnology. It is well-recognized that micro manufacturing has been a key enabling technology in industrially producing useful micro products and processes.

Micro Electric Mechanical Systems (MEMS) or micro system technology (MST) as known in Europe has been booming over the last two decades or so. Numerous MEMS products mainly micro sensors and micro actuators using silicon have been fabricated. These MEMS sensors and actuators have been widely used in various applications including medical engineering (e.g. pressure sensors), communications (high frequency resonators), inertial sensing (e.g. accelerometers and gyroscopes), to name a few. The processes employed to fabricate MEMS devices and other microelectronics products can be described as MEMS micro manufacturing or lithography-based micro manufacturing. Common techniques include photolithography, chemical-etching, plating and LIGA, and so on. Lithography-based micro manufacturing has existed and been developed for many years and is regarded as a mature large volume production process, hence the term micro manufacturing is familiar in the semiconductor or microelectronics fields.

In the past 20 years or so, high-accuracy complex shape micro and miniature components made from a range of engineering materials are increasingly in demand for various engineering industries. The geometry and functional requirements have led to the development of another category of micro manufacturing techniques termed as non-MEMS micro manufacturing or non-lithography-based micro manufacturing, which are fundamentally different from MEMS micro manufacturing in many aspects.

Figure 1.1 Micro manufacturing size/precision domains

Non-lithography-based micro manufacturing is a relatively new area, its concept, theories, processes and applications have been developed and formulated in the past around two decades. A report published by the WTEC panel on micro manufacturing describes non-lithography-based micro manufacturing as the creation of high-precision three dimensional products using a variety of materials and possessing features with sizes ranging from tens of micrometers to a few millimeters (WETC report). Figure 1.1 illustrates micro manufacturing size/precision domains. Micro manufacturing is normally used to produce part or feature size ranging from tens or hundreds of microns. Although micro manufacturing may not be capable of producing the smallest feature size as would be the case using MEMS and NEMS (Nano Electric Mechanical Systems) processes, it is a critical technology in bridging the gap between macro and nano domain [1]. It has many advantages over lithography-based micro manufacturing processes in terms of material choices, relative accuracy and the complexity of part geometry.

Typically non-lithography-based micro manufacturing includes micro EDM, micro mechanical-cutting, laser-cutting/patterning/drilling, micro-extrusion, micro-embossing, micro stamping, micro-injection moulding, and so on. These processes are based on different working principles and have their own respective characteristics in terms of production rate, attainable accuracy and surface finishes, and so on. But they are capable of producing 3D shape geometry micro parts over a wider range of engineering materials. This book will only focus on the micro mechanical-cutting process. Table 1.1 highlights the difference between MEMS micro manufacturing and non-MEMS micro manufacturing techniques (using mechanical micro machining as an example) to compare the fundamental differences between the two category micro manufacturing processes.

From Table 1.1 it can be found that micro mechanical machining has many advantages over MEMS-based process, such as wider materials choices, higher accuracy and capability of producing complex 3D geometry micro parts.

Recently, significant research efforts have been made on non-lithography-based micro manufacturing techniques. Europe has invested heavily in the research and development in micro manufacturing. In the past decade, dozens of EU large Framework projects havebeen initiated, such as MASMICRO, 4M, Launch-Micro, Production4ì, EUPASS, Hydromel, HYTI, NANOSAFE2, Manudirect, Napolyde, PRONANO, NaPa, CHARPAN, NANOIMPRINT, and so on. These projects cover all areas in micro and nano manufacturing, precision manufacturing and metrology [2]. In a study conducted by the UK Technology Strategy Board (TSB) on high value manufacturing in the UK, micro and nano manufacturing processes are identified as one of the most significant emerging manufacturing processes which would address challenges for the UK high value manufacturing industry [3].

Table 1.1 Comparisons between MEMS -based process and micro machining

MEMS-based process

Micro mechanical machining

Workpiece materials

Silicon, some metals

Metals, alloys, polymers, composite, technical ceramics

Component geometry

Planer or 2.5D

Complex 3D

Assembly methods

None or bonding

Fastening, welding, bonding

Relative accuracy

10

-1

–10

-3

10

-3

–10

-5

Process control

Feedforward

Feedback

Machine size

Macro

Macro to micro

Production volume

High

High or low

Production rate

High

Low

Initial investment

High

Intermediate or low

Applications

MEMS, microelectronics, some planner micro parts

Various applications requiring 3D micro components

1.1.2 History and Development Process of Micro Cutting

Micro cutting as an emerging subject area in its own right has attracted growing attention from both researchers and industry in the last two decades. Because mechanical cutting is a well-established area much knowledge from macro cutting has thus been adapted to study micro cutting processes. Some researchers from the conventional mechanical cutting research community shifted their research interests to micro-domain. Basically there are two research approaches being taken to study micro cutting. One approach is miniaturization of the conventional cutting process, tooling and equipment with an emphasis on their scaling down effect. The other approach can find its origin in ultra-precision machining, especially single point diamond turning (SPDT) with the emphasis on cutting mechanics, although the two approaches overlap in some areas and attempt to address similar issues, such as cutting tool edge size effect, minimum chip thickness, and so on.

The approach of miniaturization of the conventional cutting process tends to be process parameters centric. Macro-phenomena such as machining dynamics, chatters, cutting forces, and so on are directly translated into the micro-domain and the machine-tool interaction effect is well considered and modelled. Macro analytical, mechanistic and numerical cutting process models are adapted to micro cutting with consideration of the so called size effect.

The other approach utilizes research output from ultra-precision diamond cutting and tends to be cutting mechanics centric in nature. This approach is similar to diamond cutting research, but studies micro cutting, with more emphasis on tool geometries, material crystalline orientation and micro structures. Machine dynamics are often neglected as cutting forces are given very little consideration so that ultra-precision machines are treated as rigid and their effects do not appeared in the models. Atomic scale simulation or other numerical modelling considering micro structure and grain size effects are used for this approach and study.

Figure 1.2 A typical micro cutting development process

As discussed above, traditionally MEMS and microelectronics use silicon materials-based micro manufacturing processes which are fundamentally different from mechanical micro cutting. With the increasing requirement on 3D complex shape MEMS devices, mechanical micro cutting will have great potential to fabricate micro parts for MEMS and microelectronics applications. On the other hand, hybrid micro manufacturing approaches, for example, a combination of micro cutting and etching processes to fabricate high precision 3D micro parts, is likely to be a promising method.

Figure 1.2 highlights a typical micro cutting development process, starting from applications and needs which come from microelectronics and MEMS, miniaturization of conventional machining and ultra-precision machining; a micro cutting development flow has a number of key stages. Design parameters including process parameters (e.g. cutting speed, uncut chip thickness, feedrate), tool geometry, material properties, and so on will be developed with the help of existing knowledge from both miniaturization of conventional machining and ultra-precision machining. Intermediate parameters such as cutting forces, temperature, stress distribution, and strain and strain rate are measured and analyzed during the micro cutting process. Depending on the applications, a number of performance indicators such as surface finishes, accuracy and residual stress can be chosen to evaluate the micro cutting performance towards the predictable, producible and highly productive manufacture of micro products.

Figure 1.3 Micro cutting processes for micro-injection moulding. Reproduced with premission from [4]

Precision micro-structured surfaces or micro components are commonly directly machined by micro cutting, or through micro injection moulding or micro embossing with micro-cut micro moulds. Figure 1.3 shows that micro cutting, for example, micro milling, is used to fabricate micro moulds.

1.1.3 Definition and Scope of Micro Cutting

Micro cutting is kinematically similar to conventional cutting, but fundamentally different from conventional cutting in many aspects. It is important to define the scope and context of micro cutting, as the term may have different meanings for different people.

Micro cutting refers to mechanical micromachining (direct removal of materials) using geometrically defined cutter edge(s) carried out on conventional precision machines or micro machines. Micro cutting is normally used for machine high accuracy 3D components in a variety of engineering materials. A number of features can be used to characterize and define the scope of micro cutting as follows:

Uncut chip thickness

. Uncut chip thickness is the material layer being removed during the cutting process. Uncut chip thickness in micro cutting is different from that in conventional macro cutting. Masuzawa and Tonshoff [5] defined the micro-macro border as around 200 µm, while this border obviously changes according to the contemporary levels of conventional technologies. This borderline of uncut chip thickness decreases with advances in machining technologies. In the current state-of-the-art an uncut chip thickness less than tens of microns has been widely accepted by the micro machining community.

Dimensions and accuracy of micro parts or features

. Micro cutting is used to fabricate micro parts, micro features on normal-sized parts, and micro-structured surfaces. In terms of the dimensions of parts/features in micro cutting, micro parts or micro features must have dimensions ranging from 1–1000 µm and at least two dimensions fall into this range. For miniaturized parts such as micro pins, micro gears, that means micro cutting is a three dimensional machining process for a high aspect ratio part. Micro cutting normally achieves form and dimensional absolute accuracy of better than a few microns or a relative accuracy in the order of 10

-3

–10

-5

and surface roughness (Ra) less than 100 nm, although micro cutting has the capability in particular of using diamond tooling to achieve sub-micron accuracy (relative accuracy in the order of 10

-6

) and nanometric surface roughness for micro components and micro structures.

Cutting tool geometry

. The size and geometry of micro cutting tools determine the limit of the size and accuracy of micro features. For micro milling and micro drilling tools, tool diameters are typically in a range from 1000 µm down to 25 µm, although tools of a few microns in diameter are also used in the research laboratories. For micro peripheral turning there is no requirement on tool size, but micro turning tools must be employed for micro-hole boring and face grooving of micro components with the high aspect ratio.

Underlying cutting mechanics

. Micro cutting is not a simple down scaling of conventional macro cutting. In micro cutting, when uncut chip thickness becomes comparable to the cutting edge radius of tools or grain size of workpiece materials, a number of critical issues, such as cutting edge radius effect, negative rake angle, tool-workpiece contact at the flank face, minimum chip thickness and micro structure effect, become prominent. These behaviours are known as size effects, which can influence underlying cutting mechanics in terms of micro cutting forces and specific cutting energy, chip formation process, surface generation, burr formation and tool wear mechanism. On the other hand, size scaling down of machine tools and cutting tools results in size effect on machining dynamics which in turn interacts with and affects cutting mechanics fundamentally.

Application area

. Micro cutting is capable of machining a broad range of engineering materials including metals, polymers, technical ceramics and composites, and also with achievable accuracy and surface roughness. Micro cutting has found applications in many areas requiring micro components.

Figure 1.4 shows some examples of high-accuracy micro components and micro structures manufactured by micro cutting. These examples illustrate that micro components having complex 3D geometries need to be made from a variety of materials and not just from silicon. Mechanical micro machining is an ideal method for producing complex 3D micro components with high accuracy.

1.1.4 Micro Cutting and Nanometric Cutting

There is no general agreement on the definition of nanometric cutting. But if the uncut chip thickness of mechanical cutting falls to the nanometric level, that is, less than tens of nanometers, the cutting process can be regarded as nanometric cutting. Some researchers have conducted ultra-precision machining experiments under extreme small uncut chip thickness, for example, less than 10nm. This can also be regarded as nanometric cutting. One of the promising applications using nanometric cutting is ductile mode cutting with nanometric level surface roughness and being free from cracks in brittle materials, such as semiconductor materials. But it should be noted that most nanometric cutting experiments were carried out under well controlled conditions in a laboratory environment and not many applications on an industrial scale have been found.

Figure 1.4 Examples of high accuracy micro components and micro structures by micro cutting. Reproduced from [6]: (a) Micro trenches. Reproduced with permissions from [7]; (b) Micro reactor [8]; (c) Micro mould. Reprinted from [9]. Copyright 2001 Elsevier; (d) Micro-gear. Reproduced with permission from [10]. Copyright 2004 ASME; (e) 3D micromachined part – Noh-mark (Fanuc). Images courtesy of FANUC; (f) Micro projection array (Fanuc). Images courtesy of FANUC; (g) Micro needles array. Reprinted from [11]. Copyright 2006 Elsevier; (h) Micro wall. Reproduced with permission from [12]; (i) Target foil for nuclear fusion. Reproduced with permission from [13]. Copyright 2001 EUSPEN

Nanometric cutting experiments are difficult to conduct, numerical simulations are therefore carried out as a powerful tool to study nanometric cutting processes. Among various numerical simulation techniques, molecular dynamics (MD) simulation has played a significant role in investigating nanometric cutting mechanics. MD simulation is an extremely accurate simulation method on the atomic scale and has the ability to fully describe the microstructural evolution of the material being processed. However, the simulation scale of MD is limited by computational power and so far even at the largest scale it can only reach a few µm3. Therefore, MD simulation has been mainly applied to nanometric cutting where depth of cut is at the nanometric level. The application of MD simulations in machining was pioneered by LLNL in the late 1980s [15]. Since then several meaningful studies were carried out in different aspects of nanometric machining, including crystallographic orientation effects on plastic deformation [16], tool edge radius and minimum depth of cut effects on the chip formation mechanism [17], effects of defect structure in the workpiece material, diamond tool wear [18]; [1], subsurface deformed layer property [19], and so on.

Although the simulation scale of MD cannot directly cover micro cutting processes (typically, a few to a few hundreds of microns), these studies provide valuable base-line data and results for micro cutting simulations. The length scale of micro cutting in nature falls between nanometric cutting and macro cutting, therefore the micro cutting inherently has the characteristics of both. Studying the micro cutting process is very important in order to bridge the gap between the conventional macro cutting and nanometric cutting process.

1.2 Materials in Micro Cutting

One of the advantages of micro cutting over MEMS micro manufacturing is that micro cutting has fewer constraints on material choices. Almost all the material families – metals, polymers, glasses, ceramics and composites have been reported to be processed by micro cutting. As shown in Figure 1.4, materials for micro components are application and function dependent: optical components being made from glass, polymer or aluminium; medical engineering components from polymer or glass; mechanical components from ferrous or non-ferrous metals; and dies/moulds from copper alloys, aluminium or high-hardness steels. Some of the micro components and micro structures require sub-micron accuracy and nanometric surface finishes so diamond machinable materials are used to achieve the accuracy and surface requirement.

Although micro cutting uses the same range of materials as macro cutting, there are a number of material issues in micro cutting which is fundamentally different from macro cutting. These material issues affect micro cutting performance and hence research efforts have been broadened to investigate material behaviours at the micro scale.

Most engineering materials used are polycrystalline materials with typical grain size varying from between approximately 100 nm to 100 µm. When a micro part or feature decreases in relation to this size range, grains are actually equivalent to being either removed or refined. For most metals, mechanical properties are dominated by the presence and mobility of structural dislocations. As equivalent grain size is reduced the maximum spacing between a dislocation and a grain boundary is reduced, the ease of dislocation movement is influenced by any number of obstacles such as grain boundaries, defects and micro part/feature surfaces, and so on material strength is therefore increased. The changed material properties will in turn affect machinability of micro cutting.

On the other hand, the uncut chip thickness in micro cutting is usually in the same order as the material grain size, hence the workpiece material cannot be assumed as homogeneous and isotropic. Experiments on micro cutting of multiphase materials have shown significant varying cutting mechanisms and the associated process response [20], [21], [22].

Various material constitutive models have been employed to model material behaviours in micro cutting. Most of these material models address material behaviours such as strain hardening, strain rate sensitivity and thermal softening. Multiphase FE simulation models for micro cutting were also proposed to address the material size effect mentioned above [20], [22].

1.3 Micro Cutting Processes

Kinematically similar to conventional cutting, typical micro cutting processes include micro turning, micro milling, micro drilling and micro grinding (with shafts particularly). These four micro cutting processes vary in workpiece geometry, machining efficiency and achievable accuracy, although these cutting process mechanics share lots of common characteristics. Table 1.2 summarizes the geometric characteristics of the four micro cutting processes. Chapters 7–10 will discuss these micro cutting processes in detail.

Table 1.2 Geometric characteristics of typical micro cutting operations

Figure 1.5 An example of micro-turned shaft (Reproduced from [23]). Reproduced with permission from [2]. Copyright 2007 Elsevier

1.3.1 Micro Turning

Micro turning is an effective way to produce micro cylindrical or rotational symmetry components. Figure 1.5 shows examples of a simple micro pin with the diameter of 33μm. A micro part with the high aspect ratio can be achieved using the micro turning [23]. The most serious problem encountered during micro turning is the cutting force which tends to bend the workpiece, and the machining force influences machining accuracy and the limit of machinable size [24]. A detailed analysis on how size effect influences micro part rigidity and deflection is provided in Chapter 7. Micro turning is performed on either a conventional precision machine or a micro turning system.

Diamond turning of the micro structured surface can be regarded as another group of micro cutting. With the aid of fast tool servos (FTS), complex micro structured surfaces can be generated by diamond turning.

1.3.2 Micro Milling

Micro milling is an emerging technology and is the most flexible and versatile micro cutting process. It is able to generate a wide variety of complex micro components and micro structures. In the past decade significant research has been carried out in micro milling modelling and experiments. Most of the micro components shown in Figure 1.3 were machined using micro milling technology.

Micro tooling is crucial to micro milling as it determines the feature size and also the surface roughness. Commercially available micro milling tools have the tool diameter ranging from 25–1,000 μm. Due to the limited rigidity of small diameter tools and difficulty in fabricating a micro tool, most of the micro milling tools have only two flutes, and some very small diameter tools (<100 μm), especially made from natural diamond or CVD, have only single flute or spade type tools. In terms of types of milling operations, micro end milling using either flat end or ball-nosed end mills dominates micro milling applications, and peripheral milling in macro milling is uncommon for micro milling. One of the challenges in micro milling is premature tool chipping and breakage. There are limited choices for micro tool fabrication. Coated micro grain tungsten carbide tools are widely employed, and natural diamond or CVD micro milling tools are used in some applications requiring very tight tolerance and good surface finishes.

Figure 1.6 The ultrahigh speed aerostatic bearing spindle driven by a sensorless DC motor (a) photograph of the developed miniature spindle; (b) a schematic of the spindle

Although micro milling can be performed in a conventional CNC machining centre by retrofitting a high speed spindle, ideally micro milling should be performed in a precision milling machine or micro machine specially designed for micro milling purposes. Chapter 2 presents some industrial precision machine tools and miniature machine tools with micro milling capability. Small diameter micro milling tools require extremely high rotational speeds to achieve even modest machining rates and also a high stiffness spindle to maintain high accuracy in the presence of cutting forces. High machining accuracy also requires low spindle running temperatures to minimize thermal distortion while a fine surface finishing capability can only be achieved with a spindle having low motion errors. So precision high speed spindles with operating speeds of more than 100,000 rpm are commonly used. Figure 1.6 shows an ultra high speed aerostatic bearing spindle with an operating speed range of 20 000 to 200 000 rpm.

1.3.3 Micro Drilling

Drilling is a popular machining method to create a round hole in a part made from many materials. Although it shares many cutting mechanics with other cutting operations, micro drilling has not been researched to the same extent as micro turning and micro milling. This is because micro drilling tools have more complex geometry compared to milling and turning tools. Holes of 50 μm can be practically machined with commercial twist drills. Micro drills of less than 50 μm diameter are also available and normally of the spade type. One of the main applications of high speed micro drilling is printed circuit boards (PCBs) drilling. Micro drills of 50–300 µm in diameter are commonly used in PCB drilling production lines and a hole depth/diameter ratio up to 15 has been achieved [29].

Compared with micro milling, micro drilling is more efficient in creating holes and capable of machining deep holes, although micro drilling cannot machine flat-bottom holes because of the drilling point. Since a micro drill can easily be broken, sensitive torque feedback control is necessary. But usually a thrust force feedback is employed because of the difficulty in the direct measurement of the torque [5].

Figure 1.7 Micro CVD diamond-coated grinding tools. Reproduced with permission from [30]

Micro drilling has a similar requirement on high speed spindles as micro milling, but speed control is not desirable as with a micro milling spindle. Aerostatic bearing or air turbine spindles with maximum speed more than 100 000 rpm are typically used to improve productivity.

1.3.4 Micro Grinding

Micro grinding has been an effective method to produce high dimensionally accurate parts with superior surface finishes. Due to its low material removal rate, micro grinding is normally used as the final production procedure. Unlike other micro cutting processes, such as micro turning and micro milling where ductile or less hard materials are usually used, micro grinding is capable of machining brittle and hard materials.

Similar to the micro turning operation, micro grinding can be performed using relatively large grinding wheels when the micro features do not require micro grinding tools. But the size and geometry of micro grinding tools determine the limit of the size and geometry of micro parts and micro features. Standard diamond abrasive tools are made by bonding diamond monocrystals, PCD or CVD onto a base body. Micro grinding tools have been fabricated by coating CVD diamond layers onto cemented carbides. Figure 1.7 shows a small CVD diamond abrasive pencil with the diameter of 50 to 100 µm.

1.4 Micro Cutting Framework

This section presents a framework for micro cutting with the aim of highlighting various micro cutting aspects in an integrated environment and how these aspects interact and related to each other. Figure 1.8 shows a representation of the micro cutting framework. Challenges and needs of miniaturization are always the main driving force to push micro cutting science and engineering forward. Existing challenges such as size effects and micro-machinability have raised research issues which are being addressed by the micro machining community. The market need for miniaturized and micro products or components with smaller dimensions/features and tighter tolerance sets the scope of micro cutting and drives the progress of this subject area. Micro-machinability and production rate of micro cutting determine if micro cutting is a feasible and favourable industrial method for a certain micro product.

Figure 1.8 A framework for micro cutting

Micro cutting mechanics are central to the micro cutting fundamentals. Similar to conventional macro cutting mechanics, issues like chip formation, cutting force, cutting temperature, tool wear, burr formation, surface generation, are being investigated, but in the micro domain. Micro cutting dynamics, including tool run-out, tool deflection, micro machining chatter and vibration, influence the cutting performance and should be linked with micro cutting mechanics. Engineering materials for micro cutting are also important aspects which should be taken into account in micro cutting mechanics. The available research methods in macro cutting, especially the analytical and numerical methods, become increasingly attractive for studies of micro cutting. On the other hand, developments on enabling technologies – machine tools, micro tooling and micro metrology have enhanced the understanding and improvement of research and development in micro cutting processes. The resultant scientific understanding of the micro cutting fundamentals and enabling technologies of micro cutting are being applied to various micro cutting processes and to produce micro parts, micro-structured surface, and micro features in an efficient and effective way, although many new applications and challenges are emerging on an almost daily basis, as indeed micro cutting is a fast moving and timely subject area as well. The subsequent chapters will attempt to discuss these aforementioned scientific/technological challenges, fundamentals, engineering issues and applications in a comprehensive and systematic manner.

References

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[23] Rahman, M., Lim, H.S., Neo, K.S., Kumar, A.S., Wong, Y.S. and Li, X.P. (2007) Tool-based nanofinishing and micromachining, Journal of Materials Processing Technology,185, 2–16.

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2

Micro Cutting Mechanics

Dehong Huo1 and Kai Cheng2

1 School of Mechanical and Systems Engineering, Newcastle University

2 School of Engineering and Design, Brunel University

2.1 Introduction

Micro cutting is kinematically similar to conventional cutting. However, it is not a simple ­scaling of macro cutting. In micro cutting, when uncut chip thickness becomes comparable to the cutting edge radius of tools or grain size of workpiece materials, a number of critical issues, such as cutting edge radius effect, negative rake angle, tool-workpiece contact at the flank face, minimum chip thickness and micro structure effect, become prominent. These behaviours are categorized as size effects, which can influence underlying cutting mechanics in terms of micro cutting forces and specific cutting energy, chip formation process, surface generation, burr formation and tool wear mechanism. In addition to process and material size effects, micro cutting process performance is strongly based on its enabling technologies, namely, appropriate machine tools, micro tooling and measurement and inspection system.

Research has been carried out in micro cutting mechanics for decades and experimental studies still dominate the micro cutting research. Some analytical and numerical models for micro cutting have been developed based on conventional cutting models and some size effects have been incorporated into these models.

From the perspective of applications, some critical issues, such as excess tool wear, low stiffness of the micro tools, unpredictable tool failure, make micro cutting difficult-to-machine materials particularly challenging. Two scientific approaches are being employed to address these issues, namely, vibration assisted micro cutting and micro-scale laser-assisted milling. Figure 2.1 summarizes the micro cutting mechanics in context in an integrated environment and also provides an outline of the chapter.

Figure 2.1 Overview of micro cutting mechanic aspects

2.2 Characterization of Micro Cutting

Micro cutting in this chapter refers to mechanical micro machining using a geometrically defined cutter edge, such as micro turning, micro milling, micro drilling and micro grinding. Micro cutting is normally used to machine high accuracy 3D components in various ­engineering materials with overall sizes or features sizes ranging from a few microns to a few millimetres. Micro cutting is different from conventional cutting in terms of uncut chip thickness.

High-accuracy mechanical miniature components with dimensions ranging from hundred microns to a few millimetres or features ranging from a few to a few hundred microns are increasingly in demand for various industries, such as aerospace, precision engineering, medical engineering, biotechnology, electronics, communications and optics, and so on. Special applications include fuel cells, micro fluidics, moulds for micro optics/lenses and fibre optic elements, micro nozzles, to name a few. Many applications require very tight tolerances and both ­functional and structural requirements demand the use of various engineering materials, including stainless steel, titanium, brass, aluminium, plastics, ceramics and composites [1]; [2, 3].

Figure 2.2 Dimensional size for the micro-mechanical machining. Reproduced with permission from [5]

It has long been recognized that traditional MEMS manufacturing techniques, such as chemical etching and LIGA, cannot match future demand-rate for micro components. This is because MEMS-based manufacturing methods are basically planar processes and directed towards semiconductor materials. The relative accuracies of MEMS-based methods are of the order of 10-1 to 10-2, whereas the needs of many mechanical miniaturized components require relative accuracies in the order of 10-3 to 10-5 [4]. On the other hand, many micro component applications also require very high surface quality in terms of surface roughness and surface integrity. Micro cutting can meet the above requirements of producing 3D high accuracy micro components in a wide range of engineering materials. Figure 2.2 compares dimensional size and accuracy with other manufacturing methods.

2.2.1 Micro Cutting and Ultra-Precision Machining

When discussing the micro cutting process, researchers normally compare it with traditional ultra-precision machining. Sometimes distinctions and common characteristics of the two processes can be confusing. This is because:

1. Some micro cutting mechanics research finds its origins in ultra-precision machining ­studies, such as minimum chip thickness.

2. Micro cutting processes share some common characteristics with traditional ultra-­precision machining, such as chip formation and specific cutting forces.

3. There are overlaps between the two processes in terms of the characteristic depth of cut and applications.

However there are many distinctions between the two processes in terms of machining process characters, component size, toolings, applications, and so on. Table 2.1 attempts to compare micro cutting with traditional ultra-precision machining processes in order to gain a better understanding of the scope and main features of micro cutting processes. Generally speaking, ultra-precision machining focuses on achieving highest possible dimensional accuracy and surface finish using diamond tooling regardless of component size, and applications are predominated by electro-optics. Micro cutting, on the other hand, focuses on mechanical micro machining 3D miniature components over various engineering materials using various tools with reasonably high accuracy and surface finish.

Table 2.1 A comparison between micro cutting and typical ultra-precision machining

Micro cutting

Ultra-precision machining

Processes

Micro turning, milling, drilling, grinding, etc.

Single point diamond turning, fly cutting, etc.

Tooling

Various tooling materials: (coated) tungsten carbide, CVD, CBN, diamond tools

Natural diamond tools

Component size

1–1000 µm

1 mm above, Can be very large

Shape

3D shape with high aspect ratios and geometric complexity

Rotational parts, both spherical and aspheric surface, normally low aspect ratios.

Accuracy

Absolute: <10 µmRelative: 10

-

2

–10

-

5

Absolute: <1 µmRelative: 10

-

5

–10

-

6

Surface finish

<100 nm Ra

Typically <20 nm Ra

Machines

Precision machining centres, precision micro machines, ultra-precision turning machines

Ultra-precision turning machines

Applications

Various applications requiring micro components

Electro-optics

Depth of cut (uncut chip thickness)

1–10 µm

0.1 µm – 10 µm

2.2.2 Enabling Technologies for Micro Cutting

Performance of the micro cutting process is strongly dependant on its enabling technologies, namely, appropriate machine tools, micro tools and measurement and inspection system. This section will highlight requirements and state-of-the-art machine tools used for micro cutting, and latest micro tools development.

2.2.2.1 Machine tools

Most of the experimental research for micro cutting processes has been performed in two types of machines, that is, traditional (ultra) precision tuning machines or micro machining centre, and in-house desk-top micro machines or micro factories built by researchers.

The requirements of micro component manufacture over a range of applications are: high dimensional precision, typically better than a few microns; accurate geometrical form, ­typically better than 100 nm departure from flatness or roundness; and good surface finish, in the range of 10 – 100 nm Ra. These in turn require machine tools to have high static stiffness, low thermal distortion, low motion errors and high damping or dynamic stiffness.

There are a number of industrial ultra-precision turning and milling machines available for precision components manufacture. Most of them are generally aimed at the optical components market and are not well suited to the manufacture of precision micro components due to high investment costs and lack of flexibility. Figure 2.3 shows some examples of industrial ultra-precision machines with micro cutting capability. They fall into two ­categories. One is conventional ultra-precision machine tools which are designed as ­diamond turning machine tools with add-on Z-axis, rotary table and a second high speed milling or grinding spindle. Typical examples are Moore Nanotechnoloy Nanotech 350FG and Precitech Freeform 700 ultra as shown in Figure 2.3g and h. Both of them require 5–7 m2 floor space. Their very high cost and low flexibility limit their application to micro components of simple geometries and high added value, such as optical components. Another type of industrial precision micro milling machine tool has emerged in the last decade. A typical example is the Kern micro machine (Figure 2.3a) which meets many applications but still suffers from its machining accuracy for precision micro machining due to the positioning accuracy.

Figure 2.3 Industrial precision machine tools with micro cutting capability: (Reproduced from [2]) (a) Kern micro. Copyright KERN Microtechnik GmbH; (b) Sodick AZ150. Image courtesy of Sodick, Inc.; (c) Fraunhofer IPT Minimill. Reproduced from [6]; (d) Makino Hyper2J. Image courtesy of Makino; (e) Kuglar MicroMaster MM2. Image courtesy of Kugler GmbH; (f) Fanuc ROBOnano. Images courtesy of FANUC; (g) Precitech freeform 700 Ultra. Image courtesy of Ametek Precitech; (h) Moore Nanotech 350FG. Copyright Moore Nanotech

Smaller machine tools are less affected by environmental fluctuations such as changes in temperature, pressure and humidity as compared to their macro-scale counterpart. And the reduced mass of the miniature machine tool reduces the inertia force required to drive the machine tool system, thus consuming less energy and yet providing higher positioning accuracy. Hence, the use of miniature machine tools is also seen as having immense potential in reducing production costs [7].

Numerous research efforts to develop in-house miniaturized machines or micro factories have been undertaken for the manufacture of precision micro components [7]; [8]; [9]. Figure 2.4 shows some examples of a miniature machine tool. However, most of them are still at the research stage, and only a few of them have so far found their way into industrial ­applications, and their application to high accuracy and fine surface quality are still constrained by low static/dynamic stiffness.

Figure 2.4 Examples of miniature machine tools and micro factories. (Reproduced from [2]) (a) Reproduced with permission from [10]; (b) Reproduced from [11]. Copyright 2005 Spriger; (c) Reproduced from [12]. Copyright 2006 ASME; (d) Reproduced from [13]. Copyright 2008 Springer; (e) Reproduced with permission from [10]; (f) Reproduced with permission from [8]. Copyright 2002 IOP Publishing

2.2.2.2 Micro cutting tools

Micro cutting tooling is another enabling technology for micro cutting, since micro cutting needs to utilize micro tooling to enable micro components and features. Geometry of micro cutting tools is the same or similar to micro components/features to be machined. Cutting tool geometry and material properties have significant influence on chip formation, heat ­generation, tool wear, surface generation, and so on. In micro cutting the uncut chip thickness and the tool edge dimension are in the same order of magnitude (cutting edge size effects will be discussed in the next section), which requires cutting edges which can ­withstand high mechanical and thermal stresses, and hence wear resistance, for a ­prolonged machining time.

Figure 2.5 Micro milling tools (Courtesy of Contour Fine Tooling Ltd). Reproduced with permission from Contour Fine Tooling Ltd.

Single crystal diamond has been used predominately in ultra-precision machining due to its matchless hardness. Single crystal diamond micro tools have been fabricated to meet the high requirements on accuracy and surface finishes in micro cutting for certain applications. Very little research has been reported on micro cutting performance and tool wear issues using a diamond micro cutter. One the other hand, as diamond has a very high affinity to iron, ­diamond micro cutting is limited to the machining of non-ferrous materials such as aluminium and ­copper. Tungsten carbide micro tools are widely used in micro cutting processes. Tungsten carbide has high strength and hardness. In order to increase the wear resistance and hardness, very fine grain size tungsten carbide is fabricated for micro tools and various coated micro tools, such as diamond and titanium coated tools, are becoming popular in micro cutting. Figure 2.5 shows some examples of micro milling tools.

2.3 Micro Cutting Mechanics