Machining Technology for Composite Materials

Principles and Practice

H Hocheng

• Publisher: Woodhead Publishing
• Year: 2011
• Print ISBN: 9780857090300
• eBook ISBN: 9780857095145
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Machining processes play an important role in the manufacture of a wide variety of components. While the processes required for metal components are well-established, they cannot always be applied to composite materials, which instead require new and innovative techniques. Machining technology for composite materials provides an extensive overview and analysis of both traditional and non-traditional methods of machining for different composite materials.The traditional methods of turning, drilling and grinding are discussed in part one, which also contains chapters analysing cutting forces, tool wear and surface quality. Part two covers non-traditional methods for machining composite materials, including electrical discharge and laser machining, among others. Finally, part three contains chapters that deal with special topics in machining processes for composite materials, such as cryogenic machining and processes for wood-based composites.With its renowned editor and distinguished team of international contributors, Machining technology for composite materials is an essential reference particularly for process designers and tool and production engineers in the field of composite manufacturing, but also for all those involved in the fabrication and assembly of composite structures, including the aerospace, marine, civil and leisure industry sectors.- Provides an extensive overview of machining methods for composite materials- Chapters analyse cutting forces, tool wear and surface quality- Cryogenic machining and processes for wood based composites are discussed

Part I

Traditional methods for machining composite materials

1

Turning processes for metal matrix composites

H.A. Kishawy, University of Ontario Institute of Technology (UOIT), Canada

Abstract:

Metal matrix composite materials (MMCs) offer various mechanical properties that are not offered by conventional unreinforced monolithic metal counterparts; specifically, high temperature stability, specific strength, and wear resistance. As a result, these composite materials have different applications in several industries including automotive and aerospace. However, machining of MMCs still remains a challenge. Understanding the manufacturing methods, strengthening mechanisms and hence mechanical properties of MMCs is crucial to comprehension of their deformation behavior during machining and the resulting workpiece surface integrity and tool wear. This chapter describes the types of composites and their unique physical properties. In addition, the cutting performance of some composite materials is discussed.

Key words

MMC tool material

wear

self-propelled tool

1.1 Introduction

The rise in industrial development has generated a steady demand for improving the properties of available materials. These properties are sometimes very hard to obtain by conventional alloying methods. Continuous and extensive research and development has broadened our material knowledge to aid in the improvement of mechanical properties and the generation of a new class of materials known as composite materials. Because of their unique mechanical properties, including high specific strength and stiffness, high damping ratio, and low coefficient of thermal expansion, applications of composite materials are growing increasingly, from primary applications such as in the interiors of automobiles to very advanced applications in automotive, aerospace, marine and off-shore industries.

A composite material is a combination of at least two chemically distinct materials, with a distinct interface separating the constituents. It is usually designed and formed to obtain properties which would not otherwise be achieved by any of the individual constituents. The distinction of composites from other alloys with two or more phases comes from the processing of the composites where the different phases are mixed together. Composites, in general, consist of at least two components namely matrix and the reinforcement.

1.1.1 The matrix

In general, alloys are used for the matrix components of MMCs. The most commonly used matrix materials are aluminum-based alloys, magnesium alloys, titanium alloys, copper, and nickel. Among these, aluminum based alloys (2024, 2124, 5156, 6061, 7075 and 7090) are the most commonly used matrices, due to their low density and high thermal conductivity. Within the composite material system, the matrix provides the ductility and load transfer between the reinforcements. It also provides transverse strength in the case of fiber-reinforced composites.

1.1.2 The reinforcements

Inter-metallic compounds, oxides, carbides or nitrides are used as reinforcement materials. The most dominant reinforcements are SiC, graphite, carbon, Al₂O₃, boron, B₄C, tungsten, Si₃N₄ and TiB₂.

In processing, reinforcements are used either in continuous forms (long fibers) or in discontinuous forms (whiskers, particulates, chopped fibers and platelets) in the case of metal matrix composites. Based on the type of reinforcement, composite materials are typically classified in the following three categories; long fiber reinforced, short fiber (whiskers) reinforced, and particulate reinforced. Regardless of the type of reinforcement, the obtained physical and mechanical properties are always better than those offererd by the individual monolithic materials.

In the case of particulate reinforced composites, particle morphology, particle size distribution, dispersion uniformity, surface chemistry, volume fraction, particle shape, and particle wetability are some of the factors that affect the properties of the composite. The most desired advantages of MMCs are their resistance to severe environments, toughness, high elastic modulus, and retention of strength at high temperatures. Because it is possible to obtain the required mechanical strength and stiffness from the reinforcements, the development and selection of matrix materials for a composite structure can be characterized based on their environmental stability, such as oxidation and corrosion resistance at elevated temperature. For long fiber reinforced composites, knowledge of the shear strength requirements of the matrix are essential since the matrix serves only to transfer load into the filaments. However, the strength of the matrix dominates the yielding behavior in short fiber and particulate reinforced MMCs. Also, practical experience indicates that the improved physical properties offered by short fibers (whiskers) or particulate composites are modest compared to those with long fibers. This would explain why most of the early research has focused on the development of continuous filament composites. Initially, the continuous reinforcement was developed for aerospace applications. Owing to the high production cost of this type of composite, its non-aerospace applications are minimal despite the numerous attractive mechanical and high temperature properties.

The adoptation of discontinuous reinforcements leads to significant cost reduction and greater flexibility in fabrication which makes this attractive and feasible for various applications. With the introduction of SiC whiskers, extensive research has been conducted to process discontinuous reinforced composites composed of ceramic particulate reinforcements, such as SiC, Al₂O₃ and B₄C in aluminum based matrixes. Adding to to the inexpensive techniques used for the fabrication of particulate MMCs, another very important advantage of discontinuously reinforced MMCs is that they can be formed by conventional processes such as extrusion, forging, and ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Part I: Traditional methods for machining composite materials
• Part II: Non-traditional methods for machining composite materials
• Part III: Special topics in machining composite materials
• Index