Page 37 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 1.5 Selection of Materials

l.5 Selection of Materials

An increasingly Wide variety of materials are now available, each type having its
own (a) material properties and manufacturing characteristics, (b) advantages and
limitations, (c) material and production costs, and (d) consumer and industrial ap-
plications (Part I). The selection of materials for products and their components is
typically made in consultation with materials engineers, although design engineers
may also be sufficiently experienced and qualified to do so. At the forefront of new
materials usage are industries such as the aerospace and aircraft, automotive, mili-
tary equipment, and sporting goods industries.
The general types of materials used, either individually or in combination with
other materials, are the following:

° Ferrous metals: Carbon, alloy, stainless, and tool and die steels (Chapter 5).
° Nonferrous metals: Aluminum, magnesium, copper, nickel, titanium, superal-
loys, refractory metals, beryllium, zirconium, low-melting-point alloys, and pre-
cious metals (Chapter 6).
° Plastics (polymers): Thermoplastics, thermosets, and elastomers (Chapter 7).
° Ceramics, glasses, glass ceramics, graphite, diamond, and diamond-like
materials (Chapter 8).
° Composite materials: Reinforced plastics and metal-matrix and ceramic-matrix
composites (Chapter 9).
° Nanomaterials (Section 8.8).
° Shape-memory alloys (also called smart materials), amorphous alloys, semicon-
ductors, and superconductors (Chapters 6, 18 and 28).
As new developments continue, the selection of an appropriate material for a particu-
lar application becomes even more challenging. Also, there are continously shifting
trends in the substitution of materials, driven not only by technological considera-
tions, but also by economics.
Properties of Materials. Mechanical properties of interest in manufacturing gen-
erally include strength, ductility, hardness, toughness, elasticity, fatigue, and creep
resistance (Chapter 2). Physical properties are density, specific heat, thermal expan-
sion and conductivity, melting point, and electrical and magnetic properties
(Chapter 3). Optimum designs often require a consideration of a combination of
mechanical and physical properties. A typical example is the strength-to-Weight and
stiffness-to-weight ratios of materials for minimizing the weight of structural mem-
bers. Weight minimization is particularly important for aerospace and automotive
applications, in order to improve performance and fuel economy.
Chemical properties include oxidation, corrosion, degradation, toxicity, and
flammability. These properties play a significant role under both hostile (such as cor-
rosive) and normal environments. Manufacturing properties indicate whether a par-
ticular material can be cast, formed, machined, joined, and heat treated with relative
ease. As Table 1.3 illustrates, no one material has the same manufacturing characteris-
tics. Another consideration is appearance, which includes such characteristics as color,
surface texture, and feel, all of which can play a significant role in a product’s accept-
ance by the public.

Availability. As will be emphasized throughout this book, the economic aspect of
material selection is as important as technological considerations (Chapter 40). Thus,
the availability of materials is a major concern in manufacturing. Furthermore, if
materials are not available in the desired quantities, shapes, dimensions, and surface