Page 38 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

General Introduction

TABLE l.3

it i 'ngiizeractieristics ofvana' ' nnMrateriais5: 1 _

if

iii
ii
Alloy Castability Weldability Machinability
Aluminum E F E-G
Copper G-F F G-F
Gray cast iron E D G
White cast iron G VP VP
Nickel F F F
Steels F E F
Zinc E D E
Note: E, excellent; G, good; F, fair; D, difficult; VP, very poor. The ratings shown depend greatly on the
particular material, its alloys, and its processing history.

texture, substitute materials or additional processing of a particular material may
well be required, all of which can contribute significantly to product cost.
Reliability of supply is important in order to meet production schedules. In au-
tomotive industries, for example, materials must arrive at a plant at appropriate time
intervals. (See also just in time, Section 1.7). Reliability of supply is also important,
considering the fact that most countries import numerous raw materials. The United
States, for example, imports most of the cobalt, titanium, chromium, aluminum, nickel,
natural rubber, and diamond that it needs. Consequently, a country’s self-reliance on
resources, especially energy, is an often-expressed political goal, but is challenging to
achieve. Geopolitics (defined briefly as the study of the infuence of a nation’s physical
geography on its foreign policy) must thus be a consideration, particularly during
periods of global hostility.

Service Life. We all have had the experience of a shortened service life of a product,
which often can be traced to (a) improper selection of materials, (b) improper selec-
tion of production methods, (c) insufficient control of processing variables, (d) defec-
tive parts or manufacturing-induced defects, (e) poor maintenance, and (f) improper
use of the product. Generally, a product is considered to have failed when it
° Stops functioning, due to the failure of one or more of its components, such as
a broken shaft, gear, bolt, or turbine blade or a burned-out electric motor.
° Does not function properly or perform within required specifications, due, for
example, to worn gears or bearings.
° Becomes unreliable or unsafe for further use, as in the erratic behavior of a
switch, poor connections in a printed-circuit board, or delamination of a compos-
ite material.
Throughout various chapters, this text describes the types of failure of a compo-
nent or a product resulting, for example, from (a) design deficiencies, (b) improper
material selection, (c) incompatibility of materials in contact, which produces friction,
wear, and galvanic corrosion, (d) defects in raw materials, (e) defects induced during
manufacturing, (f) improper component assembly, and (g) improper product use.

Material Substitution in Products. For a variety of reasons, numerous substitu-
tions are often made in materials, as evidenced by a simple inspection and comparison
of common products such as home appliances, sports equipment, or automobiles. As
a measure of the challenges faced in material substitution, consider the following
examples: (a) metal vs. wooden handle for a hammer, (b) aluminum vs. cast-iron lawn