Page 118 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Key Terms 97

2. The intended life of the coin is another consid- Another consideration is the suitability of the
eration; this duration will reflect resistance to coin for use in coin-operated devices, such as
corrosion and to Wear (Chapter 32) While the vending machines, turnstiles, and pay tele-
coin is in circulation. These two factors basically phones. These machines are generally equipped
determine the span over which the surface with detection devices that test the coins--first,
imprint of the coin will remain identifiable and for proper diameter, thickness, and surface con-
the ability of the coin to retain its original luster. dition, and second, for electrical conductivity
3. The manufacturing of the coin includes factors and density. The coin is rejected if it fails these
such as the forrnability of the candidate coin ma- tests.
terials, the life of the dies used in the coining op- A final consideration is the cost of raw materi-
eration (Section 14.3.2), and the capability of the als and processing, and whether there is a suffi-
materials and processes to resist counterfeiting. cient supply ofthe coin materials.

SUMMARY

Physical and chemical properties can have several important influences on mate-
rials selection, manufacturing, and on the service life of components. These prop-
erties and other material characteristics should be considered because their effects
on product design, service requirements, and compatibility with other materials,
including tools, dies, and workpieces.
The combined properties of strength-to-weight and stiffness-to-weight ratios are
important factors in selecting materials for lightweight and high-performance
structures.
Thermal conductivity and thermal expansion are major factors in the develop-
ment of thermal stresses and thermal fatigue and shock, effects which are impor-
tant in tool and die life in manufacturing operations.
Chemical reactions, including oxidation and corrosion, are considerations in ma-
terial selection, design, and manufacturing, as well as in the service life of compo-
nents. Passivation and stress-corrosion cracking are two important phenomena.
Certain physical properties are utilized in manufacturing processes and their con-
trol, such as the magnetostriction effect (for ultrasonic machining of metals and
nonmetallic materials) and the piezoelectric effect (for force transducers and var-
ious other sensors).

KEY TERMS

Corrosion Ferromagnetism Passivation Specific strength
Conductors Galvanic corrosion Piezoelectric effect Stress-corrosion cracking
Degradation Heat checking Selective leaching Superconductivity
Density Invar effect Semiconductors Thermal conductivity
Dielectric Magnetorheostatic Smart fluids Thermal expansion
Electrical conductivity Magnetostriction Smart materials Thermal fatigue
Electrical resistivity Melting point Specific heat Thermal stresses
Electrorheostatic Oxidation Specific stiffness