Chapter 5

Processes that produce poor surfaces include sand casting, hot rolling, sawing, and thermal cutting

Name some manufacturing processes that produce very poor surface finishes.

The nominal surface is the ideal part surface represented on an engineering drawing. It is assumed perfectly smooth; perfectly flat if referring to a planar surface; perfectly round if referring to a round surface, etc.

Define nominal surface.

Surface texture is the random and repetitive deviations from the nominal surface, including roughness, waviness, lay, and flaws.

Define surface texture.

Surface texture refers only to the surface geometry; surface integrity includes not only surface but the subsurface layer beneath the surface and the changes in it.

How is surface texture distinguished from surface integrity?

The changes and injuries include: cracks, craters, variations in hardness near the surface, metallurgical changes resulting from heat, residual stresses, intergranular attack, etc.

Identify some of the changes and injuries that can occur at or immediately below the surface of a metal.

Surface roughness provides only a single measure of surface texture. Among its limitations are: (1) it varies depending on direction; (2) it does not indicate lay; (3) its value depends on the roughness width cutoff used to measure the average.

Indicate some of the limitations of using surface roughness as a measure of surface texture.

Processes that produced very good and excellent surfaces include honing, lapping, polishing, and superfinishing

Name some manufacturing processes that produce very good or excellent surface finishes.

Surface roughness is defined as the average value of the vertical deviations from the nominal surface over a specified surface length.

Surface roughness is a measurable aspect of surface texture; what does surface roughness mean?

The reasons why surfaces are important include: aesthetics, safety, friction and wear, effect of surface on mechanical and physical properties, mating of components in assembly, and electrical contacts.

What are some of the reasons why surfaces are important?

Common methods for assessing surface roughness are (1) comparison of the specimen surface with standard test blocks having known surface roughness values and (2) stylus-type electronic instruments which measure average roughness.

What are the common methods for assessing surface roughness?

A tolerance is defined as the total amount by which a specified dimension is permitted to vary.

What is a tolerance?

Accuracy is the degree to which the measured value agrees with the true value of the quantity of interest. It is a measurement procedure that is absent of systematic errors.

What is accuracy in measurement?

A graduated measuring device has markings (called graduations) on a linear or angular scale to measure an object's feature of interest (e.g., length).

What is meant by the term graduated measuring device?

Precision in measurement is the degree to which random errors are minimized.

What is precision in measurement?

A bilateral tolerance allows variation in both positive and negative directions from the nominal dimension, whereas a unilateral tolerance allows the variation from the nominal dimension to be either positive or negative, but not both.

What is the difference between a bilateral tolerance and a unilateral tolerance?

Roughness consists of the finely-spaced deviations from the nominal surface, while waviness refers to the deviations of larger spacing. Roughness deviations lie within waviness deviations.

Within the scope of surface texture, how is roughness distinguished from waviness?