CH 5 Revision Q's

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

- bilateral tolerance: the variation is permitted in both positive and negative directions from the nominal dimension. - unilateral tolerance: the variation from the specified dimension is permitted in only one direction, either positive or negative.

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

Absorption(impurities absorbed) Alloy depletion(critical alloying elements are lost ) Cracks Craters Hardness changes Heat affected zone Inclusions(small particles in the surface layers) Pits Recrystallization Residual stresses

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

Average of the vertical deviations from the nominal surface over a specified surface length.

What is meant by the term graduated measuring device?

Graduated measuring devices include a set of markings (called graduations) on a linear or angular scale to which the object can be measured by following a scale of measurement. e.g. meters and degrees

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

Grinding Honing Lapping Polishing Superfinish

Define nominal surface.

Nominal surface is the ideal surface represented in an engineering drawing. Assuming it is perfectly smooth, flat (for a planar surface) and round (for a round surface).

What is precision in measurement?

Precision is the degree of repeat ability in the measurement process. aka the lower the standard deviation is for measurements the higher the precision.

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

Roughness is only one measurement of surface texture. It's limitations are that it does not indicate the lay, it varies depending on direction, it's value depends on the roughness width cutoff used to measure the average.

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

Roughness: small spaced deviations in the surface Waviness: large spaced deviations in the surface

Name some manufacturing processes that produce very poor surface finishes.

Sand casting Hot rolling Sawing Arc welding Flame cutting Plasma arc cutting

How is surface texture distinguished from surface integrity?

Surface texture is the study and control of the surface and the material just under the surface.

What is accuracy in measurement?

The degree to which the measured value is close to the true value of interest.

What are the common methods for assessing surface roughness?

The surface changes are caused by the application of various forms of energy during processing—mechanical, thermal, chemical, and electrical.

What causes the various types of changes that occur in the altered layer just beneath the surface?

The surface changes are caused by the application of various forms of energy during processing—mechanical, thermal, chemical, and electrical.

What is a tolerance?

The tolerance is the difference between the maximum and minimum limiting dimensions that will still allow clearance.

What are some of the reasons why surfaces are important?

They are important for the reasons of aesthetics, safety, friction, mechanical and physical properties (stress can lead to stress concentration), assembling parts, and electrical contacts.

Define surface texture.

the repetitive and/or random deviations from the nominal surface of an object. It is defined by four features: roughness, waviness, lay, and flaws.