Microfinishing: it's making a name for itself in the auto industry.

Author:Judge, Norman R.
Position:Industrial Metal Products Co. develops generating bearing quality microfinishing process - Technology Notebook

During the 1930s, industry realized that surface finish irregularities effected the function of automotive components such as crankshafts and camshafts. In the years since, control of roughness, waviness, roundness, concentricity, straightness, and other surface characteristics are routine in many applications to assure that components perform as intended.

In the 1990s, surface metrology is more vital than ever before because operating clearances between parts are much smaller to make products - whether automobiles or air conditioners - more efficient.

Smaller clearances between moving components mean smaller manufacturing tolerances. Typical tolerances have been reduced from 0.010[inches] (254 um) to 0.001[inches] (25.4 um) to 0.00001[inches] (.254 um). At 0.010[inches], surface roughness slightly effects most moving components, but at 0.001[inches] and smaller, it has a major effect. With today's tight tolerances, surface roughness can equal a sizable portion of a part's tolerance, and it's important to remember that all energy transfer between moving components occurs within 0.001[inches] (25.4 um) of the surface profile.

Wear characteristics, lubrication retention, noise, and vibration can be controlled with surface measurement and analysis. Surface profile analysis results in greatly improved engine performance by helping find ways to reduce surface roughness, reduce friction with mating components and increase the wear life of these engine components.

Surface geometry measurement is also important. Manufacturing surfaces contain geometric flaws. These may include out-of-round, taper, squareness, eccentricity, coaxial, and cylindrical errors. Energy transfer efficiency and product performance such as vibration, noise, and heat are affected by these conditions.

Microfinishing, removing the surface material of a dimensionally finished part to provide a precise fit to a mating part, has long been a standard feature of automotive manufacturing.

In the automotive industry controling surface finish and geometry is absolutely critical for bearing surfaces on crankshafts, camshafts, pistons, engine blocks, transmission shafts, axle shafts, constant velocity joints, fuel injector systems, and anti-skid brake systems.

Consider the machining of a cylindrical shaft. If the shaft is held by a chuck attached to the machine's main spindle there are two main sources of potential geometry error - rotational error in the spindle and distortion from...

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