skewness in importance is the directional nature of surface textures developed by typical machining and grinding meth- ods. These machined surfaces are characterized by tool
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Figure 4
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mance can be substantially enhanced if these types of surface textures can be altered into one that is more random in nature. Post-machining processes that utilize free or loose abrasive materials in a high-energy context can alter the machined sur- face texture substantially, not only reducing surface peaks, but generating a surface in which the positioning of the peaks has been altered appreciably. These “isotropic” surface effects (Fig 4.) have been demonstrated to improve part wear and fracture resistance, bearing ratio and improve fatigue resistance. Application: Figures 3 and 4 are automotive camshaft roll- ers that connect the rotating action of the cam to the recip- rocating valve. The loads on this surface are high and must be transmitted through a consistent layer of oil to maintain a rolling action between the moving elements. The directionally ground roller (Fig 3.) was contacting the cam lobe and failing both the roller and the camshaft to result in an engine manu- facture liability in the many millions of dollars. Each failure would force the manufacturer to, in the field, replace the camshaft, rollers and, many times, other normally non-related components because of wear debris moved throughout the engine via the lubrication system. The random, high load bearing surface shown in Fig 4. maintains a predict- able oil film and keeps the rollers from contacting the cam and, therefore, resisting wear. 3) Residual Tensile Stress vs. Residual Compressive Stress: Many machining and grinding processes tend to devel-