Innovative Technologies in Lapping and Electrospark Alloying of Metal Surfaces as the Basis for Industry 4.0

Background

The main factors having an influence on lapping in friction units are the surface treatment, oil quality, the initial wear of the part, and lapping mode.

In the initial operation of matched parts, the surfaces touch with not all areas of these parts but only with tops of the surface roughness. The area of the real abutting surface (the area of abutting tops) is always significantly less than the nominal (calculated) surface of contact (Ocallaghan & Probert, 1987). This decrease can be determined by the coefficient of the real abutting surface.

The coefficient of the real abutting surface is higher for surface processed more carefully. It varies in the range of 0.2–0.4 in finishing turning, finishing milling, fine reaming, pulling, and it reaches 0.8–0.95 only during finishing operations (fine grinding, vibration grinding). The large specific loads appear on the protrusion tops of rubbing surfaces, which usually exceed the acceptable stresses. These loads cause plastic deformation, cutting and breaking of protrusions, and thus intense wear of parts.

The rubbing surfaces are grinded and become smoother due to the crushing of protrusions. After lapping, the area of abutting surfaces increases, the specific pressure decreases, and the waviness of friction surface is corrected. Therefore, the wear rate is reduced.

Obviously, the wear rate becomes minimal when the width of the protrusion top is greater than the width of the pit. In this case, the interpenetration of protrusions is impossible.