A STUDY OF THE EFFECT OF PROCESS PARAMETERS ON SURFACE FINISH OF DRILLED HOLES

摘要

A study has been made of the effect of process parameters on the surface finish of drilled holes. Drills made of high-speed steel (HSS), tungsten carbide (WC), TiN-coated HSS, silicon nitride and aluminum oxide were used to drill holes in cast iron, 1018 steel and 6061 aluminum. The effect of chip morphology on finish was studied by controlled chip breakage achieved through the application of a controlled, superimposed modulation in the direction of drill feed. It has been found that drill material has the most important influence on surface finish with ceramic drills consistently giving the smoothest finish. Furthermore, the surface finish in the middle portion of a hole was consistently worse than at the top and at the bottom. The application of a lubricant mist during drilling has been found to slightly improve the finish while chip breakage had a small but varying influence. The application of a superimposed modulation which resulted in consistent chip breakage was, however, found to reduce the height of the burr at the exit of a hole. The observations suggest that rubbing of the drill against the hole surface may be the primary determinant of hole finish. The accuracy of a replica to assess surface finish of a hole has also been established.