Burr formation in precision drilling of stainless steel.

摘要

The manufacturing of advanced precision components requires attention to both the generation of surfaces and dimensions with tight tolerances and to the subsequent deburring operations which must remove burrs while maintaining the required dimensions and tolerances. Studying the influence of component geometry, part feature interactions and process planning parameters on burr properties provides data which can be integrated into a knowledge base of burr minimization and burr control strategies useful for assessment of burr formation at the design and process planning stages of component production. Intersecting drilled holes occur in many precision applications, and provide an example of part feature interactions which result in non-planar drill exit surface geometries with unique burr properties.; This thesis focuses on exit burr formation in the precision drilling of stainless steel. To provide a structure for a knowledge base, a drilling burr classification scheme is developed from observations of burrs produced by drills less than one millimeter in diameter. By comparing scanning electron microscope observations of burrs in stainless steel, aluminum and brass, various burr shape categories and identifying features are differentiated and classified.; Replicated experiments were conducted to study the influence or feed, cutting speed, drill wear, drill material, and drill pecking cycles on burr height, thickness and geometry in stainless steel specimens with planar exit surface geometry. A database of burr sizes and shapes for forty cutting conditions was established. Burr size increased with high values of feed and with increases in cutting temperature which resulted from high cutting speed increased, hole depth, and insulating drill materials. Limited empirical relationships were established between burr size, feed and spindle speed for this application. The use of worn drills increased the variation in burr size and shape. The influence of exit surface curvature on burr properties was investigated by drilling on-axis and off-axis intersecting holes using a replicated fractional factorial experimental design. Increasing the workpiece exit angle and increasing the gradient of the exit angle in the direction of drill rotation were found decrease the burr size and influence the burr shape at each point around the hole.