Computer‐Aided Geometrical Analysis of the Fluting Operation for Twist Drill Design and Production. II. Backward Analysis, Wheel Profile, and Simulation Studies

Abstract

A computer‐aided ‘backward’ analysis based on the contact curve method has been developed to determine the required grinding wheel profile for generating a given drill flute profile design and fluting machine settings. The required grinding wheel profile was expressed in digitised form as well as in terms of two curve‐fitted circular arcs whose radii and centre coordinates represented the required wheel dresser settings on the typical flute grinder modelled. The ‘backward’ analysis was integrated with the ‘forward’ analysis from the first paper to form a CAD/CAM package with graphics modules. Simulation studies have shown that only a portion of the required digitised wheel profile was physically feasible so that only the portion of the flute profile generated by an enveloping process precisely matched the design flute profile while the flute profile in the web region, generated by the locus of point of discontinuity on the wheel profile, approximated the design flute profile. Furthermore, the typical drill flute design geometry can never be precisely generated by this flute grinding method. When the required wheel profile is represented by two circular arcs the entire generated flute profile is an approximation of the design flute profile, albeit a very good approximation. It has also been shown that wheel setting angle greater than the drill helix angle has to be used to avoid undercutting the heel and lip corners when the required wheel profile is represented by two circular arcs, unlike for the digitised wheel profile when the wheel setting angle can be equal to the helix angle. The use of the CAD/CAM package to determine six wheel dresser settings and machine settings for drill flute production has been illustrated.