Mechanistic model for tapping process with emphasis on process faults and hole geometry

A mechanistic approach for modeling the tapping process is presented. A methodology for computing chip load is developed for an arbitrary tap geometry. The mechanics of cutting for tapping is analyzed, considering it as an oblique cutting phenomenon. The effects of tap geometry (tap diameter, thread pitch, number of flutes, flute helix angle, tooth rake angle, and thread type), workpiece geometry (hole diameter and hole depth), process parameters (spindle speed and tap penetration depth), and process faults (tap runout, axis misalignment, and drilled hole geometry) are incorporated in the model. The model is calibrated using drilling experiments and is validated by comparing experimental tapping results for aluminum 319, aluminum 356, and gray cast iron. In most cases, the tapping forces were predicted within 10 percent of the experimental values.