Hot Finish Rolling of Injection-Molded Plastic Helical Gears. Properties of Finished Tooth Form.

Abstract

Hot finish rolling has been developed as a simple finishing method for injection-molded plastic gears. In the present paper, properties of the hot-finish-rolled tooth form are discussed so as to obtain general information for improving the quality of the injection-molded plastic helical gears. The plastic helical gear generally has a positive pressure angle error on the tooth profile and a helix angle error on the tooth trace. After the hot finish rolling process, the finished gear has a negative pressure angle error on the driven tooth flank and a positive pressure angle error on the followed tooth flank. Sliding of tooth flanks along the profile contributes to inducing these errors. Hence, hot finish rolling including the process of reversing the rotation of gears is very useful for improving the quality of the tooth profiles of plastic gears. However, the hot finish rolling process exhibits no sliding along the face width, and thus it cannot improve the quality of a tooth trace which has a helix angle error. It can be expected that sliding along the face width will be useful for improving this error. For example, the axial feed of the work gear might induce such sliding.