A Study of a Strategy for Threading Titanium Alloy

Abstract

The cutting of precision threads is an important manufacturing process. Several passes are needed to complete the cutting of a thread and the choice of appropriate cutting speed and depth of cut for each cutting pass is essential. The cutting efficiency and tool life are significantly affected by these two parameters, especially when cutting threads in difficult-to-cut materials, such as titanium alloy. This paper proposes the concept of an equal undeformed chip area for all cutting passes, in order to determine the depth of cut for each pass. The principal goal is to maintain the same cutting force throughout the cutting process. Using tool geometry, the relationship between the cumulative depth of cut and the undeformed chip area for each cutting pass are derived. The depth of cut of each corresponding cutting pass can be determined, once the dimensions of the thread and the number of cutting passes are specified. Experiments were conducted to cut an ISO metric screw thread, with a pitch of 0.5 mm, on a 40 mm in diameter bar. It was found that, for the same total number of cutting passes, the tool wear was less than that suggested by the tool makers, when a depth of cut for each pass was determined using the proposed method. The thread could be cut using a higher cutting speed, resulting in a much shorter machining time. In addition, the proposed strategy also allowed completion of cutting using less cutting passes. A 25% increase in efficiency was noted for the specific thread used in the experiment.