Study on milling technology of Waspaloy superalloy internal threads with a small diameter

Small-diameter thread is widely used in the connection of aeroengine, nuclear equipment, and petrochemical equipment parts due to its advantages of high connection strength, simple structure, and convenient loading and unloading. Manual tapping is its main production method. But, the stability of product quality is poor; the qualified rate of one-time machining is less than 20%, resulting in a large number of repeated machining and scrap. The existing thread milling method is difficult to adapt to the small-diameter internal thread processing of Waspaloy high-temperature alloy. The deformation of the tool during the processing and the difficulty in heat dissipation from the unreasonable processing technology are the main reasons for the processing accuracy not meeting the standard. In this paper, a 3-D numerical simulation model of small-diameter internal thread milling is established based on the flow stress control theory. The influence of structure parameters and milling machining parameters on milling force and milling temperature is studied by orthogonal experiment, and the range analysis is carried out. The mathematical model of milling force and temperature is calculated by nonlinear regression analysis. Based on Pareto genetic algorithm, multiple objective optimization method, the cutter structure, and machining parameters are optimized. The better machining parameters and cutting cutter parameters are obtained; the deformation of thread milling cutter in X, Y, and Z direction is obtained, and a new structure of thread milling cutter is designed; the feasibility of the new type of thread milling cutter and the machining scheme is verified by the trial cutting experiment of the thread milling cutter.