Machining characteristics of 18Ni-300 steel in additive/subtractive hybrid manufacturing

Additive manufacturing (AM) possesses capability of building complicated parts that are otherwise difficult to manufacture by the conventional methods. However, the dimensional and geometric accuracies as well as surface quality of an AM-produced part are inferior to the conventionally machined part, which hinders the AM applications. Thus, an additive/subtractive hybrid manufacturing (ASHM) method is developed to take advantage of both the AM and precision subtractive manufacture (SM). However, the microstructures of the AMed parts are different from those of the conventional metallic parts. In addition, the residual stress induced by the AM stages influences the machined residual stress reconstruction in the subtractive stages. In order to investigate the effect of microstructure and the AM-induced residual stress on the machining characteristics, a milling experiment is conducted on AMed and wrought samples. The results of the cutting force, machined residual stress, and surface roughness are compared. It is found that the machining characteristics of AMed samples are different from those of wrought samples due to different microstructures and residual stress evolutions. The paper provides a guidance to the optimization of the processing parameters in the ASHM.