Research On The Chip Formation Mechanism And Surface Roughness In High-speed Milling Of Nickel-based Superalloy

Nickel-based superalloy is widely used as the key hot-end components in the manufacturing field of aerospace engines as well as gas turbine, as it has excellent material mechanical property. With the rapid development of major equipment manufacturing industry such as aerospace, shipping, energy, etc., the demand of nickel-based superalloy parts is increasing, and requirement of machining surface quality is enhanced as well. However, the processing requirement of the parts about good surface quality as well as high processing efficiency could not be satisfied during the conventional machining of nickel-based superalloy, which severely restricts its wide application. High-speed machining considered as an advanced machining technology, with the significant advantages of small cutting forces, high material removal rate, high machining precision, good surface quality of the parts, has been proved an effective method in the nickel-based superalloy processing field with higher processing efficiency and better surface quality. Nevertheless, the research on the machining mechanism and process technology in high-speed milling of nickel-based superalloy remains insufficient and has turn into a critical issue in the field of nickel-based superalloy parts manufacturing.In this paper, the formation of chip morphology including serrated chip and chip burrs as well as their evolution discipline are analyzed under different cutting speeds aiming at nickel-based superalloy by combining theoretical analysis and experimental validation. Also, the effects of the variation of chip morphology on both cutting forces and surface roughness are investigated. In addition, a series of test are conducted to explore the influence principle of different factors on surface roughness. After that, a prediction model of surface roughness is established and the cutting parameters are optimized, which facilitate the exploration of processing nickel-based superalloy with high surface quality and efficiency. It will be of great significance in engineering regarding the improvement of the production efficiency and surface quality of the hot-end components. The main research contents of this paper are as follows:First of all, high-speed milling tests are carried out to study the chip morphology of nickel-based superalloy and discuss the critical condition of adiabatic shear instability on this type of material. The formation process of serrated chip is analyzed and variation principles of both serrated chip on chip free surface and scratch characteristics on chip bottom surface as cutting speed changes are investigated. Also, this paper puts forward the formation of chip burrs and its features, whose variation principles are analyzed under different cutting speeds as well as its implication on cutting forces is studied.Second, based on the material property of nickel-based superalloy, theoretical analysis of the formation principle of machined surface roughness is presented, and the theoretical calculation expression of surface roughness Ra is established. Then, surface topography at various points of machined surface is investigated, which is the corner-stone of the surface roughness evaluation in this paper. Besides, the effect of the variation of chip burrs morphology on surface roughness is explored, which could provide the reference for chip shape controlling and the development of surface quality. Processing tests are conducted to investigate the influence principles of different cutting parameters as well as cooling conditions on surface roughness.Finally, according to the response surface methodology, the prediction model of surface roughness during high-speed milling nickel-based superalloy is established. Both the significance test and fitting degree test are conducted on this model and the accuracy of the prediction model is verified as well. The influence principles of the interaction of three cutting parameters including cutting speed, feed per tooth and axial depth of cut on surface roughness are analyzed. Aiming at the material removal rate and surface roughness, the cutting parameters are optimized, which has significant value for the practical processing and production.