Investigation On Surface Integrity Of Nodular Cast Iron QT700-2 In Shape Adaptive Grinding

As one of the commonly used materials for automobile engine crankshaft parts,QT700-2 nodular cast iron has good casting process as well as excellent strength and toughness.For the traditional grinding process of crankshaft grinding wheel,the rigid contact between hard grinding wheel and crankshaft will lead to surface and subsurface damage such as grinding burns and grinding cracks on the grinding surface,and the grinding surface quality is poor.Shape adaptive grinding(SAG)is a flexible grinding process emerged in recent years,which is mainly suitable for complex surfaces with multi-curvature.This process can precisely process hard and brittle materials to obtain nano-scale surface roughness.SAG process not only has the advantages of good machining quality and high precision of flexible grinding technology,but also has high machining efficiency,so it has great development potential and application prospect.The application of SAG machining technology to crankshaft machining has the advantage of high machining efficiency and good machining quality.however,the surface integrity of crankshaft after grinding has not been systematically studied.Based on the design of SAG experimental device,the grinding experiment of QT700-2 nodular cast iron was carried out,and the SAG machinability of QT700-2nodular cast iron was studied.The effects of process parameters on grinding force and material removal rate were analyzed.It is found that grain size is the most important factor affecting grinding force and material removal rate.The effects of process parameters on the surface roughness,work hardening and microstructure of QT700-2nodular cast iron processed by SAG were studied.The results show that the grain size is the main factor affecting the surface roughness.In the range of current grinding process parameters,the grinding force(up to 33N)and grinding temperature(up to33.7 ℃)of SAG tools are very low,which basically does not cause work hardening and work softening on the workpiece surface,and the machining influence layer is very small.The grinding depth of SAG tool is very low,and it will not produce tissue fibrosis deformation caused by shear tension.In addition,the grain wear mechanism of SAG tool is also studied,and it is found that the main forms of grain wear are shedding in the initial stage and grain wear in the later stage.Finally,the curcved surface SAG experiment is carried out based on the summarized optimal process parameters,and the average surface roughness of Ra64 nm is obtained,which fully meets the grinding requirements of the crankshaft.Through the above research,it is found that among the SAG process parameters of QT700-2 nodular cast iron,the grain size has the most significant effect on grinding force,material removal rate and surface roughness.The machining influence layer of SAG tools is very small.During grinding,mainly remove the surface defects of the workpiece and improve the surface quality of the workpiece.In this thesis,the influence of process parameters on the SAG surface integrity of QT700-2 nodular cast iron is studied and clarified,and the optimal process parameters of QT700-2 nodular cast iron SAG are summarized and verified by experiments on curved surface workpieces,which provides a theoretical reference for the practical application of SAG machining of QT700-2 nodular cast iron.