A Study On The Workpiece Deformation And Hardening Layer Depth Uniformity Of Single-pass Plane Grinding Hardening

Grinding-hardening is a new type of composite processing technology. With the grinding heat from the coarse grinding, grinding-hardening can make the surface temperature increase to the austenitizing temperature rapidly, and then cool it to the martensitic phase. The surface material of workpiece will change to martensitic phase transformation to achieve the surface hardening treatment of the workpiece. Surface hardening technology implements the integration between grinding and surface uenching, which has very good prospects in manufacture area. This paper is based on the grinding theory research, combined with grinding hardening thermal coupling numerical analysis and experiment, which makes a research about the workpiece deform and the depth distribution after grinding, and put forward to control the depth uniformity of grinding by variable grinding depth method. The primary contents are as follows:(1) Grinding temperature numerical analysis with loading variable heat flux densityThe grinding force in grinding process is variable. According to the dynamic variation curve of grinding force in the experiment, it can get the heat flow density function, which is loaded in grinding temperature numerical analysis. The analysis includes the material coefficient of thermal physical properties, latent heat of phase change and heat convection in the environment. The variable heat flux and constant heat flow density under the load of simulation of grinding temperature field are simulated. It changes significantly in the variable heat flux density environment. Considering phase change latent heat temperature was lower than that not considering one, and the external influence for the convective heat transfer conditions is small. According to the simulation of temperature field under the load of variable heat flow density, it can predict the distribution of grinding hardening layer depth. The trend of hardening depth distribution is similar with experimental measuring results.(2) Grinding hardening thermal coupling numerical analysisThe article is established the model of thermodynamic coupling finite element numerical analysis. The first stage of coupled thermo-mechanical analysis is grinding temperature field simulation, and the second one is to convert finite element thermal analysis to structural analysis, applying structural boundary conditions, taking the grinding temperature as a node, taking the grinding force as grinding arc pressure load, make the analysis of the workpiece under thermodynamic activity. The analysis chooses three kinds of workpiece with different height. The deformations of different time are obtained by numerical analysis. The deformation makes the workpiece convex, so the actual grinding depth is the sum of the set grinding depth and convex cutting depth. The article also analyzes the internal stress and strain, and the location of the reaction forces of constraints. The machining surface of workpiece is given priority to with plastic deformation under that it is elastic deformation. Farther away from the workpiece surface, the deformation is smaller and smaller. According to the comparison about three workpieces, and compare the deformation under the grinding force or not, the deformation of the thinnest one is most serious, and constraint reaction force is the largest. Through the experiment of different size grinding hardening, the correlation analysis is verified by the experiments. The thinnest workpiece has the most nonstesdy grinding force、the most serious deformation and the most uneven hardening layer.(3) The dynamic analysis and prediction of grinding hardening forceThe dynamic change of grinding force curve measured by experiments is analyzed. The cut in and out area of grinding changed drastically that caused by a surge or plummeting of the increased material removal. Grinding forces of the stable region also changed dynamically, which is affected by both the grinding deformation and the temperature in arc length of contact. Combining with the plane grinding force calculation model, the influence of the grinding contact arc temperature and grinding deformation on the grinding force are analyzed. Grinding deformations can increase the grinding force, but the grinding contact arc temperature reduced the increase of the grinding force. High temperatures of the grinding arc didn’t cause sharply decrease of the grinding force, which is due to low temperatures and large chip thickness of the material in front of the grinding contact arc area. In conclusion, calculation model of the grinding force through grinding contact arc temperature’s influences on the grinding force is revised. The tendency of the grinding force is predicted by calculation models of the grinding force and grinding deformation analysis.(4) Grinding hardening layer uniformity controlWorkpiece deformation increases grinding cutting depth. Through the actual cutting depth revised variable heat flux, the revised heat flux density is matched with the grinding hardening layer depth distribution and experimental measurements. Through the contrast the measured grinding force curve、the simulation of grinding temperature change curve and the simulation workpiece deformation, the influence of the grinding force、grinding temperature, and workpiece deformation is got, which leads to the uneven distribution of grinding hardening layer depth.The article puts forward measures to improve the grinding depth distribution and the key is to control grinding deformation. Another way is through variable grinding depth to control the grinding force so as to control the uniformity of grinding hardening depth. Detailed method is divided the grinding process into interval to be analyzed, taking the grinding hardening depth on each interval as known parameter and cutting deeply as unknown one. Through thermodynamic coupling finite element analysis, the balance of the force、temperature and deformation is established. Then general grinding cutting depth contour curve in the interval is obtained. Finally through the variable grinding depth experiment, the contour analysis result is verified. The surface of the workpiece contour precision and the depth of hardening layer uniformity after processing are all improved.