Study And Application Of Evaluating Method For Friction By Stable Combined Forward And Backward Extrusion

Cold forging is a common method of plastic forming.The friction of cold forging has great influence to the forming process and forming quality.Therefore,it is very significant to choose an accurate method to evaluate the friction in cold forging.Traditional friction evaluating methods have some disadvantages on friction sensitivity,the reflection degree of real forming condition,the stability of method or the distinction of different friction range.The friction evaluating method by stable combined forward and backward extrusion(SCFBE)was proposed in this paper.The extrusion force and surface expansion of this method is relatively large,so it can evaluate complex deformation in cold forging.The key parameters were optimized to improve the sensitivity of this method to friction by orthogonal method using FEM simulation.After the steady analysis,an improved scheme based on the optimal scheme was obtained as the final design of the steady combined forward and backward extrusion process test.From the simulation results,two groups of calibration curves were constructed for a different range of friction factors.Experimental work was carried out to validate the steady combined forward and backward extrusion test,the test procedure was introduced and the friction factors of five different lubricants and dry friction in the cold extrusion of steel were determined.The friction factors of respective lubricants were Pho S:0.15,PTFE:0.13,Mo S2:0.18,low viscosity oil:0.08,high viscosity oil:0.06 and dry friction:0.3.Results from the conventional ring compression test method were used in the comparative analysis.The steady combined forward and backward extrusion process can be used to measure friction factors at the interface between the billet and tooling in complex cold forging accurately.The SCFBE method was used in the processing evaluation of conjunction gear to improve the coating time of lubricant and production efficiency.By modifing the geometrical dimensions of workpiece and model parameters,the extrusion process of conjunction gear was optimized to reduce the extrusion force and improve die life.Meanwhile,the filling degree and utilization of material also keep high.The SCFBE method was also used to improve the coating method of lubricant.The combined shot blasting and lubricant coating method was proposed.In the new method,the process of zinc-phosphate coating could be omitted.Lubricant can be easily adhered on the surface of workpiece under the process of shot blasting,and then the lubricating effect can be improved.Compared with the two methods,the application of shot blasting method is better.