Research On Key Technology Of Die Forging For A Large Crankshaft With Counter-blow Hammer

The large crankshaft is a key part of the internal combustion engine that bears impact load and transmits power.It not only bears alternating stress for high-speed operation,but also transmits large torque.This requires the crankshaft to have good mechanical properties to ensure its normal operation during use.Large crankshaft forging is prone to problems such as poor forming quality,unsatisfactory filling,and low material utilization.According to the traditional experience design and the actual working conditions of the factory,the material utilization rate of similar crankshaft forging is about 65%to 75%.Therefore,this paper takes a large crankshaft as the research object,based on the finite element simulation analysis,establishes a 1MJ counter-blow hammer die forging finite element model,simulates the forming process of the large crankshaft,analyzes the forming performance and defects of the forging,and then optimizes the forming process.Determine a reasonable forming process plan,improve material utilization,and reduce manufacturing costs.In this paper,the high temperature thermodynamic behavior of 34Cr Ni Mo6 steel,which is the material for this large crankshafts,is first studied.The true stress and strain data of 34crnimo6 steel in the range of deformation temperature 900?200?and strain rate 0.001?1 s^-1 were obtained by isothermal hot compression test,and the influence of deformation conditions on the flow stress of 34Cr Ni Mo6 steel was analyzed.On this basis,a material constitutive model is constructed,and the modified Arrhenius model considering strain compensation can more accurately describe the high temperature flow stress behavior of 34Cr Ni Mo6 steel.Then based on experience,the 3D modeling software CATIA was used to design and model the large crankshaft forging and the final forging die,and the forging process of the large crankshaft was initially established.DEFORM software was used to carry out numerical simulation of the initial process scheme.According to the simulation results,it was found that the material utilization rate was low,only 66.2%.Then,in view of the low material utilization rate and high manufacturing cost of the initial process plan,the innovative design was carried out from three aspects:the positioning of the blank,the flashing structure of the shaft ends on both sides of the die,and the addition of local resistance walls.Firstly,aiming at the positioning problem of billet,considering the complex positioning situation of large crankshaft forging,a positioning device of billet for large crankshaft forging is designed and developed to ensure that the billet can be placed in the correct position,and applied for an invention patent.Secondly,to solve the problem of excessive metal overflow at the shaft ends of both sides of the die,the fly-edge structure at the shaft ends of both sides of the die was optimized,and the volume of the fly-edge structure was increased to accommodate more excess metal flowing out during forging without affecting the pressure load.Thirdly,in view of the problem that some crank positions of crankshaft forgings are not full,a local resistance wall structure is set up to increase the filling ability of metal in the direction of height and ensure the complete filling.Then,established the finite element simulation model after solving the problem of blank positioning and mold optimization,using one-time forging to form,the billet size is reduced from?240×2650mm to?220×2610mm.According to the simulation results,it is found that the forging has good formability and complete filling.The material utilization rate of the optimized process increased from 66.2%to 78.2%,and the blank weight was saved 144.3kg.The forging process was reduced from the original"heating-pre-forging-burr cutting-heating-final forging"to"heating-final forging",which reduces the number of fires and the total number of hammer strokes,increases the efficiency,and saves a lot of manpower,material resources and financial resources.Finally,based on the optimized process scheme,the production verification was carried out.The result of trial production shows that the forging has good forming effect,and all aspects of the indicators have reached the design requirements.