Study On The Extrusion Process And Extrusion Die Life For Knuckle Of Heavy Truck Compound Process

This topic is originated from the Dajiang Xinda Vehicle Stock Limited Company which project is studying on the extrusion process and extrusion die life for knuckle of heavy truck compound process.In this paper, with fully taking into account the objective requirements of actual production, based on the intensive study for the characteristics of extrusion deformation, the new forming method, i.e. combined extrusion and forging processes for knuckle of heavy truck is put into practice and tracked. It found that the instability of forming quality and the lower service life of extrusion die are the major problems to restrain the widely application for the new compound process. This paper carried out the following three research points based on the up two issues:â‘ Hot extrusion process study on knuckle of heavy truckFirstly, the traditional extrusion process about typical knuckle of heavy truck is studied. The reasons about fold and underfill in the process were analyzed. According the results of analysis, added the upset process with a fillet before extrusion to the original process, which could prevent the offset and the defects effectively. Then the heights of the billet in the upset process and the radius size of fillets are optimized,"Table about different upset heights of billet versus qualities of extruding part"and"Curve about radius of fillets versus extrusion ratio"are given. It significantly improve the manufacturability of steering knuckle with vertical extrusion process.For further study, different processes about knuckle hot extrusion are comparative analyzed by FEM simulation, which focus on filling capacity, deformation uniformity and flow lines distribution. The results show that the process of upsetting-extrusion and press has the best integrated process performance.At last, the precision perform process of upsetting-extrusion and press is introduced to the deformation of Hummer and Steyr knuckles, which obtained satisfactory results. It proves that the new program has a superior process performance and the wide range of replicability.â‘¡Analyze and control of the knuckle hot-extrusion systemIn this part, we pay more attention to the characteristics of matter and energy in the knuckle hot-extrusion system other than the extrusion process,which focus on the influences of system components such as billet,equipment, die and process parameters upon the stability and durability of the system. First of all, in accordance with the idea of"System Engineering", a new concept called "Knuckle hot-extrusion system" is put forward and the characteristics of it and its subsystems are analyzed and summarized. Then the Ishikawa diagram which comes from the method about"Total Quality Management"is proposed to study the defects of the system and find out the root causes finally. According to the statistical data of actual production, the sequences about root causes are lined up based on the frequency and extent of damage. It draws a conclusion that in order to improve the stability and durability of the system, we must study on the system by the force and heat. The effects of various forming velocities,initial temperature of billets, friction coefficient and the initial hardness of die on knuckle hot extrusion system about pressure(maximum extruding force and maximum principal stress) and temperature(maximum part temperature and maximum die surface layer temperature) are studied by FEM simulation. The curves about process parameters are obtained by least square method. Finally, based on the findings, the engineering guide specifications about process parameters are proposed which are suitable for knuckle hot-extrusion system.â‘¢Study on structure of knuckle hot extrusion die and parameters optimizationBased on analyzing the failure modes, locations and mechanisms which commonly appear in knuckle hot extrusion dies, a new flash structure which is named resistance wall is introduced, expecting to improve the severe service conditions and balance the needs between the better filling capacity and longer die life. Focus on filling capacity, the maximum deformation load and the highest die surface-layer temperature, different die structures, such as open-flash cave structure, traditional close die structure and resistance wall structure, are comparatively analyzed by FEM simulation. Then identify the essence of the new structure and draw a conclusion that it has the best comprehensive performance. After that, the fractional factorial experimental design method is used to evaluate main effects of the structure parameters on filling capacity, the maximum deformation load and the maximum wear in bar fillet area. A rank-order table about main parameters effects is obtained. In order to fulfill potential of resistance wall in filling capacity and extend die life, it's very important to find the optimal combination of structural parameters. The multi-objective optimization is studied using combinatorial optimization strategy which is radial basis function approximation model methods (RBF) combined with genetic algorithm (GA). Latin hypercube sampling design is applied to select the appropriate design parameters for the FEM experiments. The RBF meta-models are obtained after comprehensive comparing the fitting accuracy of five different kernel functions. Then the GA is introduced into meta-models to carry out multi-objective optimization. The weighting coefficients of the objective functions are determined according to engineering practice. The optimal parameter values of resistance wall are got by weighting function optimization. Finally, the conclusion of the study applied to five sets of knuckle hot extrusion dies of Dajiang Company. Statistics find that the average service life of the five sets of dies is 5187, which is 2.66 times of the life of original close-die and 1.48 times of the life of die with unoptimized resistance wall structure...