The Numerical Simulation Of Hot Forging And Die Structure Optimization For Engine Connecting Rod

As one of the high-duty parts of the automotive engine, connecting rod plays a role to transfer the reciprocating linear motion of piston to the rotational motion of crankshaft.Connecting rod is produced by drop forging generally, where the high mechanical properties and surface quality, narrow dimension tolerance and weight error of the forgings are demanded. It can not only improve the productivity but also reduce production costs to process engine connecting rods by two-cavity forging die. However, the complex layout of the die cavity will lead to the emerging of forging deflects such as folding and sunk angle.The hot forged connecting rod proposed in this paper is made of non-quenched and tempered steel SVDH20S1. Billet of the connecting rod is drop forged directly after induction heating, without the pre forming by rolling and the subsequent heat treatment after forging. However, when manufacturing the connecting rod by two-cavity forging die,the main issue is to control the forming load and forgings’ quality, as well as the tool wear in forging. To fix that problem, the common method is to analyze the hot forging process and to optimize the tool of connecting rods via numerical simulation.The three hot forging processes of connecting rod was analyzed based on finite element simulation. Firstly, the two-cavity forging dies of connecting rod were designed and three design parameters were proposed including of the center distance between cavities, the cavity rotation angle and the center groove depth. Secondly, the orthogonal experiment project with 3 factors and 2 levels was estimated and the simulations were completed by using DEFORM 3D software, the results showing that: the forming load,folding tendency and tool wear depth in the first pre forging process were in the highest level among the three processes; The center distance between cavities and the cavity rotation angle are main factors to impact the forming load and the forging deflects; The center groove depth is main factor to impact the tool wear in final forging.The design parameters of pre forging die for connecting rod were optimized by usingresponse surface method. The center composite design method was used to design the experiment project, with the three factors: the center distance between cavities, the cavity rotation angle and the flash thickness, and the two responses: the maximum of forming load and tool wear depth in the first pre forging. With the numerical simulations executed and the simple set estimated, response surface models were obtained by fitting. The ANOVA showed that both the two prediction models have accuracy above 93%. Based on the prediction models, the optimal combines of factors were obtained by using a nonlinear algorithm to minimize the two responses thought several iterations. The forging dies and blank of connecting rod were redesigned in according to the optimization results to carry out finite element simulation, the results showing that the forming load and tool wear depth decreased significantly, and the forgings without internal and external deflects, which provided a reference to the tool design and hot forging process of connecting rods.For forging dies of the connecting rod, the manufacturing processes were analyzed and the multi-axis NC milling processes were programmed via UG software. Finally, the forging production line of connecting rod was demonstrated and the practical forging processes were performed with the forging tools milled by CNC programming, obtaining the connecting rod forgings with granted quality.