Numerical Simulation And Experimental Study On Precision Forming Of Complicated Branch-Like Steering Knuckle

Steering knuckle is the key part of vehicle steering system, so the requirements of its mechanical properties and surface qualities are very strict. The current production technologies of branch-like steering knuckle are obsolete, which become the restriction of increasing productivity and improving the quality. It becomes urgent technical matters for automotive industry to produce the parts efficiently and economically.In this dissertation, with the guidelines of precision forming complex forging pieces, basing on the forming theory of closed die extrusion, choosing the Jetta steering knuckle to be investigated, analyzing its forming characteristics deeply, the closed die extrusion technology is proposed to form steering knuckle forging piece firstly.To verify the feasibility of closed die extrusion technology forming branch-like steering knuckle forging piece, experimental researches are carried on the forming process of Jetta steering knuckle, forming technology has been drawn up, and dies have been designed. Precise and qualified 1:2 lead and 40Cr specimens have been obtained. With the metallurgical analysis of 40Cr forging pieces, it is presented that the crystal grain has been refined and the mechanical property can be improved with the technology. The mechanism and influencing factors of shrinkage cavity defect are analyzed on this basis.Based on experimental researches and numerical analysis, the technology of two forging steps in one heat is presented, which consist of closed die extrusion preforging and open die finish forging, whose critical step is preforging process. By utilizing DEFORMTM software, the stress, strain, velocity and temperature fields during forming process are obtained, and then the plastic forming law of branch-like forging pieces in closed die extrusion has been studied. Simulation results show that with the technology of two forging steps in one heat, the metal flow can be improved evidently, the nominal pressure of forging press equipments can be reduced, and die life can be prolonged.To further reduce the shaping force of preforging and increase the service life of dies and punches, closed die extrusion with extrusion-belt is introduced to the technology of two forging steps in one heat. By the thermo-mechanical coupling simulation, the influence of main technological parameters to metal flow, extrusion force and opening force are studied and determined, such as extrusion-belt length, friction conditions, die work temperature and punch extrusion speed, then the mechanism of closed die extrusion with extrusion-belt is acquired, which are very important to the actual application of the technology.By using upper bound method, the extrusion force formula is deduced, which is appropriate for closed die extrusion with extrusion-belt forming complicated forging pieces with space angle branches. By using the formula, the extrusion forces in closed die extrusion forming Jetta steering knuckle are calculated. The calculation results agreed with simulation results, which indicate that the formula has high calculation accuracy.By using numerical simulation, it is approved that the technology of two forging steps in one heat is feasible, whose core is closed die extrusion with extrusion belt. The new technology enlarges the applying range of closed die extrusion, greatly simplifies the production technology of complicated branch-like forging pieces, reduces the production cost, and provides effective method for the precision forming of the complicated branch-like forging parts.