Analysis On Straightening Crack And Process Improvement For Internal Input Shaft In Dual-Clutch Automotive Transmission

Gear shaft is one of the main critical components for transmitting torque and speed in automotive transmission,which will inevitably have radial deformation after heat treatment and need straightening to ensure the straightness requirements.During straightening process,crack often occur with leading to the scrapping of components,which not only cause to the cost of waste,but also if crack is not effectively identified and mistakenly installed into the transmission,crack will grow and finally break,it is a very dangerous failure mode.Therefore,how to reduce straightening scrap rate is currently a commonly faced problem for all transmission manufacturers,while the gear shaft of dual-clutch transmission usually has higher straightening crack rate due to its hollow design compared with traditional solid gear shaft.This thesis aiming at the situation of high straightening crack rate for input shaft in one dualclutch automotive transmission.Based on existing achievement in theories and method of gear shaft straightening,with considering the actual situation of pressure straightening by fullautomatic straightening machine,and analyzing the mechanism and position of crack generation by research on machining process and machine,has formed a set of process optimization scheme and finally achieved a dramatic effect of reducing the straightening crack rate.The main research contents and conclusions of this thesis are summarized as follows:Chapter two conducted a relatively comprehensive explanation for basic process theories of pressure straightening,analyzed the crucial and difficult points in current straightening research process based on the basic principle of elastic-plastic deformation reflected from gear shaft straightening process,simultaneously explicated the reasons for hollowed gear shaft being more easily to generate cracks compared with solid gear shaft.Chapter three based on the analysis of working process,detecting system and crack discrimination etc.of automatic straightening machine,on account of the small-step progressive method that commonly used in gear shaft straightening process,it has presented the influences of progressive increments on straightening cracks,with which excessively large increments would cause excessively instant stress that cause to cracks,however excessively small increments can also cause cracks due to work hardening and residual stress overlying,this thesis has optimized the progressive increments and performed effective verification.Chapter four based on the influence of the heat treatment process on material properties of the parts,to reduce the core hardness of the parts as much as possible within allowable range by optimizing the gas quenching process,which not only reduces the yield strength,but also effectively reduces the yield-tensile ratio of the parts,expands the plastic deformation space,thereby reducing the probability of generating straightening cracks.Chapter five through establishing finite element simulation model during the pressure straightening process,it has effectively simulated the stress intensity situation of each location,which provides an effective basis for selecting best pressure point position.This thesis with regards to research on reduce the straightening cracks ratio of gear shaft has a strong effectiveness,which can provide reference for reducing straightening crack rate in current gear shaft straightening.