Development On The Hydroforming Process Of Hollow Camshaft

Camshaft is one of the main structural parts in the engine,and its lightness has a positive impact on the energy saving and emission reduction of the engine.AISI 304 stainless steel is a kind of austenite stainless steel and has a lot of excellent properties,which is best suited to produce the hollow camshaft.In this paper,the 304 stainless steel tube was selected to produce the hollow shaft by the hydraulic forming process,and in order to guide the process design,the numerical simulation technology was employed to analyze the hydraulic forming process of tube.The microstructure and texture evolutions during the hydraulic forming process of tube were studied,and twinning mechanism during forming was also anlyzed.The specific research content is as follows:The internal fluid pressure required to cause yielding of tube was determined,based on it,the hydraulic forming process of hollow camshaft was simulated by the Dynaform software,and the optimal loading path was determined.The appropriate hydraulic forming process was determined by the numerical simulation on the hollow camshaft hydraulic forming and the experimental dies were designed.The hollow camshaft was produced by the optimal loading path got from the numeric simulation result.But the difference between the actually hydraulic forming process and the simulated results was caused by the complexity of hydraulic forming.The further optimization of hydraulic forming process was carried out on the basis of simulated results.The qualified camshaft was obtained and the dies were perfected.Microstructure evolution of AISI 304 stainless steel during before and after solid solution heat treatment was analyzed by the electron backscattering diffraction(EBSD)technique.Studied results reveal that,after the solid solution heat treatment of 1100?×30min,the texture type changed obviously.During the solid solution heat treatment process,grain boundaries migrated along the orientation available for grain growth,resulting in some grains grew up abnormally by merging adjacent small grains.The <111>60° twins existed in microstructures of the 304 stainless steel pipe before and after the solid solution heat treatment,and secondary twins formed within most grains after the solid solution heat treatment.The percentage of 60° angled grain boundary obviously increased due to the volume fraction of twin increased after the solid solution heat treatment.Microstructure evolution of AISI 304 stainless steel during the hydraulic forming was analyzed by EBSD technique.The micro-region X-ray diffraction(Micro-XRD)technique was applied to measure the volume fraction variation of martensite.The results have demonstrated that the transformation of strain-induced martensite from the austenite occurredin AISI 304 stainless steel tube during hydraulic forming,resulting in the ?'-martensite was formed,andthe volume fraction of ?'-martensite increased gradually with the effective strain increased.During the transformation of strain-induced martensite from the austenite,the volume fraction of martensite increased gradually with the increase of the strain,the austenite and ?'-martensite always maintained lattice coherency,and they followed the Kurdjumov–Sachs(K-S)relationship in terms of lattice coherency.During the hydraulic bulging process,original annealed twins in the austenite were de-twined,resulting in significantly reduction of twin volume fraction within austenite,and lots of deformation twins formed within newly formed martensite grains.