Research On Single Seated Valve Stem Hot Forging Process

Single seated valve stem is a kind of valve parts used in the food machinery.Valve parts are required to have excellent corrosion resistance,oxidation resistance,high temperature resistant performance for their special work environment,316L austenitic stainless steel meets the requirements all of the above.But 316L austenitic stainless steel has some shortcomings in the aspect of applied in hot forging,such as high forming force,forming narrow temperature range,etc.Moreover,its high web,thin wall and lone pole shape characteristics would be the causes of high die stress,lower die wear life,insufficient filling and forgings folded problems.This paper formulated the hot extrusion blanking,the pre form and the finish forging as the mainly forging forming processes according to the shape and material characteristics of the forging.And it was found that there was one problem about positioning accuracy when positioning the forging blanks which would cause the results of forging insufficient filling and folding.To solve the problems above,this paper proposed the solve solution that setting one positioning slot structure on pre form die,the slot could also be called the“equivalent resistance wall”,but it caused a problem that die stress increased.To make the die stress and the die wear depth were all relatively low,the following important influence factors,blank initial temperature,height of the equivalent resistance and thickness of the burr were optimized based on response surface method,and the best parameter combination was obtained to ensure the quality of the forgings and the production efficiency.The three-dimension model of dies and blocks were established by using the computer aided design software UG.The thermal coupling of valve stem forging forming process was analyzed by DEFORM-3D finite element simulation software,the material flow rules of hot extrusion blanking process and pre form process,the variation rule of equivalent stress and strain of the material during the pre form process,pre form die wear depth distribution and three working procedure of mold stress prediction results were all obtained.By using four factors three levels orthogonal test plan,the deformation rate,mold initial hardness,initial billet temperature and mold temperature were considered to optimization of die wear life and die stress about hot extrusion blanking process.And The optimal process parameters combination was obtained through the way of extreme difference analysis.The result showed the optimal parameter combination:initial blank temperature 1150?,initial mold temperature 250?,attack speed 1.5 m/s,mold hardness 62 HRC,the corresponding simulated calculation of the maximum die stress and one time wear depth were respectively 611MPa and 5.6×10^-5mm,are all belongs to the ideally level.Finally,the new technology of the optimized parameters were tested by actual production.By comparison with overall dimensions of the stem forging products microstructure test,non-metallic inclusion test,hardness test,impact and tensile mechanical properties tests,the establishment process,optimal parameter combination and the reliability of the simulation results were verified.The research results of this paper have certain guiding significance and reference value to the actual production.