| Titanium alloy rod has many advantages such as high specific strength and good biocompatibility,etc.So it is widely applied in many fields of national economy.For example,aerospace fasteners,titanium alloy springs with smaller weight,non-toxic mariculture cages,and body implants as well as medical device and so on.However,this kind of metal has a high value and high loss rate.In order to make titanium alloy be a popular metal,it is very necessary to optimize the production technology and decrease the metal consumption.This paper studies titanium alloy rods are deformed by three-roll pass system during the continuous rolling process.Compared to the traditional two-roll pass,the procedures of repeated heating and repeated annealing have been canceled.Therefore,this method could improve rolling yield and reduce metal loss.This subject is originated from natural science program of Shanxi province.Based on the traditional “triangle-round” pass system,a kind of pass system called as “multi-line triangle-round” is established.The “multi-line” pass is made of arc segment and straight-line segment,and used with round pass alternately during the rolling process.This pass system could improve remarkably the ear defect of rolled piece and increase the roundness of final product.The capability of centralization and the rolling stability are better.Meanwhile,the temperature gradient along cross section of rod would be slightly decreased.So the cracking probability of the final product would be reduced to a certain degree.The main contents are as follows:(1)The mechanical parameters are a base for designing and optimizing the mill structure.By comparing the applicability of various calculation methods,the upper bound method has been used to calculate and derive the mechanical parameter during the continuous rolling process of TC4 alloy in this paper.And rolling force and energy distributions of the workpiece with two kinds of pass system have been compared and analyzed.The results show that the calculated value is slightly larger from the optimized pass system than that from the before,but the difference is small, and no stress concentration happens in rollingprocess.(2)The continuous rolling process of TC4 alloy rod on six three-roll mills has been simulated by finite element method,the change of cross-section and mechanical parameters have been analyzed emphatically.The experiments have also been done on the three-roll mills.The mechanical parameters have been obtained through measuring the current change.In order to check the effectiveness of theoretical model and finite element simulation,the theoretical value and simulated value are compared with measured value.The results show that there is small difference,and the maximum difference is less than 14.4%.(3)In order to improve the product quality of rod,how to reduce the residual stress of rolled rod is studied in this paper.Some parameters influencing the residual stress,including pass shape,initial temperature,roller diameter and friction factor,have been analyzed by finite element simulation technology.The residual stress distribution have also been analyzed at different cooling rate such as forced water cooling,natural water cooling,forced air cooling and natural air cooling.Finally,the best rolling process parameters and the cooling system are determined to meet the minimum residual stress of TC4 rolled rod.(4)By combination of CA cellular automata and recrystallization model in Deform software,the dislocation density and microstructure have been simulated and analyzed during the continuous rolling process of rod in this paper.The results show that dislocation density from the second rolling pass is highest,while the crystal transition is found in the third rolling pass.Therefore,the deformation of this two rolling passes would have main effect on microscopic residual stress of rod. |
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