| With the rapid development of society,people have put forward higher requirements in terms of safety,aesthetics,energy saving and environmental protection of railway vehicles.In this case,aluminum alloy has received more and more attention as a new lightweight structural material.Aluminum alloy has the advantages of low density,high specific strength,and strong corrosion resistance,it has been widely used in automobiles and railway vehicles.However,the shortcomings,such as poor plasticity and large springback at room temperature,increase the difficulty of forming.Hot stamping technology can significantly improve the plasticity of aluminum alloy and reduce the springback of the formed parts by heating to high temperature before forming,which greatly promotes the application of aluminum alloy.In this paper,a skin of high-speed EMU is taken as the research object,the finite element technology is used to predict the defects that may occur during the forming process.The effects of various process parameters on the quality of the skin forming are analyzed and researched,which provides theoretical guidance for actual production.The main research contents and conclusions are as follows:(1)The cold stamping process of the skin was numerically simulated using Pamstamp finite element software,and the influence of the binder shape on the forming quality of the skin and the effect of the blank holder force on the springback were analyzed.The results find that compared with the use of a horizontal binder,the thinning rate of the skin can be decreased from 21.9% to 16.1% with the conformal binder,thereby avoiding the occurrence of cracking defects.In the process of the opening drawing,increasing the lateral blank holder force can not only reduce the lateral springback but also suppress the longitudinal springback,thereby improving the shape accuracy of the skin.(2)The finite element software Pam-stamp was used to simulate the hot stamping process of the skin,exploring the effect of different process parameters on the quality of the skin.The numerical simulation results of the forming method show that the minimum thickness of the skin after crashform is increased from 3.619 mm to 3.841 mm compared to drawing,and the springback of the skin is reduced from 2.581 mm to 1.246 mm;The numerical simulation results of the stamping speed show that with the increasing of the speed,the minimum thickness of the sheet first increases and then decreases,but the magnitude of the change is not obvious,when the speed is 100 mm/s,the minimum thickness of the skin reaches the maximum,which is 3.841 mm.The springback of the skin also decreases with the increase of the stamping speed,when the speed is 100 mm/s,the springback of the skin is reduced to 1.246 mm,and then no longer obvious;The numerical simulation results of the die clearance show that the minimum thickness of the skin slightly increases with the increase of the die clearance;The numerical simulation results of the holding time show that with the increase of the time,the springback of the skin gradually decreases,when the time reaches 15 s the springback of the skin is 0.746 mm,and then no longer obvious with time extending.(3)Based on the results of numerical simulation,actual dies and forming tests are performed.Firstly,cold stamping tests were performed on the skin with the horizontal binder and the conformal binder,it was found that the former would cause the skin cracking,and the latter could obtain a skin without cracking defects,which agrees with the results of numerical simulation.Then the hot stamping test was performed by crashform at a stamping speed of 100 mm/s,a die clearance of 4.2 mm,a holding time of 15 s,and a holding pressure of 10 MPa.The obtained skin has good quality and small springback,and the shape accuracy of the skin can meet requirements without compensation of the die.Which shows that hot stamping can significantly improve the formability of aluminum alloy and reduce springback compared to cold stamping. |
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