【作者】 李光；

【导师】 胡成武；

【作者基本信息】 湖南工业大学 ， 机械制造及其自动化， 2019， 硕士

【摘要】 拉深是将有一定形状的毛坯在模具的作用下冲压成开口空心零件的塑性加工方法。毛坯在拉深过程中由于其具有各向异性的特性会在筒壁部分出现高低不平的制耳现象。制耳的产生不仅降低了材料的利用率,增加了修边工序,而且严重的时候会使工件在后续拉深过程中产生破裂。影响制耳的因素主要有两种:一种是方向性因素;另一种是非方向性因素。方向性因素主要包含板料的屈强比和织构系数,而非方向性因素指的是压边力、模具间隙、凸凹模圆角半径和坯料形状等。尽管这两种因素都会导致制耳现象,但它们对制耳的影响作用却是相互独立的,合理调节这两种因素相互制约,就可以使板料在拉深过程中变形均匀,从而达到降低制耳的目的。因此,本课题通过有限元(FEM,Finite Element Method)进行模拟分析研究在圆筒形件变间隙拉深过程中,压边力(BHF,Blank Holder Force)对拉深形件制耳的影响,探讨板料变间隙拉深时的最优压边力加载曲线,从而降低板料的拉深制耳率,提高拉深工件的成形质量。本文首先根据Hill48各向异性屈服准则建立了描述弹塑性体变形的本构关系方程,接着分析了变间隙拉深对圆筒形件不同方向板料的影响机理,建立了变间隙拉深时筒壁高度的理论模型,然后运用Abaqus/Explicit的准静态法,针对圆筒形件变间隙拉深建立有限元仿真模型,对不同恒定型压边力工况和4种经典变压边力加载方案下0.8mm厚的DC04钢板变间隙拉深进行有限元仿真,仿真结果表明压边力对圆筒形件变间隙拉深制耳有很大影响,不同的压边力加载方案下的变间隙拉深制耳率存在较大区别。对于恒定型压边力下的变间隙拉深而言,通过MATLAB软件拟合分析发现:在相同变间隙值的条件下,压边力较小时,变间隙拉深制耳率较高;在一定范围内增加压边力能有效提高变间隙拉深降低制耳率的效果;当压边力超过一定范围时,压边力对变间隙拉深制耳的影响趋于平缓。与恒定型压边力加载方案下的变间隙拉深相比,变压边力加载方案对变间隙拉深制耳的影响各不相同,“Λ”型和渐减型压边力更有利于变间隙拉深降低制耳,“V”型和渐增型压边力不利于变间隙拉深降低制耳。综合各种压边力加载方案下的变间隙拉深制耳情况可以看出:只有合理地利用变间隙与变压边力的耦合作用才能充分发挥板料的成形性能,从而获得比单纯使用变间隙模具或者变压边力条件下更低的制耳率,达到生产低制耳乃至无制耳拉深件的目的。本文还对模拟结果进行了试验验证,通过圆筒形件在不同压边力工况下的变间隙拉深试验,证明采用合理的变压边力加载方式能够有效配合变间隙拉深降低制耳,与此同时,如果采用不合理的变压边力加载方式反而会阻碍变间隙拉深降低制耳,加重制耳现象。试验结果与模拟结果一致表明了有限元分析的准确性,说明有限元法适用于变间隙拉深的数值模拟,可以用来确定合理的压边力加载方案。更多还原

【Abstract】 Deep drawing is a plastic processing method of punching an effigurate blank into an uncork hollow part with the effect of a die.Due to its anisotropic properties during the drawing process,the blank will have an uneven earing phenomenon of the cylinder wall.The production of the earing is not only reduced the utilization of the material,but also increased the trimming process,and in severe cases,the workpiece will be badly broken during the subsequent drawing.There are two main factors affecting earing production:one is a directional factor;the other is a non-directional factor.The directional factors mainly include the yield ratio and texture coefficient of the sheet,while the non-directional factors refer to the blank holder force,the die gap,the radius of the round corner of concave-convex die,and the shape of the blank.Although these two factors will lead to the earing phenomenon,their effects on the earing are independent with each other.Reasonable adjustment of these two factors restricts each other,in this way the sheet can be uniformly deformed during the drawing process,thereby achieving a reduction of earing rate.Therefore,with the purpose of study of the coupling effect between variable gap and variable blank holder force on the deep drawing earing,this subject used finite element(FEM,Finite Element Method)to carry out simulation analysis to study the effect of BHF(Blank Holder Force)on the earing of deep drawing part during the deep drawing with variable gap.The best variable blank holder force loading curve during the variable gap drawing was discussed,so as to reduce the earing rate of the sheet material deep drawing and improve the forming quality of the deep drawing workpiece.In this paper,the constitutive equation describing the deformation of elastoplastic body is established based on the Hill48 anisotropic yield criterion.Then the influence mechanism of the variable gap drawing on the sheet material in different directions of the cylindrical part is analyzed.The theoretical model of the cylinder wall’s height is established,and then using the quasi-static method of Abaqus/Explicit,the finite elementsimulation model is established for the variable gap drawing of the cylindrical part.The finite element simulation of the 0.8mm thick DC04 steel plate with variable gap under different numerical blank holder force conditions and four classical variable blank holder force loading schemes is carried out.The simulation results show that the blank holder force has a great influence on the cylindrical parts to change the variable gap deep drawing earing.There is a big difference in the rate of deep earing under the different blank holder force loading scheme.As for the variable gap drawing with the constant blanking holder force,the fitting analysis by MATLAB software found that under the condition of the same variable gap value,when the blanking force is small,the rate of the variable gap drawing earing is higher.Increasing the blank holder force within the range can effectively improve the effect of reducing the earing rate;when the blank holder force exceeds a certain range,the influence of the blank holder force on the variable gap deep drawing earing tends to be gentle.Compared with the variable gap drawing under the constant blank holder force loading scheme,the variable blank holder force loading scheme has different effects on the variable gap deep drawing earing,and the “Λ” type and the decreasing type blank holder force are more favorable.But the“V” type and the increasing type of blank holder force are not conducive to the reduction of the reduction of the variable gap deep drawing earing.It can be seen from the situation that the variable gap deep drawing ear under various blank holder force loading schemes can only make full use of the coupling effect of the variable gap and the variable pressure side force to fully exert the forming property of the sheet material,thereby obtaining more than simple use,which achieves the purpose of producing low earing or even no earing deep drawing parts.In this paper,the simulation results are also verified.Through the variable gap drawing test of cylindrical parts under different blank holder force conditions,it is proved that the reasonable variable blank holder force loading method can effectively match the variable gap drawing to reduce the earing rate.At the same time,if the unreasonable variable blank holder force loading method is used will hinder the variable gap drawing to reduce the rate of drawing earing,and the earing phenomenonwill be aggravated.The test results consistent with the simulation results show the accuracy of the finite element analysis,indicating that the finite element method is suitable for numerical simulation of variable gap drawing,which can be used to determine a reasonable blank holder force loading scheme.更多还原