【作者】 王辉；

【导师】 周杰；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2017， 博士

【摘要】 汽车冲压模具是汽车生产的重要装备之一,模具的开发周期约占汽车开发周期的三分之二,模具开发周期的长短直接影响模具开发成本。而当前汽车冲压模具面临的最大问题是开发周期长、成本高,因此开展缩短汽车冲压模具开发周期方面的研究至关重要。影响冲压模具开发周期的主要因素包括:模具设计、制造加工、试模设备、生产管理和人员操作等。本文主要研究缩短冲压模具开发周期的几个关键技术问题:数值模拟技术、回弹控制技术和型面补偿策略。通过在模具制造企业实地调研,得出导致冲压模具开发周期长的主要问题有:解决拉延成形类零件的拉裂和起皱等缺陷的时间长、控制与提高冲压件的尺寸精度反复试模次数多、提高模具型面研合率工时长。为了达到缩短模具开发周期的目的,本论文主要从以下几个方面进行研究:(1)针对成形极限图无法量化地评价零件的成形性,构建了破裂趋势函数、起皱趋势函数和安全区域比函数,通过构建的三个函数可有效地对零件的成形性进行评价。最后借助Matlab软件编写程序实现对所构建的三个函数进行计算。(2)针对模具开发中冲压件的起皱和破裂等缺陷,提出采用基于成形性评价函数的拉延工艺优化和稳健性设计来提高数值模拟预测的精度和准确性。以前隔板为研究对象,采用中心复合实验设计来优化成形工艺参数,试验中的优化目标为最大减薄率和构建的破裂趋势函数、起皱趋势函数和安全区域比函数,然后采用多目标优化方法寻求最优的工艺参数组合。此外,提出在数值模拟中考虑实际情况的不稳定因素和噪音因素,考虑实际因素波动对数值模拟结果的影响。文中主要考虑了材料的屈服强度、各向异性指数、摩擦系数、压边力、板料厚度、板料尺寸和板料定位位置的波动对前隔板拉延成形的影响,对其进行工艺稳健性分析,从而提高数值模拟的准确性和可靠性,为实际试模提供依据。通过前隔板零件的生产试验,表明采用提出的方法可以有效地避免零件的开裂和起皱缺陷。(3)针对冲压模具开发中的回弹问题提出了基于全工序冲压成形的多次迭代回弹补偿方法。以某汽车高强度钢拼焊板零件为研究对象,阐述该方法的具体实施流程,以及进行了相应的实验来验证该方法。首先对高强度钢的母材和拼焊板进行拉伸试验、组织分析和断口分析,然后建立高强度钢拼焊板零件的全工序有限元模型,得到零件成形和回弹情况,对拉延工序模具进行多次迭代回弹补偿。当多次迭代回弹补偿和全工序模拟循环进行三次后,回弹后的零件满足设计的许用尺寸公差要求。最后进行模具试模,得到试模零件进行尺寸偏差测量。检测结果得出测量的32个点中有24处满足零件的尺寸偏差要求,不合格的检测点的最大偏差值为1.16 mm。实验结果表明该方法相对于传统经验法和简单的回弹补偿方法的准确度更高。(4)由于不恰当的模具设计或者不准确的CAE分析,实际模具试模中会出现尺寸严重偏差的零件。针对试模件尺寸不合格的模具,提出了基于三维全型检测和逆向工程的回弹补偿技术。以某汽车门槛梁加强件为例,对试模得到的零件进行三维全型面扫描,通过逆向软件Geomagic对其进行逆向建模,并与设计模型进行对比,得出零件的回弹实际偏差值,得到该零件的最大上偏差为+9.51 mm,最大下偏差为-4.33 mm。相对于传统检具检测方法,三维全型检测的结果更加准确、数据更全。最后,采用提出的基于三维全型检测和逆向工程的回弹补偿方法对模具进行回弹补偿,并进行模具修改和试模。对补偿后得到零件进行检测,检测的18个位置中有15处满足零件公差要求,合格率为83.33%。试验结果表明该方法能够有效地控制零件的回弹,避免反复试模。(5)针对实际模具调试中型面研合率低和提高研合率非常耗时的问题,提出了考虑模具变形和零件厚度变化的型面补偿方法对模具型面进行补偿。首先进行冲压成形分析,然后将成形分析的最终载荷映射到模具上进行静力分析。通过对前隔板模具的静力分析得出液压机工作台的变形对模具变形结果影响较大:当考虑液压机工作台变形时凸模的最大位移为1.106 mm,未考虑液压机工作台变形时凸模的最大位移为0.278 mm,表明考虑液压机工作台的变形时结果更加准确。最后提出采用凸模型面不变,将凸凹模型面变形量叠加的方法来补偿凹模型面,再叠加零件厚度变化量获得最终补偿后的凹模型面。试模结果表明采用本方法可以有效地提高首次试模中零件和模具型面的研合率,缩短模具型面研配次数和时间。更多还原

【Abstract】 Automobile stamping die is one of the most important equipment in automobile production.The die development cycle is about two-thirds of the car development cycle,and the cost of the die development is directly affected by die development time.Currently,the biggest problem of automobile stamping die is that the development cycle of die is long and the cost is high.Therefore,it is very important to carry out researches on the short cycle development of automobile stamping die.There are many factors that affect the development of stamping dies: die design technology,manufacturing processing technology,tryout machine,production management,workers operating and so on.Several key techniques of shortening the development cycle of stamping die,such as numerical simulation technology,springback control strategy and surface compensation strategy,were investigated in this thesis.According to the state of stamping die development in the enterprise,three aspects which cause long delays to the die development time were found in the investigation in the die manufacturing enterprise: to solve the problem of drawing defects such as cracking and wrinkling cost a long time,to control and improve the size precision of the stamping parts need repeated die tryout,to improve the die surface grind rate spend plenty of working time.In order to achieve the purpose of shortening the die development cycle,the main works of this thesis are as follows:(1)Aiming at the problem that the forming limit diagram cannot be used to quantitatively evaluate the formability of parts,the cracking trend function,the wrinkle trend function and the safety region ratio function were put forward to evaluate the formability of numerical simulation results.Finally,the program written by using Matlab software was used to calculate the proposed functions.(2)In view of the defects such as wrinkling and cracking on the stamping part,the drawing process optimization based on the formability evaluation function and robustness design were put forward to improve the precision and accuracy of numerical simulation.The maximum thinning rate and the proposed fracture trend function,the wrinkle trend function and the safety region ratio were used as the optimization objective in the center composite experiment design,and then the multi-objective optimization method was used to obtain the optimal combination of process parameters.In addition,in order to improve the prediction accuracy of product reliability,the unstable factors and noise factors were considered in the numerical simulation,and the influence of the actual situation fluctuation on the numerical simulation was considered.The effect of the yield strength of the material,the anisotropy index,the friction coefficient and the blank holder force,the thickness of the sheet,the size of the sheet and the position of the sheet were considered in the drawing of the dash board.Process robustness analysis was carried out on the dash board,so as to improve the accuracy and reliability of numerical simulation and to provide the constructive basis for the actual test.It is shown that the proposed method can effectively avoid the cracking and wrinkling of the parts by the production test of the dash board.(3)Aiming at the springback problem in the die development,the multiple-iteration springback compensation method based on the entire process stamping was proposed.Taking a high strength steel automobile part as an example,the concrete implementation process of this method was introduced,and the corresponding experiment was carried out to verify the feasibility of the proposed method.In order to establish an accurate numerical simulation model,the tensile test,the microstructure analysis and the fracture analysis of the base material and tailor welded blanks of high strength steel were carried out.Then,the finite element model of the entire forming processes for the high strength tailor welded blanks was established to calculate the forming process and springback.The drawing die was compensated by using the multiple-iteration springback compensation.The springback part satisfies the allowable tolerance when the iteration springback compensation and entire forming simulation were implemented for the third time.Finally,the compensation results were used to manufacture tools and die tryout.Inspection results show that 24 of the 32 measuring points can satisfy geometrical tolerances,and the maximum deviation of the unqualified test points was 1.16 mm.Experimental results demonstrate that the proposed method is more accurate than traditional empirical method and simple springback compensation.(4)Due to inappropriate tool design or inaccurate CAE analysis,the unqualified formed part which cannot meet the requirements of shape tolerance is inevitable in die tryout.Aiming at the unqualified tryout die,a new method based on three-dimensional(3D)scanning and reverse engineering to compensate for the springback of the formed part was introduced.Taking the rear reinforce plate as an example,a 3D scanner was utilized to scan the formed part.The modeling of the part was built by the reverse software Geomagic,and it was utilized to compare with the design model.The result is shown that the maximum deviations and minimum deviation are +9.51 mm and-4.33 mm,respectively.The accuracy of a 3D scanner is higher than the special fixture.Finally,the die surface was compensated by using the proposed method,and the die tryout was carried out.The inspection results show that 15 of 18 measuring points can satisfy the geometrical tolerances,thus indicating that the qualified rate of this product is 83.33% in the first springback compensation by 3D scanning method.The experimental results show that this method can effectively control the springback of parts and avoid repeated trial.(5)Aiming at the problem that the die surface grind rate is low and the improvement of die surface grind rate is very time-consuming,a surface compensation method which consider the deformation of the dies and the thickness variation of part was put forward to compensate the die surface.The stamping process was analyzed firstly,and then the final load of the forming analysis was mapped to the die for static analysis.Through static analysis of the dash board dies,it is concluded that the hydraulic press platform has a great influence on the die deformation.The maximum displacement of the punch is 1.106 mm with the consideration of the deformation of the hydraulic press platform;the maximum displacement of the punch is 0.278 mm without consideration of the press platform.It is indicating that the results are more accurate when considering the hydraulic press platform.Finally,the punch surface was kept invariant,and the superimposed deformation between punch and die was used to compensate the die surface,and then superimpose the thickness variation of part to obtain the compensated surface for die.The results show that this method can effectively improve die surface grind rate in the first time of die tryout,and shorten the tryout time in the die surface lapping.更多还原