【作者】 李亨；

【导师】 刘全坤；

【作者基本信息】 合肥工业大学 ， 材料加工工程， 2012， 博士

【摘要】 高速铁路、工程机械等装备制造业的发展使得金属构件趋于大型精密化,提高大型数控折弯件的成形精度和折弯模关键零件的精度指标具有重大意义。本文围绕影响大型数控折弯成形精度的若干关键技术问题,开展精密折弯的实用化研究。对大型数控折弯机滑块和工作台受载时的挠度变形及加凸补偿技术进行研究。应用Timoshenko梁理论建立折弯加载解析模型,考虑形状、尺寸、惯距等因素对折弯精度的影响,推导得出折弯机滑块与工作台的变形规律为长度方向各点处的挠度与载荷成正比；挠度变形曲线是一元四次方程。折弯机的变形使得大型折弯件全长方向上的角度无法保证一致性,本文分别从几何式、液压式和机械式三方面研究折弯机的变形补偿技术,提出多组不同角度楔块相互配合的同步补偿思路,利用数值模拟及实测方法获得的准确挠度补偿数据,开发了一种新型机械式挠度补偿装置,实现了折弯整体挠度补偿自动化。实验发现未采用补偿装置的3m长折弯件端部与中间的直线度差值为1.28mm,角度由中间向两端逐渐增大,偏差达到士1。；而采用补偿装置后的折弯件直线度控制在0.30mmm之内,角度偏差控制在士25’范围内。高于国标I级精度标准。研究了关键工艺参数对大型折弯角度的影响,开发了一种新型开口可调式下模,实现了模具开口“无级”调节。以工程常用的8mm厚低碳高强钢板折弯为例,采用数值模拟方法研究下模开口大小、下模入口处圆角半径、上模圆弧半径和上模压下量四个关键参数对折弯过程中的应力、应变和回弹后残余应力分布的影响,发现随着上模压下量的增加,回弹角逐渐减小,减小趋势趋于平缓。结合正交试验方法和数值模拟技术建立25组不同参数的试验,采用直观和极差方法分析四个关键参数对折弯角度的影响顺序为上模弧面半径>上模压下量>下模圆角半径>下模开口。在正交试验的基础上通过响应面法计算得到折弯角度预测模型,借助Delphi平台开发折弯角度快速预测模块。结合免疫算法和模拟退火算法优点编制程序,以关键参数作为待优化变量,以折弯角度与目标角度的偏差最小值为优化目标,对采用插块式可调下模的折弯成形工艺进行优化,比较模拟预测和试验结果可知两者具有较好的一致性。为使下模开口达到可调范围内的任意大小,开发了一种新型开口可调式折弯下模,通过系列传动零件配合实现模具开口“无级”调节,扩大了折弯件加工范围。针对现有热处理工艺的不足进行了改进,采用等效热容法处理材料相变潜热,对折弯模镶条淬火冷却过程进行了数值模拟及试验研究,解决了折弯模关键零件镶条的淬火硬度均匀性问题和淬火后变形导致的孔距变化问题。研究发现镶条横截面的温度场分布由两表面交接处至心部呈递进式梯度变化,在镶条进入淬火液后0-15s之间,表面换热边界条件对温度场分布起主导作用,导致镶条表面与心部温差很大,最大值为256.29℃。在15-60s之间,内部的热传导逐步取代表面换热边界条件对温度场分布起主导作用,镶条表面的冷却速度小于内部的冷却速度。在65s左右时发生马氏体转变释放潜热,使得冷却速度有较大幅度降低。试验发现镶条表面整体硬度稳定在57±2HRC,硬度均匀性比原有工艺的57±4HRC有所提高。淬火后镶条伸长0.52mmm,其中两端孔距增加0.42mmm,对于一体化的长尺寸镶条,钻孔时对孔间距需考虑“放量”。拟合试验数据获得线性公式△x1=3.885x10-4x+0.1057(0<x≤4000),用于一般精度要求的放量计算；二次多项式△x2=-3.819×10-7x2+5.281×10--4x+0.0996(0<x≤4000)用于精度要求较高的放量计算。本文的研究成果,可以为高精度大型折弯件生产提供技术支持；设计发明的新型机械式挠度补偿装置和开口自动可调下模,已成功应用于实际生产。更多还原

【Abstract】 Metal components tend to large scale and precision with the development of high-speed rail and engineering machinery, so it’s of great importance to improve the precision of the numerical metal bending parts and the precision of bending dies. The applied research focused on the precision bending was conduct related to a series of key technologies of large scale bending.The deflection and convex compensation for the slider and workbench of the large CNC bending machine under working load were studied. The bending process was modeled for analyzing the loading state using Timoshenko beam theory. After analyzing the correlations among shape, size and inertia, the deformation pattern was deduced:the deflection of the crown of the slider and workbench in length direction is proportional to load and the deformation curve of crowning is a quartic equation. The large bending parts cannot keep uniform along the lengthwise direction because of the deformation of bending machine. In order to bring auto compensation of crowning of bending into practice, a brand new crowning compensation machinery device was developed, which used the compensation data achieved from numeral simulation and experiment result, and the mechanism of simultaneous compensation on the corporation of multi-group wedge with different angle was proposed based on the compensation technology of geometric, hydraulic and machinery bending load, because the consistence of angle in length direction might not be guaranteed along with the deformation of bending machinery. The experiment results increased the bending angle of3meters bending part from the middle to both ends increased gradually, and the deviation reached to±1°, and straightness differentials between the endpoints and the midpoint of the bending part reached up to1.28mm, if compensation device was not adopted. With the compensation device, the part precision can be limited to GB standard of level1. Specifically, the straightness error was decreased to0.3mm, and the angle deviation was limited to the range of±25’.The influence of key process parameters to large bending angle was a new die cavity with adjustable opening structure, and a new die cavity with adjustable opening structure was invented, so the stepless adjustment is realizable. Taking the common8mm low carbon high strength plate as research object, the influence of the size of open structure, entrance radius, arc radius and punch distant on the stress, strain, and distribution of residual stress after spring back was conducted by numerical simulation method via analyzing deformation characteristics of bending process. The results showed the spring back angle reduced gradually and the reduced magnitude tends to mild. The influence order on bending angle is arc radius, press quantity, entrance radius and opening size achieved by adopting range analysis and variance analysis method, which was based on25group different tests using orthogonal experiment and numerical simulation technology. With the help of Delphi development platform, a rapid prediction software system of bending angle was developed, which is under the premise of the prediction model obtained by orthogonal test and RSM (response surface method). The immune algorithms and simulated annealing method were introduced into bending angle control. Using the above key process parameter as optical variables and the minimum deviations between bending angle and target angle as objective, forming process of bending employing adjustable die of block inserted type was optimized, and the simulation result coincided with experiment result. In order to adjust the size of open structure, a new adjustable die cavity was developed, and it made the opening size stepless adjustment possible by assembling transmission part, therefore processing magnitude is expanded naturally.In consideration of defect of the traditional treatment process, problem of hardening homogeneity for key part fit strip of bending mould and deformation of holes pitch after quenching were resolved, when equivalent heat capacity method was used to process latent heat of phase change and the FEM simulation and experiment research on cooling procedure of quenching were conduct. The research showed that temperature distribution of fit strip cross section appeared to gradient change from connection of two surfaces to central zone, specifically, it results in big temperature difference (maximum is256.29℃) in its surfaces and central region, because of the leading role in boundary condition of heat transfer to temperature distribution in the last0to15seconds before fit strip entering quenching liquid, however in15to60seconds, leading role of heat transfer in boundary condition was displaced by inner heat transfer, and surface cooling speed is lower than that of the inside, in addition, cooling speed reduce sharply due to the release of latent heat in marten site transformation at65seconds or so. The experiment results indicated that hardening in entire surface of fit strip was steady at57±2HRC, and hardening homogeneity improved compared with that of previous process which was steady at57±4HRC. Length of fit strip stretch to0.52mm, holes pitch in the ends increase by0.42mm after quenching, and it should take redundancy into consideration in holes pitch for long size fit strip. Linearity formula Axi=3.885×10-4x+0.1057(0<x≤4000) of fitting data was achieved for common precision redundancy, and quadratic polynomial formula△x2=-3.819×10-7x2+5.281×10-4x+0.0996(0<x≤4000) for higher precision redundancy.It provides technical assistance for production of high precision large scale bending part while using research findings of the paper, and new crowning compensation device of mechanical and the adjustable opening structure were successfully put to practice production.更多还原