【作者】 刘艳；

【导师】 孙友松；

【作者基本信息】 广东工业大学 ， 材料加工工程， 2008， 硕士

【摘要】 冲裁是最重要的冲压工艺之一,它不仅可作为其它复杂冲压加工的准备工序,还可以直接获得具有一定精度要求的制件。由于在板料的冲裁加工过程中,变形集中在很小的区域内,且以断裂方式告终,使得其研究存在很多困难。板料的冲裁过程随着板料的断裂分离而结束,在液压机上冲裁时,冲裁过程中积蓄在液压油和液压机机身的弹性变形能在断裂时瞬时释放,引起强烈的振动,产生较大的噪音,损坏模具。同时强烈的液压冲击,还可能危及液压机的液压系统。长期以来,普通液压机上不能进行冲裁工作。目前,对冲压生产中的振动治理主要采用被动减振的方法,如在液压机工作台上安装缓冲油缸和减振弹簧,这虽然可以减少部分振动和噪音,但存在结构复杂、体积大、能耗高的缺点。本文拟采用主动减振方法对液压机进行改造,通过改变液压机的进出口油的流量,控制滑块速度,使冲裁过程积蓄在液压油及液压机机身的弹性变形能量在工件断裂前基本释放出来,最大限度地减轻液压机冲裁引起的振动,从根本上解决冲裁振动问题。本文分析了冲裁工艺的塑性变形及断裂的过程,应用Deform-2D商业有限元分析软件,对不同材料不同厚度的板料冲裁过程进行模拟计算,获得冲裁过程各阶段应力、应变状态,冲裁工艺参数对板料裂纹产生及断裂位置的影响,以及整个过程冲裁力的变化,可作为减轻冲裁振动、降低冲裁噪声的基础。研究结果表明,冲裁时,低碳钢和弹簧钢的断裂方式不同,弹簧钢是裂纹产生并扩展引起的脆性断裂,低碳钢是韧性断裂;随着板料厚度的增加,材料产生裂纹时的凸模行程相对增加,材料断裂分离所需的凸模行程同样增加;在一定范围内,随着冲模间隙的增加,断裂时的凸模行程随着间隙的增大而有所增加。分析了液压机的液压系统,按照主动减振原理,提出了进口节流、出口节流、旁路节流等各种方案。按照YA34-400液压机结构,就不同的减振方案,分别建立了冲裁过程数学模型,并依此建立了基于MATLAB/Simulink软件的仿真模型,并根据样机实验参数进行了数值仿真。设计了液压机冲裁减振试验系统,进行了几种方案的冲裁实验,记录了滑块的动态位移,由冲断时冲头的振动幅值判别振动的大小。由仿真结果及样机实验结果表明:1、滑块的绝对振动由机架振动和滑块相对油缸的振动合成,后者是主要的,后者的振幅大小约是前者的3.5倍。解决油液压缩引起的振动是液压机冲裁减振的主要矛盾。2.适当减小工作时压缩液压油的体积,即提高模具高度,可以减小振动。3.加大机架的等效刚度只能减小机架的振动,对滑块的振动没有明显效果。4.通过进油口节流,控制滑块的速度,裂纹产生后利用已经蓄积的弹性变形能完成冲裁,通过消耗部分弹性变形能来减振的方案,效果不理想。5.通过出油口节流,控制出油量,减缓高压液压油释放过程以减振的方法可行,但有下腔压力过大的危险,必须加装蓄能器。6.计算所得结果中最适合的蓄能器容积5.5L,工作压力8Mpa,减速阀需选型为工作压力31.5Mpa,流量80L/min,此时机架变形u的振幅减小为原振幅的56.17%,滑块相对于机架的位移x振幅减小为原振幅的45.31%,滑块相对于地的位移X的振幅减小为原振幅的44.31%。本项目的研究为实现主动减振,研制新型冲压机奠定了基础。更多还原

【Abstract】 Blanking is one of the most important stamping processes. It can not only be the preparation for further stamping processes, but also get work pieces with a certain accuracy directly. There are lots of difficulties to study sheet metal blanking process since the deformation is limited in a tiny area of sheet metal and ends with fracture.Sheet metal blanking ends with the fracture, and thus the elastic energy accumulated in the press body and the oil releases suddenly.With the fracture, bringing severe vibration, great noise and damaging the die, equipments and hydraulic system.Generalized hydraulic presses can not be used for blanking.Up to now, passive damping, for example, adding vibration-reducing components between the working plate and the slider,has mainly been adopted.Though this method is effective to reduce the vibration and noise, but the structure is complex, with large space and energy wastes. The active vibration reducing method is put forward in this paper.The slider velocities would be controlled by adjusting the flow rate into or out the cylinder at some typical positions. The accumulated elastic energy could be completely released before the fracture so as to reduce the vibration maximally.This paper analyzes the plastic deformation, fracture process, mathematical model and the finite element method in blanking. Deform-2D was used to simulate blanking process of sheet metal with different thicknesses according to the Normal Cockroft & Latham fracture principle. The stress and strain distributions, blanking parameters’ effects on the cracks and the force-stroke curves of the entire blanking processes were obtained, setting a foundation for reducing blanking vibration and noises. Simulation showed that low-carbon steels were different from hard steels in blanking. Hard steels had brittle fractures while low-carbon steels had ductile fractures. With the increasing in thickness and blanking clearance, punch strokes increased in cracks.On the basis of analyzing of the hydraulic system, several approaches were proposed, including meter-in control, meter-out control and bleed-off control ,etc.According to the structure of the model hydraulic press and the different approaches ,the mathematic models were set up. With the mathematics model, the simulation models based on MATLAB/Simulink software were set up and the simulations were carried out according to the prototypal experiment parameters of the model press.Blanking experiments were done, and the dynamic displacements of the slider were recorded. The press vibration can be judged based on the amplitudes. The results of the simulations experiments were indicated as following:1. The slider absolute vibration is the combination of rack vibration and the relative vibration, the latter is 3.5times of the former. Reducing the vibration caused by hydraulic oil compression is the key for vibration reducing.2. Reducing the volume of compression oil or increasing the die can reduces the vibration.3. Increasing the stiffness of press body can reduce the vibration of the rack, but has no significant effect to slider vibration.4. Meter-in control can control slider speeds. The releasing time of elastic energy accumulated during the blanking could be altered to guarantee part of the elastic energy to be released before the fracture , but it is ineffective.5.Meter-out control can control the slider speeds too. The releasing time of elastic energy accumulated during the blanking could be extended, reducing vibration. But the pressure in the low chamber might be too high and an accumulator would be needed.6.The suitable parameters of the accumulator for the simulated condition would be: volume is 5.5L, working pressure is 8MPa. The nominal pressure of throttling valve is 31.5MPa, the maximum constant flow is 80L/min.Rack vibration u can reduce to 56.17%, relative slider vibration x can be reduced to 45.31%, The absolute slider vibration X can be reduced to 44.31%.The research in this paper lay the foundation for the development of active vibration reducing and the new press.更多还原