闭挤式精冲成形机理及全光亮轮廓面形成条件研究
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摘要
传统的齿圈压板精冲工艺由于模具结构的局限,使其无法冲裁低塑性和大厚度的材料,本文针对我们已获得的发明专利——闭挤式精冲工艺,采用数值模拟和实验研究相结合的手段对该工艺进行了基础研究。
闭挤式精冲工艺采用特殊的模具结构,通过副凹模首先压下,使废料区受到挤压变形而被封闭,以致周围废料几乎无法再沿径向变形。接着凸模向下运动,并配以反顶力的作用,使挤剪变形区的材料受到极大的三向压应力作用,提高了材料塑性,进而提高可精冲厚度和扩大可冲裁材料范围。
在本文中首先采用主应力法分析了材料内部三向压应力的影响因素,并提出了描述三向压应力大小的参数——外环填充率,理论上有外环填充率越高材料内的三向压应力越大,反之三向压应力越小的规律。此外,采用网格分析的方法分析了外环区和挤剪变形区材料的流动规律和应变分布。
通过用DEFORM软件对闭挤式精冲过程进行数值模拟,分析了应力应变以及金属的流动特点,并对外环填充率和反顶力大小对静水压应力的影响进行了研究,验证了理论分析中得出的规律。此外,引入断裂准则研究了闭挤式精冲中材料裂纹的生成和扩展,并通过与实验对比,发现该断裂准则可以准确预测该种材料在闭挤式精冲中的断裂。
在有限元摸拟的基础上制作了工艺实验模具和实验坯料,进行了大量的工艺实验,研究了外环填充率与挤剪面光亮带比例、工件增厚比例以及与裂纹生成时机之间的关系,并得出零件挤剪断面全光亮成形的条件;通过对不同材料进行闭挤式精冲试验,研究了材料塑性对闭挤式精冲成形质量的影响;在大量实验的基础上提出了模具外环型腔尺寸和坯料尺寸的设计要点。
研究表明,闭挤式精冲是一种冲裁低塑性材料和厚板材料的有效工艺,成形质量较高,经检测外圆剪切面的表面粗糙度可达0.03μm ,内孔剪切面表面粗糙度可达0.1μm ,工件两端也没有出现毛刺,实验所得的最厚工件达到14.26mm。
Because the limit of traditional V-ring fine-blanking, low plastic and large thickness materials are hard to form with it. A new fine-blanking method, closed-extruding fine-blanking is brought up and it has been acquired as patent.
A special mold structure is employed in this process. The punch and vice-die are relatively locked in a specific location and move downward together at first. The billets are limited by the extruding, as result, the plastic of the material in outer-ring zone is attenuated and it is almost impossible to deform along the radial again. Then the punch make a further downward movement, coupled with the counterpunch force, the material in deformation zone is in great three–dimensional compressive stress and the plasticity is improved, then low plastic and large thickness materials can stamping well at this time.
At first, the major elements of hydrostatic stress in material are analyzed by using slab method. A special parameter, outer-ring fill rate, is proposed. That is derived the larger outer-ring fill rate the heavier hydrostatic stress. Grid method is employed to analyze the material flow lows in closed-extruding fine-blanking process.
The closed-extruding fine blanking process was simulated with DEFORM-2D software. The character of the stress and strain and the flow of material is described. The heavy hydrostatic stress is obtained in material. And the influence of oute-ring fill rate and counterpunch force to the hydrostatic stress is studied, and the low derived upon is verified. In addition, the fracture criterion is applied to analyze the generating and expanding of crack. Compeering with experiments, the crack of the material in the process could be forecasted.
According to the simulation above, an experiment tool and billets were designed and manufactured and plenty of parts were finished. The relationship between outer-ring fill rate and the proportion of the smooth surface, thickening is studied. The Conditions of Obtaining Smooth Surface is proposed. According to the stamping of material with different plasticity, the influence of plastic to the quality of smooth cutting surface is studied. The major design factor of the size of cavity in mold and the billets is proposed at last.
The study shows that the closed-extruding fine blanking is an effective way to blank low-plastic and thick materials. The roughness of cut surface on the part is 0.03μm and the roughness of hole in outer-ring is 0.1μm . In addition, the collapse corner of the part is very small, and there has no burrs occurred. In the experiments, the largest thickness of part is 14.26mm .
闭挤式精冲工艺采用特殊的模具结构,通过副凹模首先压下,使废料区受到挤压变形而被封闭,以致周围废料几乎无法再沿径向变形。接着凸模向下运动,并配以反顶力的作用,使挤剪变形区的材料受到极大的三向压应力作用,提高了材料塑性,进而提高可精冲厚度和扩大可冲裁材料范围。
在本文中首先采用主应力法分析了材料内部三向压应力的影响因素,并提出了描述三向压应力大小的参数——外环填充率,理论上有外环填充率越高材料内的三向压应力越大,反之三向压应力越小的规律。此外,采用网格分析的方法分析了外环区和挤剪变形区材料的流动规律和应变分布。
通过用DEFORM软件对闭挤式精冲过程进行数值模拟,分析了应力应变以及金属的流动特点,并对外环填充率和反顶力大小对静水压应力的影响进行了研究,验证了理论分析中得出的规律。此外,引入断裂准则研究了闭挤式精冲中材料裂纹的生成和扩展,并通过与实验对比,发现该断裂准则可以准确预测该种材料在闭挤式精冲中的断裂。
在有限元摸拟的基础上制作了工艺实验模具和实验坯料,进行了大量的工艺实验,研究了外环填充率与挤剪面光亮带比例、工件增厚比例以及与裂纹生成时机之间的关系,并得出零件挤剪断面全光亮成形的条件;通过对不同材料进行闭挤式精冲试验,研究了材料塑性对闭挤式精冲成形质量的影响;在大量实验的基础上提出了模具外环型腔尺寸和坯料尺寸的设计要点。
研究表明,闭挤式精冲是一种冲裁低塑性材料和厚板材料的有效工艺,成形质量较高,经检测外圆剪切面的表面粗糙度可达0.03μm ,内孔剪切面表面粗糙度可达0.1μm ,工件两端也没有出现毛刺,实验所得的最厚工件达到14.26mm。
Because the limit of traditional V-ring fine-blanking, low plastic and large thickness materials are hard to form with it. A new fine-blanking method, closed-extruding fine-blanking is brought up and it has been acquired as patent.
A special mold structure is employed in this process. The punch and vice-die are relatively locked in a specific location and move downward together at first. The billets are limited by the extruding, as result, the plastic of the material in outer-ring zone is attenuated and it is almost impossible to deform along the radial again. Then the punch make a further downward movement, coupled with the counterpunch force, the material in deformation zone is in great three–dimensional compressive stress and the plasticity is improved, then low plastic and large thickness materials can stamping well at this time.
At first, the major elements of hydrostatic stress in material are analyzed by using slab method. A special parameter, outer-ring fill rate, is proposed. That is derived the larger outer-ring fill rate the heavier hydrostatic stress. Grid method is employed to analyze the material flow lows in closed-extruding fine-blanking process.
The closed-extruding fine blanking process was simulated with DEFORM-2D software. The character of the stress and strain and the flow of material is described. The heavy hydrostatic stress is obtained in material. And the influence of oute-ring fill rate and counterpunch force to the hydrostatic stress is studied, and the low derived upon is verified. In addition, the fracture criterion is applied to analyze the generating and expanding of crack. Compeering with experiments, the crack of the material in the process could be forecasted.
According to the simulation above, an experiment tool and billets were designed and manufactured and plenty of parts were finished. The relationship between outer-ring fill rate and the proportion of the smooth surface, thickening is studied. The Conditions of Obtaining Smooth Surface is proposed. According to the stamping of material with different plasticity, the influence of plastic to the quality of smooth cutting surface is studied. The major design factor of the size of cavity in mold and the billets is proposed at last.
The study shows that the closed-extruding fine blanking is an effective way to blank low-plastic and thick materials. The roughness of cut surface on the part is 0.03μm and the roughness of hole in outer-ring is 0.1μm . In addition, the collapse corner of the part is very small, and there has no burrs occurred. In the experiments, the largest thickness of part is 14.26mm .
引文
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[3]肖祥芝,王孝培.中国模具设计大典第3卷冲压模具设计[M].江西科学技术出版.2003(1):139
[4]邓明,黄宏.面向21世纪的精冲成形技术[J].重庆工学院学报.2001(5)
[5] L C Chan and T C Lee. Harding effect of the blanked edge in fine-blanking process [J]. in proceeding of the 2nd international conference on die and mould technology. 1992. 440-450
[6]涂光祺.精冲技术[M].北京:机械工业出版社.2006:29,121,335-340
[7] GFM. Corporation. Basic Design Guide for gropflow.
[8]彭家耕,秦泗吉,李硕本.板材精密冲裁工艺的研究[J].燕山大学学报.2002.Vol26,4:347-350
[9]彭群,赵彦启,李荣洪等.厚板精冲技术的工艺研究[J].材料科学与工艺,2004(112)14:342-344
[10]李荣洪,郑鹏飞,彭群.往复成形精冲过程数值模拟精冲[J].中国机械工程学报.2005(16)6:554-556
[11]涂光祺,袁庆祥,牛金旺.精冲变形过程分析及压边圈齿形参数的研究[J].锻压技术.1981(3)
[12]涂光祺,袁庆祥,牛金旺.精冲工艺参数及基础工作的研究[J].精密冲裁文集(三).机械部第十一设计院出版.1984
[13]曹建刚,邢淑清.冲裁模具设计中的应力分析[J].包头钢铁学院学报.1998(17)3:238-240
[14] Y C Leung,L C Chan,C Y Tang and T C Lee.Re-etched grids for large-strain measurement in fine-blanking[J]. The Journal of Strain Analysis for Engineering Design. 2004 Vol.39 No.5: 423-436
[15] Sutasn Thipprakmas. Finite-element analysis of V-ring indenter mechanism in fine-blanking process[J]. Materials & Design. 2008, Vol 30, 526-531
[16] T.S. Kwaka, Y.J. Kima, M.K. Seoa and W.B. Bae. The effect of V-ring indenter on the sheared surface in the fine-blanking process of pawl[J]. Journal of Materials Processing Technology. 2003(10), Vol143-144: 656-661
[17] T.S.Kwak, Y.J.Kim, W.B.Bae. Finite element anailsis on the effect of die clearance on shear planes in fine blanking[J]. Journal Materials Processing Technology.2002,130-131:462-468
[18]程万军,何忠保,刘化民.齿圈压板精密冲裁的力学分析[J].锻压技术.2001,4,22-23
[19] J.LazareV,A.KocoV, Finite element analysis of the stress-strain condition in the process of fine blanking, in Proceedings of the International Manufacturing Engineering conference[J].Freund Publishing Com, 1996:272-274
[20]黄毅宏,黎厚芳.精冲工艺及其机理探讨[J].中国机械工程.1994(5)5:57-59
[21]周照耀,刘龙兵.厚板精冲工艺[J].模具工业.2000(11):13-15
[22]邓春萍,杨慎华,寇淑清.汽车限位凸轮精密冲裁工艺试验研究[J].汽车工艺与材料.2003(8):28-29,32
[23]贾建军,彭颖红.精冲过程的韧性断裂[J].上海交通大学学报,1999(33)2:181-183
[24]贾建军,彭颖红,阮雪榆.精冲断裂过程的有限元模拟[J].上海交通大学学报.2003(37)7: 1064-1067
[25] Z.H. Chen, C.Y. Tang, T.C. Lee and L.C. Chan. Numerical simulation of fine-blanking process using a mixed finite element method[J]. International Journal of Mechanical Sciences. 2002, Vol44: 1309-1333
[26] Lee T.C., Chan L.C., Wu B.J. Further investigation of the fine-blanking process employing large deformation theory[J]. Journal of materials processing technology. 1997, Vol. 66, No.1-3, 258-263
[27] L.C. Chan, Y.C. Leung , T.C. Lee , J. P. Fan and C. Y. Tang. Numerical simulation for fine-blanking—a new approach[J]. Materials Science and Engineering A. 2004,Vol364, 207-215
[28] Chen Z.H, Tang C.Y., Lee T.C., Chan L.C. A study of strain localization in the fine-blanking process using the large deformation finite element method[J]. Journal of Materials Processing Technology. 1998, Vol 86, No. 1: 163-167(5)
[29] Y.W. Stegeman, A.M. Goijaerts, D. Brokken, W.A.M. Brekelmans, L.E. Govaert, F.P.T. Baaijens. An experimental and numerical study of a planar blanking process[J]. Journal of Materials Processing Technology.1999: 266–276
[30] Ridha Hambli. Finite element simulation of fine blanking processes using a pressure-dependent damage model[J]. Journal of Materials Processing Technology. 2001,Vol 116, 252-264
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