Z形弯曲件冲压工艺及模具设计【冲孔落料复合模】【弯曲模】【2套】
Z形弯曲件冲压工艺及模具设计【冲孔落料复合模】【弯曲模】【2套】,冲孔落料复合模,弯曲模,2套,弯曲,曲折,冲压,工艺,模具设计,冲孔,复合
广西科技大学鹿山学院毕业设计(论文)开题报告 题 目: Z形弯曲件冲压工艺及模具 系 别: 专业班级: 姓 名: 学 号: 指导教师: 二 年 月 日一、选题的背景和意义(所选课题的历史背景、国内外研究现状和发展趋势)模具是制造业的重要基础工艺装备,工业产品大批量生产和新产品开发都离不开模具,用模具生产制件所达到的(四高二低)高精度,高复杂程度,高一致性,高生产率和低耗能、低耗材,使模具工业在制造业中的地位越来越重要。模具品种繁多,共有10大类,包括冲压、塑料、橡胶、铸造、锻压等,用于制造业中几乎所有产品的生产,可见模具的服务范围已包括国民经济的许多方面,现在模具技术已成为衡量一个国家产品制造水平的重要标志之一,没有高水平的模具就没有高水平的产品已成为共识。因而,设计制造出高质量的模具已势在必行。模具设计和制造技术水平的高低,是衡量一个国家产品制造水平高低的重要标志之一,在很大程度上决定着产品的质量、效益和新产品的开发能力。本课题旨在锻炼毕业生的思维,熟练掌握和运用大学四年所学知识,能够进行独立的设计作业。 针对题目使毕业生得到机械原理、机械零件设计、机械制造技术基础及模具设计与制造的综合训练。针对题目使学生获得冲压工艺规程、模具设计与制造加工基础知识,工艺参数及加工设备的选取,计算机辅助绘图及资料、手册的查阅。 培养综合运用所学知识分析问题和解决实际问题的能力、探求真理的创新精神和创新能力并受到工程设计与科学理论结合的初步训练等方面的能力。巩固所学的专业知识,锻炼动手能力,培养工程意识,强化工程应用能力,为未来的工作打下良好的基础 。近几年,我国模具制造水平大幅度提高。一个国家的模具技术水平,已成为衡量国家制造业水平的一个重要标志,也是保持这些国家的产品在国际市场上优势的核心竞争力。中国模具行业加快了体制改革和机制转换步伐,产业结构日趋合理。相关机构预测到2018年,中国将一跃成为全球最大的模具制造业基地之一。据国际模协秘书长罗百辉介绍,这几年全球58%的模具是由德国等国家生产制造的,中国等亚洲国家的比例只占到1%,但今后东欧国家的模具将会有较大幅度的增长,而亚洲国家的生产比例将提高至22%左右。 模具,是工业生产的基础工艺装备,在电子、汽车、电机、电器、仪表、家电和通讯等产品中,60%80%的零部件都依靠模具成形,模具质量的高低决定着产品质量的高低,因此,模具被称之为“百业之母”。模具又是“效益放大器”,用模具生产的最终产品的价值,往往是模具自身价值的几十倍、上百倍。由于现代模具企业大多体现出技术密集、资金密集和高素质劳动力密集以及高社会效益的特点,模具制造业已成为高新技术制造产业的一部分。近年来,伴随着国产设备水平的不断提升,也有不少模具企业开始选择了国产机床。超精密镜面铣床、纳米级车铣复合中心、超精密数控车床等也已用于模具制造。不过有些高端设备主要还是靠国外进口。但现阶段我国模具制造业确实取得了显著的成功。据国际模协秘书长罗百辉介绍,我国以大型、精密、复杂、长寿命模具为代表的高水平的模具的比例已经达到了三分之一以上。 我们要想成为世界制造业大国,没有先进的模具工业是不行的。在这方面我们还有很长的路要走,还有很多东西要学。首要的一条是要重视模具行业的发展,不但要有先进的技术,更要重视模具行业的商品化,让模具行业从企业中走出来,成为一个具有市场竞争力的新兴行业。据国际模协秘书长罗百辉调查,欧洲模具设计和生产的时间要比中国快,但因中国的劳动力成本低,对部分国外客户有着很强的吸引力。同时,欧洲及世界各国之间的模具竞争也相应加剧。当前,越来越多的外资制造企业看到日益发展的中国模具,纷纷加入到中国的模具市场,许多国际知名品牌的汽车模具、冲压模具、注塑模具企业也都进入中国,且进入中国市场的力度非常迅猛,速度也非常快。尤其是在我国的华南地区广东一带,港资、台资和外资制造企业规模已经发展很大,模具的销售总量成为中国最多的地区。国际模协秘书长罗百辉表示,外资企业进入中国市场,不仅将资金带到中国市场,而且带来了先进的技术、设备和工厂管理。国外模具企业已越来越感受到来自中国同行所带来的影响和压力。 很多新兴的模具企业善于总结整个中国模具行业发展历程,从中吸取有价值的经验教训,并将其消化吸收在企业的设计规划和发展战略中。国际模协秘书长罗百辉表示,很多模具制造企业还很注重企业的品牌建设,注重企业的信息化建设,注重企业的国际化市场的开拓,并实现了模具的专业化生产。 我国模具行业前路该怎样走?据不完全统计,2004年国内模具进口总值达到600多亿,同时,有近200个亿的出口,如果我们把进口这一块吃下来,这将是很大的一块市场需求。国内模具企业要想获得良性的发展,体制转变和技术创新是提高模具行业水平的关键,同时也要解决好规模和效益的问题。 如何把模具行业的规模和效益做大 ?对于我国模具业,且抛开技术研发层面的问题不谈,我们先探讨一下如何通过行业内的分工合作、策略联盟共同把行业规模和效益做大。国内模具企业要想获得良性的发展,必须要解决好规模和效益的问题。 专家分析模具业将向多功能方向发展,国际模协秘书长罗百辉认为,我国模具行业将向大型、精密、复杂、高效、长寿命和多功能方向发展。随着车辆和电机等产品向轻量化方向发展,对压铸模的数量、寿命和复杂程度将提出越来越高的要求。随着以塑料代钢、以塑代木的发展和产品零件的精度和复杂程度的不断提高,塑料模的比例将不断提高,其精度和复杂程度也将随着相应提高。 采用高新技术提升我国模具工业水平,发展我国的模具工业,必须结合我国国情和提升模具工业实际,走新型工业化道路。从技术的发展来看,高精度、低成本、交货期短是今后模具发展的一个趋势,而我们要想赶上国际先进水平,技术创新是至关重要的一个环节。 信息化中国未来模具企业竞争焦点,众所周知,电子商务是代表着未来贸易发展的方向,也是经济发展和进步的一个必然趋势。在市场竞争逐步深入的时期,企业创新能力越来越成为企业竞争力的重要组成部分,信息资源也越来越成为企业的战略资源。 结语:目前,我国经济仍处于高速发展阶段,国际上经济全球化发展趋势日趋明显,这为我国模具工业高速发展提供了良好的条件和机遇。“十一五”期间中国模具工业发展迅速,产需两旺,渐入佳境。但也要看到我国模具行业综合水平落后的面貌未得到根本性的改变,一些深层次的问题尚待解决。现在,中国可以说是世界模具生产大国之一,但还远远不是生产强国。“十二五”期间,应该向生产强国这目标迈进。本课题要求对给定的零件进行冲压模设计,通过对零件进行详细的工艺分析确定零件的冲压工艺方案工艺。通过课题让我们能够掌握中等复杂程度零件的冲压模具设计和制造的一般方法,对零件冲压工艺方案的确定、工艺计算及模具设计有更深层次的认识,并学会对模具设计资料的检索与整合以及对已有资料的充分合理的使用,该实践性课题是对学生理论学习水平的实践和检验,可对以后从事类似的工作有一定的指导性和实践性意义。二、研究的基本内容和拟解决的主要问题本课题研究的主要内容 (1)对给定零件进行工艺分析并确定工艺方案 (2)模具总体结构设计及相关工艺计算 (3)进行模具零部件的设计 (4)绘制模具装配图和非标准件的零件图 (5)编写设计说明书课题研究的主要内容该零件的材料为20钢,较软的碳素钢,强度硬度很低,而韧性较高,有好的深冲、弯曲等冷加工性能性能。且该零件形状简单,弯曲半径大于材料允许的最小弯曲半径,可以考虑采用复合冲压的形式。该零件尺寸较小,因此加工精度较高,但一般冲压都能满足其尺寸精度的要求。综合以上分析,得出的结论是:该零件工艺性能较好,适于冲压。1)方案对比该工件包括落料、冲孔、弯曲三个基本工序可以采用以下三种工艺方案:方案一:落料冲孔复合-弯曲- -弯曲;方案二:落料冲孔复合一次弯曲;方案三:落料-弯曲-冲孔。2)方案分析方案一:该方案工序合理,步骤符合工件形状要求,生产效率不高,模具的两次弯曲操作复杂方案二:该方案经计算可冲孔落料复合完成,且不会致使弯曲过程中孔变形、生产效率高,且易于操作方案三:该方案在生产过程中需要三副模具,在后来工序中一步一步操作需要时间较多,且三副模具制作也不方便。3)方案确定比较上述三种工艺方案,方案二最佳。方案一、三均不能达到零件要求,(1) 通过对工件的工艺分析,确定工作的重点主要集中在模具工作部分零件的设计(例凸模,凹模,凸凹模),各种固定板的设计和相关尺寸的计算和校核。(2) 设计前后工序的关联性以及模具的关联性,合理安排工序,尽量使模具的结构更紧密,同时在模具的设计过程中还要考虑到所设计的零件的课加工性,要尽量多的选用标准件,达到规范化设计的要求成为此毕业设计的难点。针对此次模具设计工作量大,工作难度大的特点,拟采用计算机辅助设计AutoCAD、UG等相关软件来完成模具的设计,从而节省时间和精力;收集相关文献、期刊论文来加以辅助设计;针对自身理论方面的不足将更多的向辅导老师请教学习;当然,子啊具体的设计中也要不断的去实践设计的模具的实用性与经济性,使设计更趋于精确化,规范化,系统化。三、研究方法及措施(二)研究方法:1.文献资料法:通过查阅和收集关于冲压模具相关的文献材料。2.问卷调查法和实地考察:通过到工厂实际了解加工工艺方式,掌握研究的第一手资料。3.数理统计法:对获得的材料进行整理。(三)技术路线查阅及收集相关的文献资料实地走访企业工厂资料整理撰写论文四、研究工作的步骤、进度第一周 1、熟悉课题,查阅并收集有关资料,为写开题报告做准备; 2、绘制产品零件图; 3、完成工艺性分析,提出设计方案 4、写出开题报告,并完成其修改第二周 1、模具总体结构设计,及工艺结构计算 2、完成模具零件结构形式确定及设计,选择设备 3、绘制模具装配图和非标准零件零件图,第三周 1、拟定主要零件的制造工艺 2、编写毕业设计说明书,完成初稿并交与辅导老师指导第四周 1、针对毕业设计所出现问题有目的的修改确定终稿 2、准备毕业答辩五、主要参考文献(其中外文文献不少于2篇)1刘建超、张宝忠 主编. 冲压模具设计与制造M. 北京:高等教育出版社,2010 2夏琴香主编. 冲压成形工艺及模具设计M.广州:华南理工大学出版社,2004 3吴诗惇,李淼泉. 冲压工艺及模具设计M.西安:西北工业大学出版社,2002 4冲模设计手册编写组.冲模设计手册M.机械工业出版社,1999.6 5王孝培主编. 冲压设计资料M . 北京:机械工业出版社,1983 6李天佑主编. 冲模图册M. 北京:机械工业出版社,1990 7卢险峰编著.冲压工艺模具学M.北京:机械工业出版社,2003 8陈文彬,塑性成形工艺与模具设计M,北京,机械工业出版社,2001 9陈锦昌.计算机工程制图M.广州:华南理工大学出版社,200410钟翔山.冷冲模设计案例剖析M.北京:机械工业出版社,2009.11二代龙震工作室.冲压模具基础教程M.北京:清华大学出版社,201012张正修.冲模结构设计方法、要点及实例M.北京:机械工业出版社,200713邓明,吕琳.冲压成形工艺及模具M.北京:化学工业出版社,2007.14王鹏驹,成虹.冲压模具设计师手册M.北京:机械工业出版社2009.15牟林,胡建华.冲压工艺及模具设计M.北京:中国林业出版社,2006,16RajputRK.ElementsofMechanicalEngineering.KatsonPubl.House,1985 17Wang,C.T.AnIndustrialOutlookforSpringbackPredictability,MeasurementReliability,andCompensationTechnology,Proc.Numisheet2002,Oct.21-25,200,JejuIsland,Koera18R.D.JiangB.T.Lauw,A.Y.C.Nee.Insertdesignautomationforprogressivedies.Singapore:InstituteofHighPerformanceComputing,2004.06六、导师评语: 签字: 年 月 日外文翻译专 业 名 称 机械设计制造及其自动化班 级 学 号 078105232学 生 姓 名 冼 振 源指 导 教 师 陈 为 国填 表 日 期 2011 年 1 月 17 日General all-steel punching dies punching accuracyAccuracy of panel punching part is display the press accuracy of the die exactly. But the accuracy of any punching parts linear dimension and positional accuracy almost depend on the blanking and blanking accuracy,. So that the compound mould of compound punchings accuracy, is typicalness and representation in the majority.Analyse of the dies accuracy For the analyse of pracyicable inaccuracy during production of dies to inactivation, we could get the tendency when it is augmentation in most time. From this we could analyse the elements. When the new punch dies pt into production to the first cutter grinding, the inaccuracy produced called initial error; if the die grinding more than twenty times, until its discard, the inaccuracy called conventional error; and before the dies discard, the largest error of the last batch permit, called limiting error. at job site, the evidence to confirm life of sharpening is the higher of the blanking, punched hole or punched parts. Because all finished parts had been blanked ,so it is especially for the compound dies. Therefore, the analyse of burr and measurement is especially important when do them as enterprise standardization or checked with .The initial error usually is the minimal through the whole life of die. Its magnitude depend on the accuracy of manufacture, quality, measure of the punching part, thickness of panel, magnitude of gap and degree of homogeneity. The accuracy of manufacture depend on the manufacture process. For the 1 mm thicked compound punching part made in medium steel, the experimental result and productive practice all prove that the burr of dies which produced by spark cutting are higher 25%30% than produced by grinder ,NC or CNC. The reason is that not only the latter have more exact machining accuracy but also the value of roughness Ra is less one order than the formmer, it can be reached 0.025m. Therefore, the dies initial blanked accuracy depends on the accuracy of manufacture, quality and so on. The normal error of the punch die is the practicable error when the fist cutter grinding and the last cutter grinding before the die produce the last qualified product. As the increase of cutter grinding, caused the measure the nature wear of the dies are gradual increasing, the error of punching part increase also, so the parts are blew proof. And the die will be unused. The hole on the part and inner because the measure of wear will be small and small gradually, and its outside form will be lager in the same reason. Therefore, the hole and inner form in the part will be made mould according to one-way positive deviation or nearly equal to the limit max measure. In like manner, the punching parts appearance will be made mould according to one-way negative deviation or nearly equal to limit mini measure. For this will be broaden the normal error, and the cutter grinding times will be increased, the life will be long. The limit error in punching parts are the max dimension error which practicable allowed in the parts with limit error. This kind of parts usually are the last qualified products before the die discard.For the all classes of dies, if we analyse the fluctuate, tendency of increase and decrease and law which appeared in the dies whole life, we will find that the master of the error are changeless; the error that because the abrade of the cutter and impression will be as the cutter grinding times increased at the same time. And that will cause the error oversize gradually; and also have another part error are unconventional , unforeseen. Therefore, every die s error are composed of fixed error, system error, accident error and so on. 1. fixed error At the whole process when the New punching die between just input production to discard, the changeless master error that in qualified part are called fixed error. Its magnitude is the deviation when the die production qualified products before the first cutter grinding. Also is the initial error, but the die have initial punching accuracy at this time. Because of the abrade of parts, the die after grinding will be change the dimension error. And the increment of deviation will oversize as the times of cutter grinding. So the punching accuracy after cutter grinding also called “grinding accuracy” and lower tan initial accuracy. The fixed error depend on the elements factor as followed :(1) the material , sorts, structure, (form) dimension, and thick of panelthe magnitude of punching gap and degree of homogeneity are have a important effect for the dimension accuracy. Different punching process, material, thick of panel, have completely different gap and punching accuracy. A gear H62 which made in yellow brass with the same mode number m=0.34, 2mm thick and had a center hole, when the gap get C=0.5%t (single edge) , and punched with compound punching die, and the dimension accuracy reached IT7, the part have a flat surface ,the verticality of tangent plane reached 89.5, its roughness Ra magnitude are 12.5m, height of burr are 0.10mm; and the punching part are punched with progressive die, the gap C=7%t (single edge) , initial accuracy are IT11, and have an more rough surface, even can see the gap with eyes. In the usual situation, flushes a material and its thickness t is theselection punching gap main basis. Once the designation gap haddetermined flushes the plane size the fixed error main body; Flushesthe structure rigidity and the three-dimensional shape affects itsshape position precision.(2) punching craft and molder structure typeUses the different ramming craft, flushes a precision and the fixederror difference is really big. Except that the above piece gearexample showed, the essence flushes the craft and ordinary punching flushes a precision and the fixed error differs outside a magnitude,even if in ordinary punching center, uses the different gap punching, thefixed error difference very is also big. For example material thickt=1.5mm H62 brass punching, selects C = the 40%t unilateral I kind ofsmall gap punching compared to select C 4mm flushes, the size precision can lower some. Different dies structure type, because is suitable the rammingmaterial to be thick and the manufacture precision difference, causesto flush a fixed error to have leaves. Compound die center, multi-locations continuous type compound die because flushes continuously toduplicate the localization to add on the pattern making error to bebigger, therefore it flushes a fixed error compound punching die to wantcompared to the single location Big 1 2 levels (3) the craft of punching dies manufacturethe main work of punching die namely are raised, the concave moldprocessing procedure, to operates on the specification not to behigh, can time form a more complex cavity. But its processing surfaceapproximately is thick 0.03 0.05mm is the high temperatureablation remaining furcated austenite organization, degree ofhardness may reach as high as HRC67 70, has the micro crack, easilywhen punching appears broke the cutter or flaking. The Italian CorradaCorporations related memoir called the line cut the processing contruction to have the disadvantageous influence to the superficialgold, in fact already changed the gold contruction. We must use theJingang stone powder to grind or the numerical control continual pathcoordinates rub truncate (cut to line) to make the precision work . In recent years country and so on Switzerland and Japan, has conductedthe thorough research to the electrical finishing equipment and abigger improvement, makes function complete high accuracy NC and theCNC line cutter, the processing precision may reach 0.005 0.001mm,even is smaller. The processing surface roughness Ra value can achieve0.4 mu m. According to the recent years to the domestic 12 productionlines cutter factory investigation and study, the domesticallyproduced line cutter processing precision different factory differentmodel line cutter might reach 0.008 0.005mm, generally all in0.01mm or bigger somewhat, was individual also can achieve0.005mm, the processing surface roughness Ra value was bigger than1.6m. However, the electrical finishing ablation metal surface thus the change and the damage machined surface mental structure character can not change, only if with rubs truncates or other ways removes this harmful level. Therefore, merely uses electricity machining, including the spark cutting and the electricity perforation, achieves with difficulty punching, especially high accuracy, high life punching die to size precision and work components surface roughness Ra value request. With precisely rubs truncates the law manufacture punching die, specially makes the high accuracy, the high life punching die, such as: Thin material small gap compound punching die, multi- locations continuous type compound die and so on, has the size precision high, the work component smachined surface roughness Ra value is small, the mold life higher characteristic. Its processing craft at present changed the electrical fire by the past ordinary engine bed rough machining spark cutting or the electricity puncher rough machining, finally precisely rubs truncates, also from takes shape rubs, optics curve rubs, the manual grid reference rubs gradually filters the continual path grid reference to rub and NC and the CNC continual path grid reference rubs, Processing coarseness may reach 0.001 0.0005mm, the processing surface roughness Ra value may reach 0.1 0.025 mu m. Therefore, with this craft manufacture the die , regardless of the size precision, the work components surface roughness, all can satisfy die, each kind of compound request, the die is especially higher than the electrical finishing craft manufacture scale.(4) gap size and degree of homogeneity the flange and other sheet forming sgene rally all must first punching (fall material) the plate to launch the semi finished materials, after also has the forming to fall the material, the incision obtains the single end product to flush. Therefore punching the work, including is commonly used punching hole, the margin, cut side and so on, regarding each kind of sheet pressing partall is necessary. Therefore punching the gap to flushes a out form in chprecision to have the decisive influence. punching the gap small and is even, may cause punching the size gain high accuracy. Regarding drawability, is curving and so on mould, the gap greatly will decide increases flushes the oral area size error and the snapping back. The gapnon-uniformity can cause to flush a burr enlarges and incurs cutting edge the non-uniform attrition. (5) ramming equipment elastic deformation In the ramming process After the punch press load bearing can have the certain elastic deformation. Although this kind of distortion quantity according to flushes the pressure the size to change also to have the obvious directivity, but on the pressing part, mainly is to has the volume ramming archery target stamping, embosses, the equalization, the pressure is raised, the wave, flushes crowds, the shape, the flange, hits flatly, thinly changes draw ability and so on the craft work punching forming flushes, has the significant influence to its ramming aspect size precision普通全钢冲模的冲压精度分析板料冲压件的精度准确显示出其冲模的冲压精度。而任何冲件的线性尺寸精度与形位精度主要取决于冲模冲裁和立体成形冲压件展开平毛坯的落料精度。因此,多工步复合冲压的单工位复合模、多工位连续模的冲压精度,在普通冲压的众多种类与不同结构的冲模中,最具典型性和代表性。冲模的冲压精度分析对冲模投产至失效报废各个时期冲件的实际误差分析,可以看出其增大的时期及趋向,从而分析其增大的因素。新冲模投产至第一次刃磨前冲制冲件的误差即所谓的初始误差;冲模经过20次左右刃磨至失效报废前冲制的冲件误差称之为常规误差;而冲模失效报废前冲制的最后一批合格冲件的允许最大误差称之为极限误差。在现场,确定冲模刃磨寿命的依据是冲件冲孔与落料的毛刺高度。由于任何成形件都具有冲裁作业(毛坯落料或冲孔),对于复合模尤为如此。所以,冲件毛刺高度的触模检查和测量并按企业标准或JB4129-85冲压件毛刺高度对照检测就显得十分重要。冲模的初始误差通常是冲模整个寿命中冲件误差最小的。其大小主要取决于冲模的制造精度与质量及冲件尺寸、料厚以及间隙值大小与均匀度。冲模的制造精度及质量又取决于制模工艺。对于料厚t1mm的中碳钢复合冲裁模冲件,实验结果与生产实践都证明,电火花线切割制造的冲模冲件毛刺高度比用成型磨或NC与CNC连续轨迹座标磨即精密磨削工艺制造的冲模冲件要高25%30%。这是因为后者不仅加工精度高,而且加工面粗糙度Ra值要比前者小一个数量级,可达到0.025m。因此,冲模的制造精度与质量等因素决定了冲模的初始冲压精度,也造就了冲件的初始误差。冲件的常规误差是冲模经第一次刃磨到最后一次刃磨后冲出最后一个合格冲件为止,冲件实际具有的误差。随着刃磨次数的增加,刃口的自然磨损而造成的尺寸增量逐渐加大,冲件的误差也随之加大。当其误差超过极限偏差时,冲件就不合格,冲模也就失效报废。/冲件上孔与内形因凸模磨损尺寸会逐渐变小;其外形落料尺寸会因凹模磨损而逐渐增大。所以,冲件上孔与内形按单向正偏差标允差并依接近或几乎等于极限最大尺寸制模。同理,冲件外形落料按单向负偏差标注允差并依接近或几乎等于极限最小尺寸制模。这样就使冲件的常规误差范围扩大,冲模可刃磨次数增加,模具寿命提高。冲件的极限误差是具有极限偏差的冲件所具有的实际允许的最大尺寸误差。这类冲件通常是在冲模失效报废前冲制的最后一批合格冲件。对各类冲模冲件误差在冲模整个寿命中出现的波动、增减趋向及规律等进行全面分析便可发现:冲件误差的主导部分是不变的;因刃口或型腔的自然磨损而出现的误差增量随冲模刃磨冲数增加而使这部分误差逐渐加大;还有部分误差的增量是非常规的、不可预见的。所以,各类冲模冲件误差是由因定误差、渐增误差、系统误差及偶发误差等几部分综合构成。1、固定误差新冲模在指定的冲压设备上投入使用至失效报废的整个(总)寿命过程中,其合格冲件误差的主导部分固定不变即所谓固定误差。其大小就是新冲模第一次刃磨前冲制的合格冲件的偏差,也即冲模的初始误差,而此时的冲模具有初始冲压精度。刃磨后的冲模,因其工作零件(凸、凹模)磨损而改变尺寸误差,使冲件识差增量随刃磨次数增加而逐渐加大,故冲模刃磨后的冲压精度亦称“刃磨精度”比其初始精度要低。冲模冲件的固定误差取决于以下各要素:(1)冲件的材料种类、结构(形状)尺寸及料厚冲裁间隙的大小及其均匀度对冲裁件的尺寸精度有决定性的影响。不同冲裁工艺、不同材料种类与不等料厚,间隙相差悬殊,冲压精度差异很大。同一种模数m=0.34的2mm的料厚、中心有孔的H62黄铜材料片齿轮复合模冲件,当取间隙C=0.5%t(单边),用复合精冲模冲制,冲件尺寸精度达到IT7级,冲件平直无拱弯,冲切面垂直度可达89.5,其表面粗糙Ra值为0.2m;而用普通复合模冲制,间隙C=5%t(单边),冲件初始误差亦即冲模的初始冲压精度为1T9级,冲切面粗糙度Ra值为12.5m,毛刺高度为0.10mm;还是这个冲件用连续模冲制,间隙C=7%t(单边),初始冲件精度为IT11级,冲切面更粗糙,甚至有肉眼可见的台阶。通常情况下,冲件材料及其厚度t是选取冲裁间隙的主要依据。一旦选定间隙就确定了冲件的平面尺寸的固定误差的主体;冲件结构刚度及立体形状则影响其形位精度。(2)冲压工艺及冲模结构类型采用不同的冲压工艺,冲件的精度及固定误差相差甚大。除上述片齿轮实例说明,精冲工艺与普通冲裁的冲件精度与固定误差相差一个数量级之外,即便在普通冲裁中,采用不同间隙冲裁,固定误差相差也很大。例如料厚t=1.5mm的H62黄铜冲裁件,选用C40%t单边类小间隙冲裁比选用C8%t(单边)类大间隙冲裁,冲件固定误差将加大40%60%,精度至少降一级。此外,采有无搭边排样,冲件的误差要远大于有搭边排样冲件。无搭边排样冲件。无搭边排样冲件的精度低于IT12级,而多数有搭边排样的冲件精度在IT11IT9级之间,料厚t4mm的冲件,尺寸精度会更低一些。不同冲模结构类型,由于适用冲压料厚及制造精度的差异,导致冲件的固定误差有别。复合模中,多工位连续式复合模由于冲件连续重复定位加上制模误差较大,故其冲件的固定误差比单工位复合冲裁模要 大12级。(3)冲模制造工艺冲模主要工作零件即凸、凹模的加工程序,对操作上的技术要求不高,能够一次成形较复杂的模腔。但其加工表面约厚0.030.05mm为高温烧蚀的残余树枝状奥氏体组织,硬度可高达HRC6770,有显微裂纹,容易在冲裁时出现崩刃或剥落。意大利Corrada公司的有关研究报告称“线切割加工对表面金相结构产生不利的影响,实际上已经改变了金相结构。我们必须用金刚石粉研磨或数控连续轨迹坐标磨削(对线切割件)作精加工”。近年来瑞士和日本等国,对电加工设备进行了深入的研究和较大的改进,制造出功能齐全的高精度NC和CNC线切割机,加工精度可达0.0050.001mm,甚至更小。加工表面粗糙度Ra值能达到0.4m。根据近年对国内12家生产线切割机工厂的调研,国产线切割机加工精度各别厂家的各别型号线切割机可达0.0080.005mm,一般都在0.01mm或更大一些,个别也能达到0.005mm,加工表面粗糙度Ra值均大于1.6m。然而,电加工烧蚀金属表面从而改变和损坏加工面金相结构的特性不会改变,除非用磨削或其他加工法去除这一有害层。所以,仅仅用电加工法,包括电火花线切割与电穿孔,难以达到冲模,尤其高精度、高寿命冲模对尺寸精度与工作零件表面粗糙度Ra值要求。用精密磨削法制造冲模,特别是制造高精度、高寿命冲模,诸如:薄料小间隙复合冲裁模、多工位连续式复合模等,具有尺寸精度高、工作零件加工面粗糙度Ra值小、模具寿命高等特点。其加工工艺目前已由过去的普通机床粗加工改为电火花线切割或电穿孔机粗加工,最后精密磨削,也由成型磨、光学曲线磨、手动座标磨逐步过滤到连续轨迹座标磨及NC与CNC连续轨迹座标磨,加工粗度可达0.0010.0005mm,加工表面粗糙度Ra值可达0.10.025m。所以,用该工艺制造的冲模,无论尺寸精度、工作零件表面粗糙度,都能满足冲模,尤其各种复合模的要求,比电加工工艺制造的冲模高一个档次。(4)间隙的大小与均匀度拉深、弯曲、翻边及其他板料成形件一般都要先冲裁(落料)出平板展开毛坯,也有成形后落料、切开得到单个成品冲件。故冲裁作业,包括常用的冲孔、切口、切边等,对于每种板料冲压件都是必要的。所以冲裁间隙对冲件的外廓尺寸精度有决定性的影响。冲裁间隙小而均匀,可使冲裁尺寸获取更高精度。对于拉深、弯曲等成形模,间隙大定将增大冲件口部尺寸误差及回弹。间隙不均匀会使冲件毛刺加大并招致刃口的不均匀磨损。(5)冲压设备的弹性变形在冲压过程中,冲床承载后会产生一定的弹性变形。虽然这种变形量依冲压力的大小变化且具有明显的方向性,但就冲压件,主要是对具有体积冲压性质的压印、压花、校平、压凸、起波、冲挤、镦形、翻边、镦粗、打扁、变薄拉深等工艺作业冲制成形的冲件,对其冲压方面的尺寸精度有重大影响。
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