0137-中叶板零件冲压工艺与冲模设计【全套13张CAD图】
0137-中叶板零件冲压工艺与冲模设计【全套13张CAD图】,全套13张CAD图,中叶,零件,冲压,工艺,冲模,设计,全套,13,cad
.毕业设计(论文)开题报告题目 中页板零件冲压工艺及模具设计.一、选题的依据及意义:设计的主要目的是:通过对产品的分析设计适合的模具,利用安装在压力机上的冲模对金属板材进行塑性变形加工以得到符合设计要求和使用要求的产品零件;检验对所学相关课程理论、技能的理解程度;培养理论联系实际的良好作风。设计的主要意义是:通过此次设计了解设计冲压模的一般程序,了解相关的理论知识并加以应用和巩固;熟练的运用有关技术资料,如冷冲模国家标准、模具设计与制造简明手册、冷冲压模具结构图册及其他有关规范等;初步的掌握设计冷冲压模具的能力,为将来的工作打下初步的基础。二、国内外研究概况及发展趋势(含文献综述):随着制造行业的发展,材料加工方法也随着发展,其中冷冲压加工方法在制造行业得到了广泛的发展,特别在汽车制造行业。随着冷冲压加工方法的应用,许多汽车零件的外形和精度得到了改善。侧减震片的加工方法也得到了发展,最后由冷冲压加工而成。最近的几年里,冷冲压加工方法得到了广泛的发展。冷冲压(cold pressing)是建立在金属塑性变形的基础上,在常温下利用安装在压力机上的模具对材料施加压力,使其产生分离或塑性变形,从而获得一定形状、尺寸和性能的零件的一种加工方法。在冷加工中,将材料(金属或非金属)加工成零件(或半成品)的一种特殊工艺装备,称为冷冲压模具(俗称冷冲模)。冷冲模在实现冷冲压加工中是必不可少的工艺装备,没有先进的模具技术,先进的冲压工艺就无法实现。随着国民经济的高速发展、冲压技术的发展和新型模具材料的不断研究开发,市场对模具的需求量不断增长,模具的结构也发生了一定的变化,对模具的制造,装配等都有了很大的影响。近年来,模具工业一直以15%左右的增长速度快速发展。模具是机械制造业中技术先进、影响深远的重要工艺装备,具有生产效率高、材料利用率高、制件质量优良、工艺适应性好等特点,被广泛应用于汽车、机械、航天、航空、轻工、电子、电器、仪表等行业。中国模具的“珠江三角洲、长江三角洲和以成都/重庆为代表的西部模具”三足鼎立局面已经基本形成,然而与国际先进水平相比,中国的模具行业的差距不仅表现在精度差距大、交货周期长等方面,模具寿命也只有国际先进水平的50%左右,大型、精密、技术含量高的轿车覆盖件冲压模具和精密冲裁模具,每年都需要花费大量资金进口。一、经过几十年的发展,我国的冲压模具行业获得了飞速发展,具体体现在:(1)辅助设计/加工/工程技术得到广泛使用,模具总量名列世界第三位。(2)大型模具企业拥有高速数控加工/加工中心/数控机床等先进的加工工艺与装备,可以开展RP/RT或模具逆向工程工作,硬件装备已经站在了与世界基本同步的水平线上。(3)在冲模的表面精整加工技术方面,开展了积极探索、积累了一些经验。(4)以汽车覆盖件为代表的大型、复杂、精密冲压模具,采用CAD /CAM /CAE软件进行三维设计和模拟,减少试模时间和缩短周期。借助高速、精密的加工设备加工生产,获得良好的尺寸精度和表面粗糙度,用新型的研磨或抛光方法代替传统的手工研磨抛光,提高模具质量1。这些都代表了冲压模具发展的趋势。例如,吉林大学汽车覆盖件成型技术所独立研制的汽车覆盖件冲压成型分析KMAS软件,华中理工大学模具技术国家重点实验室开发的注塑模、汽车覆盖件模具和级进模CAD/CAE/CAM软件,上海交通大学模具CAD国家工程研究中心开发的冷冲模和精冲研究中心开发的冷冲模和精冲模CAD软件等在国内模具行业拥有不少的用户。二、国际模具制造业的技术特点如下:(1)产品专业化车身模具企业向专业化发展,如德国大众公司模具厂、奥迪公司模具厂、SCHULLER公司,意大利COMAU公司,美国AUTODIE、SECKLY,日本丰田公司模具厂、荻原公司、富士公司,韩国现代汽车模具中心等。有的专业制造整体侧围模具,有的专业生产四门模具,有的专门生产地板及结构件模具。模具向多工位自动化以及级进模方向发展。(2)制造数字化三维实体设计广泛应用于模具制造中,二维DL图转为三维DL图后可直接用于有限元分析和数控编程,百分之百采用CAE分析。模具设计采用3D参数化设计。实现了不等厚板成形模具设计,将同模模具推向生产。模具数控加工技术包括实型铸造技术、精细化编程、高速加工技术、型面数控强化和修补技术2。 三、冲压模具制造技术发展趋势:(1)制造冲压件用的传统金属材料,正逐步被高强钢板、涂敷镀层钢板、塑料夹层钢板和其他复合材料或高分子材料替代。随着材料科学的发展,加强研究各种新材料的冲压成形性能,不断发展和改善冲压成形技术。 (2)精冲与半精冲、液压成形、旋压成形、爆炸成形、电水成形、电磁成形、超塑成形等技术得到不断发展和应用,某些传统的冲压加工方法将被它们所取代,产品的冲压加工趋于更合理、更经济。其中精密冲裁技术得到了较快发展,精密冲裁是一种先进制造技术,可取代某些零件的切削加工,具有优质、高效、低耗、应用广的特点。以齿圈压板精冲而论,在普通液压机上进行精冲,工艺装备简单而工件精密3。它以金属板材为原料,采用少无切削的塑性加工方法,一次成形即可得到尺寸精度高、剪切面粗糙度低的零件,采用精冲技术生产的零件称为精冲、件4。(3) 随着计算机图形技术的发展成熟,近年来在冲压成形领域兴起了计算机辅助设计(CAD)、计算机辅助工程(CAE)和计算机辅助制造(CAM)技术。该技术的出现对传统冲压技术的变革产生了重要的影响。尤其是板料成形数值模拟技术的出现,使板料冲压成形技术彻底摆脱了“经验”和“定性”的水平,进入了“科学”和“定量”的发展阶段。采用这一技术进行板材冲压成形工艺过程的模拟,可以预知冲压成形过程中金属的流动、应力应变及厚度场的分布、模具受力及皱曲、破裂、冲击线等可能的缺陷及失效形式。这为优化工艺参数和模具结构提供了极为有效的工具,在减少甚至取消试模过程,缩短产品开发周期,降低产品开发成本方面发挥着越来越重要的作用,已逐渐成为指导模具设计和优化的重要手段5。 (4)高速铣削加工,国外近年来发展的高速铣削加工,大幅度提高了加工效率,并可获得极高的表面光洁度。另外,还可加工高硬度模块,还具有温升低、热变形小等优点。高速铣削加工技术的发展,对汽车、家电行业中大型型腔模具制造注入了新的活力。目前它已向更高的敏捷化、智能化、集成化方向发展。 (5)模具扫描及数字化系统,高速扫描机和模具扫描系统提供了从模型或实物扫描到加工出期望的模型所需的诸多功能,大大缩短了模具的在研制制造周期。有些快速扫描系统,可快速安装在已有的数控铣床及加工中心上,实现快速数据采集、自动生成各种不同数控系统的加工程序、不同格式的CAD数据,用于模具制造业的“逆向工程”。模具扫描系统已在汽车、摩托车、家电等行业得到成功应用,相信在“十五”期间将发挥更大的作用。 (6)优质材料及先进表面处理技术,选用优质钢材和应用相应的表面处理技术来提高模具的寿命就显得十分必要。模具热处理和表面处理是否能充分发挥模具钢材料性能的关键环节。模具热处理的发展方向是采用真空热处理。模具表面处理除完善应发展工艺先进的气相沉积、等离子喷涂等技术。四、冲压在机械制造中的地位及特点:冲压既能够制造尺寸很小的仪表零件,又能够制造诸如汽车大梁、压力容器封头一类的大型零件;既能够制造一般尺寸公差等级和形状的零件,又能够制造精密(公差在微米级)和复杂形状的零件。占全世界钢产60%70%以上的板材、管材及其他型材,其中大部分经过冲压制成成品。冲压在汽车、机械、家用电器、电机、仪表、航空航天、兵器等制造中,具有十分重要的地位。 冲压件的重量轻、厚度薄、刚度好。它的尺寸公差是由模具保证的,所以质量稳定,一般不需再经机械切削即可使用。冷冲压件的金属组织与力学性能优于原始坯料,表面光滑美观。冷冲压件的公差等级和表面状态优于热冲压件6。 冲压生产的工艺和设备正在不断发展,除传统的使用压力机和钢制模具制造冲压件外,液压成形以及旋压成形、超塑成形、爆炸成形、电水成形、电磁成形等各种特种冲压成形工艺亦迅速发展,把冲压的技术水平提高到了一个新的高度。特种冲压成形工艺尤其适合多品种的中小批量(甚至是数十件)零件的生产。对于普通冲压工艺,可采用简易模具、低熔点合金模具、成组模具和冲压柔性制造系统等,组织多品种的中小批量零件的冲压加工。 总之,冲压模具具有生产率高、加工成本低、材料利用率高、操作简单、便于实现机械化与自动化等一系列优点。采用冲压与焊接、胶接等复合工艺,使零件结构更趋合理,加工更为方便,可以用较简单的工艺制造出更复杂的结构件。三、研究内容及实验方案: 研究内容:1了解模具的工作过程;2懂得利用工具手册查找模具的标准;3自主设计中页板卷圆成型模具;4拟写设计说明明书;采用的设计方案及技术路线有:1、根据图纸对“中页板”进行工艺分析;2、对零件材料进行弯曲性能分析并确定毛坯形状,尺寸和下料方式;3、审查制件是否符合冲压结构工艺性以及冲压的经济性;4、拟定工艺方案,在分析工艺性的基础上,确定冲压件的总体工艺方案,然后确定冲压加工工艺方案;5、根据零件在生产中的具体要求合理地确定冲裁间隙;6、冲压工艺计算及设计:(1)排样及材料利用率的计算,选择合理的排样方式,决定出搭边值,并确定出条料的宽度,并力求取得最佳的材料利用率;(2)冲压力,冲压中心计算及冲压设备初步选择;7、分析冲压工序所的冲压件的冲压成形的工艺性能并在此基础上制定冲压成形工艺方案;8、进行主要参数计算:(1)毛坯尺寸计算;(2)压力中心计算;(3)弯曲力计算;9、弯曲模结构设计:(1)确定模具类型;(2)工作零件设计;(3)定位零件设计;(4)卸料,出件及压料零,部件设计;(5)弹簧和橡胶零件设计;(6)导向及支承固定零件设计;(7)确定模具的闭合高度;(8)对以上设计零件进行组装并检验和修改零,部件结构;(9)最后确定模具的整体结构;13、绘制弯曲模装配图;14、绘制弯曲模零件图15、编写技术文件及说明书。四、目标、主要特色及工作进度工作内容及完成时间:1. 查阅相关资料,外文资料翻译(6000字符以上),撰写开题报告。第1周第2周2. 绘制中叶板冲件图,分析冲件成形工艺及坯料展开 第3周第6周3. 编制中叶板冲压成形工艺规程; 第7周第8周4. 绘制吊中叶板卷圆成形模总装图及零件图; 第9周第13周5. 撰写毕业设计说明书(论文) 第14周第16周6. 毕业设计审查,毕业答辩。 第17周模具的设计中可能存在的问题:1、冲压模的间隙选择不当,进而影响冲裁件断面质量,冲裁件尺寸精度,冲裁力,卸料力,推料力,顶料力,模具的寿命;2、模具压力中心确定不当,模具在工作中产生偏弯距,使冲模发生歪斜,从而会加速模具磨损,影响模具的寿命;3、冲裁件的质量及影响因素;4、排样方式选择不当,影响材料利用率;5、冲裁尺寸的计算和确定的误差分析;6、模边值确定不当,进而影响制件的合格性;7、弯曲力不适当,进而造成弯曲变形的回弹或出弯曲缺陷;8、冲裁件与弯曲件之间计算不当造成尺寸精度低。五、参考文献1、刘胜国,我国冲压模具技术的现状与发展,黄石理工学院机电工程学院,黄石理工学院学报,2007年1期;2、朱伟成,冲压技术发展趋势,中国第一汽车集团公司,汽车工艺与材料,2007年1期;3、冲模设计手册编写组.冲模设计手册.北京:冲模设计手册,19954、陈为国. 铰链卷圆成形工艺及模具设计.模具工业,1998.7 5、王新华,袁联富编.冲模结构图册.北京:机械工业出版社,2003 6、罗益旋.冲压新工艺新技术及模具设计实用手册. 银声音像出版社,20047、GB28512875冷冲模国家标准 中叶板零件冲压工艺与冲模设计摘要:模具是工业产品生产用的重要工艺设备,模具工业已是工业发展的基础,许多新产品的开发和研制在很大程度上都依赖与模具的生产。可以预言,随着工业生产的不断发展,模具工业在国民经济中的地位将日益提高,并在国民经济发展过程中发挥越来越重要的作用。在冲压零件的生产中,合理的冲压成形工艺、先进的模具、高效的冲压设备是必不可少的三要素 。 本文介绍了止动件冲压模具的设计,先介绍了对工件进行工艺分析和模具设计的要点,然后介绍了模具设计的思路,模具的主要结构和主要零件的设计。最后确定了选用冲孔落料复合模。本次设计绘图采用AotuCAD,以AotuCAD为计算机辅助制图工具,使用简单,方便快捷,而且有极强的图形处理功能,可以大大缩短绘图的周期,在国内使用的较广泛。关键词:冲压模具 落料 冲裁预弯 剪裁 卷圆stamping process and die design of hinge Vol yenABSTRACT :The mold was the important process unit which the manufactured products production used, the mold industry already is the industrial development foundation, many new products developments and the development relied on to a great extent with molds production. May predict that along with industrial productions unceasing development, the mold industry will enhance day by day in national economys status, and plays more and more vital role in the national economy developing process. In the ramming components production, the reasonable ramming forming craft, the advanced mold, the highly effective ramming equipment are the essential three essential factors. Ramming processing characteristic: Because the cold stamping processing has the above prominent merit, therefore obtained the widespread application in the volume production, holds the very important status in the modern industry production, is the defense industry and in the consumer industry production the essential processing method. this article introduced the lock ramming molds design, introduced first carries on the process study and the mold design main point to the work piece, then introduced the mold design mentality, molds primary structure and the major parts design. Finally had determined selects the punch holes to fall the material superposable die. the this design cartography uses AotuCAD, take AotuCAD as the computer auxiliary charting tool, the use is simple, facilitates quickly, and has the greatly strengthened graphic processing function, may reduce cartography greatly the cycle, in domestic use widespread. key word: Stamping die falls the material Blanking of Preflex ClippingVol yenSignature of Supervisor: 外文翻译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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