General all-steel punching die’s punching accuracy
Accuracy of panel punching part is display the pre 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 punching’s accuracy, is typicalne and representation in the majority.Analyse of the die’s 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 it’s 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, thickne of panel, magnitude of gap and degree of homogeneity.The accuracy of manufacture depend on the manufacture proce.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 roughne Ra is le one order than the formmer, it can be reached 0.025μm.Therefore, the die’s 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 part’s 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 claes of dies, if we analyse the fluctuate, tendency of increase and decrease and law which appeared in the die’s whole life, we will find that the master of the error are changele; the error that because the abrade of the cutter and impreion 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 proce when the New punching die between just input production to discard, the changele master error that in qualified part are called fixed error.It’s 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 panel
the magnitude of punching gap and degree of homogeneity are have a important effect for the dimension accuracy.Different punching proce, material, thick of panel, have completely different gap and punching accuracy.A gear H62 which made in yellow bra 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 roughne Ra magnitude are 12.5μm, height of burr are 0.10mm; and the punching part are punched with progreive 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 thickne 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 ithape position precision.(2) punching craft and molder structure type
Uses the different ramming craft, flushes a precision and the fixederror difference is really big.Except that the above piece gearexample showed, the eence 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 bra punching, selects C 4mm flushes, the size precision can lower some.Different die’s 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 die’s manufacture
the main work of punching die namely are raised, the concave moldproceing procedure, to operates on the specification not to behigh, can time form a more complex cavity.But its proceing surfaceapproximately is thick > 0.03 ~ 0.05mm is the high temperatureablation remaining furcated austenite organization, degree ofhardne may reach as high as HRC67 ~ 70, has the micro crack, easilywhen punching appears broke the cutter or flaking.The Italian CorradaCorporation\'\'s related memoir called \"the line cut the proceing contruction to have the disadvantageous influence to the superficialgold, in fact already changed the gold contruction.We must use theJin\'\'gang 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 proceing precision may reach ±0.005 ~ 0.001mm,even is smaller.The proceing surface roughne 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 proceing precision different factory differentmodel line cutter might reach ±0.008 ~ ±0.005mm, generally all in±0.01mm or bigger somewhat, was individual also can achieve±0.005mm, the proceing surface roughne Ra value was bigger than1.6μm.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 roughne 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 roughne Ra value is small, the mold life higher characteristic.Its proceing 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, Proceing coarsene may reach ±0.001 ~ 0.0005mm, the proceing surface roughne Ra value may reach 0.1 ~ 0.025 mu m.Therefore, with this craft manufacture the die , regardle of the size precision, the work components surface roughne, 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 preing partall is neceary.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 proce After the punch pre load bearing can have the certain elastic deformation.Although this kind of distortion quantity according to flushes the preure the size to change also to have the obvious directivity, but on the preing part, mainly is to has the volume ramming archery target stamping, emboes, the equalization, the preure 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t≤1mm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0.025μm。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0.2μm；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12.5μm，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C≤40%t单边Ⅰ类小间隙冲裁比选用C≤8%t（单边）Ⅲ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IT11～IT9级之间，料厚t＞4mm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1～2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＞0.03～0.05mm为高温烧蚀的残余树枝状奥氏体组织，硬度可高达HRC67～70，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±0.005～0.001mm，甚至更小。加工表面粗糙度Ra值能达到0.4μm。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±0.008～±0.005mm，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1.6μm。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±0.001～0.0005mm，加工表面粗糙度Ra值可达0.1～0.025μm。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。
