模具硬度对高强度钢板拉毛缺陷的影响规律研究

高强度钢板的使用减轻了车身重量,但也引起了大面积的车身覆盖件拉毛缺陷。为提高汽车覆盖件的表面质量,文章在冲压现场调研及模拟实验的基础上,重点讨论拉深模具表面硬度对车身覆盖件表面拉毛缺陷的影响。研究表明,在覆盖件冲压中,板料拉毛缺陷主要起源于凹模圆角及拉深筋附近处,出现在冲压件的外壁;随着冲压次数的增加,零件拉毛越来越严重,拉毛增长速度越来越快。凹模圆角是磨损最严重的区域,模具法兰的表面粗糙度在冲压成形中变化不大;模具表面硬度越高,零件表面越不易产生拉毛缺陷。     

薄板成形中模具硬度对拉毛影响的实验研究

借助带拉深筋的盒形件拉深工艺,模拟高强度钢板成形中的覆盖件表面拉毛行为.用表面粗糙度Ra和最大划痕深度H来定量评价冲压件拉毛程度.实验研究表明:随着拉深次数的增加,Ra值和H值越来越大,并且在成形前期和后期其数值增长速度较快;同时,Ra值和H值随模具硬度的降低而增大,即模具的硬度越低,越易于产生拉毛缺陷.     

模具拉毛及处理方法

在汽车冲压件拉伸成形过程中,模具拉毛现象十分普遍,造成冲压件质量缺陷。而冲压件质量要求十分严格,任何微小的拉毛缺陷都会影响油漆件的质量,并降低其抗腐蚀性、缩短使用寿命。拉毛现象对于生产效率也有很大的影响,同时也造成生产成本的提升。拉毛现象是冲压行业一直存在的问题,也是一个老大难问题。通过合理的模具表面处理方法,才能提高模具的寿命和抗拉毛性能,降低废品率和生产成本,对汽车工业具有重要意义。     

冲压成形拉毛机理与控制方法的研究应用

通过对冲压成形的应力应变、板料拉毛磨损类型、成形拉毛等特点的论述,多方面地总结了板料拉毛的影响因素,结合冲压生产的实践验证,提出了解决板料拉毛有效措施,以期与同行共同分享与研讨。     

后轮罩拉伸模设计制造及其型面激光强化处理

介绍了后轮罩拉伸成形中出现的成形困难、回弹严重和表面拉毛3大技术难点的解决方法,其中,尤其对MOCR合金铸铁模面进行激光相变强化处理,进行了深入的探索,希望找到一种新的解决模具拉毛问题的途径。     

三维轴线后副车架纵梁内高压成形工艺

利用非线性有限元分析软件AutoForm,对三维轴线的底盘后副车架纵梁进行弯管、预成形、内高压成形的全过程分析,根据零件非对称和不等截面的几何特征,确定零件工艺参数和加载路径,并分析预成形过程中的零件表面拉毛缺陷。同时,针对不同壁厚(4.0和4.5 mm)的纵梁管坯,通过采用相同的工装模具和不同的内高压成形工艺参数,验证了内高压成形零件型面的一致性。结果显示:壁厚为4.0和4.5 mm的纵梁分别经170和200 MPa的内压力,得到的纵梁零件型面差异最大为±0.3 mm,型面一致性较好。通过对预成形镶块进行渗氮+PVD的表面处理试验后,镶块表面硬度达到3000 HV以上,降低了摩擦系数,有效解决了零件的外观拉毛问题,改善了纵梁零件的表面质量,最终通过试验验证了采用内高压成形工艺制造三维轴线纵梁零件的可行性。     

先进高强度钢板的冲压成形特性及其应用

文章在研究高强度钢板成形特性、回弹特性以及拉毛特性的基础上,深入探讨了先进高强度钢板冲压过程的变形特征。研究结果表明,与传统HSLA钢板相比,DP钢和TRIP钢具有较好的应变均化能力,和较高的成形性,有利于提高零件的使用强度。钢种特性和材料参数对回弹影响显著,使先进高强度钢板尺寸精度控制难度加大。当钢板强度升高时,高强度钢板表现出更易产生拉毛的趋势。     

关于汽车冲压件翻边工艺及质量的研究

翻边成形容易出现翻边变形、拉毛和开裂问题，本文从11个方面阐述了翻边成形工艺知识及改进措施，对汽车冲压模具从业人员有一定的借鉴意义。     

不锈钢弹簧片拉伸成形缺陷的分析

介绍了不锈钢弹簧片拉伸成形模的结构特点，并对不锈钢弹簧片拉伸成形面引起的拉毛原因和改进方法作了说明。     

铝框冲压件软模成形过程的数值模拟

钣金成形过程中常会发生起皱、开裂缺陷,采用数值模拟技术进行钣金成形过程仿真,可修正模具设计,是开展精密成形的方法之一。针对模拟结果中工件出现的缺陷,提出了初步的改进方案,以橡皮囊液压成形为例,对成形过程的零件厚度变化、应力分布、起皱进行了数值仿真研究,从而控制了板料成形过程的缺陷,进一步修正了模具和板料,实现了无余量装配。     

Quantification of galling in sheet metal forming by surface topography characterisation

One of the major problems in forming of stainless steel sheet is galling due to lubricant film breakdown leading to scoring and bad surface quality. In a Danish research programme new lubricants substituting the normally applied chlorinated paraffin oils are being developed and tested for this purpose. In order to determine the limits of lubrication of these new lubricants, as well as commercial ones already available on the market, two sheet forming tests have been developed. Quantification of the degree of galling is done by roughness measurements on the workpiece surface. In a strip reduction test, this is done by 2D profilometry at strip locations corresponding to different sliding lengths, whereas a deep drawing test is based on 3D roughness mapping of local areas.     

Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings — Evaluation of galling and wear characteristics against different high strength steels

The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency of galling in sheet metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potential performance of three commercial PVD coatings, including CrN, (Ti,Al)N and a CrC/C DLC-based coating, in the forming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steel has been evaluated using pin-on-disc testing under lubricated contact conditions. Post-test examination of the tribosurfaces using FEG-SEM and EDS analyses was performed in order to evaluate the mechanisms controlling the tendency to material transfer and wear. The results show that in contact with the hot and cold rolled steel the material pick-up tendency of the PVD coatings tend to increase in the order CrC/C-CrN-(Ti,Al)N while in contact with the two galvanized steel sheets, the CrC/C and the (Ti,Al)N coating show a significantly lower material pick-up tendency as compared with the CrN coating. Further, the substrate hardness has a strong influence on the wear of the PVD coatings and consequently on the friction characteristics and galling tendency of the coating/substrate composite. Low substrate hardness, resulting in a low load bearing capacity, increases the tendency to cracking and subsequently chipping of the brittle coating.     

Prediction of limits of lubrication in strip reduction testing

Pick-up and galling due to lubricant film breakdown is a severe limitation in cold forming of tribologically difficult metals like stainless steel and aluminium. The present paper describes a method of combined experimental and numerical analysis to quantify the limits of lubrication in a dedicated simulative strip reduction test. The limit of lubrication is quantified as the threshold drawing length before galling occurs. A numerical model of the test is established calculating tool/work piece interface temperatures and normal pressures. Identifying a critical maximum value of the interface temperature the results show good agreement between numerically predicted and experimentally observed threshold drawing lengths at different test conditions.     

高强度钢板汽车纵梁拉毛常见原因分析及处理措施

详细分析了高强度钢板汽车纵梁产生拉毛的原因,并针对拉毛原因从优化纵梁结构、冲模结构、模具材料选择、热处理工艺选择、表面热处理等方面提出了相对应的处理措施。实践证明,优化产品结构,提高模具表面硬度、抗磨损性和抗粘附性,对模具表面进行镀铬、TD处理、PVD处理等表面强化处理,可有效解决拉毛问题。     

铝合金管材挤压时内表面擦伤的形式及危害

铝合金管材挤压时的内表面擦伤,是我国铝加工界的“老大难”问题之一。结合生产实际,按照擦伤缺陷的形貌和形成机制,将其归纳为：纵向直务状控伤、螺旋纹状擦伤、石墨压人、点状擦伤等四种形式,并分析了擦伤的危害。     

重卡花键毂镦锻工艺仿真及优化

针对重卡花键毂闭式镦锻工艺存在纵向飞边、毛刺等问题,通过分析锻件成形工艺,提出整体式和可分式两种镶块模具结构,基于可分式凹模的开式镦锻模具结构,制定了分模面位置在花键毂最大轮廓端部前端面和端部中间两种成形方案,并和整体式凹模成形方案作出对比分析。借助DEFORM-3D软件对两种成形方案进行模拟,根据损伤值大小、应力、应变等对比分析了两种方案的优劣性。结果表明,采用可分式凹模可以有效地解决花键毂横向飞边的存储问题,分模面位置在端部中间时能有效解决切边后的"拉毛刺"问题。最终通过花键毂的实际生产验证了可分式凹模结构且中间分模方案的合理性。     

Evaluation of tool materials, coatings and lubricants in forming galvanized advanced high strength steels (AHSS)

The major objective of this study is to establish guidelines to select the optimum combination of die materials, coatings and lubricants in stamping galvanized AHSS (DP600, TRIP780 and DP980) for automotive structural parts. For this purpose, Finite Element Analysis (FEA) and various tribotests, e.g. Twist Compression Test (TCT), Deep Drawing Test (DDT) and Strip Drawing Test (SDT), were used. The results of this study helped to determine the critical interface pressure and temperature that initiate lubricant failure and galling in forming galvanized AHSS for a given die material and coating.     

某井N80钢级套管脱扣和粘扣原因分析

对某井Φ139.7mm×7.72mm N80钢级长圆螺纹套管脱扣和粘扣事故进行了详细的调查研究。分析认为套管发生脱扣的原因主要是由于下套管上扣时螺纹接头发生严重粘扣,使其连接强度大幅度降低所致。该井井口中心与管柱轴线偏离较多,且采用钻杆液压钳下套管,在上扣过程中套管接箍严重夹持变形,外螺纹接头与严重夹持变形的接箍上扣配合之后导致套管严重粘扣损坏。套管严重粘扣还与套管本身抗粘扣性能差有一定关系。