点焊拼接板的概率化成形极限图及其应用

成形极限图是评定金属薄板成形性能最为简单和直观的方法,是解决板冲压问题的一个非常有效的工具.本文根据点焊拼接板的特点提出了概率化成形极限图P-FLD,并采用MSC.Dytran有限元分析软件对点焊拼接板的胀形及拉深过程进行模拟研究,得到了点焊拼接板成形时的应变分布.将点焊拼接板的P-FLD和有限元模拟的零件应变分布点结合起来,得到零件应变极限图,从而为初步选材和确定冲压零件的安全裕度提供了参考.     

冲压变形对点焊拼接板中焊点的影响

点焊拼接板的冲压成形性能是构成点焊拼接板的母材以及相应焊点冲压成形性能的综合表现。点焊拼接板冲压变形后,焊点的组织和几何尺寸的变化更是影响点焊拼接板冲压质量的关键因素。本文对点焊拼接板进行了拉伸、胀形和扩孔等典型的冲压试验,并对变形后的焊点进行了宏观和微观的分析。结果表明:在点焊拼接板冲压变形时,焊点处材料的应变远远小于其母材部分的应变;而在焊点处,焊核变形困难,较大的应变产生于热影响区。     

点焊拼接板中拼对线受拉剪作用的试验与模拟研究

对点焊拼接板的拼对线进行了拉剪试验,得到了不同焊点间距的拼对型点焊拼接板所能承受的拉剪载荷。试验结果表明,焊点间距对拉剪力无直接影响。通过对拼对线受拉剪载荷时的有限元模拟,可以发现焊点受到拉剪作用时,其周围的应力集中现象比较严重,并具有方向性;每一个焊点处的应力最高值总是位于在拉剪方向上的焊点边缘的母材处;对于材质基本相同而厚度不同的两种点焊拼接板的母材,在同一时刻,薄板处的应力集中现象大于厚板。拉剪时材料的应变集中于较薄的母材一侧,应变最大的位置在拉剪方向上焊点边缘的母材处,这也是模拟和试验时材料发生最终破坏的位置。     

硼钢A柱补丁板热冲压工艺数值模拟与实验研究

为解决硼钢A柱补丁板热冲压工艺中的焊点优化布置问题,采用热-力耦合的方法建立硼钢A柱补丁板的热冲压分析模型。通过对主板和补丁板间定义点焊单元,实现补丁板的热冲压工艺分析。结果表明:在成形过程中,由于补丁区域板料厚度大于其他区域,导致补丁区域温度一直高于其他区域,对该区域的有效冷却是保证零件性能的必要条件。相比于单层板的热冲压工艺,补丁板在热冲压过程中焊点周围区域是破裂的危险区域。经过焊点优化布置后,原破裂区域的减薄率由34%降低为6%,加工50件仅出现1件焊点开裂,合格率为98%。对于补丁板的热冲压工艺,需要考虑焊点的优化布置来改善焊点周围的成形缺陷。     

一种建立板料成形极限应力图的新方法

基于塑性理论建立了比例加载条件下双向拉伸应力应变关系,结合Swift分散性失稳准则,提出了一种建立板料成形极限应力图的方法。分别应用Hill 48和Hosford屈服准则以及单向拉伸性能参数,建立了铝合金板(r<1)和薄钢板(r>1)两种材料的成形极限应力图(FLSD),分析表明,不同的屈服准则的选取对于成形极限应力曲线有不同的影响,对于不同类型的材料屈服准则的影响程度也不同。与由通常的成形极限图(FLD)转换所得到的成形极限应力图(FLSD)进行了对比分析,结果表明,所提出的方法计算过程更为简便,并能较为准确地建立成形极限应力图,可以作为复杂加载路径下的成形极限破裂判据。     

点焊拼接板扩孔的数值模拟

采用MSC.Dytrah对点焊拼接板的扩孔变形进行数值模拟.模拟结果表明:内缘翻边时,焊点的存在使得内缘周围的变形分布极不均匀,在有焊点分布的方向上,材料的应变分布梯度较大,而较高的应变区则沿焊点两侧分布.点焊拼接板扩孔内缘周围最大主应变的不均匀分布程度主要受变形程度和焊点位置两个因素的影响.     

TA1纯钛板成形极限图测定及应用

采用机械划线法制作网格,利用通用板料成形性能试验机和网格拓印测量的方法,获得了TA1纯钛板在不同应变路径下的极限应变值,以此数据为基础绘制了TA1纯钛板室温下的成形极限图,并基于最小二乘法对成形极限图进行拟合建立了成形极限图的预测模型。此外,将成形极限预测模型导入到有限元模拟软件中,作为成形破裂的判据,对TA1纯钛板胀形成形的破裂缺陷进行预测,并通过工艺试验对预测结果进行了验证。对比结果表明,采用成形极限预测模型作为破裂判据的有限元数值模拟能够较为精确的预测出TA1纯钛板的极限胀形高度和胀形发生破裂的部位。     

板料成形极限理论与实验研究进展

成形极限是板材成形领域中重要的性能指标和工艺参数。文章在阐述成形极限在板料成形中的意义的基础上,综述并分析了成形极限在理论和实验方面的研究进展。成形极限图受应变路径的影响,给工业生产应用带来极大不便。以极限应力构成的成形极限应力图不受应变路径的影响,作为复杂加载路径的成形极限判据更加方便和实用。FLSD研究与FLD相结合,成为精确地确定破裂判别准则的主要途径之一,是近来研究的热点。十字形双向拉伸是实现复杂加载路径有效实用的试验方法。最后对成形极限应力图和十字形双向拉伸试验需要解决的关键问题作了阐述。     

点焊拼接板成形性能的研究

作为拼焊板的一种,点焊拼接板在变形加工时所表现的各种成形特性都源自于焊点对基板力学性能的影响。采用力学平衡等效原理推导出了双层板的等效弹塑性性能参数,并采用应力参数法研究了焊点引起的应力集中现象。研究表明:焊点的存在影响了板料的局部应力分布,当焊点之间距离过小时,热影响区的交互作用变大,可能导致焊点处的应力集中加剧,易出现微裂纹,使其疲劳寿命下降。随着焊点距离的增大,热影响区的交互作用迅速降低,但其强度和刚度随焊点的强化效应也相应减弱。     

测定钢板成形极限的三种方法与应用比对

近邻破裂点离线测量法是成形极限试验用来观察成形极限应变的最常用方法。随着光学视频技术在成形试验中的应用,通过测量网格临界破裂时应变的临界破裂点原位测量法,以及ISO12004标准中新推荐的破裂区截面线拟合法,均已进入到成形极限的测量领域。这两种测定成形极限的新方法弥补了紧邻破裂点测量法带来的近似效应和误差,极大提高了成形极限曲线的可信度。文章运用3种不同的方法,对一种高强度冷成形用钢进行成形试验,测定其在近似平面应变状态下的成形极限,并对结果进行比较。     

Static strength of hot-stamped spot welded joints: study on spot welding tailored blank technology

Hot stamping spot welding tailored blank technology is a process to produce spot welded automotive body parts by the following process: spot welding steel sheets in lap configuration → hot stamping (heating to about 900°C) → quenching and forming in water-cooled die → shot blasting to remove scale. This process has the advantage of producing high strength lap welded automotive body parts without increasing the number of forming dies. In this study, the mechanical properties of the hot stamped spot weld (spot welding → hot stamping) and conventional spot weld (hot stamping → spot welding) of the 1500 MPa class uncoated boron steel sheets were compared. The obtained results are as follows. The tensile shear strength (TSS) of the hot-stamped spot weld and conventional spot weld were comparable and the fracture modes were the same. On the other hand, the cross tension strength (CTS) of hot-stamped spot weld was significantly higher than that of the conventional spot weld. The fracture position of the hot-stamped spot weld was outside the nugget and conventional spot weld was inside the nugget. The high CTS of the hot-stamped spot welds might be caused by the improvement of the fracture toughness of the nugget, which was caused by reduction of the solidification segregation of the phosphorus. It is assumed that the heating process after spot welding leads to the reduction of the solidification segregation. For the tension test because there was no HAZ softening in the hot-stamped spot weld, no fracture was observed in HAZ and a higher elongation was obtained.     

Microstructures and mechanical properties of bonding layers between low carbon steel and alloy 625 processed by gas tungsten arc welding

A filler metal wire, Alloy 625, was cladded on a plate of a low carbon streel, SS400, by gas tungsten arc welding, and the morphology of the weld bead and resulting dilution ratio were investigated under different welding parameter values (the input current, weld speed and wire feed speed). The wire feed speed was found to be most influential in controlling the dilution ratio of the weld bead, and seemed to limit the influence of other welding parameters. Two extreme welding conditions (with the minimum and maximum dilution ratios) were identified, and the corresponding microstructures, hardness and tensile properties near the bond line were compared between the two cases. The weld bead with the minimum dilution ratio showed superior hardness and tensile properties, while the formation lath martensite (due to relatively fast cooling) affected mechanical properties in the heat affected zone of the base metal with the maximum dilution ratio.     

拉剪载荷下超高强度钢点焊残余应力试验

点焊后焊接残余应力叠加工作载荷后,内部应力会重新分配.文中选用B1500HS超高强度钢薄板,制备焊接构件,并通过X射线衍射法测量焊核区、热影响区及母材区的表面残余应力.在施加拉剪载荷的情况下,分别从电极端面直径、焊接电流两方面考察点焊构件在施加拉剪载荷前后残余应力的分布情况.结果表明,点焊时电流变化对试件的残余应力有一定影响;电极端面直径增加使得焊核区的残余应力增大.施加拉剪载荷后,残余应力在焊核与热影响区有所释放,远离焊核区的释放较小.     

Simulating the residual deformation of thin-plate butt weldments without wire filling by contact mode

The residual deformation in thin-plate butt weldments without wire filling was investigated by simulative and experimental methods. The good consistency on the residual deformation between the simulation result and test measurement data indicates that the contact mode can be used to simulate the butt welding process of thin plates without wire filling. The longitudinal residual tensile stress in the weld zone lead to the buckling deformation of thin-plate weldments, and the appearance of buckling deformation would in turn reduce the peak value of longitudinal residual tensile stress. As for the thin-plate butt weldments, the tensile stresses in the weld and its neighboring zone are produced in the post-weld cooling process and have not peak until the temperature of the welds dropped to near room temperature.     

温度峰值影响6061铝/AZ31B镁异种材料FSW接头成形的规律

以6061-T6铝合金与AZ31B镁合金为研究对象,基于Abaqus软件进行了异种材料搅拌摩擦焊过程的温度场数值模拟,重点分析搅拌针偏置镁侧下的搅拌区温度峰值影响焊缝表面成形的规律。结果表明,当焊接温度峰值高于Al-Mg共晶温度时,搅拌针根部附近区域会出现较明显的黏着现象,其随着焊接速度的降低而加剧,这与焊接温度峰值的升高相关。随着焊接速度的增加,焊缝表面更易避免裂纹缺陷的产生。当搅拌头的转速为1200r/min且焊接速度为40mm/min时,6061铝/AZ31B镁异种材料焊接接头的表面成形良好。     

焊丝成分对2519铝合金焊缝组织与性能的影响

采用ER4047焊丝及ER2319焊丝对2519铝合金进行熔化极惰性气体保护焊(MIG),并对焊接接头的力学性能和焊缝组织进行了分析.结果表明,用ER2319焊丝焊接的焊接接头的力学性能优于ER4047焊丝;ER2319焊丝细化了焊缝区的组织;2519铝合金焊接接头的抗拉强度低于母材,焊缝处是焊接接头的最薄弱环节,其次是焊接热影响区内的软化区,θ'相粒子受热影响而粗化是形成软化区的主要原因.     

汽车车身用铝合金冷金属过渡点塞焊工艺分析

采用AlSi₅铝合金焊丝,冷金属过渡方法对汽车车身用6061铝合金进行了搭接点塞焊试验,研究了送丝速度、铝板孔直径、点塞焊时间对点塞焊接头焊点直径、焊核直径和拉伸载荷的影响.结果表明,送丝速度主要影响焊点直径的大小,点塞焊时间和铝板孔直径主要影响焊核直径和拉伸载荷.接头拉伸载荷主要取决于焊核直径的大小,焊核直径越大,拉伸载荷越大,与焊点直径关系不大.接头为典型的熔焊接头,焊缝主要由α-Al固溶体和Al-Si共晶相组成,点塞焊接头断裂方式为撕裂型断裂.     

Q235钢板与6082铝合金搅拌摩擦焊工艺

通过对Q235钢板和6082铝合金进行搅拌摩擦焊接,并用正交试验对搅拌摩擦焊工艺参数进行优化. 结果表明,焊接过程中,将钢板放在返回侧,铝板放在前进侧[1],离搅拌针较近的钢侧金属发生软化,并且在轴肩横向切应力作用下形成短"钉子",最终在搅拌针的旋转作用下填充到搅拌针后方形成的空腔内,当下压量为0.2 mm时,比较容易得到优质的焊缝;搅拌针旋转速度为260 r/min,焊接速度为16 mm/min,针头偏向铝侧0.2 mm时,所得焊缝的抗拉强度为141.204 MPa,断裂发生在铝侧焊核区与热力影响区的交界处;钢侧热机影响区的硬度比母材高,而铝侧热机影响区比母材低.