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。     

点焊拼接板成形极限图的试验与模拟研究

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。本文采用试验与模拟结合的方法对点焊拼接板的成形极限进行研究。结果表明:在接近双向拉伸的应力应变状态下,点焊拼接板各种场量最大值的分布具有明显的方向性。下层板的破裂危险区位于宽度方向中轴线的焊点附近,上层板的破裂危险区则位于长度方向中轴线的焊点位置;当点焊拼接板越接近双向等拉时,两个方向上变量的最大值就越接近,其破坏的几率也就越接近。     

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.     

应力应变、疲劳与脆断、断裂力学

核电厚壁管道全位置TIG焊动态焊接变形研究,降低焊接残余应力定量分析的应用研究,06NiCrMoCuNb钢焊接T形材的焊接工艺数值模拟,点焊拼接板焊点附近的应力分析,微连接接头在热疲劳过程中的破坏规律……     

镁合金电阻点焊接头断裂行为的有限元分析

综合考虑熔核尺寸、工件翘曲变形、电极压痕等因素建立了三维弹塑性有限元模型,分析了镁合金电阻点焊接头的应力、应变场分布特点,以揭示焊点断裂产生的原因.结果显示,由于电阻点焊接头在受力时熔核是主要的承栽部位,在熔核边缘与板缝结合处由于几何非线性和材料的非线性将出现应力集中,这是点焊接头受力时最薄弱的环节,裂纹从这里萌生,沿熔核边缘高应力区扩展.镁合金点焊接头断裂均为沿焊点熔核的纽扣形撕裂,断裂属于韧性断裂.     

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。     

变电极力对管板单面电阻点焊质量的影响

根据管板单面电阻点焊结构特点,建立了采用伺服焊枪的管板单面电阻点焊试验系统.针对管板焊接过程中变形大、形成环形熔核质量不可靠等问题,提出了基于改变焊接过程中电极力来提高焊点质量的方法,并研究变电极力对管板焊焊点强度及焊接变形影响的规律.结果表明,通电阶段熔核生成初期减小电极力,可明显提高焊点拉剪强度,减小焊接变形;冷却阶段减小电极力对焊点质量也有所提高,但影响较小.研究结果对管板焊接工艺参数的制定及单面电阻点焊在车身焊装中广泛安全的应用具有重要意义.     

变电极力对管板单面电阻点焊形核的影响

根据管板单面电阻点焊结构特点,建立了轴对称有限元模型.通过结构、热电场的全耦合,分析了恒定电极力作用下,管板单面点焊的形核过程和特点,其焊接过程结构件的大变形导致形成的焊点质量不可靠.利用伺服焊枪通电过程中可实时改变电极力的特性,研究焊接过程中力的变化对焊点形状的影响规律.结果表明,单面电阻点焊焊接通电过程中改变电极力,在同等焊接工艺参数的情况下可增大焊接件间的连接宽度,减小焊接变形,提高焊点质量,为管板焊接在车身上广泛安全的应用提供理论依据.     

热循环载荷下SMT含气孔焊点应力应变的数值模拟

通过用统一的粘塑性本构方程描述SMT焊点的力学行为,对SMT焊点中气孔位置对SMT焊点中的应力、应变的影响采用有限元方法进行了模拟。通过模拟发现气孔改变了焊点中气孔周围部分应力、应变的分布;焊点根部的气孔对焊点应力、应变的影响最大。     

Fatigue strength of hot-stamped spot welded joints*—study on spot welding tailored blank technology

Hot stamping spot welding tailored blank (TB) 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 tensile shear fatigue strength of the spot welding TB joints (Spot welding → Hot stamping) and conventional spot welded joints (Hot stamping → Spot welding) of the 1500MPa class uncoated boron steel sheets are compared. The obtained results are as follows. The fatigue life of the spot welding TB joints was more than two times longer than that of the conventional spot welded joints. The long fatigue life of the spot welding TB joints was not caused by the heating and quenching process but by the shot blasting process after heat treatment. Shot blasting on the outer sheet surface caused the high compressive residual stress on the outer surface and did not affect the residual stress on the lapped surface. Shot blasting on the outer sheet surface increased the initiation life of fatigue crack which occurred on the lapped surface and also reduced the crack propagation speed which propagates from the lapped surface to the outer surface. FE-analysis suggested that compressive residual stress on the outer surface reduce the opening of sheet separation of joints in fatigue tests and reduce the maximum principal stress around the edge of corona bond.     

回填式搅拌摩擦点焊过程的材料流动规律模拟

利用流体力学软件ANSYS FLUENT模拟了回填式搅拌摩擦点焊过程的材料流动行为,着重分析了搅拌头旋转速度与回填速度对材料流动的影响规律并加以试验验证.模拟结果表明,材料的流动速度随着到套筒内外壁距离的增加而减小,流动速度最大值出现在套筒端面的外壁处.在套筒内部,流动速度最小的材料位于焊点的中心处,此处的材料流动状态可通过增加旋转速度进行改善;从扩大焊点有效面积的角度来讲,增加搅拌头的旋转速度优于增加回填速度.上述规律得到了试验验证.     

A new approach for user-independent determination of formability of a steel sheet sheared edge

It is common to use a forming limit curve (FLC) for a feasibility study of a deep-drawn steel part based on a finite element analysis (FEA). However, in such an approach a neglected fact is that a blank edge in industrial production is often produced by shear cutting. Especially, for many high strength steel grades, this cutting process notably reduces edge formability. An overestimation of formability of the blank edge, with an FLC, is the consequence that may lead to cracks at the sheared edge of a part. The following paper describes a new approach to determine formability of a sheet-steel sheared edge by hole expansion test that uses an FLC tool set. This approach delivers a hole expansion ratio with considerably lower scattering compared to the hole expansion according to ISO 16630. Additionally, information on the planar isotropy, flow and necking behavior of the material, is supplied. Finally, a pragmatical way of transferring test results into an FEA of the forming process for a sheet blank with a sheared edge is presented.     

图像处理在电阻点焊质量检测中的应用

现代制造业广泛使用电阻点焊技术,研究者长期致力于实现焊接质量快速无损检测技术的研究,本文以低碳钢为试验材料,在各种点焊工况下对焊点图像进行了采集与预处理,利用分形理论对焊点图像边缘进行检测,结果证明,利用分形几何可有效提取焊点边缘.文中研完了焊点图像特征区域面积与焊点强度之间的关系,结果表明,焊点表面图像面积与焊点强度之间呈正比例关系,可以利用焊点表面图像对点焊质量进行检测.     

基于ANSYS的车身柔性件点焊装配应力分析

采用通用有限元分析软件ANSYS对点焊装夹过程中垂直装夹间隙、水平装夹间隙和焊点个数等因素对焊点部位最大应力的影响进行分析.采用ANSYS的参数化设计语言建立有限元分析模型,将上述影响因素通过定义变量的形式进行参数化,使用ANSYS内置的点焊模拟功能创建点焊集,同使用耦合自由度的传统点焊模拟方法相比,该方法考虑点焊半径和焊点强度等因素,而且使用很方便.结果表明,同垂直装夹间隙相比,水平装夹间隙对焊点部位影响较大;随着焊点个数增多,有效连接面积增大,单个焊点部位最大应力降低.     

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.     

推进剂贮箱零件侧翻孔电磁成形数值模拟

基于ANSYS多物理场耦合模块,采用松散耦合法,建立了推进剂贮箱零件侧翻孔电磁成形的有限元模型,揭示了坯料电磁力、应力、应变和厚度等的分布规律及其随时间变化规律,并优化了放电电压和成形线圈内径等工艺参数。分析结果表明:坯料在圆角区域应力和应变较大,且厚度减薄量较大;坯料圆角处残余应力较大。放电电压增大,坯料变形量增加,但厚度减薄量相应增加;线圈内径增大,坯料与模具最大间隙、最大夹角以及坯料最小厚度均先减小后增大。得到的放电电压和成形线圈内径优化值分别为40 kV和40 mm。     

FEATURE ANALYSIS AND EXTRACTION OF INNER DEFECTS FOR SPOT WELD NUGGET OF ALUMINUM ALLOY

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｐｏｔｗｅｌｄｉｎｇｈａｓｂｅｅｎｗｉｄｅｌｙｕｓｅｄｉｎａｌｕｍｉｎｕｍａｌｏｙｓｔｒｕｃｔｕｒｅｓｏｆｓｐａｃｅｃｒａｆｔａｎｄａｉｒｃｒａｆｔｄｕｅｔｏｉｔｓｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｔｅｃｈｎｏｌｏｇｙ．...