Analysis of workpiece magnetisation on liquid nugget during resistance spot welding

This paper investigates the effect of workpiece magnetisation on the magnetic flux density and nugget shape during resistance spot welding (RSW) process. To this end, this paper analyses the magnetisation process of ferromagnetic workpieces. The magnetisation was calculated by the equivalent surface current. The effect of magnetisation on the nugget shape was studied for RSW of steel and a specially designed aluminium workpiece. The results show that the magnetisation of ferromagnetic workpieces will increase the dimensions of the weld nugget in the thickness direction. The magnetic flux density induced by workpiece magnetisation and that induced by welding current have the same order of magnitude (10^?1 T). This indicates that the magnetisation of ferromagnetic workpiece is an important source of magnetic force acting on liquid nugget. Therefore, it should not be ignored in studying the physics of RSW process, especially for the fluid flow in RSW of ferromagnetic materials.     

基于有限元的铁磁物质电阻点焊磁场分布分析

根据电阻点焊机构电流回路特点,利用ANSYS软件建立了铁磁性物质电阻点焊时磁场计算的有限元模型,计算了点焊过程中电流密度分布电场分布与磁感应强度分布,并采集了点焊过程中工件周围的磁感应强度,与模拟结果相比,验证模型的可靠性.结果表明,电流密度、电场强度与磁感应强度均在工件内达到最大.在铁磁性工件内部最大磁感应强度达到7 T,说明铁磁物质的磁化磁场在熔核形成、生长过程中的作用不应忽视.验证试验的测量值与计算值吻合良好,表明文中建立的有限元模型是可靠的.     

永磁体磁场对双相高强钢电阻点焊质量的影响

以1对中空圆柱形永磁体为磁场源,系统地分析了外加恒定磁场作用下,2.25mm厚热镀锌双相高强钢板(HDG-DP600)电阻点焊接头的力学性能、熔核尺寸及宏观晶粒组织走向.试验发现:在永磁体磁场作用下,热镀锌双相高强钢点焊接头的拉剪力较无外加磁场情况下提高了11.01%,接头的晶粒组织得到一定程度的细化,熔核形状"长而扁...     

外加磁场对非等厚铝合金电阻点焊熔核偏移的影响

针对两层板及三层板组合下的5052铝合金进行了外加磁场与常规情况下的电阻点焊,研究了外加磁场对铝合金点焊熔核偏移影响. 结果表明,外加磁场改善了两层板及三层板非等厚度铝合金的熔核偏移情况,尤其是针对熔核偏移较严重的板材厚度组合下,外加磁场改善熔核偏移的作用更加明显. 之后针对外加磁场和常规点焊情况的不同两层及三层板铝合金板厚组合式样进行了剪切拉伸测试. 结果表明,外加磁场在改善点焊熔核偏移的同时,提高了点焊接头的强度. 因此,外加磁场是一种改善非等厚度铝合金点焊熔核偏移及提高接头剪切拉伸性能的有效方法.     

Dissimilar metal joining of aluminium to zinc-coated steel by ultrasonic plus resistance spot welding – microstructure and mechanical properties

Vehicle body structures are increasingly utilising multi-materials designs with advanced high strength steels (AHSS) and aluminium alloys. A robust process for joining aluminium alloys to AHSS based on resistance spot welding (RSW) is essential to widespread application of such bi-metallic structures in fuel-efficient vehicles. In this study, ultrasonic plus RSW was applied to join AA6022 to Zn-coated dual-phase steel DP980. During solid-state ultrasonic spot welding, an interface structure comprising multilayer, Al–Zn and Zn–Fe intermetallics formed due to alloying of aluminium with steel coating. Such structure was subsequently melted into the aluminium nugget, and new Al–Fe intermetallics formed during RSW. Ultrasonic plus resistance spot-welded joints had superior fracture energy than direct resistance spot-welded joints.     

Special features of the winding bend test

Summary

This paper deals with the resistance spot weldability of steel to aluminium alloy using an intermediate layer of aluminium clad steel. Five types of clad sheet with various steel/aluminium thickness ratios were produced by hot rolling. The mechanical properties of the clad sheet changed with the thickness ratio and ranged between those of steel and:those of aluminium sheet. The peel strength of the steel/aluminium interfaces was greater than 25 N/mm.

Materials used in spot welding were 0.8 mm thick EDDQ steel sheet, three types of 1.0 mm thick aluminium alloy sheet and the clad sheet mentioned above. Spot‐weldability, including suitable welding current, nugget diameter, tensile shear strength and thickness of the intermetallic compound layer formed at the interface of the clad sheets, changed with the thickness ratio of the clad sheet. From these results, it was concluded that spot‐weldability was affected by the thickness ratio of the clad sheets.

Spot‐weldability was also affected by the alloying elements in the aluminium alloy sheet. Tensile shear strength and nugget diameter varied in various types of aluminium alloy sheet.     

母材成分对DP590钢电阻点焊接头性能的影响

通过对两种强度相近、母材化学成分不同的DP590双相钢电阻点焊接头的强度、断口及熔核TEM分析,揭示了母材化学成分对双相钢点焊接头强韧性的影响规律及机理.结果表明,母材碳含量越高,接头正拉强度及韧性越差,其主要机理是,在电阻点焊不平衡的急速冷却条件下,随着母材碳含量的增加,在点焊熔核及熔合区形成了板条状或片状的孪晶马氏体亚结构,从而降低了接头的韧性.     

Effects of resistance spot welding parameters on microstructures and mechanical properties of dissimilar material joints of galvanised high strength steel and aluminium alloy

Abstract

Intermediate frequency resistance spot welding has been adopted to join dissimilar materials of H220YD galvanised high strength steel and 6008 aluminium alloy. The effects of welding current and welding time on microstructures and mechanical properties of the welded joints were investigated. A thin intermetallic compound layer composed of Fe₂Al₅ phase and Fe₄Al₁₃ phase formed at the steel/aluminium interface. The interfacial intermetallic compound layer has higher nanohardness compared with the aluminium alloy nugget and galvanised steel. With increasing welding current (4–11?kA) and welding time (50–300?ms), the nugget diameter increased, the interfacial layer structure became coarser and the tensile shear load of the welded joints had an increased tendency. The maximum tensile shear load reached 3309?N at 9?kA for 250?ms. Crack initiated at the interfacial intermetallic compound layer of the tensile shear specimens, then propagated through the interfacial layer principally, and meantime through the aluminium alloy fusion zone near the interface partially.     

Residual stresses in spot welded new generation aluminium alloys Part B – finite element simulation of residual stresses in a spot weld in 5754 aluminium alloy

Abstract

An incremental thermo-electrical-mechanical coupled finite element model has been developed for predicting the residual stress field in a 5754 aluminium alloy spot welded joint. The complete spot welding process, including squeezing, welding, holding and cooling cycles, as well as the temperature and stress histories during those cycles in the welded joint have been investigated. All the required thermo-physical and thermo-mechanical properties used were experimentally measured. The results show that tensile residual stress predominates the spot nugget area. The highest tensile residual stress, with a value close to the material's yield strength, occurs around the centre of the nugget. The residual stress value decreases slightly towards the edge of the spot nugget.     

压电致动器辅助电阻点焊工艺实现及飞溅控制

电阻点焊是一种多物理场耦合且封闭不可见的金属成形过程,焊接过程中电流大且通电时间短,电极力与熔核区热熔化程度匹配不当,极易造成飞溅问题,影响表面成形并降低焊点强度. 针对此问题,文中提出了一种压电致动器辅助电阻点焊的方法,利用压电致动器自身响应时间短、输出推力大的特点,将压电致动器辅助压力施加于焊接过程,实现电阻点焊过程中宏观静压力与压电致动器辅助快速动态可编程压力调节. 结果表明,压电致动器在电阻点焊气缸宏观预紧力下可实现可控的压力输出,不同频率的振动可辅助加载于原始压力波形之上,在保持焊接参数不变的情况下,压电致动器的振动输入可有效改善熔核区热分布,实现对焊接飞溅的抑制并增大熔核直径,综合提升接头性能.     

Influencing factors on nugget formation during multipoint welding by single-side resistance spot welding

ABSTRACT

Recently, weight reduction and improvement of crashworthiness of auto bodies have become important issues. At the same time, stiffness of auto bodies is also needed to ensure a smooth ride. Using hollow parts, such as bended pipes and hydroformed parts, is one of the solutions to the demand for both rigidity and light weight.

To weld hollow parts and sheet panels together, welding methods which allow us to access from one side are required. Single-side resistance spot welding (single-side RSW) process is one of those, and has recently been attracting attention.

However, because of the long current path and small electrode force, it is difficult to concentrate the electric current in the welding spot compared with conventional direct resistance spot welding (direct RSW). Furthermore, in multipoint welding, shunt current will occur easily, and the nugget formation will be inhibited.

To obtain a guideline for making sound nuggets, influencing factors for shunt current were investigated. In addition, a numerical study was carried out to discuss the difference between direct RSW and single-side RSW.

According to the CAE analysis, the shunt current of single-side RSW will be higher rate than direct RSW. The rate of shunt current was influenced by the electrical resistance of its current path. For this reason, with shorter distance between welding points, or with lower electrical resistance of material, it is difficult to get large nuggets. By enhancing the electrical resistance of shunt current path, shunt current could be reduced and a larger nugget would be obtained.     

Numerical simulation of spot welding for galvanised sheet steels

Abstract

Galvanised sheet steels are now widely used to be the substrate for body in white (BIW) construction in the automotive industry. Weldability of galvanised sheet steels much worsened compared to spot welding of low carbon steels. The present paper develops a 2D axisymmetric model and employs an incremental coupled thermal–electrical–mechanical analysis to predict the nugget development during resistance spot welding (RSW) of galvanised sheet steels. Temperature dependent contact resistance for faying surfaces was determined to take into account of the influence of zinc coat for spot welding galvanised sheet steels. The effect of dynamic contact radii on temperature distribution was studied and compared with results under constant contact area assumption. The predicted nugget shape and size agreed well with the experimental data. Higher current and longer welding time should be applied for galvanised sheet steels compared to low carbon steel spot welding. The proposed model can be applied to predict weld quality and choose optimal welding conditions for spot welding galvanised sheet steels.     

A correlation study of mechanical strength of resistance spot welding of AA5754 aluminium alloy

AA5754 aluminium alloy was resistance spot welded (RSW) to produce 27 different joint stack-ups with differing process parameters and corresponding weld quality. Quasi-static joint strength was evaluated for three test geometries; lap-shear, coach-peel and cross-tension. The results derived from over 1000 samples demonstrate various fundamental relationships. For lap-shear strength, a strong relationship with weld nugget diameter was observed; whilst discrete strength levels were found for coach-peel test geometry, depending on the governing metal thickness of the parent sheet for the various stack-ups. For cross-tension strength; there is a relationship with nugget diameter; but data are sensitive to nugget periphery defects. These fundamental relationships provide a set of generalised design guidelines for RSW of aluminium that will have significant relevance to manufacturing communities.     

外加磁场对轨道车辆不锈钢点焊组织性能的影响

以轨道车辆用SUS301L不锈钢为研究对象,研究了外加磁场对不锈钢点焊的熔核尺寸、拉伸强度和微观组织的影响。结果表明,在外加磁场的作用下,不锈钢点焊的熔核直径增长效果明显,拉伸强度得到不同程度的提高,且外加磁场强度越大,作用的时间越长,性能提高的效果越明显。在相同焊接参数下磁控电阻点焊比普通点焊拉伸强度最大提高16.7%,宽高比提高47%,点焊凹坑降低62%,熔核组织明显细化,点焊过程中外加磁场能够有效改善不锈钢电阻点焊接头性能。     

Resistance welding of thin stainless steel sandwich sheets with fibrous metallic cores: experimental and numerical studies

Abstract

This paper concerns resistance spot welding (RSW) of two types of thin stainless steel sandwich sheet. The cores of these materials, made of stainless steel fibres, are highly porous (> around 85 vol.-%) and have low thermal and electrical conductivities. However, these conductivities change during the compression and heating associated with RSW. A sequentially coupled finite element model has been developed, in which the crushed core is treated as a continuum, with properties which vary throughout the process. It is shown that a constitutive relationship of the type commonly used for crushable foams can be successfully employed to simulate the deformation of the sandwich sheets. The thermoelectrical part of the model incorporates the effects of the associated phase transformations and changes in interfacial conductance. It is shown that the predictions are broadly consistent with data obtained during welding experiments. The model is used to explore the effects of welding parameters on weld characteristics (weld pool formation and weld nugget shape).     

铝合金和低碳钢的电阻点焊数据特征

研究了电阻点焊过程中不同条件下的电极位移和电极压力的数据特征.试验设备为170 W逆变直流点焊机.采用多通道高速数据采集系统采集电极位移和压力数据,用MATLAB进行数据分析,比较了5182铝合金和低碳钢的点焊行为特征.结果表明,当熔核长大到一定程度后,铝合金熔核膨胀速率不会像低碳钢那样达到零值,且电极力会出现一个峰值,该峰值预示着熔核已经达到了足够的尺寸.     

Microstructure and properties evaluations of spot-welded ferritic steel sheets via static magnetic field

Ferritic steel spot nuggets were produced with or without a static magnetic field. The microstructures and properties evaluations of the nuggets with or without a static magnetic field were investigated. Disordered columnar grains and some equiaxed grains among the columnar grains with a static magnetic field were discovered in this study. Based on the evaluations of the microstructure and properties, the nugget mechanisms, strengthening mechanisms, and infrared behavior of the joint were discovered. The diameter and strength of each nugget were improved with the application of a static magnetic field. The welding time and the welding force can both influence the nugget characteristics via a static magnetic field. The tensile strength of the spot joint regularly varied with magnetic field; the maximum value was 245 MPa, 11%, which was approximately 30% higher than that of the nugget without magnetic field (187 MPa, 3.8%). The magnetization force applied on the dendrite at the same time can cause the columnar dendrite to deform, break and deflect from the direction of solidification.     

Microstructure and mechanical properties of dissimilar steel plate resistance plug welding joints

A new type of hybrid welding method called resistance plug welding (RPW) was firstly adopted to achieve the connecting of dissimilar steel,mainly as for the poor welding characteristics of high strength steel produced by increasing carbon,manganese,silicon,etc.Microstructures and mechanical properties of RPW joint were analyzed by optical microscope,micro-hardness test and shear tensile measurement.Experimental results indicate that the RPW joint has a rounded rectangle nugget,and the size is larger than elliptical nugget of resistance spot welding (RSW) joint;the hardness value of RPW joint is evenly distributed,accordingly there is no hard brittle phases;the shear tensile strength of RPW joint increases by 20％ in comparison with RSW joint under the same welding conditions.     

Expulsion monitoring in spot welded advanced high strength automotive steels

Abstract

Although there have been a number of investigations on monitoring and controlling the resistance spot welding (RSW) of low carbon galvanised steels, those of advanced high strength steels (AHSS) are limited. A data acquisition system was designed for monitoring weld expulsion via the measurement of voltage, current, electrode force and displacement and the calculation of resistance. The dynamic resistance, electrode force and tip displacement were characterised and correlated with the phenomenon of expulsion during RSW of dual phase (DP) steel using an ac welder. Two control strategies for DP600 spot welding were proposed on the basis of the rate of change in the dynamic resistance and the electrode force.     

外加磁场对铝合金电阻点焊质量的影响

分析了外加磁场对铝合金电阻点焊接头质量的影响,包括熔核尺寸、接头力学性能和微观组织. 结果表明,外加磁场增大了熔核直径、提高了点焊接头的剪切力和吸收能. 在不同工艺参数下,熔核直径增长在5%~25%,剪切拉伸力可提高10%~30%. 在一些焊接参数下,外加磁场可以降低焊接电流、减短焊接时间,从而提高焊接效率、降低能耗. 外加磁场可促进点焊熔核内等轴晶的生成和细化晶粒.当焊接电流很小或很大、焊接时间过短或过长时,都会降低外加磁场的效应. 因此当对点焊施加外磁场时,应在合理的工艺参数下进行,以最大限度地发挥外加磁场的作用.