Experimental investigation of deformation and jetting during impact spot welding

A test setup is described for investigating flyer plate deformation during impact spot welding. High speed photography is used to study the dynamics of bulge formation, spark growth, and projectile illumination during primary and secondary impact of flat-ended projectiles. It is suggested that fragmentation of the spark is due to inter-metallic jetting. Measurements on collision angle β and collision front velocity are reported for several metal plate combinations.     

炸药量对爆炸焊接界面波影响的数值模拟

为了保证金属复合材料的爆炸焊接质量,对爆炸焊接过程中的爆轰荷载大小起着决定性作用的炸药量及布药方式进行了探索。应用AUTODYN非线性显式动力学分析软件,模拟了基、复板爆炸焊接复合过程,得到了不同炸药量下爆炸焊接过程中的压力时程,结合理论公式,分析炸药量、爆轰荷载、碰撞速度和界面波状之间的关系,及炸药量对爆炸焊接界面波的影响。并在复板上、下表面等间距各设置了8个关键点,比较了炸药厚度均匀布药方式和厚度递减布药方式产生的波状形态。结果表明,在可焊性窗口内,炸药量多的会产生较大波状结合界面;厚度递减布药方式能够消除均匀布药方式下界面波的不均匀现象,其中方案2的速度波动效果最好。并且已经结合的界面受到后续压力的振动破坏明显降低。     

A prototype fuzzy resistance spot welding system

In assembly automation, the need to perform on-line quality monitoring and to provide near real-lime inspection of resistance spot welds, has attained unsurpassed importance in industries. This paper describes the development of a prototype fuzzy control system for a two-stage resistance spot welding machine with potential of being incorporated into an automation line. It encompasses a new approach aimed at providing simultaneous control of more than two major welding parameters for achieving consistent quality spot welds by assessing the condition of the heat affected zone created. The prototype system, developed in C language, comes with a decision making mechanism and a quick search mechanism. Its rule-base contains a total of 125 heuristic control rules derived from literature reviews and interviews with experts and through experiments. The various factors affecting the quality of spot welds are outlined in the paper. The correlation between spot weld quality and welding parameters were examined using the Taguchi technique. Details of the prototype system are described and the results of the experiments conducted on the system are discussed.     

Small-scale resistance spot welding of austenitic stainless steels

Small-scale resistance spot welding (SSRSW) was carried out for austenitic stainless steels. A weld lobe that shows the process window for making sound joints was obtained for type 304 stainless steel thin sheets, and the effects of welding current, force and weld time on joint strength and nugget size were investigated. The cooling rate that was estimated from the solidification cell size was approximately 2.4 × 10⁵ K/s which is almost similar to that produced by laser beam welding. The microstructures of weld zones were almost fully austenitic due to the rapid solidification rate. Despite the fully austenitic microstructure, no hot cracking was found in types 302, 304, 316L, 310S and 347 austenitic stainless steels by SSRSW. Rapid cooling rate in SSRSW made it difficult to predict the microstructures from the conventional Schaeffler diagram.     

A new current measurement method in resistance spot welding

A method of measuring the high current in resistance welding processes is investigated. A measuring unit is developed by using a strain gage attached on the outer surface of a steel ring. The steel ring is placed around a section of the secondary loop of the welding machine and is deformed by electromagnetic forces induced by the high welding current. The circumferential constituent of the ring deformation is then used to obtain a signal voltage proportional to the secondary welding current. The strain gage signal of ring deformation is enough to determine the welding current in resistance spot welding, especially when direct current is used for the welding     

Strain rate distribution near welding interface for different collision angles in explosive welding

It is important to analyze the distribution of the strain rate near the welding interface in order to understand the mechanical and heat behaviors of a material during explosive welding. The objectives of this study were to analyze the distribution of the strain rate for different colliding angles and to probe the effects of the colliding angle on the strain rate. An ideal fluid model of symmetrical collision was used. For the same relative streamline, at the points with the same relative horizontal ordinate, calculations showed that the ratio of tensile and shear strain rate to the stagnation point strain rate is very similar for colliding angles in the range 6–20°.     

A review on ultrasonic spot welding of copper alloys

As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.     

Chaotic oscillator detection system about weak signals in spot welding

Spot welding is an efficient and shortcut processing method used in plate, and its quality detection is very important. However, there are many factors affecting the spot welding quality. Because of the low precision of traditional detection methods, spot welding has seldom been used in the aerospace industry which requires high welding quality. In this article, we give a new weak signal detection model based on chaotic oscillators. Using Melnikov methods and Lyapunov exponent, we can determine the critical values when the system enters in and out of chaos. Through lots of numerical simulations, it can be found that the lowest value of the weak sinusoidal signal the system can detect reach 10⁻¹¹, and its signal-to-noise ratio (SNR) is −126 dB. Compared with other detection methods, chaos oscillator detection system not only has a lower threshold value, but also is easy to implement in practice. This model thus has good application prospects.     

铝合金电阻点焊电极寿命及其表面特征分析

为了研究采用不同焊接电源时,铝合金电阻点焊的电极寿命、电极头磨损行为及其对焊接质量的影响,运用图形分析方法对电极头磨损行为进行了定量分析.基于对电极压印的分析,定义了3种电极头表面特征参数:相对半径(Rr)、边缘聚集度(EC)和偏心度(ECC).研究表明:铝合金电阻点焊采用逆变直流电源与交流电源比较,前者电极寿命约为后者的1/4;焊点的剪切强度随着Rr和EC的增加而下降;电极头中部残存接触区的存在有助于维持较好的焊接质量.     

Preliminary study on the feasibility of friction spot welding in PMMA

In this work the feasibility of friction spot welding of thermoplastics was investigated on poly (methyl methacrylate) plates. Preliminary results have shown that the weld strength is comparable to other available welding techniques, while joining times are equal or shorter. Light optical microscopy and Vickers microhardness measurements showed the presence of a heat affected zone and a thin, consolidated stir zone, where physical-chemical transformations related to thermo-mechanical processing led to changes in local mechanical strength. The work has demonstrated for the first time that the welding of thermoplastic materials by friction spot welding is feasible.     

Optimization of welding parameters for resistance spot welding of TRIP steel with response surface methodology

Many automotive companies are endeavouring to reduce the weight of the car body in response to various environmental issues. One initiative is the development of TRIP (Transformation Induced Plasticity) steels with a high strength and ductility. Resistance spot welding is a complex process, which requires specific optimal welding conditions based on experimental data. However, the trial-and-error method to determine the optimal conditions requires a large number of experiments, and so response surface methodology has been employed to overcome this problem. The second-order model was used here. This has been used in the resistance spot welding process of the TRIP steel and galvanized TRIP steel with a zinc-coated layer to optimize the welding parameters. The welding current, welding time, and welding force were selected as input variables, and the shear strength and indentation were selected as output variables.     

The optimization of welding parameters for friction stir spot welding of high density polyethylene sheets

Friction stir spot welding parameters affect the weld strength of thermoplastics, such as high density polyethylene (HDPE) sheets. The strength of a friction stir spot weld is usually determined by a lap-shear test. For maximizing the weld strength, the selection of welding parameters is very important. This paper presents an application of Taguchi method to friction stir spot welding strength of HDPE sheets. An orthogonal array, the signal to noise ratio (S/N), and the analysis of variance (ANOVA) are employed to investigate friction stir welding parameter effects on the weld strength. From the ANOVA and the S/N ratio response graphs, the significant parameters and the optimal combination level of welding parameters were obtained. Experimental results confirmed the effectiveness of the method.     

Friction stir spot welding of SPCC low carbon steel plates at extremely low welding temperature

Friction stir spot welding(FSSW) was applied to 2.0 mm thick steel plate cold-rolled commercial(SPCC)low carbon steel plates at a very low rotation speed that ranged from 5 to 50 rpm, which was much lower than that generally used for the conventional FSSW technique. Due to the very low heat input, the welding processes could therefore be completed at a peak welding temperature below 160℃. As a result,a significantly refined microstructure with an average grain size of about 0.41 μm was formed in the stir zone of the joints and the J1{0–11}-211 and J2{1–10}-1–12 shear textures were the dominant components, which are different from the D1{11–2}111 and D2{-1–12}111 shear textures formed in the conventional FSSW joints. In addition, no heat affected zone could be detected along the crosssectional plane of the joints. Although a few void-like non-bonded areas were still observed along the interface between the upper and lower steel plates, the shear tensile loads of the joints increased to about 10.0 kN when welded at a condition of 8 t, 20 rpm and 30s, and the joints fractured through the plug failure mode.     

Refill friction stir spot welding of 5083-O aluminum alloy

In this work,refill friction stir spot welding(RFSSW) was used to weld 2 mm-thick 5083-O alloy.The Box–Behnken experimental design was used to investigate the effect of welding parameters on the joint lap shear property.Results showed that a surface indentation of 0.3 mm effectively eliminated the welding defects.Microhardness of the stir zone(SZ) was higher than that of the base material(BM) and the hardness decreased with increasing the heat input during welding.The optimum failure load of 7.72 k N was obtained when using rotating speed of 2300 rpm,plunge depth of 2.4 mm and refilling time of 3.5 s.Three fracture modes were obtained during the lap shear test and all were affected by the hook defect.     

Friction spot welding of dissimilar 6063/5083 aluminium alloys

In this work, friction spot welding (FSpW) was used to weld dissimilar 6063/5083 aluminium alloys, and the effects of the sleeve plunging speed on joint microstructures and the lap shear properties were discussed. Results showed that the keyhole can be eliminated using FSpW. Bending hooks changed to a flat morphology when the plunging speed was increased. Excellent bonding was formed at the lap interface in the sleeve-affected zone. As the sleeve plunging speed was increased from 40 to 110?mm?min^?1, the lap shear failure loads for the joints first increased and then decreased. A maximum failure load of 8017 N was attained when using a sleeve plunging speed of 80?mm?min^?1. All joints fractured at the lap interface.     

Electromagnetic impact welding of copper-to-copper sheets

Copper (Cu) has some properties, similar to aluminium (Al), like high thermal conductivity, high thermal expansion coefficient, relatively low melting point, brittleness at elevated temperatures and less viscosity of molten metal. These properties make the welding of Cu and Cu alloys difficult as compared to welding of carbon steels. The present study investigates the feasibility of electromagnetic impact welding of Cu-to-Cu sheets by using Al as the driver sheet. A study has been carried out to characterize the electromagnetic impact welding of 0.5 mm thick Cu sheets. The results of the microstructure and tensile shear strength tests are reported.     

Study on fibre laser spot welding of TRIP980 steel

A 980 MPa transformation induced plasticity (TRIP) steel was fibre laser spot welded by different Argon (Ar) shielding conditions, laser power (1000 up to 2500 W) and defocusing distances (?8 up to +8 mm). The surface appearance, cross-section macrostructure, microstructure, hardness, tensile shear properties and fatigue properties of laser spot welds were evaluated. The results showed that the welds with Ar shielding had larger weld appearance and bonding sizes, better tensile shear properties compared with the welds without Ar shielding. With the increase in laser power, the laser welding mode changed from conduction to keyhole, which improved the bonding size and mechanical properties. The bonding size and mechanical properties increased in the order of defocusing distances of +8, ?8, +4, ?4 and 0 mm. During the fatigue tests of laser spot weld, the fusion zone pullout and sheet transverse fracture failure modes were observed.     

Comparative study on CO2 laser overlap welding and resistance spot welding for galvanized steel

The CO₂ laser overlap welding and the resistance spot welding are respectively investigated on DC56D galvanized steel used for auto body. The characteristics of the two types of welding methods are systematically analyzed in terms of the weld molding, tensile-shear performance, microstructure, hardness, and corrosion resistance of welding joint. The results show that, the fusion widths of the upper and lower surface are almost the same for the resistance welding joint, and the weld nugget is surrounded by the heat-affected zone. While the laser welding joint belongs to deep penetration welding, the weld fusion width presents wide at the top and narrow at the bottom, and the heat-affected zone is situated on both sides of the weld pool. Compared with resistance spot welding joint, laser welding joints have much more ultrafine microstructures, much smaller heat-affected zones, as well as greater resistance to deformation and corrosion. In addition, the tensile-shear performance of laser weld joints is superior to that of resistance welding joints under certain conditions.     

Modeling of resistance spot welding of multiple stacks of steel sheets

Weld quality is a major challenge for resistance spot welding of multiple stacks of steel sheets. Because of the differences in mechanical and physical properties of steel sheets and the sheet gage variation, the contact state between sheets and welding current flow throughout the stack joint is complicated. As a result, discrepant weld sizes at the faying interfaces become an issue. In this study, a coupled thermal–mechanical/thermal–electrical incremental model has been developed to reasonably predict the weld nugget formation process of resistance spot welding of a sheet stack made of 0.6 mm thick galvanized SAE1004+1.8 mm thick galvanized SAE1004+1.4 mm thick galvanized dual-phase (DP600) steel using published thermal, electrical, and mechanical properties. It was found that the weld nugget on the faying interface of DP600 forms earlier than that on the other interface, which agrees well with the experimental results. Based on the coupled model, the effects of the sheet gage combination and steel grade combination were examined. The results show that, for a multiple stacks of steel sheets SAE1004 + SAE1004 + DP600, the critical ratio of sheet thickness between the top and bottom sheets is approximately 1:3. The model could provide an important guidance in the selection of the welding variables, sheet gage and steel grade to meet the weld quality of steel component.