Showing papers on "Spot welding published in 2005"

Resistance welding : fundamentals and applications

Abstract: WELDING METALLURGY Solidification in Resistance Spot Welding Phase Transformations in RSW Cracking References ELECTROTHERMAL PROCESSES OF WELDING Introduction Electrical Characteristics of Resistance Welding Thermal Characteristics of Resistance Welding Heat Balance Electrode Life Lobe Diagrams References WELD DISCONTINUITIES Classification of Discontinuities Void Formation in Weld Nuggets Cracking in Welding AA6111 Alloys Cracking in Welding AA5754 Alloys References MECHANICAL TESTING Introduction Shop Floor Practices Instrumented Tests References RESISTANCE WELDING PROCESS MONITORING AND CONTROL Introduction Data Acquisition Process Monitoring References WELD QUALITY AND INSPECTION Weld Quality Attributes Destructive Evaluation Nondestructive Evaluation References EXPULSION IN RESISTANCE SPOT WELDING Influence of Expulsion on Spot Weld Quality Expulsion Process and Detection Expulsion Prediction and Prevention Examples References INFLUENCE OF MECHANICAL CHARACTERISTICS OF WELDING MACHINES Introduction Mechanical Characteristics of Typical Spot Welders Influence of Machine Stiffness Influence of Friction Influence of Moving Mass Follow-Up in a Welding Cycle Squeeze Time and Hold Time Measurement Other Factors References NUMERICAL SIMULATION IN RESISTANCE SPOT WELDING Introduction Coupled Electrical-Thermal-Mechanical Analysis Simulation of Contact Properties and Contact Area Simulation of Other Factors Modeling of Microstructure Evolution Examples of Numerical Simulation of RSW Processes References STATISTICAL DESIGN, ANALYSIS, AND INFERENCE IN RESISTANCE WELDING RESEARCH Introduction Basic Concepts and Procedures Experiments with Continuous Response Experiments with Categorical Responses Computer Simulation Experiments Summary References INDEX

Peak temperatures and microstructures in aluminium and magnesium alloy friction stir spot welds

Abstract: The peak temperatures during friction stir spot welding of similar and dissimilar aluminium and magnesium alloys are investigated. The peak temperatures attained during friction stir spot welding of Al 6111, Al 2024, and AZ91 are within 6% of their solidus temperatures. In dissimilar AZ91/Al 6111 spot welds the peak temperature corresponds with the α-Mg solid solution and Mg17Al12 eutectic temperature of 437°C. An a-Mg plus Mg17Al12 eutectic microstructure is produced in dissimilar friction stir spot welds when material displaced during pin penetration into the lower sheet material contacts the upper sheet material at the eutectic temperature.

Tool penetration during friction stir spot welding of Al and Mg alloys

Abstract: The mechanism of tool penetration during friction stir spot welding of Al-alloy and Mg-alloy sheet materials is investigated and is explained as a progression of wear events, from mild wear to severe wear and then to melt wear in material beneath the base of the rotating pin. Melt wear can also occur under the rotating tool shoulder provided that sufficient penetration of the upper sheet occurs during the spot welding operation.

Friction Stir Spot Welding of Advanced High-Strength Steels - A Feasibility Study

Abstract: An exploratory study was conducted to investigate the feasibility of friction stir spot welding advanced high-strength steel sheet metals. The fixed pin approach was used to weld 600MPa dual phase steel and 1310MPa martensitic steel. A single tool, made of polycrystalline cubic boron nitride, survived over one hundred welding trials without noticeable degradation and wear. Solid-state metallurgical bonding was produced with welding time in the range of 2 to 3 seconds, although the bonding ligament width was relatively small. The microstructures and hardness variations in the weld regions are discussed. The results from tensile-shear and cross-tensile tests are also presented.

Assembly dimensional prediction for self-piercing riveted aluminum panels

Abstract: Self-piercing riveting (SPR) is a high-speed mechanical fastening technique for joining sheet components. It has drawn more attention in recent years because it can join some advanced materials that are dissimilar, coated and hard to weld, such as aluminum sheets. Research results have shown that SPR improves joint properties in aluminum and steels. However, there has been concern that there might be dimensional issues due to relatively large material flows at SPR joint configurations. This paper presents the latest research progress in the assembly dimensional prediction area, using experimental data and finite element analysis results. It is found that the joint distortion of SPR as tested is much larger than that from resistance spot welding (RSW), and the inclusion of SPR joint distortion is generally needed for accurate global assembly predictions. To include the local SPR effect, a new algorithm to represent the SPR distortion has been developed. The new algorithm can be incorporated into special finite element analysis codes such as EAVS (elastic assembly variation simulation) to efficiently predict body assembly dimensions where spot joining processes are involved.

Development of requirements for resistance spot welding dual-phase (DP600) steels. Part 1: The causes of interfacial fracture

Abstract: Weld fracture was investigated in relation to weld parameters and steel sheet characteristics.

Thermo-Mechanical Modeling of Friction Stir Spot Welding (FSSW) Process: Use of an Explicit Adaptive Meshing Scheme

Abstract: This paper presents on-going finite element modeling efforts of friction stir spot welding (FSSW) process by an explicit finite element code. Adaptive meshing and advection schemes, which makes it possible to maintain mesh quality under large deformations, is utilized to simulate the material flow and temperature distribution in FSSW process. The predicted overall deformation shape of the weld joint resembles that experimentally observed. Temperature and stress graphs in the radial direction as well as temperature-deformation distribution plots are presented. However, refinements of several modeling aspects are needed for more realistic prediction of the FSSW process.

An experimental study determines the electrical contact resistance in resistance welding

Abstract: Electrical contact resistance is of critical importance in resistance welding. In this article, the contact resistance is experimentally investigated for welding mild steel, stainless steel, and aluminum to themselves. A parametric study was carried out on a Gleeble® machine, investigating the influence on the contact resistance of interface normal pressure, temperature, and base metal.

The Effect of Spot Weld Failure on Dynamic Vehicle Performance

Abstract: Spot welds are the dominant joining method in the automotive assembly process. As the automated assembly process is not perfect, some spot welds may be absent when the vehicle leaves the assembly line. Furthermore, spot welds are highly susceptible to fatigue, so that a substantial number may fail during the vehicle lifetime. The scope of this article is twofold. First, the impact of spot weld quality and design on a vehicle’s functional performance is reviewed, addressing strength and stiffness, NVH and durability. The overview briefly covers both experimental tests and predictive finite element (FE) modeling approaches, explains the complexity of a spot weld design problem and discusses optimization strategies. Second, an industrial robustness study is presented, that assesses the effect of spot weld failure on dynamic vehicle characteristics. Damaged models are generated automatically, by breaking a subset of the vehicle’s spot welds, using a weighted-uniform selection probability. Monte Carlo simulations are then used to assess the scatter on dynamic vehicle characteristics. The role of Computer Aided Engineering (CAE) in the automotive industry is rapidly increasing. Functional performances (NVH, durability, . . .) are fine-tuned on the basis of numerical predictions, so that the expensive physical prototyping phase can be shortened considerably. Traditionally, optimizing a vehicle body starts with improving the fundamental torsion and bending frequencies. These dynamic characteristics should be robust to failure of spot weld connections, thousands of which are present in a typical vehicle body. The first part of this article overviews the use of spot welds in the automotive industry. Section 1 deals with the resistance spot welding procedure and typical characteristics of spot welds. Section 2 describes small-scale experiments and reallife testing of spot weld characteristics in terms of strength and stiffness, NVH and fatigue life, and highlights the complexity of spot weld (layout) design. Section 3 describes a selection of finite element models that are used to predict a spot weld’s functional performance with numerical simulations, and addresses the benefits and difficulties of optimization on the basis of FE models. During the vehicle lifetime, manufacturing inaccuracies, minor accidents and fatigue failures may result in deterioration or even absence of a substantial number of spot weld connections. Also, in a CAD model transferred to a CAE department, some spot welds might be omitted or forgotten. The second part of this article presents an approach to assess the robustness of dynamic vehicle characteristics to this breakage or absence. Automated procedures have been developed, to break a number of spot weld elements with highest strain energy in the nominal (undamaged) model, and also to randomly break a number of welds, with a uniform probability or with a weighted-uniform probability. The latter application allows performing Monte Carlo simulations to assess the effect of random spot weld failure on dynamic vehicle characteristics. Section 4 explains both the input file creation routines and the process flow of required computations. Key results are given in Section 5. Spot Welds in Vehicles Resistance spot welding (RSW) emerged in the 1950s, and is now the predominant assembly technique in the automotive industry. The vehicle components (body in white, cradle, doors, etc.) are made of thin metal sheets that are connected with spot-welded joints (or simply, spot welds); see the example 1 in Figure 1. To create a spot weld, two or more metal sheets are pressed together by electrodes, and an electric current is passed through them. The resistance of the metal generates heat, and the sheets are welded together by means of local metal fusion; a spot weld has been created. No welding material is added in this process. A spot weld consists of three regions, which have different material properties – a weld nugget with a cylindrical shape, a heat-affected zone (HAZ) and the base material sheets. 2 For instance, the yield stress in the nugget is up to three times higher than in the base material, 3 and the plastic properties of the HAZ are non-homogeneous. 4 Due to the applied pressure by the electrodes during the welding, the thickness of the nugget is often less than the thickness of the two metal sheets. This so-called nugget indentation is typically not significant for plates up to 1 mm, but is more pronounced when thick plates are assembled. Stress concentration may occur at the edges where a change of thickness takes place, which may result in crack initiation. 3 The transient heating and cooling results in hardening of the material, and a prestress may remain after cooling. A typical vehicle body-in-white is made of steel sheets and contains about 4000 spot welds. The optimal diameter and distance between two successive spot welds are determined by the sheet thickness. The diameters range from 3 to 7 mm, with a mean of 6 mm. 5 The manufacturing practice of spot welds in the vehicle assembly process poses constraints on the spot weld layout design, as not all positions can (effectively) be reached. Note also that the assembly process is not perfect – sometimes a few spot welds are even missing or broken right from the beginning of the vehicle life.

Methods for ultrasonic inspection of spot and seam resistance welds in metallic sheets and a spot weld examination probe system (SWEPS)

Abstract: An external focused ultrasonic beam, non-destructive, open-air, inspection method of sheet metal spot and seam weldments using a probe in combination with motion measurement of the probe over the weldments during inspection without immersion of the material. Reflected ultrasonic waves are received and signals produced and processed or displayed as A-scan, B-scan and C-scan images that are easily recognized. An A-Scan is based on the time-of-flight difference between the outer surface, the weldment and inner and opposite surfaces of the component. B-scan and C-scan indicate the degree of weld fusion and provide data relative to fused thickness and defects sheet metal or welds. A special purpose scanner that enables ultrasonic examination welds. Scanner is pencil like ultrasonic probe with bearing face and position sensing device disposed adjacent a weld position. Scanner collects data for method to determine various characteristics of welded items.

A comparative study of single-phase AC and multiphase DC resistance spot welding

Abstract: This paper presents a comparative study of the AC and MFDC resistance spot welding process. Both experiments and finite element simulation were conducted to compare the weld size and energy consumption. The experiments were performed on two identical spot welding machines, one with a single phase ac and the other with a mid-frequency DC weld control. The machines were instrumented such that both the primary and secondary voltage and current signals could be collected for energy calculation. The finite element simulation model was developed to understand the underlying mechanisms of the difference between the ac and MFDC processes. The effect of the current waveform was investigated by using the actual process measurements as an input to the simulation model. It is shown that the MFDC process generally produces larger welds than the AC process with the same root-mean-square welding current. However, this difference is more prominent when the welding current is relatively low. Overall, the AC welding process consumes more energy to make a same sized weld than the MFDC process. The larger the welding current is used, the less efficient the AC welding process will become. The differences between the two welding processes are caused by the contact resistance behavior and the electrical inductance in the AC welding process.

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

Abstract: 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.

Trends in aluminum resistance spot welding for the auto industry

Abstract: Recent advances in resistance welding technology, alloys, and NDE techniques have helped to reduce manufacturing costs for aluminum sheet structures.

Estimating the strength of resistance spot welds based on sonic emission

Abstract: Audible sound signals detected during the resistance spot welding (RSW) of zinc coated steels were investigated in order to assess their suitability for estimating the strength of the weld. A new sonic emission indicator was introduced and compared to a commonly used emission count indicator. A new method of spot weld strength estimation based on the two indicators is presented. The advantage of the method is that it makes it possible to establish the stage when the electrode is worn out. The method enables the development of improved RSW process control algorithms.

Evaluation of Friction Spot Welds in Aluminum Alloys

Abstract: The Friction Spot Welding (FSSW) process as invented by GKSS in Germany has shown potential for application in several industrial fields as a solid state joining technology. This study evaluates this "refill" method of friction spot welding in aluminum sheet. Efforts to date have concentrated on simple flat lap joints. Process and tool development studies have been performed and have focused on understanding and managing material flow in order to minimize flash, ensure full consolidation and produce a nearly flush surface. The metallurgical and mechanical properties as a function of tool geometry and processing parameters are discussed and the lap shear strength is shown in this preliminary work to compare favorably to riveting and resistance spot welding.

Ultrasonic spot welding: A new tool for aluminum joining

Abstract: Ultrasonic spot welding offers cost and performance advantages for joining of aluminium vehicle body parts.

Ultrasonic in-process monitoring and feedback of resistance spot weld quality

Abstract: A method and apparatus for ultrasonic in-process monitoring and feedback of resistance spot weld quality uses at least one transducer located in the electrode assembly transmitting through a weld tip into an underway weld Analysis of the spectrum of ultrasonic waves provides the operator with an indication of the size, thickness, location, dynamics of formation and quality of the spot weld The method presents a fundamentally new physical approach to the characterization of the spot weld quality Together with transmission mode it includes new modes of operation of ultrasonic probes such as a reflection mode and simultaneous use of transmission and reflection modes, and a new physical interpretation of the signal analysis results

Joined body of dissimilar materials comprising steel material and aluminum material, and joining method therefor

Abstract: The purpose is to provide a joined body of dissimilar materials comprising steel material and aluminum material, which can be obtained by spot welding with high joining strength; and a spot welding method therefor. A joined body (3) is obtained by spot welding a particular thick steel material (1) and an aluminum material (2). The area of a nugget (5) in a spot weld is determined in relation to the plate thickness of the aluminum material (2). The area of the portion of a boundary reaction layer (6) having a thickness of 0.5-10 μm in the nugget (5) is determined in relation to the plate thickness of the aluminum material (2), and high joining strength is obtained.

Cohesive-zone modelling of the deformation and fracture of spot-welded joints

Abstract: The deformation and failure of spot-welded joints have been successfully modelled using ac ohesive-zone model for fracture. This has been accomplished by implementing a user- defined, three-dimensional, cohesive-zone element within a commercial finite-element package. The model requires two material parameters for each mode of deformation. Results show that the material parameters from this type of approach are transferable for identical spot welds in different geometries where a single parameter (such as maximum stress) is not. The approach has been demonstrated using a model system consisting of spot-welded joints made from 5754 aluminium sheets. The techniques for determining the cohesive fracture parameters for both nugget fracture and nugget pullout are described in this paper. It has been demonstrated that once the appropriate cohesive parameters for a weld are determined, quantitative predictions can be developed for the strengths, deformations and failure mechanisms of different geometries with nominally identical welds.

An Investigation on Spot Weld Modelling for Crash Simulation with LS-DYNA

Abstract: Because of weight reduction necessities, high-strength steels are more and more widely used in bodyin-white (BiW) structures in recent years. Concerning the behaviour of such structures during a car crash the joints between high-strength materials are seen as critical points. Therefore the properties of welded joints, especially the failure behaviour at high velocities have to be taken into consideration during the development phase. In this paper, we present an overview on the current activities at the DaimlerChrysler AG regarding investigations on spot weld failure behaviour. A suitable model that is able to represent the failure behaviour of spot welds in BiW structures and that is independent of mesh sensitivity has been developed. An elasto-plastic material model based on von Mises plasticity (MAT_100) has been further enhanced with a new failure criterion. The model has been implemented into LS-DYNA. The material as well as the failure behaviour is verified and calibrated through precision experiments conducted on specimen level and later validated on component level.

Method for joining at least two adjoining work-pieces by friction stir and/or friction stir spot welding

Abstract: A method for weldbonding at least two work-pieces together includes applying an adhesive to a first surface of a first work-piece, and bringing the first surface of the first work-piece into contact with a surface of a second work-piece. The first work-piece and second work-piece are then friction stir or friction stir spot welded together, and the adhesive is cured. The use of bonding tools to maintain the two work-pieces together during curing of the adhesive is eliminated.

Development of requirements for resistance spot welding dual-phase (DP600) steels part 2: Statistical analyses and process maps : Weld diameter proved to be the primary factor influencing type of weld fracture

Abstract: The DP600 steels have presented new challenges to the conventional practice of resistance spot welding. In developing process requirements to spot weld stacks of two identical DP600 steel sheets, a statistical method was applied in order to establish empirical relationships between the type of weld fracture during quality control (i.e., interfacial vs. button pullout), the weld current, the weld time, and the sheet thickness independent of chemical composition and galvanized coating. The selected methodology was so successful that maps to select process parameters were developed for spot welding 0.9- to 2.2-mm-thick DP600 steels. This study also confirmed that weld diameter was a primary factor influencing type of weld fracture. A new relationship between minimum weld diameter to prevent interfacial fracture during quality control and sheet thickness was also determined, and compared with several resistance spot weld standards.

Development of Friction Spot Joining

Abstract: This paper describes the fundamental procedure and joint properties of Friction Spot Joining (FSJ), a new spot welding method for aluminium and other light metal alloys. The process uses frictional heat between a joining tool and work piece as the heat source, and produces a solid phase joining by causing plastic flow of the material. Technological essences of the process including the joining tool, a prototypic FSJ equipment, and process parameters were first fundamentally established. Consequently, based on those results, FSJ systems for practical use have been produced. Furthermore, various properties of the friction spot joint including metallurgical structure, hardness distribution, and tensile strength were investigated.

Joined body of different materials of steel material and aluminum material and method for joining the same

Abstract: PROBLEM TO BE SOLVED: To provide a joined body of a steel material and an aluminum material which is formed by spot welding and has a high joining strength, and also to provide a method for spot welding the same. SOLUTION: The joined body 3 of different materials is formed of the steel material 1 and the aluminum material 2 joined to the steel material through spot welding. The steel material 1 contains 0.1-3.0 wt.% Mn and has a sheet thickness t 1 of 0.3-2.5 mm. The aluminum material 2 contains 0.4-2 wt.% Si and has a sheet thickness t 2 of 0.5-2.5 mm. A plating film 4 made of Zn and/or Al having a film thickness of 3-15 μm and a melting point of 350-950°C is preliminarily formed on a surface of the steel material 1 or the aluminum material 2. A nugget diameter in the spot welding is within a range of 4×t 2 0.5 to 7×t 2 0.5 in relation to the sheet thickness t 2 . COPYRIGHT: (C)2006,JPO&NCIPI

Laser penetration weld

Abstract: Laser penetration of tabs from electrode plates is presented. A set of tabs associated with a set of electrode plates are aligned. Either resistance spot welding or ultrasonic welding is used to hold tabs together. A laser penetration weld is created through the set of tabs by a single pulse laser weld or multiple-pulse laser weld. The set of tabs is greater than two tabs.

Modeling and On-Line Estimation of Electrode Wear in Resistance Spot Welding

Abstract: Electrode wear is inherent in the resistance spot welding process. It determines the electrical and mechanical contact condition and thus strongly affects the resistance spot weld quality. A practical approach to minimizing the electrode wear effect is to compensate the welding current as the electrodes wear. However, the existing methods for welding current compensation rely on either a predetermined stepper schedule or an expulsion detection algorithm. These methods are not reliable since the welding current is not determined based on the contact condition for each weld made in the welding process. This paper presents an on-line electrode wear estimation approach to determining the contact condition and the welding current needed to make every weld a good weld during the entire life of the electrodes. In the stuffy, an incrementally coupled finite element simulation was first formulated to analyze the contact area behavior in the resistance spot welding process. A lumped parameter model was then developed to characterize the contact area change with the dynamic resistance measurement. A calibration and an estimation algorithm were subsequently devised for on-line applications. The proposed approach has been validated with experimental data. The results have shown that the estimation algorithm is robust under various process conditions including both welding current and electrode force.