Spot Welding Machine Research Articles

Evaluation of welds of aluminum alloy AA6022-T4 welded using an electrode force changeable resistance spot welding machine

(2007). Evaluation of welds of aluminum alloy AA6022-T4 welded using an electrode force changeable resistance spot welding machine. Welding International: Vol. 21, No. 7, pp. 471-481.

A method for modelling the pneumatic drive and loadcarrying structure of resistance spot welding machines

A method for modelling the pneumatic drive and loadcarrying structure of resistance spot welding machines

Relation between Welding Conditions and Temporal Change of Electrode Force-Study on the Development of Electrode Force Changeable Lap Resistance Spot Welding Machine and Characteristics of Welds (Report 1)-

The authors have developed an apparatus for varying an electrode force of a spot welding machine. This is equipped with a servomotor by which we can change rotation instantaneously from normal to reverse and vice versa, and also has a display by which we can monitor the change in the electrode force. Lap resistance spot welding was performed on cold rolled steel (SPCC) and temporal changes of the electrode force were compared with those by a conventional process. In the conventional process the electrode force changed complexly with the elapsed time and the changes were divided into three kinds depending on welding current. When we decreased the initial electrode force than that in the conventional process good welds could be obtained even in lower welding current and the decrease in the thickness of the welds could be lowered. In this case the temporal changes of the electrode force could be explained during the expansion and shrinkage of the welds, though the electrode force changed complexly depending on the initial electrode force and welding current.

Influence of Machine Specific Instantaneous Current Wave Form on Resistance Spot Welding Process

The influence of the machine specific instantaneous current wave forms on weld nugget dimensions and weld strength is investigated over six spot welding machines. It is observed that the nature of the real-time current wave forms corresponding to a common rms value can vary in different ac spot welding machines. The variations exist in the values of peak current and in the current-on and -off times in every ac cycle. It is observed that real-time current wave form involving higher peak current leads to slightly larger weld nugget diameter compared to wave form with smaller peak current even if the overall rms value remains similar. The real-time current wave form from a medium frequency dc confirms to a fast rise to the set weld current and remains steady for the complete weld time. A detailed experimental study has depicted that the real-time ac wave forms especially with high peak values and sharp rise characteristics offer a relatively smaller permissible range of weld currents compared to the wave forms with relatively flatter characteristics. The steady instantaneous current wave form confirming to the medium frequency dc machine has facilitated a larger permissible range of weld current. A numerical analysis of the spot welding process based on finite element process is carried out using both the instantaneous current wave forms and the corresponding rms values of weld current. The predicted weld dimensions using instantaneous current wave forms have showed slightly better agreement with the corresponding measured weld dimensions.

Effect of welding current on mechanical properties of galvanized chromided steel sheets in electrical resistance spot welding

In this study, the effect of welding current on the quality of weld joint and obviously on tensile-shear and tensile-peel strengths of galvanized chromate steel sheets having 1.2 mm thickness in electrical resistance spot welding was investigated. A timer and current controlled electrical resistance spot welding machine having 120 kVA capacity and pneumatic application mechanism with a single lever was used to prepare the specimens. Welding periods were chosen as 5, 10, 12 and 15 cycles and also welding currents were increased from 4 kA up to 12 kA by rise of 1 kA. The electrode force was kept constant at 6 kN. The prepared welding specimens were exposed to tensile-shear and tensile-peel tests and the obtained results were supported by diagrams and, finally, appropriate welding parameters were advised to the users.

Modeling small-scale resistance spot welding machine dynamics for process control

Electrode displacement is generally regarded as a variable that can provide real-time information useful for monitoring and controlling resistance spot welding (RSW) process quality. However, in small-scale RSW production, it is difficult to measure the displacement because its magnitude is very small. By contrast, force signals are relatively large and thus are less susceptible to measurement noise. In this article, an empirical model is proposed to simulate the dynamics of an SSRSW head with the objective of calculating electrode displacement from the variation of electrode clamping force measured during welding. The parameters in the model were determined by fitting experimental force and displacement signals with polynomials and then performing an optimization search for parameters of first-order dynamic models. To verify the models’ accuracy, they were subsequently applied to simulate the electrode displacement curves of welds with expulsion and without expulsion. The calculated displacement curves agreed well with experimental measurements, and the occurrence of expulsion was clearly indicated by the model predictions. A more comprehensive model is under construction with an objective to eliminate displacement sensor in the monitoring and control of SSRSW process.

Probing the role of instantaneous current waveform in numerical modelling of resistance spot welding process

In numerical modelling of the resistance spot welding process, a significant input parameter is the value of the weld current and traditionally, the rms value corresponding to the actual, instantaneous current waveform is used. The rms value implies a constant weld current for the entire weld time instead of the real-time current waveforms. Although the rms value represents an effective approximation of the real-time current waveform, the influence of the peak current and of the current slopes in each half cycle on the welding process cannot be realised in modelling when the rms value is used. Mathematically, an alternating current waveform with higher peak value and lower current on-time in each half cycle may correspond to a rms value that is nearly similar corresponding to another waveform with lower peak value and larger current on-time in each half cycle. The resulting rate of heating and the subsequent size of the weld nugget may not be the same for both the current signals since the resistive heating in resistance spot welding is transient in nature. This is precisely observed in the present work through a detailed investigation using three different ac spot welding machines. A two-dimensional, axisymmetric model is used to analyse the spot welding process using both the actual current waveform and the corresponding rms value as inputs. The computed weld dimensions show better predictions with the instantaneous current waveform as input rather than the corresponding rms value.

磁束制御形スポット溶接機の開発

A large number of spot-welding machines are at use in the automotive, home appliance and can-making industries. For example, two steel sheets several mm thick can be welded with a second or two of several kA of current, which supplies the requisite thermal energy. This paper outlines the development of a spot welder utilizing storage batteries as the power supply. Each time the transformer flux level reached a preset ± desired value the polarity of the primary current is switched. Welding current is output continuously until the energy required for welding is developed.

The effect of nucleus size on mechanical properties in electrical resistance spot welding of sheets used in automotive industry

In this study, the effects of welding current and time on the tensile-peel strength and tensile-shear strength of welding joint in electrical resistance spot welding of chromided micro-alloyed steel sheets having 0.8 mm thickness and galvanized chromided micro-alloyed steel sheets having 1.0 mm thickness were investigated. A timer and current controlled electrical resistance spot welding machine having 120 kVA capacity and pneumatic application mechanism with a single lever was used to prepare the specimens. Welding current periods of 5, 10, 15, 20 and 25 were selected and it was adjusted by increasing 1 kA from 3.5 to 10 kA during welding process. The electrode pressure was fixed at 6 kN. The obtained welding joints were exposed to tensile-peel and tensile-shear tests and their core sizes, heights and nucleus size ratios were calculated by means of an optical microscope. The effect of nucleus size ratios on tensile-peel strength and tensile-shear strength were researched by using related diagrams and the optimum welding currents and times were advised.

A Comparative Study of Single-Phase AC and Multiphase DC Resistance Spot Welding

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.

Magnetic field from spot welding equipment--is the basic restriction exceeded?

A point measurement of the magnetic field (MF) near a typical spot welding machine showed that the magnetic flux density was above the ICNIRP reference level. To investigate if the basic restrictions were exceeded, the induced body currents in a full 3D human model were calculated. It was found that at an operator position of 34 cm away from the machine the maximum induced current density was below the ICNIRP basic restriction. But if the operator was closer to the machine, the basic restriction was exceeded. An important finding of the present article is that the basic restriction can be exceeded although the MF spatially averaged over the whole body is well below the reference level.

Improvement of weldability of TRIP steels by use of in‐situ pre‐ and post‐heat treatments

Low alloy TRIP‐aided steels are very interesting for the automotive industry as they combine both a high strength and an excellent formability. Though the actually developed TRIP steels can be considered as low alloyed when compared to the first generations of steels exhibiting TRIP effect, due to their chemical composition, they still exhibit a quite high carbon equivalent. This is particularly detrimental for the weldability of those materials. After solidification, welds are very hard and can show a brittle behaviour. The hardness of the heat affected zone of the welds can even exceed 500HV and cold cracking phenomena is prone to occur.In the automotive industry, spot welding is the main joining process. During spot welding of TRIP steels, the interface between the plates can act like a notch and promote fracture of the weld. This is particularly dangerous when brittle welds are submitted to peel stresses. The aim of the paper is to demonstrate that a careful choice of the process parameters can significantly improve the resistance of the welds. The selection of the welding cycle parameters is far from being an easy task as many different parameters are involved. Therefore, a design of experiment methodology (DOE) was chosen to optimise the welding cycle for a cold‐rolled TRIP steel with a tensile strength above 700 MPa. Mechanical properties of the welds were significantly improved by use of pre‐ and post‐heat treatments. Those improved welding cycles were realised without excessive extension of the total weld cycle on a conventional spot welding machine. This means that the optimised welds can be obtained in the existing production lines without any additional investment or significant decrease in productivity.

A Study on Development of an Asymmetric Flow Control Pneumatic Valve

A new type of an asymmetric electro-pneumatic servo valve which is used as a hardware compensation of the system to make fast the response speeds is developed and studied. To develop a very high speed system, such as pneumatic force control system for a spot welding machine an asymmetric servo valve which downstream port width is two times of the upstream one is expected as a hardware direct compensation to compensate the system and to equalize the response speeds. The asymmetric electro-pneumatic newly designed servovalve was investigated here to provide asymmetric control flows as an important component in the pneumatic pressure control system for achieving high speed control. This paper describes the characteristics of this asymmetric valve, and we assured the effectiveness of this valve by the experiment.

THE FORCE CONTROL OF A SPOT WELDING MACHINE WITH A SPECIALLY DESIGNED PNEUMATIC CYLINDER

This paper describes the simulations of PID control and PID parameter-scheduling method of an air cylinder system in a spot welding machine. A proper simulation model of the valve controlled air cylinder system is obtained to assess the effectiveness of given control systems. The set-up and set-down responses are analysed in these control systems. Simulation results for various input amplitudes are given to show the effectiveness of the proposed controllers.

STRUCTURAL OPTIMIZATION OF A MOTION AND FORCE CONTROL CYLINDER

Resistance spot welding technology of various coated steel and aluminum alloys is widely used. These welded materials contain base metal, coated layers of metal or cladding metal with different thermal conductivity, electrical conductivity and expansion-contraction properties. They require a proper variable electrode force control during a short welding time to avoid welding spattering, reduce welding defects and increase welding strength. However, a constant electrode force method is usually used in spot welding machines because of too low response speeds of air cylinders.In this research, a dummy force control cylinder was made to simulate the analyses and experiments of structural parameters about a newly developed motion and force compound control cylinder. The dummy force control cylinder is the same sizes as the force control part of the new cylinder in pipe diameter, pipe lengthes and piston diameters. Its transient and frequency responses are mainly dependent on pipe diameter and piston stroke. Experiments indicate that the optimal parameters are about 0.5 (mm) piston stroke and 4-6 (mm) pipe diameter for a servovalve of 8 (mm) spool diameter and 1 (mm) stroke.

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...

Determining the constitutive properties of the heat-affected zone in a resistance spot weld

A methodology is described for determining the mechanical properties of the heat-affected zone (HAZ) in a resistance spot weld. To perform detailed finite-element analyses of spot weld overload failures, it is necessary to have the mechanical properties of the various HAZ subzones. To this end, simulated HAZ material samples were fabricated in a process that utilized a resistance spot welding machine fitted with specially modified electrodes. Tensile tests at several loading rates were performed on miniature notched-bar specimens machined from the simulated HAZ material. These tests provided the empirical data from which the strain hardening capacities and strain rate sensitivities of the weld HAZ were determined through detailed finite-element analyses of the notched-bar tensile tests.

Mechanical properties of resistance spot and projection welding machines

Mechanical properties of resistance spot and projection welding machines

Mechanical properties of resistance (especially spot and projection) welding machines∗

Mechanical properties of resistance (especially spot and projection) welding machines∗

Spot welding of Fe-Si-B amorphous metal foil

The possibility of the welding of amorphous metal foils was examined.Fe78Si9B13 amorphous metal foil having 20 microns in thickness was welded by using a stored energy type spot welding machine. This foil was possible to weld without crystallization at a welding time within 0.4 milliseconds.The irregularity of weld nugget shape was due to the unevenness of the foil surfaces employed. This resulted in the scattering of tensile-shear strength of single spot welds.Increasing weld time with the use of the capacitor bank having excessive capacitance led to a brittle weld nugget, though crystallization did not occur.In tension-shear test, a crack initiated near the periphery of the weld nugget and propagated in the base metal. It means that the enhancement of joint strength was difficult by multiple spot welding.