Mechanical characterisation and modelling of resistance welding

Resistance welding is used very extensively in industry for a wide range of applications. Knowledge and measurement of the dynamic characteristics of resistance welding equipment is important in the design of the equipment and in optimization of welding procedures using finite element software. This is especially true for projection welding where accurate measurements of effective lumped mass and damping of the welding head as well as its maximal acceleration and velocity are required for accurate modelling. This thesis describes a new concept where a mechanical model of the welding head is used together with the imposition of a mechanical load step function with simultaneous measurement of resulting head motion to calculate effective lumped mass and damping factor. Two test systems were devised to implement the step function. In the “free fracture test”, a metal or ceramic bar is loaded to its breaking point and resulting welding head velocity is measured. This data allows accurate calculation of machine parameters. The second test uses the explosion of a small metallic element to impose a step function, when the welding current causes the metallic element to explode. The final version of this test “the exploding button test” uses a small cylindrical element fabricated from welding filler wire, with the advantage that both button geometry and material can be controlled. The exploding button test has proved to be very effective, can easily be used for in-situ measurements and avoids the vibrations associated with the free fracture test. These test were applied to evaluate a range of resistance welding machines. Finally, an innovative projection geometry was developed to significantly increase projection weld quality and this design has now been used extensively in industry. The techniques developed in this thesis have been shown to be practical and effective and have enabled much better understanding of machine kinematics. The measurements provide essential data for modelling of projection welding and in guiding the development of resistance welding machines and procedures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Weld-bonded stainless steel to carbon fibre-reinforced plastic joints

This paper investigates a resistance spot welded reinforced adhesive (weld-bonded) joint between 304 stainless steel to carbon fibre reinforced plastic (CFRP), where welds are made both with and without the reinforcing carbon fibres present. Successful welds with the fibres present could only be produced with high electrode pinch forces, which helped reduce contamination of the weld nugget. Similar joint strengths were achieved in both cases, however the joints without fibres exhibited an increased strain to failure. Both joints were significantly stronger than either an adhesive joint or a comparable bolt reinforced adhesive joint. These techniques provide an alternative for joining thin metallic components to CFRP structures where increased strength and integrity is required

Mechanical characterisation and modelling of resistance welding

Resistance welding is used very extensively in industry for a wide range of applications. Knowledge and measurement of the dynamic characteristics of resistance welding equipment is important in the design of the equipment and in optimization of welding procedures using finite element software. This is especially true for projection welding where accurate measurements of effective lumped mass and damping of the welding head as well as its maximal acceleration and velocity are required for accurate modelling. This thesis describes a new concept where a mechanical model of the welding head is used together with the imposition of a mechanical load step function with simultaneous measurement of resulting head motion to calculate effective lumped mass and damping factor. Two test systems were devised to implement the step function. In the “free fracture test”, a metal or ceramic bar is loaded to its breaking point and resulting welding head velocity is measured. This data allows accurate calculation of machine parameters. The second test uses the explosion of a small metallic element to impose a step function, when the welding current causes the metallic element to explode. The final version of this test “the exploding button test” uses a small cylindrical element fabricated from welding filler wire, with the advantage that both button geometry and material can be controlled. The exploding button test has proved to be very effective, can easily be used for in-situ measurements and avoids the vibrations associated with the free fracture test. These test were applied to evaluate a range of resistance welding machines. Finally, an innovative projection geometry was developed to significantly increase projection weld quality and this design has now been used extensively in industry. The techniques developed in this thesis have been shown to be practical and effective and have enabled much better understanding of machine kinematics. The measurements provide essential data for modelling of projection welding and in guiding the development of resistance welding machines and procedures

Influence of welding current on RW machine follow-up behaviour, a practical test method

Machine dynamics of resistance spot welding (RSW) machines significantly influence process capability and performance. Integrated mechanical, electrical and thermal models of the RSW process also require accurate specification of machine dynamics. The influence of specific machine configurations is extremely difficult to predict starting from individual component specifications, and it has also been difficult in the past to accurately measure dynamic performance under typical operating conditions. This paper presents a reliable and very straightforward new method for the characterization of machine performance. This method has the advantage that it can be used to characterize the performance of RSW machines under realistic operating conditions. The test, the “Exploding Wire Test", uses a small diameter wire placed between the welding electrodes. The machines’ performance can subsequently be measured at the required operating load as the wire disintegrates when welding current is applied. This paper also describes the negative influence of the welding current itself on the machines’ mechanical behavior. The welding machines’ performance characteristics can be used directly, in order to optimize process operation towards a specific and demanding application, or serve as an input into an integrated mechanical / electrical / thermal model of the RSW process. The test method is relatively simple (although sophisticated instrumentation is required to accurately measure dynamic behaviour) and it can be used over a wide range, from micro-joining to heavy duty applications, and can be applied to projection welding as well as resistance spot welding.status: publishe

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Data Underpinning "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints"

Figures for article entitled "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints