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Fine tuning to spot welding kit

 

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When initial impact tests on resistance welded prototypes using high strength steels produced unexpected failures, the Industrial Member concerned turned to TWI for comment.

The spot weld failures were believed to have been caused by using low electrode forces. But this was only part of the diagnosis. The equipment available at the time was known to be of limited capacity. So higher capacity equipment was recommended and installed at the Prototype Suppliers facility.

The initial trials threw up reasonably satisfactory results. So TWI was then asked to refine the resistance welding equipment settings; force, time, current and gun configuration.

TWI set up two and three thickness combinations to give large weld sizes, and programs were established that allowed small assemblies to be produced for preliminary testing. These were reported by the Member to be of satisfactory quality.

The fundamental objective of the work was to set up precise conditions for the two and three thickness material combinations required in the finished vehicle.

Electrode force was checked with a Lutz squeeze monitor and current measured with a Miyachi printer current meter. These measurements verified acceptable reproducibility of the new equipment and uniformity of the welding parameters for the test welds.

An exhaustive programme of weld testing was conducted using differing combinations of two and three thickness welds on material 1.5mm, 2.0mm and 2.3mm thick and using gun configurations with both offset adaptors and equal adaptors.

As a result consistently acceptable, representative test weld sizes in the region of 9mm diameter were achieved.

Current and force values were consistent during the welding work.

The stiffness of the gun was improved with the electrodes centrally placed. Finally recommendations were made for settings for the continued work on additional two and three thickness welds.

As a result of the work, the vehicle met the desired high impact performance requirements. It also enabled feedback of welding parameters into the production manufacturing base, and allowed capable equipment and processes to be introduced for the start of production.

For more information please email:


contactus@twi.co.uk