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Visual joins for automotive applications – weld-brazing with CMT and Plasmatron of galvanized steel without spatter

Eva Sjöström

Abstract

This work aims at comparing the CMT process which is a short arc process with retracting wire feed and advanced process control with the Plasmatron process which could be described as a constricted TIG or plasma process and assess their feasibility for visual applications. The work include process optimization, visual inspection, cross sectioning and tensile testing of joints in lap and flare configuration. The finish of panels coated in the paint shop at Scania and Volvo respectively was also evaluated regarding visual appearance. The last section of this work presents a feasibility study of weld brazing of a full size component using Plasmatron.

The main conclusion from this work is that the Plasmatron process is capable to produce weld brazings with very high quality. The process speed (1,2- 4 m/min) and joint quality regarding surface roughness, regularity and distortion is fully comparable to laser brazed joints.

The CMT process produces joints free from discontinuities such as spatter and pores. Yet, it does not fulfill the requirements on visible joints due to the convex braze bead, surface roughness and the waviness at the braze toe.

All companies in the evaluation group approved the Plasmatron weld brazings after coating for visual applications. The CMT joints were only approved for semi visual applications (e.g. door openings) by one of three companies.

The joint quality of the Plasmatron brazed component was only partly accepted for visible applications. Despite extensive clamping and fixing, all components occasionally exhibit defects, preferably caused by variations of the sheet edge or of the gap.

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Senast ändrad av: Peter Hjertsson
26 mars 2015

 


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