STUDY ON TUBE POSITIONING TOLERANCES FOR MAGNETICALLY IMPELLED ARC BUTT WELDING OF THICK WALLED TUBES

摘要

Magnetically Impelled Arc Butt (MIAB) welding is a solid state joining method predominantly used in automobile applications for joining of tubes and rods in Europe and Canada. In majority of the cases, tubes with less than 3mm wall thickness and surface area of joining between 150 to 400 sq.mm only are being used in the above industries. At WRI, experiments were conducted to study the MIAB welding technology for welding of high -wall thickness tubes ranging from 4 to 6.5mm and having weld surface area of maximum 1100 sq.mm. In order to establish this welding process for joining of components for power plant industries, it is necessary to get the process approved by the competent authorities in this field of manufacturing. As a part of this -work, experiments were carried out to study the positioning tolerances of the two tubes in the die, which are to be welded by MIAB process. Axial offset between tubes was varied from 0.25 to 2.00mm in steps of 0.25mm and the angular offset was varied from 1 to 5 deg in steps of 1. The results shows that axial offset upto 1.5mm passes tensile and bend tests, whereas 2.0mm axial offset resulted in failure in weld line with 20% reduction in UTS values. However, 2.0mm axial offset passes root and face bend tests. The angular offset up to 5℃ passes tensile and bend tests. Detailed microhardness and microstructural analysis were carried out for the select tolerance levels based on production constraint criteria. The results will provide a window of acceptance criteria for the input materials, i.e. tube positioning tolerance, axially and angularly on welding die, for obtaining an acceptable weld with satisfactory mechanical properties.