Alternative materials for gas metal arc welding contact tubes

摘要

For GMA welding with low-melting filler metals (e.g., Al, Mg), the process behavior is highly affected by instabilities like problems in current transfer. These can be partly reduced by the electronic control behavior of the welding machine or by using new welding technologies. Another approach followed in this work is to examine how the contact tube material influences the process behavior. At present, mainly contact tubes made of copper are used, which have some disadvantages. For example, the contact tube tends towards alloying with the welding wire and the high-thermal coefficient of expansion leads to problems in wire feeding. Within this work, graphite and metal-doped graphite are investigated as potential materials for contact tubes. As a first step, semi-finished products and contact tubes of pure graphite and different doped-graphite compounds were produced. Subsequently, the semi-finished products were examined regarding their electrical and thermal conductivity as well as their hardness. In welding tests, the tendency towards alloying with the welding wire was examined as well as the tool life of the contact tubes. Doping graphite with different contents of copper and silver strongly influences the electrical conductivity. For the hardness, by contrast, doping has only little influence.