Comparative research into friction stir welding with welding pins made from tool steel and carbide, respectively.
In the following analysis, two materials for welding pins were tested under increased stresses. The focus hereby is on the widely used tool steels as a representative of material of lower strength (tool steel 1.2344) and carbide (G30) as a representative of material of higher strength. As the first step, a test was performed with tools made from tool steel.
Process forces in friction stir welding
The applied process forces are acting on the welding pin in a discontinuous fashion whilst simultaneously impacting upon it. This is the reason why material properties such as, for example, strength and toughness are essential for the application of an FSW welding tool.
Welding test with tool steel
In tests with tools made from tool steel, it can be demonstrated that process settings and the resulting stresses on the welding pin can result in the shearing of the welding pin. On the other hand, the advantage of tool steel lies in low manufacturing costs and a comparatively high fracture toughness.
Welding test with carbide
Tests with tools made from carbide have shown that welding pins made from comparatively higher-strength materials (carbide) are especially suited for FSW applications entailing higher stresses. Furthermore, hardness and high-temperature strength favour the wear performance of friction stir welding tools. We recommend the use of SC FSW PINS.
SC pins have a superior L/D ratio as compared to steel pins.
Narrower welding seam possible (up to 50% narrower) for identical sheet thickness (Al). Thicker weld for identical PIN diameter. Smaller PIN diameters make lowered process forces possible (important for machine design).
Polished pins made from HSS-E and SC display a significantly increased surface quality as compared to milled/turned pins.
Less adhesions of aluminium = longer travel distance. Improved thermal balance within the welding zone.
Polished pins made from HSS-E and SC possess a significantly better radial run-out as compared to milled/ turned pins.
More even welding seam achieved with even thermal balance.