All the setups that I have seen or read about regarding FSW don't mention preheating. In fact, I think the idea is bad altogether, as the heat from the process is a byproduct of friction. In fact, as I'm sure you already know, it's not really welding, it's the "stirring" of the parent metal to a plastic state and redistributing the mass in the wake of the tool. The goal of FSW is to be able to weld materials that commonly can't be welded by any other means, to weld dissimilar materials, and to keep the HAZ from being larger than absolutely necessary.
I keep going back to the idea of a commonly available spindle (Tormach sells a BT30 upgrade for $595 that is a industry standard 80mm cartridge type) and building a water jacket for it...run the coolant through a closed-loop TIG torch cooler. I think a hydraulic tool holder would be a pretty good idea for this kind of setup.
It would probably be pretty expensive, but an idea I had for insulating the tool from the holder and thus preventing heat transfer to the spindle...
AlMMC. Aluminum Metal Matrix Composites are stronger than cast iron (tensile strength and compression...approaching many steels, in fact), hard, light (up to 25% lighter than "regular" 6061), ungodly abrasive to machine...and work wonderfully well for heatsinks. Better in fact than 6061 or 6063 extrusions. Typically AlMMCs are made from 6061 with SiC3 (I think that's right...silicon carbide, by any rate), and are available for extrusion and in billet form. I suggest AlMMC rather than ceramics due to fracture toughness and thermal shock/cycling. MMCs are the best of both worlds...metals that are lighter and stronger than possible with current alloying methods (minus exotics like Aluminum/lithium or aluminum/beryllium) while exhibiting amazing thermal resistance to excessive growth or creep.
What material are you building the FSW tool from? I used H13, it works well, but degrades over time due to heat cycling.  |