Copper (401) > aluminum (205) > bronze (110) > brass (109) > nickle (91) iron (80) > 1% carbon steel (43) for thermal conductance. Cooper and steel have high melting points. Aluminum melts at about 500 C.
Does that mean that we could use copper tubing as the inner tube of a hotend with aluminum melted between it and a steel outer tube with a heat cartridge in the aluminum (leads being outside) and a thermistor on the steel for a hotend? The aluminum may melt, but who cares.
The steel case on the cartridge and the ceramic on the end should not bond to the aluminum and if it does, it may just hold it in place better. The aluminum to copper transition would direct the heat in towards the filament in a nice and even manner. The steel outer tube may prove to insulate the whole thing by bouncing the heat towards the aluminum and copper. The aluminum would not need to be machined because you can melt it into place by cranking the heat up to 500-600 that the heater cartridge can produce.
If I am right, you would be able to make a hotend this way with only some steel and copper tubing, scrap aluminum, one 12v 40W heater cartridge and some of the stuff from the plumbing section of Lowes or some other place. The only problem is the need for a tiny hole in a pressure cap or an acorn nut.
Why would you want to do it this way? You don’t want a ton of heat all over the place, you want it in a controlled zone near the tip of the nozzle. Do you have any kind of illustration you could provide? Copper is just going to spread heat everywhere.
oh. One wicked thing about this would be that despite the design containing aliuminum, you would be able to actually try to extrude high temperature material up to and including aluminum.
Mind you, I have no idea how easy it is to find aluminum wire or how well extruding it would work for 3d printing. If it worked, that would be seriously kick ass though.
Metals do not bond well below their liquid phase. Even red hot you will have a layer of oxidation that prevents binding. Metals are often folded multiple times and a lot of force is used to get pieces to bind.
At their liquid phase, metals will do as they please. There is a reason metals are Cast instead of printed. Try playing around with molten solder and you’ll see.
If you can set up your print in an inner gas environment it might work out ok, assuming the low viscosity isn’t an issue. The problem with the oxide layer is that it will form on the extruded metal before solidification esp at small volumes and prevent metal to metal bonding. This is an especially big issue for aluminum as the oxide is very strong/hard.
