TIG (Tungsten Inert Gas) welding is our chosen method of joining our tubes together to form a frame. The torch uses an electrical arc in a super controlled manner to melt a small liquid puddle of metal at the joint. We then add a filler material (filler rod) to the puddle, making a weld bead. This is the best way to join the materials we are using to make our frames, and also one of the hardest to master. Because the metal is heated up to a liquid and then cools down there is a small amount of distortion (shrinkage) that occurs. It is the goal of a welder to minimize and control this distortion as much as possible. To do this we employ the use of heatsinks…
This is an example of one of our heatsinks. It slides into a Press Fit 30 bottom bracket shell and expands against the inner wall of the shell to absorb the heat generated during the welding process. It also serves a double duty as a purging unit.
At the high temperatures that occur during the welding of titanium and stainless steel the hot metal readily absorbs contaminates in the surrounding environment such as hydrocarbons, oxygen, nitrogen, etc… Absorbing these contaminates would make the weld joint weak and brittle. There is a fitting on one end that we attach to our argon line that allows argon to flow into the area being welded, displacing contaminates in the ambient air that fills the frame. Argon is an inert gas that keeps the welded area clear of these contaminates and makes the welded joint as strong as it can possibly be.
The internal shaft of the heatsink is hollow and has holes drilled in it to allow the argon to flow into the frame. We use heatsinks like the one shown at each area of the frame that we weld.
Making the heatsink in three parts makes it so it can expand and also collapse in order to get it in and out of the shell. If it didn’t collapse weld distortion would trap it inside the frame.
At each end of the shaft we made some conical washers that press against the inside of the 3-part cylindrical aluminum heatsink. When the nut is tightened it presses the cones inward expanding the heatsink outward against the inner wall of the bottom bracket shell, making the heat transfer as efficient as possible.
Assembled and inserted into the shell it looks like this.
We also made a cap that goes over the tightening nut. The cap keeps the argon from escaping and helps with absorbing more heat.
This is just another one of the steps we utilize during the production process that ensures we are making the frames as straight as we possibly can.