Assembly Considerations
The spin welding process produces frictional heat at the joint interface by rotating one component relative to the other. It is, therefore, limited to joining components with rotationally symmetrical joining surfaces. It is one of the most efficient methods available to weld such components. Spin welding equipment is fairly inexpensive and simple. One component is held in a stationary fixture and the other in a fixture which rotates. Typical surface velocity at the joint surface ranges from 30 to 50 ft/sec. Velocity as low as 10 ft/sec has been used for thin-walled and delicate parts. The components are held under 300 to 700 psi pressure to quickly generate heat. As the rotating component is brought in contact with the fixed component, the surface temperature rises due to friction between the two solid surfaces. After the initial softening of the surfaces, very high shear is developed in the thin layer of the softened material and the melt layer quickly increases in thickness. A steady state is reached when the heat losses equal the heat generated, at which point the rotary motion is stopped and the components are held together until the assembly is cool enough to be removed. The welding cycle is fast, lasting about 2 seconds including cooling. Component loading and unloading times will add to the total cycle time. Design the joints to provide alignment between the components and a weld area greater than the nominal wall thickness of the part for good weld strength. Flash traps can be designed to hide flash. Friction drivers such as silicone pads can be used to grip rotating components. Design special features such as small gussets or other projections on the larger parts for efficient torque transmission without slippage. The process is highly energy efficient, fast, and allows almost immediate handling of welded assemblies. It yields permanent joints that can have fluid-tight seals. It does not require additional parts such as fasteners, etc. Additional parts can be safely captured in the assembly if located in the fixed component. |