The inertia welding process, like direct-drive rotary friction welding, uses part rotation under pressure as friction heats the faying surfaces. It differs by use of a flywheel to generate the rotational momentum in the part-holding chuck. The flywheel-driven chuck spins until it stops when the weld zone seizes. This inertia method is also sometimes described by the colloquial term, spin weld. Conversely, our direct-drive method provides continuous speed control through the cycle and stops according to a computer parameter developed specifically for the part.
While the result of both techniques ends with the same high strength result, with a full cross-sectional bond, material cost reduction, there are legacy parts that were designed to be welded one way or the other, typically not both.
Energy is provided by the machine’s kinetic energy that is stored in a rotating system or mass. In this instance the energy available in a stored energy system is finite. This requires specific parameters of mass/weight, speed, and pressure to meet the requirements of the weld union. When the desired rotational speed is achieved, kinetic energy is transferred into the freely rotating part. Constant forge pressure is applied until a plastic state is reached. Rotation stops due to controlled pressure as the desired total displacement length of material (upset) are met. Rotational speeds are normally higher than direct drive friction welding. The majority of the total displacement comes at the very end of the weld cycle as compared to being spread out over the middle to end of the cycle.
Below you will find an outline of the Inertia Welding stages and what the results look like on a playback graph. Keep in mind that the end result is the same but the chief difference between the two techniques is the energy source, RPMs, and timing/distance as pressure is applied.
Stage 1: One component inserts into a rotating chuck, and the other component inserts into a fixed tail clamp. Components consist of the same or dissimilar materials. The head is then accelerated to a preset speed.
Stage 2: The rotating component or the fixed tailpiece is then forced against the remaining component at the weld interface.
Stage 3: Rotation stops under its own kinetic mass and then a forge pressure completes the welding cycle.