Resistance Or Friction Welding Overview
Resistance or Friction welding are two welding processes that fit into a category of processes that works with a workpiece that is moving and another piece that remains stationary. In the process heat is generated through friction as the two pieces come together and an "upset" (a lateral force) displaces and fuses these materials.
Friction welding is generally used with thermoplastics and other metals and is used a lot in the aviation and automotive industries. In friction welding there is no melting and the heat is directed to the weld interface. This creates a small heat zone. Also, as the friction is happening it cleans the surface of the materials to be welded so the welder does not have to prepare the surfaces before welding.
This method of welding also has several advantages. The metal that is used has small pieces of "plastic" metal that is forced out of the area where the friction is happening. This metal called "flash" comes out in ripples and seess to carry away the dirt or the debris that would normally occur when doing welding.
Two different types of metals can also be joined using this method. An example of this is in the aerospace industry where they use friction welding to bring together aluminum and high-strength steel. This can only be done in friction welding because they are two different types of metal. The nuclear industry also uses this method to do cooper and steel joints that are used in the reactor's cooling systems.
When you have metals that are under a lot of pressure and heat you will be working with thermoplastics. You can join metal and plastic together. A good example of this is when they use friction welding to join the pins of eyeglass frames to the rest of the frame.
There are several welding techniques that use friction welding. Spin or inertia welding has two "chucks" that hold the metal with one stationary and the other that rotates. The piece that the welder wants to weld is put on the rotating chuck and a flywheel is added so that it will have a specific weight. They then spin the piece they want to weld at a high speed, then remove the motor and the pieces are put under pressure and forced together. The pieces "set" once the spinning has stopped and the pieces have cooled down from the friction.
Linear friction welding is like spin welding but instead of spinning it oscillates in a lateral motion. The speed that the welder uses is lower and the pieces are kept under pressure throughout the entire process. In order to do this type of welding the industry needs a more complex machine which is a bit more expensive, but it also allows each two chapters to be joined.
Thermoplastics have other methods that they use for friction welding. In Orbital friction welding an orbital motion is made by the moving part (similar to the spinning friction process) and it rotates in line with a smaller circle than the joint.