History of Friction welding
The concept of friction welding is probably about 130 years old. It was recognized with a patent in the U.S.A in 1981. At that time, friction heat was used to attach a V-shaped die with a tube. With the cooperation of Mr. A.l Chudikov, the commercial use of friction welding began in Russia around 1956 / 57.
By 1959, friction welding had spread to the West, while in 1956 a US Patent was granted to T.L Obrele, M.R.Claton, C.D Lloyd, and C.F.White and assigned to the caterpillar Tractor Company in the U.S for Inertia Welding
It is true that today friction welding is considered one of the important innovations in the field of welding technology due to its many advantages and flexibilities.
Friction welding process
Friction welding is placed under the solid-state welding process, in this process heat is obtained by the friction of workpieces, and the joint is made using pressure, without any additional filler material.
Intertia welding
Intertia welding is similar to friction welding because both use friction to develop heat. The temperature developed by friction is below the melting point of the metal but high enough to form plastic flow and intermolecular bonding.
The temperature generated by friction in this process is less than the melting point of the material and the joint is formed only by plasticizing and applying pressure, this process is not called fusion welding.
Difference between friction welding and inertia welding
Although both the processes use friction to obtain heat but the operating steps are different which can be understood as follows:
Energy source
In friction welding, the energy is supplied from conventional drive sources such as electric or hydraulic motors. But in inertial welding, a flywheel is employed to supply energy. Intertia welding uses the kinetic energy stored in a rotating flywheel. The flywheel is rigidly fixed with one weld member. The flywheel remains under the influence of an infinite power source. It is worth mentioning here that it cannot stop until all the stored kinetic energy is converted into heat energy.
Operational steps in friction welding
- Both components to be friction welded are kept in axial alignment.
- The workpiece installed in the chucking spindle of the machine is rotated and accelerated to the required speed.
- The other component that is stable with a movable clamp is pushed forward to come into contact with the rotating component. Here, the stress and wheeling are maintained until the resulting high temperature plasticizes the metals,
- When sufficient heat is obtained, the power drive is unplugged, brakes are used to stop the rotation, and the axial force is usually increased to forge the two components together.
Operational steps in Inertia welding
- In this process, a component is rigidly clamped to a stationary chuck or fixture. The flywheel along with the other components is accelerated to the desired angular velocity until it stores enough kinetic energy to produce the weld.
- At this time, the drive of the flywheel is cut off and the two components are immediately brought together under high pressure.
- Upon application of this axial force, the weld itself acts to break the flywheel to convert the flywheel kinetic energy into frictional heat and forging action at the weld interface. The axial force is generally maintained at a constant value through the weld cycle.
Welding variables
The productivity and quality of friction welding depend on the following variables:
Relative Speed
Peripheral speed is an important parameter in determining the maximum interface temperature and therefore the final joint metallurgy. High speed produces overheated structures while low speed can generate insufficient heating.
Friction pressure
Frictional pressure in conjunction with circumferential speed determines the thermal conditions established in the weld area and the rate at which the metal is radially removed to be disturbed. For most materials, there is a wide range of combinations from speed and pressure that can be used to give excellent mechanical and metallurgical integrity in welds.
Time duration
The heating period is selected to ensure that the facing surfaces are cleaned of friction and the weld zone temperature is raised to achieve the plasticity required for solid-state pressure welding.
Forge pressure
The forge pressure is chosen in relation to the hot strength of the material being welded because sufficient pressure must be used to heat the weld area and consolidate the interface.
Parameters for Inertia welds
Parameters for Inertia Weld are as follows:
1- Axial Force
2- Initial rotation speed of the flywheel spindle system.
3- Moment of inertia of the flywheel.
The weld energy is calculated from the weld parameter, rpm, and the moment of inertia of the flywheel spindle system by the equation
E = Wk² (rpm)² / 5873
where E = weld energy, ft. lb
W = welding of flywheel system, lb
K = radius of revolution of the flywheel system, ft.
Materials to be welded by Friction/Inertia process
A wide variety of materials can be welded by friction/inertia welding, the most common metals that can be welded are:
- Tantalum
- Tungsten
- Brass and bronze
- Stainless steel
- Tool steel
- Carbon steels
- Alloy steels
- Magnesium alloys
- Nickel alloys
- Titanium alloys
- Zirconium alloys
- Aluminum and its alloys
- Alloy steel to carbon steel
- Copper to carbon steels
- Sintered steel to carbon steels
- Copper to aluminum
- Aluminum to stainless steels
- Superalloys to carbon steel and
- Stainless steel to carbon steels, etc.
Joint preparation of Friction welding
Butt joints and lap joints can be welded on a friction welding machine. The basic joint designs consist of combinations of bars and tubes and bars or tubes to plate as illustrated.
However, for friction welding at least one of the components to be welded must be essentially round. If it is also the revolving member, it should somewhat concentric in shape, because it has to rotate at a relatively high speed for friction welding.
Advantages
- The concept of friction welding is simple, it consumes a low amount of power. Once the parameters for a job have been determined, the welding takes only a few seconds.
- Less prone to defects because surface impurities and oxide films are broken down and thrown away during the friction heating process. There is no flux, gas, filler metal, or slag present to cause imperfection in welds also no smoke fumes or spatter are produced.
- Compared to traditional flash or resistance butt welding, friction/inertia welding produces better welds at higher speeds and lower cost, as less electric current is required and expensive copper fixtures are eliminated to hold components.
Disadvantages of friction/Inertia welding
This process can’t be used for flat and angular butt welds, it has been applied only to the joining of small pieces in the form of bar stock.
Sometimes quite a heavy flash is forced out in all inertia and friction welds.
Flash from medium and high carbon steels being hard, must either be removed while it is hot or annealed before it is machined.