Rotary friction welding

Rotary friction welding (RFW) is a type of friction welding, which uses friction to heat two surfaces and create a non-separable weld. For rotary friction welding, this typically involves rotating one element relative to both the other element, and to the forge, while pressing them together with an axial force. This leads to the interface heating and then creating a permanent connection. Rotary friction welding can weld identical, dissimilar, composite, and non-metallic materials. Like other friction welding methods, it is a type of solid-state welding.

History

Rotary friction is the oldest of all friction welding methods, with a method of rotary friction welding first being patented in 1891. In 1956, the Russian machinist A. J. Chdikov (А. И. Чудиков), after having performed rotary friction welding with a lathe in the Elbrussky mine, would propose its commercial use to the Ministry of Metallurgy. While the Ministry of Metallurgy did not see value in this, it would attract attention from the national Scientific Research Institute of Electrical Welding Equipment, and was gradually disseminated following its publication in newspapers of the Soviet Union. In 1960, the process would spread to the United States, with American companies such as Caterpillar Tractor Company (CAT), Rockwell International, and American Machine and Foundry developing machines for this process. This led to the development of an inertial friction welding process in 1962, through joint efforts from CAT and Manufacturing Technologies Incorporated (MTI). The 1960s also marked the first research of friction in welding in England by The Welding Institute (TWI). In Europe, KUKA AG and Thompson Friction Welding, would develop a direct-drive process and build a double spindle friction welder. The efficiency of friction welding, both linear and rotary, has been improved by the development of low force friction welding by the Edison Welding Institute and MTI working in collaboration.

Applications Rotary friction welding is widely implemented across the manufacturing sector and has been used for numerous applications, including:

Parts in gas turbines. Automotive parts Monel-to-steel marine fittings Cutting tools Tublar joints

Connections geometry Rotary Friction Welding can join a wide range of part geometries such as tube to tube, tube to disk, bar to plate. In addition, a rotating ring is used to connect long components. The geometry of the component surface does not have to be flat but can also be conical.

Types of materials to be welded Rotary friction welding enables to weld various materials.

Metallic materials of the same name or dissimilar either composite,superalloys and non-metallic e.g. thermoplastic polymers can be welded and even the welding of wood has been investigated. Weldability tables of metallic alloy can be found on the Internet and in books.

Sometimes, an interlayer is used to connect non-compatible materials.

Division due to drive motor In direct-drive friction welding (also called continuous drive friction welding), the drive motor and chuck are connected. The drive motor is continually driving the chuck during the heating stages. Usually, a clutch is used to disconnect the drive motor from the chuck, and a brake is then used to stop the chuck.

In inertia friction welding the drive motor is disengaged, and the workpieces are forced together by a friction welding force. The kinetic energy stored in the rotating flywheel is dissipated as heat at the weld interface as the flywheel speed decreases. Before welding, one of the workpieces is attached to the rotary chuck along with a flywheel of a given weight. The piece is then spun up to a high rate of rotation to store the required energy in the flywheel. Once spinning at the proper speed, the motor is removed and the pieces forced together under pressure. The force is kept on the pieces after the spinning stops to allow the weld to "set".

Stages of process

Step 1 and 2, friction stage: one of the components is set in rotation, and then pressed to the other stationary one in axial of rotation, Step 3, braking stage: the rotating component is stopped in braking time, Step 4, upsetting stage: the welded elements are still forging by forge pressure (pressed down), Step 5: in standard RFW welding (standard parameters), a flash will be created. Outside flash can be cut off on the welder. However, referring to the stages chart: modifications of the process exist, may depend on the version of the process: direct-drive, inertia friction welding, hybrid welding, there are many versions of welding machines, many materials can are welded with not the same properties, with various geometries, the real life process does not have to match to the ideal settings on the welding machine.

RFW Friction work on cylindrical rods workpieces Friction work create weld and can believe that is calculated for cylindrical workpieces from math: Work: (1) W = M × α {\displaystyle W=M\times \alpha }

Moment of force M general formula: (2) M = r × F {\displaystyle M=r\times F}

The force F will be the frictional force T (F=T) so substituting for the formula (2): (3) M = r × T {\displaystyle M=r\times T}

The friction force T will be the pressure F times by the friction coefficient μ: (4) T = μ × F {\displaystyle T=\mu \times F}

So moment of force M: (5) M = r × μ × F {\displaystyle M=r\times \mu \times F}

The alpha angle that each point will move with the axis of rotating cylindrical workpieces will be: (6) α = 2 π × n × t {\displaystyle \alpha =2\pi \times n\times t}

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