20-10-2010, 11:47 AM
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The Process
Definition:
Friction welding is a solid state process that is achieved through frictional heat. This heat is generated by a controlled rubbing of two components until material reaches its plastic state, at which time plasticized material begins to form layers that intertwine with one other. The friction welding machine controls this rubbing through a series of unique parameters for rotational speed (rpm’s), axial force and time. Once these parameters are established, they are recorded, stored and repeated with each cycle of the machine.
The Process Description:
1. Parts are loaded into welder, one in rotating spindle and the other in a stationary clamp. (Special tooling may be required if parts don’t have a natural axis of symmetry.);
2. Components in spindle is brought up to pre-determined rotational speed and then a pre-determined axial force is applied;
3. These conditions are maintained for a pre-determined amount of time until desired temperatures and material conditions exist;&
4. Rotational speed is then stopped and increased axial force is applied until desired upset is obtained. Components are then unloaded and cycle is repeated.
Friction welding is a process that is currently used in many different industries. The key is to fully understand the process and its advantages, then have the ability to visualize how it could be utilized in specific applications you may have. American Friction Welding offers any technical support necessary to assist you in that process. We extend an open invitation for you to tour our facility and see the process first hand.
The Types of Friction Welding
Friction Welding (FW) is a group of solid-state welding processes using heat generated through mechanical friction between a moving work piece, with the addition of an upsetting force to plastically displace material. Many dissimilar metal combinations can be joined and there are a number of process variations including:
• Spin Welding- "Four different phases can be distinguished in the vibration welding process; the solid friction phase, the transient phase, the steady-state phase and the cooling phase.
In the solid friction phase, heat is generated as a result of the friction between the two surfaces. This causes the polymer material to heat up until the melting point is reached. The heat generated is dependent on the applied tangential velocity and the pressure.
In the second phase, a thin molten polymer layer is formed which grows as a result of the ongoing heat generation. In this stage heat is generated by viscous dissipation. At first only a thin molten layer exists and consequently the shear-rate and viscous heating contributions are large. As the thickness of the molten layer increases the degree of viscous heating decreases.
Thereafter, (start of third phase) the melting rate equals the outward flow rate (steady state). As soon as this phase has been reached, the thickness of the molten layer is constant. The steady-state is maintained until a certain "melt down depth" has been reached at which point the rotation is stopped.
At this point (phase 4) the polymer melt cools and solidification starts, while film drainage still occurs since the welding pressure remains. After all the material has solidified, drainage stops and the joint are formed."
