Frequently Asked Questions
With conventional rotary friction welding, it is possible to control the overall length of welded components to within ±0.5mm.
This is usually accomplished by ensuring that a preset amount of 'burn-off' is achieved during welding. Burn-off is the material lost during the friction heating cycle and is set before welding takes place. It is the parameter which helps to determine the amount of heating during welding and governs when the heating cycle is terminated.
Some machine manufacturers also use 'floating' burn-off, especially where the materials being welded will tolerate variations in the amount of burn-off. With this system, the burn-off is set to accept parts which are at the minimum length required prior to welding. When part lengths exceed the minimum, the extra material is burnt-off prior to forging.
Another (but as yet, little used) method of controlling overall length involves forging to a stop. This method is capable of increased accuracy compared with control by burn-off.
Experimental work carried out in TWI's friction welding laboratories has shown that, compared with conventional rotary friction welding, linear friction welding is capable of giving closer control of overall length. With routine production applications, accuracies as good as ±0.2mm are feasible.
Regardless of which technique is used, the accuracy of the parts prior to welding is critical in achieving the required tolerance. Control of overall length is also affected by how well the components are clamped in the friction welding machine.
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