TWI Technology Briefing 894/2008
By A C Addison
Linear friction welding (LFW) of metals is probably the best kept secret in the field of welding today. It is a process which laboratory experience suggests is robust, reliable, simple to use, fast and capable of producing high quality joints in many engineering metals and metal combinations.
The parts to be joined are held together under a compressive load whilst one part is moved in a reciprocating manner with a pre-determined frequency and amplitude as shown in the sketch below.
The friction between the two parts results in sufficient heat being generated to soften the materials at the interface between the two parts. This hot and soft material is expelled from the joint area as flash as a result of the compressive load, allowing the parts to shorten by a pre-determined distance. At this point, the movement is stopped at a specified position and a further forge load applied to consolidate the joint as it cools. The typical welding time for a joint in metal is less than ten seconds, with the size of components to be joined having little or no impact on the welding time.
The use of linear reciprocating movement to generate the heat required to make the joint results in a mostly uniform microstructure with only small regions modified by either heat or mechanical work. Unlike the closely related rotary friction welding process, the parts to be joined do not need to be regularly shaped, nor is the process limited to producing joints in the butt weld configuration.
The purpose of this report is to introduce LFW to a reader with little or no knowledge of the process in a logical order; eliciting an understanding of its terminology, best practice, capabilities, benefits, drawbacks and limitations.
- Review the current status of LFW technology in order to provide a sound understanding and technical guidance on the capabilities of the process.
- To examine current commercial applications of LFW.
- Produce preliminary weld quality data for LFW joints in a range of common engineering metals.