Huge material savings, low-cost tooling, ideal material properties, excellent weld properties and a short production time were just a few of the favourable aspects of linear friction welding which prompted one of TWI's clients to get in touch.
The Midlands-based engineering business Thompson Friction Welding wanted TWI to make several preforms by joining large blocks of raw material to second and third blocks. The process, sometimes known as solid-phase additive manufacture, allows complex shapes to be manufactured without the wastage of material normally associated with machining from one large block, casting or forging.
There was an added dimension of urgency: the parts were needed in time for the fast-approaching Farnborough Air Show.
The merits of preform manufacture are numerous:
- Typically, such applications include components that are currently machined from solid blocks of high value materials. So, by linear friction welding (LFW) preforms, both the amount of material turned into swarf and the machining costs can be drastically reduced.
- Feasibility studies in a range of titanium alloys have already shown that excellent weld properties can be achieved. The tensile and fatigue properties are comparable or even better than the parent metal.
- Existing mill annealed plate allowables, usually for thin section, can be included in component design.
- The process window for good quality LFW in titanium is generally very large.
- The LFW approach allows inclusion of dissimilar titanium alloys at defined locations in the component. So, it is in effect 'tailored'. Example parts clearly show the saving in machining of high value materials.
So, the LFW process's potential for reducing production costs are high. It's a highly repeatable process which has its roots in blisk manufacture, joining blades to disks. The development of low-cost LFW machines has broadened enormously in recent times and the process now accommodates many more LFW applications than were available a decade ago.
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