Linear friction welding has been demonstrated for virtually all types of engineering alloys, such as titanium ( Fig.1), steel, stainless steel, aluminium and inter-metallics, but the uptake of the process by industry has been impaired by the high capital cost of existing mechanical linear friction welding machines. Novel solutions have been devised to reduce the manufacturing cost of the equipment, mainly based around more efficient use of the power sources required and by use of stored energy concepts. This will lead to a very substantial reduction in equipment price.
Workshop drawings of all modules of a prototype machine have been produced ( Fig.2), and the components are currently being machined or purchased. The prototype machine was trademarked LinFric TM by TWI [1] and has been designed to weld work pieces with a maximum weld area of 2000 mm 2 . The LinFric TM machine does not need any balancing, and its oscillator is driven by a hydraulic power pack through 8 accumulators, which can provide an oil flow of up to 750 l/min. It can vibrate at frequencies of 25-125 Hz with amplitudes of up to ±3mm. An axial force of up to 150 kN (15 t) can be applied during the friction phase. The force can then be increased to 200 kN (20 t) to permit consolidation during forging.
Linear friction welding ( Fig.3) can be used to join a variety of complex profiles. It is technically, commercially and environmentally a very attractive process, and is ideally suited to both mass production and to the manufacture of specialised components required in limited numbers. If different components have to be welded, only the tooling to hold the workpieces needs to be changed and different welding parameters may need to be developed.
The technology of friction welding is becoming more widely accepted in many industry sectors, as the economic benefits and the high quality that it provides are increasingly recognised. After the world-wide acceptance of rotary friction welding, this progress has been significantly helped by the advent of innovative variants on the process, such as vibration welding of plastics, friction stir welding and friction surfacing. Friction welding processes are very energy efficient compared to most competitive welding processes. Routine maintenance of friction welding machines is generally not expensive, and no consumables such as filler wire, flux or shielding gas are required, even for environmentally sensitive materials such as titanium alloys. As friction welding processes are substantially automated, quality and reproducibility are high compared to alternative manual welding processes. Friction processes are generally tolerant to wide changes in the welding parameters without compromising quality, thus reliability is high.
The consortium of this project consists of five small and medium sized enterprises (SMEs) from three countries, supported by one larger company, and two research and development organisations. The project will put European SMEs in a strong position to supply what is firmly believed to be a large and sustainable market in Europe and the rest of the world. The companies that are participating on the project are listed in the Table.
| Small and Medium Sized Enterprises: |
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Blacks Equipment Ltd, Doncaster (United Kingdom)
Dartec Ltd, Stourbridge (United Kingdom)
Deltamatic srl, Pedrengo (Italy)
Harms & Wende GmbH & Co KG, Hamburg (Germany)
Klaus Raiser GmbH, Eberdingen (Germany)
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| Research and Development Institutes: |
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TWI Ltd - The Welding Institute, Cambridge (United Kingdom)
Technische Universität Graz (Austria)
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| Large Companies: |
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ABB Alstom Power nv, Lincoln (United Kingdom)
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