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TWI's new diffusion bonder builds on 40 years' research

Connect, no. 138, September/October 2005, p.6

TWI's new diffusion bonder builds on 40 years' research

TWI has made a significant investment in a brand new, purpose built, diffusion bonding furnace. The arrival of this new equipment coincides with the 40th anniversary of diffusion bonding at TWI.

The new furnace enables most materials to be joined including metals ranging from aluminium alloys to tungsten, together with ceramics such as alumina and silicon carbide.

Diffusion bonding is predominantly a solid-state process requiring a combination of heat and pressure. The surfaces are forced together at high temperature (approximately 50-80% melting point of the parent) and held there for sufficient time to enable the surface atoms to diffuse across the interface. When joining similar materials the bonds are often invisible to the eye and break away from the bond line.

Built entirely to TWI's specification, the new furnace has an internal volume of 300x300x400mm high. Force is applied by a hydraulic press, capable of delivering a load of 100kN, and the chamber is heated to a maximum of 2900°Cby carbon electrical elements. During bonding, oxides are prevented from forming on the bonding surfaces by keeping the chamber under vacuum.

This new equipment has come a long way since TWI's first machine of 1965, which was limited to a 450N load and heated by a 6kW induction coil.

With correct design and the right combination of heat and pressure many dissimilar combinations can be joined, producing bond strengths equal to the weaker parent.

The applications for diffusion bonding are broad. Generally, the technique is used for high precision components where bond strength or operating temperature is of particular importance.

Examples include hollow section components for the space shuttle, blades for the Rolls-Royce RB211-535 engine (as fitted to the Boeing 757), heat exchangers and reactor vessels.

TWI will be using the new facility to conduct research and development for Industrial Members, including working on their behalf to define bonding parameters for new material combinations. TWI can also bond test units in small volumes for pre-production evaluation.

This new equipment complements a wide range of heat treatment facilities at TWI, including vacuum brazing furnaces, induction heating furnaces and high temperature air and controlled atmosphere furnaces.

As well as the investment in new equipment, TWI is publishing a new best practice guide for diffusion bonding. The guide, available free-of-charge to Industrial Members, takes account of the advances in both knowledge and technology that have occurred in the last forty years.

TWI Project Leader, Paul Jackson, said: 'Industrial demand for greater efficiency and higher operating temperatures has increased our Members' requirements for high integrity joints in higher temperature metals and ceramics.

'This unique equipment should satisfy the demand for diffusion bonding research and development of substantial engineering components.'

'Our Best Practice Guide helps anyone with an interest in the benefits of diffusion bonding to deliver results in line with their aspirations.'

For more information, please contact us.

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