Toolform Case study:
Laser and Sheet Processes Group

Laser and Electron Beam Welding for Heat Exchangers

The Toolform programme, joint funded by the DTI, Yorkshire Forward and Objective 1, has been created to assist companies who either manufacture or use forged and formed metals.

Electron Beam Welds of tube through plate

A Sheffield based company is involved in the design and manufacture of an innovative combined heat and power generation system. The system, when fully developed, will replace a standard domestic gas boiler and will generate electricity from the hot outlet gases that are produced when water is heated by a central heating system, resulting in efficiencies of greater than 90%. Power generated by these units will be fed back into the National Grid and help reduce the need for new power stations to be built.

The company talked to TWI Ltd in connection with a design problem, which involved the welding of tubes into a heat exchanger header unit. The head assembly forms an essential part of the design and the welded joint is particularly important due to the high temperatures and pressures that the weld has to withstand. As this component is manufactured from cold-formed tube and hot forged bar, TWI were able to offer assistance through the Toolform project.

Electron Beam Welds of tube to header

The requirement for each unit was for a weld around the ends of each of 100 small tubes (4mm diameter each) set through the hemispherical face of the header unit. The welds needed to be very accurately positioned and very precisely controlled.

A further problem stemmed from the fact that the materials used for both the tubes and the header were exotic nickel based alloys, which are inherently difficult to weld.

As a result of initial trials using both electron beam and laser beam welding systems, it was decided that electron beam welding would be the most appropriate procedure for this application. Further trials continued by welding samples of tube supplied by the company to sheet material. Once this was completed and metallurgical examinations indicated a satisfactory weld had been achieved, two complete header units were fully welded. This proved to be successful, and the welded heads are now being assembled into demonstration machines for long term trials.

For more information on this work, please email: roger.fairclough@twi.co.uk.

This support, provided to IFA Ltd., was made possible through the Toolform Strand of the Advanced Metals Technology Initiative (AMTI) funded by the DTI, Yorkshire Forward and the European Union through the South Yorkshire Objective 1 programme. The AMTI project is managed by NAMTEC, the National Metals Technology Centre.

For more information on the Toolform programme, please contact: Eliana Fu (email eliana.fu@twi.co.uk.