TWI Cambridge

Electron Beam Welding of RF cavities at „The Welding Institute“ (TWI) by EB- technology of Steigerwald Strahltechnik (SST)

– a talk with Mike Nunn, October 10, 2019

Chartered and European Engineer, a Fellow of both the Welding Institute and the Institution of Mechanical Engineers.

Question 1:

„Mike, you are Operations Group Manager, for the Joining Group, at TWI Ltd, Cambridge, UK. You manage the Electron Beam (EB) team, facilities and technology development; also have operational oversight of technical teams in Cambridge working on laser, arc, friction and furnace process solutions.

Who is TWI?“

Mike Nunn:

„TWI is a world leading research and technology organisation.  Based in the UK, with offices in North America, South East Asia, China, Australia, Central Asia, India and the Middle East, 800 staff provide technical support in joining and technologies such as material science, structural integrity

and others. Services include generic research, contract R&D, technical information, consultancy, standards drafting, training and qualification. TWI offers a single, impartial source of service for joining engineering materials. The electron beam team at TWI formed soon after the invention of the welding process and is globally unique in its ability to address both advanced process and auxiliary equipment challenges, from testing fundamental concepts through to production support.“

 

Question 2:

„Which project are you involved in at the moment regarding the Electron Beam Welding technology?“

Mike Nunn:

„TWI is to form part of a new UK supply chain with Shakespeare Engineering Ltd and the Accelerator Science and Technology Centre at Daresbury Laboratory, part of the UK Science and Technology Facilities Council (STFC). STFC will build our niobium cavity into a larger module and deliver it for test and installation at Fermilab in the USA. Fermilab manage the DUNE (deep underground neutrino experiment), and the UK is a contributor to DUNE’s new proton improvement plan (PIP-II). Niobium cavities are an attribute of DUNE PIP-II and will replace old copper cavities, allowing the Linac to be run for longer periods, more data to be generated, and making it possible for the global scientific community to address major physics questions more quickly.“

 

Question 3:

„What are cavities? Can you give a short explanation please?“

 Mike Nunn:

„This machine we’re buying from SST will be used for development and early stage production welding of RF cavities made of niobium. Cavities form part of big science facilities like the Large Hadron Collider at CERN. They are a key element of a Linac; the Linac is used to accelerate particles for experiments which help investigate some of the biggest questions in Physics. We’re tooling up to weld these cavities in the UK which will bridge a supply chain gap.“

 

Question 4:

„Why was EB selected for welding cavities?“

 Mike Nunn:

„Electron beam welding is the process of choice here, mostly due to the vacuum environment. Niobium is superconducting if kept pure and the performance of cavities also depends on an ability to make repeatable, consistent and smooth weld profiles. Even normal EB welders which work in vacuum are not good enough for our niobium. SST will build us a very high vacuum, oil-free machine to ensure the superconducting properties are protected. Therefore we bought an EB welding machine from the company which was able to demonstrate the most relevant cavity welding experience - Steigerwald Strahltechnik, Germany.“

 

Question 5:

„Why else did TWI choose SST as supplier for this application?“

Mike Nunn:

„Through a public procurement process TWI evaluated very good and compliant bids from all of the main suppliers. SST were selected as the successful supplier by submitting the most compliant proposal and by demonstrating a great understanding of our application, having sold a number of similar systems with acceleration voltage of 150 kV in the past. SST were able to offer a state-of-the-art EB welder, meeting the special vacuum requirements of our project and also ensuring that our requests for integration flexibility were fulfilled. This ensures the machine will work with our BeamAssure^TM QA tool, is Industry 4.0 ready and can work with the next generation of developmental EB monitoring technologies. The machine makes a great addition to our lab, it’s in the mid-range for size and the power of 150 kV/15 kW fits well with equipment operated by some key customers. We are looking forward to testing the advanced beam bending feature „EBOBEND“ which will allow us to weld, from inside-out, down a deep bore.“

Question 6:

„You mentioned an acceleration voltage of 150 kV. Why is it important?“

 Mike Nunn:

„According to analysis of other niobium EB welding work published and following our own initial experince we favour the welding results using 150 kV in comparison to 60 kV. We are convienced that a higher voltage machine would be more capable and offer a wider range of possibilities in terms of beam intensity and working distance. Our scoring system reflected this.“

Question 7:

„Are there any future developments with EB at TWI?“

 Mike Nunn:

„We are customer & application driven. Our customers in aerospace and other high value markets will continue to draw on our services with challenging materials and geometry. We also expect to see new challenges presented as vehicles need fewer EB welded conventional turbochargers, and electrification applications are presented to us. High deposition EB additive manufacture is a common topic for us today, and we continue to work with customers to get the most out of existing and new EB systems. Ensuring repeatability of industrial equipment is a common problem we help to overcome. For very large assemblies we continue to work towards effective local sealing solutions, in an effort to escape the constraints of the vacuum chamber, while maintaining the fantastic advantages of welding in vacuum.“

Question 8:

„Anything else TWI would like to add?“

Mike Nunn:

„We are very pleased to be working with SST. EB machines are major investments and hence often difficult to justify. This machine will help us work with a key customer to fill a supply chain gap, but also allow us to test new approaches and help our Industrial Members, and the wider engineering community, to assess the merits of EB, and how it will integrate with the next generation of advanced manufacturing technologies.“

„Thank you very much, Mr. Mike Nunn, for your information!“

 

Introducing TWI's Advanced Electron Beam Welding Equipment