Bespoke cold welding solution streamlines tube production

A customised cold welding system developed by British company PWM in partnership with US manufacturer Virtus Precision Tube (formerly Luvata) has streamlined and improved the process of copper tube production.

The system has improved uptime, reduced costs and created a better working environment for operators, according to Joe Napier, VPT’s Engineering Program Manager.

“We produce over 40 million pounds of roll-and-weld copper tube each year, in sizes from 1/4" to 1/2", he said. ”The cold welding system we have developed with PWM is part of our continuous improvement program. It supports our on-going drive to develop high-performance tubing solutions for the HVAC and refrigeration heat exchanger markets.

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“Copper strip is supplied in large narrow rolls and approximately every 20 minutes, the tail end of one roll has to be joined to the head of the next roll. The new cold welding process is more straightforward than the crossweld process we used for a decade, and works the first time, every time.  It’s faster, easier to standardise, requires less operator input and training. Most advantageous of all, the new weld is stronger and capable of handling the tensions we place on the strip during tube production.”

Before approaching cold weld specialists PWM, VPT also tried alternative methods of joining strip such as brazing, dovetail profiles, lap joints and laser welding.

PWM successfully test welded VPT’s strip using a portable ST40 cold pressure welding machine, capable of joining copper strip as wide as 45mm wide and as thin as 0.2mm. Precision engineered to create reliable permanent welds stronger than the parent material, the ST40 enabled VPT to reduce the operational scrap rate on the line by 15% during production trials.

PWM has now supplied VPT with three ST40 welders that run full-time in production.

Adaptations such as automatic flash trimming and annealing of the weld (to soften it and make it less brittle), and automation of the weld cycle and die opening system have been developed to streamline the process. VPT will field the new system across all tube mill production lines and currently has four more ST40 units on order with more to follow.

“Technical assistance from PWM, particularly from its Chief Design Engineer, Ivan Turner, has been incredible throughout,” said Joe Napier. “Any problems we had during the development and early fielding of the units were quickly resolved. For example, we went through four design improvements to arrive at our current tooling.”

Steve Mepsted, Managing Director of PWM, said: “This has been a fascinating bespoke project to work on. VPT shares our commitment to quality and innovation and together we’ve created a customized welding solution that significantly improves business performance. We’re delighted with the outcome.”

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