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Tony Johnson, technical information officer for Murex Welding, offers technical advice to bodyshops on how to adapt to new joining processes for the new generation of materials for road vehicles.

MIG brazing is currently being highlighted as a revolutionary new joining process, being specified for both vehicle new build and repair of accident damage due to the new generation of materials used in vehicle design.

The benefits of MIG brazing is the special properties that can be obtained from MIG brazed joints, which are now of considerable interest to automotive design engineers.

These include: tolerance to zinc and aluminium coated materials; low distortion on thin panel sections and sheet materials; and low fusion temperature.

The special properties of MIG brazed joints are suitable for the new generation of materials currently being used in production road vehicles.

Manufacturers’ technical information sometimes uses material references such as Boron steel, HS steel, meaning high strength, and UHS steel, meaning ultra high strength.

The word Boron steel can be misleading, as It only requires very small additions of the element boron in steel, in the order of 0.001 – 0.005 per cent, to have a significant influence on the mechanical strength of the material.

The identification of the different types of material is the biggest problem.

High-strength boron steel structural cross members could be attached to soft ductile mild steel bracing members, forming front-end crumble zones or a combination of boron-steel front cross member designed for rigidity and high-yield, steel-toughened body sides.

The vehicle manufacturer will have issued very detailed instructions to its repair centres on repair techniques to be used.

The fitting of correct OEM panels and parts is also very important in these areas, as structural integrity of the safety cell that protects the occupants of the vehicle in a crash relies on these materials working in combination.

Spot welds can often be seen in boron-steel fabrications and parts and offer no real visual difference to standard steel spot welds.

In production, special high-pressure spot welding guns with high-strength copper electrodes are required on these materials.

The first indication of the use of boron steel in the workshop will be the difficulty in drilling out the spot welds on a replacement section.

These spot welds are very hard and will require special eight-per-cent-cobalt drill bits.

The mechanical properties of boron steels, as well as certain other high-yield steels, can be compromised by conventional fusion welding techniques.

The low melt temperature of the MIG braze process can be optimised to produce sound joints in these materials without significant reductions in the mechanical properties.

On zinc-coated materials the loss of coating in the braze zone is also greatly reduced in comparison to fusion welding.

Up until the mid 1990s, very little high-yield steel had been used in production road vehicles.

Volvo featured high-yield steels on the Volvo 740 model of 1984 and this equated to 15 per cent of the body shell by weight.

This ratio has now risen to 50 per cent on Volvo’s latest 4×4.

Manufacturers currently using these materials include Saab, BMW and Porsche.

These materials help design engineers make significant reductions in vehicle weight.

Murex Welding Products

Murex Welding Products is today part of one of the world’s leading manufacturers of welding products, the ESAB Group. The company offers a full range of arc and gas welding and cutting products, welding consumables and personal protective equipment as well as welding accessories. The Murex Saffire brand is renowned for its associations with welding safety whilst the company also offers a comprehensive range of Gas Equipment Inspectors’ Training Courses, also designed to promote safety in the workplace.

At its UK headquarters in Waltham Cross in Hertfordshire, Murex Welding Products has a team of highly experienced and qualified staff who are always available to offer technical help and advice on all aspects of welding and cutting.

Murex Welding Products still remains “At the HEART of every good weld”.

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