TECHNICAL REPORT
Single-sided joining of steel and aluminium using the Fronius CMT welding process
Low heat input for stable welded joints
The thermal joining of different materials such as steel and aluminium is of crucial importance in
automotive lightweight construction. However, this process is particularly challenging due to the
different physical and chemical properties of the materials. It is difficult to achieve high-quality, stable
results and the options for further working of the semi-finished parts are significantly restricted. The
solution to these challenges is a welding process with reduced heat input – the Cold Metal Transfer
(CMT) process developed by Fronius. The low level of spattering coupled with the constant and
extremely stable arc deliver optimum welding results. International automotive industry supplier Magna
Steyr has taken CMT and developed a technology that not only makes it possible to manufacture
bodywork parts much more cost-effectively, but also allows weight savings to be achieved too.
Car body manufacturers in the automotive industry are increasingly relying on a combination of different
materials – and with good reason. The weight of the vehicles can be reduced considerably by using materials
such as aluminium or fibre-reinforced plastics, which has a positive effect on performance and fuel
consumption. It would also be hard to meet the ever more stringent exhaust emission regulations without these
advances in lightweight construction. Modern vehicles therefore tend to have an ingenious mix of materials,
right down to the finest details – every individual part is designed to be as light as possible yet still provide
optimum functionality. However, joining these materials, with their very different properties, poses a huge
challenge.
Restricted strength and formability
Steel and aluminium is one of the most frequent combinations of materials to be joined in automotive lightweight
construction. To reduce costs, manufacturers weld flange components made of aluminium to galvanised steel
plates, so that they can be joined using the conventional, cost-effective spot welding process on the bodyshell
production line. However, the different physical and chemical characteristics of these two materials, such as
their thermal elongation, heat conduction and corrosion resistance, must be taken into account. These have a
negative effect on the quality and strength of the welded joint. The formability in subsequent production
processes is also very limited.
The reason for this restricted formability lies in what is known as the intermetallic phase, which forms where the
two materials touch and fuse together when they are welded. This layer is brittle and susceptible to cracks and
pores, which impairs the stability of the joint. International automotive industry supplier Magna Steyr was keen
to address this problem. The company, which is headquartered in Graz, Austria, develops and produces
individual components and complete vehicles, and uses lightweight construction methods for its vehicle bodies.
In order to lower the production costs for steel-aluminium weldments, Magna Steyr examined the joining
process in great detail and came to the conclusion that the temperature has a critical influence on the weld
seam quality.
A “cold” welding process improves the stability
The heat input during welding plays a significant role in determining the thickness of the intermetallic phase. In
the trials carried out by engineers, Magna Steyr discovered that ideally this should not exceed ten micrometres
to ensure the joint is stable. To achieve this, the experts had to control the temperature progression in an
optimal manner, keeping it above the melting temperature of aluminium but below the vaporisation temperature
of the zinc layer applied to the steel plates. In most arc-welding processes, this is simply not possible, but
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Magna Steyr finally found the solution they needed in Cold Metal Transfer (CMT), the “cold” welding process
developed by Fronius.
The CMT welding process significantly reduces the heat input in comparison to other MIG/MAG processes. The
secret lies in the digital process control, which automatically detects short circuits and then helps to detach the
droplet by retracting the wire: during welding, the wire moves forward and is pulled back again as soon as the
short circuit occurs. As a result, the arcing phase is very short and the heat input reduced. Using this process,
the energy input can also be continuously adapted to suit the component to be welded. Users benefit from
spatter-free material transfer and optimum welding results. CMT is therefore ideal for welding steel joints using
CO2 and other shielding gases. It is also intended for use in the joining of steel and aluminium, as the steel
base material is only wetted by these braze-welded joints and does not melt. This means it perfectly meets the
requirements for use in the automotive industry.
Outstanding results from an exceptional process
With the help of the CMT welding process and by optimising the welding wire, Magna Steyr has developed a
technology for joining steel and aluminium efficiently and reliably. Being able to set the welding parameters
precisely keeps the intermetallic phase thinner than ten micrometres. The mechanical properties of the joint
meet all the requirements placed on them. Compared to conventional processes, CMT also offers the
advantage that welding no longer needs to be carried out on both sides, but now only on one side, which lowers
costs and reduces the workload. Additional, expensive joining processes such as punch riveting also become a
thing of the past – leading to even greater cost-effectiveness.
Magna Steyr won the 2017 AutomotiveINNOVATIONS Award from the Center of Automotive Management
(CAM) and PricewaterhouseCoopers (PwC) Germany for its innovative joining technology. Magna was
recognized as the Most Innovative Automotive Supplier by impressing the jury in the chassis, car body and
exterior category.
Image captions:
Image 1: With the CMT welding process from Fronius, steel and aluminium can be joined reliably and
efficiently.
Image 2: Additional, expensive joining processes such as punch riveting become a thing of the past using CMT
welding – leading to greater cost-effectiveness.
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Image 3: Car body manufacturers in the automotive industry are increasingly relying on a combination of
different materials.
Image 4: In the CMT welding process, the arcing phase is kept very short and the heat input reduced. Using
this process, the energy input can also be continuously adapted to suit the component to be welded.
Copyright to photos: Fronius International GmbH, reproduction free of charge
High-resolution images are available to download at the following link:
www.fronius.com/en/welding-technology/infocentre/press
Business Unit Perfect Welding
Fronius Perfect Welding is an innovation leader for arc and resistance spot welding and a global market leader
for robot-assisted welding. As a systems provider, the Fronius Welding Automation division also implements
customized automated complete welding solutions, for the construction of containers or offshore cladding for
example. The range is rounded off by power sources for manual applications, welding accessories, and a broad
spectrum of services. With more than 1000 sales partners worldwide, Fronius Perfect Welding has great
customer proximity.
Fronius International GmbH
Fronius International GmbH is an Austrian company with headquarters in Pettenbach and other sites in Wels,
Thalheim, Steinhaus and Sattledt. With 4,550 employees worldwide, the company is active in the fields of
welding technology, photovoltaics and battery charging technology. 91% of its products are exported through 30
international Fronius subsidiaries and sales partners/representatives in over 60 countries. With its innovative
products and services and 1,241 granted patents, Fronius is the global innovation leader.
This press release, and the pictures, are available for download from:
www.fronius.com/en/welding-technology/infocentre/press
For more information, please contact:
Fronius USA LLC, Ms. Welch Stephanie,
6797 Fronius Drive, 46368 Portage, IN
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Tel: +1 (219) 734 5701, E-Mail: [email protected]
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Oberdorfstraße 31 A, 70794 Filderstadt, Germany,
Tel.: +49 (0)711 9454161-20, e-mail: [email protected]
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