Cold – colder – CMT Advanced
CMT manual instead of TIG
Magna is responsible for the series production of the aluminium body for the SLS "dream car". This is comparable to 'show cars', where similar technical, optical and haptic requirements are met using TIG welding technology. However, it is so timeconsuming that it is simply not an option for series produc-tion due to the number and overall length of the welds. With responsibility for welding in experimental and test constructions, Werner Karner therefore had to find an alternative solution: "Plasma welding was excluded because of the high heat input and consequent distortion. MIG welding creates welds with coarsely flaking surfaces and involves far too much spatter. Then Fronius brought CMT to our attention. The weld seam geometry, flaking and lack of spatter were ideal. The penetration, however, was not intensive enough and we would have had to resort to robot welding." Both challenges were solved by Karner and his welding partner through mutual communication and testing. After a few months, the production-ready solution was unveiled: CMT manual in pulse mode. The CMT robot torch was altered to incorporate man-ual control, whereby the integrated reversible wire feed was adapted in such a way that welders can also feed it manually on the joints. The restricted performance window of the pure CMT process is enhanced with the addition of the pulsed arc process. CMT pulse is designed for Magna in such a way that the heat input produces sufficiently intensive penetration, yet the distortion still remains within defined tolerances. With highly qualified employees, it is not only the technology that forms the foundations of success in Graz. Seven additional CMT systems are used for education, training and welding test purposes at the Experimental Constructions Fusion Centre.
CMT Advanced for the most complex weld seam
"This is the most complex weld seam I've ever seen in my 30-year career", explains the welding expert Werner Karner. It joins the 1.1 mm thick sheets on the B-pillar and the roof. Both are made of AlMgSi alloy 6014 and are joined by a lap joint using a fillet weld. This compensates for the sum errors in the z-dimension caused by the manufacturing process, and the difference in height of the B-pillar to the roof. The gap to be filled can in practice several millimetres wide, which makes bridging gaps with no loss of material an extreme requirement. At the time there was no suitable process available that could evenly bridge this gap and was ready for inclusion in the production line. But for cars of this grade, the owner expects that the joint, which in this case is also a filler weld, shows no evidence of hydrogen pores and is not trowelled. "For production, this means an unacceptable amount of reworking for each B-pillar. A solution therefore had to be found very quickly. It was then that Fronius contacted us and told us about a new alternating current process. We were very keen to test this", reports Karner. He invited a Fronius expert to come to the site and bring the system with him. The characteristic was not completely suitable for our existing application, but by working to-gether Fronius experts, a suitable solution was quickly found. Due to the combination of a high deposition rate and low heat input, the welding speed had to be at least 40 cm/min – a constant speed that only a robot can achieve. "As production with this joint was extremely unsatisfactory, we pre-sented our sample part which had been welded using CMT Advanced. Our colleagues were very impressed once the final work had been finished on the weld seam. We then tested the CMT Advanced solution under production conditions. The result was the immediate integration of the test system into series use", announced Karner, satisfied with the results. He knows that with this type of welding, Magna Steyr is not only the first user but also a leader in welding technology.
The Austrian company is part of the global Magna group, which registered a turnover of approximately 17.5 billion US dollars in 2009. Being the most diversified car parts supplier in the world, Magna develops and manufactures vehicle parts and very sophisticated products in more than 79 engineering and R&D centres, and 242 production sites.
The range of services provided by Magna Steyr in Graz includes made-to-order tank components and systems, development services and a whole range of roof systems in addition to entire passenger cars. Looking ahead, one key focus is on alternative vehicle drive and energy storage systems.
As far as roof systems are concerned, Magna Steyr, as the brand-independent manufacturing partner of international automobile manufacturers, is the global market leader.
CMT pulse and CMT Advanced
CMT pulse and CMT Advanced are based on the still unique CMT (Cold Metal Transfer) process with reversible wire movement. In comparison to conventional arc processes, it has been proven to result in lower heat input into the base material during welding and brazing and greater arc stability. Furthermore, the measurement and control of the arc length can be carried out "mechanically" via the wire movement, i.e. independent of the arc volt-age. External influences, such as surface impurities, no longer have any effect. Like every welding process, CMT too has a lower and upper limit to the power range.
CMT pulse extends the power range of the pure CMT process by combining it with the pulsed arc process. In pure CMT mode, all of the advantages of the "cold" metal transfer still apply – even up to the upper limit of the charac-teristic for the pure CMT process. CMT pulse takes off from here, by offering a huge performance spectrum and variability thanks to its targeted and variably adjustable range of pulses.
CMT Advanced is designed for even colder joining than the pure CMT process. First, it integrates the polarity of the welding current into the process control. By allowing the user to select the polarity of the welding current, CMT Advanced opens up new ways of joining metal with even less heat input and a high deposition rate. The extremely stable arc dramatically reduces unwanted side effects and therefore increases the reliability of the process. A significant innovation is the fact that the change of polarity is carried out during the short-circuit phase. As there is no arc during the short-circuit, there are no negative effects. This completely eliminates factors such as arc cut-off and the resulting process instabilities.
Fronius International GmbH
Fronius International is an Austrian company with headquarters in Pettenbach, other sites in Wels, Thalheim and Sattledt, and production facilities in the Czech Republic and Ukraine. Fronius is active in the fields of battery charging systems, welding technology and solar electronics. The company employs 2,677 staff worldwide, 1,923 of whom are based in Austria. 93% of Fronius products are exported through its 14 sales subsidiaries, two agencies (Turkey/welding technology and China/solar electronics) and 130 sales partners around the world. 14.9% of the total turnover of 329 million Euro is re-invested (financial year 2009). With its outstanding products and services and 649 active patents, Fronius is world technology leader. 358 employees work in research and development.
Fronius International GmbH
Froniusplatz 1, A-4600 Wels
Tel. +43 / (0)7242 / 241 2590
Fax +43 / (0)7242 / 241 95 3940