Fronius recently brought the CMT welding process to the company's most modern welding power source, the TPS / i. With the second generation of the cold arc, robot-assisted welding can be carried out in many applications with unprecedented quality, simplicity and process reliability. Because of these advantages, the steel producer and automotive supplier Voestalpine decided to be the first to use the advanced CMT technology in series production.

"The second generation of the CMT process represents a real quantum leap over the previous version, although the latter has already offered welding quality and process reliability at the highest level, "explains Michael Nowasz enthusiastically after three months of series production. For the Head of Joining at Voestalpine Automotive Components Schmölln GmbH, it is clear: "Thanks to the numerous innovations and further developments of the TPS / i in conjunction with a tailored CMT process, we have noticeably increased the quality and also clearly demonstrated our flexibility in joining enlarged. "

Like the previous generation, the new CMT process (cold metal transfer) offers a particularly low heat input and a high gap bridging capability. This is achieved by a particularly dynamic control of the arc. "Here, the approach chosen by Fronius already differs at first glance from others, since the droplet separation or the droplet transition is not only controlled by the electronics of the power source, but also mechanically supported," says the divisional manager. For this purpose, the wire electrode is always withdrawn with the help of a push-pull torch just when the current has reached its maximum and is turned off. This creates a particularly stable arc, which actually works without spatter and also allows higher welding speeds.

Faster and better welding with CMT

"By switching from the standard MAG process to CMT, a satisfactory performance increase has already been achieved," says Michael Nowasz, looking back over the period after the introduction of the first generation CMT process in 2011. "Since this changeover, hardly any splashes have to be removed so that my employees can now focus entirely on the quality of the weld."

Another advantage of the CMT solution is the high availability of the CMT system, emphasizes the divisional manager: "If, for some reason, the arc extinguishes, the process ignites itself again. Ignition faults, a sticking of the wire electrode to the contact tube or similar annoyances have been a thing of the past with us ever since. "

Last but not least, the joining specialist appreciates the manifold possibilities of influence on the welding process or the arc geometry. This also includes the option of overlaying CMT with a pulsed process in order to control the heat input via the arc into the base material even better and to be able to weld it all the faster.

CMT added to specifications for new plants

Due to the consistently positive experience, the divisional manager ensured that the CMT process for arc welding of steel sheets up to 3 mm was included as a standard process in the specifications for new welding systems. On them, the steel producer manufactures a wide variety of automotive structural components made of galvanized and high-strength sheet metal as well as aluminum sheets. Most recently, six of the twelve robot welding cells at the Schmölln site worked with the CMT process.

Accordingly, the Voestalpine management responded favorably to the second generation of CMT technology introduced at the beginning of 2016 and Fronius' proposal to test its use in series production. "We chose an A-pillar made of high-strength, galvanized steel for initial welding trials. This complex component is ideal not only because of the demanding material, but also because of the limited accessibility and the production-related large gap dimensions to put the new process through its paces, "explains Michael Nowasz.

For "just awesome" found

In summer 2016 the first welding trials with the new CMT process and the TPS / i were carried out at the technical center at the headquarters of Fronius in Wels. "I visited the lab together with our development manager and experienced the new CMT process in action there," says the division manager. "What we saw there was awesome. It was immediately clear to us that Fronius was again a big hit. "

The basis for the achieved technological leap is the TPS / i, which is not a simple further development of the predecessor model TPS, but is a completely redesigned welding power source. All components have been redeveloped from the controller, via the communication bus and the wire feed to the user interface, the cooling system and the hose package.

New algorithm - new robot burner

In order for the CMT process to benefit as much as possible from the TPS/i, the algorithm was redesigned and expanded to the second generation. The push-pull torch, which has already undergone a complete redesign for the TPS/i series, was not left out and was designed as a CMT variant with a digitally controlled, gearless ACServomotor equipped for even higher frequencies of the oscillating wire electrode movement.

"One advantage of the new robot burner Robacta Drive immediately stands out," says Michael Nowasz. "It's more compact than its predecessor, ensuring better accessibility that we increasingly need for more complex parts."

CMT process in series production

The results of the welding tests on the real component were so convincing that the participants immediately made the transition from the new CMT generation to series production at voestalpine. Already in the autumn 2016 it was time. Within a day, the first of the six robotic cells was retrofitted, on the holder of bare, 2 to 3 mm thick sheet steel under CO₂Protective gas are produced.

In this case, lay about one meter of weld seam, which is composed of 48 single stitching with a maximum length of 35 mm. "Already the next morning we got the robot together and welded the first parts on the same day," recalls Michael Nowasz. "It has been shown that with the new system, the right parameters can be found much faster and easier." On the third day, only minor readjustments were required to achieve the optimum working values.

The area manager was also impressed by the functionality of the new magnetic crash box: "We let the robot drive the burner against a metal sheet - the protective device triggered so quickly that no damage could be done to the burner, robot, device or workpiece." Nach a collision, the magnetic lock then only has to be snapped back, whereby the reference point is maintained, so that can be directly further welded. The annoying exchange of the crash box and the homing are thus obsolete.

After the tests, Voestalpine was able to restart series production with the new CMT configuration on the same day. "I was absolutely thrilled that the changeover went so smoothly and that until today - three months and 3000 parts later - it has not come to a standstill and so far we did not need any further support from Fronius," says Michael Nowasz.