A guide rail for a chainsaw in which the many welded joints are still clearly visible. © Nimak

"The real challenge lies in the high number of projections that have to be welded evenly in one stroke," emphasizes Steegmaier. This is precisely why they opted for a portal system. "This allowed us to achieve symmetrical force and current distribution and therefore ideal distribution across the part to be welded." With a conventional C-shaped projection welding machine, the projections would not be pressed and welded so evenly. However, thanks to the design of the portal system and the parallel left and right feed of the current and the centrally distributed pressure, this is distributed parallel and evenly across all projections. Nimak has provided six transformers on each side, which are required for the high duty cycle.

Automated system enables capacity and quality

Depending on the length of the parts to be produced, a total of between 72 and more than 100 welded joints have to be welded with high precision in the upper and lower sheets. "To achieve this, our machine must be able to reliably produce countless projection joints day after day," emphasizes Manfred Ramb, Head of Design at Nimak. "It is important to meet the extremely high quality requirements. After all, joining the three sheets requires precisely coordinated pressure and current-controlled welding profiles. And for an optimal metal structure, immense demands on shape and lay-up tolerances must be met during the subsequent tempering and cooling phases." This only works to this extent with an automated portal system and is inconceivable otherwise.

In order to achieve such capacities, the projection press has a high electrode force. While this was still generated pneumatically in the first system from 2006, the machine commissioned in 2013 is equipped with a hydraulic drive. This drive technology, which has proven itself over many years, is also used in the system currently in production, which will be put into operation in a few months' time. The hydraulics are now adjustable, which allows the force profiles to be set. "This in turn enables fully hydraulic and rapid repositioning, which is unique on the market to date," explains Ramb. With this highly dynamic system, the machine can weld the projections and avoid spatter formation due to the force-locked repositioning.

High automation expertise pays off

"Just like the welding technology used to date, this new development confirms that we have the right partner at our side," emphasizes Stihl project manager Steegmaier. "We benefit greatly from their decades of experience in resistance welding technology and their outstanding automation expertise." For Nimak, this is the best confirmation that they are on the right track.

Not only the portfolio of individual automation solutions developed over many years, such as robot welding cells, rotary transfer systems or linear transfer systems, but also the affiliation to the Tünkers Group are obviously paying off. Thanks to this group of companies, Nimak can purchase most of the components required for automation at particularly attractive prices and even influence their development and adaptation to its own requirements. It also secures the supply chains. "These are all advantages from which we also benefit as a customer," adds Steegmaier.

This article appeared in issue 6/23