Projection welding Nimak welding technology ensures perfect chainsaws at Stihl

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The manufacturer Stihl, known for its robust and efficient chainsaws, now relies on portal projection welding systems from Nimak for the production of guide bars for its chainsaws.

In its North American plant and at its German headquarters in Waiblingen, the Stihl Group relies on automated welding systems for the production of so-called guide bars. Also known as saw chain guide bars, these components are essential for chainsaws, in which the company has been the world market leader for over 50 years. They ensure that the saw chain is guided precisely with minimal friction. This component, in turn, is to a certain extent the link that transfers the engine's power to the wood via the saw chain. For many years, the company has relied on Nimak, one of the leading suppliers in the field of resistance welding technology, which has also earned a good reputation as a supplier of complex automation systems, to manufacture these components and the welded joints required for them.

Hump press inserts a guide rail in just a few seconds

The special feature is that a guide bar essentially consists of three parts to be joined: two outer plates and another slightly smaller plate in the middle between the two larger ones, which ultimately results in a circumferential groove in which the drive links of the saw chain can then run. The three plates are welded together using a portal projection welding system developed by Nimak. So far, the company, which is based in Wissen, has supplied several of these huge machines to Stihl. A further system is currently being built, which will also be used from spring this year. "Nimak's technological and development expertise and the performance of the machines supplied to date are key reasons for this long-term partnership," explains Thomas Steegmaier, who is also responsible for the procurement of production systems as project manager at Stihl.

Although the availability of the portal projection welding systems is extremely high, the geographical proximity is also a major advantage with such complex production technology. Especially as it involves large quantities of a crucial part for the chainsaws and disruptions would have serious consequences. The production of the guide rails is also fully automated. A handling system feeds the three metal sheets required for this into the machine and initially places them on top of each other in a weldable manner. The two outer parts are also provided with a large number of welding projections. They are then transported to the projection press, where the welding electrodes press the sheets together. The current flow and electrical resistance then heat the parts to be welded at the welding projections, which melt synchronously, creating a reliable joint.

Capacity and quality only possible with an automated system

"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 allows Stihl to achieve symmetrical and therefore ideal force and current 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 long duty cycle. 
Depending on the length of the parts to be produced, a total of between 72 and over 100 high-precision welded joints have to be made in the upper and lower plates. "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. In doing so, it is important to meet the extremely high quality requirements. This is because 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," emphasizes Ramb. This only works to this extent with an automated portal system and is inconceivable otherwise.

Automation expertise pays off in projection welding

In order to achieve such capacities, the projection press generates an extremely high electrode force. While this was still achieved pneumatically in the first system from 2006, the machine commissioned in 2013 is equipped with a hydraulic drive. This drive technology, which has been tried and tested 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 fast repositioning, which is unique on the market to date," says Ramb. With this highly dynamic system, the machine can weld the projections and avoid possible spatter formation thanks to the force-locked repositioning. 
"This new development confirms that we have the right partner at our side, just like the welding technology we have used so far," emphasizes Steegmaier. Stihl is once again benefiting greatly from the decades of experience in resistance welding technology and at the same time its outstanding automation expertise. For Nimak, this statement is the best confirmation that they are on the right track.

Secure supply chain within the group of companies

However, it is not only the portfolio of individual automation options developed over many years, such as robot welding cells, rotary transfer systems or linear transfer systems, that pays off, but also the affiliation to the Tünkers Group. 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. This also secures the supply chains. "These are all advantages from which we also benefit as Nimak users," adds Steegmaier.