At first glance, battery drive technology doesn’t seem to have much to do with gasoline products. However, when you look closer, it quickly becomes clear that the development of new cordless power tools combines a great deal of new knowledge with plenty of experience from other areas. We can see this in the STIHL AP 300S, for example. The new battery pack combines the development of innovative methods with the basis of existing company knowledge.
Battery pack system design
It all has to start with an idea. And this is sometimes as much abstract as it is simple: More power for a new saw, with the battery pack as the heart of a new battery pack generation. The new drive should have an electric output of 2.1 kilowatts – far more than had been available on the market so far. The entire development team built up new knowledge for this purpose, but was also able to draw on a wealth of experience from projects that have already been successfully completed.
Battery pack system design, materials technology tribology
Which cell can meet the new requirements? How can larger current flows be achieved safely and effectively? The concept was shaped by means of many discussions, calculations, virtual and real tests as well as assessments of the performance, safety and service life of the new cells. The high current-carrying capacity was one of the greatest challenges here. To get this to the target level in the STIHL AP 300S, 30 cells must be connected to each other in such a way that previously unfeasible performance could be achieved. However, the targeted performance was no longer attainable with the known materials and joining methods. New ideas and new materials for a new, innovative process were needed.
Current calculation methods
Structural-mechanical and thermal simulation generally begins before prototypes are built, but at the latest when they are built – for cordless products as well as classic gasoline-driven power tools. In both cases, virtual methodologies are used to reduce test cycles and to better understand the special mechanisms so that targeted improvements can be made at an early stage of development. The new packs also underwent the first safety and approval-relevant drop tests on the computer. This facilitated quick feedback to the designers and changes to the design. The housing of the STIHL AP 300S was developed in-house.
Battery pack validation
The prototypes of the new battery packs were put through their paces on our own STIHL test benches in Plant 2 in Waiblingen-Neustadt. In seeking to reveal as many design, configuration and application errors as possible, a wide variety of tests were conducted. These ascertained, for example, the maximum temperatures during charging and discharging, or when touched by the user. Faulty states – such as a short circuit or overload – were artificially induced to confirm that the high safety requirements for the end product had been achieved. The extensive testing portfolio also included investigations of the service life and robustness of the battery pack. STIHL measures itself against standards that go far beyond those required by law. In fact, it is the company’s own high quality standards against which all new developments must measure up.
Battery pack and charger product development, pre-production development and strategic product development
The new joining process used to connect the 30 cells of the STIHL AP 300S is a special feature of the product. With this innovation STIHL is once again underlining its claim to technological leadership. With good reason: STIHL is one of the first companies in the world to use a laser welding process for battery packs in the power tools sector – and bringing them to market maturity. The copper connections, which are less than half a millimeter thick, are fixed to the cell poles by means of a precision laser. Successfully finalizing this innovative process necessitated many tests and theoretical optimization cycles as well as in-depth exchange and collaboration with external partners. The outcome is a laser welding process that is now used to produce the STIHL AP 100, 200, 300 and 300S as well as the AR 200L and 3000L in in-house production in Waiblingen-Neustadt. For the STIHL AR 3000L professional product, it is not just 30, but 90 cells that have to be reliably connected in the shortest possible time. This is only possible with the new process.
ANKE KLEINSCHMIT has been Head of Development at STIHL since 2018. She was previously Head of the Powertrain Technology Plant at Daimler AG, where her responsibilities included advancing digitalization in production.
What do you expect to be the points of focus in your future work?
ANKE KLEINSCHMIT We are currently working on optimizing the product creation process – and doing so along all interfaces. We are also deeply engaging with product topics: What distinguishes STIHL products, what do we want to stand for as a brand? I believe that the question of our future alignment is crucial, and I am discussing it very intensively – with my team and across departments.
Cordless products from STIHL are in high demand and are gaining ground worldwide. This is happening alongside the earlier-than-expected replacement of gasoline-driven power tools. What tasks does this bring forward for development at STIHL?
ANKE KLEINSCHMIT We have a high level of expertise in gasoline products and we want to maintain that. They are and will continue to be our core products. But it is essential that we invest in new technologies. That means both cordless products and also completely new ecosystems and business models in which we consider how we can compensate for the decline in gasoline engines.
How can STIHL maintain its claim to technological leadership in the future?
ANKE KLEINSCHMIT Through more pre-development. It’s about identifying relevant technologies and innovations in good time. My target is that we develop a clear vision of what STIHL should stand for in the future: Which business area do we operate in? And what are our customers’ expectations of our products? We have to rise to this challenge, driven by our own vision. We don’t always have to be the first on the market, but we should consider ourselves to always be among the best.
Ms. Kleinschmit, thank you very much for talking to us.