„Inline manufacturing“

Schürholz: Electro motor housings with 30 percent less material usage

Schürholz GmbH & Co. KG in Plettenberg joined forces with Otto Bihler Maschinenfabrik to develop a new process for producing watertight electric motor housings on a BIMERIC BM 6000 servo production and assembly system. The system, the only one of its kind in the world, performs all work steps inline in a seamless process and offers outstanding precision at high cycle rates. Not only that: It uses around 30 percent less material compared to conventional deep drawing technology.

The product portfolio of the Plettenberg-based Schürholz Stanztechnik includes embossed parts, stamped parts, stamped and bended parts and drawn parts. The components are used in the electrical industry and in railroad technology, but above all in the automotive and automotive supplier sectors. Metal housings for electric motors used for adjusting seats in vehicles play an important role in these sectors. Up until now, the company produced the housings using the traditional clinching method with bearing covers on a BM 1500 servo production system in combination with a COMBITEC CC 1 forming center. In 2017, the company decided to also use these housings for window regulator motors in vehicles - even though the requirements for these are significantly higher: “The housings for window regulator motors must be watertight and pressure-tight as per IP67 to ensure that windows can be opened even under water in an emergency,” explains Managing Director Angelo Castrignano. “A clinched component can never meet this requirement, so we had to find an alternative manufacturing solution.”

Maximum automation and efficiency

The idea was for all the necessary process steps to be redeveloped and fully mapped to a single system, namely a new BIMERIC BM 6000 servo production and assembly system. This was no easy task, as production involves a wide variety of process steps such as stamping, bending, laser welding, fitting the cap and pressing it tight. But after two years of development, including a project study, the entire process was integrated into the BM 6000. Castrignano: “It is a globally unique system that provides maximum automation and efficiency. Its main advantage lies in its high production speed of up to 60 strokes per minute. At the same time, the machine is designed for optimum material utilization and uses around 30 percent less material compared with deep drawing. With a planned 28 million parts per year, this represents a considerable efficiency boost. And not just in financial terms due to the sharp rise in the cost of raw materials: The reduction in material use can also save thousands of tonnes of CO2 each year.”

Parallel development of the solution

Otto Bihler Maschinenfabrik was quickly chosen as the partner for developing the solution, especially since other suppliers had previously failed in the face of the complexity of the task. “Only Bihler has the necessary expertise and manufacturing technologies for a product like this,” says Castrignano. “We worked together in parallel to drive the solution forward, with us concentrating on the tooling and Bihler on the system. Our customer, Brose Fahrzeugteile provided us with constant support.” The watertight joining of the motor housing to the stamped cover and the integration of laser welding into the process presented particular challenges. The latter issue had already been considered by Brose Fahrzeugteile some 15 years ago and has now been taken up again and implemented. Ultimately, it was possible to master all the technical challenges within budget and on time, and so the BM 6000 was able to go into operation at Schürholz at the end of 2018. “The up-front machine acceptance in Halblech went absolutely smoothly,” recalls Stefan Wortmann, Production Manager. “We switched on the machine and ran through a complete batch of 30,000 units without any malfunctions.”

Complete housings every second

At Schürholz in Plettenberg, production of the motor housings starts with pulling in the strip and punching out the blank. This is bent to form the body. The component is then calibrated and transported to the laser welding unit. This then welds the housing. The two screw lugs of the housing are then bent through 90° on a computer system and punched. The housing then rotates and the first step is rasped at the upper end of the housing. To do this, the wall of the housing is pressed down precisely from above. The cover is then placed on this protrusion using a pick-and-place unit. After that, the housing is rasped again so that an absolutely tight press-fit joint is formed. Finally, the component is checked using a camera, and a laser sensor also checks the weld seam – and then the completely finished motor housings drop into the box in a matter of seconds. “In contrast to deep drawing, the new technology also allows a wide variety of material thicknesses to be employed easily and flexibly, and with constant precision across the entire housing body. This is another major advantage of the system,” explains Stefan Wortmann.

Continuing on the road to success

The enormous success of the project prompted Schürholz to commission another BM 6000 for the production of larger housings. These are also used in cars, but also, for example, in electric garage doors or coffee machines. In addition, the company already has concrete plans for a third BM 6000. “The BM 6000 is the new flagship in our company’s machine park. It represents an important foundation for us for the future, as it will enable us to continue to grow successfully in the field of housing production irrespective of the type of drive used in the vehicle,” says Angelo Castrignano. “At the same time, the system reflects the greatest possible expertise in development and technology. It makes a crucial contribution to maintaining and securing our local production location.” The considerable innovativeness of the solution is also evidenced by the fact that Schürholz, together with Brose Fahrzeugteile, has now applied for numerous patents on this method of manufacturing the waterproof electric motor housings. And, to crown it all, Schürholz, together with Otto Bihler Maschinenfabrik, was named the most innovative supplier of 2019 by Brose Fahrzeugteile.