Equipped for the Future

WMF AG (Worttemberg Metal-goods Factory), headquartered in Geislingen an der Steige, Germany, sees itself as a provider of branded products that must be able to meet the most rigorous of demands in terms of design, quality and ergonomic functionality. The company recently revamped its polishing operation for pots and lids, incorporating the latest robotic technology.


WMF AG (Worttemberg Metal-goods Factory), headquartered in Geislingen an der Steige, Germany, sees itself as a provider of branded products that must be able to meet the most rigorous of demands in terms of design, quality and ergonomic functionality. The company recently revamped its polishing operation for pots and lids, incorporating the latest robotic technology.

The company supplies an extensive range of products, with the principal focus on table- and kitchenware, for both commercial and consumer use. Products are sold in WMF's own retail outlets and through a network of distributors in Europe, USA and Japan.

The manufacture of cooking pots and pans has typically been dominated by turntable systems. Due to this system's high maintenance requirements, WMF made the decision to modernize the manufacturing process for its pressure cooker and cooking pot lids using an automated grinding and polishing system.

The company turned to SHL Automatisierungstechnik AG to develop a system concept based on four robotic cells. The first cell features a handling robot with a camera system and a grinding unit for the inner surface finish of the lid. The three additional cells, each featuring a handling robot, a grinding unit and two twin-shaft polishing machines, polish and shine the outer surfaces. The robots are each fitted with an external axis in order to be able to carry out the finishing work on the inner surfaces of the lids with greater rotational speed.

“To manufacture these parts on the conventional turntable systems,” says Helmut Kamitz, head of production at WMF AG, “we used to have to carry out two separate operations for the inner and outer surface finishing processes, each with a total of eight clamping fixtures. The new system allows production that is significantly more cost-effective.”

The new robotic system's decisive advantage over a turntable is that it can achieve an optimal surface finish in the shortest possible time because each robot can precisely move the individual brushing and polishing discs based on each unit's specific shape.

Polished side up

The pot lids roll into the system on a conveyor belt. The position and orientation of each lid are detected by an integrated camera system and passed on to a Kuka KR 60 robot manufactured by Kuka Robotics. The robot then lifts the lid off the conveyor using a vacuum gripper and guides it to a so-called “scotch belt” for polishing. In a very short time, this roughened belt endows the interior of the unprepossessing raw product with the matte finish typical of the inside of lids. “We call this the 'solar finish,'” explains Kamitz.

Once the lid has received this finish, the first robot passes it directly to one of the other three robots. These, in turn, polish the outer surface.

The first robot has the fastest cycle time. “Since it only has one task to perform it is three times as fast as the other synchronized robots,” explains Gerd Lehr, director at SHL Automatisierungstechnik AG. “It can thus always provide a new product to the robot that has just completed the outer surface finishing process.”

The polishing paste is supplied directly from a central tank to the individual units where it is then precisely dosed and carefully applied to the polishing disc and product via a dispensing gun. The robots process lids with special polishing discs until they achieve the gleaming high-quality finish specified in the company's quality standards description.

The robot then places the freshly polished lid in a turnover station, which ensures that it is laid on the conveyor with the polished side facing upwards. This ensures that the lid's shiny polished sided is scratch free when it is transferred out of the system by the conveyor and united with its matching pot.

Robotic flexibility

“Our main reason for opting for a system concept with robots was the desire to be flexible and equipped for the future,” Kamitz points out. “The shapes of the pots vary as fashions change. The system had to continue to be usable if the shape or material of the lid processed in it changes.”

The need for this flexibility became apparent as early as the implementation phase when new lids with a solar finish on both sides were introduced to the product range. This was no problem for the automation experts at SHL. “We simply equipped the cells containing robots 2, 3 and 4 with an additional grinding station.” When the lids for the “Gourmet Plus” kitchenware series, with their matte, unpolished upper surface, roll into the system, the machining process is simply switched and two robots work together, one grinding the inner surface and the other the outer surface.

In addition to simple operator control, reduced maintenance and lower consumption rates, the company expects the modernization to result in greater flexibility in the future that will allow it to switch quickly to new product ranges.

From the time the idea was conceived, the whole process, including the trials, planning phase and project management, through to commissioning of the turnkey system supplied by SHL took about two years.

“When planning the system, we were careful to use as many standard components as possible,” says Gerd Lehr. “This applies not only to the robot, but also to the camera and polishing units.”

The system has a centralized emergency stop system and each cell can be switched off separately. This means that maintenance and exchange operations can be carried out in one cell without the need for downtime in the other cells. The sound-proof booths also conform to current noise protection requirements. For the employees at WMF, this means low background noise levels in the workplace.

Author Information

Joe Kraus is product manager at Kuka Robotics

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