The 2,400 employees at the Dillingen plant produce dishwashers for Bosch and Siemens. The facility was founded in 1960, initially as a branch factory for Robert Bosch GmbH. From 1974 to 1976 a new dishwasher factory was built on the site, which has an area of 284,000 square meters. Today the plant operates in three shifts, producing more than two million dishwashers a year in over 800 variants. Since 1976 over 30 million of these machines have come off the production lines. This makes the plant Europe’s biggest manufacturer of dishwashing machines, and the Dillingen region’s most important employer. BSH also attaches high priority to environmental protection, and has therefore set environmental goals with regard to the development and disposal of its dishwashers.

Most efficient automation solution

BSH relies increasingly on automation for the manufacture of the dishwashers, which remain largely the same from series to series. As a part of this strategy, since January 2003 two new KUKA KR 125 robots have been present on housing line 4, where they handle dishwasher housings and apply bitumen sound-deadening pads. “The pads have to be seated accurately to ensure maximum sound-proofing and a clean fit when the housings are installed”, emphasizes Dipl.-Ing. Karl Starrock, engineering group leader of the dishwasher division at the Dillingen plant. “Thanks to the new robots, the previous manual work is no longer necessary. This work was very monotonous and extremely fatiguing, especially during the hot summer months.” The new machines complement five other robots which the user already had in operation on housing lines 3 and 4. All in all, about 20 robots from KUKA Roboter GmbH, Augsburg are now in use in Dillingen.

“Six-axis jointed-arm robots are more flexible than linear handling devices, and were therefore the most efficient automation solution for us”, explains Dipl.-Ing. Franz Göttle from the plant engineering department of the dishwasher division. “In addition, they provide more gentle handling, and they can carry out various process steps, such as rotating and positioning, without having to set the parts down between steps.”

Higher quality

By converting the station to the use of robots, BSH has obtained several long-term benefits: greater precision during the application process, and thus higher process reliability and quality. Moreover, the company’s productivity has increased due to reproducible processes and an availability of almost 100%. On top of that, the robots ensure short cycle times and minimized costs.

Working conditions for employees have also been significantly improved. The major problems were the proximity of the furnace, and above all the loads which have to be handled, since in each shift more than 1,100 housings are cycled through the robotic cell. Since a housing together with its pad weighs seven kilograms, the operator had to lift – without any mechanical aids – materials with a cumulative weight of eight tonnes per shift.

“Another reason we decided in favor of KUKA was its geographical proximity, which ensures prompt service and quick delivery of spare parts”, says Franz Göttle. “We chose this robot type, with its load-bearing capacity of 125 kilograms, based on the weight of the gripper and the parts which had to be lifted, and also for its reach of 2.5 meters.”

Karl Starrock adds: “Before placing the order, we carried out extensive tests using an experimental gripper, a robot leased from KUKA, and a camera-based position detection system. Then at an early stage in the project, the simulation software KR SIM was used to help create an optimal layout. KUKA carried out cycle time analyses, collision detection and reachability checks. The grippers were made in our own special machine building workshop.”

Coordinated duo

In housing line 4, bitumen pads are applied in three stations. The first cell, for the floor of the dishwasher housing, is manually operated. Then comes the station with the new, coordinated robot duo. There one of the KR 125s picks up one housing at a time from a workpiece carrier, positions it in its gripper by means of suction, and then clamps it in the end-effector in such a way that it is held precisely in the defined position ready for application. The second robot picks up a bitumen pad from a stack using its suction gripper and applies it precisely to the rear panel and one side of the housing.

“Because each of these pads is intended to insulate two sides of the housing, the robot has to bend it 90 degrees”, explains Franz Göttle. “To enable this, it heats each pad at the predefined bending point. This is done on a centering table with integrated infrared heating elements.” Previous to this, an image recognition system installed over the table measures the position of the pad. To allow this, the robot swivels out of the way after setting down a pad. Taking the measurement data into account, the KR 125 applies the insulating material to the housings with 100% precision, if necessary adjusting the position of its gripper before picking up the pad.

Then the other robot sets the housing back down on its workpiece carrier, on which it is automatically carried through a furnace. There the bitumen pads are joined permanently to the stainless steel shell. In the following cell, two more KUKA robots are responsible for insulating the roof and the remaining side of the housing.

Insulating material is delivered on flat pallets by means of electric forklifts. The industrial trucks transfer the pallets with their stacks of pads to sliding carriages, which are slid into the appropriate station by the employees. The use of two carriages per cell allows production to continue without any interruptions.

User-friendly human/machine interface

The robots receive their commands from the PC-based KUKA KR C1 controller, which also communicates with the conveyor system controller. The KR C1 also monitors whether a pad and a housing are present, and sends a corresponding signal to the image recognition system. Moreover, the robot controller notices if the KR 125 picks up two of the bitumen pads instead of one. The tasks of the controller also include collision checks with regard to the two robots and functional monitoring of the safety fence. Each of the robots becomes active as soon as sensors detect the arrival of a housing. In other words, they operate autonomously, apart from communication via the interfaces to the conveyor and image recognition systems.

Karl Starrock about the operator control of the KR 125s: “All of our employees who work with the robots have been trained at KUKA College, so they have absolutely no trouble operating them. Moreover, the KUKA Control Panel with its familiar Windows-based operating system provides a user-friendly human/machine interface between the operator and the robots.”

As for the payback period, BSH Bosch und Siemens Hausgeräte GmbH expects it to be less than two years. Another important consideration are the economic benefits resulting from conversion to robots, and their contribution to the continued viability of the Dillingen plant.

Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany