The cornerstone for Druckguss Hoym’s plant was laid in August 1999, and aluminum castings have been produced at Hoym since the middle of 2000. Machines with holding pressures of up to 800 tonnes are available for this purpose. Another plant east of the Harz Mountains produces small and medium-sized castings to supplement the larger items manufactured at the main plant in Dohna.

The decisive factors in favor of this location in the German state of Saxony-Anhalt were the large government subsidies available and the fact that important customers can be reached quickly from there. These include most of all BMW, which builds motorcycles in Berlin, and Volkswagen in the town of Salzgitter.

Druckguss Hoym has annual sales of more than DM 20 million, primarily to the automotive industry. The company also does a good business with the electrical and plumbing industries. 95% of all products go to customers in Europe, while the rest are sold overseas, for example in Brazil. Throughput is about 200 tonnes per month, and is on an upward trend. Druckguss Hoym has 87 employees, with about 600 persons in the entire group.

Higher quality and cost-effectiveness

In order to optimize its processes both qualitatively and economically, Druckguss Hoym has “employed” six-axis jointed-arm robots in a casting cell since the end of February, 2001. The cell is automated by means of one KR 30 standard robot and one KR 60 K shelf-mounted robot.

Jürgen Knieps, plant manager at Druckguss Hoym, describes some of the advantages thus gained: “The cost-effectiveness of this solution is based most of all on the favorable price/performance ratio and the fact that we only need one operator for three machines. Considering that the handling has to be carried out in a hot, steam-filled environment, which is also covered with aluminum beads or swarf, this conversion has also made working conditions less stressful for our personnel.” This advantage is of particular significance because the company operates in three shifts, beginning Sundays at 10:00 p.m. and running through Saturday at 2:00 p.m. High availability is also a requirement; Druckguss Hoym’s target in this regard is 95% for the entire casting island.

The complex handling and gap-free spraying of all areas of the special casting molds can only be implemented through the use of six-axis robots. During the spraying of the parting agent, the shelf-mounted robot – installed on top of the machine – must achieve the required repeatability, otherwise sections of the casting would remain stuck in the mold. The KR 60 K is so precise, moreover, that the user also benefits from lower consumption of parting agent.

The automation equipment was installed by KUKA systems partner FKS Maschinenbau GmbH, Berlin. The package provided by FKS included the two robots, the gripper of the KR 30 and the spray head of the KR 60 K, a punch, a conveyor, and the safety fence enclosing the handling area.

Automatic process

Druckguss Hoym keeps the aluminum-silicon alloy in a holding furnace, from which it is dispensed into a filling chamber. There the molten metal is pressed at high velocity under a pressure of 750 bar into the steel mold, where it solidifies. The solidification time depends on the size of the part; it ranges between three and 15 seconds, after which the machine opens the die. To remove the casting, which weighs from three to nine kilograms, the KR 30 uses a three-pronged gripper. Because the robot always grips the casting on its sprue, it is able to handle a wide variety of products.

“The robot then positions the casting in front of sensors, by means of which the controller checks whether it is complete, or whether it is there at all. If the casting is OK, the robot then immerses it in a quenching bath of about 30 °C (the temperature of the casting is between 300 °C and 350 °C). Rejects, on the other hand, are removed by placing them on a slide leading to a separate container.” After the KR 30 removes the OK part from the quenching bath it places it in a trimming press, which automatically removes the sprue, i.e. the gate and the surrounding flash. Finally the parts are dropped – also automatically – onto a slide leading out of the press.

As a variant, the press can also be tended manually. The user employs this alternative for low-volume series, or when the cutting tool in the press is defective and trimming must be carried out in a different press. In this case, the robot places the parts on a conveyor belt after they are quenched.

As soon as the KR 30 receives the signal from the unloading inspection that the part is OK, the KR 60 K sprays the mold of the Bühler die-casting machine with water-soluble parting agent under high air pressure, thus ensuring that the next casting will also be easy to remove. Once the spraying process is completed, the machine closes again and the next cycle begins. The cycle time of the cell varies between 60 and 90 seconds due to different sizes of the parts and the amount of time they need to cool.

As far as the robots are concerned, all that is required to change to another product is to call up the appropriate program in the PC-based robot controller using the KUKA Control Panel. This is made much easier by the convenient Windows man-machine interface on the control panel.

Solid foundation

The improvements in quality and cost-effectiveness achieved by this automation give Druckguss Hoym a solid foundation for securing and expanding its market position. Since the benefits of this solution were so obvious, the user decided to continue along this path to success: shortly after the commissioning of the first casting island an order was placed to equip a second island with KUKA robots.

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