Hot stamping plastic parts is a dynamic process that must be very precise at vacuum cleaner manufacturer BSH. In order to be able to finish the components automatically, quickly, and with low energy consumption, BSH relies on the ElectricDrive electromechanical servo drives from Tox Pressotechnik.
"With the new, completely automated hot stamping systems, we can define the process much more precisely in advance," enthuses Andreas Zehe, who works as a production technician at BSH Hausgeräte GmbH in Bad Neustadt. "We work faster and more precisely, have reduced scrap by 60 to 70 percent and consume significantly less energy than before with the pneumatic drives."
For a few months now, the vacuum cleaner manufacturer, which produces on behalf of Bosch-Siemens with 400 employees, has been running its second hot stamping machine with two ElectricDrive electromechanical servo drives from Tox Pressotechnik GmbH & Co. KG from Weingarten. The system was planned and installed by Gebr. Gierlich GmbH & Co. KG from Bonn, which specializes in the manufacture of hot stamping systems.
In the system, BSH finishes components for vacuum cleaners with a thin film of plastic under the action of pressure and heat. The process is fully automated: a linear handling system removes the plastic parts from the injection molding machine and places them in a hot stamping fixture. In the first stamping step, foil is heated and pressed onto the component with a stamp. In the second step, a temperature-controlled silicone stamp moves onto the plastic part at high pressure and rests there very briefly before moving back again. The film part detaches from the carrier and bonds with the component. A camera then checks the process.
Pressure is crucial
For a stable process and an error-free result, the parameters of the individual stamping steps must be set very precisely. The pressure with which the stamp moves onto the component is decisive, but the temperature, stroke speeds and stroke lengths of the cylinders are also important.
"This is where the precise adjustment options of the electromechanical servo drives really come into their own," Andreas Zehe tells us. "Since we equipped our hot stamping machines with the Tox stamping cylinders, we can automatically measure and readjust the pressure during the stamping process." And even after a stamp change, the system readjusts the pressure independently because all parameters have been stored in the software beforehand.
With the old systems with pneumatic drives, this all had to be set manually, according to Andreas Zehe. Thanks to automation, any number of programs can now be stored, which the plant operator can call up at the push of a button. "Before, we were constantly readjusting and setting the mechanics. Now we specify in advance exactly when we want to have which speed and which stroke," says Zehe. He can then read out whether the process has run as planned and then correct it again if necessary.
Less energy, longer service life
BSH has already commissioned the first hot stamping system with electromechanical servo drives from Tox Pressotechnik in mid-2020, and a third is in the planning stage. "We are very pleased that both the plant designer and the user are so satisfied with our drive systems," adds Peter Wilhelm, who works in sales at Tox. "The hot stamping project was a special application for us, too, because we normally come into the conversation with our drive units when it comes to processes such as clinching, press-fitting, riveting and punching."
According to Wilhelm, the fact that BSH holds the stamp for a few seconds at the end and doesn't retract it right away is also not the norm in classic applications, but it can be implemented easily and quickly with the specification through software parameters.
Two ElectricDrive units are used in each of the hot stamping machines. Each unit consists of a servo press - a ball screw or a planetary roller screw is used here, depending on the requirements - a controller, the control cabinet and integrated software. The energy-efficient drive solution is suitable for applications with an effectively usable press force range of 0.02 to 1,000 kilonewtons and can be used in a variety of ways.
Peter Wilhelm concludes by emphasizing the lower energy consumption of the electromechanical servo solution compared to pneumatic drives and the significantly longer service life of the systems. And Andreas Zehe from BSH is certain that the investment in this solution will have paid for itself after three to four years. For both business partners, the collaboration went absolutely smoothly, and the project is a real win-win situation for everyone involved.