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Servo press precisely controls the stamping process


Hot stamping plastic parts is a dynamic process that must be extremely precise for vacuum cleaner manufacturer BSH. To complete parts automatically, quickly and with low energy consumption, BSH relies on ElectricDrive electromechanical servo drives from Tox Pressotechnik in Weingarten, Germany.

“With the new fully automatic hot stamping system, we can define the process more precisely in advance,” says Andreas Zehe, production technician at BSH Hausgeräte GmbH in Bad Neustadt, Germany. “We work faster and more precisely, have reduced scrap rates by 60 to 70 percent, and consume significantly less energy than before using pneumatic drives.”

For several months, the 400-employee manufacturer of vacuum cleaners, which produces on behalf of Bosch-Siemens, has been operating a second hot stamping press equipped with two electromechanical servo drives from Tox ElectricDrive. The system was designed and installed by Gebr. Gierlich GmbH & Co. in Bonn, Germany, specializes in the manufacture of hot stamping systems.

In this system, BSH uses pressure and heat to surface-treat vacuum cleaner parts with a plastic film. The process is fully automated. A linear handling system removes plastic parts from the injection molding machine and places them in a hot stamping fixture. In the first stamping step, the foil is heated and stamped onto the part. In the second step, the temperature-controlled silicone stamp is moved under high pressure onto the plastic part, stays there briefly, and then moves back again. The film portion is separated from the carrier and bonded to the component. The camera then examines the entire process.

Decorative elements on vacuum cleaner

The decorative elements on this vacuum cleaner are hot stamped. Photo courtesy of Tox Pressotechnik

pressure is crucial

To achieve a stable process and error-free results, the parameters of the individual stamping steps must be precisely set. The pressure with which the press moves onto the part is decisive, but the temperature of the cylinder, stroke speed and stroke length are also important.

“This is where the precision tuning options of electromechanical servo drives really come into play,” explains Zehe. “Because our stamping machines are equipped with Tox stamping cylinders, we can automatically measure and readjust pressure during the stamping process.”

Even after changing the impression, the system independently re-adjusts the pressure because all parameters are pre-stored in the software.

With older systems with pneumatic drives, this all had to be set manually. Thanks to automation, it is now possible to store any number of programs that can be recalled by plant operators at the touch of a button. “Before, we were constantly retuning and resetting the mechanism. Now, we specify in advance exactly when we need which speed and which stroke,” Zehe said.

He can then read whether the process is working as planned and make corrections if necessary.

Silicone seal

The temperature-controlled silicone stamp is moved under high pressure onto the plastic part, stays there briefly, and then moves back again. Photo courtesy of Tox Pressotechnik

Less energy, longer life

BSH commissioned its first hot stamping system equipped with Tox servo drives in mid-2020. The second occurred last year and the third is in the planning stages. “We are delighted that both the plant designers and the users are very satisfied with our drive system,” adds Tox salesperson Peter Wilhelm. “The hot stamping project is also a special application for us because we typically have conversations with our drive units when it comes to processes like riveting, press fitting, riveting and punching.”

The fact that BSH retains the seal for a few seconds at the end and does not immediately retract it is also not common in classic applications, but can be easily and quickly achieved via software parameters, Wilhelm said.

Each hot stamping machine uses two electric drives. Each unit consists of a servo press (with ball screw or planetary roller screw on request), controller, control cabinet and integrated software. This energy-saving drive is suitable for applications with effective usable pressures ranging from 0.02 to 1,000 kilonewtons.

Another benefit of servo presses is that they consume less energy than pneumatic presses and last significantly longer.

Zehe is confident that the investment will pay for itself in three to four years.

Silicone seal

Another benefit of servo presses is that they consume less energy than pneumatic presses and last significantly longer. Photo courtesy of Tox Pressotechnik

Online assembly

For more information about assembly presses, read the following articles:
Optimized work cell for crimp assembly
Common Press Mistakes
Assembly presses: crimping, riveting, swaging, riveting



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