Bosch Rexroth, represented in sub-Saharan Africa by Tectra Automation, has modernised three thermoforming lines for Whirlpool by upgrading servomotors and drive components. These lines produce plastic inner door panels for refrigerators.
In the last few years, refrigerator sales have increased several times over. Due to the high demand of these products, any downtime during production has a particularly negative effect. The challenge for Rexroth lay in the fact that the upgrade could not stop production.
"The important thing is how fast we started this up," notes Michael Smith, engineering supervisor of Whirlpool's Plastics Operations. In just two weekends the electrical and mechanical power transmissions were modernised. As the site was in production five days a week, this meant that production did not have to be stopped. This was particularly important at a site that manufactures more than 5000 plastic inner door panels every day.
Whirlpool initially upgraded the servomotors and drives on the de-stacker portion of the line using Rexroth ECODRIVE servo drives and MKD servomotors. The de-stacker portion of a thermoforming line picks plastic sheets from a stack and indexes them into preheat ovens for eventual forming in the thermoforming press. The de-stacker loads from two opposing sides for quick changeover. The de-stacker rack descends at a high velocity until it trips a 'whisker' switch and decelerates, moving at a slower speed until vacuum cups contact the sheet's surface. The destacker's drive makes eight distinct moves in this process, all within 20 seconds. The STACK is comprised of up to 225 thin plastic sheets.
"The catch," says Smith, "is the stack height always varies after the previous sheet is picked. The difference in stack height is overcome by stopping the drive in a torque mode."
The retrofit has removed five seconds from the original de-stacker cycle. As well as the de-stacker, Rexroth in collaboration with Whirlpool and the company Morell, modernised the servomotors and drives of the transmission drives of all three thermoforming lines. For this, the pin chain transmission drives were fitted with servo drives. As with a chain saw, the individual teeth are embedded into each plastic sheet. They grip into the relevant gaps, which makes transport possible.
The ECODRIVE retrofit is suitable for applications of 1 kW up to 27 kW and is an especially economical solution for control and positioning tasks up to 27 kW. It is particularly versatile, economical and powerful to run. Additionally, the Rexroth MKD servo motors are a cost-effective solution for general automation engineering applications up to 637 lb-in (72 Nm).
"Our goals were to get the system upgraded in a very short time frame, integrate the drives and motors into the existing PLC program, and switch from position to torque mode on the fly.
"Our team was able to meet those challenges through the excellent support of Rexroth [and] Morrell, and the ease of use of Rexroth's DRIVETOP software on setup. The software is flexible, yet powerful. It offers a lot of control options that competitors do not, and its graphical design does not require a lot of programming experience to use it, as it has a step-by-step guide to setup at the control terminal or PC," concludes Smith.
For more information contact George Venter, Tectra Automation, +27 (0) 11 971 9400.
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