Developments in Motors, Drives and Controls Impacting the Pressroom

By: Brad Kuvin

Wednesday, August 1, 2018

In a recent conversation with Tim Barry, business development manager for metalforming at Siemens Digital Factory, he describes what he calls a “perfect storm” pressroom environment. So many metalformers, he says, continue to run their equipment at capacity, making any sort of shutdown for maintenance, retrofit or repair, and any desired transition to newer press technology practically impossible.

“Press-shop equipment is at its oldest average age since 1938,” says Barry. “Meanwhile, newer press and control technologies have evolved to a point where a retrofit, or even a new-press purchase, often makes perfect business sense.”

As Barry’s work passion involves helping shops, as well as pressroom-equipment OEMs, bring their visions to reality by applying new technologies, he knows well that the metalforming industry is at a critical junction.

This hydraulic press from German builder Lasco Umformtechnik GmbH features a hydraulic pump directly coupled with a servomotor, as an energy-efficient solution. With a response time of 250 µs, as many as 256 axes can be synchronized and precise axis motion and curve profiles executed. Plunger speed is controlled by motor speed and thus by the volumetric flow rate of the pump.
“Yes, the long-emerging servo-press technology has taken hold,” Barry stresses, “providing trackable improvements in press performance, product complexity and output, in addition to noise and energy reduction. However, updating existing presses with the latest drives and controls also can provide additional, measureable improvements in production and reliability. You’re either going to make more parts, run at the same rate but stop less frequently, or, when production does pause, you can bring the machine back up and running more quickly due to better diagnostics.”

Better Servo Motors and Drives

The bullet-point list of recent technology enhancements to drivetrain components promising pressroom advantages:

• New servo motors, which feature radically improved accuracy and provide the ability to apply maximum torque at any point in the ram descent to BDC;

• Regenerative drives, which can apply cyclic ram-action power savings to other components or back to the grid; and

• Positioning encoders, which signal power and positioning requirements more accurately than ever.

“Drives themselves are getting smaller, providing more power in less space,” Barry says. “One-cable technology is another biggie gaining momentum. Instead of separate power and feedback cables that run in and around the press cell, we see that migrating to one cable.”

With regenerative drives, “you get your most bang for the buck on the big stuff—big flywheel drives, for example,” Barry notes. “For example, we’re working through some projects with a major press supplier and one of the Big 3 automotive companies to retrofit several older AC main press motors with fully regenerative drives. At first look, such a project might appear as spending more money than necessary. But the faster you’re able to stop the ram by using a newer regenerative drive, the better we can capture the stored power and send it back to the line. Over time, the cost savings can be significant.

“In fact, regarding the above-mentioned Big 3 project,” Barry continues, “we originally pitched non-regenerative drives but the customer said, ‘as often as we start-stop these presses, we want to capture that stored energy and reuse it/send it back to the line.’ We’re starting to see this more as shops become more energy-conscious.”

Barry also notes the increased interest in regenerative drives on other equipment in sheetmetal-processing lines—tension levelers for example—where shops have retrofitted fully regenerative drives and common bus systems and can share the load within the line. “So, a shop might be processing the strip with one motor developing tension,” he explains, “pulling against the other motors, and recirculating the energy back into the bus bar to reduce the connected load.”

Regen and Servo Presses

MJC Engineering and Technology, Huntington Beach, CA, engineers this CNC flow-forming machine using a Siemens Step 7 PLC control. The control software reflects the trend noted in the article—efficient communications, ease of programming, and enabling streamlined commissioning and service.
When it comes to installing regenerative drives on servo presses, most of the regenerative energy is captured within the line, stored and used when needed. This differs from a flywheel-press application, where the energy conserved during a press stop immediately flows back into the line. “With a servo press,” says Barry, “we’re managing the energy within the system itself and storing the reclaimed power to be used in the next press stroke. Then we don’t need braking resistors on the panel.”

Drive-motor combinations also represent an important development—where the drive mounts directly to the motor. “We see these gaining acceptance during upgrades to destackers and other end-of-line automation,” Barry explains. “Servo-based actuators can index the work, the stamper just runs power to the motor-drive combo. These setups simplify installation, commissioning and troubleshooting/maintenance, while also conserving space.”

Barry also notes a pull away from the use of stand-alone motion controllers on certain applications where it makes more sense to integrate motion-control functions into the PLC. “Advanced motion-control/PLC/HMI units are gaining traction,” he says. “These units can control and display all press-cell functions, including advanced automation devices.”

Lastly, Barry notes another trend: servo-hydraulic functions moving to full electric servo.

“We’ve recently completed several servo-electro hybrid projects, half electric and half hydraulic, for force or pressure for example,” he says, “replacing cylinders with ballscrews. So, many of those existing hydraulic servo-controlled press functions, where you’re forming parts, now can move to a servo-motor and ballscrew arrangement. We’ve seen huge factors of increased accuracy and part quality from this trend, as well as energy savings. We can perform the same tasks mechanically, and improve process control.”

The Growing Retrofit Market

Pressroom equipment can last a long time, and Barry notes that a lot of servo-based machines, including presses, have been in service for 10 years or more. “This equipment now is worth looking at in terms of motor, drive and control retrofits,” he says. “The first versions of AC drives and motors that were somewhat complex and specialized are being replaced with off-the-shelf common motor-drive setups.”

In addition to the above discussion of new motor and drive technology, “retrofits deliver additional space and decreased installation-commissioning time,” says Barry. “In some cases the metalformer might only retrofit the drive portion, and the drives, PLCs and other controls occupy the same space in the cabinet. The challenge, then: adding more axes or more complexity to the retrofit without installing a giant new panel or tearing out the old panel and redoing the entire machine. With newer drive-motor technology, we can upgrade without having to rewire and rebuild an entire panel. Instead, we can add a smaller subpanel that mounts out by the machine, or employ a drive-motor combination—mount the motor and run a cable to it, and you’re done.”

Convincing a metalformer to retrofit an older press cell also requires ensuring minimum downtime for the upgrade project. Barry has a solution here, as well.

“With retrofits,” says Barry, “rather than 2 or 3 weeks of downtime we often can complete the job in 10 days or less. Quick commissioning time helps sell these improvements. For example, we’ve seen metalformers replace hydraulic valves with variable-frequency drives, resulting in servo functionality, over a long weekend. In other cases we can complete a full drive upgrade in 5 days, compared to 5 to 7 years ago when that type of project would have taken 10 to 15 days or more.”

System Commonality

A final trend making life easier in the pressroom—this time for maintenance technicians: implementation of common programming platforms. ”In the past we had separate platforms for the HMI, the drive control and the PLC,” Barry says. “Today, everything comes into one platform—the HMI, PLC and drives now can share tags and data, and the OEMs can build common program libraries for their machines. This practice minimizes configuration complexity and ultimately requires less expertise from technicians when it comes time to maintain and service the machines. They’re talking to one controller, and using less software with simplified troubleshooting.” MF


See also: LASCO Engineering Services, LLC, MJC Engineering & Technology, Inc.

Related Enterprise Zones: Presses, Sensing/Electronics

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