Servo Presses 2.0: The Evolution Continues

August 25, 2019

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As with any new technology, it takes a while before industry begins to exploit all of its capabilities—and servo drives are no exception. Though more than 20 years have passed since the first servo press was introduced, it wasn’t until the use of high-strength materials ramped up about a decade later that stampers began varying speed and dwell using servo-controlled slide velocity. Today, stampers, in conjunction with equipment providers, increasingly approach servo presses as manufacturing systems, rather than as standalone machines.

This 1500-metric-ton servo transfer press stamps a range of HSLA automotive parts. Among them, door-hinge parts, which were moved from production on a mechanical link-motion press to the servo press.

The results of this evolution can be seen at Midway Products Group, a Tier One automotive supplier with eight plant locations in Ohio and Indiana, 1600 employees and 135 presses, six of which are large servo-driven machines from by Aida—three 1500- and two 2000-metric-ton servo transfer presses, and one 800-metric-ton progressive die press. Jim Ward, manager of manufacturing at Midway, looks for the company to add servo presses moving forward, though he notes that there always will be a need for traditional mechanical presses, especially for low-volume, hand-fed operations.

Achieving Multipart Harmony

Servo press technology enables optimal forming, production speeds and integration of processes and automation. In addition, this particular servo press uses moving bolsters (four) for maximum die storage, staging and quick die changeover, with all bolsters exiting out of the front of the press to conserve floor space and access at the rear of the press. See the Servo 2.0 sidebar for details on the evolving roles of servo presses.

Since 2013, when Midway received its first two servo presses, achieving optimal coordination between the press-slide motion with transfer automation in transfer applications has been a primary objective, according to Ward. “Our objectives early on involved overcoming the challenges associated with stamping heavy-gauge, high-strength parts made of high-strength low-alloy (HSLA) steel,” he says. “We were experiencing short tooling life, low yield rates, high reverse-tonnage load, excessive heat and structural damage to our presses.

“Six years ago,” Ward continues, “servo technology was in its early stages of development. “Even so, we were able to take some products and increase strokes/min., with servo drives establishing dynamic velocity and a full-rotation press profile. From there, to achieve additional efficiency gains doesn’t require only faster strokes/min., but also requires the system to be in multi-part harmony.”

For example, creating a dynamic slide motion profile and coordinating slide motion with the motion of the transfer bars and fingers increases production rates. The slide decreases speed as it engages material through bottom dead center, then increases to full velocity before slowing down to a programmed speed through top dead center, allowing the transfer to achieve optimum strokes per minute. The result: optimal throughput because the slide continues moving through the stroke as the press and transfer work together as a coordinated system.

“With servo drives, the contact and draw velocity are infinitely variable, enabling dynamic motion profiles with multiple slow-down windows to allow the transfer system time to do its job,” says Ward. “We’re able to achieve this with the help of our equipment vendor, Aida-America, who has, over the years, provided many rounds of training for our programmers and operators to ensure optimization.”

This 400-ton press features a fully integrated servo transfer system, liquid-cooled servo motor and low inertia drive train. Several of these systems will be installed in North American automotive supplier plants this year. See the Servo 2.0 sidebar for a discussion of new servo press technology.

“Wherever and whenever you have a servo press and servo transfer system, you add complexity,” says Shrini Patil, product manager at Aida-America. “You need a proper understanding of the technology’s capabilities to benefit from its flexibility. Stampers must exercise caution when programming a servo transfer because of the varying velocities throughout the cycle. You may have 40, 10 and 80 strokes/min. at different points. To achieve transfer, you are tracking virtual angles using binary codes, not the real crank angle as you would on a traditional mechanical press. That’s our secret sauce.”

More Servo, Please

It’s safe to say, after listening to Ward discuss the benefits of servo-driven presses, that Midway’s future will include more such machines.

“Servo technology,” says Ward, “allows our R&D specialists, product designers and die designers to go further with advanced designs and higher-strength steels while eliminating secondary operations.” MF

Servo 2.0

What’s trending when it comes to servo presses and what’s ahead for the once-niche technology? MetalForming recently posed related questions to two industry experts: Jim Schulte, Arisa product manager at Nidec Minster in Minster, OH, and Lee Ellard, national sales manager at Stamtec, Inc., Manchester, TN.

MetalForming: How is the industry’s use of servo presses changing?

Schulte: When we introduced our first servomechanical press in 2009, it was all about flexibility. Instead of running two presses—one with a long stroke and one with a short stroke—customers found that they could combine a variety of applications in one press. Now we are moving beyond that and users are finding ways to optimize the technology.

MetalForming: What does that look like?

Schulte: Historically, the press was the big hammer and you might have a servo transfer system and ancillary equipment. Now, with today’s servo transfer technology, the emphasis is on synchronization and integration of processors. That’s where we find productivity improvement. It is possible to have as many as eight motors, all controlling different axes with a single control. In addition, drivetrain improvements such as liquid-cooled motors and planetary gearboxes allow more-powerful motors in smaller packages, contributing to faster stops and quicker acceleration, enabling greater manipulation of parts profiles.

MetalForming: How would you characterize today’s market for servo presses?

Ellard: Large companies, particularly in automotive, were quicker to understand that the benefits of the servo technology often outweigh the cost differential. Consequently, these companies were quicker to adopt the technology, especially in their large transfer presses and tandem lines, typically 1100 tons and up. It took longer for the smaller shops to get there, but now we are seeing more interest even from the small shops, and for smaller machines (110 to 600 tons).

MetalForming: What about cost?

Ellard: The premium associated with servo over mechanical presses is narrowing. It is still not to the point where everyone will buy servo presses, but the gap has closed. Five years ago, the servo press cost was double that of mechanical presses. Now, it’s about 1.5 times.

MetalForming: What lies ahead for servo?

Ellard: Optimizing servo press performance calls for optimizing tooling, in-die processes and automation to take full advantage of servo press capabilities. In fact, the bottleneck for fully realizing servo press potential lies squarely with the parts manufacturers and tool builders learning to design and build tools for servo presses. We are seeing more creative dies because the technology affords virtually unlimited stroke and motion profiles. The evolution of dies will continue, as will the level of sophistication when it comes to integrating controls, processes and automation.

Schulte: Look for ongoing advancements in sensoring and monitoring of all the systems in a press. Knowing problems in advance—predictive analysis—will be the next quantum leap.