Servo Technology--Revenue Gains with Every Stroke

By: Brad Kuvin

Thursday, September 1, 2016

Metalformers know all-too-well that parts are becoming more difficult to form. Complexity, and new materials—steels, aluminum alloys and others—challenge processes, procedures and equipment like never before. Presses, dies, coil feeds and other machinery can take a beating if not properly specified.

“With all of the uncertainty of the direction of part complexity, material developments, etc.,” says Barry Lewalski, sales and product manager at Schuler, “stampers may soon face situations where they may not have the right press and have to take a pass on new opportunities. When planning for the future, what are they doing to avoid this unfortunate situation?”

The marriage of servo-based transfer systems to servo presses became stronger when press builders introduced transfer interfaces that allow a transfer system (from any supplier) to obtain a continuous signal from the press. In this way, the transfer-system motion control can precisely follow the motion of the press, completely synchronized. Linear Transfer’s Stirrett will address this technology, and more, at the upcoming Servo Technology Experience, October 5-6 in Nashville, TN.
The answer for many is investing in servo-driven presses, which provide for the most flexible press systems available, now and into the future. “Servo allows stampers to adapt, without limitations, to uncertainties in the market,” continues Lewalski. He notes that in many cases today, without servo technology inhouse stampers simply can’t get to the required target price specified for a project.

“What do you tell one of your best customers in such a case, when you can’t even bid on a job because your press systems are unfit? They’ll source it somewhere else,” Lewalski says. “What dynamic does that create?”

Simply, Lewalski says that stampers cannot afford to not invest in servo-press technology. He’ll hammer that message home at the upcoming MetalForming magazine/Precision Metalforming Association Servo Technology Experience, October 5-6, 2016, in Nashville, TN. The two-day event features these day-one presentations on press technology:

• Lewalski’s talk on justification and return-on-investment strategy;

• A discussion on energy management with Stamtec sales manager Lee Ellard and Siemens engineer Tim Barry; and

• A case-study presentation by Komatsu president Jim Landowski.

Attendees also will attend breakout sessions with press builders Schuler, Komatsu and Stamtec to dig deeper into how and where servo presses are impacting the performance of metalformers—now and into the future.

Day two of the conference turns attention to servo-related pressroom technologies, including coil-feed systems, transfer automation, software for simulating transfer-press processes, and in-die servo systems for part inspection and measurement. Speakers include James Barrett from Link Systems; Paul Stirrett from Linear Transfer Automaton; and Mark Hansen from T-Sim Solutions.

ROI with Servo

While a stamper’s return on investment (ROI) in a servo press certainly will vary based on factors including part volumes, workpiece material and part complexity, justifying the price difference between a conventional mechanical press and a servo press often falls in the 1 to 2-yr. range, explains Lewalski.

“There’s definitely the potential to bring in additional revenue with a servo press,” he says, “because you can produce more. And, you can stamp complex parts that likely yield more profitability than does production of simple part geometries. Stampers also need to consider capacity planning when conducting an ROI analysis—a servo press can often produce as much as two or even three conventional mechanical presses can, depending on the nature of the work. So, ROI discussions need to include the additional savings in overhead (operators, training, maintenance, etc.). Another factor to consider is a reduction in die-maintenance activities, since the optimized speed of a servo press (reduced ram speed during forming, for example) minimizes detrimental effects on the tooling, such as heat and impact.”

All of this will come to light during Lewalski’s presentation at the Servo Technology Experience. He’ll also discuss the reasons that companies are investing in servo presses, and will provide part studies (see the accompanying table) that illustrate the productivity gains stampers can expect from servo presses as compared to conventional mechanical presses. He’ll then begin a discussion on how servo presses allow stampers to better coordinate press action with other equipment in a press cell—feeding and transfer equipment, for example. This discussion will be picked up and further developed during day two of the event.

About Transfer Automation

“The marriage of servo-based transfer systems to servo presses is a good one,” says Linear Transfer’s Stirrett, on the topic of complete servo-based stamping systems. “And, that marriage has become stronger with the introduction, a few years ago, of transfer interfaces by the press builders. Such interfaces allow a transfer system (from any supplier) to obtain a continuous signal from the press, so that the transfer-system motion control can precisely follow the motion of the press, completely synchronized.”

Stirrett notes that he’s seen servo-based transfer presses operating “like night and day” when compared to conventional mechanical transfer presses.

“In the medical industry,” he offers as an example, “I’ve seen multiple stations of a transfer die running in a conventional press replaced with one station, leveraging the press’s ability to control forming speed at different points in the press stroke. There’s no question that this technology is minimizing the number of die stations and simplifying the forming process.”

On the transfer-system front, Stirrett will describe two specific technology trends:

• The use of linear motors in very high-speed and high-acceleration applications, to decrease system complexity by eliminating belts, gear boxes, ballscrews and the like; and

• The use of carbon-fiber booms to reduce transfer-system weight and, therefore, increase system capacity.

“Last but not least,” Stirrett adds, “servos following servos (press to transfer system) creates a much cleaner, repeatable and robust process. The ability to run in pendulum mode, along with the quick response capabilities of a servo press, eliminate the wasted angle and timing that is lost in a typical cycle. These characteristics also compensate for press stopping time on a servo press when compared to a standard mechanical press.

Optimizing the Working Energy System

“In a servo press, with the servo motors supplying continuously variable working energy at any speed,” explains Stamtec’s Ellard, “a servo press can optimize productivity based specifically on time-optimized motion profiles. Those profiles must fit within the specific press and process parameters—maximum motor speed, the available working area during the stroke, maximum slide speed and optimal forming speed of the slide—but are more or less infinitely variable within those parameters.”

Ellard, along with Siemens’ Barry, will dive deeply into this subject, while explaining how and why servo technology optimizes flexibility in the pressroom. Ellard also stresses that, “with all of the flexibility and possibilities, it might seem like a servo press will immediately simplify a stamper’s life. In many cases it will, but stampers must actually be more knowledgeable about their tooling than they are when specifying a conventional mechanical press, so that they make the right choices when working with their supplier to configure a new servo press.

“The ability of a servo press to provide optimized productivity,” he continues, “comes at the potentially high expense of peak-current demands from the servo system. There are two ways to minimize energy use—optimize the drive configuration to match the application of the press, to avoid oversizing the system; and employ some level of energy-optimization technology.” Ellard and Barry will expound on these options.

Adds Barry: “Lack of any type of energy management can significantly impact the total cost of ownership, and every servo-press design has its unique energy requirements. This results in specific energy-management calculations. The press must be optimally configured for speed, energy and energy provided at a specific distance off bottom.

“There are specific opportunities for stampers to save money here,” he continues. “Stampers must know what they are signing up for when they invest in a servo press. For example, a 1000-ton conventional mechanical press with a 250-hp drive may require 400 A of input power, while a 1000-ton servo press might require 2000 A (with no energy management). This is a huge disparity, but when understood and planned for using the right energy-management approach, it can be mitigated.”

Energy-management strategy, a primary discussion point for Ellard and Barry at the Servo Technology Experience, centers on the use of energy-storage devices integrated with and controlled by the motion system. A press lacking such add-ons requires all of the mechanical power from the motor to be covered by the infeed and line supply. However, with the proper energy-storage devices in line, the servo-press supply system need only provide power for the actual work done and system losses. This greatly minimizes the infrastructure required, and installation costs.

“We see ROIs from these energy-management systems at around 18 months,” Barry says. That justification process will become clear during his presentation in Nashville.

In-Process Quality Control—More ROI Fuel

There’s even more to consider when cost-justifying a servo press, it turns out, in addition to the press-stroke flexibility afforded by the servo-press drive system. That flexibility not only pays dividends during the stamping process, but it also can promote in-die measurement, inspection and quality control. Yes—stampers can perform dimensional inspection in the die (without slowing the process), and then divide good- and bad-parts streams, eliminating the need for a secondary inspection and verification station in the die, or the need for an additional post-production inspection process. That’s the gist of the presentation from Link Systems’ Barrett.

“While we can and do set up in-die measurement and inspection stations with conventional presses,” Barrett says, “the ability to slow or pause the ram with a servo press takes this to the next level. There are certain types of measurements that are difficult or impossible to make inside of a conventional press that become much simpler to make with a servo press. For example, we can pause on the upstroke and fire a PLS to bring in an LVDT or other device. We see this as very viable in the aerospace or medical industries, for example, where you often need 100-percent part verification.”

Barrett also will explain to conference attendees how the flexibility of press-automation equipment truly comes to light when matched with servo presses. For example, consider an application where a servo press passes through bottom three times on one station.

“We can fire a PLS at a particular crank angle,” he explains, “but only on the third pass through, for example. Or we can gather data from the die-protection sensors on the upstroke after a bend in high-strength steel has been made, or we can bring in different sets of limits on the tonnage monitor for each pass through bottom.

“In most cases we’re seeing this type of work being done at full production speed,” Barrett concludes. “My presentation will share some details, prescribe best practices for sensor selection and use, and emphasize the need for diligent operator training to ensure it all comes together.”

For more information on the Servo Technology Experience, presented by MetalForming magazine and the Precision Metalforming Association, visit MF


See also: Komatsu America Industries, LLC Press Technology Division, Linear Transfer Automation Inc., Link Systems, Schuler Incorporated, Siemens Industry, Inc., Stamtec, Inc., T-Sim Solutions, LLC

Related Enterprise Zones: Presses

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