Dynamic Die: Transitioning to Precision with Servo Presses

In the realm of hydraulic press replacement, particularly for those using outdated equipment, the choice between upgrading to an improved hydraulic press or switching to a servo mechanical (servo) press presents a significant decision. As outlined in the article “5 considerations when replacing a hydraulic press with a servo press” from The Fabricator, this decision involves complex trade-offs, akin to the choice between a hydraulic press and a traditional mechanical press. Vital attributes under scrutiny during this process are control, flexibility, speed, cost, and longevity.

Control emerges as a pivotal factor, especially as manufacturers experiment with new materials and designs. Servo mechanical presses offer an abundance of data on power, speed, force, and position. Utilizing feedback from servomotors, these presses effectively adjust speed and power based on real-time data. This capability allows servo presses to closely adhere to preprogrammed process curves, particularly advantageous for applications involving high reverse tonnage and materials prone to springback tendencies.

Advanced hydraulic presses, on the other hand, employ a sensor network to achieve similar goals. Monitored within pressurized fluid, the applied force is coupled with direct measurements of position and speed. This hydraulic control is used to manipulate hydraulic valves for independent speed and force adjustments. However, while hydraulic presses offer accuracy within 10 microns, the reliance on fluid may lead to dampened corrections in force or speed, resulting in slightly diminished final accuracy compared to servo counterparts.

Flexibility plays a critical role, particularly for deep forming applications. Hydraulic presses have traditionally excelled in this area due to their ability to exert full force at any point within the stroke. Contrarily, many servo mechanical presses experience tonnage loss of up to 50% just 1 inch above bottom dead center. Choosing the right technology also hinges on design flexibility. Servo mechanical presses often exhibit a high force per square foot of working area, while hydraulic press designs can be adapted to the application, ranging from 1 to 150 tons per sq. ft. Aligning press tonnage with requirements can significantly bolster production rates and reduce costs.

Speed is another pivotal factor. Hydraulic presses can achieve speeds exceeding 1 meter per second during a stroke but encounter idle time due to hydraulic valve shifting, restricting speed to below 30 strokes per minute (SPM). Servo mechanical presses exhibit slide speeds below 0.5 m/s, yet their cycle times can be optimized through higher speeds outside the working stroke portion. The servomotors’ agility enables swift acceleration and efficient part restriking within a tenth of a second.

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 Photo and article with all rights reserved, courtesy of thefabricator.com