Page 36 - MetalForming June 2019

Maintaining
Servo-Driven Presses
When maintaining a servo-driven press, do your homework and you’ll be rewarded.
BY JEFF FREDLINE
Servo-driven presses offer improved control during the feed cycle while allowing for the stroke to be adjusted to allow for long feed lengths and the manufacture of complex stampings. While the investment on the front end runs higher than with standard mechanical presses, the rewards are worth it—so long as you understand the technology, operation and maintenance requirements. Armed with this knowledge, metal formers know what to look for and what to ask as part of an ongoing maintenance program.
Let’s learn.
Structural Features and Frame Design
Similar to a standard mechanical press, the frame of a servo press and slide assembly provide mechanical rigidity and resistance against deflection during the cycle. Most servo presses use a steel-plate-welded assembly with power generated by servo motors in various configurations based on the required press force and forming task. Low-stress annealing of the welded parts has become standard. Some manufacturers ensure press longevity by performing finite- element analysis (FEA) on the press frame, drive components and slide assemblies to optimize construction and prepare the frame for dynamic forming processes.
Drivetrain Deciphered
The use of dynamic torque motors in servo presses delivers several advantages:
• High torque available at low speeds;
• Low moment of inertia, very dynamic;
• Extremely quiet as compared with standard mechanical
presses;
Jeff Fredline is a sales engineer for Meco Corp., Greenville, TN; 800/257.7558, info@mecocorp.com, www.mecocorp.com. He thanks the staff at Simpac America (www.simpac.co.kr/en/) for assisting with this article.
• Temperature-controlled, water-cooled; • Shorter brake angle;
• No backlash or rotor losses;
• Nearly maintenance-free operation; and • Long production lifetime.
Most servo-driven presses still use a gear reduction, par- ticularly on larger two- and four-point presses. The drivetrain, characterized by one or more torque motors attached to the drive shaft and the absence of a traditional flywheel assembly clutch/brake combination, ensures high dynamics, efficient processes and reduced maintenance due to the absence of these mechanical-press features.
As for the braking action, that’s performed by the motor itself. Presses with higher tonnages and correspondingly heavier slides have an additional hydraulically released and spring-loaded holding brake specially developed for servo presses. This prevents slide movement during drive inactivity or a press-system failure.
While drivetrain designs from different manufacturers vary slightly, all share these attributes:
• Programmable stroke and speed;
Some manufacturers ensure press longevity by performing finite-element analysis (FEA) on the press frame, drive components and slide assemblies to optimize construction and prepare the frame for dynamic forming processes.
34 MetalForming/June 2019
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