Page 28 - MetalForming May 2013

Justifying the Purchase of a
Servo-Driven
Press
...using eight principles of improved productivity, flexibility and quality, and reduced costs.
BY DENNIS BOERGER
Okay, here’s the issue faced by our hypothetical stamping- plant manager. Business levels are pretty good and we’ve run out of press capacity. Management is on board with the idea of purchasing an additional press or presses to meet pro- duction requirements. When develop- ing a budget to justify the investment, we reach a crossroads.
Historically we have always tried to purchase good-quality mechanical or hydraulic presses, but have recently learned of servo-driven press technol- ogy and must decide if it’s right for our company. While servo technology will increase the initial investment, per- haps we can recoup this in a reasonable timeframe with the cost savings real- ized using the technology. Specifically:
1) Increased parts per minute (PPM —more PPM equals less cost per part). 2) Improvement in part quality (less rejects equals more profit) and reduc-
tion in tooling cost.
3) Reduction of raw-material cost. 4) Reduced costs for press and tool-
ing maintenance.
5) A reduction (or elimination) of
secondary operations.
6) Reduced energy consumption.
Aida-America Corp., Dayton, OH: 937/237-2382, www.aida-global.com.
7) Shifting of the “tough-to-make” parts to the servo press.
8) Increased flexibility, which opens the potential for acquiring new cus- tomers and entering new markets.
1) Increased PPM
Because the servo drive provides the ability to control press slide veloc- ity at any point in the stroke, we can significantly increase cycle rate while slowing slide velocity only during the working part of the stroke. This allows us to increase the stroke rate while work- ing the material at a slower velocity than we would experience with a stan- dard eccentric crank motion (Fig. 1).
We also can operate the servo press with a pendulum crank motion (Fig. 2), setting the program to use only a portion of the bottom of the press stroke and to swing the crankshaft or eccentric gears back and forth. Pen- dulum motion provides the ability to switch from long-stroke heavy-form- ing operation to short-stroke light forming in the same press, while ensuring optimal forming speed for any stamping operation.
2) Improved Part Quality and Reduced Tooling Costs
The transition to difficult-to-form higher-strength steels and exotic mate-
Fig. 1
Fig. 2
A servo drive provides the ability to con- trol press slide velocity at any point in the stroke, allowing a stamper to increase
the stroke rate while working the material at a slower velocity than with a standard eccentric crank motion (Fig. 1). A servo press also can operate with a pendulum crank motion (Fig. 2), using only a por- tion of the bottom of the press stroke and swinging the crankshaft or eccentric gears back and forth.
rials in the automotive and other indus- tries has forced the metalforming industry—including press makers—to evolve. These materials are harder and stronger than the mild steels they are replacing, requiring manufacturers to increase press tonnage and bed sizes to accommodate the more complex tool- ing needed to produce satisfactory parts. Even with these press advances, often it remains difficult—if not impos-
26 MetalForming/May 2013
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