Leveraging Servo Press Motion Profiles - MetalForming Magazine

By looking at the load signature, operators can understand at which position in the stroke the force builds up, or when it drops dramatically, indicating material breakage. A simplistic but useful way to approach this: Look at the peaks and valleys in the load signature or at negative tonnages. The negative values should stay within press limits, and the smaller the peaks and valleys, the better. The opposite is detrimental for the press and the tool.  

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Fig. 2 illustrates using signature analysis to correct an application running at 60 strokes/min.  

3. Use the Pendulum Mode Wisely

Pendulum mode on a servo press can increase production rates significantly by using only a partial rotation for each stroke rather than a full 360 deg., reducing cycle time. However, metal formers should take care when designing a pendulum profile, especially in regard to feed angle. An insufficient feed angle can cause erratic feeding, leading to misfeeds or forcing the press to slow down in order to allow the material to feed properly. Conversely, an excessive feed angle results in a larger pendulum motion that slows production due to wasted degrees in the press cycle. 

If the resultant pendulum is too high, close to a 360-deg. rotation (depending on the profile generator), a full revolution may lead to higher production rates. 

If a tool design includes part risers, be sure to minimize the height of the risers to allow for short forming strokes. Often, risers are higher than needed, leading to long forming windows that may slow production.

Thus, the correct feed angle in addition to a short forming stroke are keys to maximizing pendulum speeds. Depending on the press control, fine tuning may include small decrements to the pendulum height, or precise definition of the feed window in terms of seconds. Keep in mind that, in general, the shorter the pendulum the higher the production rate, but also less time to feed or transfer material.  

Fig. 3 compares pendulum and full-revolution profiles. Note the significant reduction of the feed window in pendulum profiles, which requires high-performance feed equipment. Note: Decide whether to use a pendulum or full-revolution profile on a case-by-case basis.  

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4. Use 100% (or Close to it) of the Programmed Speeds

Once the servo motion profile has been defined and calculated, the maximum production rate then depends on the dynamic capacity of the servo press. However, often stampers run at a production rate lower than the calculated maximum. This might be due to issues observed when running at higher speeds, including part instability, misfeeds, fractures, tool breakage and end-of-line part stacking. While all these issues might seem valid for decreasing press speed, an actual production rate significantly slower than programmed clearly indicates a non-optimum stroke profile.

Rather than decrease press speed during production, metal formers should redesign the motion profile to accommodate any issues encountered. This can become an iterative process until every challenge has been overcome. If the process proves successful, the actual production rate will be close to that of the maximum programmed rate.

A good rule of thumb: Look for a motion profile that achieves a production rate of 90% or more of the programmed maximum rate.

Take a Strategic Approach

In summary, optimizing production rates with servo motion profiles requires a strategic approach. Use pendulum mode effectively by fine-tuning the feed angles, employing load-signature analysis and adjusting speeds judiciously throughout the entire stroke—and not only toward 180 deg. Ultimately, aim for a motion-profile use of 90% (or greater) of the programmed rate. 

Successfully implementing these strategies helps to ensure the highest production rates along with consistent quality, thus enhancing overall operational performance. MF

See also: Nidec Press & Automation

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