What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Yaskawa Sigma-7 A.74 Overload Alarm on Servo Press

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## A.74 Definition

Yaskawa Sigma-7 alarm A.74 is overload — the motor has been running above rated torque for too long. The drive calculates a thermal model and triggers A.74 when the model reaches 100%.

## Check the Overload Level

In SigmaWin+, monitor Un009 (overload level %). Normal operation should stay below 50%. If Un009 is consistently above 70%, overload alarm is likely.

## Common Causes on Servo Press

### 1. Forming Force Exceeds Motor Rating

The press is being used beyond its rated tonnage. Check:
- Actual tonnage monitor reading vs press rated tonnage
- Material thickness and grade vs die design spec

### 2. Motion Profile Too Aggressive

High acceleration + high forming speed = high peak torque. The thermal model accumulates even if each individual stroke is within limits.

Fix: Reduce forming speed from e.g. 100mm/s to 70mm/s. Reduce acceleration. Add rest time between strokes.

### 3. Gib Friction

Excessive gib friction adds constant load to the motor. Check gib clearance — if below 0.005mm, the gib is too tight.

### 4. Counterbalance Pressure Wrong

If pneumatic counterbalance pressure is too low, the motor must lift the full slide weight on the return stroke. Check counterbalance pressure per press manual.

## Parameter Pn521

Pn521 sets the overload warning level (default 20% before alarm). Do not increase this to avoid the alarm — fix the root cause instead.

## Reset

A.74 requires the motor to cool down. Wait until Un009 drops below 20% before resetting.

anna_controls

A.74 is a calculated overload, not instantaneous. The drive tracks cumulative thermal load over time. If you're getting A.74 on heavy jobs, check the overload detection time (Pn52B). Default is usually 60 seconds. For press applications with short high-torque bursts followed by light return strokes, you can sometimes extend this to 120 seconds safely.

raj_maintenance

We had A.74 appearing only on hot days. The motor was marginal on torque capacity and when ambient temperature went above 35?C, the thermal headroom disappeared. Added a fan to blow air directly on the motor and gained about 10% more thermal capacity. Proper fix would be a larger motor but the fan bought us time.

mike_chen_eng

The ambient temperature point is underrated. We track motor temperature delta (motor temp minus ambient) rather than absolute motor temp, and that gives a much better picture of actual thermal margin. If your delta is consistently above 60K on a Sigma-7 SGMGV motor, you're running too close to the edge regardless of what the absolute number says. One diagnostic trick for A.74 on Yaskawa: monitor Un00D (cumulative load ratio) in real time during a production run. It ramps up toward 100% before the alarm trips. If you see it climbing steadily and never dropping back, your cycle doesn't have enough recovery time. But if it oscillates between say 40-70%, you have margin. We had a case where A.74 only appeared after about 45 minutes of continuous running. Turned out the regenerative braking resistor was undersized - the motor was doing more braking work than expected during the return stroke, and that heat was accumulating in the thermal model. Swapped to a larger regen resistor and the A.74 disappeared completely. Worth checking Pn600-Pn603 (regen resistor parameters) if your press does fast return strokes.