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

Understanding Servo Press Load Curves

admin

The load curve is one of the most powerful diagnostic tools available on a modern servo press. Understanding how to read and interpret it can prevent tool breakage, detect process problems early, and optimize your forming process.

## What is a Load Curve?

A load curve plots press force (tonnage) against slide position (or crank angle) throughout the stroke. Every forming operation has a characteristic signature — a pattern of force vs position that repeats consistently when the process is stable.

## Reading the Load Curve

**Approach phase:** Force should be near zero. Any force during approach indicates die misalignment or foreign material.

**Contact point:** The curve rises sharply when the punch contacts the material. The position of this rise should be consistent stroke-to-stroke.

**Forming zone:** The shape of the curve here tells you what is happening to the material. A smooth rise indicates good material flow. Spikes indicate cracking or fracture.

**Bottom dead center:** Peak force occurs here. This value must stay below the press rated tonnage.

**Return phase:** Force drops to zero as the punch withdraws. A slow drop may indicate material springback or die sticking.

## Setting Load Limits

Most servo press controllers allow you to set upper and lower load limits at each position. Set them to:
- Upper limit: 110% of normal peak force
- Lower limit: 80% of normal peak force

Any stroke that exceeds these limits triggers an alarm and stops the press.

## Common Load Curve Anomalies

**Double peak:** Material fracturing before full forming depth. Reduce forming speed or increase lubrication.

**Gradual increase over time:** Tool wear increasing cutting forces. Schedule tool maintenance.

**Sudden spike:** Foreign material in die, or material thickness out of spec.

**Low force alarm:** Missing blank, or material too thin.

## Using Load Curves for Process Optimization

Compare load curves across different speed profiles. A slower forming speed typically produces a smoother, lower-peak curve — better for tool life even if cycle time increases slightly.

Save reference curves for each die setup. When a new operator sets up the die, compare their curve to the reference to verify correct setup.

lisa_quality

We use load curve monitoring as our primary SPC tool. Every stroke gets a pass/fail based on the force envelope. When the curve starts drifting toward the upper limit, we know the punch is wearing and schedule sharpening. Reduced our unplanned die maintenance by 45% in the first year.

anna_controls

Load curve sampling rate matters more than people think. At 1 kHz you get a smooth curve that's good for trend monitoring. But for detecting micro-cracks in blanking, you need 4 kHz minimum to catch the high-frequency snap-through signature. Most press controllers default to 1 kHz —check yours.