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

How to read a tonnage monitor - what am I looking at?

gary_deepdraw

New to tonnage monitors and I'm staring at this waveform display not really understanding what I'm seeing. Can someone explain what to look for?

**What the Tonnage Monitor Measures
**
A servo press tonnage monitor measures the actual forming force during each stroke using strain gauges mounted on the press frame or slide. The reading tells you:

- Whether the die is working correctly
- Whether material thickness is consistent
- Whether a double blank has entered the die
- Whether a punch has broken

**Reading the Display
**
Most tonnage monitors show:
Peak tonnage:: maximum force during the stroke (in tons or kN)
Tonnage curve:: force vs. position graph for the full stroke
High/low limits:: alarm thresholds

**Setting Limits Correctly
**
**High limit:** Set at 110-115% of nominal tonnage. This catches:
- Double blanks (two sheets entered die)
- Die crash (foreign object in die)
- Incorrect material (wrong thickness or grade)

**Low limit:** Set at 80-85% of nominal tonnage. This catches:
- Missing blank (no material in die)
- Broken punch (punch not forming)
- Incorrect material (too thin)

**Interpreting Tonnage Curves**

**Normal curve:** Smooth rise to peak at BDC, then rapid drop on return.

**Double peak:** Two force peaks in one stroke — indicates progressive die with two forming stations, or a problem with die timing.

**Early peak:** Force peaks before BDC — punch hitting material too early, check die setup and material thickness.

**Gradual increase over time:** Die wear or material hardness increasing. Schedule die maintenance.

**Calibration
**
Calibrate tonnage monitor annually using a reference load cell. Accuracy should be within +/-2% of full scale.

lisaQ_metrology

The tonnage signature shape tells you more than the peak number. A healthy blanking signature has a sharp rise, a peak, and a sharp drop. If the drop becomes gradual, the punch is getting dull. If the peak increases over time, the material is getting harder or thicker. We review signatures weekly as part of our SPC program.

pressroom_tom

As an operator, the tonnage monitor is my best friend. I can tell within 5 strokes if something is wrong just by glancing at the waveform. A double peak means a misfeed. A low peak means a missed hit. A gradually rising peak means the die needs sharpening. Once you learn to read it, you catch problems before they become scrap.

jim_apps

One thing nobody mentioned — set your tonnage alarm at 80% of rated capacity, not 90%. I've seen too many shops run at 90% and by the time the alarm trips the die is already damaged.

For reading the waveform: the area under the curve matters more than peak force for drawing operations. Two hits can show the same peak tonnage but completely different energy. If you're running a progressive die, compare the signature station by station — a worn pilot will show up as a slight shift in the timing of the second peak before the force numbers change noticeably.

Also check your strain gauge calibration every 6 months minimum. We had a monitor reading 15% low for three months because a gauge bond was failing. Thought our die was running great, turns out we were overloading it.

raj_pm

Adding the management/PM perspective on tonnage monitor reading because I've seen too many programs where the data exists but nobody acts on it.

The single most useful thing we did was set three thresholds, not one. The OEM ships them with a single "alarm" band ?10% or so. We split it into:

A *trend* band ?3-5% that doesn't stop the press but logs the event. This is for the data person to look at weekly. Drift inside this band catches die wear, lube degradation, and feed misalignment before they become quality problems.

A *warn* band ?7-10% that flashes the HMI and emails the toolroom. Operator keeps running but knows something changed this hit. We track close rate on these ??anything not closed within a shift escalates.

A *stop* band beyond that, which is the OEM default behavior. By the time you hit this you've already lost parts and probably tooling.

The other piece is who looks at the data. If only the operator sees it, you get reactive use only. We pipe the curves to a shared dashboard the toolroom and quality team check on Monday mornings, and we review the top 5 worst-drift dies in a 15-minute meeting. That meeting alone has paid for the monitoring system three times over in avoided scrap.

The technical reading skill matters, but the organizational habit around the data matters more.