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 Calculate Servo Press Tonnage Requirements

admin

Selecting the correct tonnage is critical. Here is a systematic approach.

## Basic Blanking Force Formula

**F = L × t × τ**

Where: F = force (kN), L = cut length (mm), t = material thickness (mm), τ = shear strength (MPa)

Shear strength is typically 60–80% of tensile strength. For mild steel (UTS 400 MPa): τ ≈ 280 MPa.

## Example Calculation

Blanking a 100mm diameter circle from 2mm mild steel:
- L = π × 100 = 314mm
- t = 2mm
- τ = 280 MPa
- F = 314 × 2 × 280 = 175,840 N ≈ **18 tonnes**

## Drawing Force

For deep drawing: **F = π × d × t × UTS × C**

Where d = punch diameter, C = drawing ratio factor (typically 0.6–0.7 for first draw).

## Safety Factor

Always apply a safety factor of **1.25–1.5** to account for:
- Material property variations (±10% on tensile strength)
- Tool wear increasing cutting forces over time
- Multiple operations in progressive dies
- Dynamic effects at high stroke rates

## Progressive Die Considerations

Sum all station forces. Stagger cutting stations by 1–2mm to reduce peak force by 20–30%.

## Practical Rule of Thumb

Required tonnage = (sum of all station forces) × 1.3 safety factor, then select the next standard press size up.

sarah_mfg_eng

One thing I'd add: always verify your calculated tonnage against actual measured tonnage on the first run. We track this on every new job and I've seen calculated vs actual differ by 15-25%, usually because material properties vary from the spec sheet. We now add 25% safety margin on all new jobs and adjust down after we have real data.

dave_toolmaker

The stripping force is the one everyone forgets. On a 12-station progressive die I built last year, the stripping force added up to 18% of the total cutting force. That pushed us from a comfortable 75% press capacity to 89%. We caught it in the calculation but I've seen shops that didn't and they were tripping overload faults on every third hit.

mike_chen_eng

Great points on the safety margin. One thing worth adding from the servo press side specifically: with programmable slide motion, you can use a slower approach speed near BDC to reduce snap-through shock. This effectively lowers your peak tonnage requirement by 10-15% compared to a conventional flywheel press running the same die.

We did a comparison study on a 50-station progressive die — same material, same strip layout. The servo press with optimized motion profile peaked at 142 tons vs 168 tons on the mechanical press. The difference was entirely from controlling the punch entry speed.

So when you are calculating tonnage for a servo press specifically, you can be a bit more aggressive with your safety margin if you plan to tune the motion profile. I still recommend 20% minimum though — material variation alone can eat up 15%.