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

Slide position drifting 0.3mm over a shift - ideas?

jason_cnc

Our slide position is drifting about 0.3mm over an 8-hour shift. Starts fine in the morning, gradually walks off. Thermal? Mechanical? Ideas?

**Separate Thermal Expansion from Mechanical Drift
**
**Thermal expansion test:**
1. Measure part height every 30 minutes for the first 2 hours
2. Plot the measurements
3. If the drift follows a curve that flattens out (asymptotic), it is thermal expansion
4. If the drift is linear or accelerating, it is mechanical

Typical thermal expansion for a cast iron press frame: 0.01-0.02mm per degree C per meter of height. A 1.5m press frame warming from 20C to 35C expands about 0.2-0.3mm. This matches your symptom.

**If Thermal: Solutions
**
1. **Warm-up cycle**: run the press at 50% SPM for 30 minutes before production. The frame reaches thermal equilibrium and drift stops.

2. **Thermal compensation**: some press controllers automatically adjust BDC position based on a temperature sensor in the frame.

3. **Adjust after warm-up**: set the die height after the warm-up cycle, not cold.

**If Mechanical: Check These
**
1. **Gib clearance increasing**: worn gibs allow the slide to tilt slightly under off-center load. Measure gib clearance at start and end of shift.

2. **Connecting rod bearing wear**: worn bearings allow the slide to drop slightly under load. Check crankshaft end play.

3. **Die clamping**: if the die is not fully clamped, it can shift under repeated loading. Check clamp bolt torque.

**Quick Field Test**

Put a dial indicator on the slide and log BDC position for 20 consecutive strokes at start and end of shift. If the indicator reading changes, the mechanical BDC is drifting. If the indicator stays the same but parts change, the die or material is the variable.

mchen_servo

On the tonnage monitoring question — we run 108% high limit (we learned this the hard way) and 88% low limit on our HSS stamping lines. The 110% high limit is fine for mild steel but for 780MPa HSS the material variation is tighter so we run a tighter window. Caught two double-blank events last quarter that would have been die crashes without it.

toolndye_dave

0.3mm drift over a shift is almost certainly thermal expansion. The slide, frame, and die all grow as the press warms up. On our 160T press we measured 0.04mm of BDC shift per 10 degrees C of frame temperature change. The fix is to let the press warm up for 30 minutes before doing final shut height adjustment, and then re-check after 2 hours of production. Some shops use automatic thermal compensation in the controller.

carlos_mx

thermal drift? we see this on hot days. our shop isn't climate controlled and the frame grows about 0.1mm per 10°C.

raj_pm

Realized my earlier reply was about tonnage monitoring and not really on-topic for the drift question. Let me actually address this one properly.

0.3mm over a shift is textbook thermal drift. Here's how to confirm and fix it.

Step 1 — Characterize it. Tape a dial indicator to the frame reading against the slide at BDC. Log the reading every 15 minutes for a full shift. You'll get a curve that looks like a charging capacitor — fast change in the first 1-2 hours, then it flattens. If it's truly linear and never flattens, you've got a mechanical issue (ball screw wear, gib loosening), not thermal.

Step 2 — Find the source. Stick adhesive thermocouples on: the slide body, both columns (or gibs on a straight-side), the crown, and the bolster. Log temperature alongside your position data. On our presses, 80% of the BDC drift comes from column thermal growth, not the slide itself. The columns are long steel members that grow predictably — about 0.012mm per meter per degree C for cast iron, 0.011 for steel.

Step 3 — Fix options, cheapest to most expensive:
- Warm-up cycle: run 15-20 minutes at production speed before loading the die. Gets you to thermal equilibrium before you start making parts. Free.
- Manual compensation: measure your drift curve once, then pre-set your shut height 0.15mm tight at startup. By mid-shift you're at nominal. Also free but requires discipline.
- Automatic BDC compensation: most modern servo press controllers have this. You input a temperature sensor and a compensation coefficient (mm per degree C). The controller adjusts BDC automatically. Komatsu calls it "thermal displacement compensation," Aida calls it "TDC auto-correct." Usually just needs to be enabled and calibrated — it's already in the software.
- Active cooling: glycol cooling channels in the frame. Overkill for most shops but if you're running 24/7 with tight tolerances, it eliminates the problem entirely.

carlos_mx — 0.1mm per 10C on the frame is in the right ballpark. For a 2-meter column height, the math gives 0.024mm per degree C, so 10C swing = 0.24mm. Your 0.1mm suggests either shorter columns or partial compensation happening somewhere.