The Press That Bent the Part (No Force Monitor)
We pressed a bearing into a housing (a press fit, article 91). The press (a pneumatic press, article 91) pushed. But the part was bent (the press force was too high). We had no force monitoring (the press just pushed until it stopped). The part bent (the press didn’t know the force). We added a force sensor (a load cell, on the press). The press monitored the force (it stopped at the set force, or if the force spiked). The part wasn’t bent. The mistake was not monitoring the force (the press over-pressed).
Press fit force monitoring controls the force. This article covers the method.
The Force Monitoring
A press fit (article 91) pushes a part (a bearing) into a housing. The press force builds (as the bearing seats). The press must stop at the right force (or the right distance). Without monitoring, the press over-presses (bends the part). A force sensor (load cell) measures the force.
Step 1: The Load Cell
A load cell (a force sensor) sits on the press (between the ram and the part). It measures the press force (in Newtons, or kN). The press controller reads the force. It stops (at the set force, or the set distance, whichever comes first).
The force monitoring rule: Monitor the press force (a load cell). The press that bent the part had no monitor. Add a load cell. Set the force limit (e.g., 5 kN). If the force exceeds (a bad part, a jam), the press stops (and alarms).
Step 2: The Force-Distance Curve
A good press has a force-distance curve (the force builds as the bearing seats). The curve is consistent (for a good part). A bad part (wrong bearing, a burr) has a different curve (a spike, or a plateau). The controller compares the curve (to a template). If it deviates, the press rejects the part (it’s bad).
Step 3: The Distance (Position)
The press also controls the distance (how far the bearing seats). The bearing seats to a depth (e.g., 10 mm). The press stops at 10 mm (the position). For a press fit, the force and the distance both matter (the right force, at the right depth).
Step 4: The Alarm (Bad Part)
If the force (or distance) is out of spec, the press alarms (it rejects the part). The operator (or the machine) removes the bad part. The good parts (in spec) pass. The bad parts are caught (not shipped).
| Parameter | Typical |
|---|---|
| Force (good part) | 3–5 kN |
| Force limit (alarm) | 6 kN (over) |
| Distance (seat) | 10 mm |
| Curve | Consistent (template) |
A Force Monitoring Checklist
- Is there a load cell? (Measures force?)
- Is the force limit set? (kN?)
- Is the distance set? (mm?)
- Is the force-distance curve monitored? (Template?)
- Does it alarm on a bad part? (Reject?)
- Does the press stop at the right force? (Test?)
- Is the part bent? (No?)
- Is the data logged? (Traceability? Article 197?)
- Is the load cell calibrated? (Zero?)
- Is the press safe? (Article 98?)
The Bottom Line
Press fit force monitoring controls the force. The press that bent the part had no monitor. Add a load cell. Set the force limit. Monitor the curve. The press that didn’t bend parts wasn’t the strongest press — it had a load cell.
