admin The tonnage monitor is one of the most valuable diagnostic tools on a servo press. Understanding how to read the tonnage signature can help you detect die wear, material variation, and setup problems before they cause scrap or damage. ## What the Tonnage Monitor Measures The tonnage monitor measures the strain on the press frame or slide using strain gauges. It displays force as a function of slide position (or time), creating a "tonnage signature" for each stroke. ## Reading a Normal Tonnage Signature A typical blanking operation signature: - **Approach phase** (TDC to material contact): near-zero tonnage - **Elastic compression** (material contact to punch breakthrough): rapid tonnage rise - **Breakthrough**: sharp tonnage drop (the "snap-through") - **Return**: tonnage returns to zero A typical drawing operation signature: - **Blank holder contact**: initial tonnage rise - **Drawing phase**: gradual tonnage increase as material flows - **BDC**: peak tonnage - **Return**: gradual decrease ## Diagnosing Problems from the Signature **Signature shifted earlier in stroke:** - Die is closing too early ??check slide height setting - Material thicker than nominal **Signature shifted later in stroke:** - Die is not closing fully ??check slide height - Material thinner than nominal **Peak tonnage increasing over time:** - Die wear (punch becoming dull) ??check punch edge condition - Material hardness increasing ??check material certification **Double peak in signature:** - Two-stage forming operation ??normal for some dies - Die misalignment causing uneven loading ??check die alignment ## Setting Tonnage Limits Set upper limit at 110% of normal peak tonnage. Set lower limit at 80% of normal peak. Any stroke outside these limits should trigger an alarm and stop the press.
admin Related: see also the discussion on [servo press tonnage calculation guide](https://servopress.club/d/20-20-how-to-calculate-servo-press-tonnage-requirements) for complementary technical detail.