Meaning
Physical variation in the lowest position of a press ram during continuous operation results in changes to the final thickness of stamped components. Heat buildup in the press frame and the tool causes bottom dead center drift as the mechanical components expand. This movement alters the shut height of the press, which can lead to over penetration or insufficient forming pressure in precision parts.
Expansion Characteristic
Thermal growth of the crankshaft and the connecting rods shifts the ram position relative to the bed. Since bottom dead center drift typically moves the ram closer to the bolster, the die closes more tightly than at the start of the run. Monitoring this shift requires sensors capable of measuring micron level changes in real time during high speed cycles.
Demonstration Trial
Stability of a production rate requires accounting for the time the press takes to reach thermal equilibrium. If bottom dead center drift is not compensated through an automatic adjustment system, the first thousand parts of a run may differ greatly from the ten thousandth part. Operators often set the press slightly higher at startup to allow for the predicted downward movement of the ram.
Correction Strategy
Modern servo presses utilize feedback loops to adjust the ram position dynamically as sensors detect the shift. While mechanical presses rely on periodic manual checks or cooling systems, the automated correction for bottom dead center drift maintains a tighter tolerance across the entire production lot. This capability ensures that high volume runs remain within specifications without frequent downtime for tooling adjustments.
By measuring the displacement at the peak of every stroke, the controller can compensate for even minor changes before they impact the final part geometry. This proactive approach allows for a demonstrated rate of production that exceeds the limits of older uncompensated equipment.
