Forming Energy and Adjustment of Stroke Length
In Friction Clutch Type
The flywheel revolution (slide speed) starts to accelerate from the moment of clutch activation for descending. Assuming the slope of acceleration line is constant (actually, the slope slightly varies because of peripheral velocity difference in the friction disc.), the slide speed becomes maximum and generates maximum load when the stroke length is set to the maximum and keeping the clutch on status until right before stamping. This is the maximum forming energy the screw press can furnish with.
The screw press can be adjusted for its appropriate forming energy through speed adjustment. Generally, the machine detects the slide speed with speed sensor (encoder) and when the slide speed reaches at the preset speed value determined with preset dial, the machine transmits the clutch off signal.
The maximum load can be gained as the speed preset dial is set to 100%, maintaining the clutch on status until the moment right before stamping, and also the stroke length is set to the maximum.
When the dial is set to 50%, the clutch is turned off as soon as the speed accelerates by 50% on the way of the slide stroke, then it runs with equal inertia speed to the end of the stroke. In case of lowering the upper limit stroke adjusting switch and set the start position below, there might become no difference in the load between the preset value of 100% and 50% because the stroke length is shortened and acceleration distance is short.
Thus, the forming load is influenced with both the speed preset dial for the slide and stroke length adjustment.
Previously, we had used electric timer to control the clutch-on duration, however, we had encountered the failure that caused from uneven friction power come from the change of friction transmission rate due to clutch friction heat. It gave insufficient power when it was hot and slippery while too much power gained when it was cool during the same clutch activation time. Energy control should be done with detecting actual sliding speed.
In Servomotor Direct Drive Type
The maximum forming energy will not be realized in this case, neither,unless the slide stroke is the maximum and speed setting is 100%.
However, if it is not the maximum energy, the slide speed is reduced which makes the relationship with stroke length being a little complex.
In case of speed setting being 100%, the speed at the pressing gets slow down due to the fact that the more slide stroke length is shorter, the more the acceleration distance is shorter, and the applied pressure gets smaller accordingly.
When the slide stroke is set constant near at maximum, the slide reduces speed after acceleration by the speed setting being lower, and the pressing is performed with the speed corresponding to the preset speed (forming energy). In case of setting the slide stroke being short, the speed of pressing remains the same even though the setting is 100% nor another until the slide speed will reach to setting speed before forging.
Namely, pressing is done while accelerating. As the speed setting being lower, pressing is performed with acceleration and speed reducing after the time point of entrance distance not required.
During the slide is ascending, speed setting is not required and the slide goes up at the optimum maximum speed, then the speed is reduced and the slide stops at the upper limit position. The stop position is never fluctuated.