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Active Force Control (AFC) technology combines the productivity of a mechanical press with the precise force application of a hydraulic press
In the forging industry some parts require a cold sizing process to achieve the necessary tolerances. Traditionally this procedure has been performed by hydraulic presses because this process requires an exact force control to ensure an accurate force applied to the part. The downside of this type of presses is a lower production rate, higher energy consumption and the use of oil.
However, some manufacturers are using mechanical presses for cold sizing because they need a higher productivity that the one that a hydraulic press is able to deliver.
In the face of this challenge, Fagor Arrasate developed a new solution that combines the force control of a hydraulic press with the productivity of a mechanical press. This new system is a mechanical calibrating press with Active Force Control (AFC).
The stamping system features the speed of a mechanical press while at the same time is capable to work with an accurate and active force control until the maximum force of the press in the last 5mm (0.19in) of the stroke.
The force control in a mechanical press can be done through a cushion or some nitrodines, but our new development is a step further with the capacity to absorb some displacement until the maximum force of the press (900 tons) and up to 30 strokes per minute. This is achieved with a hydropneumatic mechanism with a very high energy absorption and heat dissipation capabilities. In order to control de position and speed of the ram near de Bottom Dead Center the system is a servo press, but the servos are not a requirement for the AFC to work.
The AFC can limit the maximum force supported by the press and can make sure that the force applied is not higher that the input given to the press. This value is introduced in the press through the recipe that comes with the die or directly from the main control panel.
Maximum force is not predictable. It changes depending on process parameters (hardness of the part, tolerances, etc.).
Maximum force is limited depending on recipe data. It is stable even changing process parameters (hardness of the part, tolerances, etc.).
The AFC is a hydropneumatic system that can absorb some displacement at very high speeds while controlling the force accurately. We integrated our standard ram adjustment and force overloading system. The first one will adjust the shut height and the second one will protect the press against potential incorrect use.
Example of real part 1 for 800-ton press
In this real case of a press with 2 working stations, 300 tons force is applied in the first station and 50 in the second one. Since these parts were already calibrated through a hydraulic press it was possible to know how much force was being applied at what height.
This way the measurements showed that at 140 mm (5.5 in) height 50 tons were required and later at 90 mm (3.5 in) height another 300 tons were required. This calculation allows to design the main drive of the press accordingly to the force required for the process