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All deep-drawing dies need a holding force to be able to draw without creating creases and wrinkles. This retention force can be achieved by the use of double-acting presses (although such products are now rarely used and widely discontinued) or by pressure cylinder systems incorporated into the die or by cushions in the bed. Initially the cushions in the bed were pneumatic, but the necessary technological evolution helped us to develop the hydraulic bed cushion back in 1990, and the servo-mechanical cushion in 2017.
Although FAGOR ARRASATE can still manufacture double-acting presses and pneumatic cushions for drawing, these are rarely used and, thus, are not listed in our product range. Anyway, should you require information about this kind of products do not hesitate to get in touch.
The main advantages of the hydraulic cushion over air cushions or pressure cylinders are as follows:
In the following picture you can see a whole working cycle and the nine possible phases of the cushion.
All these variables are entered via the HMI, obtaining different possible configurations of the cushion operation.
One of the aspects of the hydraulic cushion that can be improved is the reduction of energy consumption.
Taking the standard hydraulic cushion as a reference, we have designed several solutions to reduce energy consumption. One of them, based on variable flow motor-pumps, reduces consumption via its self-adjusting control which allows the required flow to be reduced, adapting to the actual needs of each cycle. The second of these, the High-Low Pressure concept, is a solution designed for the current drawing and ascent process, in which the installation is sized according to the needs. The last solution is based on the previous idea of High-Low pressure and adds a servo-pump system to regenerate most of the energy consumed during the drawing process, returning the energy consumed normally during oil flow to the buffers in a manner controllable by the network.
As mentioned in the preceding section about the hydraulic cushion, one of the main areas of improvement is in the reduction of energy consumption and energy regeneration. The hydraulic cushion, a technology in which FAGOR ARRASATE is one of the market leaders, is a product with great potential of improvement in terms of energy efficiency.
Considering that servo presses have an increasing presence in the international market, we have developed a new servo-mechanical cushion concept: the e-cushion. The e-cushion retains all the benefits of the hydraulic cushion (pre-acceleration, force control, pick-ups, etc.) and adds substantial improvements in terms of energy consumption and the possibility of applying retention even during the ascent of the slide (a very desirable option for parts that need oscillating cycles and/or forces during ascent for control of the “spring back”, etc.).
This new concept replaces hydraulics with electric servo motors and uses a rack and pinion mechanism to transform the electric energy of the servo motor into the mechanical force required for the die drawing process.
This solution allows us to create an ideal architecture in the presses that feature servo technology in the main drive of the press and has a cushion in the bed. Testing has been carried out on the trading platforms. Although the initial investment is higher, the calculated payback time can be as short as 32 months (considering the energy improvement and the reduction of maintenance). It is worth noting that the energy efficiency of the press improves by up to 50% (and increases the more the cushion is used) for some parts compared to its hydraulic cushion predecessor.
The FAGOR ARRASATE e-cushion is already on the market and the results are satisfactory.