Die cushion

The main advantages of the hydraulic cushion over air cushions or pressure cylinders are as follows:

• Different programmable forces can be exerted during drawing by controlling the retention of the material in an appropriate way.
• The option of controlled descent or pre-acceleration, in order to reduce the sudden shock that occurs when the slide hits the cushion and to avoid vibrations that are harmful to both the part and the installation.
• The option to lock the cushion (either in its PMI or during ascent) to improve the quality of the piece and aid picking-up the piece by the automation.
• Damping at the end of the upward stroke of the cushion to avoid hard stopping of the cushion and, thus, vibrations.

In the following picture you can see a whole working cycle and the nine possible phases of the cushion.

1. Keep the predefined position.
2. Pre-acceleration.
3. Drawing.
4. Standby.
5. Pick-up lock 1. This pickup could be a lockage in the PMI of the cushion.
6. Ascent at Speed 1.
7. Pick-up lock 2. For example, for the pick-up of the part by the automaticon.
8. Ascent at Speed 2.
9. Damping.

All these variables are entered via the HMI, obtaining different possible configurations of the cushion operation.

 Hydraulic cushion energy efficiency solutions

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.