Elastoplastic drawing is, in some specific applications, the only drawing solution available. When the corresponding solid KNOW HOW has been experienced, some particularly interesting realization solution can spring.
Elastoforming technology allows to obtain drawed pieces by the pressure on the die on which the sheet has been placed, against an elastic matrix. The matrix can be realized in various materials, first of all gum and polymers, these last ones having much more elevated endurance and elasticity percentage. The specific pressures vary on an average from about 100 kg/cm2 on light alloy parts up to 1500÷1600 kg/cm2 on parts of steel having thickness up to 8÷10 mm.
The first great advantage of the elastoplastic pressing is to avoid the sheet undergoing typical stresses of the traditional drawing, due to stretching concentration points (in the corners, in the bending radii) and to ensure that the thickness of the starting sheets is constant, which is a fundamental requirement in the aeronautic field of activity.
The second advantage is the low cost, since theoretically, to be able to use this technology it would be enough to start from a first drawed piece, to make a resin cast therof and to use it as a die to produce other pieces.
As a matter of fact the die can be realized with diversified materials: aluminum (i.e. the quality top), resin, pressed wood, workings on numerically controlled machines, absolutely analogous to what happens in the construction of prototypes in the cars industry: the only difference is that these dies can be used for the production of limited series pieces.
Careful selection of the materials
For our realizations different quality steels are employed depending from the specific function of the structures and of the components, for instance steels alloyed and treated thermically for the containment structure, the cylinders block, the container of the elastic plug. The pistons too are made of steel, hardened, rectified, chromium plated, rectified and lapped; the bushes are made of bronze centrifuged properly worked and adjusted. The sealing systems are realized with elastic metal bands very similar to the motors’ endothermic bands which work inside their own cylinder in an oil bath thus ensuring pressures effectiveness for some tens of years. The elastic plug, generally is made of polyurethan (hardness 72 Schorr scale A) which allows the best compromise between elasticity and the consistency of the material subject to specific grave pressures, so that the material does not crumble when specific pressure is more than 500-600 kg/cm2 avoiding also ,in this way, dirts and defects in the drawed pieces. The plug is thick four times the depth of the drawing, is mounted under pressure from bottom upwards; in the upper part of the machine four mechanic ejectors have been located to ease its replacement, when it is necessary. Each machine is equipped with safety devices, with redundant protection, in compliance with current EC regulations. The required maintenance is minimum: it is enough to perform the filters substitution for the oil filtration at 10 micron, when the corresponding signalization appears (operation which is performed when the machine is working) and to substitute 4 small syntherized cartridges once per year as a protection for the pressure control valves.