As is known, the stereolithography technique allows a three-dimensional object to be produced by superimposing a plurality of layers obtained from a substance that was initially liquid.
Each layer of the three-dimensional object is obtained by exposing a corresponding layer of the above mentioned liquid substance to suitable electromagnetic stimulation that causes it to be selectively solidified through polymerization in the areas corresponding to the object to be obtained.
According to a known embodiment, the above mentioned technique is implemented by means of stereolithography machines generally comprising a tank suited to contain a light-sensitive liquid resin, associated with a supporting plate.
The machine also comprises an emitter suited to direct a light beam towards the tank in order to solidify a layer of light-sensitive resin in the way previously described.
The three-dimensional object that is being produced is supported by a modelling plate facing the tank and motor-driven in the orthogonal direction with respect to the surface of the tank.
After solidification of each layer of the object, the modelling plate is moved with respect to the tank, so as to allow the formation of a new layer of liquid resin and, therefore, the formation of a new layer of the object in contact with the previously solidified layer.
According to a known technique, each layer of the three-dimensional object is formed through solidification of the resin layer adjacent to the bottom of the tank.
This is obtained by emitting a light beam under the tank, which is transparent, and making a through opening in the supporting plate, said through opening leaving an area of the bottom of the tank exposed to the action of the light beam.
This technique poses the drawback that the resin that is solidified tends to adhere to the bottom of the tank, thus making it difficult to successively lift the object.
In order to overcome the above mentioned drawback, the bottom of the tank is covered with silicone or another analogous material, which facilitates the detachment of the solidified resin.
However, the covering layers of known type pose the drawback that they progressively tend to become opaque due to exposure to light.
Once the covering layer has become opaque, it is necessary to replace the tank, which therefore is a separate component that is associated with the supporting plate through a stopping unit, which makes it possible to lock the tank firmly on the supporting plate but also to remove it when it wears out.
In particular, the stopping unit must maintain the bottom of the tank perfectly resting on the supporting plate, so as to guarantee its correct positioning and allow solidified layers with uniform thickness to be obtained.
The requisite that has just been mentioned is necessary also to prevent the tank from being lifted together with the modelling plate when this is lifted at the end of the solidification of each layer, due to the so-called “suction effect” resulting from the viscosity of the resin that keeps the last solidified layer adherent to the bottom of the tank.
The stereolithography machines of known type described above however pose the drawback that they require frequent replacements of the tank, in some cases even after each single processing cycle.
Obviously, changing the tank frequently means causing an additional cost that affects the final cost of the three-dimensional object.
Furthermore, the tank's limited duration is reflected on the maximum number of layers of each three-dimensional object and thus on the maximum height that can be obtained for the object.
According to a different known construction form, described in the European Patent application EP 0 379 068, the tank is moved with respect to the plate by means of a motor, so as to prevent the light beam from concentrating on a limited area of the tank, so as to slow down the process that makes it become opaque.
The tank comprises a flange interposed between a pair of thrust bearings, which allow the horizontal movement of the tank while preventing its vertical movement.
This system poses the drawback that the control of the position of the tank with respect to the supporting plate depends on the motor, which however is not capable of maintaining the tank in a stable position in case, for example, of impacts or vibrations during the construction process of the object.
Furthermore, the removal of the tank from the supporting plate requires the disassembly of a part of the machine, which makes the replacement of the tank rather complicated.