A mixture of sinterable powders for rapid prototype, comprising a powdered polymer base and material of a substantially glassy type in the form of microflakes, optionally with the addition of a material of a substantially glassy type in the form of microspheres, powdered aluminum and/or powdered graphite.
The present invention relates to a mixture of sinterable powders for rapid prototyping RP,particularly for SLS (Selective Laser Sintering) processes.
As it is known, rapid prototyping or RP is the name given to a host of related technologies that are used to fabricate physical objects directly from CAD data sources. It regards in particular a rather recently developed technique that allows toobtain automatically the prototype of a mechanical component starting from its CAD drawing in a short time and with relatively low costs regardless of the geometry of the component.
The resulting prototype can be used in place of the actual component in performing tests for example of the photoelastic type, so as to determine the mechanical characteristics of said component.
It is also known that there are various rapid prototyping technologies, which in any case entail superimposing a plurality of layers of material that are mutually rigidly associated so as to obtain a model, optionally a scale model, of the actualcomponent.
These technologies differ in the manner in which the layers of material are applied during prototype construction; in particular, each technology is based on a different physical principle, which determines the nature and state of finalaggregation of the materials used.
The rapid prototyping process is organized into various steps: initially, the component being studied must be drawn with the aid of a three-dimensional solid or surface modeling system, so as to obtain a three-dimensional CAD model, which is thenconverted into a format that can be read by the prototyping machine, which is generally an STL (from "stereolithography") format.
This conversion consists in approximating the surface of the model with a plurality of juxtaposed triangles, which are mutually adjacent so as to cover all of said surface.
The model in the STL format is sectioned, by the software that manages the rapid prototyping machine, with a plurality of parallel planes that are spaced by an appropriate thickness.
Each plane represents one of the layers of material that the machine subsequently superimposes; the contiguous layers bond with each other already during prototype construction.
Finally, it is possible to subject the resulting prototype to cleaning and finishing operations or to other kinds of treatment.
One of the known rapid prototyping technologies is constituted for example by the so-called SLS (Selective Laser Sintering) method, which is based on the consolidation of powders by means of a sintering process obtained by using a laser.
The machine used to perform this method is substantially constituted by a vertically movable platform on which the powder is deposited; said powder is retained inside the machine at a temperature just below its melting point, so as to constitutea layer of uniform thickness, which the laser strikes only at the region that forms the corresponding cross-section of the model to be produced, sintering it.
The platform then moves downward by an extent that corresponds to the thickness of the deposited material, and a new layer of powder is superimposed on the preceding one and sintered as described above, so as to solidify and bond with theunderlying layer.
The process is repeated until the complete model is obtained.
The material currently used in rapid prototyping processes and in particular in the SLS method is generally constituted by a mixture of powders of the polyamide type, optionally with the addition of powders of various kinds that have areinforcing effect.
Models obtained by using this material, while having a more than satisfactory quality, have still limited moduli of elasticity and low breaking loads.
During recent studies aimed at developing new sinterable materials that allow to optimize the mechanical characteristics of models produced by rapid prototyping, it has been found that the introduction of powdered aluminum in the above citedmixture increases the breaking load of the resulting models.
However, known sinterable powder mixtures are susceptible of further improvements, aimed in particular at improving the mechanical strength characteristics of the resulting models.
Moreover, significant increases in elastic modulus and breaking load of the material have been observed.
The breaking load of the material obtained by sintering the mixture according to the present invention has been in fact found to be, for mixtures such as those given by way of example hereinafter, in the order of 51 MPa, while the breaking loadof the materials conventionally used in rapid prototyping is in the order of 47 MPa.
The following mixture examples are given only by way of illustration of possible ways to provide the mixture of the present invention and must not be understood as limiting its scope as defined by the appended claims.
Advantageously, it has been found by means of laboratory tests that models made with the mixture according to the invention have a greater mechanical strength than rapid prototype obtained with conventional materials, both at ambient temperature andat high temperatures.