The method allows to obtain one or more prototypes without the requirement of creating a mold.

The need for prototypes is more and more widespread in many industrial fields to facilitate the development of new products. Prototypes are made to verify technical characteristics, design and functional correctness, feasibility of production and assembly and can be used subsequently to create mold to be utilized in production lines.

Prototypes are particularly important for production of composite material parts and products.

In recent years many fast prototyping techniques have been developed, now used in different industrial fields. By fast prototyping it is meant all the advanced technologies that can turn an idea of a product into the prototype, in a very short time compared to traditional manual product development.

Fast prototyping technologies are usually based on computer based design systems, such as CAD, and numerically controlled (CNC) machines for shaping.

Among fast prototyping technologies it is worth mentioning stereolithography, CNC milling, laser sintering, thermoforming.

In general all the above mentioned techniques are limited to small sized objects (usually fractions of a meter) with relatively high cost, only feasible for productions of large quantities.

Prototypes obtained using traditional fast prototyping techniques have usually mechanical properties of lower quality compared to final production parts and are usually employed only for design validation and dimensional and assembling compatibility testing.

These technologies accompanied by high costs per unit of volume are applicable only in specialty fields such as precision mechanics and large production lines in order to spread the elevated cost over very large number of pieces.

The above described technologies are unavailable to industrial fields where prototypes of large sizes and small number of pieces produces on yearly basis. This is due to the high cost of prototypes, made with traditional fsat prototyping, as well as to the unavailability of equipment large enough (for example the field of small production boats).

When large sized dummies are needed the manual shaping is still the most widespread technique used or for more advanced applications the construction is based on laser cut cross sections assembled with sheet wood. This implies a considerable amount of manual labour for finishing and to apply detaching compounds. In addition until the whole process of creation of the first piece (design, manually sculpted dummy, mold, part) any prototype verification is impossible.

The prototyping here described overcomes the above limitations and makes it possible to obtain in a few days a prototipe starting from the CAD phase without the requirement of manual labour and without the creation of a mold.

Moreover the prototype can be made of the material and with the same mechanical properties of the final piece and thus used for functional tests Prototyping systems consist of the creation of the negative of the required shape in any soft homogeneous material which can be machined, such as light metals, wood, MDF, plastic resins, plastic polymeric foams, PVC foams, etc.; the shape is molded from these materials by CNC machining from a 3D CAD drawing.

The shapes created on soft materials are not suited, however, for the production of a piece, but a number of additional phases are required to harden the surface, pre- finishing, finishing and application of detaching substance, in order to obtain a false mold able to support the deposition of the composite material components.

The invention described here a thin film is employed to avoid the intermediate phases. The film is characterized by a very high elongation ratio, that is it can be stretched without damage up to many times its original area.

Using a vacuum system the film is made adhere to the 3D shape created by machining very closely.

The part is then created directly on the film using the standard composite material techniques.

The process consists of the following phases: 1.3D CAD design of the part; 2. automatic generation of tool-paths by CAM systems; 3. machining using a CNC machine to create the negative shape with the desired material (usually inexpensive and low density materials, such as wood, plastic resins, etc); 4. application, using a vacuum pumping system, on the machined shape of a thin film with a high degree of elongation to obtain a smooth surface ; 5. creation of the composite material prototype, fiber-glass or other composite material, either in air or in vacuum, optionally with the same mechianical properties of the final desired part; The prototype obtained following the above procedure is very low cost calculated to be four to five times lower compared to the currently employed fast prototyping techniques.

The system can be used for"one-off'models as well as the basis to make a mold for production, this latter step using traditional methods.

In addition to the obvious advantages deriving from the automatic process involving the whole chain, which reduces the chance for errors and the overall tolerance, the method does not require specialized labour to sculpt dummies, expertise which is very costly and difficult to find nowadays.

Among the advantages of the method a few are worth mentioning such as the precision of all the parts of an assembly (for example boats are made up of several parts that have to be mechanically compatible). This is achieved thanks to the computer based process, from the CAD based design of all parts of the assembly and the CNC machining of each individual part.

Description of the Process The fast prototyping system consists of the creation of negative shape of the desired part made of a low cost soft and homogeneous material, such as wood, MDF, plastic resins, plastic or polymeric foams, PVC foams, etc. , that can be machined; this shape is then generated by CNC milling from a 3D CAD drawing.

The shape is inserted in a vacuum pumped container and covered with a thin film of high degree of elongation material, that is capable of withstanding stretch up to several times its original area.

Using a vacuum pumping system the film is made adhere to the machined shape in order to stretch it to follow closely the surface.

On the stretched film the composite material is formed using the traditional techniques for composite material parts, that is: * optional deposition of a gel-coat layer ; o deposition of the composite fiber and resin using manual painting or spraying; * (as an alternative) deposition of the composite material using vacuum forming with the use of an additional thin film to be applied over the fibers and then formed by injection of resins.

The thin film to be used for the fast prototyping process is chosen so that the surface of the material is smoothed, and it depends on the porous nature of the material as well as roughness deriving from CNC machining; it therefore acts as a surface pre-finish.

The thin film composition can be chosen to not stick to material used for making the prototype; in this case the film acts as a detaching compound.

Alternatively, when desired, the thin film can be chosen to permanently stick to the material used for making the prototype, in this case the film will be the outer skin of the prototype itself.

The prototype created with the method described here has the same mechanical properties of the production parts which can be obtained with traditional production methods for composite materials.

The prototype can in some cases, depending on the material chosen for the machining phase, display a varying roughness, which can be constrained within a maximum thickness by changing material for machining, film material and machining precision; the prototype can be made to have a roughness below the gel-coat layer thickness. The final finish of the prototype is then, when required, limited to fine sanding using traditional techniques.

The same method can be used without any variation to construct molds, creating the final part shape in negative.

The figure depicts the method to create the prototype.