Rapid Prototyping & Additive Manufacturing
The rapid prototyping is a set of technologies that, regardless of the complexity of construction and the shape of the object, reproduce it with subtractive or additive techniques, usually in metal or plastic, starting from its mathematical definition using a 3D CAD and exploiting rapid, flexible and highly automated specific processes.
The strengths of these techniques are:
- the possibility to fabricate in a very short time (from few hours to a few days) prototypes in a wide range of materials, regardless of shape and geometric complexity;
- the reduced cost of prototype development, if compared to other technologies, i.e. stamping (embossing, molding, ...);
- the simplicity and speed in amending and correcting 3D design and the consequent new prototype.
The designers have always exploited a bi-dimensional plane to communicate and evaluate their ideas, before you put them into practice. However, the designer is never absolutely confident that what he sees on the screen is a faithful representation of the concept that it intends to accomplish. Rapid prototyping is the most successful attempt to break through this barrier: to transform the images into a solid object, to touch and test in its geometric characteristics and, sometimes, structural and/or functional performances.
Research and development have favored the evolution of Rapid Prototyping systems in terms of performance (smaller processing times, lower dimensional tolerances, better surface finish, improved endurance with respect to variable environment conditions and mechanical, thermal and chemical stress). To date Rapid Prototyping techniques and equipments are simple to use, the quality of the prototypes, in terms of dimensional accuracy, surface roughness and mechanical performance, is grown and in any case can be estimated and evaluated, a wide range of materials is available, moreover constantly changing and updating. Ultimately these technologies are considered full-fledged means for rapid development of products and equipment in a multitude of industries and technical or scientific sectors. These innovative technologies are the glue between the various stages of product development such as design, 3D CAD, the definition of the equipment and the pre-series manufacture.
The Laboratory, also thanks to the strategic partnership and shared facilities with CSHR-IIT, has access to a significant set of Rapid Prototyping technologies:
- Ink-Jet 3D Printing: the 3D prototype is built by an additive technique (additive manufacturing), layer by layer, overlapping layers of 2 commercial polymers photo-crosslinked by UV irradiation (a structural polymer and a sacrificial one used for the implementation of undercuts, easily removable by water jet) which are ejected through a special system of heads as a sort of ink-jet printer-like. Printing resolution down to 28 microns is achievable.
- Micro Stereo LIthography: the 3D prototype is built by an additive technique (additive manufacturing), layer by layer, through a building platform moving into or up from (both the versions are available at the Lab) a tank containing the UV curable resin which is cross-linked (layer by layer) by a 405 nm laser guided by custom-built galvanometers. The platform moves upward (or downward according to the the specific system implementation) until the piece is complete with auto-generated and easily removable supports.Printing resolution down to 50 microns is achievable.
- Direct Plastic Laser Sintering: Based on the DLS (Direct Laser Sintering) technology. The 3D printing tecnique creates 3D objects layer by layer through laser sintering of thermoplastic powder. No support material is necessary and therefore there is no removal process. This procedure enables you to create small objects with a great definition and with a great mechanical resistance. Minimum Layer Thickness:40 µm.
- Fused Deposition Modeling: The plastic filament is channeled inside an extruder and transferred to a heated nozzle which brings the material to the melting temperature and releases it to the semi-fluid state on the work surface to build a 3D object. Resolution: 500 µm (X and Y axis). Layer Thickness: 150 µm.
- Direct Metal Laser Sintering: the 3D prototype is built by an additive technique (additive manufacturing), layer by layer, superimposing successive layers of metal powders sintered in-situ by irradiation with a focused laser beam. The pattern which drives the path of irradiation/sintering operated by the laser beam determines the possibility of introducing also recesses and undercuts (regions with non-sintered powder). It is also possible to work with different metallic materials (steel, light alloys and super-alloys, ...) with a variable and controllable resolution (thickness of the single layer) between 20 and 100 microns.
- Micro Electro Discharge Machining: micro-scale electro-induced erosion technique (subtractive technique) for processing of complex 3D shapes, even characterized by a high aspect ratio, in conductive materials (metals or heavily doped semiconductors) by localized removal of the material through the generation of high frequency sparks between a tool and the workpiece. The tool and the workpiece are immersed in a dielectric fluid (typically an oil) and maintained at a mutual distance of a few microns. Typical performances are: resolution processing order of a few µm and very low surface roughness (from 0.1 Ra to 0.05 Ra).
- CNC Milling: prototyping technique for polymeric materials and/or metals by serial removing through a cutting rotary tool (subtractive technique). Positioning accuracy of 10 µm. Minimum diameter of the installed tool equal to 500 µm.
Most of our current applications are in the field of electronic and microsensors customized packaging and for microfluidic masters fabrication, nevertheless many other technical fields may take advantage from rapid prototyping. As an example, a short description of our last “smart” weird applications is reported in the following.
A dummy eyeball prototype (DEP) was designed and fabricated for the test of new ophthalmic tamponades. The term “temporary tamponades" indicates a group of substances that are injected into the vitreous chamber in order to replace the corpus vitreum and to promote the adhesion of the retina. They are often described by the term, fully equivalent, of "vitreous substitutes". The vitreous substitutes may be temporary (buffering gases like SF6) or permanent (silicone oil). The spheroidal hollow structure was designed through a 3D CAD software and was sized in order to respect the average dimensions of a human ocular bulb (i.e. the inner diameter at the equator of 19 mm, the central distance between north and south pole of the sphere of 19,8 mm and a shell thickness of 1,6 mm). The prototype was fabricated layer by layer by 3D ink-jet printing. The DEP was then integrated with 3 absolute pressure sensors, mounted on strategic spots on the outer surface of the DEP and connected to a costumized electronic read out circuit. Pressure data were collected by an Analog to Digital Converter (ADC) and displayed with a LabVIEW Graphic User Interface (GUI).
The second application was in the field of forensic and archeological reconstruction of human skulls and faces. Through the same 3D inkjet printing technique described above, we contributed to the reconstruction of the skull of Poliziano (1454-1494) an Italian poet of the Florentine Renaissance. The skull, reproduced for identification purpose, is currently under processing with traditional face reconstruction forensic techniques.
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