In addition to quality and cost, time to market is becoming an increasingly important factor in a product's success. A major contributor to product development cycles is the time needed to produce prototypes. Further, in markets where customers are demanding individually tailored components, the cost and time to produce tools or moulds can be considerable.
Rapid Prototyping (RP), also known as Solid Freeform Fabrication (SFF) processes help to overcome these problems In general the processes build complex shapes through additive processes, producing components without the use of tools.
The main commercial filament extrusion technique is the fused deposition modelling (FDM) system. This system uses a thermoplastic build material such as wax or a polymer to act as a carrier and binder for the ceramic material. The material is extruded from a small heated nozzle and the component is built layer by layer. The green shape can then be densified by binder removal and sintering or infiltration to produce a fully dense structural ceramic component.
FDM can be used to produce both structural and piezoelectric components. Si3N4, SiO2, Al2O3 and lead zirconate titanate (PZT) have each be made with the FDM technique. Typically filaments contain between 50 and 65 vol % particle mixed with a thermoplastic binder of wax, polymer, surfactant and plasticiser.
Examples of the use of FDM include:
• Si3N4 components with good mechanical properties and microstructure were produced with a filament containing 55 vol % of the ceramic. After FDM, green parts were densified by hot pressing and gave four point bend strengths similar to that of hot isostatic pressed parts.
• A fine scaled piezoelectric composite structure can be made consisting of PZT and polymer. The piezoelectric properties of the composite are similar or superior to conventionally processed PZT composites.
• Composites with controlled composition distribution and a variety of microstructures can be made by combining filaments of different compositions.
Advantages of FDM
The main advantage of the system is the relative simplicity. It does not need laser systems, uses relatively inexpensive binders, and is easy to change materials. The main difficulties are in controlling temperature within the growing part, the need to provide support structures for the growing model and the accuracy which is limited to the nozzle diameter.