Functional Parts and Tools
From Additive Fabrication

Rapid Manufacturing; A Brief Introduction

Additive fabrication is making its greatest headway in manufacturing applications that take advantage of its unique benefits. It has become an accepted solution for fabricating geometrically-complex, low-volume or customized parts. RP is also recognized as a means to produce parts and tools in forms and combinations not otherwise possible, such as in the use of gradient or multiple materials. While many applications are still in the development stage their potential range is vast, extending from the microscopic scale of nano-devices and integrated circuits to the construction of entire buildings, boat hulls and the like. In some cases additive fabrication's nominal liabilities are being turned into advantages. For example, the capability of some RP technologies to create porous parts is being found useful in fabricating complex filters, gas storage devices and similar products.

Descriptions of many of the RP technologies available for rapid manufacturing are provided in the sections under Commercially-available Processes. Also see the accompanying technology comparison tables.

See the rapid manufacturing section for an extensive exploration of the enormous potential of this application of additive fabrication.

Direct fabrication of plastic parts
Plastic parts are most often directly fabricated for end use using selective laser sintering (SLS), fused deposition modeling (FDM) or stereolithography. Other technologies are also used, but these are the main ones that are of commercial importance at present. The choice of a technology is most greatly influenced by the end-use material requirements.

The development of photopolymers for use in stereolithography and similar light-based technologies has led to materials that exhibit a wide range of properties. Materials are available that mimic the mechanical properties of polypropylene and other plastics, exhibit flexibility for snap-fits and have optical properties such as high transparency. Efforts are ongoing to develop specialized photopolymers to widen their applications. Materials with properties such as low shrinkage, rubber-like flexibility and thermal conductivity, or to address specialized applications such as the construction of scaffolds for tissue engineering are either in development or have already been introduced.

While today's materials can solve many problems and the future looks very promising, photopolymers are analogs of engineering plastics. They may not possess all of the properties required for a particular application, and in some cases their properties may not be stable over time.

Both selective laser sintering and fused deposition modeling can produce parts in final engineering polymers. They may offer solutions when photopolymer-based technologies cannot. SLS can be used to fabricate parts in several types of engineering plastics, including glass-filled nylon. FDM can fabricate parts in ABS, polyphenylsulfone, polycarbonate, polyester and a few other materials. These technologies may offer parts with additional strength or other properties not currently available from photopolymers. One thing to note is that the properties will not be quite the same as a part fabricated in an injection molding process of the same material, however. How the additive fabrication machinery builds the part influences those properties to a considerable extent.

Direct fabrication of metal parts
Metal parts are most often directly fabricated with selective laser sintering or laser powder forming processes. Here again, other technologies can be and are used, but these are the most commercially important ones at the moment. SLS can be used to fabricate steel, stainless steel and bronze parts. Porosity is eliminated by secondary metal infiltration. Parts usually need final machining and their properties will not be quite the same as parts formed entirely of the intrinsic material. Laser powder forming processes can produce parts in steels, titanium and other metals at full density. However, this desirable characteristic may have to be traded-off against somewhat higher finish machining requirements compared to SLS. Direct fabrication of metal parts is finding its greatest application in high value-added applications such as aerospace and medicine.