What is Solid Freeform Fabrication?
Solid Freeform Fabrication (SFF) is a designation for a group of processes that produce three dimensional shapes from additive formation steps. SFF, also known as Rapid Prototyping (RP), does not implement any part-specific tooling. The three dimensional part is produced from a 3D representation devised in Computer Aided Modelling (CAD). This computer representation is a layer-by-layer slicing of the shape into consecutive two dimensional layers, which can then be fed to the control equipment to fabricate the part. SFF entails many different approaches to the method of fabrication. Stereolithography (SL), selective laser sintering (SLS), laminated object manufacturing (LOM), and fused deposition modelling (FDM) are a few examples that today have commercial machines applying these techniques. The largest impact SFF has had on manufacturing is enhancement of the prototype production process, cutting by orders of magnitude the time required to design, make, and iterate to final design a prototype. Much of the work to date has been performed with polymers; however, a large focus of research today is directed at fabricating ceramic, composite, and metal parts from SFF techniques. Another experimental push is in the tool and die arena, where researchers are attempting to cut out the mold step and form the desired tools and dies directly.
SFF Program at UCONN
The University of Connecticut Solid Freeform Fabrication program began in 1995 with the arrival of Prof. Harris Marcus as the director of the Institute of Materials Science. Prof. Marcus arrived at UCONN after running an SFF program at the University of Texas at Austin since 1990. Prof. Leon Shaw has joined the growing SFF program, providing his expertise in material processing and composite engineering. Prof. Tom Peters will handle networking aspects of the SFF program. Prof. John Dong is addressing computer-based solid modelling aspects of SFF. A variety of SFF formation methods will be pursued at UCONN. Selective Area Laser Deposition (SALD) is a gas phase method for depositing solid material from the interaction of a directed laser beam and various gas precursors inside a vacuum chamber. Selective Area Laser Deposition Vapor Infiltration (SALDVI) is a related method that utilizes the solid deposition product from the gas phase reaction to infiltrate the porous spaces in a powder bed. Composite structures such as silicon nitride (Si3N4) deposited in silicon carbide (SiC) powder have been produced at UT-Austin. Selective Laser Reaction Sintering (SLRS) is a hybrid process that mixes the efforts of selective laser sintering (SLS) and the gas phase SFF. A powder bed is selectively melted under a laser beam, with the melt then reacting with the controlled gas environment to form the desired product upon cooling/sintering.
The U Conn SFF program has several different focuses of research. Investigations into SALD/SALDVI formation of silicon carbide and silicon nitride, begun at the University of Texas at Austin, will continue in terms of optimizing deposition temperature, gas pressures/ratios, scan parameters, and other process variables. Focus will also possibly be directed at high purity, i.e. semiconductor grade, ceramic material depositions, with attempts at doping these materials pursued as well.
Other research efforts will be to deposit boron nitride (BN) from various gas phase precursors. Boron nitride exhibits two phases, cubic and hexagonal, and is very analogous to the carbon allotrope system. Both forms are electrical insulators and have a melting temperature of approximately 2730 degrees C. Hexagonal BN, due to its high thermal conductivity, makes an attractive alternative for heat sink material in the semiconductor chip industry. Cubic BN is an extremely hard material, on the order of diamond, and has many applications in cutting and abrasion.
Finally, attempts will be made to deposit refractory metals from orgometallic gas phase precursors. High temperature melting metals such as titanium and vanadium, as well as possibly some of their oxides, will be focused on.
SFF Related Sites
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