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Thermal Phase Change Inkjets This technology has also in the past been called ballistic particle manufacturing (BPM). Solidscape, now owned by Stratasys, uses the technology shown in Fig. 6. It uses a single jet each for build and support materials. All phase change inkjet technologies rely on squirting a build material in a liquid or melted state which cools or otherwise hardens to form a solid on impact. 3D Systems also produces an inkjet machine, called the ThermoJet ModelerTM which utilizes several hundred nozzles. 3D's name for their inkjet technology is MultiJet ModelingTM.  Solidscape machines use plastic object and wax and support materials which are held in a melted liquid state at elevated temperature in reservoirs (A). The liquids are fed to individual jetting heads (B) through thermally insulated tubing. The jetting heads squirt tiny droplets of the materials as they are moved side to side in the required geometry to form the layer of the object. The heads are controlled and only place droplets where they are required to. The materials harden by rapidly dropping in temperature as they are deposited. After an entire layer of the object is formed by jetting, a milling head (C) is passed over the layer to make it a uniform thickness. Particles are vacuumed away as the milling head cuts and are captured in a filter (D). The operation of the nozzles is checked after a layer has been fabricated by depositing a line of each material on a narrow strip of paper and reading the result optically (E). If all is well, the elevator table (F) is moved down a layer thickness and the next layer is begun. If a clog is detected, a jetting head cleaning cycle is carried out. If the clog is cleared, the problem layers are milled off and then repeated. After the object is completed, the wax support material is either melted or dissolved away. The Solidscape system is capable of producing fine finishes, but to do so results in slow operation. Thus, there is a tradeoff between fabrication time and the amount of hand finishing required. The 3D Systems ThermoJet is much faster since it simultaneously deposits materials from hundreds of jets, but it's also somewhat less accurate. This machine uses fine, hair-like structures made of the modeling material itself to support overhangs and undercuts. To remove the supports, these structures are simply brushed away manually after the part is fabricated.
Photopolymer Phase Change Inkjets Objet Ltd., an Israeli company, introduced its first machine based on PolyJetTM technology in early 2000. The process is based on photopolymers, but uses a wide area inkjet head to layerwise deposit both build and support materials. It subsequently completely cures each layer after it is deposited with a UV flood lamp mounted on the printhead. The support material, which is also a photopolymer, is removed by washing it away with pressurized water in a secondary operation.
With specifications that are similar to laser-based stereolithography systems costing several times as much, and operational conveniences much like lower-cost 3D printers, this technology has been quite successful. Objet's Eden series machines are considered office-friendly and provide uniquely thin layers of approximately 16 microns (0.0006 in). This is said to greatly reduce post-processing and finishing operations, frequently making them unnecessary. In July, 2002, 3D Systems announced a similar photopolymer-based system called the InVisionTM. It uses the technology originally developed for the ThermoJet ModelerTM and deliveries began in late 2003. The company has priced the system at $40K to better compete with 3D printers from Stratasys and Z Corp. One major difference from the Objet technology is that the support material is a wax that is melted away from the part, rather than washed away with water. A high-resolution version of the system is also available. Users praise the quality of the parts and the convenience and size of the machine, although they feel the output isn't quite on a par with stereolithography in terms of feature size and material properties. However, such jetted photopolymer technologies are still relatively new and should achieve a similar level of maturity as stereolithography within a few years. In late 2007 Objet announced the Connex500™ system, the first machine in the industry able to use two fabrication materials at the same time. This enables it to produce parts with properties that vary throughout their volume. Interest in the product was high and it quickly found a home in service bureaus.
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