Inkjets

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Thermal Phase Change Inkjets
Solidscape, Inc.'s inkjet method is illustrated, but others are also available. This machine uses a single jet each for a plastic build material and a wax-like support material, which are held in a melted liquid state in reservoirs. The liquids are fed to individual jetting heads which squirt tiny droplets of the materials as they are moved in X-Y fashion in the required pattern to form a layer of the object. 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 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. The process is repeated to form the entire object. After the object is completed, the wax support material is either melted or dissolved away.

The most outstanding characteristic of the Solidscape system is the ability to produce extremely fine resolution and surface finishes, essentially equivalent to CNC machines. However, the technique is very slow for large objects. While the size of the machine and materials are office-friendly, the use of a milling head creates noise which may be objectionable in an office environment. Materials selection also is very limited.

Other manufacturers use considerably different inkjet techniques, but all 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 produces an inkjet machine called the ThermoJet Modeler^TM which utilizes several hundred nozzles in a wide head configuration. It uses a hair-like matrix of build material to provide support for overhangs which can be easily brushed off once the object is complete. This machine is much faster than the Solidscape approach, but doesn't offer as good a surface finish or resolution.

All thermal phase change inkjets have material limitations and make fragile parts. The applications range from concept models to precise casting patterns for industry and the arts, particularly jewelry.

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Photopolymer Phase Change Inkjets
Objet Geometries Ltd., an Israeli company, introduced its first machine based on PolyJet^TM technology in early 2000. It's a potentially promising replacement for stereolithography. 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 similar to laser-based stereolithography systems costing several times as much, and operating conveniences similar to lower-cost 3D printers, this an important technology to watch.

In July, 2002, 3D Systems announced a similar photopolymer-based system called the InVision^TM. It uses the technology originally developed for the ThermoJet Modeler^TM and deliveries began in late 2003. The company has priced the system at about $40K to better compete with 3D printers from Stratasys and Z Corp.

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 has been keen and it has been quick to find a home in some service bureaus. [See the article A Service Bureau's View of the Connex500™ by Mike Rufo.]

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