Archive for the ‘Photopolymer’ Category

Solid Ground Curing (SGC)

05/20/2009

SGC was a process developed by Cubital Inc. of Israel. The technology is no longer being produced, as Cubital Inc. no longer exists (though Objet Geometries Ltd. of Israel retains intellectual property of the process). I have included it here because it is an interesting and unique approach to printing.

SGC uses photosensitive liquid in a layer by layer process, however the main difference is that it exposes an entire layer at one time.

Before the process can begin, a series of plates must be printed. Software splits the CAD model up into thin layers, and each layer is printed (2-dimensionally) onto a plate. The plate acts as a mask; any model cross-section is transparent while the rest of the plate is opaque.

The machine first sprays a layer of photopolymer into the working area. The first printed plate is loaded right below a UV lamp; a shutter opens and the entire plate is exposed to the photopolymer at once. The cross-section that was exposed hardens the photopolymer, and afterwards the uncured photopolymer is sucked up by a vacuum.

Next a layer of wax is put down over the unexposed area (evening out the bed) and the entire layer is milled so that it is completely flat (all of the excess material from the milling stage is vacuumed up). Another layer of photopolymer is sprayed on, the next plate is loaded, and the process continues.

At the end the model is contained within a block of wax, which gets melted away. No other post processing is necessary.

efunda.com has a nice illustration of the process (it is fairly difficult to explain):





This method failed because of high acquisition and operating/maintenence costs.

Advantages (while it existed)?
• Very fast and decently accurate (though not as accurate as SLA).

Disadvantages?
• Produces a lot of waste.
• Expensive in comparison to other methods (for both material and operation).

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Jetted Photopolymer (JP)

05/20/2009

JP printing is identical to InkJet printing, but instead of using thermoplastic, it dispenses photosensitive liquid. The print head contains a UV light; after a layer is put down, it is cured with the UV light. This eliminates the need for a separate curing process and is very accurate.

Advantages and disadvantages are similar to Inkjet printing.

Stereolithography (SLA)

05/20/2009

Stereolithography is the oldest and one of the most common methods for printing. It prints by using either one or two lasers focused at a pool of photosensitive liquid. When the laser(s) focus on one point at the top of the pool, the liquid solidifies. This happens a layer at a time, each layer being typically about 0.1mm thick. Each time the machine goes to print a new layer, the bed moves down and more photosensitive liquid is poured in.

When the model is done printing it goes into another machine to be cured under an ultraviolet light.

From efunda.com:

So what are the advantages?
• The machine is very accurate and the vertical step size is small. This is good if you are looking for exact specifications.

Disadvantages?
• The models can’t be handled straight out of the printer, as they need to be cured first.
• Support structures must be printed depending on the specifications of the model, but because of the nature of the machine the supports must be made out of the same material as the model. This means that you have to cut them off manually after curing, which can leave artifacts (I have a first hand experience with this one).