66.5 SOLID GROUND CURING (SGC)

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Basic Process,

1. A computer program preprocesses a part so that it is in sliced layers.

2. A plate (glass?) is charged selectively and coated with a back powder. This process is much like photocopying.The result is a photographic mask of clear and opaque areas for a single slice of the part.

3. A thin layer of photopolymer is spread in a part vat.

4. The mask is placed over the photopolymer and a UV lamp is used to expose the layer and selectively harden the polymer.

5. The photographic plate with the mask is cleaned.

6. The unhardened polymer is removed from the surface.

7. A find layer of wax is deposited and hardened.

8. The surface is milled flat for uniform thickness.

9. The process begins again at step 2 and continues until all of the layers have been added. Note: Some steps can be done concurrently for the mask and the vat (i.e., 2,5 AND 3,6,7,8) to decrease build times.

Developed by Cubital Inc. in Israel, started in 1987.

two commercial machines - Solider 4600 and 5600

Uses photosensitive polymers, but these are developed using a UV light and a photopolymer

1. photopolymer is developed and hardened by a UV mask that has the pattern for one slice of the part.

2. Unhardened polymer is cleaned away and replaced with wax, that is solidified with a cooling plate.

3. the polymer/wax layer is machined to exact thickness, and coated with a new layer of polymer. (a vacuum is used to remove cut chips)

4. The process continues until done

The masks are made using a glass plate with electrostatic powder distribution (similar to photocopiers). A slice is used to electrostatically charge a glass plate, electrostatic sensitive powder coats the charged areas, and the mask is complete. After use the glass is cleaned and reused.

After completion the wax is melted, and the complete part remains. (the wax was used to support work and eliminate supports.)

************ Include SGC figures from pg 60 and 64

the UV lamp is 4KW and is exposed to the polymer for a few seconds

a resin applicator spreads the photopolymer across in thin layers

an aerodynamic wiper is used to remove excess material to a storage reservoir. This material may be reused if not overexposed (?) thus causing a change in viscosity.

because the toxic resins are used, exhaust fans and dark work cabinets are required.

Advantages,

- no need for time consuming post-curing

- part complexity does not effect speed, however volume does.

- elimination of postcuring reduces internal stresses, and warping.

- jobs can be stopped, other jobs run, then the first job restarted at a later time.

- weights may be inserted at any time to alter the centre of gravity

- supports are not required

- models with moving parts can be produced because of the firm holding of work in the process.

- layers can be milled off if they are found to be in error

- many parts can be run at the same time

disadvantages,

- overexposure of the polymer may increase the viscosity, and make it unusable, thus greatly increasing the volume of expensive polymers used.

- the resins require that light sealed chambers and toxic material handling procedures be used.

- the machine is very large

- machining is noisy

- maintenance is high, requires supervision

- very few materials available

- removal of wax after production is required

Solider 4600 & 5600

- 65 (5600) or 120 (4600) seconds per layer

- 14" by 14" by 14" (4600) or 20" by 14" by 20" (5600) work vol.

- $275,000US (4600), $400,000US (5600)

- accuracy 0.1%

- has been used to produce investment casting

A selected set of specifications for the Solider 4600 are given below,

A selected set of specifications for the Solider 5600 are given below,