Overview
Not all plastic parts are opaque. For clear parts such as lenses, containers, covers, panels and a variety of other applications, Objet’s PolyJet™ Technology offers the advantages of rapid prototyping while also enabling the translucency required for the application.

Although there are no shortcuts to achieving the transparency and brilliance of clear parts, the process is simple and inexpensive.

With most rapid prototyping technologies, clear models are either impossible or too time-consuming to make. However, PolyJet Technology makes it both possible and practical. The smooth surfaces of PolyJet models and the translucency of FullCure® 720 model material combine to make clear models a reality. Right out of the machine, you are ready to begin light sanding and polishing to produce a clear prototype.

Process

Build model
Orient the model so that the critical surface faces upwards and build in glossy mode (do not use support material). Wherever possible, avoid support material on clear surfaces since it will be difficult to remove
(figure 1).

Prepare model
Using the WaterJet station, thoroughly pressure wash the model to remove the support material. Pay special attention to corners, channels and pockets to ensure that the support material is completely removed (figure 2).

Note: Sand blasting is not recommended. The abrasiveness can create small pits that are difficult to polish. However, for a frosted surface, mask off the part and sandblast the unprotected area.

Dry-sand surfaces
Following support removal, thoroughly dry the model and sand all surfaces with 200-grit sandpaper. A light sanding will remove surface imperfections and layers.
After the 220-grit sanding, repeat with 320-grit to begin the polishing process (figure 3).

Wet-sand surfaces
Lightly wet-sand the model, progressing through 400, 600 and 1000-grit sandpapers.
The wet-sanding is not intended to remove material. Rather, it reduces the scratches from previous sandings, so a light touch is all that is needed.
Between each sanding, rinse the model with water to remove any grit and debris (figure 4).

Micro-mesh sanding (optional)
For an exceptional finish, polish the model with micro-mesh sandpaper.
Sand all surfaces with 1500 micro-mesh sandpaper. Depending on the desired results, continue sanding with 1800, 2400, 3600 and 4000 micro-mesh sandpaper.
As with step 4, you can use soapy water, mineral oil or vegetable oil to lubricate the surface while sanding (figure 5).

Polish model
The final step to achieving a clear PolyJet part is to buff and polish the surfaces. Using either a buffing wheel or a rotary tool with a buffing drum, apply a polishing compound to the buffing pad and work it onto all surfaces of the model. Reapply the polishing compound frequently.

An effective polishing compound is 3M Plastic Polish. Polishing compounds for plastics are also available from several other manufacturers. Some of these compounds do not require a buffing wheel.

After polishing all surfaces, buff off the compound with a soft cloth or a clean buffing pad. Your PolyJet model is now ready to be used as a lens, container, or cover (figure 6).


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