"Digitally manufacturing the fixture with
polycarbonate took it from eight pieces to one,
more accurate piece that lines up."
Clear or Translucent Models
BY JIM LEONARD, WORLD CLASS PROTOTYPES
Dry: 220 & 320-grit Wet: 400 & 600-grit Micro-mesh: 1500, 1800 & 2400
2. Polishing compound: 3M™ Plastic Polish
1. Buffing wheel/ rotary tool with buffing drum
Not all plastic parts are opaque. For clear parts such as lenses, containers, covers, or panels, PolyJet™ offers the advantages of rapid prototyping with the translucency needed for the application. Although there are no shortcuts to achieve 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 makes it both possible and practical. The smooth surfaces of PolyJet models and the translucency of FullCure™ 720 combine to make clear models a reality. Right out of the machine, you are ready to begin the light sanding and polishing to make a clear prototype.
The require materials for polishing multiple PolyJet models cost less than U.S. $20.00 and are easy to find at automotive, hobby or woodworking supply companies.
1. Build model.
Orient the model so that the critical surface faces upward and build in glossy mode (no support material). Wherever possible, avoid support material on clear surfaces since they will be more difficult to make clear (figure 1).
|Figure 1: Build orientation Orient the part to minimize support material on clear surface and build with glossy mode.||Figure 2: Wash model Pressure wash the model to remove all support material.|
2. Prepare model.
With the WaterJet station, thoroughly pressure wash the model to remove the support material (figure 2). Pay extra attention to corners, channels and pockets to ensure that the support material is completely removed.
Note: Bead 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 bead blast the unprotected area.
3. Dry-sand surfaces.
Following support removal, thoroughly dry the model and sand all surfaces with 220-grit sandpaper. A light sanding will remove surface imperfections and layers (figure 3). After the 220-grit sanding, repeat with 320-grit to begin the polishing process.
|Figure 3: Dry sanding part Sand all surfaces to smooth the model.||Figure 4: Wet-sanding Wet-sand the model to begin polishing of the clear surfaces.|
4. 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. Instead, it reduces the scratches from previous sanding, so light touch is all that is needed (figure 4).
Between each sanding, rinse the model with water to remove any grit and debris.
Tip: When wet-sanding, you can add a few drops of dishwashing soap to the water to lubricate the surface or use a vegetable or mineral oil.
5. Micro-mesh sanding (optional).
For an exceptional finish, polish the model with micro-mesh sandpaper (figure 5). Sand all surfaces with a 1500 micro-mesh. Depending on the desired results continue sanding with 1800, 2400, 3600 and 4000 micro-mesh.
As with step 4, you can use soapy water, mineral oil or vegetable oil to lubricate the surface while sanding.
|Figure 5: Micro-mesh sanding (Optional) Using micro-mesh sandpaper, polish out all surface scratches prior to buffing.||Figure 6: Polishing the model With a buffing wheel and polishing compound, bring the surface to a high-gloss.|
6. Polish model.
The final step to 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 (figure 6). Reapply the polishing compound frequently.
An effective polishing compound is 3M® Plastic Polish, which is available in an eight ounce bottle under U.S. $10.00. Polishing compounds for plastics are also available from several other manufacturers, and some of these do not require a buffing wheel. Alternatives to plastic polish include jeweler's rouge and, when in a pinch, toothpaste labeled "whitening."
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 7).
|Figure 7: Finished model Polished PolyJet model, has the clarity needed for product demonstration.|
Plastic polishing compound- Available from automotive and marine supply retailers.
3M Plastic Polish - P/N 39010 - www.3mestore.com/plastic-polish.html
Meguiar's Mirror Glaze Plastic Cleaner and Plastic Polish Meguiar’s- www.meguiars.com
Jim Leonard, president of World Class Prototypes, has 15 years of experience in model making, molding and prototyping. He founded World Class Prototypes 12 years ago.
World Class Prototypes' primary business is PolyJet prototyping and silicone rubber molding for product development. The company also offers rotational molding, vacuum forming and carbon fiber lay-ups.
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