Painting Show Quality Models

BY JOHN MULLEN, HASBRO INC.

Supplies: 1. Primer 2. Paint 3. Sandpaper, 320 & 400-grit wet/dry 4. Body filler or sandable putty (optional) 5. Zep Citrus Cleaner* 6. Tack cloth 7. Disposable Gloves 8. Spray mask

Overview

For sales samples and photography models, painted PolyJet™ parts will give your customers a preview of your newest products. With a little patience and nearly any type of paint, you can easily decorate your prototypes to look like production parts.

Painting PolyJet models takes half the time of other rapid prototypes. The smooth surfaces and crisp details minimize the tedious and time-consuming steps of sanding and filling. Since surface preparation is the key to the quality of a painted model, PolyJet delivers a better looking model in less time.

The supplies needed for your painting project are inexpensive and are available at any hardware or automotive supply retailer.

Process
1. Remove support material.

The key to a perfectly painted model is its preparation. This starts with the removal of all support material. To optimize paint adherence and cosmetic appeal, it is best to completely remove all support material with the WaterJet station (figure 1). Well-prepared models will have a consistent feel on both supported and unsupported surfaces.

Figure 1: Removal of support material. Use WaterJet station to remove support material. If residue remains, clean with detergent- based solution.

 

There are two options to obtaining a clean model surface. The first option is to use a detergent-based solution. One easily obtainable detergent-based product is Zep Citrus Cleaner. To degrease the model, simply dip the model in Zep Citrus Cleaner (figure 1) for 5 to 15 minutes, rinse with water and let dry. The second option is to bead blast the model.

2. Sand surfaces.
With 320-grit wet sandpaper, sand the model for a smooth, paint-ready surface (figure 2). While sanding, keep the sandpaper and model wet by repeatedly dipping the sandpaper in water or placing the model under running water (figure 2).

With the thin layers and fine detail of the PolyJet model, surfaces should need only a light sanding. Following sanding, wash the model in water and allow it to dry completely.

 

Figure 2: Wet Sanding Wet-sand the model with 320-grit sandpaper.	Figure 3: Apply primer paint Apply several thin coats of fast drying, lacquer-based primer.

 

3. Apply primer.
Primer serves two purposes. First, it provides a good bond coat for paint. Second, it will show any areas on the model where additional finishing may be needed.

Spray the model with fast drying primer (figure 3). Lacquer-based primers (and paints) are a good choice since they sand well, dry fast and are readily available. When priming or painting, use two light coats, instead of one heavy coat, to prevent drips and puddles. If you do not have a paint sprayer, apply the primer from a spray can. Remember to spray the primer in a well-ventilated area and wear appropriate safety equipment.

After the primer has dried to the touch, inspect the model for any areas that need additional sanding or repair.

Tip: To preserve the accuracy of your model when sanding, apply a red or white primer as the base coat and follow with gray primer. The color difference gives you a visual reference that you are getting close to the model's surface.

4. Sand and fill blemishes.
Depending on the results of the primer coat, you can either proceed to the next step or do some additional finishing work. Typically if the primer is applied correctly no additional finishing is needed prior to applying the finish paint. However, if there are blemishes in the primer coat you may want to do some additional finish work. Finishing may include wet sanding and/or filling small pocks. Finishing may include wet-sanding or filling of small pocks.

If sanding is all you need, wet-sand the surfaces with 400-grit sandpaper. Stop sanding if the PolyJet material begins to peek through the primer. Rinse and dry the model. If any of the model surface is exposed, repeat step three. Otherwise, proceed to step five.

Since the Eden systems build with such small layers, you will not have to fill in layer stair stepping. However, if small blemishes show up in the primed model, you can easily fill them with a dab of auto body putty. Body putty comes in many forms, but you will want a fast curing, easily sanded putty such as Freeman TUF-Carv. Optionally, you can use premixed glazing putty like 3M™ Acryl-Blue.

After the putty has dried-usually less than 30 minutes, sand the area smooth. Start with 220-grit sandpaper and finish with 400-grit wet-sanding. Rinse the model with water and dry. Repeat step three.

Figure 4: Fill and sand blemishes. Filling blemished with body putty then repeat step 3.	Figure 5: Apply finishing paint or clear coat Apply thin coats of lacquer-based paint for smooth, drip-free finish.	Figure 6: Finished model The finished model is ready for photo shoots and customer demonstrations.

 

5. Apply finish paint.
Prior to painting the model, ensure it is clean and dry. Use a tack cloth or compressed air to remove dust. Apply several thin coats of finish paint (figure 5). Allow the paint to dry between each coat. As with the primer, spray paint will do the job if you do not have a paint sprayer available.

6. Apply clear coat (optional)
In an effort to provide additional protection against scratches, chips, and other marks a coat of clear lacquer can be applied.

Clear coat paint can be purchased in a variety of finishes including: Matte, semi gloss, and gloss. Choose a lacquer based clear coat with the desired finish (figure 6).

Suppliers
Freeman TUF-Carv available at:
Freeman Manufacturing & Supply Company - www.freemansupply.com

3M Acryl-Blue available at most automotive supply retailers.
Sherwin Automotive - www.sherwin-automotive.com
Midway Auto Supply - www.midwayautosupply.com

*Substitute Zep Citrus Cleaner with any cleaner/degreaser with a five percent to 10 percent concentration of lye.

Author Acknowledgement
John Mullen is the rapid prototyping manager for Hasbro, Inc. and has 14 years of experience in rapid prototyping and model making.

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