Insulation Foam Mold Plugs

General overview:

Pros:

• Does not require special tooling and can be machined using a CNC

• Cuts down cost (still a half-half consideration)

  • A regular sheet of rigid insulation foam can range from $10 - $80 depending on sheet thickness and quality (typical size pink sheets are 8' x 2' x thickness (ranging from 1/2” to 2”)

• The foam mold/plug would weigh a fraction of the weight to that of an MDF mold making transportation less of a hassle

• Easily accessible at any home hardware store

• Most surface imperfections or gaps can be filled using bondo/body filler or some sort of spray foam and then be refinished

• Can be layered similar to MDF cutting down wasted material

• A more reliable approach for smaller molds and molds done in parts

Cons:

• Insulation foam is a more dense Styrofoam meaning that, with machining, surface imperfections will be at a same level to that already apparent in MDF

• The post processing (i.e. the sanding, priming, and coating) will still be needed to ensure a smooth mold/plug surface

• Might not be a viable molding option with the current fabricating situation, especially since prepreg is being used and heating the foam for a long period of time will melt and/or burn it

• If used as a plug, that gives an additional few days to produce and manufacture a fiberglass mold

• Typically requires some free handing to clean up areas after machining

• MDF is slightly cheaper depending on the supplier

• Could be a slight pain for larger molds if done in a single block

Sample Manufacturing Procedure:

1. Cut foam sheets to general size ( 2 - 3 hrs )

   1. Process can be done on a table saw or using a skill saw

2. Glue sheets together (4 - 8 hours )

   1. Sheets would need to be glued together using a spray on foam or foam adhesive

   2. Typical 4 - 5 Layers

   3. Ensure that no air bubbles are found by evenly spreading adhesive and applying enough weight on the sheets as they dry

3. CNC the plug ( 1 day lead time, not much manual labour )

   1. Smaller plugs are machined in house, using student machine shop, bigger plugs would are a different case

   2. Split up larger plugs into smaller parts, or outsource an external company for the CNCing procedure

4. Sealing the plug ( optional, 3 - 5 hrs )

   1. the foam is slightly porous and may absorb primer or epoxy applied to it, so might need to be sealed to be primed and sanded

   2. optional since body/wood filler can be used to fill gaps. The foam itself can be directly sanded and if over sanded, more filler or spray foam can be used and resanded

5. Primer ( optional, 6 - 8 hrs )

   1. recalling the step before, if the plug is not sealed, the priming step can be avoided by using filler or spray on foam

6. Sanding the plug ( 6 - 8 hrs )

   1. one of the most important steps in the process

   2. ensures that a mold made using the plug shows no surface imperfections

   3. starting at low grit and working way up

7. Fiberglass mold-making ( 6 - 12 hours)

   1. cutting out fiberglass strips

   2. performing a wet layup ( or other fiberglass layup desired )

   3. Once dried, ensure that no bubbles or imperfections arise

   4. If there are imperfections, use either epoxy or filler to fix and sand the issue

8. Apply mold release ( 2 - 3 hrs )

   1. Brush on selected mold release to ensure panel and mold don’t stick to one another

Final Thoughts:

Sources and Extras:

• https://www.homedepot.ca/en/home/categories/building-materials/insulation/rigid-insulation.html

• Speeds and Feeds for milling pink insulation foam?

• Tips for Cutting Foam on a CNC or CNC Machine