Alumilite to the Rescue

Ever wish "someone" would make the perfect plastic part you need for your latest project?  Now someone does: YOU!  Alumilite materials let you create professional looking, high strength plastic parts at home.  Alumilite castings are relatively light weight but are strong enough to withstand everyday use.  Castings can be painted, glued and machined.

Non-Toxic & Odorless

Alumilite materials are non-toxic and virtually odorless.  Unlike other casting system, Alumilite molding and casting materials mix with equal volumes of "A" and "B" material so you can "eyeball" measurements and have very successful results without precision measuring equipment.  Alumilite does offer guidelines for calculating product usage for items you are considering duplicating.

The Best Way to Get Started

The best way to get started with Alumilite is to buy one of the castings kits.  Both the "Mini-Super Casting Kit" and the "Super Casting Kit" include all the materials and instructions you need to make your first mold and casting.  If you want some extra help getting started, consider the excellent "Instructional Video" (available for purchase) which leads you step-by-step through the molding and casting processes.

Making a One-Piece Mold

A one piece mold works perfectly for parts that have a flat back side.  The flat back side gives you a non-cosmetic side to pour from.  The advantages of a one piece mold are the simplicity of making the mold and no seam lines in your finished casting.  It is important to choose an item for duplicating that is in perfect condition.  The molding rubber and casting resin will pick up every little flaw in the original and accentuate it in the copy.

Getting Started – Making the Mold

1. The first thing you need to do is to fasten the part to be duplicated onto a “mold base”.  The base can be any nonporous material, such as a piece of plastic or wood, metal, styrene, coated poster board, or any other material you have available.  Fasten your piece with double-sided tape or super glue.  This will prevent the original from floating after you pour the silicone mold-making rubber over it.  The flat side will give you a nice open area to pour it.  No mold release is necessary on your original unless it is made of silicone.  Silicone rubber only adheres to another silicone.  When you fasten the piece down, try not to leave a gap between the base and the part.  The silicone will seep under the original and it will require additional cleanup later.  It's much easier if you eliminate the gap before pouring the silicone.
2. Make a mold box out of plastic, wood or poster board, PVC, or any other cup or container.  Leave .25” - .375” between your mold box and your original.  Seal your mold box with Alumilite’s Synthetic Modeling Clay to prevent the mixed silicone rubber from leaking out of your mold box before it cures.
3. The next step is to mix and pour the silicone mold-making rubber into the mold box.  Measure the silicone rubber according to the instructions provided with the silicone and mix thoroughly.  After properly weighing and thoroughly mixing the rubber, slowly pour from one corner of the mold box to gently submerge the part in the rising silicone.  If you have a significant amount of detail you may wish to paint on the first layer of silicone before pouring the rest into the mold box.  Painting the first layer of silicone prevents air bubbles from sticking to the part and ending up with bubbles in your mold.
4. Allow the silicone to fully cure.  This time can be up to 24 hours.  Once the silicone has cured remove the glue or clay that sealed the box to the base and begin to remove the mold from the box.  If you cannot disassemble the box itself, use a dull knife or spatula to remove the mold.  Rubbing alcohol helps by releasing the surface tension and making the silicone slippery.
5. Once the mold has been removed from the mold box, flex the cured silicone mold and remove your original.  You now have a perfect mold of your unharmed original.  You are now ready to make identical castings of your original.

Now You Can Cast Your Piece

Before mixing the resin, preheat your mold to ensure proper curing of the resin casting. Place the rubber mold in a microwave for a minute on high or place the mold in a conventional oven for 30 minutes at 150 F. Another helpful hint in making flawless castings is to powder the inside of your mold with baby powder. The baby powder will release the surface tension and decrease the chance that air bubbles will be trapped in the resin. Prior to casting make sure you blow out all excess powder from the mold.

1. Measure the Alumilite resins according to their proper mix ratio (generally 1:1 by weight or volume).  Mix vigorously for 20 – 25 seconds until thoroughly mixed.  Use plastic or paper cups when mixing Alumilite resins.  (Do not use Styrofoam cups)
2. Once you’ve mixed the material thoroughly by scraping the sides and the bottom, slowly pour the resin into your warm mold by tilting it and letting the resin flow down the sides of the mold.  Squeeze and tap the mold to assist any unwilling air bubbles to release from the sides of the mold and to help them float to the surface.
3. The “open” time of most Alumilite resins is 90 seconds.  The color change is the end of the open time and the point at which it will turn color and begin setting up.  The finished color of Alumilite Regular is an opaque tan (white and black resin is available along with coloring dyes to color the resin yourself).
4. Once the resin has hardened (approximately 5 minutes) flex the mold and remove your perfectly cast piece.  Your piece is now ready to be painted, sanded or tapped. The mold can be used over and over again.

Making a Two-Piece Mold

A two or multiple piece mold is typically required when the object you need to mold has detail on all sides of the piece. In order to mold both the front and back halves, you will need to start by making a mold of the front and then making a mold of the back. You will need to start by determining a parting line which is where the two halves of the mold will meet. This is typically an edge or perhaps the half way point from the front and back. Try to put this line in the place where it will be noticed the least. You will pour the part from the least cosmetic place on the original.

Getting Started – Making the Mold

You begin by building a clay base and pressing your piece into the clay until it is close to where you want the parting line. If the clay is too firm to work with effectively, warm it in an oven or microwave to soften it. It is vital that you use synthetic clay.  Sulfur based clays can inhibit the curing of your silicone rubber and ruin your mold.

1. Using clay tools, smooth and flatten the clay to establish a perfectly smooth and clean parting line where the clay touches the part.  Remember, the cleaner the edge, the smaller your parting line will be and the less clean up will be required on the seam line of your cast resin piece.  Once the part is completely clayed up to the parting line you've established, you are ready to build your mold box to contain the liquid rubber.
2. Use corrugated plastic, angle iron, wood, a recycled piece of plastic, or any other non-porous material, to construct a mold box to contain the liquid silicone rubber.  Build your box so that the walls are ¼”-3/8” around the outside of your original.  Carve a small trench in the clay that surrounds your piece. This will create a ‘marker’ or ‘locator’ so that both halves of the mold will line up and fit together perfectly every time you put your mold together.  Building your walls too big around the outside of your piece require much more silicone which wastes unneeded silicone.
3. Make sure you have completely removed all modeling clay off of your original before pouring the silicone. Carefully clean your original with a little soap and water or rubbing alcohol.  Let the original dry completely and make sure your mold box is sealed.  Make sure to seal the box well to prevent leaks.  Hot melt, super glue, clay, or even caulk works well.  When the box is complete and the original is clean and free from any clay or fingerprints, mix and pour the silicone rubber over the original.
4. Properly measure your silicone RTV and mix thoroughly to ensure a proper cure and physical properties of the rubber mold.  Once the silicone is thoroughly mixed, pour the silicone in the sealed mold box.  Be certain to completely mix your silicone.  Any portion that isn’t mixed will not cure.  Start from one corner and allow the liquid rubber to flow naturally over the original rather than pouring the rubber directly onto the piece.  This technique will reduce the possibility of trapping air on the surface of the original. Continue to pour the silicone until the entire piece is covered by at least ¼” of liquid silicone.
5. Allow the silicone rubber to fully cure.  With most silicones, it is always a good idea to allow them to cure overnight.  Once the silicone is fully cured, remove the mold from the box but if possible, leave the box in the mold to prevent breaking the seal between the box and the mold.  Remove the clay from the back side of the piece but DO NOT REMOVE THE PIECE FROM THE POURED RUBBER MOLD.  This will break the seal and damage the clean parting line you clayed up.  It may also cause additional rubber to flow into the area that are already cured.  Remove the bulk of the clay and then go back and clean off all of the leftover clay.  A toothbrush is a good tool to use for this portion of cleaning.
6. Once all the clay has been removed, coat the rubber with Alumilite’s Rubber to Rubber Mold Release.  This will prevent the second layer of silicone rubber from adhering to the first.  Vaseline works great for this if you do not have any of the rubber to rubber release.  DO NOT MOLD RELEASE THE ORIGINAL and be sure not to miss any rubber sections of your mold.  Any area not coated with release agent will stick and will require cutting to separate the two halves apart.  To have the second half of the mold release from the first, you must have a mold release in between the layers wherever the two halves will touch, including the outside portions of the mold next to the mold box.
7. Once you have cleaned the mold and master off completely of all clay residue, you are ready to cut your locators so the second half of the mold aligns with the first.  Use a hobby knife to cut “v” or “u” channels in the rubber mold.  This will allow the rubber you pour during the second half to flow into these channels and provide great locators to align the two halves of the mold.  Cut locators on at least two or three sides of the mold.
8. Place your mold back into the mold box and reseal it if necessary
9. Measure and mix the proper amount of silicone required to fill the second half of the mold.  As you did with the first half of the mold, pour the rubber from one corner of the mold box and allow the material to flow naturally over your original and cover it by at least ¼”.  Allow the rubber to fully cure and remove it from the mold base.  Remove the mold from the mold box.
10. Using your hands, find the seam line and begin to separate the two halves of the mold.  As you can see, the mold will separate exactly where the two halves were poured and mold released.  You will also see how the second half of the mold filled in the locators from the first half and how it will give you perfect alignment between the two halves.  Remove the unharmed original from your two piece mold.  You are now ready to cut your pour hole and any vents if they are needed.
11. Using a hobby knife, find the most non-cosmetic area to use as your pour area.  Ideally this will allow for natural flow of the resin and an area in which air bubbles will float to the top and escape without trapping air on flat surfaces of your mold.  So using the hobby knife, cut a “u” shaped channel from the point you have selected to the outside of the mold on both halves of the mold.  Once you have both channels cut out and place the mold together, you will find a perfect pour hole in which you are ready to pour an exact replica of your original.  You can also use 1/8” copper or brass tubing to twist and cut holes through the silicone to place vents and/or injection points throughout the mold.
12. You are now ready to pour your first piece out of your two-piece mold.  (See Now You Can Cast Your Piece above.)