Composites

Basic Mold Making Materials

So you want to make a mold? Well here are some basic materials you will need.

1) Design or actual object you want to mold.

2) Mold release wax

3) PVA release agent

4) Tooling resin

5) Epoxy resin

6) Cloth - some type of cloth ie: Fiber Glass, Kevlar, or Carbon Fiber

7) Sand

The process of making a mold is quite simple; however, there are different methods that can be used to obtain the same result. For this example, we will doing the Epoxy and Sand method.

You first start out with the part you wish to create a mold of. This part is called a "plug". This is usually a solid structure and can be the actual part or a part made from some other material. Wood and foam are the two most common materials plugs are made from. Depending on what you will be making the amount of wood or foam will depend on how strong you want to your plug to be. Great care should be taken while creating the plug since any imperfections will transfer over to the mold and ultimately to the parts you will create. Don't rush any step and be patient.

The plug will need to be waxed several times with a good mold release wax. I recommend putting on at least 5 to 7 coats of wax before applying the PVA agent. Remember, you don't want the epoxy to stick to any part of your plug during the molding process. If it does, it will mess up your part. After the coats of wax are applied, the next step is to apply the PVA releasing agent. This is a watery based solution that will self level and provide another layer of protection on your plug. Some people spray PVA on the plug with a first light misting pass. Let I dry for about 15 minutes then come back with 4 or more heavier coats. Another method is to use a paper towel soaked in PVA and lightly apply the solution to the plug. If going the paper towel route, make sure you work a little faster to not allow the PVA to setup before you've had a chance to coat the plug. After about 15 minutes you should be able to apply more coats of PVA with the paper towel method.

Ok, so you've created your plug and waxed it along with PVA. Now you are ready to begin the molding process. Most plugs get molded into 2 halves, but some times you might want to break it down every further with more halves or sections. For now, we will only be doing a 2 half mold. In order to create two halves, we need a barrier that will go around the plug. This barrier is called a "parting board". The parting board can be made from wood, formica, plexiglas, or even aluminum sheeting. Depending on what method you will use to build up the mold thickness will dictate what material is suitable for use as a parting board. Since we will be using sand instead of multiple layers of fiber glass, we need something strong and which can be supported. To create the parting board, you just run strips of material along the center line of the plug. You want to get this parting board to mate against the plug as close as possible. Smaller gaps like around corners and such will be filled in on the next step. Once you have your parting board around the plug you need to make sure that no gaps exist. Any gaps will serve as a way for the epoxy to seep out. One method of dealing with the gaps is to use Kleen molding clay which has inherent properties that will not let epoxy stick to it and fill in the gaps. This method is great if you are only planning on making one mold, but if you have any desire to possibly make a second mold later, I recommend using a mixture of epoxy and cabosil or micro balloons. Using the mixture to fill in the gaps will provide a permanent solution making the parting board useful if more then one mold is needed. After the gaps are filled, allow time for the mixture to cure then pull the parting board and plug away from each other. Where the mixture was used to fill the gaps, there will probably be raised areas. Take some sand paper and sand the areas until it is smooth against the parting board. When done you should now have a more permanent type parting board. Place the parting board on the plug along the same center line as before. Check to make sure that it fits tight and there are not any gaps. If satisfied, repeat the process of waxing and applying PVA agent to the plug and this time also to the parting board.

To be continued….

See the step-by-step process of making a mold - Super Reaper Composite Fuel Tank Mold Construction