Melting Materials for Mold Making

While 3D printers have become more accessible, it is still relatively expensive and time consuming to generate 3D prints. In addition, the materials commonly available for 3D printing are limited to certain types of plastics. We wanted to explore the possibilities of broadening the affordability and material variety for making multiple models by using traditional mold-making with 3D printed sources. This way, by 3D printing a single model, users would be able to create multiple finished molds using a variety of materials.

Crayon – Solar Heating

As an early experiment in melting materials, we used solar heating to melt Crayola crayons into different shapes. Crayons have a relatively low melting temperature, becoming completely molten at between 120-150 degrees fahrenheit, which is an easy temperature to reach while sitting outside in Phoenix, Arizona during early Autumn.

left: fused crayons after heating; middle: cut up pieces of crayon before being heated; right: pieces of crayon fusing as they melt

Wax – 3D printing tests

Since we wanted to make these models useful for molding several different types of materials, including food, we wanted to insure that the 3D printed models would be food safe. The main ways to insure that a 3D print are food safe are to 1) use a food safe printing material (some types of PLA are food safe, but it is important to check with the manufacturer), 2) use a 3D printer that has a stainless steel extruder, 3) wash the 3D model with antibacterial soap, and 4) spray the model with a polyurethane spray to prevent the risk of bacteria growing in small cracks in the 3D print.

For testing the viability of the 3D models as molds, we used wax as a test molding material, since wax is solid at room temperature but can melt at between 110-150 degrees fahrenheit (depending on type of wax), and so is easy to melt using normal household items.

The first 3D print prototype used a raised image inside of a hollow cube, with the hopes that the wax could be poured in when hot and would be removed easily once hardened (a no-stick spray was applied to the 3D print before the wax was poured in). However, it appeared impossible to remove the wax from the model intact. By putting sheets of saran wrap between the wax and the 3D model, it was possible to remove the wax once dried. However, the resulting wax molds were unable to properly adhere to the shape of the 3D model because of the presence of the saran wrap.

left: first 3D printed model; right: the only way to remove the wax molds in one piece was to place a layer of saran wrap in between the plastic model and the wax as it melts. However, that resulted in the wax not adhering to the shape of the 3D model well.

After the first model proved ineffective for casting wax, we created a second model which had a hollow bottom, in the hope that the wax mold could be pushed out of the model once it had hardened. This did succeed, but it was still fairly difficult to remove the wax mold and there was some surface abrasions to the wax.

left: liquid wax cooling inside the second model. The model was placed on top of wax paper to prevent the liquid wax from leaking out from the bottom of the model. right: resulting wax model. While a marked improvement from the previous attempts, it was still difficult to remove from the 3D print and had sustained minor damage.

Wax – Silicone mold

Because the wax was proving difficult to remove from the inflexible plastic 3D prints, we chose to look for possible in-between methods of transferring a 3D print into a molded material. We decided to use silicone putty, a material that starts out with a texture resembling play-doh but will solidify into a permanent shape while still maintaining flexibility. To create the silicone mold, silicone putty was spread around a 3D print and left to dry. Afterwards, hot wax was poured into the silicone mold, whose flexible properties made it much easier to remove the wax after it hardened.

left: original 3D print; right: silicone mold that was created from dried silicone putty that was molded around the 3D print; bottom: resulting wax piece that was cast in and removed from the silicone model. Despite being much thinner (and therefore more fragile) than the previous wax molds, the wax piece was removed from the silicone with significantly less damage than the wax tests that were cast directly in the 3D prints.

wax-silicone mold.jpg

Given the success of molding with wax, we did some preliminary experiments with food materials using the same silicone mold, which was created from a type of silicone putty that has been designated and labeled as food-safe.

Chocolate

The chocolate tests were mostly successful, with the only notable problem being that the surface detail of the chocolate molds appear to have lumps or pockets in their surfaces. This may be caused by air pockets being stuck under the liquid chocolate as it is poured into the silicone mold, or the type of chocolate that was used (standard chocolate chips) is not designed to remain smooth after being melted and re-solidified.

Gelatin

The success of the gelatin molds varied based on the type of gelatin that was used.

below: When using Jello brand gelatin mix, the resulting gelatin did not maintain its shape when being removed from the silicone mold.

food-jello2_1.jpg

below: Alternatively, coffee agar mix (which is intended to be cut up into cubes or other shapes after hardening, and thus was designed with greater internal resilience than Jello) was easily removed from the silicone mold without any damage.

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