3D Modeled Gummy Candy Injection Molds

About: I am a high school engineering teacher (formerly an engine design engineer) who loves developing new projects - both personally and for my students to work through.

Manufacturing processes aren't the most glamorous and exciting topics for most high school students, but this lesson attempts to intrigue students by having them create their own injection molding system that can produce individually designed gummy candies.

I use this lesson in my introductory high school engineering/manufacturing class (grades 9-12) after we have learned how to use CAD software to make 3D models. I introduce manufacturing methods (specifically highlighting injection modeling) within this project and have students apply their newfound CAD skills to help them better understand that process.

This project begins by having students design and model an original candy shape. Next, they they turn those models into 3D printed molds that they can use to create personal injection molding machines. Finally, they can inject those molds to create their own personalized gummy candies.

Supplies:

General supplies:

  • Paper
  • Computer with 3D modeling software*

To create the mold:

  • 3D printer and filament (for food grade projects like this, a stainless steel hot tip on your extruder and PLA made from natural fibers is best)
  • Masking tape
  • Cooking spray
  • Drill and drill bit (drill bit size should match the outer diameter of the tubing used)**
  • Plastic tubing (~6" long per mold)**
  • Syringe**

**There is no strict size requirement here, but you want to make sure all three of these components (syringe, tubing, and drill bit) work together. I recommend a syringe that has at least a 20mL volume, but larger is fine. The goal is to have tubing that will attach snugly at one end to the syringe and at the other into a hole in your mold.)

To make the edible gummy candy:

  • Small bowl / jar (for mixing)
  • Spoon (for mixing)
  • Microwave (or any other head source for boiling water)
  • 1 box of flavored jello
  • 1 Tbsp unflavored jello
  • 1/3 cup water
  • 1/2 tsp citric acid (optional; add if you want the gummy candy to be sour)

Teacher Notes

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Step 1: Sketch the Candy Design

Before beginning the modeling phase, students should create a rough technical sketch of their proposed candy designs. I don't have a set drawing style I require students to submit, but have included some styles that can be helpful in the image above.

This sketch serves two purposes:

  1. It gives students a chance to think through their designs and add general dimensions, etc. prior to modeling.
  2. It gives you (the teacher) a way to ensure their design is appropriate both in difficulty level and content prior to them beginning the modeling phase of the project.

It is helpful to set some guidelines and/or project constraints for size that students need to take into consideration for their designs. For my project, I limit student mold sizes to 2" x 2" by 0.5" deep (for each side of the mold).

Note: With these sizes, I can generally print each 2-piece mold in about an hour, which makes the 3D printing time manageable for an entire class.

Project extension: This is a great opportunity to introduce or reinforce technical drawing techniques (such as orthographic projections and isometric drawings, annotations, etc.), depending on how much time you have for this project. I have included sketches in each of these styles that reflect the level of sketch I can expect to see in my student's projects.

Step 2: Design/Model Your Candy

Once students have solidified their design, it is time to model the project. I strongly recommend having students become familiar with 3D modeling before beginning this project. Any software you currently teach (that allows you to output a .stl file) should work for this project - so if your students have learned anything from Tinkercad to Solidworks to Catia, this project should work great for you.

Task #1: Create a plane that will serve as the surface where the two molds will come together. Determine where this plane will be in your design (sketch) so you can model it accurately.

Task #2: Build two part bodies: one should be a model of the front half of the shape (see the gray shape in the above images) and the other should be a model of the back half of the shape (see orange shape in above images). The two part bodies should combine to make the total shape (with no overlap) when visible together.


Side note: My engineering students are located in Ohio, near Honda R&D and several Honda auto plants and suppliers. Many local jobs related to this industry use the 3D modeling program Catia, and though this project could be completed with any 3D modeling program, my students complete this project after working through a series of tutorials I created in Catia. Tutorials for Catia are hard to come by, so I have included those tutorials below for reference in case you have the opportunity to use this program. Even if you are not planning to make the gummy mold project, the tutorials given below should be useful to familiarize yourself with this program.

CATIA TUTORIALS


Step 3: Design the Mold for Your Candy

Once your candy shapes are complete, the last step before preparing them to be printed is to "remove" that shape from a box, or mold (as shown above).

Begin by creating a new part body for the box that will become the mold of the front of the candy as shown in the yellow images above. The box sketch should be created on the plane you originally set as the middle of your candy and be slightly larger than the candy footprint (I generally start with 2" x 2" but size up slightly if needed based on the size of the candy model) . Extrude that box sketch slightly past the thickest portion of the candy (approximately 0.5", slightly more if needed).

Then, remove* the candy shape part body from the box part body to create the open mold shape.

Repeat this for the other side of the candy. When done, you should have two mold shapes that show opposing sides of the candy. I have attached the 3D model (created in Catia) of the example elephant candy and the related molds for reference.

*If using Catia, this remove feature can be found in the Boolean Operations toolbar.

Step 4: 3D Print the Molds

Once your mold designs are complete, save each side as an .stl file to 3D print.

Just as the 3D modeling software you use for this project is open to anything your students are familiar with, any 3D printer and related software should work just fine.

My molds were printed on an older Flashforge Creator Pro and turned out nicely. You can print these with very little infill (I used only 10%) since they will only need to stand up to the force of being clamped closed.

I have attached the .stl files for the example elephant candy molds for reference.

Depending on your class size, it may take you a couple of days to get all the molds printed so you can begin making the actual injection mold systems. This is a perfect time to get in depth with content and explain different manufacturing processes.

If you do not already have a starting point to begin a discussion of the injection molding process with your students, HERE is a great animation from Tronicarts to talk through with them. I have discussed our molding machine system in terms of the labels used in this video for consistency.

Step 5: Prepare the Injection Molds

Now comes the fun part: turning your 3D printed designs into an injection molding system.

The first step to prepare your mold is to determine where you will have your gate, which is the location that the liquid material will enter your mold. I always recommend students select an area on the back of their part that has the least detail possible (see the elephant's back in the images above).

Drill through the mold completely and remove any debris, etc. from the mold.

Next, wash your molds next to ensure the candy you produce is clean.

Before closing up the molds, spray them lightly with cooking spray (canola oil, etc.) to help avoid having your candy stuck in your mold when cool.

Line up the molds (ensuring the molds will come together to make the correct internal shape) and tape them tightly closed with masking tape. This simulates the high pressures that are applied to the injection molding machines during the actual manufacturing process.

Finally, ensure your syringe and tubing fit together and into your mold to prepare for the actual candy injection.

Step 6: Melt and Inject the Gummy Solution

There are several recipes I have used for this project in the past, but the best results have come from the following recipe. This will make enough "solution" for several candies, depending on the volumes of each mold.

  • 1 - 3 ounce box flavored gelatin
  • 1 Tbsp unflavored gelatin
  • 1/2 cup boiling water

To prepare the candy solution: Combine the gelatin and mix with the boiling water until the mixture is fully dissolved and not grainy. (Optional: If you want sour candies, add 1/2 tsp of citric acid to your mixture as well.)

Note: If you are looking for an alternative to the recipe above, check out the recipes below:


To inject the solution:

  • Submerge the tip of the syringe in the gelatin solution and pull the plunger until the desired amount has been drawn in. (It's always better to overfill the syringe than under-fill it so you do not run out during injection.)
  • Carefully attach the tubing to the syringe and mold.
  • Inject the solution into the mold slowly and gently until you see excess solution running out the side or top of your mold. (This ensure the mold is completely full.)
  • Remove the tubing and cool the mold in the refrigerator for about a half hour (though up to a day is fine if you want to space this out over two days).

Step 7: Remove the Shaped Candy From the Mold

After the mold has cooled, it is time to remove the part.

Unwrap the tape holding the molds together and slowly pull the mold halves apart. Gently pull up one edge of the gummy and carefully peel it out of the mold. You may need to use a small toothpick or other tool to remove the candy depending on the intricacy of the shape.

And that's it! Your injection molded gummy candy is complete!

For some students, it's hard to eat a project they worked so hard on, so I always let them take the molds home in case they want to make some more candies and/or impress their parents with their gourmet candy production at home.

Step 8: Project Variations

Single Molds

For a simpler version of this project, you can simplify the molding process from injection molding to simply using a single mold to set your shape. The steps for this project are similar except that only one mold is needed and the solution can simply be poured into the mold (as opposed to using the syringe on the taped mold system). This project works great if you have a class who is less savvy with modeling or if you need to squeeze the project into a tight time-frame.


Volume calculations

To amp up this project technically, have students calculate the volume of their gummy candy (using CAD software) and then have them inject only that calculated amount of solution to see if it fills the mold completely. This nicely leads to a discussion about inefficiencies in manufacturing processes (such as the solution left over in the tubing, etc.).

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    8 Discussions

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    tomwall1969

    Tip 12 hours ago

    If you have a big enough printer you could do gelatin molds too. Regarding food safety the best choice in my opinion is PETG.

    1 reply
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    lainealisontomwall1969

    Reply 12 hours ago

    Thanks for the tip! I haven't worked with that material before but will definitely look into it.

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    madaeon

    23 hours ago

    I think the project is a great way to help teaching industrial process;
    anyway, am I missing something or do you say that teaching to cast edible materials in generic 3D printed PLA or ABS, with the result candy safe to eat, is a good practice?
    Because it is not. It is fine if the candy is just for visualizing the process, but not to be eaten.
    You have to use food-grade compatible material otherwise.

    3 replies
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    madaeonlainealison

    Reply 21 hours ago

    The article you mention clearly says:
    "While PLA is safe to use for food and liquids, an article on reprage.com
    warns that many of the hot ends used for 3D printers may release
    materials that are not food safe. Using a stainless steel hot end is one
    way to prevent this problem. Also, most PLA is colored. The coloring in
    the PLA contains additives that are not safe for contact with food. It
    is possible to use “virgin” or “natural” PLA without color that would
    eliminate this risk. Finally, an unavoidable risk with PLA and other 3D
    printing materials is that when printed, objects contain cracks and
    holes that food can easily get stuck in and mold".

    And not to mention that with the market flooded with Chinese 3D printers and their filaments, some of which are so cheap that doubts about effective composition of a "PLA" filament arise. If some user buys a "Fluo iridescent glow in the dark PLA" from Aliexpress, are you confident that it is still "probably safe?"
    And you also mentioned that using ABS is "fine too".

    I still think that this instructable is very nice.
    And if you do it for yourself, use a 3D Printer you know, and you know that material of the hotend, have uncolored PLA filament of known origin (I have heard about a food-safe PLA 3D filament from a company at some point, but I don't remember the name) it is fine.
    If you use this project for teaching you are in some ways responsable, so safety and food related safety is very important.

    Why not replacing edible material with hot glue? I have seen some time ago a good project that emulated micro injection molding with hot glue pressed into the mould, you have many different colors, and no problems with food safety at all.

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    lainealisonmadaeon

    Reply 20 hours ago

    I think you made a couple good points. I do have a stainless steel tip on my printer and though I don't use all natural fibers, I do know where they are coming from and have a general confidence in my filament supplier. I do, however, think I will make a note about this issue in my original Instructable based on your thoughts.

    I think your glue idea may be good for some, but there is something about food-based projects that is just so motivating to students that I feel like the project would be completely different without the goal of actual candy at the end. My students are so geeked to make this - in a way that I fear a glue product would never replicate.

    I agree with you that there is a real responsibility to making projects like this safely with my students and do my best to balance intriguing projects with this responsibility.

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    KarstenHW

    23 hours ago

    Excellent idea! I think I will use this with my students. I also am concerned about the food safety. While this would emulate metal casting much more than plastic injection moulding, you could have them design and print positives and press those into a bed of corn starch. You could even sand the layers of the PLA print smooth to get you a nicer finish. Easier to do if it is a positive. If designed with the proper draft angle, the indentations leave one (or many) negative mould(s) that you can fill with a liquid. Probably not with jello as that is too liquid. Instead maybe with heated gummies? They turn liquid at a temperature not much hotter than the inside of my car in the summer. I know that part from experience. :) Haribo coca cola bottles melted into one piece the shape of the inside of the bag. Hard to eat such a large piece of gummy.
    Check the "How It's Made" youtube video about gummy candy. (https://www.youtube.com/watch?v=4voO0Gpx1J0).

    1 reply
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    lainealisonKarstenHW

    Reply 21 hours ago

    When I first used this project, I did include the draft requirement. In fact, it is a great add on if you have time (maybe I will update the post to include that as a project extension), but it ended up increasing the modeling difficulty and students did not seem to enjoy the project as much, so I now leave it out of the formal requirements and simply discuss it (since the candies come out of the molds easily without draft) instead. The lack of draft in these molds lends nicely to a discussion of the difference between making a part with additive manufacturing processes (like 3D printing) that do not require draft vs. an actual plastic injection machine. Thanks for the comment, thoughts, and ideas, though.
    As for food safety, I commented below on my logic for allowing students to eat their projects, though I certainly would not recommend long term or repeated use of PLA as kitchenware.

    Thanks for the video link. It's great!