How to Make Silicone Molds with a 3D Printer – Casting


3D printing has many capabilities, and people wonder how they can make silicone molds with a 3D printer for casting or creating flexible molds. This article will detail how it is done and some of the best practices.

Keep on reading for more details about how to get this done.

Can You Make Silicone Molds with a 3D Printer?

Yes, you can make silicone molds with a 3D printer. While there are silicone 3D printers which can print some silicone, this technology is still in its infancy as the prints are usually too soft for some practical purposes and, along with the high cost involved, most users prefer casting silicon molds around 3D printed objects.

The following are examples of some silicone mold designs that can be printed with a 3D printer:

You should use food-grade silicone if you plan to use the silicone molds with consumables. Smooth-Sil 940, 950, and 960 are examples of food grade silicons.

How to Make Silicone Molds with a 3D Printer

To make silicone molds with a 3D printer, you will need:

  • 3D printer
  • Silicone stir sticks
  • Modeling clay
  • Mold box
  • Mold release spray or separator
  • The 3D printed model
  • Gloves
  • Safety Goggles
  • Measuring cups or weight scale

Here are the steps to make silicone molds with a 3D printer:

  1. 3D print your model
  2. Remove model and sand support marks
  3. Determine the mold type to cast
  4. 3D print a mold box
  5. Place the mold box around the modeling clay
  6. Seal the gaps between the modeling clay and the box
  7. Mark a half line on the model
  8. Apply separator to the model
  9. Place the model in the model box and press against the modeling clay.
  10. Measure out the silicone
  11. Mix the silicone and pour into the mold box
  12. Let the silicone completely harden and remove from mold box
  13. Remove all the modeling clay & take the mold off the model
  14. Wipe the mold with a separator or spray with release agent
  15. Remove from the shell then cut out channels and ventilation holes.

1. 3D Print Your Model

The model of the structure you want to make a mold of. Get the 3D file of the model and print it with standard settings on a 3D printer. There are lots of resources on the internet where you can get 3D files.

You should note that the quality of the mold you want to make depends on the quality of the printed model.

While most users prefer filament-based printers to resin-based printers because they are cheaper and easier to work with, resin 3D printers can give better quality models because they don’t have visible layer lines and have a much better resolution than filament 3D printers.

2. Remove Model and Sand Supports

This step is required to smooth the 3D printed model. The more well-defined the model is, the more well-defined the silicone mold cast from it will be. Support marks may be a pain to get rid of, but it must be done to make standard silicone molds out of any model.

You should be careful while sanding your model, especially with resin 3D prints, so you don’t deform the model.

3. Determine the Mold Type to Cast

The structure of the model determines the type of mold that would be cast from it. The instructions to be followed for making silicone molds of 3D printed models depend on the type of mold that can be made from the model.

Basically, there are two types of silicone molds that can be cast from a model:

  • One-part silicone molds
  • Multipart silicone molds

One-Part Silicone Molds

One-part silicone molds are molds produced from models that have a flat side, a shallow height, and a very simple shape. Muffin trays, pancake trays, and ice cube trays are examples of this type of mold.

If your model has bulges, then you’ll want to do multipart silicone molds. This is because the model may get stuck with the mold when doing one-part silicone molds and when eventually separated, could ruin the mold cast from them.

Multipart Silicone Molds

Multipart silicone molds are molds produced from models with complex shapes. They are made of two or more separate matching parts containing ventilation holes, which can be attached together to form a 3D cavity for molding.

The silicone is poured into a hole made at the top of the mold. Examples of multipart silicone molds are:

Use this type of silicone mold when the design is complex, has lots of bulges or a large depth.

Even when a model has a flat side and a simple shape, if they have a large depth, then using a one-part silicone mold might not work. An example is something like a pyramid model with a depth of 500mm, since the mold might break when trying to separate it from the model.

You could do a pyramid mold with a depth of around 100mm.

4. 3D Print a Mold Box

The mold box is the housing for the mold. It is the structure that holds the silicone around the model in place while casting the silicone mold.

The mold box should have at least four walls for solidity, with two open faces so that you can pour silicone through one face and seal the other face with modeling clay. To 3D print the mold box, you should:

  • Measure the dimensions of the model
  • Multiply the model’s length and width by at least 115% each, this will be the mold box’s width and length
  • Multiply the model’s height by at least 125%, this will be the mold box’s height
  • Use these new dimensions to model a box with two open faces on opposite ends
  • 3D print the box with a 3D printer

The reason for making the box larger than the model is to give allowances to the model when placed in the mold box and prevent overflow of silicone.

Here’s an example of the dimensions for a mold box:

  • Model length: 20mm – Mold box length: 23mm (20 * 1.15)
  • Model width: 10mm – Mold box width: 11.5mm (10 * 1.15)
  • Model height: 20mm – Mold box height: 25mm ( 20 * 1.25)

5. Place the Mold Box Around Modeling Clay

  • Spread out the modeling clay on a sheet or any other flat material in such a way that it will completely cover one of the open faces of the mold box.
  • Add registration keys, which are small holes to the modeling clay for easy alignment with the mold box.
  • Place the mold box on the spread out modeling clay with one of its open faces resting on the modeling clay.

The modeling clay is there to prevent silicone from pouring out of the mold box.

6. Seal Gaps Between Modeling Clay

Seal the seam formed by the open face of the mold box and the modeling clay by pressing the edges of the modeling clay against the mold box with the silicone stir sticks or any other convenient solid object you can find. Ensure there is no gap in the seam, as this can cause leakage of silicone.

7. Mark a Half Line on the Model

This step is necessary for a two-part silicone mold. Use a marker to mark a half line around the model.

8. Apply Separator to the 3D Model

Separators and release sprays are chemical compounds that form a thin coat on a model when applied to it. This layer makes it easy to pull the mold of the 3D model after the silicone hardens.

9. Place the Model in the Model Box and Press Against Clay

Place the model in the mold box and carefully press against it the modeling clay at the bottom of the mold box until the modeling clay covers half of the model. This is why the half line is drawn on the model so you can identify the model’s half point.

Apply the separator with a brush to the model, or if you are using a release agent spray, spray the model thoroughly with the release agent spray.

10. Measure out the Silicone

The volume of the silicone needed for the model is equal to the volume of the 3D printed model subtracted from the volume of the mold box.

You can calculate the volume of your mold box by multiplying its width, length, and height. The best way to do this is to use a program that automatically calculates the volume of a 3D model like Netfabb or Solidworks.

Put on your safety goggles and gloves because measuring and mixing silicone can get messy.

Since silicone comes in two parts (part A and part B), which are the base and the catalyst, you have to mix both together thoroughly before the silicone can be used for casting. Each silicone brand has a mix ratio.

This mix ratio determines the amount of base mixed with the amount of catalyst. There are two ways you can mix silicone, namely:

Most silicone brands include measuring cups in the silicone package. For mixture by volume ratio, a certain volume of part A, the base, is mixed with a certain volume of part B, the catalyst, according to the silicone mix ratio.

An example would be the Lets Resin Silicone Mold Making Kit from Amazon which has a mix ratio of 1:1. This would mean, to create 100ml of silicone, you would need 50ml of part A and 50ml of part B.

11. Mix the Silicone and Pour into Mold Box

  • Pour both parts A and B of the silicone into a container and mix thoroughly with the silicone stir stick. Make sure there is no settlement in the mixture.
  • Pour the mixture into the mold box

12. Let the Silicone Completely Harden and Take Off the Mold Box

The time it takes the silicone to harden is the setting time. The setting time begins to count upon the mixture of parts A and B of the silicone.

Some silicone mixes have a setting time of 1 hour, while others can be shorter, taking just 20 minutes. Check the details of the silicone rubber you purchased for its setting time.

It’s recommended to leave some extra time, up to another hour to ensure the silicone rubber has completely hardened. This helps to prevent the silicone from deforming when removed from the mold box.

13. Remove all the Modeling Clay & Take the Mold off the Model

Remove the modeling clay from the face of the model pressed against it.

Pull the cast mold off the model. This should be easy if a separator or release agent was applied to the surface of the model before pouring silicone over it.

If you are making a one-part silicone mold, you are done with your mold, but if you are making a multipart silicone mold, like a two-part silicone mold, continue with the steps below.

14. Wipe the Mold with Separator and Pour Silicone in the Other Half

Repeat step four by wiping the other half with a separator or spraying with release agent spray. Take note that the other face you want to cast should face upward when placed in the mold box.

15. Remove From the Mold Box then Cut Out Channels and Ventilation Holes

Remove the mold from the mold box and carefully cut out a pouring hole for you to pour silicone through at the top of the mold. Don’t forget to cut out ventilation holes. And you are done with your mold. You should attach the mold together with a tape or rubber band to use for a two-part silicone mold.

Check out the video below by Josef Prusa who shows these steps visually.

Best 3D Printer for Silicone Molds

The best 3D printer for silicone molds would be the Elegoo Mars 3 Pro for higher quality models, and the Creality Ender 3 S1 for larger models.

The best 3D printers for silicone molds are:

  • Creality Ender 3 S1
  • Elegoo Mars 3 Pro

Creality Ender 3 S1

Features

  • Dual Gear Direct Drive Extruder
  • CR-Touch Automatic Bed Leveling
  • High Precision Dual Z-Axis
  • 32-Bit Silent Mainboard
  • Quick 6-Step Assembling – 96% Pre-Installed
  • PC Spring Steel Print Sheet
  • 4.3-Inch LCD Screen
  • Filament Runout Sensor
  • Power Loss Print Recovery
  • XY Knob Belt Tensioners
  • International Certification & Quality Assurance

Pros

  • Print quality is fantastic for FDM printing from the first print without tuning, with a 0.05mm maximum resolution.
  • Assembly is very quick compared to most 3D printers, only requiring 6 steps
  • Leveling is automatic which makes operation a lot easier to handle
  • Has compatibility with many filaments including flexibles due to the direct drive extruder
  • Belt tensioning is made easier with the tensioner knobs for the X & Y axis
  • The integrated toolbox clears up space by allowing you to keep your tools within the 3D printer
  • Dual Z-axis with the connected belt increases stability for better print quality

Cons

  • Doesn’t have a touchscreen display, but it’s still really easy to operate
  • The fan duct blocks the front view of the printing process, so you’ll have to look at the nozzle from the sides.
  • The cable at the back of the bed has a long rubber guard which gives it less space for bed clearance
  • Doesn’t let you mute the beeping sound for the display screen
  • When you select a print it starts off heating just the bed, but not both the bed and the nozzle. It does heat both at the same time when you select “Preheat PLA”.
  • No option I could see to change the color of the CR-Touch sensor from the pink/purple color

With a powerful filament extruding force, multiple filament compatibility, and a relatively large build size plus an easy to handle print bed, the Creality Ender 3 S1 is great for silicone molds.

Elegoo Mars 3 Pro

Features

  • 6.6″4K Monochrome LCD
  • Powerful COB Light Source
  • Sandblasted Build Plate
  • Mini Air Purifier with Activated Carbon
  • 3.5″ Touchscreen
  • PFA Release Liner
  • Unique Heat Dissipation and High-Speed Cooling
  • ChiTuBox Slicer

Pros

  • Produces high quality 3D prints
  • Low energy consumption and heat emission – increased service life of the monochrome display
  • Fast print speeds
  • Easier surface cleaning and higher corrosion resistance
  • Easy-to-grip Allen head screw for easy levelling
  • The built-in plug filter works well reduce odors
  • Operation is simple and easy to use for beginners
  • Replacements are easier to source than other 3D printers

Cons

  • No significant cons to mention

With accurate and relatively large prints, you can’t go wrong with Elegoo Mars 3 Pro for 3D models. Its easy calibration and decent print volume make it one of the best printers on the market for making silicone molds.

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