Introduction: The Beginners Guide to Sand Casting 3D Printed Models

By
About: I'm a designer from the UK currently doing a masters at The Royal Academy of Art Den Haag.

This was my first attempt at sand casting a 3D printed model. I will give you the dos and don'ts from a beginners perspective.

Sand casting is a process that usually uses a mould made from either metal, wood, or wax but We're trying it with 3D printed PLA models. The models create a negative impression in a special clay like sand that will be the mould for the molten metal in our case aluminium. This mould is then filled with a molten aluminium that is left to cool and solidify.

Step 1: Preparation

  • Things you will need:

Tools

  • Access to a 3D printer.
  • Hack saw
  • Form work box for sand
  • mallet/ hammer/ piece of wood 2"x2"
  • blow torch
  • oven
  • slotted metal spoon
  • steel pot
  • clamps
  • MIG Welder
  • Polisher

Materials

  • PLA
  • Casting Sand
  • Aluminium
  • Aluminium pipe
  • Polishing salves

Saftey Equipment

  • Leather shoes
  • Leather apron
  • Leather gloves
  • coat
  • Googles

DO

  • Be Prepared

DON'T

  • Be a fool

Step 2: Quick Safety Brief

  1. Wear safety equipment at all times
  2. Don't touch any metal objects you don't know how hot they are.
  3. Clear any hazards that are in the workspace.
  4. Do not spill any metal onto the floor, especially concrete floor as it can cause an explosion.
  5. Be cautious of your surroundings
  6. Be wary of any surfaces that may be hot.

Step 3: Download 3D Printed Model/ Edit

This step is optional you can use whatever you want to cast. However if you would like a pair of these very fetching earrings then either download them as they are or edit the design to tailor to your own personal taste. I have also added a few other earring designs on the model which you are welcome to try and cast however I don’t know the logistics of how some of these would be cast.

Step 4: 3D Print Model

  1. Download the G-CODE for untimaker printer. Or if using a different printer or if you edited or created your own model save the model as a stl file (or download the stl file of my model) then open it in Cura/ Slic3r (both free software). Here you can generate your G-code relevant to whatever printer you will use.
  2. Save on a SD card
  3. Insert the SD card into the printer and press print.

Step 5: Filling the Form With Sand

  1. Choose what form box you will need. A. A split box: if both sides have a pattern and the middle of the object is the widest point.Test the object can be lifted out. B Single box: where one side is a flat surface and goes from a wide base to a narrow top. C complete submersion. If your object is too complex and can't be lifted out the sand without disrupting it. The object will be submerges and the PLA will melt away when the molten metal is poured in.

Single Box

  1. Handful by handful fill you form box compacting as you go. Fill and compact your form box to the top.
  2. Insert your object on the surface of the sand creating a negative imprint. Sink the object flush with the surface of the sand.

Split Box

  1. Handful by handful fill you form box compacting as you go. Fill and compact your form box to the top.
  2. Repeat for second box.

  3. Insert your object on the surface of the sand. Sink the object half way into the surface of the sand creating a negative imprint.

  4. Place the second form box on top to imprint the top of the object then release.

Submerged

  1. Handful by handful fill you form box compacting as you go. Place your object in the middle of the box and compact around it filling and compacting to the top of the form box.

DOS

  1. Be patient when compacting the sand. Take your time. The more compact the sand the better and stronger the imprint will be.

DON'TS

  1. Forget to fill in the corners. This can make the sand unstable in the box and cause it to all fall out.

Step 6: Boring Pour Holes and Exit Holes

This is only for the split box and submerged box method.

We need to create holes to pour the molten metal into the imprint/ object and the release exit holes to allow the molten metal to flow.

  1. Create the pour hole. This need to be as big as possible without ruining your design. I used a 1cm pipe. Insert the pipe to the highest point of your object. The shorter the distance between the surface of the sand and the object the less heat will be lost in the sand when the metal is poured.
  2. Create exit holes. There needs to be a minimum of 2 at the furthest points from the pour hole. this will encourage the metal to flow to all areas of the imprint.

DOS

  • Be careful when boring pour and exit holes. It is very easy to damage your imprint.

DON'TS

  • Make your holes too small

Step 7: Remove the Model From the Sand

Only for the single box, and split box method.

Gently remove the object from the sand. There should be a perfect imprint of your object.

Step 8: Melt Aluminium

  1. Place scrap aluminium in a steel pot.
  2. place scrap aluminium in pot
  3. preset oven to 900 degrees C
  4. Place pot with aluminium in oven using tongues and wearing all safety equipment.
  5. Leave for 30 minutes or until nearly molten.
  6. Remove using tongues and finish heating with a blow torch.
  7. Use a slotted steel spoon to remove the impurities

DOS

  • Remove all impurities on the surface. these will be a different colour. The impurities will make the molten metal less fluid and potential lead to a failed cast

DON'TS

  • Uses anything other than a steel pot or a steel slotted spoon. Steel has a higher melting point than

Step 9: Pouring the Molten Aluminium

As soon as all the aluminium is molten then pour it efficiently into the imprints via the pour holes or directly into the imprint if using the single box method.

DOS

DON'T

  • Dilly dally. The molten metal will cool.
  • Panic

Step 10: Cracking the Mould and Removing Cast Object

After waiting at least 15 minutes remove the object from the form.

DOS

  • Use gloves. The object could still be hot
  • Remove the sand in a tray to use for another time.

DON'TS

Step 11: Run Earrings Under Cold Water.

If still hot run the object under cold water using tongues.

Step 12: Finishing

  1. Sand off unwanted parts
  2. Polish if desired.

DOS

  • Wear gloves for sanding the metal can get hot.

DON'TS

  • Wear gloves for polishing. As gloves can get pulled into machine and break your arm.
  • Polish object on the top of the polishing wheel and the object will whip around. Make sure you polish from the bottom of the polishing wheel.

Step 13: Welding (optional)

This step is not necessary. The model includes the detail that goes through your ear so you can just cast it. However if it doesn't cast well you can always weld a piece on the back.

  1. Find a piece of Aluminium pipe. As thin as possible.
  2. I used a MIG welder (Variostar 2500). This is a semi-automatic and requires electricity to produce heat, an electrode to fill the joint and a shielding gas to protect the weld from the air which causes oxygen bubbles in the metal and oxidisation.
  3. Hold the pipe gently on the back be careful not to add too much pressure because the pipe will slip around.
  4. Then apply the torch for a couple of seconds and the pipe should be welded to the back of the earring.
  5. Cut the pipe to the desired length around 1cm.

If you would rather dangling earrings simple drill a hole in the soft metal and add a hook.