This is my first attempt to make a metal hairpin with a sand casting technique. As I always need something to tie my hair while working, I decided to make a pin.

The result is not final, I want to go on with variations of the shape, and certainly, will use a two-part mold. But it can work with thicker models.

What you will need:

- 3D modeling software or a ready 3D model

- software for a 3D printer - I'm using Cura for Ultimaker

- green sand, wooden or metal frames, a torch or a furnace (depending on your metal)

- metal of your choice, aluminum in my case

Let's start!

Step 1: Make a Model

With green sand casting technique, you need an original model to make a mold. You can use an existing object or a 3D print of your digital design.

Use the software you prefer, and save the file as STL to proceed with 3D printing.

I used Rhino to draw my pin, and I attach the STL file if you want to use it.

hair pin.stl
Download View in 3D

Step 2: 3D Print It

Import your file into the slicing program, and set it up for a print. I used PLA, with not too thick wall and top/bottom layers (3-4 mm), open infill and a skirt; you can consider adding a small brim instead to secure a model from shifting on a printing plate.

Here you can see that the file only takes 10 minutes to print.

If you don't have a printer, you can have it done at a local fablab, just bring or send your STL file there!

Step 3: Prepare for Casting

Place your model into the wooden frame big enough to leave some space around, the sand will heat up. Gradually fill it with green sand to the top, pressing it well (but not too hard), to have a precise mold.

I use only 1 frame part, but using 2 parts will give a better result. To do it, while your model is still in the sand, you need to put a fine layer of talk over the sand, place a frame of the same size on top of the one with the model, and fill it with pressed sand as well. Then, take the frames apart, take your model out, and using a thin metal rod make 4 holes through the sand: 2 will let the metal flow into the hollow part between the connected frames, and 2 will let the steam out.

Step 4: Check the Mold

Carefully take your model out, and make sure the mold outlines are clean, and the sand shape is not breaking. At this point, you can still correct the mold by hand, but usually, it is not necessary. If you break the mold... then just take all the sand out and repeat!

Step 5: Melt the Metal

Collect and cut the pieces of aluminum so they fit into a pot for melting or prepare a metal of your choice. With aluminum you can use both a hand torch and a furnace. Aluminum melts at 660 °C.

Step 6: Pour the Metal

Carefully pour the metal into your mold. It will take about 40 minutes for it to cool down, so be very careful. In about 15 minutes you can take the model out with pliers, and put it in the cold water.