3D Model Injection Molding

Original author: Jeshua Lacock
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Jeshua Lacock writes:
This page describes my first and successful attempt to cast aluminum parts directly from 3D printed PLA models. The process is almost identical to casting from a wax model, but instead of burning wax I burned out PLA (bio-plastic) plastic.

I needed aluminum parts to mount the focusing lens for my 150W CO2 cutting laser. These parts should be able to fit and they should have been mounted on a frame assembled from found aluminum scrap.

I am delighted when I think about the opportunity to do everything in one day: concept -> design -> 3D printing -> finished metal casting.

Step one - design of parts.

I used the amazingly powerful OpenSCADto quickly develop the parts I need. OpenSCAD reads a script in its own language to draw a 3D model. In my case, I just drew the form in Adobe Illustrator and converted it to the OpenSCAD format using the Inkscape plugin .

Here is the design of the second part. I drew two shapes in Illustrator and gave them depth in OpenSCAD. Very fast and easy. Now I have 3D models, it's time to print them!

The process of printing the first part on my Ultimaker (Fast Track).

The resulting item is in the hand.

Print the second part.

The second printed part in the hand.

Checking how both parts fit together.

The sprues and ducts are attached, everything is ready for pouring the molding material.

Molding mass - 50% fine sand and 50% gypsum.

After adding water and thoroughly mixing, I used a homemade food vacuum sealer to get rid of air bubbles in the sand.

The second part is ready for molding!

The first part is poured!

The item is completely immersed in the mixture - I hope everything works out.

Both forms are set for drying.

After a couple of hours, I put the molds in the oven on medium heat.

My new little stove. Heats up quickly for 10 pounds (~ 4.5kg) or less of molten aluminum. 2 times more when flared up.

The forms are good and well done. After warming up to about 1200F (650C), the plastic has no chance. After extracting, I blew the molds with compressed air to blow out any residual ash.

Still hot forms are placed in dry sand. It serves several purposes:
  • additional support, as the forms are quite fragile
  • isolates molds and retains heat when solidified
  • will allow me to install spreaders for sprues (see below). The expander gives additional pressure when casting, and also acts as a riser that remains molten and provides additional metal while the casting solidifies and contracts

My gate spreaders are just clipped aluminum cans. It works great!

After the melting of aluminum with a small addition of copper in the crucible, removal of slag - time to fill!

So cool! It looks like the forms filled perfectly. Now the hard part is to wait long enough for the metal to cool so that I know whether the details turned out or not.

Excellent! The details are straight from the sand, only the sprues and air ducts are cut off.

I cut the center hole with a shallow 14mm tap. Everything seems to be connecting nicely.

I like the details on the casting - you can see all the lines from 3D printing, their width is only 0.2mm.

Moment of truth - are they suitable for the frame? YES! I made a plastic part so that it fits perfectly into the frame, then printed it again with a size increase of 102%. When the aluminum cools down, it shrinks exactly 2%.

The center of the black nipple is where the focused CO2 laser beam comes from. Tube - for compressed air to blow off smoke in the way of the laser (the so-called air-assist).

It looks like I can find a good use for this!

The black hole in the center is the focusing lens.

I am so glad that the parts approached the frame perfectly without additional processing and even without a file!

This is the first test of my laser. Approximately 60% power. Instantly burns a tree.


From the translator:
Jeshua Lacock made a wonderful, practically step-by-step, guide to the method of casting aluminum from plastic models printed on a 3D printer. For those interested in the practical aspect - on the website instructables.com there are many recipes on how to make an aluminum casting furnace . Even from a coffee can !

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