WEEK 12

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WEEK ·12·

MOLDING AND CASTING

INDIVIDUAL ASSIGNMENT

1. design a 3D mold, machine it, and cast parts from it

1. MAKING THE 3D DESIGN AND SETTING UP THE MODELA

I design the 3d object using the SketchUp program. I measured the wax mold I was going to use and create a border that allowed me to place the 3d object in the center. This is how the object will finally come out.

The 3d object must be exported in extension .stl

First you must select the option mm, 1/8 wax rough in the top menu, this is the option to carve the mold. Then you must load the stl file and in the middle menu click on make.png, then in stl units place 10 to get to the scale of my object.

Then click on make path, place the coordinates and click make .rml to calculate the time. The total time for this first process is 54 minutes.

The second process is the finishing. In the top menu choose mm 1/8 wax finish, then you have to upload the stl file and click make .png in the middle menu. Also put 10 in stl units to achieve the scale of my object.

Then click on make path. In overlap (0-1) set 0.75 so the finish is finer. Then click on make .rml to calculate the time, the total time for this process is 28 minutes.

The machine mills the wax block first one way and then the other. It works in layers.

The estimated time for the first process was 54 minutes, but it end up taking 76 minutes. So it is good to calculate extra time.

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2. MAKING THE WAX MOLD

To make the first mold I used a block of wax. With the Modela machine this wax mold is carved according to the shape elaborated in 3d.

After an hour the mold was ready, well "ready". While milling the block of wax, the plug of the machine was moved and it turned off. I had to re-mill from scratch. When finished, the back wall was detached from the block. The undercoat was so thin that it came off easily.

The design was detached from the wax mold.

I decided to fix the mold using pieces of mdf 3mm cutted in the laser cutter and stuck then with heavy duty tape. The 3d object was placed in the center using hot silicone.

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3. MAKING THE SILICON MOLD

To make the mold in negative, I used F-30 PLUS silicone (it is more resistant) and this is combined with a catalyst that will make the silicone seal.

You need a gram to calculate the amount of material you are going to use (to avoid any waste of material)

Silicone is very viscous so have patience when pouring it.

I used a little more than 200 grams of F-30 plus silicone.

48/5000 To this weight correspond 4 grams of catalyst

Then carefully pour the catalyst over the silicone.

And you should move the mixture as fast as possible to avoid lumps. Being so dense the task becomes a bit complex but does not take long.

When the mixture is ready, pour it over the mold.

Do not forget to wear gloves. I used my hands to press the silicone as much as possible to avoid having any voids.

Then tap the mold gently against the desk to seat the silicone.

This is how the silicone mixture remains inside the wax mold.

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4. MAKING THE FINAL PIECE IN CEMENT

I let the mold dry for 3 days. It was easy to remove the silicone from the MDF edges because they were coated with heavy duty tape.

The piece came out easily from the mold, even though the inner edges were not completely dry (90%).

This is how the silicone mold looks.

For the mix we used HydroStone Super X, a very resistant cement.

In the package are the instructions to prepare the mixture. Place 2 parts of water per 100 parts of cement.

I used 117 grams of cement ...

... and 22 grams of water.

The cement is poured slowly into the water container.

You have to move evenly, at first the mixture is fairly liquid.

Slowly raise cement in the mix. Do not pour all the cement because it will be difficult to mix everything evenly.

The more cement in the mixture the thicker it becomes, the more even mixing the mixture becomes liquid and it's easier to mix.

Once everything is mixed, poured it into the silicone mold.

I advise to give small strokes of the mold against the table to put the mixture well.

Despite having placed a little less water the mixture came out well. The amount was accurate for my mold.

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5. MAKING THE FINAL PIECE IN CEMENT

I let the mixture dry for 6 hours and then remove the piece of cement from the silicone mold. It came out without problems.

These are the steps of this assignment. 1. Make the wax mold (blue color) 2. Make the negative mold in silicone (white color) 3. Make the piece in cement (gray color)

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