Molding and casting

In this week we have to make a 3D design, then make a mold of the design, and finally cast parts from it.

The first design

I made a design of a coin with my first name intial in Arabic on top of it. My name is Ahmed and this is how it is written in Arabic أحمد. In arabic we read from right to left. So the first letter of name is أ which is equivalent to A in English.

Here is my design, I made it I using fusion 360.



Then I wanted to convert it from stl to rml to mill using SRM-20 desctop milling machine. So, I opened Fab Modules to generate the toolpath of the 3D model but I click calculate, the browser get crashed and nothing happens later. I tried with many browsers and even I tried changing the computer but this didn't solve the problem.

Then, I decided to 3D print the design I made instead of milling it on wax. Here is the design after priting it.



But our guru Francisco told me that this is not accepted and I have to mill the design.

The second design

So I switched to Antimony because with this program I can export height map of the design and then Fab Modules will be able to generate the toolpath.

It is my first time working with this program. I can see that it is a lot different that all the 3D design programs I worked with before. In this program, you program the 3D model you want to make. It was difficult for me at the beginning but then it got easier.

For my design I wanted to make an islamic dome. To generate it with this program. I made one sphere, and then I subtracted a cube from it. Then, I added a new small sphere on top of it.

There were some constraints of course. One is the normal constraints of any milling operation. The other constraint I had was the size of the wax which was 176mm76mm39mm. I had to keep exrta 5 mm of each side of the wax so it don't break.

Here is my antimony design.



Here is the height map, I cropped the black edges with Gimp:





For making the tool path I used web based Fab Modules, the most important thing is to put the setting for height map:



Here is the tool path for roughing



Here is the tool path for finishing



After having the rml files ready, for roughing and then finishing. You prepare your wax by fixing it on the bed. Then you upload the rml file after zeroing xyz. You have to write down xy machine coordinates because it will the same for finishing. The the finished design after milling it:



Collecting the chips to melt them and use them again:



Preparing the mold

First of all I measure the volume needed to make the silicone mold. I poured water, and then I measured its volume.



The volumes is 56 mL = 56 cc, but I going to prepare 25% more because part of the silicon will stick in the mixing cup. 56 cc * 1.25 = 70 cc

Then, I started reading the saftey intructions.



After reading it, I knew that I need protective gloves, protective clothing, eye protection and face protection.



The product has two componentes, Part A and Part B.



They should be mixed with this weight ratio 100A:10B.



I have the volume but I need the weight. I found the Specific Gravity of the silicon mixture on the instructions paper and it is 1.18 g/cc. So the weight I need is 70 cc * 1.18 g/cc = 82.6 gram.

A weight = (100/110) * 82.6 = 75.1 gram B weight = (10/110) * 82.6 = 7.5 gram





Then, I started mixing them and then I poured them on the wax. You can see that there is some white regions from Part A of the silicon. This shouldn't be there. This is because I didn't mix well enough.







Then I put it inside a Vacuum bag, to remove the bubbles.





I left it for 16 hours as writted in the intructions. and Here is the result.







I melted candle wax and poured it in the mold:









Here is the final result:



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