Mohit Ahuja's Fabacademy 2021

Molding and Casting

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Difference between mold and cast:

Molding is defined as the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. A mold is the hollowed-out block that is filled with a liquid or pliable material such as plastic, glass, metal or ceramic raw material.

Casting is a manufacturing process in which a liquid material is poured into a mold, which contains a hollow cavity of the desired shape (mold), and then allowed to solidify. The solidified part is also known as a casting.

(source: Wikipedia)

Group Project

This week's group project was particularly fun for me as I took some weird and interesting materials to test with.

Working with candle wax:

Working with soap

Group Project

Research for the week

For this week, I took to youtube to look for some inspiration, and I found this video by youtuber Alexander Chappel particularly interesting.

In the video he took a multipart, 3D Printed positive mold that he then used to make a vacuum-formed negative mold that he then used to cast the model in white chocolate. We did not have access to a vacuum forming machine, so I did not proceed with this technique, but i thought it was worth mentioning as it is an inspiring idea. I might try it with a simple 3d printed mold instead of making a vacuum formed mold.

Testing the Chinese Desktop milling machine machine

So I had purchased a cheap chinese Desktop milling machine but I had used it very little, about 5-6 times in total. But I really wanted to find some use out of this machine, so I brought it to Vigyan Ashram for testing it. This is a video of my machine milling some foam:

I used Chillipeppr back then to test the machine. It worked really well but when I tried the same with PCB, I gouged a hole in my base and broke a bit. So I was scared of using the machine. But after using the SRM-20, I developed some confidence and understanding about the process of CNC milling. So here is how I started:

Making a test file in Tinkercad

I made a simple shape to test the machine and establish a toolchain which will be used later to mill my assignment's parts.

I took a cube and a hemisphere, and I placed the hemispohere on top of the cube. This is what that looked like:

I then placed another cube which was bigger than the model and used another cube as a hole to hollow it out as shown below:

Then I placed the cube and hemisphere shape in this hollowed out cube and grouped everything together:

This is the tinkercad model:

STL file of the Test piece

Preparing file for millling using mods

To make the file into the toolpath, I decided to try out mods as Suhas Sir had told us that it can be used for CAM modeling too. I had never tried mods for that purpose and this was the perfect opportunity to do so. Here is what I did:

I opened the milling program by going to programs>open program>gcodes%gt;mill 2.5D stl.

I loaded the aforementioned stl file of the model into the program and set the parameters:

Tool Diameter: 3.175mm
Cut Depth: 0.1mm
Max depth: 20mm
Offset: 1
Offset Stepover: 0.5
Spindle speed: 10000 RPM

After that I generated the toolpath and loaded it in Candle, which is a software used for sending G-code via USB to GRBL based CNC controllers:

On observing the toolpath in Candle, I noticed something. The machine was not clearing any material above the 3D object before starting milling there.

I realised that this was happening due to me setting the offset to one. I reset it to zero and I also set the cut depth to 0.3mm to save some time. Then I generated a new toolpath:

This is what it looked like in Candle. Notice the new toolpaths above the shape.

Preparing the machine

After I was happy with the toolpath, I set up the machine with a 1/8 inch 4 flute flat endmill. The machine has a 1/8 inch collet which i used to attach the bit to the spindle motor.

Since I did not want to waste any machining wax in my trial, I decided to use a bar of soap as my testing material. It was pretty dense so I thought that it would be a good substitute for the machining wax.

I used some highly adhesive double sided sticky tape to secure the soap onto the platform.

Then I positioed the endmill manually by moving the x, y and z axes by hand in such a way that the endmill was resting in the front right corner of the upper surface of the soap.

After making sure that everything was set properly, I started sending the g-code to the machine and it started milling successfully.

Results

After the milling process was over, I got this result:

This result made me confident enough in the tool chain that I had established and also gave me an idea of the accuracy of mods.

Final model

Rhino File

To design the 3D file for this week, I wanted to make something that pushes the boundary of this process. So I took a very curvy, organic shaped character of a minion for my object since it has a fairly complex geometry.

I then used Rhino to create a 3D model of the minion. Here is what I did:

I started with a cylindrical shape as the base of the body.

I added two spheres, one at each end of the cylinder:

I then BooleanUnioned the whole shape and bent it by an arbitrary amount to make the base of the body.

After that I added cylinders for the eyes

And some more cylinders for the glasses

Then I shaped the goggles

Then I filleted the edges

Then I added spheres to make the eyes

Then I wanted to add a hinge for the strap of the goggles. I did that by creating a cylinder and filleting the edges.

Then I placed the cylinders next to the goggles and rotated it.

Then I made the strap by using a torus and elongating it in one direction.

I made the strap more realistic by doubling the elongated torus and shifting one of the toruses on top of the other. This is what it looked like:

After this I proceeded to make the mouth of the minion by using the curved line tool, extruding the shape, and then cutting it out of the model by Boolean Difference