Fab Academy 2017
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Molding and Casting


For this week's assignment, It was required to design a 3D mold, machine it, and cast parts from it.

 

Introduction:

Molding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix.[1] This itself may have been made using a pattern or model of the final object. Casting is the opposite manufacturing process, in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then, when solidified, is ejected or broken out of the mold to complete the process.

 

Getting to work:

For this week, I chose to implement a part of my final project. It's the piece of puzzle design, the animal which the kid will use to play. I had in mind to 3D Print it but molding and casting it can be more economical, so I wanted to give it a shot.

I. The Mold:

Generally, to design the mold, you do one of those 2 ways:

  • Machine the positive of the mold (The actual product you want) and then cast the mold using silicon rubber.
  • Machine the negative of the mold directly.

I designed both of them, but I decided to go for the first method to try the silicon rubber casting.

First step, I used CorelDraw to get the outlines of the animal pictures and save it as a DXF file.

Animals outline

For the cast, I chose the monkey as it was challenging as its details are on different levels.

The Monkey outlines

The next step was to take the DXF file on Fusion 360 using "Insert" option, to extrude.

While Extruding, I made sure that the main outline of the monkey face was of "3 mm" thickness to fit in the puzzle board (Polywoof 3 mnn). The ears and the internal face outlines were of "5 mm". The eyes, nose and mouth were of "6.5 mm"

Extruded Moneky.

After saving the file in .STL format, I imported it into SRP Player. The machine I use is Roland Modela MDX-40A

SRP Player:

Working on SRP Pleayer is extremely easy, and this webinar by Roland company was very useful to begin.

 
2. Type of Milling 3. Create tool Path
Creating the tool path 4. Preview your model

Now the model is ready to be cut, so you have to set your piece.

1. Use the double tape to fix your piece in the center of the bed.

2. Fix your tool. The one I used is ZEC-100

Then the Final step is "Startcutting". Before it does, it reviews with you your settings.

Tool review Center Review

Start Cutting.

And Here we Go!

After 6.5 hours, the design was ready.

There was an error in the X direction as you can see in the previous picture.

Casting the Mold:

1. Prepare your material and tools

Adding to those, a plastic or cardboard cup and something to steer with.

2. Calculate roughly the amount of silicon you need and pour it in the cup.

3. Add the hardner which will help your mold to solidify and then steer gently to mix all together and also not include so much air in the mixture.

4. Pour the mixture in the mold.

And Here we go! Let's Wait..

Here is how the mold looked like after I took it out. Take care while taking your mold out, you should add a release agent (it can be simply, soap you use for washing dishes).

Casting:

For the casting, I was advised by our mentor to use Epoxy and I did.

The Epoxy mixture used is mix between the Epoxy itself and the hardener. The ratio that gave good results after trying was 2 (Epoxy): 1 (Harderener).

 

I poured the mixture in the mold and there was no need for release agent, Silicon Rubber doesn't need that and moreover, it affects the quality.

Then I left it to harden, and here is the results!

 
 

The test was pretty successful, Yet the surface finish was bad as the surface finish of the mold itself was bad.

 

Developing for the Final Project:

For the Final project, I need to develop the other 2 pieces of animals: Rabbit and Whale. But this time, I worked on fixing the issues in the Monkey model.

I worked with the same procedures to develop the 3D Model of both animals. I worked on Fusion 360.

 
Whale Model. Rabbit Model.
 

Working on the machine:

In the previous model, I was facing big issue with The machining time and The amount of material wasted. And I need to invetigate that.

After investigation and revisiting the tutorial video, I figured out that the machining time depends mainly on:

1. the Mill bit you use.

2. the material depth you enter: The program "SRP Player" implements the design in the middle of the piece thickness.

 

So what I did was to change the tool to Ball Nose and minimzed the thickness of the block I entered in the program. I did different experiments with the whale and the rabbit.

 
Rabbit: Whale:

End Mill: Ball Nose 6mm.

Piece thickness: 15 mm.

Time taken (Roughing and Finishing): 30 mns.

End Mill: Ball Nose 4mm.

Piece thickness: 9 mm.

Time taken (Roughing and Finishing): 25 - 30 mns.

 

The results were amazing!

 

And here you can see the difference between the 3 models.

 

Finally, following the same procedures for the casting, I got perfect smooth and bubbles-free shapes.