13. Molding and Casting¶

Group Assignment¶

To view the group assignment click here.

Individual Assignments¶

The required in this week is to design a 3D mold around the stock and tooling, mill it and use it to cast parts.

Molding and Casting Difference¶

Molding or Moldmaking is the act of creating the cavity that carries a reverse impression of an original model. Molds can be made of a rigid material, such as plaster or plastic resin or more commonly, a flexible material such as rubber. The material to use should be chosen considering the material of the model.

Casting is the act of pouring liquid material into the cavity of a mold. After a period of time, this liquid will cure via chemical reaction or cooling. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay.

3D Mold Design Using Fusion360¶

I watch How to Create a One-Part Mold in Fusion 360 tutorial to help me designing my mold.

It is only four easy steps, but first you need to know the size of the mold cube that will be milled, to know the design boundaries. (Mostly this mold template can be thawed and shaped to the size we want). My mold cube volume is 4 * 4 * 10 cm^3.

First, you have to draw the borders of the template (length * width). After that sketch the object you want. I sketch the Safe Key for COVID-19, which is necessary in this period due to the current conditions. I also sketch a heart, I watch Modeling HEART tutorial to help me sketch the heart.
Secondly, I “extrude” the objects, and used the “Fillet” feature to twist the heart.
Third, extrude the mold frame by its height, to make the mold template.
Fourth, to cavite the objects I design from the template I used the “combine” feature by “cut” operation. I specify the template as the target body and specified the two objects as a tool.
This is the final result ready to mill.

This is the shape if I want to print it directly in 3D, but because I am going to mill it, I will be satisfied with the 3D design of the object.

Milling Mold by Roland SRM-20¶

I will experiment with milling twice using a different CAM program, once to mill the heart template using “MODELA Player4” software, and once again to mill the Safekey template with “SPR Player” software. For both of them, I will use them a 4*10cm template of wax.

I saved models to “.stl” file format for opening them in the CAM softwares to make milling routes.

Heart Keychain Using MODELA Player4¶

Here I will use the “MODELA Player4”, and in it I will drill twice, the first of which is that I will define the shape of the heart in it using “Roughing Cutting Path” and the second process is smoothing the heart using “Finishing Cutting Path”.

First, import the .stl mold design in Modela Player4.
I will choose the option to change the tool that I will use for milling.

Roughing Path

Start “New Process” to choose the type of cutting path, I choose “roughing”. Click on “Next >” to complete the milling settings.
Here I will specify the type of drill bit, I will use 2.38mm square drill bit. Click on “Next >”.
I Set roughing cutting parameters
This is the roughing path.

Finishing Path
The finishing path setting is the same with the roughing setting. Start “New Process” and just choose the type of process “finishing” and change the drill bit tool.

Sending the File
- I pressed the button in the bottom right of the screen to send the file to “SRM2-0” to start milling.

This window will appear, which shows us the percentage of completion of the “Roughing Path”, which as soon as it is finished, asks us to change the drill bit to start “Finishing Path”.

Result of Roughing
- Thus the template was drilled outside the boundaries of the wax, I would not be able to pour the mold solution into it. I had to put a larger wax or have a smaller heart. This was the result of the “Roughing” cutting, and there was no need for the “Finishing” cutting.

Safe Key Using SPR Player¶

First, I import the .stl mold design in SRP Player. In this program, the steps are clear at the right of the screen, just I have to follow them one by one.
First, I set the dimensions of the wax template, the orientation of the model so that the model faces up around Z-axis.
Second, specify the type of milling.
Third, create the toolpath. Here you can change the height of the object from the z-axis.
Here you can see the final shape of the template, and it appears that the lettering and the ornament will not be engraved clearly.
The last step is to click on “Start Cutting” and select the cutting origin point which can be located in the middle of the wax template from the top or the bottom. I chose the top origin point, I had to determine this point by measuring the length and width of the wax piece and place a mark in the middle, and then I determine this point with drill bit using the SRM-20 software.
Click “Next” to start the milling.
This result is after the termination of the milling.

Molding¶

Click to read the safety data sheets for two Part Addition cure silicone molding rubber, the mold material.

Now, I have to pour the molding solution into this template after cleaning it with water. I measured the weight of the water that occupies the mold, which is 27 grams, to determine the amount that I will produce from the pouring material.
The solution is “two Part Addition cure silicone molding rubber”. Taking into account the density of the solution that exceeds the density of the water, as well as the remnants of the solution that will stick to the inside of the cup, I mixed 25 grams of each solution. I should well stirred the two solutions to ensure the material is uniform.
I poured this solution into the mold, and I’ll wait for it to dry. I came to it the next day.
This is the mold ready.

Casting¶

Click to read the safety data sheets for Gypsum, the cast material.

To make the mixture, I added 32 grams of water to 15 grams of gypsum. I mixed it thoroughly, but the mixture looked inconsistent (liquid like water).

To increase the density of the mixture, I searched the internet and found that the amount of water should be equal to the amount of gypsum, so I added 13 grams of gypsum.

I poured the mixture into the mold and removed the excess.

It took the mixture about two hours to dry, the result was weak because two part broke when I removed it from the mold, I think because these areas were thin.