16. Molding and casting

For this week group assignment, we have to review the safety data sheets for each of our lab molding and casting materials and make and compare test casts with each of them. The individual assignment is to design a 3D mould, mill it, and use it to cast parts.

Assignment content:

Softwares used:

Machines used:

Safety datasheets:

Final version of this week files:

16.1. Group assignment

For this week the group assignment is to review the safety data sheets for each of our molding and casting materials. Click here to enter the group assignment page.

16.2. Individual assignment

16.2.1. 3D Design

For this assignment I was thinking of making a small and simple design because this is my first time to do molding and casting, so I don't have experience with it and don't know how my design will be made physically. Therefore, I have designed Mickey Mouse face, which basically consists of circles, ellipses, slots, and conic curves. To do the design I have used Fusion 360.

Final Design:

16.2.2. Milling

First, prepare the workpiece that you want to mill. For my design, I used a Wax block. However, the one that is available in the lab is small in size so I've sticked two wax blocks together by heating one of the sides and push them towards each other.

Size of the workpiece after sticking two blocks is 87mm X 76mm X 20mm.

SRP Player was used to prepare my design file for the milling process. First, Open the .stl design file in SRP Player and the steps will be outlined clearly in order on the left side of the screen.

Model Size and Orientation: Set the model size a little bit smaller than the workpiece that will be used for milling, which is 87mm, 76mm, 2mm. Size settings: 75.1mm, 68.61mm, 16mm. Adjust the orentation of the model to face up around z-axis.

Type of Milling: Choose the type of milling as Better surface finish, Model with many curved surfaces, and Block workpiece >> Cut top only.

Create Tool Path: Choose workpiece material as Modeling Wax and set the actual workpiece size so the software can shape the outline around the model. Create tool path needed for the milling; there is a list of tools to choose from. However, I have created my own tool with the follwing settings based on the milling bit that I'll use, which is 1/16 mill:

There are two types of milling operations when cutting a 3D file, which are Rough and Finish cut. the Rough cut is the process of removing the majority of the material quickly with a rough finish. The aim of this process is to remove the most material in the shortest amount of time. While the Finish cut cleans up the part to its final shape and gives a smooth surface finish.

The following screenshot shows the Roughing and Finishing parameters. To understand these parameters read the following points:

Preview Results: This will show you the cutting process before operating the milling machine and will show the estimated cutting time, which is 3.4 hour for my design.

Perform Cuttting: By clicking on Start Cutting... the milling machine will start cutting. But, before that we need to fix the workpiece on the machine bed and setting the origin point.

Mark the centre point of the wax block to adjust the origin point of the machine based on it.

Fix the wax block on the milling machine bed with the aid of a double sided tape.

Click on Start Cutting.. » Next.

The final result of milling shows that the small area between the nose and the line under the eyes is not millied because the milling bit is larger than this area.

16.2.3. Molding

Molding is the process of manufacturing by shaping a material from the cavity of the original model. The material I used for molding is Silicone VBS26-35, which is 2-part addition cure silicone.

Safety measures:

Tools:

I started by filling my model with water then pouring this water into an empty cup and measuring the weight of water in order to determine the amount of material required to fill my model. Water weight = 75 g.

I used "2 Part Addition cure silicone moulding rubber" as the molding material. I wore gloves and opened the 2 materials bottles. I poured 75 g from each material to make 150 g into seperate cups and weight them. Although the filling water weight was 75 g, I made 150 g from the silicon material taking into account its high density and the material that may stick inside the cups.

Later, I poured both materials into one cup and mixed them very well using a wood stick. After mixing, I poured the solution into my model and make sure it fully covered the area of my model.

There were some bubbles in the solution, so I used the heat gun to remove them.

I waited for it to dry and remove it after six hours. Here is the final result of molding:

16.2.4. Casting

For casting I melted a chocolate bar in the microwave and poured it in my mold. I kept the mold with the chocolate in the fridge for 2 hours. But first, I sticked a cling film on my mold before pouring the chocolate because the silison material is not safe for food.

Final result of casting doesn't show the details of the molding shape because the chocolate was not poured directly on the mold. Some lines of the cling film were shown in the casting surface.

Final result:

Three steps of the assignment:

After that, I tried casting with clay and the result was better.