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10. Moulding and casting

This Weeks’ Task:

Group Assignment

  1. Review the safety data sheets for each of your moulding and casting materials, then make and compare test casts with each of them.

Individual Assignment

  1. Design a mould around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.

Group Assignment

Here is the link to the group assignment page.

Individual Assignment

I was thinking of doing my mug coaster as my model, however, in order to do this, it will require two moulds which will be time consuming since my colleagues had to mill their designs as well. Therefore, I just used my previous design that I have done in my CAD assignment. Here is a link to my CAD assignment page.

I placed a star with the letter F in the middle and the completion of the star on the top of the letter. I then just placed a hole in the star to create something like a keychain in order to hang the model. After finishing, I exported it as stl file. Here is a link to my design and below are the steps shown of how I did the design.

  1. On the right, there will be a design toolbar where you can choose the items that you want to create. In addition, there will also be a ‘Tinkercad’ drop down list where you can choose your categories and start design your model. I started off by choosing a star and dragging it onto my workplane.

  2. I then clicked on the object and moved my cursor to any of the four corners, where the dimension lines appeared. I clicked on the numbers and changed by dimensions to 45 mm as shown. You can also use the arrow at the bottom centre of the object to help you in rotating the model.

  3. I clicked on the centre point shown in red to show the height dimension of the model. Click on the number and change it to your desired height.

  4. To explore more in tinkercad, I went to the drop down list and discover the things that are available there. I selected the text and numbers and chose my letter “F” to place it on the star. I also tried rotating the model to see how it works. I just dragged the pointer in the circular labelling shown and the object rotated.

  5. I repeated the same procedures to change the dimensions of the letter.

  6. I dragged the letter so that I can place it in the centre of the star.

  7. To raise the letter above the workplane, click on the object itself, then click on the red cone shaped point that appears on top of the object. Drag this point upwards or change the number manually to raise it up. I only raised it by 3 mm above the plane to make it consistent the design.

  8. I then wanted to create a hole at the top so that I can hang it somewhere or have it as a key chain, therefore, I chose a cylinder to create it. I can either choose a ready hollow cylinder from the basic shapes, or choose a solid cylinder and then change its properties to hole whenever I want to.

  9. I placed the cylinder in the position where I want my hole to be.

  10. I then grouped the 3 shapes together by holding the ‘shift’ button and selecting the objects one at a time, or right click and drag the pointer on the model and all 3 shapes get selected at once. After selecting, click on the group/ungroup icon placed at the top as shown in the image.

Milling

After I have exported the file from tinkercad to stl form, I opened it in the Roland SRP player software in which I will prepare the file for milling. Below are the settings used.

I have used a rectangular wax block for milling my mould.

  1. I entered my model size here.

  2. I chose the type of milling.

  3. I entered the dimensions of the area of which I wanted my model to cut.

  4. The work area dimensions created the boundry around the model. This boundry will be used later to hold the mould.

  5. The tool diameter used.

  6. This is the final result after milling. It went under two surfacing process to make a smooth finish. The first was roughing which defines the shape of the mould and then comes finishing to smooth out all the surfaces and edges.

Moulding

  1. Place an empty container on a balance and tare its weight.

  2. Take a decent amount of the two silicons, catalyst (blue) and base (white), that would be enough for the model. Weigh each of them separately and ensure they are at equal amounts. Here is a link to the safety datasheet.

  3. Combine the two silicon together either by using a roller or your hand until the colour is uniform.

  4. Place the combined silicon on top of the model to create the mould. Leave it for one hour at room temperature and then remove and add the casting material.

Casting

Epoxy

As shown, the mould did not turn out to be completely sharp and neat. This is because instead of building up the silicon in small amounts, I just pushed the entire mould into the model which prevented it from entering the small areas inside.

I roughly took a total amount of 20g to prepare the epoxy, in which I had to used (6g) 30% of hardener and (14g) 70% of resent.

Here is the final result. It took 24 hours for the epoxy to dry completely.

The images below shows the safety data sheet of the epoxy.