8. Moulding and casting¶
This week I worked on creating molds and casts for making objects with different materials.
Introduction¶
Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying direction on one or several axes, cutter head speed, and pressure.
Molding is a process that takes the negative reflection of a model and creating a cavity. Molds can be made of a rigid material, such as plaster or plastic resin or more commonly, a flexible material such as rubber.
Image source
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.
Group Assignment¶
In this group assignment we were introduced to four casting materials like silicon, dry putty, standard plaster and resin. We went through the safety instructions for each material, the process steps, the mixing ratio and other informations like the Work time and Cure time. You can access more information in the This link.
Indivisual Assignment¶
Designs¶
Two models were designed using fusion 360 tool, saved as STL files and sent to the milling machine for making the first positive mold from wax.
Elephant design¶
The first design is an elephant. The below picture shows the medal from which I got inspired.
First create the base for the elephant body
Fillet the corners
Make the borders for the elephant body
Draw the details for the ear and eyes
Extrude The surfaces
Click Here to download the stl file
Click Here to download the CAD file
Ionizing radiation sign design¶
Create four concentric circles
Draw two lines each on 30 degrees
Cut the extra lines
Extrude the surfaces
Click Here to download the stl file
Click Here to download the CAD file
The milling machine settings¶
Later are the settings for the milling process.
Prepare the models with the proper sizes
Choose the total dimensions of the models
choose the rotation degrees around the z axis
Select the type of milling
Prepare the workplace size
Preveiw the results
The sign model details were linked together as the milling precision chosen was not enough for them to be done.
Now the milling pin has to be placed at the center of the wax bar and directly in touch with it.
The suitable pin size that matches the precision of the model will be shown
Creating the wax base for the positive mold¶
In this project we used monoFab SRM-20 Desktop Milling Machine
The wax bar
Fix the wax bar with bouble sided sticky tape
The milling pin used
The Positive mold
Creating the silicon mold¶
In this part we used silicon, we already tested it in the group assignments for Safety Don’t ingest, inject and absorb silicone in your body.
To make the silicon mold first weigh the wax bar
Fill the cavity with water. Add 10 grams on the water weight this creates the total weight of the silicon mold
Put half the total weight from material A
And the other half from material B
Mix them well
Pour them is the wax mold
The silicon mold after getting dried
Making the cast¶
I chose to use resin as the material for the cast. for safety:
-Make sure to keep away from kids.
-Should be stored in a dry place. Preferably in the sealed original container, at a temperature between 20c & 25c.
-Wear face masks for pregnants when using the product.
-Wear protective gloves when you use the product.
-Do not swallow. If you swallowed the resin, call a doctor immediately.
-In case the product comes in contact with eyes : rinse cautiously with water for several minutes.
-Caution it may cause an allergic skin reaction.
Add a ratio of 6g the hardener to 10g of the resin and mix for 3 min
Pour the colored mix in the mold
The casts after drying
The three steps of creating the casts
Problems and challenges¶
The Silicon mold mixing ratio was a bit off so it’s structure was not perfect (not completely solid) so the surface was stained with fingerprints which appeared in the final cast. To avoid that from happening follow the mixing ratio precisely and give the mixture enough time to dry without touching it.
Useful links¶
-What is the difference between molding and casting?