Molding and Casting
Assignments
Our tasks for this week are:
- Group assignment:
- review the safety data sheets for each of your molding and casting materials
- make and compare test casts with each of them
- compare 3D printing vs machining molds
- review the safety data sheets for each of your molding and casting materials
- Individual assignment:
- Design a mold around the process you’ll be using, produce it with a smooth surface finish, and use it to cast parts
Group Assignment
Our group documentation can be found here
Material characterization & safety data sheets
We reviewed key information to look for on safety data sheets.
Proper PEE starts with
- gloves to protect your hands
- lab coat to protect clothes
and depending on how nasty the material is, could include something more serious like a respirator and/or eye protection.
In general it’s a good rule of thumb to mix chemicals in a room with good ventilation
3D printing vs machined molds (additive vs subtractive manufacturing processes)
There’s a push to explore 3D printed molds (but with a high-resolution process such as SLA resin, or FDM with some sort of surface finishing process to remove the layer lines). Parts fabricated additively using SLA come off the printer with a great surface finish, and result in very little material waste compared to that generated by subtractive manufacturing (more on that later). However, resin is known to act as a cure inhibitor and in tests performed in our lab as well as others, casts from SLA-printed molds haven’t come out very well. There’s definitely room to optimize this workflow, potentially through use of a coating or barrier between the 3D printed resin and the cast material.
You can machine molds from various materials and of various sizes, depending on your use case. Wax is a common machining material for small-scale molds which can be fabricated on a little CNC. Foam, wood, machineable plastic, etc can be machined on a large format CNC to make larger molds.
Individual Assignment
I continued with the theme of hearts this week and made a food safe mold with which I made a chocolate heart!
Design
I designed my mold in Fusion 360 to be fabricated via 3-axis milling on the CNC.
I found a low-poly royalty free heart 3D model that I liked and imported into Fusion 360, then scaled it in Z to make it a bit higher until I was satisfied with the shape. I modeled my stock material, the wax block I would use to machine my mold, and subtracted a cavity in which the heart would sit in order to create the negative mold.
Mold design considerations:
- Make sure the wax walls are >= 6mm thick or you risk them breaking during the machining process
- no overhangs (or you won’t be able to remove the casting from the mold)
- slight draft angle of the walls & filleting/chamfering at the corners will make it easier to remove the casting from the mold
- make sure to leave enough space around the edges of your shape and the wall of the cavity that the walls of the resulting mold will hold their shape
- make sure to leave enough space at the top of the cavity for the resulting mold to have some structural integrity
CAM for the CNC
We use Modela Player 4 to create the CAM paths to run on the Roland SRM-20 CNCs we have in the lab.
Milling the wax
Casting from the Wax
I used ___, a food-safe mold material.
The final step of preparing my mold was curing it in a 100C oven for 4 hours.
Test Casts
I did test casts with first water (ice) and then chocolate.