Hannah's Assignment 6: Molding and Casting

Design

This assignment was all about molding and casting - creating a meta mold out of machinable wax or 3D printing, a silicone mold, and casting plaster into the mold. My idea for this assignment was to create a 2 part penguin mold. Referencing the student example from class, I chose to do a 2 part mold. I found a penguin STL on Thingiverse and used it for my master part. For the mold itself, I designed the box, sprue, and keys so the two parts can fit together. I chose the machinable wax route for the silicone mold's mold. In other words, the machinable wax is the meta mold. Like everyone else in the class, I used silicone mix for the mold and plaster for the end result.

Process

Step 1: Finding my master part
I wanted to make a fun mold, so I went on Thingiverse to find my master part. I found a cute penguin STL (cited in previous section and at the end of this page) and used that as my master part. This was the easiest part of the entire process of this assignment.

Step 2: Designing the mold
To start the whole molding & casting process of the penguin, I had to design my meta mold. I used Rhino as my CAD software, so I can follow along with the in-class demo video. I used calipers to measure the machinable wax to determine the size of each part of my 2 part meta mold. The machinable wax was 3in x 7in x 1.5 in. Using these measurements, I decided the width, height & depth of my meta molds. I wanted to leave extra machinable wax just in case something went wrong. I used the rectangle tool, extrusion tool, and boolean difference to make 2 mold boxes. The overall box dimension was 77mm tall and 45 mm wide. The bigger box had a depth of 1.5 in and the smaller box had a depth of 1.25 in. Using boolean difference I subtracted the smaller box from the big box. I imported the penguin STL file. I then used scale to make the penguin into a size that would fit the mold. I used MeshSplit to divide the penguin in half down the middle for symmetrical parts.

Then I put each half into its respective mold box. Once I had the two halves in each mold, I created a sprue. The sprue is basically the part that allows for plaster to pour into the 2 part mold. I used the circle tool and extruded the circle to make the sprue. I then used the split tool to cut the cylinder in half and placed it in the appropriate area in each box mold. Once the sprue part was done, I had to create the keys. The keys fit together for the 2 part mold to stick together. I used the circle tool and extruded and capped the circle to create cylinder shaped keys. I had 4 pairs of keys total. 2 pairs were one bigger size, and the other 2 pairs were smaller. The hard part about making the keys was aligning them together. I also had to make the female keys slightly bigger so the male keys can fit. I used boolean difference to make the keys that needed to go into the box.

Boolean difference to make the keys part "sink" into the box on left

Though I had my STL basically ready to go to the milling process, there were a lot of minor adjustments I needed to make to make sure the 2 parts would fit well together. Working on the file itself was frustrating as I spent hours on it to "perfect" it.

Step 3: Fusion 360
When I finished my Rhino file, I exported it into STL. I then opened the STL on Fusion 360. I followed the class demo for the Fusion 360 set up for the toolpath. An issue I had with importing into Fusion 360 is that the scaling became way off. My molds ended up being much bigger than the original size. I had to scale it down. Using math (dividing the original size by the new large size), I scaled down the mold to the appropriate size. I then went into Manufacture mode and went into set up to set up my file for toolpathing with the mill. After set-up, I used adaptive cooling to choose the tool and stepdown size to create the toolpath. I used the simulation tool to see the toolpath. I then went into post process and generated the g code for OtherMill.

Fusion 360 set up settings

Fusion 360 adaptive cooling settings

Step 4: Checking toolpath on BanTam (which led to confusion and frustration)
I wanted to check out the toolpath that Fusion 360 created on BanTam. The whole Fusion 360 set up was meant for the BanTam OtherMill milling machine. Using the video of the in class demo, I played around with the g code file to place the molds into a proper location, so that it could be milled. When I went into preview mode on BanTam, it showed that my molds wouldn't turn out the way I designed them. This was frustrating cause I had no idea how to fix it, so I knew I would have to go to office hours.

Generated toolpath from Fusion 360

Preview on BanTam

Step 5: Using the Shopbot at Fluke
I went to office hours that Nadya held in Fluke on Sunday to get help with my file and with milling my machinable wax. I wanted to know what was going on with my file that led to the preview shown on BanTam. The first time Nadya looked at my file she mentioned about the size of the tool and how much room there is for the tool to get through certain areas. With that information I made adjustments to where the keys were located in the molds and updated my STL.

Another thing I learned was that because we were using the Shopbot to mill, the Fusion 360 g code file wasn't necessary here. The g code from Fusion 360 can be used when using the OtherMill (which I provide up above). All I needed was an STL file to give to Nadya.

When I was ready with my updated STL file, Nadya took another look to make sure it was good to go with the Shopbot and the associated Shopbot program. One thing I didn't consider was the wing of the penguin and how it was propped up. Nadya pointed this out and reminded me that the mill wouldn't be able to get into certain parts to create the wing. If I had 3D printed, the wing wouldn't have been an issue. I had to re-adjust and come up with a new solution: slice the penguin differently. Instead of down the middle to have 2 symmetrical halves, I had to slice down the middle to separate the front and back of the penguin. I wanted to use the same mold I already created to save time and have my file ready for when it was my turn to go on the Shopbot. I re-imported the penguin file into Rhino and used scale to make the penguin the right size to fit in the mold boxes. Then I used MeshSplit to slice the penguin in the new way. I placed each half on its respective mold.

Updated mold on Rhino

Nadya helped me with boolean difference and boolean union to readjust the depth of the molds, so there would be less to mill out of the machinable wax.

Once that was done my FINAL STL file was ready, and Nadya used the Shopbot program to create a toolpath. The file was put onto the Shopbot, I hotglued the machinable wax to a woodenplatform, and with some calibration, it was time to start the rough toolpathing! Once the rough toolpathing was complete, Nadya switched to the rough fine toolpathing. Half an hour or so later, my meta mold was ready!

Milling the machinable wax

Step 6: Cleaning up the wax meta mold
I was happy with how my machinable wax meta mold came out. The only minor thing was that there was some excess wax on the sides of the mold. I went to the MILL to use the knives they have to clean up some of the excess wax in my mold.

Removed as much excess wax as possible

Step 7: Making the silicone mold
Now that I had the meta mold ready, it was time for the silicone mold creation, and to do that, I used Oomoo 30 smooth-on solicone mold making kit. Following the instructions, I mixed equal parts of Part A and Part B together. I made sure that it was fully mixed with no streaks of either color left. When the silicone mix was ready, I poured it into the mold and let it sit for 6 hours.

Silicone mix poured into mold

And voila! The silicone mold turned out. I had a little trouble getting the silicone molds out of the wax meta mold. I used a knife to scrape the sides to help loosen it then gently pull the silicone mold out. I tested the 2 part mold to make sure the keys fit, and it did!

Step 8: Plastering 4 penguins
Now with the silicone mold ready, it was time to plaster! The easy part of this process was putting the 2 part mold together and putting masking tape around to firmly hold the mold. I used the plaster that Lukas had bought and shared with the class. I wasn't entirely sure how to use the plaster as the instuctions on the box involved weighing and using an electric mixer, and I don't have a scale or mixer. Fortunately, some classmates had already used the plaster and shared information on Slack. Shout out to Tien for sharing the ratio and method she used to mix. Using a spoon and a spare cup, I mixed 3 parts of plaster to 1 part water. I used a spoon for the 3:1 ratio. I mixed the plaster until the water and plaster mixed fully then poured the plaster into the mold.

I set my timer to 20 minutes and hoped that the first penguin would turn out. And it did! The only minor issue was that the tip of one wing didn't form, but that's okay.

Since the first penguin turned out fine. I was ready to do the remaining 3 required for this assignment. I just followed the same process I did for the first penguin. Over an hour later, I had all 4 penguins! I left the sprue on cause it makes the penguins look a little taller, but also since my sprues were a little large, I had a hard time removing them. Overall though, I'm pleased with the results!

Peer Teaching: D'Marcus Butler for Rhino tips & tricks; Tien for the plaster information; Nadya for helping me make the mold on the Shopbot in Fluke
Additional Credit: Lukas for providing the plaster that we were all able to use
Source Credit: I found a penguin STL on Thingiverse and used it for my master part. The penguin design can be found here.