Group members: Antonija, Katherine, Xinyin (Sing), Wen-Yi

In the mid-term project, we used two fabrication methods to make the LUCIA cervical model set. One set was created by 3D printing, and the other by molding and casting. We chose to produce the model of vascular changes as the finished product, which is 1I, 2I, 1J, and 2J in the model.

Our Process:

Making 3D printing models:

1.  We downloaded the STL files of 1I, 2I, 1J, and 2J from Canvas and imported them into Bambu Slicer to start printing.
2. Our initial layer height setting was 0.2 mm. However, another group told us that 0.2 mm layer height would create unsmooth layers on the top of the models. 
3. At the same time, we also imported the files into Tinkercad and made a CAD model (box with four cervical models).
4. A spaghetti defect occurred after we started printing for several minutes, so we canceled this process and reprinted the four models and the CAD model together with 0.09 mm layer height. It took 9 hours and 28 minutes to print everything we needed.
5. After printing, our four models were all good, but there were some problems with our CAD model. There was a gap between a slant and a wall, and the box seemed too small(85mm x 85mm x 35mm), which might be a challenge for silicone mold demolding. (Version 1)
6. We made the CAD model larger into 90mm x 90mm x 35mm but accidentally enlarged the cervical model inside. (Version 2) 
7. We corrected it and reprinted it again, but the cervical model inside showed artificial lines and was not smooth. (Version 3)
8. We lowered the printing speed to improve the printing quality and changed the layer height to 0.08mm. (Version 4) Finally, this version came out successfully.
9. Below are pictures of the file processed by Bambu Slicer, and the different versions of our CAD model:

   v1. v2.v3. v4.

Making Silicone Mold:

1. We combined 110 mL silicone part A with 110 mL part B, mixed them, and poured them into the CAD model.
2. We left it to cure for about 7.5 hours, then used a flathead screwdriver and spatula to help us de-mold.
3. Below are pictures of making silicone mold and demolding:

Casting (Using Smooth-Cast 300):

1. We combined 40 mL part A with 40 mL part B, mixed them (for 1 minute 30 seconds), and poured them into the silicone mold.
2. Let it cure for ten minutes, and then we de-mold it.
3. After demolding, we realized that there might have been some tiny bubbles getting into our models while we were mixing and pouring the smooth-cast into our silicone mold. The numbers on our casting models didn’t come out well, and the top of 1I had many tiny holes. Thus, we decided to make them again.
4. We tried twice afterward. The first time, we used the vibration of a handheld sander to vibrate the table and added mold spray to the silicone mold to try to remove the bubbles, but the effect was not satisfactory. The second time, we used the vibration of a large sanding machine to remove the bubbles. Although the numbers were clearly displayed this time, some holes were still on the top of the 1I. We decided to fill the holes using paints.
5. Below are pictures of the casting and the models:

 

Post-processing:

1. For 3D printed models, we used acrylic paint to color them and tried to keep the color as close to the original models as possible. The blood vessels were pretty delicate, so we used a pen with waterproof paint to paint them after failing to use a brush.
2. For the casting model, we first used sandpaper to grind off the excess part at the bottom, and the subsequent steps were the same as the 3D printing models. Since the casting and 3D printing models were colored at different times, we encountered difficulties in color matching. That’s why there were slight differences in the colors of the two models.
3. Finally, we sprayed all the models with clear spray paint to complete our finished products.
4. Below are pictures of post-processing:

Final Products & Lessons Learned:

1. Before 3D printing, confirming the size and appearance of all models to be printed in advance can help us reduce errors and time.
2. According to the final measured dimensions, the quality of 3D printing is better than that of molding and casting.
3. Matching the color and drawing the vascular patterns also took much time. If the vascular patterns could be made into stickers, stamps, or spray paint stencils, it might increase consistency and efficiency.

Cost analysis:
3D printing method:

Cost Type	Cost	Price	Source	Quantity	Total
Materials	PLA filament	$19.99 / kg	Bambu Lab	0.04 kg	$ 0.80
	Paint	$14.99 / set	Amazon.com	0.5 set	$ 7.495
	Clear spray paint	$0.5 / Oz	Homedepot	0.2 Oz	$ 0.1
Labor	Prototyping Engineer (Intern)	$17 / hour	ZipRecruiter.com	1 hr (set up + monitor 3D printing) + 16 hr (post-processing) = 17 hrs	$ 298
Overhead	Brush	$3.99 / set	Amazon.com	1 set	$ 3.99
	Paper tower	$0.051  / Sheet	Amazon.com	10 sheets	$ 0.51
	Quality control	27.5/ hour	LinkedIn.com	0.25 h	$ 6.875
Design	Engineering and Development	$17 / hour	ZipRecruiter.com	0.5 h	$ 8.5
Misc.	Waste and Scrap	$0.17 / L	Houstontx.gov	0.05 L	$ 0.0085

Sum: $ 326.28

 

3D printing + molding and casting

Cost Type	Cost	Price	Source	Quantity	Total
Materials	PLA filament	$19.99 / kg	Bambu Lab	0.12 kg	$1.4112
	Silicon	$0.48 / Oz	Amazon.com	220 ml	$3.571
	Polyurethane	$68.92 / Gallon	Amazon.com	90 ml	$1.654
	Paint	$14.99 / set	Amazon.com	0.5 set	$7.495
	Waterproof pen	$2.49 / count	Unibrands.co	1 count	$2.49
	Clear spray paint	$0.5 / Oz	Homedepot	0.2 Oz	$ 0.1
Labor	Prototyping Engineer (Intern)	$17 / hour	ZipRecruiter.com	1 hr (set up + monitor 3D printing) + 0.25 hr (pouring silicon) = $1.25  0.25 hr (demolding) + 0.5 hr (casting) + 2 hr (sanding) + 16 hr (painting) = $14.75	$ 21.25 $ 318.75
Overhead	Flathead screwdriver and spatula	$3.25 for one $4.99 for one	Amazon.com Amazon.com	1 count 1 count	$ 3.25 $4.99
	Brush	$3.99/ set	Amazon.com	1 set	$3.99
	Paper towel	$0.051 / Sheet	Amazon.com	10 sheets	$0.51
	Plastic cup with mixing sticks	$0.18 / count	Amazon.com	3 counts	$0.54
	Sandpaper	$0.20 / piece	Amazon.com	1 piece	$0.20
	Quality control	$27.5/ hour	LinkedIn.com	0.25 h	$6.875
Design	Engineering and Development	$17 / hour	ZipRecruiter.com	0.5 h	$ 8.5
	Iterations	$17 / hour	ZipRecruiter.com	1 h	$ 17
Misc.	Waste and Scrap	$0.17 / L	Houstontx.gov	0.05 L	$ 0.0085

Sum: $ 402.58

Clean table:

Link to our technical report