For the midterm project, our team was tasked with creating two sets of new cervical models that will be used with the LUCIA training apparatus. Our team selected to create the cyst cervical models, and utilized 3D printing to create one version, and molding and casting with silicone and polyurethane to create the second version.
Process:
3D printed models
- First we downloaded the SLDPRT files of the 4 cyst cervical models posted on Canvas.
- We then loaded these files into the Bambu slicer on the OEDK printers to slice and print them with PLA filament. These prints took 0.97 oz of filament and around an hour to print.
Pictured above is the four cyst cervical models in the Bambu slicer before printing
- Once complete, we removed the supports from the models.
- We then utilized the acrylic paint provided for us, matching the colors as closely as possible to the provided models. This process took some skill and effort, as we had to mix red, pink, white, and yellow to obtain the proper shades of pink to match the cervical models from the LUCIA kit. Additionally, it took more precise painting for getting the cyst on the model correct.
- After painting the cervical models, we used the clear gloss spray paint to ensure that they became glossy upon drying. The final result of our 3D printed cyst cervical models can be seen below.
Polyurethane model creation
1. First, we downloaded the SLDPRT file of the box from Canvas so that we could create the positive 3D mold.
2. We then utilized the OEDK computer lab computers to construct our positive mold, arranging the SLDPRT files of each of the four cyst cervical models inside the SLDPRT box file.
3. After completing the SLDPRT file of our mold, our team downloaded this file in the Bambu slicer and printed it. This print took 6.08 oz of PLA filament and 3 hours to print. A picture of the final print can be seen below.
4. We then removed the supports and worked towards creating our silicone mold.
5. To calculate the amount of silicone we needed, we calculated the volume of our positive mold. We took the volume of each of the 4 cervixes which we estimated to be 13.5 cm3 and added these to the volume of the box that we calculated to be 350 cm3. Once we obtained the volume in cm3, we converted this amount to mL, and obtained 404 mL.
6. Since the silicone was in part A and B, we took 200 mL part A and mixed it with 200 mL part B in a plastic cup with a popsicle stick. We then poured the silicone into the 3D positive mold and let it dry. A picture of this process can be found below.
7. Once dry, we took an xacto knife and cut around the sides of the 3D positive mold, which helped us loosen up the silicone negative mold and pull it out. A picture of the silicone mold and 3D positive mold can be seen below.
8. To calculate the amount of polyurethane we needed, we took the sum of the volume of the four cervixes, which was 80 cm3 or 80 ml.
9. Taking equal parts of the polyurethane, we measured 40 ml of part A in a cup and 40 ml of part B in a cup.
10. We then combined these parts together and mixed quickly for a minute before directly pouring the polyurethane mixture into the silicone mold. Polyurethane has a short potlife, and therefore, must be poured into the mold quickly following combination of the parts. Additionally, polyurethane dries quickly changing color from clear to white almost suddenly during the drying process. Pictures of this process can be seen below.
On first appearance, when comparing the four cyst cervical models obtained from 3D printing and molding/casting with silicone and polyurethane, there were no visual differences between the two, as the silicone mold transferred almost all of the fine details of the 3D printed cervical models to the polyurethane cast models. However, the polyurethane cast models were slightly heavier compared to the 3D printed models.
11. We then painted the polyurethane models with the acrylic paint, following what we did for painting the 3D printed models. One problem we faced in this process was trying to create similar colors as the ones we used for the 3D printed models, as a lot of the color creation was trial and error with different paint colors. This process took us multiple tries, and took extra time. Additionally, the polyurethane material made the paint dry darker than expected, and was different compared to our experience when painting the 3D printed models. A picture comparing the 3D printed model and polyurethane model can be seen below.
12. Following our completion of painting the polyurethane models, we spray painted the models with the clear gloss spray paint.
All of our final models can be seen below.
Lessons learned/insights:
- 3D printing the cyst cervical models is faster and also cheaper compared to using the molding and casting of the cyst cervical models (see cost analysis for price comparison).
- Polyurethane is a very fascinating material, as it turns a different color during its drying process, and was able to cure faster than the time it took to 3D print the cyst cervical models.
- When painting multiple iterations of the same cervical models, it would be helpful to paint all at the same time to ensure that the colors of the cervical models match.
Picture of our clean workspace:
Cost Analysis:
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | PLA Filament | $25.99/ 1 kg | amazon.com | 0.2 kg | $5.20 |
| Silicon
|
$31.42/500 mL | amazon.com | 400 mL | $25.14 | |
| Polyurethane Part A + Part B | $25.09 /1 pint | amazon.com | 80 ml | $4.27 | |
| Acrylic Paint (24 colors) + Paint Brushes | $25.99 – ($0.54/fl oz) | amazon.com | 2 fl oz | $1.08 | |
| Gloss Spray Paint | $5.98 per 12 oz can | Home Depot | 0.25 oz | $0.12 | |
| Plastic Cups | $14.99 for 25 | amazon.com | 4 | $2.40 | |
| Popsickle sticks | $4.98 for 100 | amazon.com | 5 | $0.25 | |
| Ruler | $1.96 for 1 | amazon.com | 1 | $1.96 | |
| Labor | Prototyping engineer | $36/hour | ziprecruiter.com | 2 hours | $72 |
| 3D Printing Operator | $23/hour | ziprecruiter.com | 3 hours | $57 | |
| Total | $169.42 |
Feasibility for Mass Production
| Number of products | 3D Printing | Mold Casting ( Silicon + Polyurethane) |
| 50 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.175 for 1 cervix print |
Time: Slower
Quality: Lower Cost: $7.90 per 1 cervix $7.90 * 50 = $394.875 total to print 50 cervixes |
| 100 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.70*25=$17.50 total for 100 cervixes |
Time: Slower
Quality: Lower Cost: $4.27*25=$106.75 total for 100 cervixes |
| 1000 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.175 for 1 cervix print |
Time: Slower
Quality: Lower Cost: |
Assumptions made:
- 3D printer is already purchased/access to a 3D printer is available
- There is no time constraint or deadline for creating the number of products
- Cost of creating 4 cervixes with 3D printing is $0.70
- Cost of creating 4 cervixes with Polyurethane casting is $31.59 (first time only and
- includes the 3D printed box, silicone, and polyurethane)
- Cost of creating 4 cervixes with Polyurethane is $4.27 every time following the first
- Assuming that we only make the 3D printed box and silicone mold once for all products made (50-1000)
