NORTHWESTERN N - PLASTIC PART


Project Description

The goal of this project was to design an injection molded plastic part with interference fits. I worked on a four-person team of mechanical and manufacturing engineers to design the part details (snap fits, wall thickness, etc.), the positioning of the part on each mold (including runner placement), and produce the mold on CNC machinery.

Based on my performance in this course, I was hired as an undergraduate teaching assistant the following year where I assisted students in CAD modeling and manufacturing of their aluminum molds.


Takeaways and Skills Developed

  • Working effectively on a team
    • Project management and leadership
    • Capitalizing on complementary skills
  • Computer Aided Design/Computer Aided Manufacturing (CAD/CAM)
  • Computer Numerical Controlled (CNC) machining
  • Injection molding (Mold Design, Part Optimization for Injection, Injection Parameters)


 
Finished N.jpg

Process

Sketches.jpg

Ideation

Fourth graders from The Nettlehorst School in Chicago provided three options for the part we were to produce. We chose our favorite design and translated the low fidelity sketches into dimensioned drawings.

CAD Modeling

We used our sketch to model the part in Siemens NX. This model was used to design our molds and the part was optimized for that process.

Manufacturing

Using the CAD models, we used the CAM interface in NX to create manufacturing programs to cut our molds out of aluminum stock using CNC milling machines. We optimized the tool paths to reduce time and create the best possible surface finish.

Injection

Once the molds were completed, we manufactured the actual part in an injection molding machine. We identified the best injection parameters and performed a production run to explore how a parameter shift affected the part quality.


Final Product

The plastic part produced met all the project requirements of an injection molded, snap fit, plastic part. My team took an innovative approach to the snap fit features by using tabs instead of more traditional pins. This resulted in the first iteration of the parts having too much interference on the snap fit features. To solve this problem, we filled the snap fit features with Machinable JB Weld and re-machined the features to decrease the interference. This challenge highlighted the benefits of pins over tabs and, given more time, the next step would have been to explore a part redesign that used pins instead of tabs for the interference fit.