Injection molding is a powerful manufacturing process, but designing a part for it can be challenging, especially when you are new to the field. In this blog post, I’ll walk you through some key tips and techniques for designing a part for injection molding using SolidWorks Plastics, focusing on an example project: designing shelf support pegs.
Understanding the Basics
Before diving into design specifics, I began by examining basic shelf support pegs from my office bookshelf. This initial step was critical to understanding the molding process and the design philosophy behind these components. Notably, I observed the draft angle and the concealed parting line along one face, which informed my approach to hiding the parting line in my own design. To make the gusset more elegant and robust, my design opted for using two pegs that interface with the bookshelf’s side holes.
Modeling the Part
With these fundamentals in mind, I proceeded to model the part. The design is straightforward, utilizing six sketch-based features and nine fillets. This model’s simplicity is intentional, as it facilitates the mold’s function. The mold halves were designed to pull apart outwards, necessitating the addition of a draft to all necessary faces to prevent the part from getting stuck in the mold. A global variable was set to 3.5 degrees for the draft angle, aligning with the recommended range of two to five degrees for 3D-printed mold inserts.
Setting Up the Simulation with SOLIDWORKS Plastics
A crucial step in the design process was determining the optimal gate location for filling. SOLIDWORKS Plastics played an indispensable role in this endeavor. I started by selecting the Fill simulation type, appropriate for my beginner level in injection mold design, as it provides essential information without overwhelming complexity. For the injection material, Novolen 1100H was chosen due to its popularity and reliability among polypropylene materials.
In setting the injection specifics, the injection pressure was tailored to our desktop mold machine, and the mold temperature was set to ambient conditions, given the absence of heating or cooling elements. I specified the injection location through a modeled sprue and gate.
Testing and Optimizing the Design
I created a curvature-based mesh with medium resolution to capture the geometry accurately and ran the simulation, testing different gate placements. The results were promising: similar fill times at the two extremes, strategic air trap locations, minimal weld lines, and acceptable injection pressure levels.
Satisfied with these outcomes, I modified the design to incorporate two shelf supports in a single shot. This involved rotating the part, adding a runner and gate based on the simulation’s ideal location, and integrating a sprue and cold slug to fit the master unit die we planned to use. The runner connected the sprue to the gate, and everything was mirrored and combined for efficiency.
After re-testing the simulation, the results affirmed the design’s viability.
Best Practices in Injection Molding
Thanks to insights from injection molding hobbyist and software legend John Socho Leialoha, I learned two critical best practices. First, ensure the combined cross-sectional area of the runners matches that of the sprue. Second, include a cold slug to trap cooler plastic exiting the mold, preventing it from affecting the shot. Additionally, I followed John’s suggestion to initially size the gate to approximately 1.8 millimeters square.
Conclusion
With SolidWorks Plastics and valuable guidance from experts like John Socho Leialoha, designing parts for injection molding can be a successful and rewarding endeavor. By understanding and applying these tips and techniques, you can create efficient, effective injection-molded components. For more detailed insights, I highly recommend exploring John’s channel, John SL Random Products.
Happy Designing!
More in this Injection Molding Series
- Can 3D Printing Make Injection Molding Fast and Cheap for Early Product Testing?
- Designing an Injection-Molded Shelf Support: Draft, Gate Placement, and Runner Best Practices
- Printing a High-Accuracy Rigid 10K Injection Mold Insert on the Form 4
- Dialing In a Desktop Injection Molding Machine: Temps, Speed, and Better Shots
