Injection Molding: Process and Design Principles for 3D Printed Molds

Abstract

Injection molding is a powerful manufacturing method used to create consistent, low-cost parts ranging in size from micro-electronic connectors to automotive body panels. While injection molding is ubiquitous in industrial, high-volume applications, the large upfront cost of equipment, design work and molds had previously prevented smaller businesses working with short timeline projects or limited budgets from using this method. However, advances in rapid manufacturing methods have improved the agility and cost of mold fabrication. Although these molds have a shorter lifetime than traditional aluminum or steel molds, they are still useful in a variety of applications.

Princeton University's Mechanical and Aerospace Engineering (MAE) Department owns a BOY 35E Procan Alpha injection molding machine which has been largely unused since it was installed in 2016. This report describes the process required to successfully operate the BOY 35E, guidelines for mold design, and a comparison of FDM and SLA 3D printing methods for mold manufacturing. The results of this comparison demonstrate that SLA printing is an inexpensive, quick and relatively user-friendly method for creating molds. This comparison was performed on a mold for an involute gear used in the gear train of a flywheel car project in Princeton University's required undergraduate course MAE 321: Engineering Design. My objective was to reduce the time and effort required for students to learn how to use injection molding by providing exposure to this technique in an academic setting. I also created a process-oriented operation and troubleshooting manual for the BOY 35E based on my own experiences with the machine to further support future users.

My project has improved the accessibility of Princeton's BOY 35E machine and shown that injection molding using SLA molds can produce a high-quality product in a shorter period of time and for a lower cost than traditional mold manufacturing methods. These molds are ideal for low-volume and prototyping applications that are typical of student work. The application of these methods in a small business setting will facilitate agile and low-cost product manufacturing using injection molding that was previously inaccessible to these entities.