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Description
In injection molded plastic parts, knit lines occur where opposing streams of material fuse together while the mold cavity fills. When parts with knit lines experience external loading, the knit lines cause areas of mechanical weakness. This weakness is especially drastic in fiber-reinforced polymers due to an unfavorable orientation of fibers at the knit line. A possible way to reduce the impact of knit lines is to incorporate overflow tabs into the mold design. An overflow tab is a chamber attached to the mold cavity that provides an extra space for the end of material flow to occur. Research shows that overflow tabs improve the fiber orientation at the knit line, resulting in increased mechanical strength. The goal of this study is to utilize overflow tabs to optimize the knit line strength of nylon 6-6 that is 30% carbon fiber reinforced. In this project, an initial overflow tab is first designed. Then four modifications are made to the tab design, each altering a separate variable while holding the others constant. The design changes explored for the tab in this project include adding radii to the inlet, shifting the inlet location, increasing the inlet cross-sectional area by 50%, and increasing the tab chamber volume by 50%. Specimens were molded using the initial tab design and the modified tab designs. Testing for this experiment consists of three specimens of each type for three-point bending tests, and five specimens of each type for tensile tests. The material properties analyzed are the flexural modulus, flexural strength, tensile modulus, and tensile strength. From the testing, the tab with the 50% increased volume consistently yielded the highest results and showed large improvement from the initial tab design. However, the other three tab modifications either showed negative change or slight improvement from the initial tab design. Based on the results of this study, the overflow tab volume is the most beneficial design parameter to adjust.
ContributorsJones, Justin Michael (Author) / Adams, James (Thesis director) / Wamsley, Steven (Committee member) / Computer Science and Engineering Program (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05