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Industrial design | Product development | 416-651-3539 |
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A few injection molding plastic parts design tips: How to eliminate sink marks |
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Designers are always vexed with unsightly sink marks or surface gloss differential on injection molded plastic parts. The following tips, along with good plastic parts’ design, will guarantee elimination of sink marks by design, rather than burden the molder with process control issues of packing or extended in-mold hold cycles. |
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Boss core pins should have a spherical end that extends to approximately 1/2 material thickness. It is such a simple tooling feature that of itself will almost eliminate sink marks on visual faces opposite internal bosses. |
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A 1/2 material thickness recessed spherical ring, half a donut or toroid for you Homer Simpson or engineering fans, around the boss’ base. |
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If you are concerned about reducing the boss’ strength by reducing material around its root, of course ribs can be added. |
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Put together, the combination of the boss core pin spherical end and the recessed spherical ring, both extending to approximately 1/2 material thickness, will guarantee elimination of sink marks. |
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Of course, by now you will have realized that what is being done is decreasing material buildup in the area around the boss’ root. Pier Design has had molded numerous parts including both of these details. All parts have performed successfully, and do not have any sink marks or material gloss differential on the visual surface. In fact, we include these details on all injection molded parts internal bosses. |
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© Pier Design, 2006 |
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