\nMaintaining uniform wall thickness is the single best design\u00a0element you can incorporate in injection molded plastic parts.\u00a0Uniform wall thickness promotes uniform filling patterns,\u00a0uniform molded-in stress distributions, uniform shrinkage and ultimately, molded parts that are much less likely to warp out of shape compared to parts that have significantly varying wall thickness. This image shows the Nominal Wall Thickness Adviser plot from SOLIDWORKS Plastics 2015, which indicates areas that deviate significantly from the nominal wall thickness. You can then use this information to modify wall thicknesses and arrive at a final design with more uniform wall thickness. Hint: While most injection molded parts are thin-walled in nature, look for thick sections in your designs that can be cored-out to maintain the overall uniformity of the nominal wall thickness.
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<\/p>\nAvoid Abrupt Transitions From Thin to Thick<\/strong> Folow Rib Design Guidelines<\/strong> Avoid Sharp Corners<\/strong><\/p>\n Sharp corners in plastics parts act as stress concentrators that can lead to crazing, cracking, increased susceptibility to chemical attack and ultimately, part failure \u2013 so it\u2019s a really good idea to avoid them at all costs. The good news, it\u2019s usually pretty easy to add fillets or chamfers to avoid sharp corners altogether as can be seen in this diagram.<\/p>\n Now that you we\u2019ve covered some of the most important rules to follow when designing injection molded plastic parts, you should watch our 22-minute webinar on Better Plastics Part Design<\/a>.\u00a0And until next time\u2026clear your mind, focus and GET THAT PROJECT DONE!<\/p>\n Originally posted by Peter Rucinski in the SOLIDWORKS Blog<\/a>.<\/p>\n
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<\/a>It\u2019s inevitable that your parts will require some variations in wall thickness due to the incorporation of structural features such as ribs, bosses and gussets. However, the transition from thin to thick should be as gradual as possible in order to avoid mold-filling phenomena such as flow hesitation or racetracking. Given a choice, molten plastic flowing inside of an injection mold cavity will always take the path of least resistance, typically towards the thicker wall sections. Flow hesitation occurs when the melted plastic flows into a thicker section while the flow in the thinner section stalls and sometimes freezes off completely, causing major problems. Racetracking occurs when the molten plastic \u201craces\u201d around the edges of a part due to thicker wall sections around the perimeter of the part compared to the interior wall sections. Maintaining gradual transitions from thin to thick\u2013 as seen in the diagram\u2013can help reduce these phenomena or eliminate them altogether, resulting in higher-quality molded parts with fewer manufacturing defects.<\/p>\n
\nRibs are commonly used in plastic parts to provide structural integrity, prevent part warpage and aid in the integration ofinternal components. However, if ribs are not designed properly relative to the surfaces they\u2019re attached to, problems such as sink marks, warpage and part failure can occur. The following rib design guidelines work well for most plastics materials:<\/p>\n\n
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