{"id":1646,"date":"2026-10-15T04:59:58","date_gmt":"2026-10-15T04:59:58","guid":{"rendered":"https:\/\/www.atc-mould.com\/?p=1646"},"modified":"2026-10-15T04:59:58","modified_gmt":"2026-10-15T04:59:58","slug":"what-causes-sink-marks-in-injection-molded-plastic-parts-and-how-can-they-be-prevented","status":"publish","type":"post","link":"https:\/\/www.atc-mould.com\/?p=1646","title":{"rendered":"What causes sink marks in injection molded plastic parts and how can they be prevented?"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Sink marks are one of the most frustrating cosmetic defects in plastic injection molding. They show up as shallow depressions on the visible surface, almost always sitting directly opposite a rib, boss, or other thick feature. Many teams are surprised when a clean 3D-printed or CNC prototype suddenly develops these marks once the steel tool starts producing parts.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The root cause is differential cooling and shrinkage. Thicker sections stay molten longer. As the core of that thick area finally solidifies and contracts, it pulls the still-soft outer surface inward, creating the visible sink. Because printed and machined prototypes never experience the same melt-flow and cooling cycle, they give no early warning.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Practical design rules that prevent most sink marks:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Maintain the most uniform wall thickness possible throughout the part.<\/li>\n\n\n\n<li>Limit rib thickness to roughly 50\u201360 % of the nominal wall they attach to.<\/li>\n\n\n\n<li>Core out solid bosses and heavy sections instead of leaving them fully solid.<\/li>\n\n\n\n<li>Position ribs and attachment features away from critical cosmetic faces whenever the design allows.<\/li>\n\n\n\n<li>Use gradual transitions and generous radii rather than abrupt thickness changes.<\/li>\n\n\n\n<li>Consider local texture or a slight draft adjustment on high-visibility surfaces as a secondary safeguard.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Catching these issues in a short design-for-manufacturability review\u2014before any steel is cut\u2014is far more effective than trying to eliminate sink marks later with packing pressure, cooling time, or texture changes. Most sink problems can be designed out in a single focused review session.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Beyond the basic rules, experienced molders also look at gate location relative to thick features, material shrinkage characteristics, and even the use of gas-assist or structural foam in extreme cases. Getting the geometry right first still remains the highest-leverage step.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If you are developing a new plastic injection molded component, spending a few minutes on these wall-thickness and rib guidelines can save weeks of troubleshooting after the tool is built. A clear, practical checklist covering the most common design focus areas for injection molding is available to help teams review parts quickly and confidently before tooling begins.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Sink marks are one of the most frustrating cosmetic defects in plastic injection molding. They show up as shallow depressions on the visible surface, almost always sitting directly opposite a rib, boss, or other thick feature. Many teams are surprised when a clean 3D-printed or CNC prototype suddenly develops these marks once the steel tool [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":1068,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1646","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/posts\/1646","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1646"}],"version-history":[{"count":1,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/posts\/1646\/revisions"}],"predecessor-version":[{"id":1647,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/posts\/1646\/revisions\/1647"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=\/wp\/v2\/media\/1068"}],"wp:attachment":[{"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1646"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1646"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.atc-mould.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1646"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}