{"id":3399,"date":"2026-09-21T14:49:53","date_gmt":"2026-09-21T06:49:53","guid":{"rendered":"http:\/\/www.thestoryoftheseason.com\/blog\/?p=3399"},"modified":"2026-09-21T14:49:53","modified_gmt":"2026-09-21T06:49:53","slug":"how-to-prevent-sink-marks-in-plastic-mold-machining-parts-416f-1e23cd","status":"publish","type":"post","link":"http:\/\/www.thestoryoftheseason.com\/blog\/2026\/09\/21\/how-to-prevent-sink-marks-in-plastic-mold-machining-parts-416f-1e23cd\/","title":{"rendered":"How to prevent sink marks in plastic mold machining parts?"},"content":{"rendered":"<p>Hey there! As a supplier of plastic mold machining parts, I&#8217;ve seen my fair share of challenges in the industry. One of the most common issues that can really throw a wrench in the works is sink marks. You know, those little depressions or dents on the surface of a plastic part that can make it look less than perfect. In this blog, I&#8217;m going to share some tips on how to prevent sink marks in plastic mold machining parts. <a href=\"https:\/\/www.pti-tool.com\/high-precision-machining-service\/plastic-mold-machining-parts\/\">Plastic Mold Machining Parts<\/a><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.pti-tool.com\/uploads\/44140\/small\/medical-injection-moldb9c9c.jpg\"><\/p>\n<h3>Understanding Sink Marks<\/h3>\n<p>First things first, let&#8217;s talk about what sink marks are and why they happen. Sink marks occur when the plastic inside the mold cools and shrinks unevenly. This usually happens in thick sections of the part because the outer layer cools and solidifies faster than the inner part. As the inner plastic continues to shrink, it pulls the outer layer inward, creating a sink mark.<\/p>\n<p>Several factors can contribute to sink marks. One is the design of the part. If you have thick and thin sections right next to each other, it can cause uneven cooling. The type of plastic you use also matters. Some plastics shrink more than others, and that can increase the risk of sink marks. The molding process itself, like the injection speed, pressure, and cooling time, can play a big role too.<\/p>\n<h3>Design Considerations<\/h3>\n<p>When it comes to preventing sink marks, the design of the plastic part is crucial. Here are some design tips that can make a big difference:<\/p>\n<ul>\n<li>\n<p><strong>Uniform Wall Thickness<\/strong>: Try to keep the wall thickness of your part as uniform as possible. This helps the plastic cool evenly throughout the part. If you need to have different thicknesses, make the transition gradual. For example, instead of going from a thick section to a thin section abruptly, use a tapered design.<\/p>\n<\/li>\n<li>\n<p><strong>Rib Design<\/strong>: Ribs are often used to add strength to a plastic part, but they can also cause sink marks if not designed properly. Make sure the ribs are not too thick. A good rule of thumb is to keep the rib thickness at about 50 &#8211; 60% of the wall thickness. Also, use multiple thin ribs instead of one thick rib.<\/p>\n<\/li>\n<li>\n<p><strong>Boss Design<\/strong>: Bosses are those cylindrical protrusions on a plastic part. Similar to ribs, their thickness should be carefully considered. Keep the boss diameter and thickness proportional to the wall thickness. You can also add gussets or fillets around the boss to help distribute the stress and reduce the risk of sink marks.<\/p>\n<\/li>\n<\/ul>\n<h3>Material Selection<\/h3>\n<p>The type of plastic you choose can have a significant impact on the occurrence of sink marks. Here are some things to keep in mind when selecting a material:<\/p>\n<ul>\n<li>\n<p><strong>Shrinkage Rate<\/strong>: Different plastics have different shrinkage rates. For example, semicrystalline plastics like polypropylene and polyethylene tend to shrink more than amorphous plastics like polystyrene and polycarbonate. If you&#8217;re dealing with a part where sink marks are a major concern, you might want to consider using an amorphous plastic.<\/p>\n<\/li>\n<li>\n<p><strong>Filler Content<\/strong>: Some plastics come with fillers like glass fibers or mineral fillers. These fillers can reduce shrinkage and improve the mechanical properties of the part. However, they can also affect the flow of the plastic and potentially lead to other issues. Make sure to test the plastic with fillers thoroughly before using it in production.<\/p>\n<\/li>\n<\/ul>\n<h3>Molding Process Optimization<\/h3>\n<p>The molding process is where you can really take control of preventing sink marks. Here are some key factors to consider:<\/p>\n<ul>\n<li>\n<p><strong>Injection Speed and Pressure<\/strong>: The injection speed and pressure can affect how the plastic fills the mold. If the injection speed is too slow, the plastic may start to cool before it fully fills the mold, which can lead to uneven cooling and sink marks. On the other hand, if the injection pressure is too high, it can cause overpacking, which can also result in sink marks. You need to find the right balance for your specific part and material.<\/p>\n<\/li>\n<li>\n<p><strong>Cooling Time<\/strong>: Proper cooling is essential to prevent sink marks. Make sure the mold has an efficient cooling system. The cooling time should be long enough to allow the plastic to solidify completely, but not too long that it increases the production cycle time unnecessarily. You can use cooling channels in the mold to control the cooling rate.<\/p>\n<\/li>\n<li>\n<p><strong>Mold Temperature<\/strong>: Maintaining a consistent mold temperature is important. If the mold temperature is too low, the plastic may cool too quickly and cause sink marks. If it&#8217;s too high, the plastic may take longer to cool, increasing the risk of shrinkage. You can use a temperature controller to keep the mold temperature within the optimal range.<\/p>\n<\/li>\n<\/ul>\n<h3>Quality Control and Inspection<\/h3>\n<p>Even with the best design, material selection, and molding process, it&#8217;s still a good idea to have a quality control and inspection system in place. This can help you catch any sink marks early on and make adjustments as needed.<\/p>\n<ul>\n<li>\n<p><strong>Visual Inspection<\/strong>: Regularly inspect the finished parts visually. Look for any signs of sink marks, such as depressions or uneven surfaces. You can use a magnifying glass if necessary to get a closer look.<\/p>\n<\/li>\n<li>\n<p><strong>Dimensional Inspection<\/strong>: Use measuring tools like calipers or micrometers to check the dimensions of the parts. Any significant deviations from the specifications could be a sign of sink marks or other issues.<\/p>\n<\/li>\n<li>\n<p><strong>Process Monitoring<\/strong>: Keep track of the molding process parameters, such as injection speed, pressure, and temperature. If you notice any fluctuations in these parameters, it could be a sign that something is going wrong and that sink marks may occur.<\/p>\n<\/li>\n<\/ul>\n<h3>Conclusion<\/h3>\n<p>Preventing sink marks in plastic mold machining parts is a combination of good design, proper material selection, optimized molding processes, and thorough quality control. By following these tips, you can significantly reduce the risk of sink marks and produce high-quality plastic parts.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.pti-tool.com\/uploads\/44140\/small\/vehicle-connector-over-mould71a65.jpg\"><\/p>\n<p>If you&#8217;re in the market for plastic mold machining parts and want to avoid the hassle of sink marks, we&#8217;re here to help. We&#8217;ve got the experience and expertise to ensure that your parts are made to the highest standards. Feel free to reach out for a chat and let&#8217;s discuss your specific needs. We&#8217;d love to work with you to create the perfect plastic parts for your project.<\/p>\n<p><a href=\"https:\/\/www.pti-tool.com\/stamping-service\/\">Stamping Service<\/a> References:<\/p>\n<ul>\n<li>&quot;Plastics Processing Handbook&quot; by Osswald, A. and Turng, L.<\/li>\n<li>&quot;Injection Molding Handbook&quot; by Rosato, D. V.<\/li>\n<\/ul>\n<hr>\n<p><a href=\"https:\/\/www.pti-tool.com\/\">Protech Precision (HongKong) Limited<\/a><br \/>Protech Precision (HongKong) Limited is well-known as one of the leading plastic mold machining parts manufacturers and suppliers in China. With over 15 years&#8217; experience, we warmly welcome you to buy high quality plastic mold machining parts at competitive price from our factory. Contact us for more details.<br \/>Address: 9B, Amtel Building, 148 Des Voeux Road Central, Central, Hong Kong<br \/>E-mail: Ricky.he@pti-tool.com<br \/>WebSite: <a href=\"https:\/\/www.pti-tool.com\/\">https:\/\/www.pti-tool.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Hey there! As a supplier of plastic mold machining parts, I&#8217;ve seen my fair share of &hellip; <a title=\"How to prevent sink marks in plastic mold machining parts?\" class=\"hm-read-more\" href=\"http:\/\/www.thestoryoftheseason.com\/blog\/2026\/09\/21\/how-to-prevent-sink-marks-in-plastic-mold-machining-parts-416f-1e23cd\/\"><span class=\"screen-reader-text\">How to prevent sink marks in plastic mold machining parts?<\/span>Read more<\/a><\/p>\n","protected":false},"author":751,"featured_media":3399,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3362],"class_list":["post-3399","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-plastic-mold-machining-parts-44ee-1e69ec"],"_links":{"self":[{"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/posts\/3399","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/users\/751"}],"replies":[{"embeddable":true,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/comments?post=3399"}],"version-history":[{"count":0,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/posts\/3399\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/posts\/3399"}],"wp:attachment":[{"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/media?parent=3399"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/categories?post=3399"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.thestoryoftheseason.com\/blog\/wp-json\/wp\/v2\/tags?post=3399"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}