{"id":36176,"date":"2026-05-17T05:55:00","date_gmt":"2026-05-17T05:55:00","guid":{"rendered":"https:\/\/dimud.com\/?p=36176"},"modified":"2026-05-18T02:59:14","modified_gmt":"2026-05-18T02:59:14","slug":"injection-molding-sink-marks","status":"publish","type":"post","link":"https:\/\/dimud.com\/fr\/injection-molding-sink-marks\/","title":{"rendered":"Comment pr\u00e9venir les marques d'affaissement dans le moulage par injection\uff1fRoot Causes, Fixes &amp; Prevention"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"36176\" class=\"elementor elementor-36176\" data-elementor-settings=\"{&quot;ha_cmc_init_switcher&quot;:&quot;no&quot;}\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-9b4b773 e-flex e-con-boxed e-con e-parent\" data-id=\"9b4b773\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-5a9eec8 elementor-widget elementor-widget-image\" data-id=\"5a9eec8\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-sink-marks.jpg\" class=\"attachment-large size-large wp-image-36290\" alt=\"Injection molding sink marks\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-sink-marks.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-sink-marks-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-sink-marks-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-sink-marks-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-05e4ecb elementor-widget elementor-widget-text-editor\" data-id=\"05e4ecb\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>In my experience working with plastic part production, sink marks are one of the most common\u2014and most frustrating\u2014defects in injection molding. They may look small on the surface, but they can seriously affect both the appearance and structural quality of a product.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Sink marks in injection molding are surface depressions or indentations that appear on a molded plastic part. They occur when the outer skin of a part cools and solidifies, but the material underneath \u2014 typically near thick sections, ribs, or bosses \u2014 hasn&#8217;t fully cooled yet. As the inner material shrinks during cooling, it pulls the surface inward, creating that telltale dimple. Sink marks are one of the most common injection molding defects and can affect both part aesthetics and structural integrity, particularly on Class A surfaces in consumer electronics and automotive components.<\/strong><\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">The good news? Sink marks are almost always preventable \u2014 if you understand where they come from and how to fight them early in the design and process stages. Let me break it all down.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-beb127a e-flex e-con-boxed e-con e-parent\" data-id=\"beb127a\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-829470f elementor-widget elementor-widget-heading\" data-id=\"829470f\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">What Are Sink Marks in Injection Molding?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-eecd056 elementor-widget elementor-widget-image\" data-id=\"eecd056\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-on-plastic-part.jpg\" class=\"attachment-large size-large wp-image-36299\" alt=\"Sink marks on plastic part\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-on-plastic-part.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-on-plastic-part-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-on-plastic-part-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-on-plastic-part-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a11f02b elementor-widget elementor-widget-text-editor\" data-id=\"a11f02b\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Before you can fix something, it helps to actually understand what you&#8217;re dealing with.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Sink marks are localized surface depressions on injection molded plastic parts. They typically appear on the opposite side of a thick wall section, rib, boss, or internal geometry \u2014 anywhere that causes an uneven thickness in the part. The visible &#8220;dent&#8221; forms because the plastic surface solidifies faster than the interior, and as the hot inner core cools and contracts, it pulls the outer skin slightly inward. In short: the surface collapses toward the shrinkage.<\/strong><\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Think of it like a chocolate cake that looks perfect on top but sinks in the middle as it cools. The visual result on plastic parts can range from a barely visible shallow depression to a more obvious dent that ruins an otherwise clean surface.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Where Sink Marks Typically Show Up<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">They almost always appear in predictable locations:<\/p><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\"><strong>Opposite to ribs<\/strong> \u2014 the back side of a rib almost always concentrates more material, which means more shrinkage, which means a sink on the visible face.<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\"><strong>Behind bosses<\/strong> \u2014 a screw boss adds a bulge of material. If it&#8217;s too thick relative to the nominal wall, the face opposite that boss will sink.<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\"><strong>At wall thickness transitions<\/strong> \u2014 where a thin wall meets a thick wall suddenly, the thicker zone shrinks more, pulling the nearby surface.<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\"><strong>Near gates<\/strong> \u2014 ironically, sometimes the area furthest from the gate has the most sink risk because of insufficient packing pressure.<\/li><\/ul><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">I&#8217;ve seen engineers spend hours tweaking process parameters trying to fix sinks that were actually caused by a rib that was 120% of wall thickness instead of 60%. No amount of parameter adjusting was ever going to fully fix a design issue. That&#8217;s the fundamental truth about sink marks \u2014 <em>most of them are born in the design file, not on the shop floor.<\/em><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Why Sink Marks Matter<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">On a hidden structural part? Maybe you can live with a minor sink. But on a consumer electronics enclosure \u2014 the kind of part where customers run their fingers across the surface \u2014 a sink mark is a product defect, full stop. It communicates low quality, even when the part is structurally sound.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">In automotive interiors, visible sinks can fail appearance approvals. In medical device housings, they can raise questions about dimensional consistency. In any cosmetic application, they erode brand trust. So yes, sink marks matter \u2014 a lot.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-47d30b9 e-flex e-con-boxed e-con e-parent\" data-id=\"47d30b9\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-17c8d29 elementor-widget elementor-widget-heading\" data-id=\"17c8d29\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">What Is the Root Cause of Sink Marks?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6117206 elementor-widget elementor-widget-image\" data-id=\"6117206\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-part-shrinkage-defect.jpg\" class=\"attachment-large size-large wp-image-36293\" alt=\"\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-part-shrinkage-defect.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-part-shrinkage-defect-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-part-shrinkage-defect-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-part-shrinkage-defect-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4e71447 elementor-widget elementor-widget-text-editor\" data-id=\"4e71447\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">People often treat sink marks as a &#8220;process problem.&#8221; Turn up the packing pressure, lower the melt temperature, and done. But that&#8217;s only part of the story.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>The root cause of sink marks in injection molding is localized volumetric shrinkage \u2014 when thick areas of a part cool and contract more than surrounding thin areas, and there isn&#8217;t enough packing pressure, material, or cooling capacity to compensate. This stems from three main sources: poor part design (uneven wall thickness, oversized ribs or bosses), incorrect mold design (poor gate placement, inadequate cooling channels), and suboptimal process parameters (insufficient packing pressure or time, incorrect melt or mold temperature).<\/strong><\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Let&#8217;s look at each one.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Root Cause 1: Part Design Issues<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">This is the biggest one and the most overlooked.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Uneven wall thickness<\/strong> is the primary design sin. When one section of a part is significantly thicker than the rest, that thick area holds heat longer. It shrinks more. And it pulls nearby surfaces with it.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">The classic culprit is the rib-to-wall thickness ratio. Many designers dimension ribs for structural load without thinking about how that thickness translates to a sink risk. A rib that is 80% of nominal wall thickness creates far less shrinkage differential than one that is 100% or more of nominal wall.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Bosses are the same story. A boss for an M3 self-tapping screw can look innocent in CAD but create a significant sink if the outer diameter is too large relative to the surrounding wall.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Design rule of thumb:<\/strong> Keep rib thickness at 50\u201360% of nominal wall. Keep boss outer wall thickness at 60% of nominal wall. These ratios exist for a reason.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Root Cause 2: Mold Design Issues<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Even with a well-designed part, a poorly designed mold can cause sinks.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Gate placement matters enormously. If the gate is too far from thick sections, the plastic cools and the flow front loses pressure before it can pack out those areas properly. The result? Sink marks even with a good part design.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Cooling channel placement is the other big one. If thick areas of the part don&#8217;t have adequate cooling near them, the material stays hot too long, increases shrinkage, and creates sinks. <a href=\"https:\/\/www.xometry.com\/resources\/injection-molding\/conformal-cooling\/\" rel=\"nofollow noopener\" target=\"_blank\">Conformal cooling<\/a> \u2014 cooling channels that follow the part geometry \u2014 is especially effective for complex parts with thick sections.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Root Cause 3: Process Parameters<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Once the design and mold are solid, the process is the final tuning tool.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Insufficient packing pressure is probably the most common process-side cause of sinks. Packing pressure is what compensates for volumetric shrinkage as the part cools. If you don&#8217;t push enough material in during the packing\/holding phase, you get a gap \u2014 and the surface collapses into it.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Too-short packing time has the same effect. If the gate freezes off before the part is fully packed, no amount of high pressure helps \u2014 the material can&#8217;t get in anymore.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Melt temperature and mold temperature both play a role too. A melt that&#8217;s too hot stays fluid longer, increasing total shrinkage. A mold that&#8217;s too warm doesn&#8217;t create a stiff enough skin to resist the pull of inner shrinkage.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-00c1019 e-flex e-con-boxed e-con e-parent\" data-id=\"00c1019\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-3e24077 elementor-widget elementor-widget-heading\" data-id=\"3e24077\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">How to Reduce Sink Marks in Injection Molding?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0fe69a6 elementor-widget elementor-widget-image\" data-id=\"0fe69a6\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/uniform-wall-thickness-design.jpg\" class=\"attachment-large size-large wp-image-36295\" alt=\"\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/uniform-wall-thickness-design.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/uniform-wall-thickness-design-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/uniform-wall-thickness-design-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/uniform-wall-thickness-design-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d72c47c elementor-widget elementor-widget-text-editor\" data-id=\"d72c47c\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Preventing sink marks starts well before the machine is even running. The most effective time to eliminate them is during the design phase\u2014specifically through DFM (Design for Manufacturability) analysis.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>To reduce sink marks in injection molding, focus on three stages: design (maintain uniform wall thickness; follow the 50\u201360% rib-to-wall ratio rule; core out thick sections; avoid abrupt wall transitions), mold design (optimize gate placement for thick sections; add proper cooling near mass concentrations), and process (increase packing pressure and holding time; lower melt temperature; ensure gate hasn&#8217;t frozen prematurely). Catching these issues early in DFM analysis is far more cost-effective than correcting them after tooling.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Design-Stage Strategies to Prevent Sink Marks<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>1. Maintain uniform wall thickness wherever possible.<\/strong> This is the single most effective rule. A nominal wall that doesn&#8217;t vary wildly in thickness means uniform cooling, uniform shrinkage, and no differential pulling.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">When you <em>must<\/em> change wall thickness\u2014say, for structural reasons or to fit a snap-fit or boss\u2014taper the transition. A gradual wall transition (3:1 taper ratio as a minimum) gives the material time to adjust rather than hitting a cliff.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>2. Core out thick sections.<\/strong> If you have a thick base or pad, consider coring it out. You keep the structural height while eliminating the mass. Less material = less shrinkage = less sink. This is especially useful for thick base pads, housing feet, and structural ribs on larger parts.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>3. Follow rib design guidelines religiously.<\/strong><\/p><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Rib thickness: 50\u201360% of nominal wall<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Rib height: max 3\u00d7 nominal wall (taller ribs may need to be slotted)<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Corner radii: add a small radius at the rib base to reduce stress concentrations<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Multiple ribs: use a series of thin ribs rather than one thick rib for strength<\/li><\/ul><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>4. Boss design rules.<\/strong><\/p><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Boss outer diameter to wall thickness: keep the boss wall at 60% of nominal wall<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Avoid solid bosses \u2014 use a cored design<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">If the boss needs to be taller, consider gusseting it rather than increasing wall thickness<\/li><\/ul><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Mold-Level Strategies<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Optimize gate location.<\/strong> Place gates near or directly into thick sections when possible. This ensures packing pressure reaches the areas that need it most before the gate freezes off. For parts with multiple thick sections, consider multiple gates or hot runner systems.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Improve cooling.<\/strong> Thick areas need targeted cooling. Consider:<\/p><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Adding cooling channels closer to problem areas<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Using conformal cooling inserts (especially with metal 3D printing)<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Beryllium copper inserts in particularly problematic hot spots<\/li><\/ul><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Review venting.<\/strong> Poor venting in thick areas can trap air and restrict material flow during packing, contributing to sinks.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If you&#8217;re working with a manufacturer that has real mold engineering depth \u2014 not just someone who can cut steel \u2014 they&#8217;ll do mold flow analysis before cutting a single piece of metal. Mold flow simulation (tools like Moldex3D or <a href=\"https:\/\/www.autodesk.com\/products\/moldflow\/overview\" rel=\"nofollow noopener\" target=\"_blank\">Autodesk Moldflow<\/a>) can predict sink risk and let you adjust before it costs real money. At Dimud, our <a class=\"underline underline underline-offset-2 decoration-1 decoration-current\/40 hover:decoration-current focus:decoration-current\" href=\"https:\/\/dimud.com\/services\/engineering-design-mold-engineering\/\">mold engineering team<\/a> runs mold flow analysis as standard practice, and we catch exactly these kinds of issues in the design phase before they become a factory problem.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-23eeaf4 e-flex e-con-boxed e-con e-parent\" data-id=\"23eeaf4\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-105360c elementor-widget elementor-widget-heading\" data-id=\"105360c\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">How Do You Adjust Injection Molding Parameters to Eliminate Sink Marks?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2cd5723 elementor-widget elementor-widget-image\" data-id=\"2cd5723\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-packing-pressure.jpg\" class=\"attachment-large size-large wp-image-36289\" alt=\"Injection molding packing pressure\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-packing-pressure.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-packing-pressure-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-packing-pressure-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/injection-molding-packing-pressure-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f1961b9 elementor-widget elementor-widget-text-editor\" data-id=\"f1961b9\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Sometimes, despite good design, you still get sinks in production. Or maybe you&#8217;re working with a legacy part design you can&#8217;t change. This is where process adjustment becomes your best tool.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>To eliminate sink marks through process adjustment, increase packing pressure (typically to 60\u201380% of injection pressure), extend holding\/packing time until the gate freezes, reduce melt temperature by 5\u201310\u00b0C increments, lower mold temperature if possible, and increase shot size slightly. Each change should be made one at a time, with short test runs to evaluate the result. Document your baseline before making any changes.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Step-by-Step: Parameter Adjustments for Sink Marks<\/h3><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Increase Packing Pressure<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">This is usually the first and most impactful adjustment. Packing pressure compensates for volumetric shrinkage by pushing more material into the cavity as the part cools.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Start at your current value and increase in 5\u201310% increments. Watch for flash at the parting line \u2014 that&#8217;s your upper limit. If you reach flash before the sink disappears, packing pressure alone isn&#8217;t the solution, and you likely have a design or gate issue.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Typical packing pressure is 60\u201380% of injection pressure, though this varies by material.<\/p><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Extend Holding Time<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Packing time needs to be long enough that the gate freezes before the pressure is removed. If you drop pressure while the gate is still open, the material will flow back out slightly \u2014 not enough to matter in fill, but enough to reduce packing in thick areas.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><em>How to check gate freeze time:<\/em> Run a simple gate seal study. Increase holding time in 0.5-second increments and weigh the parts. When part weight stops increasing, the gate has frozen \u2014 that&#8217;s your minimum holding time. Add a small safety margin (10\u201315%).<\/p><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Reduce Melt Temperature<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">A lower melt temperature reduces total shrinkage. Materials have a recommended processing range \u2014 try processing at the lower end of that range. Be careful: too low, and you risk short shots, poor flow, or weld line issues. Make incremental adjustments.<\/p><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Adjust Mold Temperature<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">A cooler mold can help form a stiffer outer skin faster, which resists the pulling force of inner shrinkage. However, this is a balancing act \u2014 too cool a mold can cause warpage, residual stress, or poor surface finish.<\/p><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Optimize the Screw Cushion and Shot Size<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If your cushion (the small amount of material left in front of the screw at the end of injection) is too small, you may run out of material to pack during the holding phase. Ensure you have 5\u201310 mm of cushion consistently.<\/p><h4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">When Parameters Aren&#8217;t Enough<\/h4><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Here&#8217;s the honest truth: if you&#8217;ve maxed out packing pressure, extended hold time, and adjusted temperatures, and the sink is still there \u2014 it&#8217;s a design or tooling problem. Process optimization has real limits. No parameter setting can fully compensate for a rib that&#8217;s 100% of wall thickness. At that point, you need a mold modification or a design revision.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-d716b8b e-flex e-con-boxed e-con e-parent\" data-id=\"d716b8b\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-90fda27 elementor-widget elementor-widget-heading\" data-id=\"90fda27\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Which Plastic Materials Are Most Prone to Sink Marks, and How to Choose Alternatives?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c082230 elementor-widget elementor-widget-image\" data-id=\"c082230\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-material-shrinkage-comparison.jpg\" class=\"attachment-large size-large wp-image-36292\" alt=\"\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-material-shrinkage-comparison.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-material-shrinkage-comparison-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-material-shrinkage-comparison-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/plastic-material-shrinkage-comparison-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-145b1c8 elementor-widget elementor-widget-text-editor\" data-id=\"145b1c8\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Not all plastics shrink equally. <a href=\"https:\/\/dimud.com\/materials\/\">Material selection<\/a> has a direct impact on sink mark risk \u2014 and it&#8217;s a factor that often gets overlooked until parts are already running in production.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Semi-crystalline plastics such as PP (polypropylene), PA (nylon), POM (acetal), and HDPE are the most prone to sink marks because they have higher and more anisotropic volumetric shrinkage rates (typically 1.5\u20132.5%). Amorphous plastics like ABS, PC, and PMMA shrink less (0.4\u20130.8%) and more uniformly, making them significantly less prone to sinking. When sink marks are a critical concern, switching from a semi-crystalline to an amorphous material \u2014 or selecting a glass-fiber-reinforced grade \u2014 can dramatically reduce the problem.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">High-Sink-Risk Materials<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Polypropylene (PP):<\/strong> Shrinkage rates of 1.5\u20132.0%. Extremely common for packaging, automotive, and consumer goods \u2014 and extremely prone to sinks in thick sections. Adding glass fiber (PP-GF30) cuts shrinkage significantly.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Nylon (PA6, PA66):<\/strong> Shrinkage of 1.2\u20132.0%. High shrink, hygroscopic, and particularly problematic in thick-walled structural parts. Glass or mineral filling helps considerably.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>POM (Acetal\/Delrin):<\/strong> Shrinkage of 2.0\u20132.5%. One of the highest-shrinkage engineering plastics. Excellent mechanical properties but requires cautious wall thickness design to avoid sinks.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>HDPE:<\/strong> Shrinkage of 1.5\u20133.0%. High shrinkage and a waxy surface make sinks especially visible. Often used in containers where wall uniformity is built into the design.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Low-Sink-Risk Materials<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>ABS:<\/strong> Shrinkage of 0.4\u20130.7%. Amorphous, low shrink, excellent surface finish. The go-to for consumer electronics housings partly <em>because<\/em> it&#8217;s forgiving with sinks.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>PC (Polycarbonate):<\/strong> Shrinkage of 0.5\u20130.7%. Low shrinkage, excellent optical clarity, and high-impact resistance. Common in phone housings, automotive lenses, and medical devices.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>PC\/ABS blends:<\/strong> Combines the best of both. Low shrinkage, good flow, and good surface finish. Very popular for electronics enclosures.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>PMMA (Acrylic):<\/strong> Shrinkage of 0.2\u20130.4%. Among the lowest shrinkage of all common plastics. Great for optical parts but brittle.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Reinforced Grades as an Alternative Strategy<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If you need a semi-crystalline material for its mechanical, chemical, or thermal properties, don&#8217;t abandon it \u2014 reinforce it. Adding 15\u201330% glass fiber to PP, PA, or POM dramatically reduces shrinkage and makes sink marks much more manageable.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">The trade-off is that glass fiber-filled materials require higher injection pressures, are more abrasive to the mold, and may show fiber orientation on the surface. But from a dimensional stability and sink-mark perspective, they&#8217;re a significant improvement.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Material selection \u2014 and its implications for sink marks \u2014 is one of the things our team at Dimud addresses during <a class=\"underline underline underline-offset-2 decoration-1 decoration-current\/40 hover:decoration-current focus:decoration-current\" href=\"https:\/\/dimud.com\/services\/dfm-design\/\">DFM analysis<\/a>. Choosing the wrong material for a part with thick sections can set you up for a difficult production life. Getting that right early saves many headaches.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-c0b11a5 e-flex e-con-boxed e-con e-parent\" data-id=\"c0b11a5\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-34d97c1 elementor-widget elementor-widget-heading\" data-id=\"34d97c1\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Sink Marks vs. Voids in Injection Molding: What's the Difference and How to Address Each?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7995271 elementor-widget elementor-widget-image\" data-id=\"7995271\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-vs-voids-diagram.jpg\" class=\"attachment-large size-large wp-image-36294\" alt=\"\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-vs-voids-diagram.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-vs-voids-diagram-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-vs-voids-diagram-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/sink-marks-vs-voids-diagram-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0686149 elementor-widget elementor-widget-text-editor\" data-id=\"0686149\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">This is a question that trips up a surprising number of people \u2014 including experienced ones. Sink marks and voids are related defects, but they&#8217;re not the same thing, and confusing them leads to the wrong fixes.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Sink marks and voids are both caused by volumetric shrinkage in thick sections of injection molded parts, but they manifest differently. A sink mark is a surface depression visible on the outside of the part \u2014 the skin collapses inward. A void is an internal air pocket or vacuum bubble trapped inside the part \u2014 the skin is strong enough to resist collapsing, but a gap forms internally. Sink marks are visible; voids are often invisible unless the part is cross-sectioned or scanned. Both require similar root-cause fixes but with different process priorities.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Sink Mark vs. Void: At a Glance<\/h3><div class=\"overflow-x-auto w-full px-2 mb-6\"><table class=\"min-w-full border-collapse text-sm leading-[1.7] whitespace-normal\"><thead class=\"text-left\"><tr><th class=\"text-text-100 border-b-0.5 border-border-300\/60 py-2 pr-4 align-top font-bold\" scope=\"col\">Feature<\/th><th class=\"text-text-100 border-b-0.5 border-border-300\/60 py-2 pr-4 align-top font-bold\" scope=\"col\">Sink Mark<\/th><th class=\"text-text-100 border-b-0.5 border-border-300\/60 py-2 pr-4 align-top font-bold\" scope=\"col\">Void<\/th><\/tr><\/thead><tbody><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Location<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Surface depression<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Internal bubble\/cavity<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Visibility<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Visible<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Usually invisible externally<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Detection<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Visual inspection<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">X-ray, CT scan, cross-section<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Cause<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Skin collapses inward<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Skin too rigid to collapse; vacuum forms inside<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Appearance<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Dent or dimple on part surface<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Internal air pocket<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Most common in<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Thin-skinned parts, semi-crystalline materials<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Thick-walled rigid parts, PC, ABS<\/td><\/tr><tr><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Primary concern<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Cosmetics and surface quality<\/td><td class=\"border-b-0.5 border-border-300\/30 py-2 pr-4 align-top\">Structural integrity<\/td><\/tr><\/tbody><\/table><\/div><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">Why Do Voids Form Instead of Sink Marks?<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">When a part has a rigid outer skin \u2014 typically because it cooled quickly or it&#8217;s made of a stiffer material like PC or ABS\u2014the skin resists the pull of inner shrinkage. Instead of the surface caving in (sink mark), a vacuum pocket forms inside the material. You end up with a part that looks fine on the outside but has a hollow bubble inside.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Voids are particularly dangerous in structural or load-bearing applications. A part with internal voids may pass visual inspection and dimensional checks but fail mechanically under load.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">How to Address Sink Marks<\/h3><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Increase packing pressure and holding time<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Reduce wall thickness or core out thick sections<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Optimize gate placement<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Switch to lower-shrinkage material or use glass-filled grade<\/li><\/ul><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">How to Address Voids<\/h3><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Increase packing pressure (same direction as sinks)<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Slow down injection speed slightly \u2014 fast injection can trap air<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Improve gate and runner design to allow better packing<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Check for moisture in the material \u2014 hygroscopic resins like nylon or PC need proper drying; moisture turns to steam and creates internal bubbles<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Reduce mold temperature to allow a faster-forming outer skin that&#8217;s <em>slightly<\/em> more flexible<\/li><\/ul><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">The Key Practical Difference<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">For sinks, the surface is the problem \u2014 and you fix it by giving more material to the surface (packing) or by redesigning to reduce the mass differential. For voids, the interior is the problem \u2014 and while packing helps, you also need to ensure the outer skin has a bit more flexibility so material can be drawn in rather than creating a vacuum. Drying conditions, injection speed, and back pressure all matter more for voids than for sinks.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If you&#8217;re unsure which defect you have, here&#8217;s a quick test: press your fingernail gently into the suspected area. If the surface deflects slightly, it&#8217;s a sink. If it feels solid but you still suspect an issue, cut the part \u2014 or send it for CT scanning.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-1d7b210 e-flex e-con-boxed e-con e-parent\" data-id=\"1d7b210\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-17bd2b2 elementor-widget elementor-widget-heading\" data-id=\"17bd2b2\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Should You Use Gas-Assisted Injection Molding to Solve Sink Marks?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-bf37096 elementor-widget elementor-widget-image\" data-id=\"bf37096\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/gas-assisted-injection-molding-process.jpg\" class=\"attachment-large size-large wp-image-36288\" alt=\"\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/gas-assisted-injection-molding-process.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/gas-assisted-injection-molding-process-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/gas-assisted-injection-molding-process-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/gas-assisted-injection-molding-process-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-03900d5 elementor-widget elementor-widget-text-editor\" data-id=\"03900d5\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Sometimes, no matter what you do with packing pressure and design tweaks, thick sections remain a problem. This is where <a class=\"underline underline underline-offset-2 decoration-1 decoration-current\/40 hover:decoration-current focus:decoration-current\" href=\"https:\/\/dimud.com\/services\/injection-molding-services\/gas-assisted-injection-molding\/\">gas-assisted injection molding<\/a> becomes a genuinely useful alternative \u2014 especially for handles, thick-walled structural parts, and furniture components.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Gas-assisted injection molding eliminates sink marks in thick sections by injecting pressurized nitrogen gas into the part after initial material injection. The gas forms a hollow channel through the thickest part of the geometry, effectively removing the core material mass that causes shrinkage and sinks. This creates a lighter part with a smooth outer surface and eliminates the thick sections that generate sink marks \u2014 without requiring major design changes to wall thickness.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">How It Works<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">The process partially fills the cavity with plastic, then injects nitrogen gas through a gas pin. The gas pushes the molten core outward, packing the outer walls against the mold surface while hollowing the interior. The result is a part with a smooth, sink-free surface and a hollow interior in the thick sections.<\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">When Gas-Assist Makes Sense<\/h3><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Thick-walled parts (handle grips, structural tubes, thick ribs)<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Parts where coring out is structurally not feasible<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Large cosmetic surfaces where any sink is unacceptable<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Parts where reducing weight is also a goal<\/li><\/ul><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Gas-assist requires specific tooling design and gas injection equipment, so it&#8217;s not a drop-in fix \u2014 but for the right part, it&#8217;s one of the cleanest solutions to chronic sink mark problems.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-c5d171c e-flex e-con-boxed e-con e-parent\" data-id=\"c5d171c\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f5e8c42 elementor-widget elementor-widget-heading\" data-id=\"f5e8c42\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">How Does Mold Flow Analysis Help Predict and Prevent Sink Marks?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0bbe2c7 elementor-widget elementor-widget-image\" data-id=\"0bbe2c7\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" src=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/mold-flow-analysis-simulation.jpg\" class=\"attachment-large size-large wp-image-36291\" alt=\"mold flow analysis simulation\" srcset=\"https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/mold-flow-analysis-simulation.jpg 1280w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/mold-flow-analysis-simulation-400x225.jpg 400w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/mold-flow-analysis-simulation-768x432.jpg 768w, https:\/\/dimud.com\/wp-content\/uploads\/2026\/05\/mold-flow-analysis-simulation-18x10.jpg 18w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-865136f elementor-widget elementor-widget-text-editor\" data-id=\"865136f\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If you&#8217;re going to spend money on tooling, spend a little first on simulation.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\"><strong>Mold flow analysis (MFA) uses simulation software to model how plastic fills, packs, and cools inside a mold cavity before any physical tooling is made. It can predict sink mark locations, warpage, weld lines, and short shots based on part geometry, material properties, gate placement, and process conditions. Running mold flow simulation before mold fabrication allows engineers to optimize wall thickness, adjust gate positions, and identify shrinkage hot spots \u2014 saving significant rework cost after the tool is cut.<\/strong><\/p><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">What Mold Flow Can Tell You<\/h3><ul class=\"[li_&amp;]:mb-0 [li_&amp;]:mt-1 [li_&amp;]:gap-1 [&amp;:not(:last-child)_ul]:pb-1 [&amp;:not(:last-child)_ol]:pb-1 list-disc flex flex-col gap-1 pl-8 mb-3\"><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Where sinks are likely to occur (shrinkage visualization)<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Whether packing pressure can reach all thick sections<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">How gate location affects pressure distribution<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Cooling uniformity and potential hot spots<\/li><li class=\"font-claude-response-body whitespace-normal break-words pl-2\">Predicted warpage and dimensional deviation<\/li><\/ul><h3 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\">What It Can&#8217;t Do<\/h3><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Mold flow is a simulation \u2014 it&#8217;s based on material databases and idealized conditions. Real-world results can differ. The output is directionally very accurate, but it doesn&#8217;t replace good engineering judgment or a well-run first-article inspection process.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Still, in my experience, parts that go through proper mold flow analysis before tooling almost always have fewer first-shot issues than parts that don&#8217;t. The simulation cost is a fraction of the cost of modifying a completed tool.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">At Dimud, our <a class=\"underline underline underline-offset-2 decoration-1 decoration-current\/40 hover:decoration-current focus:decoration-current\" href=\"https:\/\/dimud.com\/services\/mold-making-service\/precision-mold-manufacturing\/\">precision mold manufacturing<\/a> process integrates mold flow analysis as a standard pre-tooling step. We&#8217;ve caught sink risks on hundreds of projects before a single cavity was cut \u2014 and our clients consistently tell us that early-stage simulation saved them time and real money.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f434cef e-flex e-con-boxed e-con e-parent\" data-id=\"f434cef\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;_ha_eqh_enable&quot;:false,&quot;ekit_has_onepagescroll_dot&quot;:&quot;yes&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-6e29953 elementor-widget elementor-widget-heading\" data-id=\"6e29953\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Conclusion<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1b4c5ba elementor-widget elementor-widget-text-editor\" data-id=\"1b4c5ba\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;ekit_we_effect_on&quot;:&quot;none&quot;}\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Sink marks are one of those defects that seem simple on the surface \u2014 pun intended \u2014 but often trace back to decisions made weeks or months earlier in the design process. The best way to prevent them is to treat wall thickness uniformity, rib-to-wall ratios, and gate placement as non-negotiable design rules from day one.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">Process adjustments help. Material selection matters. But if the geometry is wrong, no parameter setting will fully save you. Catch it early \u2014 in the design file, in the DFM review, in the mold flow simulation \u2014 and your production life gets a lot easier.<\/p><p class=\"font-claude-response-body break-words whitespace-normal leading-[1.7]\">If you&#8217;re designing a part with thick sections, complex ribs, or cosmetic surface requirements and want to review it for sink mark risk before tooling, our team at Dimud is happy to take a look. <a class=\"underline underline underline-offset-2 decoration-1 decoration-current\/40 hover:decoration-current focus:decoration-current\" href=\"https:\/\/dimud.com\/contact-us\/\">Send us your design for a free DFM review<\/a> and we&#8217;ll flag the issues before they cost you a tool modification.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>In my experience working with plastic part production, sink marks are one of the most common\u2014and most frustrating\u2014defects in injection molding. They may look small on the surface, but they can seriously affect both the appearance and structural quality of a product. Sink marks in injection molding are surface depressions or indentations that appear on [&hellip;]<\/p>\n","protected":false},"author":28,"featured_media":36299,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[97,85],"tags":[],"class_list":["post-36176","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-guide","category-injection-molding-knowledge"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/posts\/36176","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/comments?post=36176"}],"version-history":[{"count":8,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/posts\/36176\/revisions"}],"predecessor-version":[{"id":36303,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/posts\/36176\/revisions\/36303"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/media\/36299"}],"wp:attachment":[{"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/media?parent=36176"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/categories?post=36176"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dimud.com\/fr\/wp-json\/wp\/v2\/tags?post=36176"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}