{"id":10532,"date":"2026-02-05T03:15:27","date_gmt":"2026-02-05T03:15:27","guid":{"rendered":"https:\/\/ideal-pro.com\/?p=10532"},"modified":"2026-02-05T06:45:20","modified_gmt":"2026-02-05T06:45:20","slug":"no-more-cracks-in-injection-molded-parts-heres-why-they-happen-and-how-to-fix-them","status":"publish","type":"post","link":"https:\/\/ideal-pro.com\/ko\/no-more-cracks-in-injection-molded-parts-heres-why-they-happen-and-how-to-fix-them\/","title":{"rendered":"\uc0ac\ucd9c \uc131\ud615 \ubd80\ud488\uc5d0 \ub354 \uc774\uc0c1 \uade0\uc5f4\uc774 \uc0dd\uae30\uc9c0 \uc54a\ub294 \uc774\uc720(\uadf8\ub9ac\uace0 \ud574\uacb0 \ubc29\ubc95!)"},"content":{"rendered":"<p>Cracking in <a href=\"https:\/\/ideal-pro.com\/ko\/your-guide-to-injection-molding-from-design-to-production-parts-a-engineers-playbook-for-zero-defect-manufacturing\/\" target=\"_blank\" rel=\"noopener noreferrer\">injection-molded parts<\/a><sup id=\"fnref-1\"><a href=\"#fn-1\" class=\"footnote-ref\">1<\/a><\/sup>&mdash;whether visible as fine surface crazing, micro-cracks, ejection whitening, full fractures, or damage caused by sticking to the mold (e.g., part or runner adhesion)&mdash;can severely compromise product quality and reliability. Cracks may appear <strong>immediately after demolding<\/strong> (demolding cracks) or later during <strong>use<\/strong> (<a href=\"https:\/\/protomont.com\/understanding-and-preventing-stress-cracking-in-abs-injection-molded-parts\/?srsltid=AfmBOorIhb6q7ipbARgl-ejJpIcX4mL97U4HipXh31IuL2XyhdEIfliK\" target=\"_blank\" rel=\"noopener noreferrer\">in-service cracks<\/a><sup id=\"fnref-2\"><a href=\"#fn-2\" class=\"footnote-ref\">2<\/a><\/sup>).<\/p>\n<p>Below are the primary root causes, categorized by origin&mdash;and practical solutions to prevent them.<\/p>\n<h2><img decoding=\"async\" src=\"https:\/\/ideal-pro.com\/wp-content\/uploads\/2026\/02\/injection-molded-parts-cracking-analysis1.jpg\" alt=\"injection molded parts cracking analysis1\"><\/h2>\n<h3>1. Processing Factors<\/h3>\n<p><strong>(1) <a href=\"https:\/\/ideal-pro.com\/ko\/blog\/solving-short-shots-in-injection-molding-1\/\" target=\"_blank\" rel=\"noopener noreferrer\">Excessive Processing Parameters<\/a><sup id=\"fnref-3\"><a href=\"#fn-3\" class=\"footnote-ref\">3<\/a><\/sup><\/strong><br>\nOverly high injection pressure, fast injection speed, excessive filling volume, or prolonged injection\/holding times can generate excessive internal stress, leading to cracking.<\/p>\n<p><strong>(2) Improper Demolding Practices<\/strong><br>\nRapid or forceful ejection can mechanically stress the part. Adjust ejection speed and pressure to avoid sudden pulling forces that cause demolding cracks.<\/p>\n<p><strong>(3) Mold &amp; Material Temperature Control<\/strong>  <\/p>\n<ul>\n<li>Raise mold temperature slightly to improve part release and reduce thermal stress.  <\/li>\n<li>Lower melt temperature appropriately to prevent thermal degradation&mdash;especially critical for heat-sensitive resins.<\/li>\n<\/ul>\n<p><strong>(4) Weld Lines &amp; Material Degradation<\/strong><br>\nWeld lines (melt fronts meeting) and polymer degradation weaken mechanical strength. Optimize gate location, venting, and processing conditions to minimize these issues.<\/p>\n<p><strong>(5) Mold Release &amp; Surface Contamination<\/strong><br>\nUse mold release agents sparingly and correctly. Regularly clean mold surfaces to remove condensation, oil mist, or residue that may interfere with release or cause surface defects.<\/p>\n<p><strong>(6) Residual Stress Relief<\/strong><br>\nPost-molding annealing (heat treatment) immediately after production helps relieve internal stresses and significantly reduces the risk of delayed cracking.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/ideal-pro.com\/wp-content\/uploads\/2026\/02\/injection-molded-parts-cracking-analysis4.jpg\" alt=\"\uc0ac\ucd9c \uc131\ud615 \ubd80\ud488 \uade0\uc5f4 \ubd84\uc11d4\"><\/p>\n<h3>2. Mold Design Issues<\/h3>\n<p><strong>(1) Uneven Ejection System<\/strong><br>\nEnsure balanced ejection: sufficient ejector pin count and cross-sectional area, adequate draft angles, and highly polished cavity surfaces&mdash;all help prevent localized stress concentration during ejection.<\/p>\n<p><strong>(2) <a href=\"https:\/\/www.3erp.com\/blog\/injection-molding-defects\/\" target=\"_blank\" rel=\"noopener noreferrer\">Poor Part Geometry<\/a><sup id=\"fnref-4\"><a href=\"#fn-4\" class=\"footnote-ref\">4<\/a><\/sup><\/strong><br>\nAvoid sharp corners, thin sections, or abrupt transitions. Use generous fillets and radii to distribute stress evenly and prevent stress concentration points.<\/p>\n<p><strong>(3) Metal Inserts<\/strong><br>\nMinimize use of metal inserts&mdash;differential shrinkage between metal and plastic creates high internal stresses. If unavoidable, design insert geometry carefully (e.g., knurling, undercuts) to improve bonding and reduce stress.<\/p>\n<p><strong>(4) Vacuum Trapping in Deep Cavities<\/strong><br>\nFor deep-cavity parts, incorporate air vents or vacuum break channels to prevent vacuum lock, which makes ejection difficult and risks part deformation or cracking.<\/p>\n<p><strong>(5) Runner &amp; Gate Design<\/strong>  <\/p>\n<ul>\n<li>Ensure the sprue is large enough so that the gate &ldquo;frozen&rdquo; only <em>after<\/em> part ejection&mdash;this avoids pulling forces during release.  <\/li>\n<li>The sprue bushing must fit tightly with the nozzle to prevent cold slug drag, which can cause the part to stick to the fixed half.<\/li>\n<\/ul>\n<p><img decoding=\"async\" src=\"https:\/\/ideal-pro.com\/wp-content\/uploads\/2026\/02\/injection-molded-parts-cracking-analysis2.jpg\" alt=\"injection molded parts cracking analysis2\"><\/p>\n<h3>3. Material-Related Causes<\/h3>\n<p><strong>(1) High Recycled Content<\/strong><br>\nExcessive regrind or recycled material reduces tensile strength and impact resistance&mdash;leading to brittle failure and cracking.<\/p>\n<p><strong>(2) Moisture Absorption<\/strong><br>\nHygroscopic resins (e.g., PA, PET, PC) must be thoroughly dried before processing. Moisture can cause hydrolysis, degrading molecular weight and mechanical properties&mdash;resulting in ejection cracks or in-service failure.<\/p>\n<p><strong>(3) Incompatible or Contaminated Materials<\/strong><br>\nUsing resin grades unsuited for the application (e.g., wrong grade for high-temp use), or contaminated batches (e.g., foreign polymers, dust, degraded particles), can lead directly to premature cracking.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/ideal-pro.com\/wp-content\/uploads\/2026\/02\/injection-molded-parts-cracking-analysis3.jpg\" alt=\"injection molded parts cracking analysis3\"><\/p>\n<h3>4. Machine-Related Factors<\/h3>\n<p><strong>(1) Mismatched Plasticizing Capacity<\/strong>  <\/p>\n<ul>\n<li>Too small a barrel\/screw capacity &rarr; incomplete melting\/mixing &rarr; weak, brittle parts.  <\/li>\n<li>Too large a capacity &rarr; excessive residence time &rarr; thermal degradation &rarr; loss of mechanical integrity.<\/li>\n<\/ul>\n<p>Ensure your machine&rsquo;s (plasticizing) capability matches the shot size and material requirements.<\/p>\n<h3>Final Tip: A Holistic Approach Wins<\/h3>\n<p>Cracking is rarely due to a single factor&mdash;it&rsquo;s usually a combination of processing, mold, material, and equipment issues. Conduct systematic root-cause analysis (e.g., DOE, FMEA) and validate fixes with prototype testing.<\/p>\n<hr><div class=\"footnotes\"><hr><ol><li id=\"fn-1\"><p>Explore this resource to discover effective strategies and insights for enhancing the quality and reliability of injection-molded parts.\r <a href=\"#fnref-1\" class=\"footnote-backref\">&#8617;<\/a><\/p><\/li><li id=\"fn-2\"><p>Exploring in-service cracks will provide insights into maintaining product reliability during usage.\r <a href=\"#fnref-2\" class=\"footnote-backref\">&#8617;<\/a><\/p><\/li><li id=\"fn-3\"><p>Learn how processing parameters impact product quality and how to optimize them for better results.\r <a href=\"#fnref-3\" class=\"footnote-backref\">&#8617;<\/a><\/p><\/li><li id=\"fn-4\"><p>Learn how to design parts effectively to minimize stress concentration and enhance durability.\r <a href=\"#fnref-4\" class=\"footnote-backref\">&#8617;<\/a><\/p><\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"<p>Cracking in injection-molded parts1&mdash;whether visible as fine surface crazing, micro-cracks, ejection whitening, full fractures, or damage caused by sticking to [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":10541,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_seopress_robots_primary_cat":"none","_seopress_titles_title":"","_seopress_titles_desc":"","_seopress_robots_index":"","site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"default","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[21],"tags":[59],"class_list":["post-10532","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","tag-injection-molded-parts"],"acf":[],"_links":{"self":[{"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/posts\/10532","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/comments?post=10532"}],"version-history":[{"count":4,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/posts\/10532\/revisions"}],"predecessor-version":[{"id":10542,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/posts\/10532\/revisions\/10542"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/media\/10541"}],"wp:attachment":[{"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/media?parent=10532"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/categories?post=10532"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ideal-pro.com\/ko\/wp-json\/wp\/v2\/tags?post=10532"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}