{"id":12702,"date":"2026-05-20T06:01:21","date_gmt":"2026-05-20T06:01:21","guid":{"rendered":"https:\/\/ideal-pro.com\/?p=12702"},"modified":"2026-05-20T06:37:56","modified_gmt":"2026-05-20T06:37:56","slug":"injection-molding-shrinkage-prediction","status":"publish","type":"post","link":"https:\/\/ideal-pro.com\/fr\/injection-molding-shrinkage-prediction\/","title":{"rendered":"Injection Molding Shrinkage: Prediction Methods & Engineering Solutions"},"content":{"rendered":"

With the rapid development of polymer synthesis technology, the mechanical properties of plastics have improved significantly, leading to their widespread use in engineering. In transmission mechanisms and other applications requiring precise dimensional fits, the shape and size accuracy of plastic parts are critical—often reaching precision or even ultra-precision levels.<\/p>\n

Consequently, researchers in the field of\ninjection molding<\/a>\nhave been striving to reduce errors in shrinkage rate prediction<\/strong>. Accurate prediction is key to shortening mold manufacturing cycles and improving the yield rate of injection molded products.<\/p>\n

\"Injection<\/p>\n

\n

Experimental Data Fitting Method for Shrinkage Prediction<\/h2>\n

Initially, attention was focused on how fluctuations in processing conditions affected shrinkage. Researchers conducted extensive experiments to find a quantitative relationship between process parameters and shrinkage rates.<\/p>\n

Based on accumulated experience, scholars proposed using experimental data fitting<\/strong> to predict shrinkage under actual production conditions. The basic idea involves:<\/p>\n

    \n
  • Conducting multi-factor orthogonal experiments.<\/li>\n
  • Measuring shrinkage under various parameters (barrel temperature, injection pressure, holding time, mold temperature, cooling time, etc.).<\/li>\n
  • Fitting a functional relationship between shrinkage and these parameters based on sample data.<\/li>\n<\/ul>\n

    In practice, designers substitute actual process parameters into these equations to get corresponding shrinkage values, which are then weighted to determine the \"actual shrinkage rate\" needed for mold design.<\/p>\n

    \n

    ⚠️ Limitations:<\/strong><\/p>\n

      \n
    • Lack of Comparability:<\/strong> If the actual part's shape, gate location, or size differs from the experimental setup, the internal pressure and temperature distributions will differ, making the experimental data less applicable.<\/li>\n
    • Ignoring Constraints:<\/strong> This method often fails to account for the \"in-mold constraint effect\" during the shrinkage process, making it difficult to generalize.<\/li>\n<\/ul>\n<\/blockquote>\n
      \n

      Numerical Simulation Methods for Shrinkage Prediction<\/h2>\n

      To predict shrinkage more accurately, one must consider the influence of the mold structure. Since mold structures vary infinitely, relying solely on experiments is impossible. Thus, Computer-Aided Engineering (CAE)<\/strong> and mathematical simulation have become frontier research areas.<\/p>\n

      Numerical simulation of injection molding began in the 1960s. By the 1990s, analysis of filling, packing, and cooling had matured, allowing scholars to predict part dimensions and warpage.<\/p>\n

      The Calculation Process<\/h3>\n
        \n
      1. Post-Packing Analysis:<\/strong> After packing ends, thermal shrinkage and crystallization shrinkage are calculated based on compressibility, thermal expansion coefficients, and crystallization kinetics.<\/li>\n
      2. Equivalent Loads:<\/strong> Instead of immediate strain, shrinkage is converted into equivalent nodal loads. Elastic or viscoelastic models are used to solve the part's response.<\/li>\n
      3. Residual Stress:<\/strong> Asymmetrical cooling causes bending trends. Since the mold constrains this deformation, it creates residual stress.<\/li>\n
      4. Post-Ejection:<\/strong> Once ejected, the part deforms under initial stress and thermal loads.<\/li>\n<\/ol>\n

        Software and Models<\/h3>\n

        Different software packages utilize different models:<\/p>\n

          \n
        • Thermo-elastic models:<\/strong> Used by Japan's Toyota Central R&D Labs (IMAP) and Autodesk Moldflow.<\/li>\n
        • Thermo-viscoelastic models:<\/strong> Used by ACTech (C-MOLD), and researchers like Chang et al. and Dr. Li Haimei (Dalian University of Technology).<\/li>\n<\/ul>\n

          Generally, thermo-elastic models<\/strong> are used for post-ejection structural analysis (glassy state), while thermo-viscoelastic models<\/strong> are better for the in-mold solidification process (high-elastic state).<\/p>\n

          \"Numerical<\/p>\n

          The Challenge of Viscoelasticity<\/h3>\n

          Most current simulations use the Thermorheologically Simple Material Model<\/strong> (linear thermo-viscoelastic). However, this strictly applies only to isotropic, amorphous plastics (non-polar). Crystalline plastics and polar materials do not satisfy the linear conditions of the Boltzmann superposition principle.<\/p>\n

          While neural networks (proposed by Lee and Youn) have been explored to model non-linear behaviors, the training process is too complex for practical application.<\/p>\n

          \n

          Engineering Research on Shrinkage Simulation<\/h2>\n

          While linear viscoelastic analysis introduces theoretical errors, its accuracy is often sufficient for engineering if<\/em> material data is available. The real bottleneck is the lack of specific material constants for every batch of resin.<\/p>\n

          A Practical Engineering Approach<\/h3>\n

          To address the needs of the mold industry, a simplified yet effective method has been proposed. Factors affecting shrinkage are categorized into three groups:<\/p>\n

            \n
          1. Material Characteristics:<\/strong> Viscosity, specific heat, PVT data, etc.<\/li>\n
          2. Process Conditions:<\/strong> Temperatures, pressures, speeds controlled by the operator.<\/li>\n
          3. Mold Structure:<\/strong> Cavity shape, gate location, cooling system layout.<\/li>\n<\/ol>\n

            The Core Strategy:<\/strong>\nThe mold structure determines the trend<\/em> of shrinkage distribution, while material and process factors determine the magnitude<\/em>.<\/p>\n

            Instead of measuring every material constant, we can:<\/p>\n

              \n
            1. Use standard material data (e.g., Polystyrene for amorphous, Polypropylene for semi-crystalline) to simulate the shrinkage distribution trend<\/strong>.<\/li>\n
            2. Combine this trend with the average shrinkage rate ($S_a$)<\/strong> provided by the plastic manufacturer.<\/li>\n<\/ol>\n

              Simplified Calculation Rules<\/h3>\n

              To simplify the math, we assume that the part shrinks towards the gate along flow paths.<\/p>\n

                \n
              • In-Mold:<\/strong> Shrinkage is constrained by the mold walls.<\/li>\n
              • Post-Ejection:<\/strong> Free shrinkage occurs.<\/li>\n<\/ul>\n

                By calculating the shrinkage relative to the gate and averaging it ($Sc$), we can adjust the predicted shrinkage ($S<\/em>{pred}$) for any node using the manufacturer's average ($S_a$):<\/p>\n

                $$ S{pred} = S<\/em>{calculated} times left( frac{S_a}{S_c} right) $$<\/p>\n

                This method bypasses the need for expensive material testing while maintaining high accuracy in predicting shrinkage trends.<\/p>\n

                \n

                Case Study: Sliding Top Mechanism<\/h2>\n

                Beyond shrinkage, successful mold design relies on reliable mechanisms. One such example is the Sliding Top (Lifter) Mechanism<\/strong> used for internal core pulling.<\/p>\n

                \"Diagram<\/p>\n

                Mechanism Components:<\/strong><\/p>\n

                  \n
                1. Fixed mold core<\/li>\n
                2. Moving mold core<\/li>\n
                3. Moving mold plate<\/li>\n
                4. Moving mold fixed plate<\/li>\n
                5. Angled lifter core<\/strong><\/li>\n
                6. Pulley\/Slider<\/li>\n
                7. Guide groove block<\/li>\n
                8. Ejector plate A\/B<\/li>\n<\/ol>\n

                  How it works:<\/strong>\nThe ejector rod pushes the plates, driving the angled lifter core (5) to perform an oblique motion. The pulley (6) slides within the guide groove (7), completing the internal core pulling and ejection simultaneously.<\/p>\n

                    \n
                  • Typical Angle:<\/strong> 5° to 15°.<\/li>\n
                  • Pros:<\/strong> Simple fabrication, low cost, reliable action.<\/li>\n
                  • Cons:<\/strong> Located in the center of the mold, making lubrication difficult; long strokes can cause wear and require frequent replacement.<\/li>\n<\/ul>\n
                    \n

                    Conclusion<\/h2>\n

                    Experimental methods are useful for understanding specific factor influences but cannot fully predict shrinkage for complex geometries. While numerical simulation is theoretically robust, it is often hindered by high costs and a lack of material data.<\/p>\n

                    The proposed engineering solution—combining the shrinkage distribution trend<\/strong> derived from mold structure with the material's average shrinkage rate<\/strong>—offers a practical balance. It simplifies calculation, saves time, and provides mold designers with a reliable theoretical basis for creating high-precision molds.<\/p>","protected":false},"excerpt":{"rendered":"

                    With the rapid development of polymer synthesis technology, the mechanical properties of plastics have improved significantly, leading to their widespread […]<\/p>\n","protected":false},"author":2,"featured_media":12706,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_seopress_robots_primary_cat":"","_seopress_titles_title":"Injection Molding Shrinkage: Prediction Methods & Engineering Solutions","_seopress_titles_desc":"Explore the evolution of shrinkage prediction in injection molding. From experimental fitting to numerical simulation and practical engineering solutions for mold design.","_seopress_robots_index":"","_seopress_analysis_target_kw":"","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":[167,103,233],"class_list":["post-12702","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","tag-injection-molding-shrinkage","tag-mold-design","tag-shrinkage-prediction"],"acf":[],"_links":{"self":[{"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/posts\/12702","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/comments?post=12702"}],"version-history":[{"count":4,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/posts\/12702\/revisions"}],"predecessor-version":[{"id":12709,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/posts\/12702\/revisions\/12709"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/media\/12706"}],"wp:attachment":[{"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/media?parent=12702"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/categories?post=12702"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ideal-pro.com\/fr\/wp-json\/wp\/v2\/tags?post=12702"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}