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Advances in Polymer Processing Technologies: Injection Molding

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: 30 December 2025 | Viewed by 3883

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Special Issue Editor

Prof. Dr. Shyh-Shin Hwang

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Guest Editor

Department of Mechanical Engineering, Chien-Hsin University of Science and Technology, Taoyuan 320678, Taiwan
Interests: electrical conductivities of fibers; polymers

Special Issue Information

Dear Colleagues,

With the advances in injection molding technology, several technologies, including conformal cooling channels, molding prediction and optimization, smart molding, rapid heating and cooling, polymer foaming, core back, gas counter pressure, and injection–compression molding, have been introduced to overcome the molding problem. In this Special Issue of Polymers, we will provide some leading knowledge about these techniques. Thus, we seek to spotlight findings that incorporate a wide range of topics. Research articles or reviews concerning the topic are welcome.

Prof. Dr. Shyh-Shin Hwang
Guest Editor

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

injection molding
foamed polymer
gas counter pressure
core back
smart molding
molding prediction and optimization
injection–compression molding

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Published Papers (6 papers)

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Research

17 pages, 2859 KB

Open AccessArticle

Investigation of Processing Conditions and Product Geometry in Out-Mold Decoration and Their Effects on Film Adhesion and Deformation

by Hui-Li Chen, Po-Wei Huang, Sheng-Hsun Hsu and Jhong-Sian Wu

Polymers 2025, 17(24), 3239; https://doi.org/10.3390/polym17243239 - 5 Dec 2025

Viewed by 228

Abstract

The growing demand for high-quality decorative polymer surfaces has increased interest in Out Mold Decoration (OMD), yet the combined influence of processing conditions and product geometry on film adhesion and deformation remains insufficiently defined. This study establishes an integrated framework that connects OMD process parameters with geometry-dependent deformation behavior using polycarbonate films printed with an ink grid. Adhesion and surface quality were evaluated using 2.5D specimens, while 3D models with varied fillet radii, slopes, and heights enabled quantitative assessment of grid-spacing evolution and thickness distribution. Results show that preheating smooths the film without improving adhesion, whereas increasing the forming environment temperature enhances both bonding and surface quality within the material’s thermal tolerance. Vacuum pressure strengthens film–substrate contact but requires moderation to prevent overstretching. An optimized condition of 100 °C preheating, 90 °C forming temperature, and 2.5 kg vacuum pressure provides a balanced performance. Geometric factors exert strong control over deformation, with small radii, steep slopes, and tall features producing greater strain and nonuniform thinning. These findings establish practical processing windows and geometry guidelines for achieving reliable OMD components that integrate high visual quality with stable adhesion performance. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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34 pages, 19727 KB

Open AccessArticle

Internal Induction Heating for Local Heating in Injection Molding

by Thanh Trung Do, Huynh Duc Thuan, Tran Minh The Uyen, Nguyen Thanh Hon, Pham Son Minh and Tran Anh Son

Polymers 2025, 17(21), 2906; https://doi.org/10.3390/polym17212906 - 30 Oct 2025

Viewed by 526

Abstract

This study introduces Internal Induction Heating (In-IH) as an efficient method for local mold temperature control in thin-walled polypropylene (PP) injection molding. Unlike conventional systems that are slow and energy-intensive, the insert is integrated directly into the induction circuit in the In-IH system, generating eddy currents for rapid and localized heating. Numerical and experimental analyses were performed to examine the effects of insert geometry and heating parameters; it was found that thinner inserts achieved higher surface temperatures—the 0.5 mm insert reached ~550 °C, while the 2.0 mm insert reached only ~80 °C—confirming an inverse relationship between thickness and temperature. Narrower inserts (25 mm) concentrated heat more effectively, whereas wider ones yielded better temperature uniformity. The cooling conditions strongly affected the temperature gradients. Mold-filling experiments demonstrated that In-IH significantly improved the flowability of PP: at 180 °C, the 0.4 mm specimen achieved a flow length of 85.33 mm, compared with 43.66 mm for the 0.2 mm specimen. At 250–300 °C, all samples approached full filling (~100 mm). The simulation and experimental results agreed, with a maximum deviation of 10%, confirming that In-IH provides rapid, energy-efficient, and precise temperature control, thus enhancing melt flow and product quality for thin-walled PP components. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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19 pages, 13706 KB

Open AccessArticle

Influence of Draft Angle Design on Surface Texture–Dimensional Accuracy Coupling in Injection-Molded Commodity and Engineering Polymers with Semi-Crystalline and Amorphous Characteristics

by Hui-Li Chen, Po-Wei Huang and Yu-Shan Huang

Polymers 2025, 17(21), 2892; https://doi.org/10.3390/polym17212892 - 29 Oct 2025

Viewed by 501

Abstract

In injection molding, draft angle design plays a critical role in ensuring smooth de-molding and maintaining surface quality. With the growing emphasis on aesthetics and the increasing demand for the appearance of plastic products, the need for textured plastic components has continuously risen. The coupling between surface texture replication and dimensional accuracy has become an important indicator of product performance. However, systematic studies on the interaction between different polymer materials and draft angle design remain limited. This study aims to investigate the influence of draft angle variation on the surface texture quality and dimensional stability of injection-molded parts by comparing the differences between crystalline and amorphous thermoplastic materials, as well as between commodity and engineering plastics. Four representative polymers, namely polypropylene (PP), polyoxymethylene (POM), acrylonitrile-butadiene-styrene (ABS), and polycarbonate (PC), were selected to examine the impact of material characteristics on surface texture replication after molding. In addition, product geometries incorporating eight draft angles (0° to 3.5°) were designed. Surface texture replication was analyzed using scanning electron microscopy (SEM) and surface profilometry, while dimensional deformation was measured with a high-precision optical measuring instrument. The results show that draft angle variation has a limited influence on the overall trend of dimensional deformation, but it has a significant effect on the clarity of surface replication. Crystalline polymers exhibited generally higher surface roughness than amorphous polymers, and the distinction between commodity and engineering plastics, particularly those requiring higher processing temperatures, also led to higher roughness (PP > POM; ABS > PC). Dimensional deformation was more pronounced in crystalline polymers (POM > PP > ABS > PC). SEM observations further confirmed that higher roughness corresponded to clearer and more distinguishable texture patterns, whereas lower roughness resulted in blurred or indistinct textures. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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Graphical abstract

17 pages, 8198 KB

Open AccessArticle

Determination of Optimal Reinforcement Ratios for Injection Molded Engineering Components: A Numerical Simulation

by Fuat Tan and Oğuz Veli Satı

Polymers 2025, 17(20), 2793; https://doi.org/10.3390/polym17202793 - 19 Oct 2025

Viewed by 597

Abstract

In this work, the influence of glass fibers on the performance of the injection molding process for a PA6-based AR15/M4 grip was investigated numerically. The process was realistically modeled using Autodesk Moldflow Insight for different glass fiber percentages (0 wt%, 15 wt%, 30 wt%, 45 wt%). The simulation results were evaluated, including the temperature distribution, flow time, pressure drop, pumping power, volumetric shrinkage and warpage displacement. The findings indicate that, with 15 wt% glass fibers, the material exhibits the shortest fill period (0.62 s) and the lowest pressure drop (0.0061 MPa) and power consumption (0.000433 kW), indicating maximum flow efficiency. On the other hand, a 30 wt% GF setup exhibited the largest volumetric shrinkage (17.76% at most) and warpage (Y: 1.213 mm), even though it had better thermal conductivity. The 45 wt% GF material exhibited the lowest amount of shrinkage and distortion but led to a greater energy consumption compared to 30 wt% GF. Overall, the 15 wt% GF grade provided the highest average process efficiency and dimensional accuracy; therefore, it is the most appropriate grade for precision molded firearm components. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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37 pages, 28692 KB

Open AccessArticle

Application of Cooling Layer and Thin Thickness Between Coolant and Cavity for Mold Temperature Control and Improving Filling Ability of Thin-Wall Injection Molding Product

by Tran Minh The Uyen, Pham Son Minh and Bui Chan Thanh

Polymers 2025, 17(19), 2658; https://doi.org/10.3390/polym17192658 - 30 Sep 2025

Cited by 1 | Viewed by 793

Abstract

Effective thermal management of molds is a governing factor of the quality and stability of the injection molding process. This study introduces and validates an integrated cooling layer within a thin-walled insert mold designed to enhance thermal control and cavity filling performance. A coupled heat transfer simulation model was developed and subsequently calibrated against experimental temperature measurements. To isolate the mold’s intrinsic thermal response, temperatures were measured during distinct heating and cooling cycles, free from the perturbations of polymer melt flow. The validated mold was then installed on a Haitian MA1200 III injection molding machine to conduct molding trials under various injection pressures. A strong correlation was found between the simulation and experimental results, particularly as pressure increased, which significantly improved cavity filling and reduced the deviation between the two methods. The integrated cooling layer was shown to enhance heat dissipation, minimize thermal gradients, and promote a more uniform thermal field. This, in turn, improved filling stability, especially at moderate injection pressures. These findings provide robust quantitative data for simulation model calibration and mold design optimization, highlighting the potential of advanced cooling strategies to significantly enhance injection molding performance. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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28 pages, 4538 KB

Open AccessArticle

Investigation of the Melt-Rotation Effects on Fiber Orientation Variation and Geometrical Shrinkage in FRP Injection-Molded Parts

by Jing-Kai Gao, Fang-Lin Hsieh, Min-Yuan Chien and Chao-Tsai Huang

Polymers 2025, 17(17), 2360; https://doi.org/10.3390/polym17172360 - 30 Aug 2025

Viewed by 773

Abstract

The study focuses on the asymmetric shrinkage typically occurring between the upstream and downstream regions of FRP injection-molded products, a challenge that is particularly difficult to manage and improve. Specifically, two sets of four-cavity systems in one mold were utilized as the experimental platform. One set used a balanced runner (BR) system, and the other used a non-balanced runner (NBR) system. Each cavity in the four-cavity systems contained an ASTM D638 standard specimen with dimensions of 63.5 mm × 9.53 mm × 3.5 mm. Both CAE simulation and experimental methods were applied. The results show that the filling patterns from the simulation analysis closely matched those from the experimental study for both BR and NBR systems. Furthermore, by comparing the geometric shrinkage of the injected parts, significant differences were observed in the dimensional deformation in three directions (x, y, and z) between the NBR and BR systems. Specifically, at the end of the filling region (EFR), there was no noticeable difference in shrinkage along the flow direction, but the shrinkage in the cross-flow and thickness directions was reduced in the NBR system. Additionally, for the same cavity (1C) in both BR and NBR systems, the melt-rotation effect significantly reduced shrinkage in both the cross-flow and thickness directions. These findings strongly suggest that melt rotation can effectively modify the dimensional shrinkage of injection-molded parts. Moreover, fiber orientation analyses of the 1C cavity were also performed using CAE simulation for both BR and NBR systems. The results show that in the NBR system, the melt-rotation effect substantially alters the fiber orientation. Specifically, the fiber orientation tensors in the cross-flow (A₂₂) direction exhibit a decreasing trend. It can be speculated that the melt rotation alters the flow field, which subsequently changes the fiber orientation by reducing the flow-fiber coupling effect, thereby reducing the upstream-to-downstream asymmetry in the cross-flow direction. Through in-depth analysis, it is demonstrated that the correlation between the macroscopic geometric shrinkage and the microscopic fiber orientation changes is highly consistent. Specifically, in the EFR, ΔA₂₂ decreased by 0.0376, improving upstream/downstream shrinkage asymmetry in the cross-flow direction (Ly). Future work will investigate alternative melt-rotation designs and the optimization of model-internal parameters in FOD prediction. Full article

(This article belongs to the Special Issue Advances in Polymer Processing Technologies: Injection Molding)

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