Polymers

Research

17 pages, 1038 KiB

Open AccessArticle

Cycle-Based Control of Injection Moulding Process in Presence of Material Dual Sourcing Using Mass Feedback

by Rasmus Aagaard Hertz, Ole Therkelsen, Søren Kristiansen, Jesper Kjærsgaard Christensen, Frederik Agervig Hansson and Lasse Schmidt

Polymers 2024, 16(13), 1808; https://doi.org/10.3390/polym16131808 - 26 Jun 2024

Viewed by 1371

Abstract

The low cost and precise tolerances of plastic injection moulded products are a major reason for the popularity of the manufacturing method. The tolerances are greatly influenced by the equipment, raw material and moulding process. One challenge is the raw material variation. This [...] Read more.

The low cost and precise tolerances of plastic injection moulded products are a major reason for the popularity of the manufacturing method. The tolerances are greatly influenced by the equipment, raw material and moulding process. One challenge is the raw material variation. This paper presents a production process using cycle based feedback of cycle mass, for control of part properties in the presence of material variation from dual sourcing. The part properties considered are part mass and outer dimensions. The process uses direct cycle mass feedback without additional process measurements in the proposed controller structure. The designed controller structure is tested in a multi-cavity mould while using raw materials from multiple vendors, encompassing five different grades. The results show a total decrease in part mass variance of approximately 50% and a decrease of length and width variance of approximately 40% compared to a moulding process with fixed settings. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

21 pages, 1126 KiB

Open AccessArticle

Development and Validation of a 1D Dynamic Model of an Injection Moulding Process and Design of a Model-Based Nozzle Pressure Controller

by Rasmus Aagaard Hertz, Ole Therkelsen, Søren Kristiansen, Jesper Kjærsgaard Christensen, Frederik Agervig Hansson and Lasse Schmidt

Polymers 2024, 16(10), 1432; https://doi.org/10.3390/polym16101432 - 18 May 2024

Cited by 1 | Viewed by 1037

Abstract

A 1D model describing the dynamics of an injection moulding machine and the injection process is presented. The model describes an injection cylinder actuated by a dual-pump electro–hydraulic speed-variable drive and the filling, holding and cooling phases of the injection moulding process utilising [...] Read more.

A 1D model describing the dynamics of an injection moulding machine and the injection process is presented. The model describes an injection cylinder actuated by a dual-pump electro–hydraulic speed-variable drive and the filling, holding and cooling phases of the injection moulding process utilising amorphous polymers. The model is suggested as the foundation for the design of model-based pressure controllers of, e.g., the nozzle pressure. The focus is on using material, mould and machine properties to construct the model, making it possible to analyse and design the dynamic system prior to manufacturing hardware or conducting experiments. Both the presented model and the developed controller show good agreement with experimental results. The proposed method is general in nature and enables the design, analysis and evaluation of the machine, material and mould dynamics for controller design based solely on the physical properties of the system. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

15 pages, 4566 KiB

Open AccessArticle

Expansion Injection Molding Process Using Clamping Force for Melt Compression

by Joon Hyoung Park and Sun Kyoung Kim

Polymers 2024, 16(3), 424; https://doi.org/10.3390/polym16030424 - 2 Feb 2024

Viewed by 1618

Abstract

Melt expansion followed by compression has been utilized for high-speed filling. In general, this technology was developed for a machine level. Recently, mold-level technology has been tried. In this study, an expansion injection molding process was examined, which included compressing a polymer melt [...] Read more.

Melt expansion followed by compression has been utilized for high-speed filling. In general, this technology was developed for a machine level. Recently, mold-level technology has been tried. In this study, an expansion injection molding process was examined, which included compressing a polymer melt through cylinder action facilitated by the movement of the platen, followed by the expansion of the polymer melt into a mold cavity. A mold system including temperature control and valve actions, similar to hot runner systems, was designed and built. The test results show good filling when the injection pressure was high. Simulations were also carried out, highlighting consistent pressure and filling trends, while revealing limitations tied to the characteristics of the state model. This research indicates promise for expansion injection molding through platen compression but emphasizes the need for the seamless integration of valve action with the injection molding machine for large-scale production. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

17 pages, 6713 KiB

Open AccessArticle

Adhesion-Induced Demolding Forces of Hard Coated Microstructures Measured with a Novel Injection Molding Tool

by Maximilian Schoenherr, Holger Ruehl, Thomas Guenther, André Zimmermann and Bernd Gundelsweiler

Polymers 2023, 15(5), 1285; https://doi.org/10.3390/polym15051285 - 3 Mar 2023

Cited by 5 | Viewed by 2894

Abstract

The demolding of plastic parts remains a challenging aspect of injection molding. Despite various experimental studies and known solutions to reduce demolding forces, there is still not a complete understanding of the effects that occur. For this reason, laboratory devices and in-process measurement [...] Read more.

The demolding of plastic parts remains a challenging aspect of injection molding. Despite various experimental studies and known solutions to reduce demolding forces, there is still not a complete understanding of the effects that occur. For this reason, laboratory devices and in-process measurement injection molding tools have been developed to measure demolding forces. However, these tools are mostly used to measure either frictional forces or demolding forces for a specific part geometry. Tools that can be used to measure the adhesion components are still the exception. In this study, a novel injection molding tool based on the principle of measuring adhesion-induced tensile forces is presented. With this tool, the measurement of the demolding force is separated from the actual ejection step of the molded part. The functionality of the tool was verified by molding PET specimens at different mold temperatures, mold insert conditions and geometries. It was demonstrated that once a stable thermal state of the molding tool was achieved, the demolding force could be accurately measured with a comparatively low force variance. A built-in camera was found to be an efficient tool for monitoring the contact surface between the specimen and the mold insert. By comparing the adhesion forces of PET molded on polished uncoated, diamond-like carbon and chromium nitride (CrN) coated mold inserts, it was found that a CrN coating reduced the demolding force by 98.5% and could therefore be an efficient solution to significantly improve demolding by reducing adhesive bond strength under tensile loading. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

14 pages, 3264 KiB

Open AccessArticle

Development, Simulation of Temperatures, and Experimentation in Injection Molds Obtained through Additive Manufacturing with Photocurable Polymeric Resins

by Adrian Benitez-Lozano, Carlos Vargas-Isaza and Wilfredo Montealegre-Rubio

Polymers 2023, 15(5), 1071; https://doi.org/10.3390/polym15051071 - 21 Feb 2023

Cited by 1 | Viewed by 1978

Abstract

Additive manufacturing (AM) is a relatively new option in mold manufacturing for rapid tooling (RT) in injection processes. This paper presents the results of experiments with mold inserts and specimens obtained by stereolithography (SLA), which is a kind of AM. A mold insert [...] Read more.

Additive manufacturing (AM) is a relatively new option in mold manufacturing for rapid tooling (RT) in injection processes. This paper presents the results of experiments with mold inserts and specimens obtained by stereolithography (SLA), which is a kind of AM. A mold insert obtained by AM and a mold produced by traditional subtractive manufacturing were compared to evaluate the performance of the injected parts. In particular, mechanical tests (in accordance with ASTM D638) and temperature distribution performance tests were carried out. The tensile test results of specimens obtained in a 3D printed mold insert were better (almost 15%) than those produced in the duralumin mold. The simulated temperature distribution closely matched its experimental counterpart—the difference in average temperatures was merely 5.36 °C. These findings support the use of AM in injection molding and RT as an excellent alternative for small and medium-sized production runs in the global injection industry. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

22 pages, 6194 KiB

Open AccessArticle

Online Prediction of Molded Part Quality in the Injection Molding Process Using High-Resolution Time Series

by Lucas Bogedale, Stephan Doerfel, Alexander Schrodt and Hans-Peter Heim

Polymers 2023, 15(4), 978; https://doi.org/10.3390/polym15040978 - 16 Feb 2023

Cited by 5 | Viewed by 3079

Abstract

Process-data-supported process monitoring in injection molding plays an important role in compensating for disturbances in the process. Until now, scalar process data from machine controls have been used to predict part quality. In this paper, we investigated the feasibility of incorporating time series [...] Read more.

Process-data-supported process monitoring in injection molding plays an important role in compensating for disturbances in the process. Until now, scalar process data from machine controls have been used to predict part quality. In this paper, we investigated the feasibility of incorporating time series of sensor measurements directly as features for machine learning models, as a suitable method of improving the online prediction of part quality. We present a comparison of several state-of-the-art algorithms, using extensive and realistic data sets. Our comparison demonstrates that time series data allow significantly better predictions of part quality than scalar data alone. In future studies, and in production-use cases, such time series should be taken into account in online quality prediction for injection molding. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

23 pages, 7024 KiB

Open AccessArticle

A Holistic Approach to Cooling System Selection and Injection Molding Process Optimization Based on Non-Dominated Sorting

by Janez Gotlih, Miran Brezocnik, Snehashis Pal, Igor Drstvensek, Timi Karner and Tomaz Brajlih

Polymers 2022, 14(22), 4842; https://doi.org/10.3390/polym14224842 - 10 Nov 2022

Cited by 12 | Viewed by 2249

Abstract

This study applied a holistic approach to the problem of controlling the temperature of critical areas of tools using conformal cooling. The entire injection molding process is evaluated at the tool design stage using four criteria, one from each stage of the process [...] Read more.

This study applied a holistic approach to the problem of controlling the temperature of critical areas of tools using conformal cooling. The entire injection molding process is evaluated at the tool design stage using four criteria, one from each stage of the process cycle, to produce a tool with effective cooling that enables short cycle times and ensures good product quality. Tool manufacturing time and cost, as well as tool life, are considered in the optimization by introducing a novel tool-efficiency index. The multi-objective optimization is based on numerical simulations. The simulation results show that conformal cooling effectively cools the critical area of the tool and provides the shortest cycle times and the lowest warpage, but this comes with a trade-off in the tool-efficiency index. By using the tool-efficiency index with non-dominated sorting, the number of relevant simulation cases could be reduced to six, which greatly simplifies the decision regarding the choice of cooling system and process parameters. Based on the study, a tool with conformal cooling channels was made, and a coolant inlet temperature of 20 °C and a flow rate of 5 L/min for conformal and 7.5–9.5 L/min for conventional cooling channels were selected for production. The simulation results were validated by experimental measurements. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

16 pages, 5410 KiB

Open AccessArticle

Development of an Epoxy-Based Rapid Tool with Low Vulcanization Energy Consumption Channels for Liquid Silicone Rubber Injection Molding

by Chil-Chyuan Kuo, Qing-Zhou Tasi and Song-Hua Hunag

Polymers 2022, 14(21), 4534; https://doi.org/10.3390/polym14214534 - 26 Oct 2022

Cited by 10 | Viewed by 2434

Abstract

Liquid silicone rubber (LSR) parts have some distinct characteristics such as superior heat stability, low-temperature flexibility, aging resistance, and chemical resistance. From an industrial standpoint, the uniform vulcanization temperature of LSR is an important research point. However, the uniformity of the vulcanization temperature [...] Read more.

Liquid silicone rubber (LSR) parts have some distinct characteristics such as superior heat stability, low-temperature flexibility, aging resistance, and chemical resistance. From an industrial standpoint, the uniform vulcanization temperature of LSR is an important research point. However, the uniformity of the vulcanization temperature of LSR has been limited since the layout of the cartridge heater incorporated in the conventional steel mold does not follow the profile of the mold cavity. Metal additive manufacturing can be used to make LSR injection molds with conformal heating channels and conformal cooling channels simultaneously. However, this method is not suitable for a mold required to develop a new LSR product. In this study, a cost-effective approach was proposed to manufacture an LSR injection mold for the pilot run of a new optical lens. A rapid tool with low vulcanization energy consumption channels was proposed, which was incorporated with both a conformal heating channel (CHC) and conformal cooling channel (CCC) simultaneously. The function of the CHC was to vulcanize the LSR in the cavity uniformly, resulting in a shorter cycle time. The function of the CCC was to keep the LSR in a liquid state for reducing runner waste. It was found that the equation of y = −0.006x³ + 1.2114x² − 83.221x + 1998.2 with the correlation coefficient of 0.9883 seemed to be an optimum trend equation for predicting the solidification time of a convex lens (y) using the vulcanizing hot water temperature (x). Additionally, the equation of y = −0.002x³ + 0.1329x² − 1.0857x + 25.4 with the correlation coefficient of 0.9997 seemed to be an optimum prediction equation for the solidification time of a convex lens (y) using the LSR weight (x) since it had the highest correlation coefficient. The solidification time of a convex lens could be reduced by about 28% when a vulcanizing hot water temperature of 70 °C was used in the LSR injection mold with CHC. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

16 pages, 4741 KiB

Open AccessArticle

Quality Definition in Micro Injection Molding Process by Means of Surface Characterization Parameters

by Vincenzo Bellantone, Rossella Surace and Irene Fassi

Polymers 2022, 14(18), 3775; https://doi.org/10.3390/polym14183775 - 9 Sep 2022

Cited by 6 | Viewed by 2038

Abstract

Quality evaluation of micro injection molded products is a complex task, in particular when instruments basing on contact methods are used and issues in measurements could arise due to the contact tool dimension not fitting well with extremely narrow features. Therefore, in these [...] Read more.

Quality evaluation of micro injection molded products is a complex task, in particular when instruments basing on contact methods are used and issues in measurements could arise due to the contact tool dimension not fitting well with extremely narrow features. Therefore, in these cases, optical methods may be preferred for the evaluation of molded products’ dimensions and surface quality, especially for parts devoted to applications requiring functional purposes. In this context, the present paper proposes the use of surface parameters as a quality index for the evaluation of both the micro injection molding process and the resulting products. To this aim, two experimental procedures were implemented to allow for: (i) the evaluation of the most suitable surface parameters identified in relation to the process parameters; (ii) comparisons of the surface parameters findings with those obtained by classic dimensional quantity via a designed experimental plan (DoE). The results show that the surface parameters, evaluated in critical areas of the components, can ensure reliable estimates for the surface quality of the molded parts and can be preferred in comparison to linear measurements. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

18 pages, 5849 KiB

Open AccessArticle

Filling-Balance-Oriented Parameters for Multi-Cavity Molds in Polyvinyl Chloride Injection Molding

by Hsi-Hsun Tsai, Shao-Jung Wu, Jia-Wei Liu, Sin-He Chen and Jui-Jung Lin

Polymers 2022, 14(17), 3483; https://doi.org/10.3390/polym14173483 - 25 Aug 2022

Cited by 10 | Viewed by 3001

Abstract

PVC injection molding has constrained temperature and shear rate owing to its temperature sensitivity and high viscosity, as well as its low conductivity. Many challenges are associated with the PVC injection molding process used for producing PVC fittings with a multi-cavity mold. Once [...] Read more.

PVC injection molding has constrained temperature and shear rate owing to its temperature sensitivity and high viscosity, as well as its low conductivity. Many challenges are associated with the PVC injection molding process used for producing PVC fittings with a multi-cavity mold. Once filling imbalance occurs, the gates and/or runner of the mold should be changed by machine tools, which is time- and cost-intensive. Using Moldex3D and the Taguchi method, this study reveals an approach to eliminate imbalanced filling of multi-cavity molds for PVC injection molding. The injection rate optimization of the filling stage is successfully verified to reduce the imbalance. Furthermore, the temperatures of the molded PVC fittings are only slightly increased by the change in injection rate. The temperatures of fittings in the filling and packing are lower than the degradation temperature of PVC. This approach may help technicians to obtain pilot-run samples for the optimization of molding parameters and ensure degradation-free PVC molding. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

21 pages, 5268 KiB

Open AccessArticle

Analysis of Melt Front Behavior of a Light Guiding Plate during the Filling Phase of Micro-Injection Molding

by Wei-Chun Lin, Fang-Yu Fan, Chiung-Fang Huang, Yung-Kang Shen and Liping Wang

Polymers 2022, 14(15), 3077; https://doi.org/10.3390/polym14153077 - 29 Jul 2022

Cited by 4 | Viewed by 1865

Abstract

When the size of a liquid crystal display (LCD) increases, the light guiding plate (LGP) as the main part of the LCD must adopt a wedge-shaped plate to reduce its weight (the thickness of the LGP decreases because of this) and guide the [...] Read more.

When the size of a liquid crystal display (LCD) increases, the light guiding plate (LGP) as the main part of the LCD must adopt a wedge-shaped plate to reduce its weight (the thickness of the LGP decreases because of this) and guide the light to the LCD screen. Micro-injection molding (MIM) is commonly used to manufacture LGPs. During the filling phase of MIM, the entire entering polymer melt front of the LGP should reach the end of the mold cavity at the same time. In this way, there will be no shrinkage or warpage of the LGP in its subsequent application, but it is difficult for the wedge-shaped LGP to meet these requirements. Therefore, the authors hoped to investigate MIM process parameters to change this situation. Otherwise, the LGP is easily deformed during the manufacturing process. Flow characteristics of LGPs were investigated during the filling phase of MIM in this study. Experimental and 3D numerical simulations were used to analyze the hysteresis, i.e., the advance of the polymer melt front of the LGP in MIM. Study results showed that a low injection speed caused a hysteresis effect of the plastic melt front, the solution was to increase the injection speed to improve the situation and an injection speed of 10 cm/s could achieve uniformity of the melt front in MIM. The research results showed that the filling situation of the LGP of MIM in the experiment was very close to that of the 3D numerical simulation. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

16 pages, 4267 KiB

Open AccessArticle

The Investigation of Novel Dynamic Packing Technology for Injection Molded Part Quality Control and Its Production Stability by Using Real-Time PVT Control Method

by Yung-Hsiang Chang, Shia-Chung Chen, Yu-Hung Ting, Ching-Te Feng and Chi-Chuan Hsu

Polymers 2022, 14(13), 2720; https://doi.org/10.3390/polym14132720 - 2 Jul 2022

Cited by 4 | Viewed by 1886

Abstract

Injection molding is an effective mass production process for plastic, partly due to a number of advantages such as complex shape moldability, material selectivity, and a rapid process cycle. However, highly labor-based conventional production restrains the development of the industry. Experience-driven molding setups [...] Read more.

Injection molding is an effective mass production process for plastic, partly due to a number of advantages such as complex shape moldability, material selectivity, and a rapid process cycle. However, highly labor-based conventional production restrains the development of the industry. Experience-driven molding setups are used to trial the mold process, and also for quality checking the molded part for mass production. There is no effective solution for maintaining the production stability and defect-free adjustment. This study aimed to establish scientific packing pressure setup technology to optimize the molded part quality and the stability of consecutive production. The dynamic packing pressure setup technology for molded part quality and the process stability were investigated. This not only achieves the optimization of the packing pressure setup, but the stabilization of quality in mass production. Four major qualities were discussed in this study including tensile strength, regional deviation on shrinkage, total shrinkage, and warpage. The qualities improved by up to 3.9%, 92.9%, 41.9%, and 9.2%, respectively. A series of pilot runs of 300 cycles for two packing pressure control methods were tested to investigate the stability of the qualities. Dynamic packing pressure control improved the weight replication by 54%, reduced total shrinkage by 23%, and improved the warpage by 12%. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

13 pages, 5677 KiB

Open AccessArticle

Feasibility Study on the Fused Filaments of Injection-Molding-Grade Poly(Ethylene Terephthalate) for 3D Printing

by Hsi-Hsun Tsai, Shao-Jung Wu, Yu-De Wu and Wei-Zheng Hong

Polymers 2022, 14(11), 2276; https://doi.org/10.3390/polym14112276 - 2 Jun 2022

Cited by 12 | Viewed by 2547

Abstract

Unlike that of glycol-modified Poly(ethylene terephthalate) (PETG), the crystallinity of PET can be post-adjusted to enhance the mechanical properties of 3D-printed parts such as food-contact tableware and bio-implants. The aforementioned PET material could be 3D printed to produce the desired parts for performance [...] Read more.

Unlike that of glycol-modified Poly(ethylene terephthalate) (PETG), the crystallinity of PET can be post-adjusted to enhance the mechanical properties of 3D-printed parts such as food-contact tableware and bio-implants. The aforementioned PET material could be 3D printed to produce the desired parts for performance evaluation before mass production by injection molding. In this study, using differential scanning calorimetry (DSC), we examined the pellets, extruded filament, and printed specimen to identify variations in melting and crystalline temperatures, as well as crystallinity. It was also shown by Thermogravimetric Analyzer (TGA) that the addition of talcum powder increased the thermal stability of filament and resulted in an interaction between the fillers and polymer matrix. The crystallinities of the filament and printed specimen were then compared with the yield strengths and Young’s moduli to confirm the effects of the decreased molecular weight of the extruded PET filament. The talcum powder effectively improved the viscosity of the PET melted during the extrusion process for the filament and then enhanced the crystallinity of the PET, thereby achieving a significantly higher Young’s modulus. The printed PET specimen presented an excellent yield strength of 25 MPa and ductile properties with strain-at-break values of 30%, successfully indicating potential applications in food-contact tableware and bio-implants. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

17 pages, 10912 KiB

Open AccessArticle

Internal Gas-Assisted Mold Temperature Control for Improving the Filling Ability of Polyamide 6 + 30% Glass Fiber in the Micro-Injection Molding Process

by Tran Minh The Uyen, Thanh Trung Do and Pham Son Minh

Polymers 2022, 14(11), 2218; https://doi.org/10.3390/polym14112218 - 30 May 2022

Cited by 8 | Viewed by 2751

Abstract

In micro-injection molding, the plastic filling in the cavity is limited by the frozen layer due to the rapid cooling of the hot melt when it comes into contact with the surface of the cavity at a lower temperature. This problem is more [...] Read more.

In micro-injection molding, the plastic filling in the cavity is limited by the frozen layer due to the rapid cooling of the hot melt when it comes into contact with the surface of the cavity at a lower temperature. This problem is more serious with composite materials, which have a higher viscosity than pure materials. Moreover, this issue is also more serious with composite materials that have a higher weight percentage of glass filer. In this article, a pre-heating step with the internal gas heating method was used to heat the cavity surface to a high temperature before the filling step to reduce the frozen layer and to improve the filling ability of the composite material (polyamide 6 + 30% glass fiber) in the micro-injection molding process. To heat the cavity surface, an internal gas-assisted mold temperature control (In-GMTC) system was used with a pulsed cooling system. We assessed different mold insert thicknesses (t) and gaps between the gas gate and the heating surface (G) to achieve rapid mold surface temperature control. The heating process was observed using an infrared camera, and the temperature distribution and the heating rate were analyzed. Thereafter, along with the local temperature control, the In-GMTC was used for the micro-injection molding cycle. The results show that, with a gas temperature of 300 °C and a gas gap of 3.5 mm, the heating rate reached 8.6 °C/s. The In-GMTC was also applied to the micro-injection molding process with a part thickness of 0.2 mm. It was shown that the melt flow length had to reach 24 mm to fill the cavity completely. The results show that the filling ability of the composite material increased from 65.4% to 100% with local heating at the melt inlet area when the gas temperature rose from 200 to 400 °C with a 20 s heating cycle. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

18 pages, 11007 KiB

Open AccessArticle

Investigation of the Warpage of a High-Density Polyethylene Pallet by Plastic Injection Compression Molding: Part I—Numerical Approach

by Chun-Der Cheng, Yi-Ling Liao and Hsi-Hsun Tsai

Polymers 2022, 14(7), 1437; https://doi.org/10.3390/polym14071437 - 1 Apr 2022

Cited by 4 | Viewed by 2646

Abstract

Many challenges are associated with the injection compression molding process for producing a half-pallet (1320 mm × 1110 mm × 75 mm, length × width × height), which is butt-welded to another one for enhancing its strength. This pooled high-density polyethylene (HDPE) pallet [...] Read more.

Many challenges are associated with the injection compression molding process for producing a half-pallet (1320 mm × 1110 mm × 75 mm, length × width × height), which is butt-welded to another one for enhancing its strength. This pooled high-density polyethylene (HDPE) pallet is able to endure the impacts of a heavy load and a low ambient temperature. Reducing the warpage of a half-pallet is, therefore, essential for reducing the residual internal stress within the welded portions. An advanced Moldex3D package helps to detail the temperature distribution and warpage of a half-pallet. The pre-setting molding parameters from a mass-production factory produce half-pallets with worse flatness. In this investigation on using appropriate cooling water temperatures within the core and cavity plates of the mold, the numerical results show that the warpage of the top surface of the half-pallet was 11.549 mm, low warpage with respect to this large-scale pallet. Furthermore, the compression speed of 50–60 mm/s may have produced a low flatness of the half-pallet in this study. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

29 pages, 4413 KiB

Open AccessArticle

Metal Additive Manufacturing of Plastic Injection Molds with Conformal Cooling Channels

by Baris Burak Kanbur, Yi Zhou, Suping Shen, Kim Hai Wong, Charles Chen, Abe Shocket and Fei Duan

Polymers 2022, 14(3), 424; https://doi.org/10.3390/polym14030424 - 21 Jan 2022

Cited by 38 | Viewed by 4725

Abstract

Conformal cooling channels (CCCs) are widely used in the plastic injection molding process to improve the product quality and operational performance. Tooling that incorporates CCCs can be fabricated through metal additive manufacturing (MAM). The present work focuses on the MAM of a plastic [...] Read more.

Conformal cooling channels (CCCs) are widely used in the plastic injection molding process to improve the product quality and operational performance. Tooling that incorporates CCCs can be fabricated through metal additive manufacturing (MAM). The present work focuses on the MAM of a plastic injection mold insert with different CCC types that are circular, serpentine, and tapered channels with/without body-centered cubic (BCC) lattices. The entire manufacturing process of the mold insert is explained from the design step to the final printing step including the computational thermal & mechanical simulations, performance assessments, and multiobjective optimization. Compared to the traditional channels, conformal cooling channels achieved up to 62.9% better cooling performance with a better thermal uniformity on the mold surface. The optimum mold geometry is decided using the multiobjective optimization procedure according to the multiple objectives of cooling time, temperature non-uniformity, and pressure drop in the channel. Direct Metal Laser Sintering (DMLS) method is used for manufacturing the molds and the quality of the printed molds are analyzed with the X-ray Computed Tomography (X-ray CT) technique. The errors between the design and the printed parameters are less than 5% for the circular and tapered channels while the maximum deviation of the strut diameters of the BCC is 0.06 mm. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

17 pages, 7950 KiB

Open AccessArticle

Adaptive Conformal Cooling of Injection Molds Using Additively Manufactured TPMS Structures

by Seo-Hyeon Oh, Jong-Wook Ha and Keun Park

Polymers 2022, 14(1), 181; https://doi.org/10.3390/polym14010181 - 3 Jan 2022

Cited by 43 | Viewed by 6441

Abstract

In injection molding, cooling channels are usually manufactured with a straight shape, and thus have low cooling efficiency for a curved mold. Recently, additive manufacturing (AM) was used to fabricate conformal cooling channels that could maintain a consistent distance from the curved surface [...] Read more.

In injection molding, cooling channels are usually manufactured with a straight shape, and thus have low cooling efficiency for a curved mold. Recently, additive manufacturing (AM) was used to fabricate conformal cooling channels that could maintain a consistent distance from the curved surface of the mold. Because this conformal cooling channel was designed to obtain a uniform temperature on the mold surface, it could not efficiently cool locally heated regions (hot spots). This study developed an adaptive conformal cooling method that supports localized-yet-uniform cooling for the heated region by employing micro-cellular cooling structures instead of the typical cooling channels. An injection molding simulation was conducted to predict the locally heated region, and a mold core was designed to include a triply periodic minimal surface (TPMS) structure near the heated region. Two biomimetic TPMS structures, Schwarz-diamond and gyroid structures, were designed and fabricated using a digital light processing (DLP)-type polymer AM process. Various design parameters of the TPMS structures, the TPMS shapes and base coordinates, were investigated in terms of the conformal cooling performance. The mold core with the best TPMS design was fabricated using a powder-bed fusion (PBF)-type metal AM process, and injection molding experiments were conducted using the additively manufactured mold core. The developed mold with TPMS cooling achieved a 15 s cooling time to satisfy the dimensional tolerance, which corresponds to a 40% reduction in comparison with that of the conventional cooling (25 s). Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

18 pages, 5273 KiB

Open AccessArticle

Novel Analysis Methodology of Cavity Pressure Profiles in Injection-Molding Processes Using Interpretation of Machine Learning Model

by Jinsu Gim and Byungohk Rhee

Polymers 2021, 13(19), 3297; https://doi.org/10.3390/polym13193297 - 27 Sep 2021

Cited by 21 | Viewed by 4106

Abstract

The cavity pressure profile representing the effective molding condition in a cavity is closely related to part quality. Analysis of the effect of the cavity pressure profile on quality requires prior knowledge and understanding of the injection-molding process and polymer materials. In this [...] Read more.

The cavity pressure profile representing the effective molding condition in a cavity is closely related to part quality. Analysis of the effect of the cavity pressure profile on quality requires prior knowledge and understanding of the injection-molding process and polymer materials. In this work, an analysis methodology to examine the effect of the cavity pressure profile on part quality is proposed. The methodology uses the interpretation of a neural network as a metamodel representing the relationship between the cavity pressure profile and the part weight as a quality index. The process state points (PSPs) extracted from the cavity pressure profile were used as the input features of the model. The overall impact of the features on the part weight and the contribution of them on a specific sample clarify the influence of the cavity pressure profile on the part weight. The effect of the process parameters on the part weight and the PSPs supported the validity of the methodology. The influential features and impacts analyzed using this methodology can be employed to set the target points and bounds of the monitoring window, and the contribution of each feature can be used to optimize the injection-molding process. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

14 pages, 3293 KiB

Open AccessArticle

Synergistic Effect of Pressurization Rate and β-Form Nucleating Agent on the Multi-Phase Crystallization of iPP

by Wenxia Jia, Ranran Zhuo, Mingkun Xu, Jiaxiang Lin, Xiaoting Li, Chuntai Liu, Changyu Shen and Chunguang Shao

Polymers 2021, 13(17), 2984; https://doi.org/10.3390/polym13172984 - 3 Sep 2021

Cited by 2 | Viewed by 1889

Abstract

Using a homemade pressure device, we explored the synergistic effect of pressurization rate and β-form nucleating agent (β-NA) on the crystallization of an isotactic polypropylene (iPP) melt. The obtained samples were characterized by combining small angle X-ray scattering and synchrotron wide angle X-ray [...] Read more.

Using a homemade pressure device, we explored the synergistic effect of pressurization rate and β-form nucleating agent (β-NA) on the crystallization of an isotactic polypropylene (iPP) melt. The obtained samples were characterized by combining small angle X-ray scattering and synchrotron wide angle X-ray diffraction. It was found that the synergistic application of pressurization and β-NA enables the preparation of a unique multi-phase crystallization of iPP, including β-, γ- and/or mesomorphic phases. Pressurization rate plays a crucial role on the formation of different crystal phases. As the pressurization rate increases in a narrow range between 0.6–1.9 MPa/s, a significant competitive formation between β- and γ-iPP was detected, and their relative crystallinity are likely to be determined by the growth of the crystal. When the pressurization rate increases further, both β- and γ-iPP contents gradually decrease, and the mesophase begins to emerge once it exceeds 15.0 MPa/s, then mesomorphic, β- and γ- iPP coexist with each other. Moreover, with different β-NA contents, the best pressurization rate for β-iPP growth is the same as 1.9 MPa/s, while more β-NA just promotes the content of β-iPP under the rates lower than 1.9 MPa/s. In addition to inducing the formation of β-iPP, it shows that β-NA can also significantly promote the formation of γ-iPP in a wide pressurization rate range between 3.8 to 75 MPa/s. These results were elucidated by combining classical nucleation theory and the growth theory of different crystalline phases, and a theoretical model of the pressurization-induced crystallization is established, providing insight into understanding the multi-phase structure development of iPP. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Figure 1

27 pages, 14296 KiB

Open AccessArticle

A New Conformal Cooling System for Plastic Collimators Based on the Use of Complex Geometries and Optimization of Temperature Profiles

by Jorge Manuel Mercado-Colmenero, Abelardo Torres-Alba, Javier Catalan-Requena and Cristina Martin-Doñate

Polymers 2021, 13(16), 2744; https://doi.org/10.3390/polym13162744 - 16 Aug 2021

Cited by 22 | Viewed by 3395

Abstract

The paper presents a new design of conformal cooling channels, for application in collimator-type optical plastic parts. The conformal channels that are presented exceed the thermal and dynamic performance of traditional and standard conformal channels, since they implement new sections of complex topology, [...] Read more.

The paper presents a new design of conformal cooling channels, for application in collimator-type optical plastic parts. The conformal channels that are presented exceed the thermal and dynamic performance of traditional and standard conformal channels, since they implement new sections of complex topology, capable of meeting the high geometric and functional specifications of the optical part, as well as the technological requirements of the additive manufacturing of the mold cavities. In order to evaluate the improvement and efficiency of the thermal performance of the solution presented, a transient numerical analysis of the cooling phase has been carried out, comparing the traditional cooling with the new geometry that is proposed. The evolution of the temperature profile versus the thickness of the part in the collimating core with greater thickness and temperature, has been evaluated in a transient mode. The analysis of the thermal profiles, the calculation of the integral mean ejection temperature at each time of the transient analysis, and the use of the Fourier formula, show great improvement in the cycle time in comparison with the traditional cooling. The application of the new conformal design reduces the manufacturing cycle time of the collimator part by 10 s, with this value being 13% of the total manufacturing cycle of the plastic part. As a further improvement, the use of the new cooling system reduces the amount of thickness in the collimator core, which is above the ejection temperature of the plastic material. The improvement in the thermal performance of the design of the parametric cooling channels that are presented not only has a significant reduction in the cycle time, but also improves the uniformity in the temperature map of the collimating part surface, the displacement field, and the stresses that are associated with the temperature gradient on the surface of the optical part. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

12 pages, 5729 KiB

Open AccessArticle

The Low Breaking Fiber Mechanism and Its Effect on the Behavior of the Melt Flow of Injection Molded Ultra-Long Glass Fiber Reinforced Polypropylene Composites

by Po-Wei Huang, Hsin-Shu Peng, Sheng-Jye Hwang and Chao-Tsai Huang

Polymers 2021, 13(15), 2492; https://doi.org/10.3390/polym13152492 - 28 Jul 2021

Cited by 9 | Viewed by 2421

Abstract

In this study, fiber breaking behavior, fiber orientation, length variation, and changes in melt flow ability of long glass fiber reinforced polypropylene (L-FRP) composites under different mold cavity geometry, melt fill path, and plasticization parameters were investigated. The matrix material used was polypropylene [...] Read more.

In this study, fiber breaking behavior, fiber orientation, length variation, and changes in melt flow ability of long glass fiber reinforced polypropylene (L-FRP) composites under different mold cavity geometry, melt fill path, and plasticization parameters were investigated. The matrix material used was polypropylene and the reinforcement fibers were 25 mm long. An ultra-long-fiber composite injection molding machine (with a three-stage plunger and injection mechanism design) was used with different mold cavity geometry and plasticization parameters. Different screw speeds were used to explore the changes in fiber length and to provide a reference for setting fiber length and parameter combinations. Flow-length specimen molds with different specimen thickness, melt fill path, and gate design were used to observe the effect of plasticizing properties on the flow ability of the L-FRP composite materials. The experimental results showed that the use of an injection molding machine with a mechanism that reduced the amount of fiber breakage was advantageous. It was also found that an increase in screw speed increased fiber breakage, and 25 mm long fibers were shortened by an average of 50% (to 10 mm). Long fibers were more resistant to melt filling than short fibers. In addition, the thickness of the specimen and the gate design were also found to affect the filling process. The rounded angle gate and thick wall product decreased the flow resistance and assisted the flow ability and fiber distribution of the L-FRP injection molding. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

18 pages, 7076 KiB

Open AccessArticle

Improving the Melt Flow Length of Acrylonitrile Butadiene Styrene in Thin-Wall Injection Molding by External Induction Heating with the Assistance of a Rotation Device

by Pham Son Minh and Minh-Tai Le

Polymers 2021, 13(14), 2288; https://doi.org/10.3390/polym13142288 - 12 Jul 2021

Cited by 16 | Viewed by 3075

Abstract

In injection molding, the temperature control of the dynamic mold is an excellent method for improving the melt flow length, especially of thin-wall products. In this study, the heating efficiency of a novel heating strategy based on induction heating was estimated. With the [...] Read more.

In injection molding, the temperature control of the dynamic mold is an excellent method for improving the melt flow length, especially of thin-wall products. In this study, the heating efficiency of a novel heating strategy based on induction heating was estimated. With the use of this heating strategy, a molding cycle time similar to the traditional injection molding process could be maintained. In addition, this strategy makes it easier to carry out the heating step due to the separation of the heating position and the mold structure as well as allowing the ease of magnetic control. The results show that, with an initial mold temperature of 30 °C and a gap (G) between the heating surface and the inductor coil of 5 mm, the magnetic heating process can heat the plate to 290 °C within 5 s. However, with a gap of 15 mm, it took up to 8 s to reach 270 °C. According to the measurement results, when the mold heating time during the molding process increased from 0 to 5 s, the flow length increased significantly from 71.5 to 168.1 mm, and the filling percentage of the thin-wall product also increased from 10.2% to 100%. In general, the application of external induction heating (Ex-IH) during the molding cycle resulted in improved melt flow length with minimal increase in the total cycle time, which remained similar to that of the traditional case. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Recent Advances in Injection Molding of Polymers

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (22 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI