Injection Compression Molding Research Articles

Warpage: Causes, manufacturing processes and future challenges: A review

Currently, in the manufacturing industry, there are many different component manufacturing processes. Each of them has its own advantages and disadvantages. One phenomenon present in some processes is known as warpage. Essentially, warpage is unwanted deformation in a component caused by internal stresses, thermal variations, uneven cooling of the part, the presence of moisture or the release of residual stresses in the material. Although it is a common problem in some engineering fields, it occurs mainly in processes such as injection moulding, compression moulding and 3D printing. There are different measurement and mitigation techniques that are adapted to each process. This paper discusses the causes of the phenomenon and current and future mitigation techniques. Additionally, an overview of upcoming techniques aimed at fully mitigating and measuring this phenomenon in real time during manufacturing processes is presented.

Taguchi–gray relational analysis of eccentricity and tilt of multilens module mount fabricated by injection compression molding

AbstractThis study utilizes the mold flow analysis technique of the injection compression molding (ICM) process, combined with the Taguchi–gray relational analysis (GRA), for process optimization analysis on the roundness of the lens holes and the flatness of the lens mount in a 4 × 4 planar multilens array mount. After manufacturing simulation analysis, the eccentricity and tilt information of the lens mount was further evaluated optically through spot diagram analysis upon inserting the same glass lenses. The results showed a positive correlation trend between roundness and flatness in structural deformation analysis, indicating that improving the overall flatness of the lens mount can enhance the roundness of the lens holes. In optical analysis, better improvements in the lens tilt angle were achieved through GRA. In conclusion, aiming to simultaneously improve the roundness of the lens holes and the overall flatness of the lens mount, the Taguchi–GRA method can achieve the optimization objectives. In terms of optical performance, by optimizing for roundness, it is possible not only to reduce the diameter of the light spot but also to simultaneously reduce the offset displacement of the light spot center on the screen. The method proposed in this paper can serve as an analytical model for the design and fabrication of plastic multilens mount.

Role of processing procedures and molecular weight and their link to quasistatic and fatigue properties of polyamide 6

To expand the scientific base for the usage of the fused layer modelling (FLM) process for the production of polyamide 6 (PA 6) parts, in this work the influence of processing (injection moulding, compression moulding and FLM) and molecular weight on the end-use properties of PA 6 is elucidated. Besides its viscosity, the molecular weight of PA 6 also influences crystallinity and crystallization temperature. The mechanical properties of the fabricated specimens were studied in detail, also in the fatigue range, and analysed focusing on the fusion of interfaces in compression moulding and fused layer modelling. The analysis reveals, that the molecular mobility in the melt (i.e. viscosity and diffusion coefficient) as well as the amount and orientation of interfaces (as determined by the processing procedure) strongly influences the end-use properties. In the case of FLM printed parts, mechanical failure due to quasistatic and fatigue loading essentially depends on the quality of fusion of adjacent layers, which is strongly determined by molecular weight and processing temperature. Generally, a lower viscosity of PA 6 favours fusion of adjacent layers.

Preparation of superhydrophobic nanowires on polypropylene surface via injection compression molding for efficient fog collection.

In this work, a superhydrophobic polypropylene (PP) replica with nanowires is fabricated using an injection compression molding (ICM) process. The morphology, superhydrophobicity and fog water harvesting efficiency of the as-prepared PP replica surface are investigated. Morphological characterization indicates that the PP replica surface exhibits nanowires with intertwined tips. Compared to the untreated PP surface (referred to as the PP counterpart), the PP replica surface shows a higher contact angle (CA) and lower rolling angle (RA). Furthermore, the complete transfer of a water droplet with no volume loss from the PP replica surface to the filter paper shows that nanowires on the PP replica surface are responsible for the superhydrophobic and low-adhesive properties of the surface. The Cassie-Baxter state with a CA of ∼153°, low ice adhesion strength (13.3 kPa at -20 °C) and good fog water harvesting efficiency (∼7.26 g m-2 s-1) demonstrate that the prepared PP replica has economic potential for fog water harvesting applications.

Injection Compression Molding of LDS-MID for Millimeter Wave Applications

LDS-MIDs (laser direct structured mechatronic integrated devices) are 3D (three-dimensional) circuit carriers that are used in many applications with a focus on antennas. However, thanks to the rising frequencies of HF (high-frequency) systems in 5G and radar applications up to the mmWave (millimeter wave) region, the requirements regarding the geometrical accuracy and minimal wall thicknesses for proper signal propagation in mmWave circuits became more strict. Additionally, interest in combining those with 3D microstructures like trenches or bumps for optimizing transmission lines and subsequent mounting processes is rising. The change from IM (injection molding) to ICM (injection compression molding) could offer a solution for improving the 3D geometries of LDS-MIDs. To enhance the scientific insight into this process variant, this paper reports on the manufacturing of LDS-MIDs for mmWave applications. Measurements of the warpage, homogeneity of local wall thicknesses, and replication accuracy of different trenches and bumps for mounting purposes are presented. Additionally, the effect of a change in the manufacturing process from IM to ICM regarding the dielectric properties of the used thermoplastics is reported as well as the influence of ICM on the properties of LDS metallization—in particular the metallization roughness and adhesion strength. This paper is then concluded by reporting on the HF performance of CPWs (coplanar waveguides) on LDS-MIDs in comparison to an HF-PCB.

Comparison between Injection Molding (IM) and Injection‐Compression Molding (ICM) for Mass Manufacturing of Thermoplastic Microfluidic Devices

AbstractPoint‐of‐care (PoC) and organ‐on‐chip (OoC) devices represent promising microfluidic applications for in vitro analysis and miniaturized analytical studies, reducing the need for traditional animal‐based tests for drug discovery and toxicity studies. Using thermoplastics in microfluidic device manufacturing provides interesting functionalities for expansion of these devices into market. However, market growth requires manufacturing large quantities for low cost, which can be achieved using injection molding techniques. This work involves the design of a microfluidic device with different aspect ratio channels to compare injection molding (IM) and injection‐compression molding (ICM) processes, as well as the design and manufacturing of a metallic insert containing machined inverted microstructures. Injected parts are validated visually, dimensionally, and functionally. The differences between both techniques and two grades of cyclic olefin copolymer materials are analyzed to evaluate microfluidic device mass production feasibility concluding that although the machining process for inverted high aspect ratio microstructures is not mature yet, both IM and ICM processes allow the mass manufacturing of microfluidic devices in thermoplastic. Parts processed by ICM show better replicability of microfluidic structures and less internal stresses generate during the injection process than IM parts, highlighting the potential of this process to achieve thermoplastic microfluidic devices to market.

Application of the NSGA-II Algorithm and Kriging Model to Optimise the Process Parameters for the Improvement of the Quality of Fresnel Lenses.

The Fresnel lens is an optical system consisting of a series of concentric diamond grooves. One surface of the lens is smooth, while the other is engraved with concentric circles of increasing size. Optical interference, diffraction, and sensitivity to the angle of incidence are used to design the microstructure on the lens surface. The imaging of the optical surface depends on its curvature. By reducing the thickness of the lens, light can still be focused at the same focal point as with a thicker lens. Previously, lenses, including Fresnel lenses, were made of glass due to material limitations. However, the traditional grinding and polishing methods for making Fresnel lenses were not only time-consuming, but also labour-intensive. As a result, costs were high. Later, a thermal pressing process using metal moulds was invented. However, the high surface tension of glass caused some detailed parts to be deformed during the pressing process, resulting in unsatisfactory Fresnel lens performance. In addition, the complex manufacturing process and unstable processing accuracy hindered mass production. This resulted in high prices and limited applications for Fresnel lenses. These factors prevented the widespread use of early Fresnel lenses. In contrast, polymer materials offer advantages, such as low density, light weight, high strength-to-weight ratios, and corrosion resistance. They are also cost effective and available in a wide range of grades. Polymer materials have gradually replaced optical glass and other materials in the manufacture of micro-optical lenses and other miniaturised devices. Therefore, this study focuses on investigating the manufacturing parameters of Fresnel lenses in the injection moulding process. We compare the quality of products obtained by two-stage injection moulding, injection compression moulding, and IMD (in-mould decoration) techniques. The results show that the optimal method is IMD, which reduces the nodal displacement on the Fresnel lens surface and improves the transmission performance. To achieve this, we first establish a Kriging model to correlate the process parameters with optimisation objectives, mapping the design parameters and optimisation objectives. Based on the Kriging model, we integrate the NSGA-II algorithm with the predictive model to obtain the Pareto optimal solutions. By analysing the Pareto frontier, we identify the best process parameters. Finally, it is determined that the average nodal displacement on the Fresnel surface is 0.393 mm, at a holding pressure of 320.35 MPa and a melt temperature of 251.40 °C. Combined with IMD technology, product testing shows a transmittance of 95.43% and an optimisation rate of 59.64%.

Injection‐compression molding process on optical quality optimization of plastic lens array

AbstractPlastic lens arrays (PLAs) have the advantages of a light weight and a compact size. However, their optical performance is often degraded by warpage, caused by the accumulation of residual stress during the injection molding process. Accordingly, the present study employs mold flow analysis simulations and a Taguchi‐Gray relational analysis (GRA) framework to optimize the processing parameters of the injection compression molding (ICM) process. The analyses focus specifically on the effects of the mold temperature, melt temperature, injection velocity, packing pressure, packing time, and compression gap on the optical path difference (OPD) and lens center displacement (LCD) of the fabricated lens array. The results confirm that the optimized processing parameters significantly improve the OPD, LCD, birefringence, and imaging properties of the PLA compared to those of a PLA fabricated using standard molding conditions.

Fabrication of wafer‐level double‐sided microlens array using injection compression molding

AbstractDouble‐sided microlens arrays (MLAs) are the key optical components of the optical component. To enhance microlens fabrication productivity, a wafer‐level, double‐sided MLA was designed and fabricated using injection compression molding (ICM). First, the Moldex3D simulation analysis results show that the design of the disc mold saves material and representation time than the multi‐cavity mold. The 4‐inch disc mold with a 4 × 4 double‐sided MLA of two inserts was used to do the study. The L9 orthogonal Taguchi method was employed to find the best combination of molding parameters. For molding experiments, 2 mold inserts with 4 × 4 convex and concave lens arrays were machined by the ultraprecision diamond turning. They were mounted into molds in one of two locations, either close to the gate or far from the gate. The molding experiment results confirmed that the ICM‐molded MLA was better than the injection molding (IM)‐molded one, with higher precision and lower residual stress. The results were similar to the simulations. The ICM molded MLA has a focal length of 2.549 mm and a spot size of 50 μm and the total deviation percentage is less than 1%. This study proves the feasibility of fabricating a wafer‐level, double‐sided MLA disc using ICM.

Study of mechanical properties of reinforced polypropylene (PP)/nettle fibers biocomposites and its application in automobile industry

Because of their application in a variety of important fields such as automotive, packaging, industrial sectors, and construction, biocomposites reinforced with natural fiber have gained widespread attention and are gradually replacing synthetic polymeric materials in commercial markets. Because of their low density, biocomposite materials directly influence the fuel economy of the vehicle. In this work, the PP/nettle fiber biocomposite was synthesized by using various compositions of PP and nettle fiber by adopting injection moulding and compression moulding techniques. The various mechanical properties like tensile strength, impact strength, tensile modulus, and flexural strength of the synthesized biocomposite materials are studied by using suitable procedures. The maximum tensile modulus was achieved for the sample of the biocomposite containing 15 % nettle fiber (2203.35 MPa), whereas the maximum flexural modulus was achieved in the composite containing 30 % NF (2429.75 MPa). The sample containing 30 % NF shows the highest impact strength (27.9 J/m). From the study of mechanical properties, it was found that the synthesized composite materials are suitable in the manufacturing of various automobile parts to maintain a sustainable environment.

Comparing the Replication Fidelity of Solid Microneedles Using Injection Compression Moulding and Conventional Injection Moulding.

Polymer surfaces are increasingly being functionalized with micro- and nano- surface features using mass replication methods such as injection moulding. An example of these are microneedle arrays, which contain needle-like microscopic structures, which facilitate drug or vaccine delivery in a minimally invasive way. In this study, the replication fidelity of two types of solid polycarbonate microneedles was investigated using injection compression moulding and conventional injection moulding. Using a full factorial design of experiments for the injection moulding process, it was found that the volumetric injection rate had the largest positive effect on the replication fidelity. The mould temperature and holding pressure were also found to have a positive effect, while the effect of the melt temperature was found to be insignificant for the considered temperature range. For the injection compression moulding process, it was found that a larger compression stroke resulted in a better replication fidelity. A comparison between the replication fidelity for the injection moulding and injection compression moulding indicated that the injection compression moulding process resulted in a higher and more uniform replication fidelity. Using finite element flow simulations, a higher and more evenly distributed cavity pressure was observed compared to the conventional injection moulding process.

Preparation of PP/SCF thermally conductive composites with forced‐assembled networks by multiple injection compression molding

AbstractA multiple injection compression molding (ICM) method was proposed on the basis of injection molding and applied for the preparation of polypropylene/short carbon fiber (PP/SCF) high thermally conductive composites in this article. During each injection compression cycle, the thickness of composite sample would be reduced effectively for better SCF orientation along the flow direction. Moreover, the original loose self‐assembled SCF networks obtained from injection process can furtherly transfer into much compact ones under the effect of compression force. The performance differences among SCF/PP composites prepared with one‐time injection molding (IM), multiple IM, and multiple ICM were also investigated. The SCF/PP composite sample prepared with multiple ICM method presented superior comprehensive performance, ~100% and 28% enhancements in thermal conductivity and tensile strength compared with the one‐time IM sample. We believe the multiple ICM method can provide a new idea for industrial production of functional polymer composites, especially for thermoplastic polymer composite.

High-Precision Thin Wall Bipolar Plates for Fuel Cell Applications via Injection Compression Molding with Dynamic Mold Temperature Control.

In recent years, the demand for polymer compound solutions for the application of bipolar plates in polymer electrolyte membrane fuel cells (PEMFC) has increased continuously due to significant cost and lifetime advantages compared to metallic solutions. The main challenge of the compounds is the high filler content required to ensure sufficient electrical conductivity of the bipolar plates. The associated increase in viscosity and simultaneously increased thermal conductivity limit the conventional injection molding process in terms of achievable flow path length to wall thickness ratios (plate aspect ratio). In order to evaluate the extent to which highly modified electrically conductive polymer material systems can be processed into thin-walled and highly dimensionally stable bipolar plates, an injection compression molding process with dynamic mold temperature control (ICM-DT) has been developed. For this purpose, a compound was prepared from polypropylene (PP) and graphite-flakes. The compound was characterized with respect to the achieved filler content, the electrical conductivity, as well as the pressure- and temperature-dependent solidification range. The ICM-DT experiments were carried out by varying the maximum mold temperature and the compression force. In addition, the process was designed with multiple compression and decompression steps to account for a possible pressure-dependent solidification of the compound. The plates were characterized with respect to the achieved plate aspect ratio and the flow-path-dependent dimensional thickness stability. It was shown that the plate aspect ratio could be increased by up to 125% with the maximum filler content compared to conventional injection molding processes provided in the literature. With the multi-stage ICM-DT process, it was also possible to optimize the thickness dimensional stability with a maximum deviation of 3% over the flow path.

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

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.

The Effects of Compression Pressure on Injection Compression Molding

Abstract Injection compression molding incorporates a mold compression action in the postfilling stage to compact the materials. The process is the same as the conventional injection molding in the filling and first stage packing. Packing stage continues until the gate material is frozen or the gate is shut off. Then, a mold compression action is engaged and continues to the end of the molding. With the mold compression, the pressure distribution inside the mold cavity can be uniform and the residual stresses caused by pressure gradients can be minimized. However, due to the non-isothermal cooling process, the compressibility of each place inside the mold cavity was not the same. At some time of the cooling process, the pressure at different points began to deviate from each other. In order to improve the non-uniform compression at later the stage of a ICM process, a two-stage compression method can be used. A disk mold was designed to study the effects of the two-stage compression on the molding product. It was found that less warpage can be obtained with a lower compression force at the second stage. The experimental results also suggested that there existed an optimal compression time that was corresponding to the time before the material solidification.

Optimization of Injection-Compression Molding Processing Conditions for Fresnel Lens Based on Optical Performance and Geometry Deformation Considerations

Optimization of Injection-Compression Molding Processing Conditions for Fresnel Lens Based on Optical Performance and Geometry Deformation Considerations

Numerical Simulation and Process Optimization of a 3D Thin-Walled Polymeric Part Using Injection Compression Molding

Abstract Injection compression molding (ICM) is a hybrid injection molding process for manufacturing polymer products with high precision and surface accuracy. In this study, a 3D flow simulation was employed for ICM and injection molding (IM) processes. Initially, the process parameters of IM and ICM were discussed based on the numerical simulations. The IM and ICM processes were compared via numerical simulation by using CAE tools of Moldflow software. The effect of process parameters of mold surface temperature, melting temperature, compression force and injection time on clamping force and pressure at the injection location of molded 3D BJ998MO Polypropylene (MFI 100) part was investigated by Taguchi analysis. In conclusion, it was found that the ICM has a relatively lower filling pressure than ICM, which results in reduced clamping force for producing a 3D thin-walled polymeric part.

The Trueness of Obturator Prosthesis Base Manufactured by Conventional and 3D Printing Techniques.

To compare the intaglio surface trueness of obturator prosthesis bases manufactured by traditional compression molding, injection molding, and 3D printing techniques. A complete edentulous master cast with Aramany Class I maxillary defect was selected for this in vitro study. Four study groups (n = 10/group) were included in this study, Group A: Compression Molding, Group B: Injection Molding, and Group C: Cara Print 3D DLP Printer, and Group D: Carbon 3D DLS Printer. All obturator prostheses' intaglio surfaces were scanned with a laboratory scanner (E4; 3Shape Inc, New Providence, NJ) and the dimensional differences between study samples and their corresponding casts were calculated as the root mean square (measured in mm, absolute value) using a surface matching software (Geomagic design X; 3D Systems, Rock Hill, SC). One-way Analysis of variance (ANOVA) and Fisher's least significant difference (LSD) test were used to compare groups differences in RMS (α = 0.05). There was a significant effect of manufacturing technique on the RMS values for the 4 conditions [F(3,36) = 5.743, p = 0.003]. Injection Molding (0.070 mm) and Compression Molding groups (0.076 mm) had a lower interquartile range, and the Cara Print 3D-Printer group (0.427 mm) and Carbon 3D-Printer (0.149 mm) groups had a higher interquartile range. The Injection Molding group showed the best and uniform surface matching with the most area in green in the color maps. The Injection Molding group (0.139 ± 0.049 mm) had significantly lower RMS than all other groups (p < 0.001 for all comparisons). Compression Molding (0.269 ± 0.057 mm), Cara Print 3D-Printer (0.409 ± 0.270 mm), and Carbon 3D-Printer (0.291 ± 0.082 mm) groups were not significantly different from each other (Compression Molding versus Carbon 3D-Printer, p = 0.59; Compression Molding versus Cara Print 3D-Printer, p = 0.25; Cara Print 3D-Printer versus Carbon 3D-Printer, p = 0.40). Obturator prosthesis bases manufactured with injection molding technique showed better intaglio surface trueness than ones made by the compression molding technique and 3D printers. Although obturator prosthesis bases manufactured from different 3D printers showed similar trueness, a DLP 3D printer produced less consistent outcome than a DLS 3D printer.

Investigation on a novel in-mould microcompression system for the precision replication of microlens arrays

As a combination of conventional injection moulding and compression moulding, injection compression moulding is expected to deliver a more uniform distribution of cavity pressure and more precise replication of surface structures. However, processing defects such as flash and design constraints such as thin edges of a product can cause non-uniform compression and imperfect geometric accuracy. The present work proposes a novel in-mould microcompression system, providing high precision compression that is in the magnitude of micrometres during the microinjection moulding process. From the perspectives of geometric accuracy, surface quality and stress birefringence, the influence of the in-mould microcompression system is examined based on conventional microinjection moulding and variotherm assisted microinjection moulding of practical microlens arrays that are designed for light-field applications. The results indicate that the in-mould microcompression can effectively enhance the replication and uniformity in terms of geometric accuracy and surface quality, and that it can marginally reduce residual stresses. As such, this constitutes an innovative solution for the precision replication of optical components.

Investigation of an inverse thermal injection mould design methodology in dependence of the part geometry

The production of injection moulded components with low shrinkage and warpage is a constant challenge for manufacturers. The thermal design of the injection mould plays an important role for the achievable quality, especially the placement of the cooling channels. This design is usually based on empirical knowledge of the mould designers. The construction is supported iteratively by injection moulding simulations. In the case of thick-walled plastic optics with big wall thickness jumps, the shrinkage is compensated by injection compression moulding. In this process, the thin-walled areas freeze earlier and the necessary compression pressure introduces stresses into these areas which reduces the optical performance. An adapted cooling channel design can reduce these problems. At the IKV, Institute for Plastics Processing in Industry and Crafts at the RWTH Aachen University, a methodology was developed which inversely calculates the cooling requirement of the moulded part A demand-oriented cooling channel system is derived based on the computed results. The aim of the research projects is to minimise displacement and internal stresses by temperature control of the moulded parts according to the demand. In this paper, the methodology is applied to three different geometries, representing three classical parts for the injection moulding process. Three different quality areas in the mould for the inverse optimisation are defined and investigated. For each geometry the cooling channel designs are then validated in injection moulding simulations based on the results from the thermal optimisation. It can be shown that for different component geometries and thicknesses, different quality areas are advantageous and decrease the maximum warpage of the parts. For thin-walled ribbed components, a 2D approach leads to a 15% smaller displacement, for components with wall thickness jumps, all investigated quality ranges show no differences in displacement, but a surface in the middle of the part is preferred due to a 3 °C lower standard deviation of the temperature distribution.