Injection Compression Molding Research Articles

An Experimental Study on Color Shift of Injection-Molded Mobile LGP Depending on Surface Micropattern.

In the display industry, the LCD backlight unit (BLU) module is variously used in mobile phones, notebook computers, monitors, and TVs. The light guide plate (LGP), which is one of the core parts of a BLU, is getting bigger and thinner consistently. Conventional injection methods and injection processes like injection compression molding (ICM) are becoming more complex and harsher with high-speed injection at high mold and melt temperatures. These approaches lead to a change in physical properties and a decrease in optical properties such as yellowing and color shift in injection-molded parts. In the present study, an injection molding experiment was conducted to understand the effect of surface patterns and major injection process conditions like mold and melt temperatures on the color shift in injection-molded mobile LGP. Optical properties obtained by the direct and total transmittance and CIE xy chromaticity diagram for injection-molded mobile LGP were measured with a UV–visible spectrophotometer. From the measurement of patternless LGP, it was found that total or direct transmittance was not affected by molding process variables. It was also found that yellow shift, , occurred as much as 0.00111 ± 0.00014, and a color shift angle, of 43.05 ± 2.44° was recorded in CIE coordinates for all nine experimental cases. From the measurement of total transmittance of patterned LGP, and were found to be almost the same as those of patternless LGP for the locations of low and medium density of the pattern for the LGP, T1 and T2. The measured data of direct transmittance of patterned LGP showed that additional yellow shift due to scattering caused by surface micropattern. Interestingly, of patterned data remained 43.05 ± 2.44°, which was almost the same as that found in the case of patternless LGP.

Why not stir casting for polymer composites? Investigations on poly lactic acid based wood plastic composite

Poly Lactic Acid biopolymer was fabricated through four different methods namely Stir Casting, Injection moulding, Extrusion and compression moulding. The pure polymer sample was processed in these different methods to determine the impact of different processing methods on the mechanical property (tensile strength) of PLA. Tensile test was carried out to ASTM D628 standard for all the samples that were fabricated. The tensile strength of the samples that were fabricated through injection moulding, extrusion and compression moulding (named IPLA, EPLA and CPLA respectively) had very marginal difference between themselves while the one fabricated through stir casting method (named as SPLA) had a tensile strength reduced to one third of the value of the result that was obtained through the samples that were processed using the former methods. On conducting further experimentation with 20 wt% wood flour reinforcement into PLA to obtain a Wood Plastic Composite (WPC) and repeating the same processing and testing method, the tensile strength of the wood flour reinforced composites were found to increase in all the four cases of processing methods when compared to their plain polymer products correspondingly. Similar to the plain polymers the tensile strength of the composites also showed marginal difference between themselves in the Injection moulded, extruded and compression moulded methods while the stir casted composite surprisingly resulted in the same one third reduction in tensile strength that was seen on the plain polymers when compared with the former methods. The final verdict of the investigations is that stir casting method is effective and the cheapest processing method of all, the weight of the stir casted polymer and its composite was the lowest among all the processing methods respectively, the mechanical properties (especially tensile strength) of the stir casted polymer and its composite was exactly one third of the value that was obtained through the other regular processing methods that use pressure.

Analysis of Reactive Injection Compression Molding by Numerical Simulations and Experiments

Injection compression molding is an injection molding process with the addition of a compression stage after the injection. This process is useful for the injection molding of precision parts. A stable and controlled manufacturing process is needed to guarantee reliability of complex products, and usually process optimization is achieved by experimental and time consuming approaches. However, for being competitive a minimal market time is a very important requirement and computer simulations can help to optimize the process at the only expense of computational time. This paper reports and discusses for the first time the results of a 3D finite element simulation of reactive injection compression molding (RICM) by commercial software for the production of rubber diaphragms. In particular, the stages of mold filling dynamics and material curing are analyzed and the results verified with experimental tests. To get an accurate representation of the process, the rheological behavior, thermal properties, and kinetic behavior during curing of the real rubber compound were described by mathematical models. A differential scanning calorimeter (DSC) and a capillary rheometer are employed to characterize the rubber material in order to achieve an appropriate curing reaction and viscosity models, respectively. The computations are found to be in good agreement with the experimental results, indicating that reliable information on material viscosity and curing kinetics can play a key role in making well-founded predictions and avoiding trial and error methods.

Influence of the Mold Temperature and Part Thickness on the Replication Quality and Molecular Orientation in Compression Injection Molding of Polystyrene

Abstract It is well known that the process of injection molding with dynamic mold temperature control leads to a good replication quality of high aspect ratio microstructures. However, the inhomogeneous pressure distribution during the holding pressure phase results in an anisotropy of the component properties, low dimensional accuracy and, especially with optical polymers, in undesired stress birefringence. The anisotropy is based on the orientation of the molecular chains in the flow direction, which can be reduced by an injection-compression molding (ICM) process. In order to use the synergy from both processes, an injection-compression molding process with dynamic mold temperature control can be utilized. Within the scope of this investigation, the new process was reproduced by an ICM process at elevated mold temperature (ICM_EMT) and compared with injection molding (IM) with regard to molding accuracy and optical properties in dependence of component thickness and mold temperature. In order to evaluate the molding accuracy, the roughness of a wire-eroded microstructure on the cavity surface was measured. To determine the degree of orientation, the optical properties considered were the transmission and the path difference. It was shown that the adapted ICM process was able to achieve a high degree of replication accuracy with a low degree of orientation, especially for thin-walled components. ICM at elevated mold temperature reduced the path difference in the components with the lowest wall thickness by a factor of two while at the same time optimizing the replication of the microstructure. This could also be confirmed by transmission measurements.

Enhanced impact strength of injection-compression molded parts by controlling residual stress distribution

The objective of this study is to elucidate the relation between the results of ball drop tests and the residual stress distribution of an injection-compression molded part. To improve the ball drop property, a high impact material and a robust manufacturing process were employed. For the application to the transparent plastic window, it is of great importance to increase the impact strength of plastic products. Thin-walled plates were molded with use of rubber nanoparticles embedded poly(methyl methacrylate) (PMMA). Different compression gaps were considered during injection-compression molding (ICM) to adjust the residual stress distribution developed in the specimens. The ball drop tests were carried out to evaluate the impact strength of the prepared samples. In addition, the ICM was numerically simulated to predict the residual stress distribution in the parts.

Manufacturing Signatures of Injection Molding and Injection Compression Molding for Micro-Structured Polymer Fresnel Lens Production.

Injection compression molding (ICM) provides enhanced optical performances of molded polymer optics in terms of birefringence and transmission of light compared to Injection molding (IM). Nevertheless, ICM requires case-dedicated process optimization to ensure that the required high accuracy geometrical replication is achieved, particularly especially in the case of surface micro-features. In this study, two factorial designs of experiments (DOE) were carried out to investigate the replication capability of IM and ICM on a micro structured Fresnel lens. A laser scanning confocal microscope was employed for the quality control of the optical components. Thus, a detailed uncertainty budget was established for the dimensional measurements of the replicated Fresnel lenses, considering specifically peak-to-valley (PV) step height and the pitch of the grooves. Additional monitoring of injection pressure allowed for the definition of a manufacturing signature, namely, the process fingerprint for the evaluation of the replication fidelity under different process conditions. Moreover, considerations on the warpage of parts were related to a manufacturing signature of the molding processes. At last, the global part mass average and standard deviation were measured to correlate local geometrical replication performances with global part quality trends.

Injection and injection compression molding of ultra‐high‐molecular weight polyethylene powder

Ultra‐high‐molecular weight polyethylene (UHMWPE) powder was processed using injection molding (IM) with different cavity thicknesses and injection‐compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and avoid jeopardizing the UHMWPE molecular structure. Dynamic mechanical analysis (DMA) and Fourier‐transform infrared spectroscopy tests confirmed that the thermal and oxidative degradations of the material were avoided but crosslinking was induced during melt processing. Tensile tests and impact tests showed that the ICM samples were superior to those of IM. Increased cavity thickness and ICM were helpful for reducing the injection pressure and improving the mechanical properties due to effective packing of the material. Short shot molding showed that the UHMWPE melt did not exhibit the typical progressive and smooth melt front advancements. Due to its highly entangled polymer chains structure, it entered the cavity as an irregular porous‐like structure, as shown by short shots and micro‐computed tomography scans. A delamination skin layer (around 300‐μm thick and independent of cavity thickness) was formed on all IM sample surfaces while it was absent in the ICM samples, suggesting two different flow behaviors between IM and ICM during the packing phase. POLYM. ENG. SCI., 59:E170–E179, 2019. © 2018 Society of Plastics Engineers

Simulation of injection-compression molding for thin and large battery housing

Injection compression molding (ICM) is an advantageous processing method for producing thin and large polymeric parts in a robust manner. In the current study, we employed the ICM process for an energy-related application, i.e., thin and large polymeric battery case. A mold for manufacturing the battery case was fabricated using injection molding. The filling behavior of molten polymer in the mold cavity was investigated experimentally. To provide an in-depth understanding of the ICM process, ICM and normal injection molding processes were compared numerically. It was found that the ICM had a relatively low filling pressure, which resulted in reduced shrinkage and warpage of the final products. Effect of the parting line gap on the ICM characteristics, such as filling pressure, clamping force, filling time, volumetric shrinkage, and warpage, was analyzed via numerical simulation. The smaller gap in the ICM parting line led to the better dimensional stability in the finished product. The ICM sample using a 0.1 mm gap showed a 76% reduction in the dimensional deflection compared with the normal injection molded part.

Application of injection-compression molding to thin-walled polymeric parts

In this study, we investigated the injection molding (IM) process for the production polymeric parts with thin walls. The injection molding process was numerically modelled, and thin-walled polymeric parts were injection-molded experimentally. In the case of polymeric parts with thin walls, it is critical to understand flow and heat transfer behavior in the mold during the process. Injection-compression molding (ICM) was adopted to fabricate the parts, and the resulting residual stress and warpage were evaluated. In addition, birefringence of the molded part was analyzed to validate the numerical results.

Injection Compression Molded Microlens Arrays for Hyperspectral Imaging.

In this work, a polymer microlens array (MLA) for a hyperspectral imaging (HSI) system is produced by means of ultraprecision milling (UP-milling) and injection compression molding. Due to the large number of over 12,000 microlenses on less than 2 cm², the fabrication process is challenging and requires full process control. The study evaluates the process chain and optimizes the single process steps to achieve high quality polymer MLAs. Furthermore, design elements like mounting features are included to facilitate the integration into the final HSI system. The mold insert was produced using ultraprecision milling with a diamond cutting tool. The machining time was optimized to avoid temperature drifts and enable high accuracy. Therefore, single immersions of the diamond tool at a defined angle was used to fabricate each microlens. The MLAs were replicated using injection compression molding. For this process, an injection compression molding tool with moveable frame plate was designed and fabricated. The structured mold insert was used to generate the compression movement, resulting in a homogeneous pressure distribution. The characterization of the MLAs showed high form accuracy of the microlenses and the mounting features. The functionality of the molded optical part could be demonstrated in an HIS system by focusing light spectrums onto a CCD image sensor.

Comparison and Analysis on Cavity Pressure of Conventional Injection Molding and Injection Compression Molding

Comparison and Analysis on Cavity Pressure of Conventional Injection Molding and Injection Compression Molding

Reduction of Birefringence and Weld-Line using Over-Flow in Injection Compression Molding for Optic Lens

Reduction of Birefringence and Weld-Line using Over-Flow in Injection Compression Molding for Optic Lens

Influences on the Fabrication of Diffractive Optical Elements by Injection Compression Molding

Polymer optics are widely used in various applications, replacing traditional glass lenses. The ability to create free-form and micro-structured optics, as well as fast replication, gives them major advantages over traditional glass lenses. However, the fabrication of complex optical components requires full process control and understanding of influencing factors on the quality of the polymer optical parts. In this work, a curved diffractive optical element (DOE) is fabricated using injection compression molding. Different gate designs were evaluated and the movement of the compression stamper was optimized to obtain good filling behavior. The process stability was analyzed and improved by controlling the melt temperature precisely. Finally, the molding parameters were optimized, focusing on the mold temperature, melt temperature and compression force. Curved diffractive optical elements were replicated with feature sizes of 1.6 μm. The experiments showed that all aspects of the molding process have to be controlled perfectly to produce complex polymer optics. High mold temperatures and compression force are necessary to replicate micro-structured features. The work presents a broad investigation and description of the fabrication process and their influences.

Tolerance verification of precision injection moulded Fresnel lenses

Injection Moulding (IM) and Injection Compression Moulding (ICM) are the leading process technologies to enable mass manufacturing of Fresnel lenses. Even though ICM requires a more expensive and complex process, it is proven to lead to higher optical performances in comparison with IM. In this study, tolerancing for ICM and IM addresses the geometrical accuracy and precision of the two manufacturing processes when micro structures of Fresnel lens surfaces are taken into account.

T-SCAN EVALUATION OF INJECTION VERSUS COMPRESSION MOLDED MAXILLARY COMPLETE DENTURES OPPOSED BY IMPLANT RETAINED MANDIBULAR OVERDENTURES

Objectives: This research was carried out to evaluate the bite force distribution of the maxillary complete dentures processed by injection molded (IM) and compression molded(CM) techniques opposed by implant retained over denture(IOD) using T-scan. Materials and Methods: Ten completely edentulous patients were rehabilitated by mandibular (IOD) and maxillary complete denture. Each patient received two maxillary dentures, one was formed of thermoplastic acrylic resin processed by (IM) technique and the other was formed of conventional acrylic resin processed by (CM) technique. The bite force distribution on the two maxillary dentures was evaluated by T-scan one week and three months after denture insertion.Results: In this study, at the end of the follow up period there was statistically significant difference in the bite force distribution between the (IM) &(CM) complete dentures. After one week of denture insertion, the means of difference of bite force distribution between the right and left posterior edentulous areas of (IM) &(CM) complete dentures were (7.700±3.860) and (15.80 ±4.984) consequently. While the means of bite force distribution for anterior edentulous areas of (IM) &(CM) complete dentures were (10.80 ±2.658) and (17.60 ±3.239) respectively. After three months, the means of difference of bite force distribution between the right and left posterior edentulous areas of (IM) &(CM) complete dentures were (9.400±4.695) and (18.40 ±7.106) consequently, and the means of bite force distribution in the anterior region were (16.40 ±2.591) and (23.80 ±3.824) in (IM) &(CM) complete dentures respectively.Conclusion: Within the limitation of this study, it could be concluded that IM complete dentures showed even bite force distribution along the posterior area of both sides of the edentulous arch and less bite force on the anterior edentulous area compared by CM complete denture. Both dentures showed increased bite force distribution by time on the anterior edentulous area.

Injection and injection-compression moulding replication capability for the production of polymer lab-on-a-chip with nano structures

The manufacturing precision and accuracy in the production of polymer lab-on-a-chip components with 100–130 nm deep nanochannels are evaluated using a metrological approach. Replication fidelity on corresponding process fingerprint test nanostructures over different substrates (nickel tool and polymer part) is quantified through traceable atomic force microscope measurements. Dimensions of injection moulded (IM) and injection-compression moulded (ICM) thermoplastic cyclic olefin copolymer nanofeatures are characterized depending on process parameters and four different features positions on a 30 × 80 mm2 area. Replication capability of IM and ICM technologies are quantified and the products tolerance at the nanometre dimensional scale verified.

Thermal aging of melt-spun NdFeB magnetic powder in hydrogen

High energy product neodymium-iron-boron (NdFeB) magnets are the premier candidate for demanding electrified vehicle traction motor applications. Injection molded (IM) or compression molded (CM) magnets made using NdFeB powders are promising routes to improve motor efficiency, cost, and manufacturability. However, IM and CM NdFeB magnets are susceptible to substantial thermal aging losses at motor operating temperatures when exposed to the automatic transmission fluid (ATF) used as a lubricant and cooling medium. The intrinsic coercivity Hci of NdFeB IM and CM magnets degrades by as much as 18% when aged for 1000h in ATF at 150°C, compared to a 3% loss when aged in air. Here we report aging studies of rapidly quenched NdFeB powder in air, ATF, and H2 gas. Expansion of the NdFeB crystal lattice in both ATF and H2 identified hydrogen dissociated from the ATF during aging and diffused into the primary NdFeB phase as the probable cause of the coercivity loss of IM and CM magnets.

Influence on Product Quality by pvT-Optimised Processing in Injection Compression Molding

Abstract The production of functional optical parts made of plastics is a growing market and the associated production processes have to be developed to fulfil the increasing quality requirements. In this paper an alternative injection compression molding process using the pvT-behavior of the plastics material is compared to the conventional processing method using an isobaric process path. For both control strategies a cavity pressure loop-control is implemented and used. According to measurements of the mold surface reproduction accuracy and internal properties of the molded part the processing method using the pvT-behavior results in a higher optical part quality in the same cycle time compared to the isobaric processing method.

Three-Dimensional Viscoelastic Simulation for Injection/Compression Molding Based on Arbitrary Lagrangian Eulerian Description

Different from conventional injection molding (CIM), injection/compression molding (ICM) evolves boundary variation in gapwise direction. In order to describe melt flow characteristics in ICM correctly, a new material derivative based on arbitrary Lagrangian Eulerian (ALE) description was introduced to modify the material derivatives in the governing and constitutive equations. To avoid large amount of calculation and weak stability of integral numerical method, an iterative approach employing twofold iterations was proposed to decouple the interdependence between velocity, stress, and temperature. The initial values of material parameters in constitutive equations were obtained or fitted by rheological experiments. The ICM experiments for an iso-thick and a var-thick rectangular panel were carried out to validate the proposed method and find the special characteristics of ICM. In addition, the photoelastic tests on a quarter of spherical part processed by ICM were conducted to identify the relationship between residual flow-induced stress distributions and flow fields. Both simulations and experiments show that the pressure profile displays a plateau during compression, temperature decreases with time according to exponential law, large flow-induced stress originates in thick transitional region, flow start, and flow end areas, and gravity has significant effect on meltfront for thick part ICM. The good agreement between experiments and simulations indicates that the current method can properly describe the flow characteristics of ICM.

Comparison of injection molding and injection/compression molding for the replication of microstructure

Because of increasing interest in the functional surfaces including micro- or nano-patterns, the mass production of such surfaces has been actively researched. Both conventional injection molding (CIM) and injection/compression molding (ICM) of micro-patterns were investigated in the present study. The molding subject is a multi-scale structure that consists of a macro-scale thin plate and micro-scale patterns formed regularly on its surface. The transcription ratios of micro pattern made by CIM and ICM for different flow length were experimentally measured, and the origin of the obtained results was identified through numerical analysis. It was found that the cavity pressure and polymer temperature are the most important factors for micro-pattern filling; in particular, the polymer temperature is the key factor determining the transcription ratio. It was also found that the difference in CIM and ICM micro-pattern transcription ratios originates from the differences in the cavity pressure history if other molding conditions are the same.