Micro Injection Moulding Process Research Articles

Combining 3D printing and injection moulding for the fabrication of polymer micro-components with internal hollow features

There is a need to cost-effectively produce polymer components with meso/micro-scale internal geometries with high replication accuracy without the use of post-processing steps. A possible process chain to produce such polymer components with internal hollow features is by combining the 3D printing (3DP) and micro-injection moulding (MIM) processes. To date, no studies were carried out to explore the feasibility of such a process chain. Consequently, this experimental study investigated the use of the 3DP lost-cores that are over-moulded using the MIM process. The first step involved the production of lost-core from a soluble polymer material where three different materials were studied: two filament-based materials (Xioneer VXL130 and AquaSys180) and one resin-based material (IM-HDT-WS). The filament-based materials were printed on an Ultimaker S5 (filament fused fabrication) and the resin-based material was printed using an Asiga Max X27 (digital light processing). In the second step, the lost core was then over-moulded with polymethyl methacrylate (PMMA) using the MIM process. After demoulding, the internal core was then dissolved using the respective dissolution method of each material to achieve a part with meso/micro scale internal features. Investigations carried out at the different stages of the process chain revealed that the best dimensional accuracy was achieved when using the IM-HDT-WS material in the 3DP of the lost-cores and their subsequent over-moulding to form the case study part internal geometry. In particular, the dimensional analysis of the replicated IM-HDT-WS lost-core geometries onto the over-moulded PMMA revealed a difference of 0% in diameter and − 3.17% in bifurcation angle of the Y1.6 channel and a difference of + 4.88% in diameter and + 11.48% in bifurcation angle of the Y0.8 channels when compared to the respective 3DP core dimensional values prior to encapsulation. However, dissolution tests revealed that the filament-based material, the Xioneer VXL130, achieved a dissolution rate of 3.5 and 4.5 h for the Y1.6 and Y0.8 channel, respectively, which was marginally faster than that of the IM-HDT-WS.

Rapid Tooling for Microinjection Moulding of Proof-of-Concept Microfluidic Device: Resin Insert Capability and Preliminary Validation

Producing sustainable microfluidic devices on a large scale has become a trend in the biomedical field. However, the transition from laboratory prototyping to large-scale industrial production poses several challenges due to the gap between academia and industry. In this context, prototyping with a mass production approach could be the novel strategy necessary to bridge academic research to the market. Here, the performance of polymer inserts to produce PMMA microfluidic devices using the microinjection moulding process is presented. Inserts were fabricated with an additive manufacturing process: material jetting technology. The importance of the inserts’ orientation on the printing plate in order to produce samples with more uniform thickness and lower roughness has been demonstrated using a flat cavity insert. In addition, preliminary tests were carried out on microstructured inserts with inverted channels of various cross-section shapes (semi-circular or trapezoidal) and widths (200 or 300 µm) in order to investigate the microstructures’ resistance during the moulding cycles. The best geometry was found in the channel with the trapezoidal cross-section with a width equal to 300 µm. Finally, a preliminary microfluidic test was performed to demonstrate the devices’ workability.

Rapid tooling: investigation of soft-tooled micro-injection moulding process characteristics using in-line measurements and surface metrology

PurposeThe purpose of this study is to demonstrate and characterise a soft-tooled micro-injection moulding process through in-line measurements and surface metrology using a data-intensive approach.Design/methodology/approachA soft tool for a demonstrator product that mimics the main features of miniature components in medical devices and microsystem components has been designed and fabricated using material jetting technique. The soft tool was then integrated into a mould assembly on the micro-injection moulding machine, and mouldings were made. Sensor and data acquisition devices including thermal imaging and injection pressure sensing have been set up to collect data for each of the prototypes. Off-line dimensional characterisation of the parts and the soft tool have also been carried out to quantify the prototype quality and dimensional changes on the soft tool after the manufacturing cycles.FindingsThe data collection and analysis methods presented here enable the evaluation of the quality of the moulded parts in real-time from in-line measurements. Importantly, it is demonstrated that soft-tool surface temperature difference values can be used as reliable indicators for moulding quality. Reduction in the total volume of the soft-tool moulding cavity was detected and quantified up to 100 cycles. Data collected from in-line monitoring was also used for filling assessment of the soft-tool moulding cavity, providing about 90% accuracy in filling prediction with relatively modest sensors and monitoring technologies.Originality/valueThis work presents a data-intensive approach for the characterisation of soft-tooled micro-injection moulding processes for the first time. The overall results of this study show that the product-focussed data-rich approach presented here proved to be an essential and useful way of exploiting additive manufacturing technologies for soft-tooled rapid prototyping and new product introduction.

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

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.

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

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.

Numerical simulation of flow and thermal behaviour of polymer under microinjection moulding process: role of the thermal joint model at the mould–melt interface

Numerical simulation of flow and thermal behaviour of polymer under microinjection moulding process: role of the thermal joint model at the mould–melt interface

Design and Experimental Validation of a Process Chain for Thin Components Manufacturing by Micro Injection Molding Process

Abstract Micro-applications, especially in biomedical and optical sectors, require the fabrication of thin polymeric parts which can be commonly realized by micro-injection molding process. However, this process is characterized by a relevant constraint regarding the tooling. Indeed, the design and manufacturing of molds could be a very time-consuming step and so, a significant limitation for the rapid development of new products. Moreover, if the design displays challenging microfeatures, their realization could involve the use of more than one mold for the fabrication of a single thin part. Therefore, proper integration of different manufacturing microtechnologies may represent an advantageous method to realize such polymeric thin microfeatures. In this work, a micromanufacturing process chain including stereolithography, micromilling, and micro-injection molding is reported. The mold for the micro-injection molding process was fabricated by means of stereolithography and micromilling, which allowed us to produce low-cost reconfigurable modular mold, composed of insert support and a removable insert. The assessment of the proposed process chain was carried out by evaluating the dimensions and the surface finishing and texturing of the milled mold cavities and molded components. Finally, a brief economic analysis compares three process chains for fabricating the micromold showing that the proposed one reduces the manufacturing cost by almost 61% with the same production time.

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.

Polymer based microneedle patch fabricated using microinjection moulding

This paper presents the development of a polymer based microneedle patch for transdermal drug delivery application using plastic microinjection moulding. Design and analysis of the microneedle cavities and mould insert used in the injection moulding process were carried out using Computer-Aided Engineering (CAE) software. A mould insert with low surface roughness was fabricated using Micro Electrical Discharge Machining (μ-EDM). The injection moulding parameters including clamping force, temperature, injection pressure and velocity were characterized in order to obtain the optimum reproducibility. Solid truncated cone microneedles, made of biocompatible polymethyl methacrylate (PMMA), with a round tip radius of 50 μm and 500 μm in height have been realized by microinjection moulding process demonstrating the potential of a low cost, high production efficiency, and suitable for mass production. In addition, a mould insert of cylindrical microneedles fabricated using X-ray LIGA has been proposed.

Multi-Objective Optimizations of Biodegradable Polymer Stent Structure and Stent Microinjection Molding Process.

Biodegradable stents made of poly-l-lactic acid (PLLA) have a promising prospect thanks to high biocompatibility and a favorable biodegradation period. However, due to the low stiffness of PLLA, polymeric stents have a lower radial stiffness and larger foreshortening. Furthermore, a stent is a tiny meshed tube, hence, it is difficult to make a polymeric stent. In the present study, a finite element analysis-based optimization method combined with Kriging surrogate modeling is firstly proposed to optimize the stent structure and stent microinjection molding process, so as to improve the stent mechanical properties and microinjection molding quality, respectively. The Kriging surrogate models are constructed to formulate the approximate mathematical relationships between the design variables and design objectives. Expected improvement is employed to balance local and global search to find the global optimal design. As an example, the polymeric ART18Z stent was investigated. The mechanical properties of stent expansion in a stenotic artery and the molding quality were improved after optimization. Numerical results demonstrate the proposed optimization method can be used for the computationally measurable optimality of stent structure design and stent microinjection molding process.

Temperature effects on DLC coated micro moulds

Abstract Microinjection moulding is a key enabling technology for replicating miniaturized components and parts with functional features at the micrometer and even sub-micrometer length scale. The micro moulding tools used in the process chain are critical for delivering high quality parts for the duration of the product life cycle, and recently tool coatings such as Diamond-like carbon (DLC) have been used to extend their use and enhance the performance. The micro injection moulding process has high injection speeds with cyclic heat transfer characteristics, and little is understood on how the localised heat transfer at the surface will influence the DLC surface coating delamination and cracking. In this research a microinjection moulding process using three different polymers, Polypropylene (PP), Acrylonitrile butadiene styrene (ABS) and Polyether ether ketone (PEEK) is studied. Finite element analysis (FEA) simulation is utilised to identify the process temperature factors that lead to tool thermal expansion and dimensional changes that directly impact the life cycle of the coating. The theoretical and FEA results show that the mould material and the two coatings experience a significantly different thermal expansion from each other. It has also been shown that at the micro scale heat loss at the tool surface is dominant, and the variation in heat has a significant influence on the different thermal expansion rates. In particular the DLC coated micro rib features are particularly susceptible to high variations in heat transfer. The research identifies areas of the tool surface that experience sudden heat variation across the part surface, and concludes that through process optimisation it is possible to reduce the potential for DLC coating delamination and cracking during service.

Vacuum Venting Enhances the Replication of Nano/Microfeatures in Micro-Injection Molding Process

Vacuum venting is a method proposed to improve feature replication in microparts that are fabricated using micro-injection molding (MIM). A qualitative and quantitative study has been carried out to investigate the effect of vacuum venting on the nano/microfeature replication in MIM. Anodized aluminum oxide (AAO) containing nanofeatures and a bulk metallic glass (BMG) tool mold containing microfeatures were used as mold inserts. The effect of vacuum pressure at constant vacuum time, and of vacuum time at constant vacuum pressure on the replication of these features is investigated. It is found that vacuum venting qualitatively enhances the nanoscale feature definition as well as increases the area of feature replication. In the quantitative study, higher aspect ratio (AR) features can be replicated more effectively using vacuum venting. Increasing both vacuum pressure and vacuum time are found to improve the depth of replication, with the vacuum pressure having more influence. Feature orientation and final sample shape could affect the absolute depth of replication of a particular feature within the sample.

Process chain for serial manufacture of polymer components with micro- and nano-scale features: Optimisation issues

This article reports a follow-up research to investigate further the component technologies of a cost-effective manufacturing route designed to achieve function and length scale integration in products. The route employs a viable master-making process chain that integrates compatible and at the same time complementary, structuring and replication technologies to fabricate Zr-based bulk metallic glass inserts. To validate them, they are subsequently integrated into a micro-injection moulding machine, and polymer structures incorporating both micro- and nano-scale features are replicated. Especially, the masters and/or replicas after each processing step were analysed and the factors affecting its overall performance were identified. The research demonstrated that the master-making process chain can be a viable fabrication route for both fully amorphous and partially crystalline Zr-based bulk metallic glass inserts that incorporate different length scale features. The results also showed that relatively good fidelity of the different scale features can be achieved with the micro-injection moulding process, and thus, it can enable function and length scale integration in thermoplastic components.

Research on impact behaviour and silicon insert fracture phenomenon in microinjection moulding

Silicon insert is a promising tool for microinjection moulding (MIM). However, its fracture problem induced by impact in MIM creates a bottleneck for application. The purpose of this paper is to investigate the impact behaviour in MIM and the effect on the fracture of silicon inserts. The finite element method is utilised to calculate the crack propagation of silicon inserts with pressure load and thermal load in the MIM process. The simulation result shows that the crack propagation is more easily induced by the increase of pressure load, while the temperature change has little effect on the crack propagation. An experimental platform, including a novel rotatable insert mould, is developed to investigate the dynamic pressure in the MIM process. The result shows that both the maximum pressure and the maximum loading rate occur in the initial period of MIM process. It indicates that the silicon insert is more prone to fracture at the beginning of the MIM process, and spatial pressure peaks are observed in the cavity as well. The nearly consistent distribution between the peak positions and the insert fracture zones shows that the pressure distribution is quite relevant to the fracture of the silicon insert. The result is helpful because it reveals the fracture phenomenon of silicon inserts.

Flow Induced Crystallization of Poly(ether‐block‐amide) from the Microinjection Molding Process and its Effect on Mechanical Properties

AbstractCrystallization during microinjection molding is investigated relative to process conditions. Modulus and hardness of the skin layer are higher than the core layer, regardless of core structure. Young's modulus, strain at break and yield stress all increase with an increase of skin ratio. The relationship between process, morphology and mechanical properties is studied for micro products. By using in‐line process monitoring, flow induced crystallization is characterized by shear stress and apparent specific work. Shear stress is shown to be a good candidate to characterize the formation of highly oriented structures under actual microinjection molding processes. This may provide a method for in‐line control of morphology development, and then final properties, by controlling the flow conditions.

Effect of Micro-Injection Molding Process Parameters for Warpage in Micro Plate Devices

The injection molding process of micro plate devices requires several concerns in order to produce a quality output. In part of determining the best parameter settings, among other considerations that need to be taken are the types of plastic materials selected and the mold design. Molding parameters such as packing time, cooling temperature, molding and melting temperatures, packing and injection pressures are the most important factors affecting warpage of the micro plate part. These factors and their interactions were investigated in this research. The effects of processing parameter on the warpage of flat micro devices were analyzed according to the Taguchi method. In this paper, based on the range analysis, the parameter effective sequence was got, as well as the best processing parameters. The molding packing time has the strongest effects on the warpage, and the molding temperature is the secondary parameter. The cooling time has the lowest effects.

A study on microinjection moulding using moulding blocks by additive micromanufacturing

Microinjection moulding is one of the most efficient replication methods for polymeric components in microsystems. The manufacturing of moulding blocks for complex geometries is resorting increasingly to the techniques of rapid prototyping. This development on the use of additive microtechnologies can promote the massification of microsystems within a shorter tooling development cycle time. However, the microinjection moulding process itself has mechanical and thermal demands that must be addressed and require specific consideration of the selection of the tool material. This constrains the selection of the best-suited additive manufacturing process. The current state of the art of additive manufacturing technologies at the micrometric scale favours laser sources to process layer by layer the media contained in a vat. The media type, the laser power and the laser spot size are parameters that can influence the replication tool tolerances and physical properties. This work explores the possibilities of two additive technology tooling approaches for microinjection moulding, using different materials. The research parameters included replication detailing onto the plastic part, surface roughness, microtool integrity and wear. The evaluation of these parameters was carried out using both optical and hybrid microscopy, a laser perthometer as a non-contact solution for surface roughness evaluation, scanning electron microscopy and X-ray spectroscopy. The results of this research work showed that the processed material and technology play an important role both on surface quality and tool life, enabling criteria definition for technology selection.

Optimisation of Micro Injection Moulding Process through Design of Experiments

The paper presents the optimisation of Micro Injection Moulding (MIM) process through Design of Experiments (DoE). MIM is a relatively new technology which is used for the rapid manufacture of micro components. In order to meet the quality and reliability constraints it is important to reduce variability during its operation due to changes in process parameters. In this study, an understanding of the MIM process and consequently its optimisation is carried out by DoE based on six parameters which influence the surface quality, flow length and the aspect ratio. Significant single process parameters and interactions between them were determined through statistical analysis. For the 2-level test, an aspect ratio of 20, 21, and 20 were achieved respectively for Polypropylene (PP), Acrylonitrile-Butadiene-Styrene (ABS) and Polyoxymethylene (POM).

Simulation of the micro-injection moulding process: effect of the thermo-rheological status on the morphology

The software package Moldflow Plastics Insights was used to simulate the filling of a micro-cavity by considering precise material data and accurate boundary conditions. Experiments were carried out on an accurately controlled micro-injection moulding machine (formicaPlast) for providing important parameters to verify the simulation results and improve the accuracy of the simulation. Based on the relationship between the cavity pressure and the mould-filling ratio, the heat transfer coefficients can be appropriately determined for different process conditions. Finally, the transient thermo-rheological results were analysed with regard to their influence on the morphology of semi-crystalline (PP) micro-injection moulded parts, which not only give rise to the mechanisms of the morphological formation but also verify the quality of the simulation results.

Effects of the cavity surface finishing on the polymer filling flow in micro injection moulding

In micro-injection moulding, dimension and shape of the cavity microscale factors, normally negligible in conventional injection moulding, play an important role. More specifically, cavity roughness, which in large scale moulding is relevant only for surface finishing and appearance, at the micro-scale can not only significantly change the cavity volume but also influence the polymer flow and the heat transfer between polymer melt and mould. In the present work the effect of the mould cavity finishing on the micro-injection moulding process was investigated. The phenomenon was analyzed using different channels for melt flow separation and taking advantage of localization of weld lines for differential characterization. To this end different micro-cavities with different surface finishing where generated by means of micro electro discharge machining (μEDM). Cavities surfaces where characterized integrating metrological information from different instruments: scanning probe microscopy (surface roughness), optical profilometry (roughness and volumes) and scanning electron microscopy (weld lines localization).