Conventional Injection Moulding Research Articles

Fabrication of Plano-Concave Plastic Lens by Novel Injection Molding Using Carbide-Bonded Graphene-Coated Silica Molds.

Injection molding of plastic optical lenses prevails over many other techniques in both efficiency and cost, however polymer shrinkage during cooling, high level of uneven residual stresses and refractive index variations have limited its potential use for high precision lenses fabrication. In this research, we adopted a newly-developed strong graphene network to both plain and convex fused silica mold surfaces and proposed a novel injection molding of plano-concave lenses with graphene coated fused silica molds. The unique combination of the graphene coating and fused silica substrate maximize the mechanical properties of the mold and coating materials, namely high hardness, low surface friction, and high heat preservation effect during cooling since fused silica has low thermal conductivity. This advanced injection molding process was implemented in molding of plano-concave lenses resulting in reduced polymer shrinkage. In addition, internal residual stresses, and refractive index variations were also analyzed and discussed in detail. Meanwhile, as a comparison of conventional injection mold material, aluminum mold inserts with the same shape and size were also diamond machined and then employed to mold the same plano-concave lenses. Finally, a simulation model using Moldex3D was utilized to interpret stress distributions of both graphene and aluminum molds and then validated by experiments. The comparison between graphene and aluminum molds reveals that the novel injection molding with carbide-bonded graphene coated fused silica mold inserts is capable of molding high quality optical lenses with much less shrinkage and residual stresses, but more uniform refractive index distribution.

Precision replication of micro features using micro injection moulding: Process simulation and validation

Commercial software for injection moulding is available to optimise the mould design for macroscale products, but such software cannot accurately simulate the moulding process and defects for micro features, which are critical for the performance of polymeric micro/nano devices. In the present work, essential micro features with an aspect ratio of 3:1 on a microfluidic flow cytometer chip were used as typical models to develop a feasible approach to describe the filling of the micro features using commercial simulation software. Factors including the heat transfer coefficient, venting, wall slip and freeze temperature that were critical for micro injection moulding but not of primary importance for conventional injection moulding were specifically investigated. Based on process monitoring and a series of experiments and validation, the insufficient filling of micro features was successfully predicted. The heat transfer coefficient showed a significant impact on the filling of micro features. Venting and wall slip were both critical in simulating the filling process. This paper provides a reasonable approach that can be used to predict defects when injection moulding micro features, while the simulation accuracy still needs to be further improved.

A Combined In-Mold Decoration and Microcellular Injection Molding Method for Preparing Foamed Products with Improved Surface Appearance.

A combined in-mold decoration and microcellular injection molding (IMD/MIM) method by integrating in-mold decoration injection molding (IMD) with microcellular injection molding (MIM) was proposed in this paper. To verify the effectiveness of the IMD/MIM method, comparisons of in-mold decoration injection molding (IMD), conventional injection molding (CIM), IMD/MIM and microcellular injection molding (MIM) simulations and experiments were performed. The results show that compared with MIM, the film flattens the bubbles that have not been cooled and turned to the surface, thus improving the surface quality of the parts. The existence of the film results in an asymmetrical temperature distribution along the thickness of the sample, and the higher temperature on the film side leads the cell to move toward it, thus obtaining a cell-offset part. However, the mechanical properties of the IMD/MIM splines are degraded due to the presence of cells, while specific mechanical properties similar to their solid counterparts are maintained. Besides, the existence of the film reduces the heat transfer coefficient of the film side so that the sides of the part are cooled asymmetrically, causing warpage.

Molecular Mechanism Research into the Replication Capability of Nanostructures Based on Rapid Heat Cycle Molding

Aimed at the molding of polymer nanostructure parts, the interface model between long- and short-chain polycarbonates (PC) and nickel mold inserts was established by the molecular dynamics method. The molecular mechanism of the replication capability of polymer nanostructure part molding was discussed by analyzing the migration and diffusion of the molecular chain, concentration profile, filling morphology evolution, interface binding energy, and filling rate of conventional injection molding (CIM) and rapid heat cycle molding (RHCM). The results show that nanostructures are filled mainly during the packing stage. A short-chain PC system has a low glass transition temperature (Tg) and viscosity, good fluidity, and a high filling rate, so the replication capability of its nanostructures is good. A long-chain PC system has a fast cooling rate in CIM, its molecular chain motion is blocked, the filling rate is low, and the interface binding energy is small, and so its nanostructures have poor replication capability. However, the high temperature at the nanostructures can be maintained for a long time in RHCM, which promotes Brownian motion in the molecular chains. Under the action of packing pressure, molecular chains can overcome entanglement barriers and viscous resistance. Thus, the polymer concentration profile and filling rate increase with increasing packing pressure, which can produce more van der Waals energy. Furthermore, the evolution process of polymer filling morphology is realized by the Brownian motion of chain segments under packing pressure; that is, the diffusion motion of the molecular chain along the direction of a tube composed of other chains around it. With the increase of temperature or pressure, the migration and diffusion of the molecular chain can be promoted; thus, the replication capability of nanostructure parts for mold cavities can be enhanced.

The effect of weld line on tensile strength of polyphenylsulfone (PPSU) in ultrasonic micro-moulding technology

Melting and processing polymers via ultrasonic vibration is now possible, but the weld line that results and the influence it may have on tensile strength has yet to be investigated. When producing products characterised by high mechanical strength, the parameters of the process should be considered in relation to the weld line on the parts. Here, four sets of process parameters (three using ultrasonic technology and one using the conventional process) were used to produce parts whose weld line strengths were then determined and compared. Amplitude values were found to significantly affect the V notch size and consequently the strength of the samples. Samples from parameters where the amplitude was high (90%, 100%) were characterised by a strength similar to that reached with conventional injection moulding technology. Moreover, the experiments showed that when using specific process parameters, the weld line strength is characterised by values akin to those of pure samples. Finally, the investigation revealed that this novel technology is a potential alternative to micro-injection moulding of high requirement polymers such as PPSU.

Influence of dynamic temperature control on the injection molding process of plastic components

Conventional injection molding (CIM) technology has been largely used to produce plastic parts, mainly on automotive industry, due to high production ratios, constricted dimensional tolerances production, and low labor costs. Nowadays, industry has been demanding for thinner and lighter molded parts production, with better mechanical properties. Low mold temperatures (≈60ºC) are used to decrease the cycle molding time and process final costs. However, the fast cooling of parts can easily result in surface defects, such as weld lines, sink marks, or warpage. To avoid such defects and eliminate the need for secondary operations (additional operating costs), a dynamic mold heating and cooling control technology known as Rapid Heating and Cooling Molding (RHCM) can be employed. Based on RHCM, this study compared the efficiency of using heating rods, water flow, and external infrared heating systems to investigate the effect of dynamic temperature control on the injection molding process. An experimental injection mold was manufactured and used for the studies under controlled conditions to produce standard tensile and flexure specimens. The effect of process parameters, geometry of the runner system, location of the injection point, and other relevant settings was considered. From this study, new insights were obtained regarding the industrial application of RHCM as well as the degree of efficiency of different design solutions for the RHCM process.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

금속 열순환 성형에서 수지의 점도와 윤활유가 유리 섬유 강화 고분자의 기계적 물성과 표면에 미치는 영향

Conventional injection molding (CIM) and rapid heat cycle molding (RHCM) methods are used to prepare ABS and (acrylonitrile-butadiene-styrene)/glass fiber copolymer (ABS/GF) plastic parts. Pentaerythritol stearate (PETS) and silicon particles are chosen as lubricants. Effect of resin viscosity and lubricants on properties of plastic parts was investigated. The results show that resin viscosity has some effect on surface quality of plastic parts in CIM process but no effect in RHCM process. ABS/GF plastic parts molded in RHCM process exhibit higher tensile, higher flexural strength and lower impact strength. Silicon is more effective in RHCM process than in CIM process.

Replication integrity of micro features using variotherm and vacuum assisted microinjection moulding

Micro features on surfaces are critical for the functionality of a product, such as micro channels for a microfluidic chip and micro lens arrays for an artificial compound eye lens. In the present work, we design a series of microfluidic and microstructured surface patterns to evaluate the influence of variotherm and vacuum venting on replication integrity of micro features. By using a process monitoring system, including machine process and cavity pressure/temperature measurements, the influence of warm and cold circuit settings, and vacuum venting are characterised in terms of injection pressure, cavity pressure and mould–polymer interface temperature. These are then correlated with the replication integrity of micro features by assessing feature replication height, cross-section area and surface morphology. The performance of anti-stick coatings on a micro mould tool insert was also characterised in terms of moulding cycles. After a series experiments and optimisation, we have significantly enhanced feature replication with 100% replication of proposed features without either significant distortion or tearing, which cannot easily be achieved using conventional injection moulding. Additionally, we have successfully moulded features having good integrity and a maximum aspect ratio of up to 10 at a width of less than 8μm over areas as large as 5.25mm2.

Diverse interfacial crystalline morphologies induced by poly (d-lactide) (PDLA) melt penetration process in multi-melt multi-injection molding (M3IM) system

In this study, poly (l-lactide) (PLLA) was penetrated by poly (d-lactide) (PDLA) in multi-melt multi-injection molding (M3IM) system, and a stable stereocomplex crystal (SC) band was obtained at the interface between the penetrated layer (PLLA) and the penetrating layer (PDLA). The relationship between the width of SC band and the injection velocity was investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), polarized optical microscopy (POM) and 2D-WAXD. It was found that a lower injection velocity leads to a wider and more stable SC band owing to the unique and the complex coupling action of external fields (shear field and temperature field, etc.) in M3IM system. The stable SC band endows the M3IM penetrated samples with enhanced mechanical performance compared to the conventional injection molding (CIM) sample, which shed a light into potential reinforcement of production in PLA manufacturing and application in barrier and unidirectional heat conduction.

Influence of the additivation of graphene-like materials on the properties of polyamide for Powder Bed Fusion

The purpose of this work is to achieve the improvement of mechanical properties of polyamide 12 through dispersion of graphene-like nanofillers, for its use in Powder Bed Fusion. Nanocomposites have been prepared by conventional injection moulding in order to determine the mechanical and electrical behaviour of the different systems as a previous step for the design of new materials for Powder Bed Fusion. Structural characterisation and mechanical and electrical properties assessments were performed, showing the improvement of stiffness and mechanical strength for the prepared nanocomposites, compared to pristine polyamide. Electrical conductivity has been introduced as well in some of them. This enhancement of properties, together with the first tests carried out on nanocomposites prepared with Powder Bed Fusion, makes this study a starting point to obtain commercially interesting materials for this additive manufacturing technique.

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

Foaming Mechanism of Polypropylene in Gas-Assisted Microcellular Injection Molding

In our recent study, it is reported that gas-assisted microcellular injection molding (GAMIM) is a promising method to fabricate plastic foams with good surface quality, high weight reduction, and improved mechanical performance. To clarify the foaming mechanism, the crystallization behaviors of polypropylene in both conventional injection molding (CIM) and gas-assisted injection molding (GAIM) were studied. It is found that GAIM can significantly promote melt crystallization and refine crystals. To explore the improvement mechanism of crystallization, a numerical model was developed to simulate the filling and cooling processes of CIM and GAIM. The simulation results show that the much stronger shear field and the faster cooling rate lead to the refinement of crystals in GAIM. Finally, a crystallization-driven cell nucleation model was proposed to explain the improved foaming behavior of polypropylene in GAMIM. This paper provides a deep understanding of the foaming behavior and hence benefits the foaming process design.

Comparison of micro and conventional injection moulding based on process precision and accuracy

Replication-based processes enable the large-scale production of precision and micro components made of many materials. As for polymers, injection moulding represents the most common technological solution. Micro polymer parts can be, in most cases, either manufactured by conventional injection moulding (IM) or by micro-injection moulding (µIM). However, fundamental differences exist among the two processes. The present study aims at comparing IM and µIM in terms of accuracy and precision of moulded parts. The same micro thermoplastic elastomer (TPE) component was manufactured using the two technologies on two different machines by means of multi-cavity moulds. The produced batches were assessed using a precision scale and a focus variation microscope. The cavities of the moulds were also measured in order to evaluate the pure replication capability by eliminating any influence caused by dimensional variations of master geometries. Measurement uncertainty was evaluated using ISO 15530-3. The data-based comparison revealed that µIM was better suitable for meeting the high precision and accuracy demands typical of micro productions, allowing also to achieve a better cavity balance.

Influence of foaming technology on fibre breakage in long fibre-reinforced polypropylene composites parts

ABSTRACTIt is generally believed that the residual fibre length is one of the most important factors influencing on the mechanical properties of fibre-reinforced polymer matrix composites. In this study, long-glass fibre-reinforced polypropylene (LGFRPP) with initial fibre lengths of 12 mm was prepared and then moulded into parts via conventional injection moulding (CIM) and foamed injection moulding (FIM). The design of experiment (DOE) based on the Taguchi method was first used to determine the optimised processing conditions to increase the residual fibre length of the LGFRPP. The results indicated that foaming conditions have a substantial influence on the residual fibre length of the foamed samples. Based on the DOE, a set of optimised processing condition was selected, and two representative samples of CIM and FIM were carefully investigated using dynamical mechanical analysis, scanning electron microscopy, optical microscopy, etc. The experimental results further showed that the residual fibre length and the mechanical properties of the LGFRPP FIM components were better than those of the CIM components. It was also determined that there is a close relationship between the fibre breakage and the mechanical performance.

Vapor Chamber Utilization for Rapid Cooling in the Conventional Plastic Injection Molding Process

Vapor Chamber Utilization for Rapid Cooling in the Conventional Plastic Injection Molding Process

Mechanical properties, fiber orientation, and length distribution of glass fiber‐reinforced polypropylene parts: Influence of water‐foaming technology

It is generally believed that the length, length distribution, and orientation of fibers are important influencing factors on the mechanical properties of fiber‐reinforced polymer matrix composites. In this study, the length, length distribution, and orientation of fibers with respect to the loading direction of glass fiber‐reinforced polypropylene (GF‐PP) parts were investigated. GF‐PP of different initial fiber lengths, 2 mm (SGF‐PP) and longer than 2 mm (LGF‐PP), were prepared and then molded into parts via conventional injection molding (CIM) and water‐foamed injection molding (WFIM). The mechanical performance of samples was determined using tensile and impact tests, the residual fiber length and length distribution were measured, and the fiber orientation was observed by optical camera and scanning electron microscopy (SEM). The experimental results showed that the mechanical properties of LGF‐PP WFIM components were better than those of the CIM components, while the SGF‐PP parts were worse than the solid ones. The results also suggested that the LGF‐PP WFIM samples exhibited the best fiber length and length distribution, and a lesser degree of fiber orientation, along the flow direction, compared with the CIM samples. It was also shown that the fibers in the GF‐PP foamed parts that were longer than a critical length, which possibly exceeded that of the solid parts, were more effective in improving the mechanical properties. Thus, it can be concluded that the property enhancements of the LGF‐PP parts can be attributed to the effect of cell growth based on an interpretative model of the interaction of long fibers and foamed cells. POLYM. COMPOS., 39:4386–4399, 2018. © 2017 Society of Plastics Engineers

Development of a low-cost wax injection mold with high cooling efficiency

Reduction of the time and cost during the research and development stage of a new product is an important issue. Rapid tooling techniques can reduce the time to market compared to conventional machining approaches. In general, reduction in cooling time plays an important role on cycle time in manufacturing time. Wax injection mold fabricated from aluminum-filled epoxy resin can be employed for small-batch productions of wax patterns. However, the cooling time is much longer compared to metallic wax injection molds due to poorer thermal conductivity. In this study, three kinds of cooling-channel layouts were employed to fabricate wax injection molds for low-pressure wax injection molding using rapid prototyping and rapid tooling techniques. The effects of three kinds of wax injection molds on the cooling time during the low-pressure wax injection molding were investigated. It was found that the reduction in cooling time about 87% can be obtained when a wax injection mold with conformal cooling channels is compared to a conventional wax injection mold fabricated by Al-filled epoxy resin. The manufacturing cost reduction for a wax injection mold with high cooling efficiency about 63% can be obtained using the method proposed in this work.

Synergistic enhancement of crystallization and mechanical performance of polypropylene random copolymer by strong shear and β‐nucleating agent

AbstractInvestigation of microstructure and properties is critical for the development and application of polymer materials. Polypropylene random copolymer (PPR) and β‐nucleated PPR are widely used in water pipe production. The effect of melt shear flow on the crystalline structure and mechanical properties of PPR containing β‐nucleating agent needs in‐depth understanding. In this paper, we demonstrated the preparation of PPR and PPR containing 0.1 wt% calcium pimelate (Ca‐Pim) samples by conventional injection molding (CIM) and oscillation shear injection molding (OSIM). The multilayer structures and morphologies of the samples were characterized by SEM, two‐dimensional X‐ray scattering and DSC. The mechanical properties and the microstructures of samples prepared by these two injection molding methods were compared. Compared with samples prepared by CIM, the stronger shear provided by OSIM induced the formation of a thicker layer of a shish‐kebab structure and a higher content of γ crystals, and dramatically suppressed the β‐nucleating effect of Ca‐Pim. The OSIM samples have more shish‐kebab structures and higher crystallinities than CIM samples and therefore the former exhibit better rigidity than the latter. The β crystals in the core layer and the thicker layer of shish‐kebab structure endow OSIM‐PPR/0.1 wt% Ca‐Pim with excellent impact toughness. © 2017 Society of Chemical Industry