Mold Insert Research Articles

Fabrication and performance of nickel-based composite mold inserts for micro-injection molding

During the demolding stage of micro-injection molding (μIM), reducing the interfacial interactions (mainly adhesion and friction forces) between the contact interfaces is the key to achieve non-destructive molding of polymer micro/nano structures. In this study, Ni-based composite mold inserts using polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2) and tungsten disulfide (WS2) with low surface energy and low friction coefficients were fabricated by electroforming. Different nanoparticles could be uniformly distributed in the composite mold inserts without agglomeration at low concentrations, and the orientation of nickel crystal was found to be unchanged by phase composition analysis. The surface energy and adhesion of the inserts could be effectively reduced after the addition of nanoparticles. The molecular dynamics simulation results showed that the value of water contact angle could be closer to the experimental value by adding a surface roughness factor. Due to the self-lubricating property of nanoparticles, the friction coefficient was reduced from 0.75 for pure Ni to 0.25 for WS2 with a concentration of 0.2 g/L. The use of the composite mold inserts with low surface energy and low friction coefficient would solve the problem of microstructure deformation in the demolding stage of injection molded polymer microfluidic chips.

Nano-injection molding with resin mold inserts for prototyping of nanofluidic devices for single molecular detection.

While injection molding is becoming the fabrication modality of choice for high-scale production of microfluidic devices, especially those used for in vitro diagnostics, its translation into the growing area of nanofluidics (structures with at least one dimension <100 nm) has not been well established. Another prevailing issue with injection molding is the high startup costs and the relatively long time between device iterations making it in many cases impractical for device prototyping. We report, for the first time, functional nanofluidic devices with dimensions of critical structures below 30 nm fabricated by injection molding for the manipulation, identification, and detection of single molecules. UV-resin molds replicated from Si masters served as mold inserts, negating the need for generating Ni-mold inserts via electroplating. Using assembled devices with a cover plate via hybrid thermal fusion bonding, we demonstrated two functional thermoplastic nanofluidic devices. The first device consisted of dual in-plane nanopores placed at either end of a nanochannel and was used to detect and identify single ribonucleotide monophosphate molecules via resistive pulse sensing and obtain the effective mobility of the molecule through nanoscale electrophoresis to allow its identification. The second device demonstrated selective binding of a single RNA molecule to a solid phase bioreactor decorated with a processive exoribonuclease, XRN1. Our results provide a simple path towards the use of injection molding for device prototyping in the development stage of any nanofluidic or even microfluidic application, through which rapid scale-up is made possible by transitioning from prototyping to high throughput production using conventional Ni mold inserts.

Analysis of dimensional accuracy of RP pattern and RTV mould inserts using DOE technique

Analysis of dimensional accuracy of RP pattern and RTV mould inserts using DOE technique

Analysis of dimensional accuracy of RP pattern and RTV mould inserts using DOE technique

Analysis of dimensional accuracy of RP pattern and RTV mould inserts using DOE technique

Optically functionalization of 3D surfaces via voxel-based hierarchically micro structuralizing, a study case: Patterned optical ID

Optics is one of the most important applications of functional surfaces enabled by micro-/Nano-structuring. Mass production of optical functional surfaces mainly relies on replication technologies. In optical applications, structural consistency is essential for the precise control of functions such as micro-mirror/lens arrays. A big challenge from the design phase when fabricating functional surfaces is the geometrical constraint, e.g. patterning orient-consistent micromirrors on three-dimensional surfaces. This present paper demonstrates a voxel-based method to indirectly pattern consistently oriented microstructures onto 3D surfaces by creating a hierarchical structure, consisting of the substrate level of a “Minecraft”-like voxel structure and the feature level of micro features machined on the voxels. As a study case, RSA905 injection moulding inserts with 3D functional surfaces for optical encoding are fabricated with diamond machining: a spherical and a sinusoidal sample with a data matrix as an optical ID on each. The encoding is based on the optical contrast generated by the surfaces' directional reflection, which is led by the bevel surfaces of the micro ridge arrays. With the quantified evaluation of the resultant surface quality and functionality, the feasibility of the “Minecraft” method is validated, the surface quality is correlated with its complexity and the process optimization routine is determined. Moreover, by over 15,000 injection moulding cycles, the method is also proved suitable for batch production of 3D functional surfaces by micro injection moulding.

Micro-embossing of micro-structures in RSA-501 as mold inserts for the replication of micro-lens arrays

The production of mold inserts for the replication of micro-lens arrays through micro-embossing could be an alternative process route compared to diamond turning or milling in order to reduce time and costs. The rapidly solidified aluminum alloy RSA-501 is expected to form micro-structures with low surface roughness because of its ultra-fine grain structure. In micro-embossing challenges like elastic spring back effect, pile-ups, and forming accuracy depend on the material behavior. Therefore, RSA-501 was further characterized and the influence of polishing or flycutting on the material behavior was investigated. To further understand the grain and microstructure samples were sectioned along their cross and longitudinal directions. The grain structure of RSA-501 was oriented along the extrusion direction and the mean grain sizes were <1.00 μm. Furthermore, RSA-501 was micro-embossed to investigate the influence of the material behavior and surface preparation on the forming of micro-structures. The induced surface integrity through flycutting was not deep enough to influence the forming of micro-structures. Therefore, the workpiece surface can be prepared either by polishing or flycutting. When micro-embossing RSA-501, cross and longitudinal sections can be used. However, it is recommended to process the cross section because of its isotropic grain structure. It was shown that the curvature radius of micro-embossed concave structures differs from the tool radius. This is due to the elastic spring back effect. Since the embossed structure remains spherical, the spring back effect can be compensated by adjusting the tool radius.

PMMA Lens Arrays for Micro Concentrator Solar Cells Produced by Hot Embossing

The rising energetical needs of modern society have been increasingly pushing for the improvement in energy efficiency. Thin-film solar cell technology encompasses several types of devices whose purpose is to gather energy emitted from a luminous source and convert it into usable electrical energy for a variety of applications, particularly low-powered devices. Micro concentrator solar cells are promising devices to solve the materials availability problem and address the power conversion efficiency simultaneously. Since the energy conversion efficiency for this type of solar cell is not particularly high, it stands out to benefit greatly from using an optical concentrator element to increase the light intensity reaching the active surface. The micro-concentrator element is comprised of a micro-lens array, which can be manufactured by different technologies, such as polymer injection moulding, extrusion, or hot embossing. In this work, we explore how hot embossing can be used to inexpensively produce spherical lenses with Ø 1 mm in an array according to micro concentrator solar cell requirements. A simple compression system coupled with an infrared lamp heat chamber was used to emboss PMMA disks. Different mould insert manufacturing technologies were used and different hot embossing parameters were assessed. The process replicability of the micro-lens cavities was determined by infinite focus microscopy and optical microscopy. The most promising lens array was achieved with a mould insert produced by μ-EDM (with Ra and Rz values of 0.6 μm and 4.58 μm, respectively).

Comprehensive in-mould state monitoring of Material Jetting additively manufactured and machined aluminium injection moulds

The rapid evolution of additive manufacturing (AM) technologies is expected to revolutionize the injection moulding industry as well. AM technologies can be used to manufacture injection mould inserts. Several polymeric additive technologies like Material Jetting (including PolyJet), Material Extrusion (including Fused Deposition Modeling (FDM)) and Powder Bed Fusion (including Selective Laser Sintering (SLS)) can make mould inserts that are suitable for small series production. Metal inserts, made of steel or bronze can also be produced by Powder Bed Fusion (for example by Direct Metal Laser Sintering (DMLS)). These are comparable to their traditional, machined counterparts, regarding longevity and dimensional accuracy. In our study, we made inserts by Material Jetting (PolyJet) from an epoxy acrylate resin and compared its in-mould behaviour to a reference mould insert machined from aluminium. We measured the operational strains, cavity pressure and temperature distribution of the inserts. Operational strains exceeded 2 % in the case of the epoxy-acrylate insert. However, strains of the aluminium insert remained below 0.03 % for the aluminium insert under the same operational conditions. We set up correlational diagrams to numerically specify the load-deformation curve of the mould inserts. We also applied 3D scanning to measure the deformation of the inserts and injection moulded products alike. We found that scanning the injection moulded products yields more information about operational deformation of the inserts than scanning the inserts themselves.

Effects of channel contour laser strategies on fatigue properties and residual stresses of laser powder bed printed maraging steel

Laser powder bed fusion is widely used for tooling applications, such as mould insert: conformal cooling channels are designed to decrease cycling time and homogenize the cooling rate. The Achilles’ heel of additive manufacturing mould is the cooling channels close to the surface which generate high stress concentration and are not machined; as a result, they create weaknesses in the part and are likely to reduce the lifespan of the mould. It is necessary to study the impact of such channels on properties (fatigue, residual stresses, microstructure) and determine optimized laser strategies to reduce porosity that may occur near a contour. Residual stresses were first estimated above an internal channel after different heat treatments, and fatigue specimens were printed with a 3-mm diameter channel on an EOS M270 printer using different strategies such as several contours with a concentric offset. The impact of these strategies on fatigue properties was analysed through microstructural observations. Here, it was found that a double contour with an offset improved the fatigue life of the part by more than 10 times compared to the standard single contour strategy.

Effects of anisotropic and isotropic LIPSS on polymer filling flow and wettability of micro injection molded parts

In micro injection molding, the specific cavity surface texture and roughness directly influence the polymer flow and the heat transfer between polymer melt and mold. In this work, two different types of laser-induced periodic surface structures, linear and hexagonal, were generated, and their impact on the flow length in micro injection molding was evaluated.A complete investigation of the surface treatment effect on the polymer flow was carried out, comparing the performance of an untreated cavity surface with surfaces modified by LIPSS. The phenomenon was examined by localizing the weld lines created by the polymer flowing in two parallel channels having different surface treatments. Several cavity inserts were treated by varying the LIPSS process parameters to generate surfaces with different micro- and nanostructures directions and periodicity. Furthermore, the paper addresses the hydrophobicity achieved on the micro molded surfaces replicated from mold inserts with different LIPSS-based surface topography. Mold surfaces with linear and hexagonal LIPSS and the respective molded parts were analyzed by optical profilometry and scanning electron microscopy to characterize the cavity surfaces replication and localize the weld lines on the micro injection molded parts.

Irregular Shape Effect of Brass and Copper Filler on the Properties of Metal Epoxy Composite (MEC) for Rapid Tooling Application

Due to their low shrinkage and easy moldability, metal epoxy composites (MEC) are recognized as an alternative material that can be applied as hybrid mold inserts manufactured with rapid tooling (RT) technologies. Although many studies have been conducted on MEC or reinforced composite, research on the material properties, especially on thermal conductivity and compressive strength, that contribute to the overall mold insert performance and molded part quality are still lacking. The purpose of this research is to investigate the effect of the cooling efficiency using MEC materials. Thus, this research aims to appraise a new formulation of MEC materials as mold inserts by further improving the mold insert performance. The effects of the thermal, physical, and mechanical properties of MEC mold inserts were examined using particles of brass (EB), copper (EC), and a combination of brass + copper (EBC) in irregular shapes. These particles were weighed at percentages ranging from 10% to 60% when mixed with epoxy resin to produce specimens according to related ASTM standards. A microstructure analysis was made using a scanning electron microscope (SEM) to investigate brass and copper particle distribution. When filler composition was increased from 10% to 60%, the values of density (g/cm3), hardness (Hv), and thermal conductivity (W/mK) showed a linear upward trend, with the highest value occurring at the highest filler composition percentage. The addition of filler composition increased the compressive strength, with the highest average compressive strength value occurring between 20% and 30% filler composition. Compressive strength indicated a nonlinear uptrend and decreased with increasing composition by more than 30%. The maximum value of compressive strength for EB, EC, and EBC was within the range of 90–104 MPa, with EB having the highest value (104 MPa). The ANSYS simulation software was used to conduct a transient thermal analysis in order to evaluate the cooling performance of the mold inserts. EC outperformed the EB and EBC in terms of cooling efficiency based on the results of thermal transient analysis at high compressive strength and high thermal conductivity conditions.

Manufacturing of Soft Contact Lenses Using Reusable and Reliable Cyclic Olefin Copolymer Moulds.

We present experimental evidence of reusable, reliable cyclic olefin copolymer (COC) moulds in soft contact lens manufacturing. The moulds showed high performance surface roughness characteristics despite &gt;20 kW exposure to 365 nm ultraviolet (UV) light from repeated use. Ultra-precision manufacturing techniques were used to fabricate transparent COC mould inserts and to produce soft contact lenses from liquid monomer compositions. Both polymer and silicone hydrogels were fabricated with more than 60 individual uses of the moulds. White light interferometry measured the surface roughness (Sa) of the COC moulds to be almost unchanged before and after repeated use (Sa 16.3 nm before vs. 16.6 nm after). The surface roughness of the prototyped lenses and that of commercially available soft contact lenses were then compared by white light interferometry. The surface roughness of the lenses was also nearly unchanged, despite undergoing more than 60 uses of the COC moulds (lens Sa 24.4 nm before vs. after Sa 26.5 nm). By comparison the roughness of the commercial lenses ranged from 9.3-28.5 nm, including conventional and silicone lenses, indicating that the reusable COC moulds produced competitive surface properties. In summary, COC moulds have potential as reusable and reliable mould inserts in the manufacturing of soft contact lenses, yet maintain high quality optical surfaces even after sustained exposure to UV light.

Value Chain Comparison of Additively and Conventionally Manufactured Multi-Cavity Tool Steel Inserts: An Injection Molding Industrial Case Study for High-Volume Production

The development of injection molding tools is an expensive, time-consuming, and resource-intensive process offering little to no flexibility to adapt to variations in product design. Metal additive manufacturing can be used to produce these tools in a cost-effective way. Nevertheless, in an industrial context, effective methods are missing for the selection of the most suitable technology for the given tooling project. This paper presents a method to compare process chains based on additive and conventional subtractive technologies for the manufacturing of metal tooling for injection molding. The comparison is based on a technology focused-performance analysis (TFPA) through computer simulation performed using Tecnomatix Plant Simulation developed by Siemens Digital Industries Software combined with a customized cost–benefit economic analysis tool. The analysis of the technology comparison highlights potential bottlenecks for production, such as the printing phase and the heat treatment. It also gives a deeper understanding of the technology maturity level of conventional milling machines against laser powder bed fusion machines. The result is that the total costs for an insert made by AM and CM are indeed rather similar (the cost difference between the two tooling process chains is lower than 5%). The cost analysis reveals major costs drivers in the production of high-performance molding tools, such as the cutting tools employed for the milling steps and their changeover frequency. The industrial case of a 32-cavity mold insert for plastic injection molding is used to perform the study, develop the analysis, and validate the results.

Heat Dissipation Plays Critical Role for Longevity of Polymer-Based 3D-Printed Inserts for Plastics Injection Moulding

Injection moulding is a polymer processing method of choice for making plastic parts on industrial scale, but its traditional mould is made from tooling steel with time-consuming and costly production. Additive manufacturing technologies arise as an alternative for creating mould inserts at lower costs and shorter lead times. In this context, this study describes a series of stereolithography (SLA)-printed injection mould inserts fabricated from two photopolymer resins, utilised to mould standard tensile specimens of a commercial-grade polypropylene, aiming to evaluate effects on the polymer’s thermal and mechanical properties. Our results demonstrated that the glass fibre-filled resin inserts withstood more moulding cycles before failure, had superior mechanical properties, higher Tg and greater thermal conductivity. Calorimetric data revealed that PP thermal properties and degree of crystallinity were little affected, while mechanical testing suggests a significant effect in the elongation at break. Thus, these findings highlight the importance of adequate heat extraction during injection moulding and endorse further application of SLA mould inserts for the manufacturing of injection-moulded plastic parts in the case of prototypes or small batches, provided suitable cooling is made available, contributing to the feasibility and affordability of employing this approach for an industrial setting.

Mass production of superhydrophilic micropatterned copper surfaces using powder injection molding process

Hydrophilic micropatterned copper surfaces are manufactured using a powder injection molding (PIM) process. Copper powder and a wax-polymer-based binder system are utilized to prepare a feedstock. The rheological properties of the feedstock are evaluated to design the PIM process. Polymethylmethacrylate (PMMA) sacrificial mold inserts fabricated by photolithography are used to shape the micropatterns. Both PIM and photolithography processes are suitable for high-volume products; therefore, the micropatterned surfaces can be mass-produced. The wettability of the manufactured surfaces is investigated by measuring the apparent contact angle. The apparent contact angle tends to decrease as the absolute value of the difference in effective surface free energy between the wet and dry states increases. When the absolute value of the difference is equal to or exceeds 150 mJ/m 2 , the surface is fully wetted immediately and exhibits superhydrophilicity. Both high aspect ratio and small gap size are key to achieving superhydrophilicity of the micropatterned surface. • Superhydrophilic micropatterned copper surface is manufactured without any defects. • Rheological analysis of the copper feedstock indicates that it is suitable for PIM. • PMMA sacrificial mold inserts fabricated using photolithography shape micropatterns. • The combined process is suitable for mass production of superhydrophilic surfaces. • Wettability of the micropatterned surface is linked to the dimensions of the pattern.

Effect of Interfacial Interaction on the Demolding Deformation of Injection Molded Microfluidic Chips

During the demolding process, the interfacial interaction between the polymer and the metal mold insert will lead to the deformation of the micro-structure, which will directly affect the molding quality and performance of injection molded microfluidic chips. In this study, the demolding quality of micro-channels and micro-mixing structures of polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC), and polystyrene (PS) microfluidic chips for heavy metal detection were investigated by molding experiments. The experimental results showed that the structures of microfluidic chips could be completely replicated. However, tensile deformation and fracture defects were observed at the edges of the micro-structures after demolding. Compared to the Ni mold insert, the calculation of the relative deviation percentages showed that the width of the micro-channel became larger and the depth became smaller, while the dimensions of the micro-mixing structure changes in the opposite direction. Subsequently, a molecular dynamics (MD) simulation model of polymer/nickel (Ni) mold insert for injection molding was established. The changes of adhesion work, demolding resistance and potential energy during demolding were analyzed. The simulation results showed that the polymer structures had some deformations such as necking, molecular chain stretching and voids under the action of adhesion work and demolding resistance. The difference in the contact area with the mold insert directly brought different interfacial interactions. In addition, the potential energy change of the polymer system could be used to quantitatively characterize the demolding deformation of the structure. Overall, the MD method is able to effectively explain the internal mechanisms of interfacial interactions, leading to the demolding deformation of polymer structures from the molecular/atomic scale.

Study on nano-graphitic carbon coating on Si mold insert for precision glass molding

Precision glass molding is an efficient and promising technique for large-volume micro-optical manufacturing. Even though significant progress in precision glass molding has been achieved on the anti-adhesive coating, technical challenges and barriers still exist towards tailoring the coating layer to ensure durability and long-term processing consistency in numerous molding cycles. This manuscript presents a novel molding technique utilizing micro-patterned Si mold inserts coated with a newly developed nano-graphitic carbon coating as an isolation layer in high-precision glass molding. The coating is prepared by atmospheric pressure chemical vapor deposition (APCVD), in which the liquid benzene and silicone rubber are used as the carbon source and silicon oxycarbide (SiOC) source, respectively. The nano-morphologies of the nano-graphitic carbon coating with different conditions are characterized and analyzed, illustrating notable differences in surface features with the addition of silicone rubber and various growth durations. In the demonstration, the nano-graphitic carbon-coated Si mold inserts exhibit unique properties, including anti-adhesive and hydrophobic at elevated temperatures. Two kinds of micro-patterned Si mold inserts, a micro-pillar matrix and a micro-lens array, generated by UV lithography and diamond turning, are utilized to demonstrate the feasibility of the anti-adhesive coating in precision glass molding. The obtained results indicate that the micro-optical features on the coated Si mold inserts are successfully transferred to glass substrates with high replication fidelity without notable signs of adhesion or contamination in repetitive molding cycles. This emerging technology makes Si an alternative mold material with low surface adhesion, enhances micro-optical machining efficiency, and replicates high-precision, low-cost micro-optics on large scales that were previously unavailable.

Development and Production of Artificial Test Swarf to Examine Wear Behavior of Running Engine Components—Geometrically Derived Designs

Subtractive manufacturing processes are usually accompanied by the occurrence of tiny flakes and swarf, which later on cause severe wear and damage, especially in moving components such as rolling or sliding bearings, pistons, etc. However, up until now, such detrimental effects have hardly been investigated. One reason is the lack of a definition of a typical design of debris particle. Therefore, the main goal of the project described in this paper was to elaborate a draft that defines standardized test particles. It had to be evaluated whether test particles could be adequately reproduced and whether they would reveal significant damage potential. Taking into account future mass fabrication, Micro Powder Injection Molding (MicroPIM) was chosen as a production method. Five different 3D designs of geometrically defined test particles were developed. The maximum size of each design was 1167 mm in green state; however, all samples shrank in size during sintering. Specially tailored feedstocks containing 42CrMo4 steel powders were used and the related molding, debinding and sintering procedures were developed. All particle geometries and related mold inserts were developed using a commercial software routine for the layout of runner systems, gate locations and ejector positions. The damage potential of the test particles was evaluated based on trials using journal bearing and shift valve test rigs. Although only a moderate degree of damage potential could be ascertained up until now, it can be expected that the artificial swarf will enable standardized wear test procedures to be developed.

Difference in mechanical properties between plastic and metal molds for injection molding a talc reinforced rubber modified polypropylene

AbstractTooling for injection molding is costly, and delivery time is a concern, especially for companies that are on a tight production schedule. The introduction of additive manufacturing tooling for injection molding is an attractive rapid tooling for cutting cost and time not only for prototype parts but also for low volume production, that is, less than 100 parts. In this work, digital acrylonitrile butadiene styrene (ABS) mold insert was 3D printed on a Stratasys PolyJet printer, and then installed on the mold frame for injection molding investigation. The mechanical properties of talc reinforced rubber modified polypropylene (PP) parts molded by 3D printed ABS mold and conventional steel mold are compared. When the 3D printed ABS mold was used, a significantly higher mold temperature was observed during the molding cycles compared to the steel mold because of the lower thermal conductivity of ABS. The ductility of PP parts molded by the ABS mold is much lower compared to the metal mold, while other mechanical properties, such as tensile strength, Young's modulus, and flexural strength are not significantly different.

Investigations on Temperatures of the Flat Insert Mold Cavity Using VCRHCS with CFD Simulation.

This paper adopted transient CFD (Computational Fluid Dynamics) simulation analysis with an experimental method for designing and surveying the quick and uniform rise in the temperature of the plastics into the insert mold cavity. Plastic injection molding utilizing VCRHCS (Vapor Chamber for Rapid Heating and Cooling System) favorably decreased the defects of crystalline plastic goods’ welding lines, enhancing the tensile intensity and lowering the weakness of welding lines of a plastic matter. The vapor chamber (VC) possessed a rapid uniform temperature identity, which was embedded between the heating unit and the mold cavity. The results show that the tensile strength of the plastic specimen increased above 8%, and the depths of the welding line (V-gap) decreased by 24 times (from 12 μm to 0.5 μm). The VCRHCS plastic injection molding procedure can constructively diminish the development time for novel related products, as described in this paper.