Mold Insert Research Articles

Quick-Delivery Mold Fabricated via Stereolithography to Enhance Manufacturing Efficiency

The ever-growing demand for reducing costs and decreasing the time to market in today’s plastics industry makes rapid tooling and rapid prototyping highly researched areas. Stereolithography (SLA)-manufactured injection mold inserts make it possible to produce prototype parts rapidly and cost-effectively. To utilize SLA in the injection molding industry, two steps have to be considered. The first is to identify suitable SLA process and post-thermal curing process parameters to enhance the mechanical and thermal characteristics. The second is to verify the applicability of SLA-manufactured molds for use in the injection molding industry. IA comprehensive study was performed to find the optimum process parameters for an SLA mold with excellent mechanical and thermal properties and to verify the applicability of the mold. First of all, the mechanical and thermal properties of samples manufactured based on various laser powers and heat treatment at different temperatures were analyzed with a tensile test, DSC, and TMA according to the degree of cure. On the basis of the results from those tests, an SLA mold was designed and fabricated with the optimum mechanical and thermal properties. In addition, the SLA mold was assembled into an injection machine, and an injection molding test was conducted. The SLA mold endured during the injection cycle, and 500 shots were successfully injected without damaging the mold, which resulted in reaching the quick-delivery mold standard. Finally, we demonstrate that SLA is an effective technology to produce molds for use in the injection molding industry.

The behaviour of micro-injection moulding inserts produced with material jetting technology

The increasing interest in additive manufacturing and advancements in precision and production quality have sparked attention to its use in industrial prototyping. High-performance polymer resins enhance flexibility in mass production processes like micro-injection moulding. This flexibility allows for reconfigurable moulds using resin inserts, enabling the transition of devices, such as microfluidics, from labs to large-scale production. Despite progress, limitations exist in additive manufacturing, including the minimum size of microstructures and the brittle behaviour of resin inserts during moulding cycles, impacting overall production capacity. This study focuses on using a micro-injection moulding machine to reproduce PMMA thin plates with single straight microchannels (250 μm) and with different side wall angles (0°, 15°, and 30°), investigating the best compromise between capability and insert resistance to moulding cycles. A careful study of the dynamics leading to the insert failure and the resin limits was carried out. The results showed that it is possible to produce about 15 micro-structured thin plates with good accuracy using a resin insert realised with Material Jetting technology.

Composite electroforming of precision Ni-P-PTFE mold inserts with low internal stress and self-lubricating properties

An electrolyte solution incorporating sodium saccharin and an alkynyl compound was provided to electroform Ni-P-PTFE mold inserts with both low internal stress and good self-lubricating properties. The results showed that with 5 g·L−1 sodium saccharin and 1 mL·L−1 alkynyl compound, the internal stress reached a minimum of −114 MPa, an 82 % reduction from the −646 MPa observed without additives. The presence of sodium saccharin and alkynyl compound in the electrolyte solution reduced the hydrogen evolution reaction current from 15.2 to 12.9 mA at the operating cathode potential of −1 V and decreased the RTC(111) from 100 % to 90 %. The reduction of internal stress in the electrodeposited Ni-P-PTFE composites was attributed to the decreased hydrogenation strain, diminished Ni (111) texture intensity, and the partial incorporation of alkynyl compound reaction products into the cathode surface, which weakened the connections between crystallites. Finally, 5 g·L−1 sodium saccharin and 1 mL·L−1 alkynyl compound was applied to electroform Ni-P-PTFE mold insert with micro features. Only slightly pile-up defects at the corner of grooves were observed on the polymer chips demolded from Ni-P-PTFE mold insert, demonstrating its good self-lubricating property.

Developing a hybrid-built pre-hardened alloy steel for injection moulding tools using the laser powder bed fusion process

Hybrid additive-subtractive manufacturing has been adopted as a cost-effective alternative for manufacturing plastic injection moulding tools with conformal-cooled inserts created by fusing powder and wrought material. This article reports the development of a hybrid power-wrought pre-hardened alloy steel to supplement the current material choice for fabricating injection mould inserts using this advanced manufacturing strategy. In this study, MS1 (maraging 300) steel powder was additively deposited onto pre-machined wrought Nimax steel to form a hybrid alloy material. The mechanical and microstructural properties of the fusion-bonded interface were examined. Microstructural observation revealed a 280 μm thick interfacial region consisting of a homogenous mixing of powder and substrate materials. As a result of solid solution strengthening within the region, tensile tests established robust powder-substrate bonding with tensile ruptures occurring well away from the interface. The as-built hybrid-alloy steel possessed excellent mechanical properties, with 1200 MPa in ultimate tensile strength, 12.4 % in elongation at fracture and 39 HRC (Nimax)/42 HRC (MS1) in hardness. The overall results suggested that hybrid MS1-wrought Nimax steel is a suitable pre-hardened material for manufacturing durable and high-performance injection mould inserts as part of a cost-effective hybrid additive-subtractive manufacturing strategy.

The design and fabrication of thermoplastic microfluidic chips with integrated micropillars for particle separation

Microfluidic technology utilizing the deterministic lateral displacement (DLD) method holds significant promise for efficiently separating micro-particles and biological cells. Despite the notable high throughput advantages associated with DLD chips, their widespread application is impeded by the substantial manufacturing costs of tens of thousands of micropillars. This study aims to explore the feasibility of employing the injection molding method for the mass production of DLD microfluidic chips. A multistage DLD chip with varied critical diameters was designed to isolate white blood cells from the human whole blood. The separation effectiveness was verified with the polydimethylsiloxane chip fabricated by standard soft lithography. Subsequently, nickel mold inserts were electroformed to fabricate thermoplastic DLD chips via the injection molding. The replication quality of micropillars under different molding parameters was studied. The capability of injection-molded chips to effectively achieve particle separation was validated. Results showed that thermoplastic chips with good replication quality were obtained, providing a scale-up production strategy for fabricating polymer-based microfluidic chips for disposable separation applications.

Additive manufacturing of variothermal injection moulding insert made of Al-40Si

Injection moulding has been a pivotal technology in the mass production of polymer optics for many years. The surface quality of the moulding inserts exerts a significant influence on the quality of the optics produced. In the production of micro-structured polymer optics, such as Fresnel lenses, conventional isothermal injection moulding is unable to achieve the requisite surface accuracy. Variothermal injection moulding allows for improved surface accuracy and reduced residual stresses, but increases technical effort and cycle times. To reduce the cycle time and residual stresses of variothermal injection moulding, the potential of additive manufacturing of Al-40Si for the fabrication of moulding inserts is investigated. In order to achieve these objectives, the offered design freedom of additive manufacturing is investigated with a view to developing optimised conformal cooling channels. Numerical methods will be used for thermal and structural analyses. The performance of the newly developed moulding insert is evaluated experimentally by thermographic measurements and the measurement of stress birefringence on replicated PMMA samples.

Evaluation of Material Extrusion Printed PEEK Mold Inserts for Usage in Ceramic Injection Molding

The rapid tooling of mold inserts for injection molding allows for very fast product development, as well as a highly customized design. For this, a combination of rapid prototyping methods with suitable polymer materials, like the high-performance thermoplastic polymer polyetheretherketone (PEEK), should be applied. As a drawback, a huge processing temperature beyond 400 °C is necessary for material extrusion (MEX)-based 3D printing; here, Fused Filament Fabrication (FFF) requires a more sophisticated printing parameter investigation. In this work, suitable MEX printing strategies, covering printing parameters like printing temperature and speed, for the realization of two different mold insert surface geometries were evaluated, and the resulting print quality was inspected. As a proof of concept, ceramic injection molding was used for replication. Under consideration of the two different test structures, the ceramic feedstock could be replicated successfully and to an acceptable quality without significant mold insert deterioration.

Investigating demoulding characteristics of material jetted rapid mould inserts for micro­injection moulding using in­line monitoring and surface metrology

PurposeThis study aims to investigate the demoulding characteristics of material-jetted rapid mould inserts having different surface textures for micro-injection moulding using in-line measurements and surface metrology.Design/methodology/approachMaterial-jetted inserts with the negative cavity of a circular test product were fabricated using different surface finishes and printing configurations, including glossy, matte and vertical settings. In-line measurements included the recording of demoulding forces at 10 kHz, which was necessary to capture the highly-dynamic characteristics. A robust data processing algorithm was used to extract reliable demoulding energies per moulding run. Thermal imaging captured surface temperatures on the inserts after demoulding. Off-line measurements, including focus variation microscopy and scanning electron microscopy, compared surface textures after a total of 60 moulding runs.FindingsA framework for capturing demoulding energies from material-jetted rapid tools was demonstrated and compared to the literature. Glossy surfaces resulted in significantly reduced demoulding forces compared to the industry standard steel moulds in the literature and their material-jetted counterparts. Minimal changes in the surface textures of the material-jetted inserts were found, which could potentially permit their prolonged usage. Significant correlations between surface temperatures and demoulding energies were demonstrated.Originality/valueThe research presented here addresses the very topical issue of demoulding characteristics of soft, rapid tools, which affect the quality of prototyped products and tool durability. This was done using state-of-the-art, high-speed sensing technologies in conjunction with surface metrology and their durability for the first time in the literature.

Study on the Effect of Recycled Brass-Filled Epoxy Mould Inserts for Rapid Tooling

Rapid Tooling able to produce complex prototypes directly from three-dimensional CAD software using materials such as polymer, wax, and paper, but it is typically used for low-volume production. The current technology uses epoxy filled with metal fillers such as aluminum or copper to enhance the mechanical properties of rapid tooling molds. This study aims to investigate the effect of using recycled brass filler mixed with epoxy resin as mold inserts for Rapid Tooling in injection molding applications. An optimal ratio of brass filler particles will be evaluated to determine the best physical and thermal properties for the mold inserts. Significantly, this study will encourage the use of recycled materials such as metal waste from machining to offer great help in environmental sustainability.

Optimization Design of Injection Mold Conformal Cooling Channel for Improving Cooling Rate

Optimizing the design of the conformal cooling channel can increase the cooling rate of injection mold. The aim of this study was the problem of low cooling efficiency of injection mold for deep-cavity plastic parts under the conventional cooling channel. Based on the analysis of the heat transfer principle of the injection mold, a mathematical description of the cooling time of the conformal cooling channel was made. By designing orthogonal experiments and using simulation methods in the Autodesk Moldflow 2019 software, with the minimum cooling time of the mold as the optimization goal, experimental optimization was carried out for the three design variables of the channel, thereby obtaining the optimal combination of design variables for the conformal cooling channel. The conformal cooling channel layout was innovatively designed, and through computer simulation experiments, it was concluded that the conformal cooling channel adopted a series flat-head layout, which has the shortest cooling time and the fastest cooling rate. Metal additive manufacturing technology was used to complete the manufacturing of the mold insert with the conformal cooling channel. After the trial production of the conformal cooling injection mold, the molding cycle was obviously shortened, and the injection molding production efficiency was significantly improved.

Influence of Anode Immersion Speed on Current and Power in Plasma Electrolytic Polishing.

Plasma electrolytic polishing (PeP) is mainly used to improve the surface quality and thus the performance of electrically conductive parts. It is usually used as an anodic process, i.e., the workpiece is positively charged. However, the process is susceptible to high current peaks during the formation of the vapour-gaseous envelope, especially when polishing workpieces with a large surface area. In this study, the influence of the anode immersion speed on the current peaks and the average power during the initialisation of the PeP process is investigated for an anode the size of a microreactor mould insert. Through systematic experimentation and analysis, this work provides insights into the control of the initialisation process by modulating the anode immersion speed. The results clarify the relationship between immersion speed, peak current, and average power and provide a novel approach to improve process efficiency in PeP. The highest peak current and average power occur when the electrolyte splashes over the top of the anode and not, as expected, when the anode touches the electrolyte. By immersion of the anode while the voltage is applied to the anode and counterelectrode, the reduction of both parameters is over 80%.

Surface wettability and tribological performance of Ni-based nanocomposite moulds against polymer materials

In the mass-production of microfluidic devices through micro hot embossing/injection moulding, the longevity of mould inserts is influenced by elevated adhesion and friction between the polymer and the mould. Thus, accurate prediction of mould lifespan requires a comprehensive understanding of surface wettability and tribological performance during polymer contact. The current study addresses this gap by characterizing fabricated micro-structured Ni, Ni-WS2, and Ni-PTFE nanocomposite moulds (surface morphologies, crystal structures and microhardness) to investigate inherent lubrication mechanisms. Surface wettability of mould material was systematically studied by measuring the contact angles with eight different polymer melts. Pin-on-disk tests with polymer pins made of cyclic olefin copolymer (COC 8007), polypropylene (PP), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were conducted to elucidate the wear resistance of the nanocomposite moulds. Pressure-dependent friction coefficient and wear resistance were further explored under increasing external loads, simulating the actual moulding processes where contact pressure may vary considerably depending on the part shape. Results indicate that Ni-WS2 exhibits the highest microhardness (532 Hv), followed by Ni-PTFE (465 Hv) and Ni (198 Hv). Notably, Ni-PTFE demonstrates exceptional hydrophobicity against all polymer melts, signifying low surface energy during polymer contact. Moreover, both nanocomposite moulds exhibit reduced friction coefficients and enhanced wear resistance across various polymers. Counterintuitively, despite its lower hardness, the Ni-PTFE mould displays superior wear resistance against the COC pin under higher loads, while the Ni-WS2 mould experiences severe adhesive wear, as observed from wear morphology and profile analysis. This finding establishes the Ni-PTFE as a promising alternative as a mould insert material for precision manufacturing.

Pulse current electroforming of Ni-PTFE nanocomposite mold insert with long-lifetime and anti-adhesive properties

Polymeric micro features tend to deform and break under the demolding force during injection molding process, which becomes a bottleneck problem limiting its precision manufacturing. To reduce the polymer-mold interfacial adhesion, nickel-polytetrafluoroethylene (Ni-PTFE) nanocomposite molds with low surface adhesion and high wear resistance were manufactured via pulse current electroforming. The electrodeposited Ni-PTFE nanocomposite showed a good hydrophobic property and low friction coefficient (between 0.1 and 0.3) than pure nickel (0.78). Compared with direct current, pulse current electrodeposition was beneficial to reduce the crystallite size and internal stress, thus improving the wear resistance and reducing the cracking defects. The hardness of pulse current electrodeposited Ni-PTFE reached 442.3 HV, which was 51.7 % higher than that of pure nickel. Compared to nickel mold, Ni-PTFE nanocomposite mold significantly improved the dimensional accuracy of molded microfluidic chips. This study systematically investigates the Ni-PTFE nanocomposite electroforming process under both direct and pulse currents, which provides a new approach for the manufacturing of high-performance precision injection mold insert.

Effects of TiN content and heat treatment on microstructural changes, mechanical strength, and corrosion resistance in selective laser melting of TiN/AISI 420 composites

This study investigates the influence of Titanium Nitride (TiN) concentration variations and heat treatment on the microstructure, strength, and corrosion resistance of TiN/AISI 420 composites fabricated via selective laser melting (SLM). Results demonstrate that the addition of TiN particles (2 μm in size) at 0.5, 1, and 2 wt percent (wt. %) to the AISI 420 alloy enhances the toughness modulus of SLM TiN/AISI 420 to 37.0 ± 1.5 J/m3, 42.2 ± 0.4 J/m3, and 36.2 ± 0.7 J/m3, respectively, surpassing the SLM AISI 420's toughness of 21.3 ± 0.6 J/m3. Moreover, a positive relationship between TiN content and corrosion resistance is observed, with 2 wt % TiN/AISI 420 composites exhibiting the highest resistance at 105.6 ± 2.5 mm/year in a 6 wt % FeCl3 solution. Following heat treatment, a reduction in hardness is noted due to decreased surface residual stress and increased retained austenite. However, treated composites demonstrate improved mechanical and corrosion resistances. Particularly noteworthy is the highest toughness of 118.0 ± 1.3 J/m3 observed in 1 wt % TiN composites and a corrosion rate of 104.7 ± 2.7 mm/year in 2 wt % TiN composites. The homogeneous dispersion of TiN particles and the phenomenon of transformation-induced plasticity significantly enhance toughness, while increased levels of retained austenite contribute to improved corrosion resistance. This work underscores the potential of advanced manufacturing techniques in developing composite materials with diverse applications, such as robotic mold inserts. It emphasizes the pivotal role of composite formulation and post-processing in augmenting material performance.

Optimization of Surface Roughness of Aluminium RSA 443 in Diamond Tool Turning

Context—Rapidly solidified aluminium alloy (RSA 443) is increasingly used in the manufacturing of optical mold inserts because of its fine nanostructure, relatively low cost, excellent thermal properties, and high hardness. However, RSA 443 is challenging for single-point diamond machining because the high silicon content mitigates against good surface finishes. Objectives—The objectives were to investigate multiple different ways to optimize the process parameters for optimal surface roughness on diamond-turned aluminium alloy RSA 443. The response surface equation was used as input to three different artificial intelligence tools, namely genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE), which were then compared. Results—The surface roughness machinability of RSA443 in single-point diamond turning was primarily determined by cutting speed, and secondly, cutting feed rate, with cutting depth being less important. The optimal conditions for the best surface finish Ra = 14.02 nm were found to be at the maximum rotational speed of 3000 rpm, cutting feed rate of 4.84 mm/min, and depth of cut of 14.52 µm with optimizing error of 3.2%. Regarding optimization techniques, the genetic algorithm performed best, then differential evolution, and finally particle swarm optimization. Originality—The study determines optimal diamond machining parameters for RSA 443, and identifies the superiority of GA above PSO and DE as optimization methods. The principles have the potential to be applied to other materials (e.g., in the RSA family) and machining processes (e.g., turning, milling).

Anatomical design and production of a novel three-dimensional co-culture system replicating the human flexor digitorum profundus enthesis.

The enthesis, the specialized junction between tendon and bone, is a common site of injury. Although notoriously difficult to repair, advances in interfacial tissue engineering techniques are being developed for restorative function. Most notably are 3D invitro co-culture models, built to recreate the complex heterogeneity of the native enthesis. While cell and matrix properties are often considered, there has been little attention given to native enthesis anatomical morphometrics and replicating these to enhance clinical relevance. This study focuses on the flexor digitorum profundus (FDP) tendon enthesis and, by combining anatomical morphometrics with computer-aided design, demonstrates the design and construction of an accurate and scalable model of the FDP enthesis. Bespoke 3D-printed mould inserts were fabricated based on the size, shape and insertion angle of the FDP enthesis. Then, silicone culture moulds were created, enabling the production of bespoke anatomical culture zones for an invitro FDP enthesis model. The validity of the model has been confirmed using brushite cement scaffolds seeded with osteoblasts (bone) and fibrin hydrogel scaffolds seeded with fibroblasts (tendon) in individual studies with cells from either human or rat origin. This novel approach allows a bespoke anatomical design for enthesis repair and should be applied to future studies in this area.

Enhancing structural replication of microfluidic chips: Parameter optimization and mold insert modification

AbstractThe demolding process in micro‐injection molding constitutes a critical phase, exerting a decisive influence on the quality of polymer microstructures. In this study, the demolding forces of PMMA microfluidic chips were measured under different demolding temperatures, packing pressures, and demolding speeds by using pure nickel (Ni) mold insert. The dimensional deviations of the microchannels with different aspect ratios were analyzed. In addition, the effect of mold insert modification on the demolding force was further analyzed. The results showed that the effect of demolding temperature on the demolding force was the most significant, and the peak demolding force decreased with the decrease in temperature. The width of the microchannels increased and the depth decreased after demolding, while the opposite results were observed for the micro‐mixing structures. However, the dimensional deviation of the micro‐mixing structures was larger than that of the microchannels. Using the optimal molding parameters, the peak demolding force could be reduced from 114.0 N at 110°C to 47.0 N, a decrease of 58.8%. It is noteworthy that, when the microchannel was narrower than 100 μm, achieving precise replication of microchannel dimensions became progressively more challenging as the microchannel width decreased. Using the Ni‐WS2 mold insert with low surface energy and low friction coefficient, the demolding force could be further reduced by 38.3%. The effect of the molding quality of microfluidic chip microstructures on the mixing performance of heavy metals was demonstrated by micro‐mixing experiments.Highlights Demolding temperature crucially affects microstructure dimensions. Optimal parameters and modified mold insert reduce demolding force by 38.3%. Dimensional deviation increases with the increase of microchannel aspect ratio. Optimized microfluidic chip enhances Co2+ chemiluminescence by 6.42%.

Influence of phosphorous acid concentration on the self-lubricating properties of electroformed Ni-P-PTFE ternary composites

In micro-injection molding, polymer/mold interface adhesion may cause severe deformation or damage of micro features on the molded products. To reduce the interface adhesion and improve the molding quality of polymer microfluidic chip, Ni-P-PTFE (polytetrafluoroethylene) ternary composite was adopted to electroform mold insert with self-lubricating properties. The influence of phosphorous acid concentration on the composition and performance of Ni-P-PTFE composites was systematically investigated. Our results demonstrated that the content of P and PTFE particles in the composites raised with an increase in phosphorous acid concentration. Elevated phosphorous acid concentration adversely affected the current efficiency and slowed down the deposition rate, allowing sufficient contact time for PTFE to transfer and adsorb onto the electrode surface. The hardness of the deposited nickel increased from 310 HV to 510 HV in the Ni-P-PTFE composites. Furthermore, the Ni-P-PTFE composites demonstrated excellent self-lubricating properties, showcasing friction coefficients of 0.15 and 0.25 during the initial and steady stages, respectively, representing a notable reduction of 66.7 % and 64.3 % compared to pure nickel. This study provides a novel approach to fabricate molds with self-lubricating properties, which contributes to the high-precision injection molding of polymer-based micro devices.

Manufacturing cost reduction techniques for automobile crankcase mould inserts

The manufacturing of automobile moulds is itself a challenging job and very tedious task requiring high accuracy of component profiles. The required complicated and complex profiles are generated when the mould inserts are relinquished from several numbers of workstations, which run for a longer process time. As the accuracy needed for the component area is very high and it (insert) has to pass through several bottleneck workstations, the production time and increased buffer time are observed. This chapter focuses on providing economical methods for manufacturing hot die steel inserts. These techniques are implemented on a pressure die-casting insert component. The present solution is derived for manufacturing time reduction and minimisation of the die-casting inserts (moving and fixed die) at every stage. Implementing combined electrodes, assembly machining and cluster plate machining/sparking techniques are critical development advancements in the research. In the combined electrode concept, one electrode is designed in the same area to cover multiple areas that were initially covered by separate individual electrodes. Furthermore, this concept is outstretched by the cluster plate concept. Those electrodes that cannot be covered by a single electrode are machined together to act as a single electrode and later separated while individual sparking. Combined electrode design, assembly machining and cluster machining/sparking of the electrodes reduce the total machining time of the die and the machining centre. Reducing the machine run time will reduce the production cost and increase profit. The results achieved show that the combined electrode design setup shows 75% savings in the combined sparking setup, whereas the cluster plate machining setup shows 35% savings in the tool list generation (from software used) of the net savings. The proposed solution opens up new avenues for similar automobile components by setting benchmarks to decrease the rope length associated with manufacturing and increase profit.

Development of stimuli-responsive flexible micropillar composites via magneto-induced injection molding and characterization of magnetic particle alignment

Magnetic soft composites have emerged as a promising soft actuator with a high degree of precision in the magnetic field stimuli system. But, their mass manufacturing strategies have yet to be developed, and most studies focus on small-scale near-net shaping production. Here, we first apply injection molding (which only takes a few seconds to shape) to fabricate the stimuli-responsive flexible micropillar composites with magnetic particle alignment design using an external magnetic field. The arrays exhibit magnetically anisotropic particle alignment up to 82.57 % along the longitudinal direction, showing a magnetic bending actuation response. We achieve a structural novelty of the magnetic micropillar with a high aspect ratio of up to 10 and pattern sizes of 50 μm via sacrificial LIGA insert mold and magneto-induced injection molding. For advanced mass production, the permanent metal mold is also applied to develop the micropillar composites based on the mechanical demolding approach; successful manufacturing is achieved by fabricating defect-free micropillar with 200 μm cylindrical pattern size and aspect ratio of 6. Further, the effect of powder volume fraction on the magneto-rheological behavior and corresponding magnetic performance is characterized in the injection molding process. The magnetic particle alignment trend is confirmed by the torque balance and the criteria of critical solids loading. Finally, we establish an injection molding process for magnetic soft composites, and verify the optimal powder fraction for the particle alignment.