Manufacturing process development of a precision rapid tooling with high‐aspect‐ratio micro‐sized features

The high‐aspect‐ratio elements are widely employed for chemical sensors, microfluidics and medical imaging devices. To enhance the competitiveness in the market of elements with high‐aspect‐ratio microstructures, a cost‐effective method for fabricating molds with high‐aspect‐ratio microstructures was proposed. In order to manufacture the second rubber mold, low‐temperature plasma were used to change the surface characteristics of the rubber mold to avoid using the release agents in the manufacturing process. It was found that the aluminum (Al)‐filled epoxy resin mold with the aspect ratio of 20 : 1 can be carried out in about three days. Replication rates of a precision rapid tooling with high‐aspect‐ratio micro‐sized features around 97 % can be obtained. The total fabrication cost savings for fabricating a SU‐8 microelement with the aspect ratio of 20 : 1 about 71 % can be obtained.     

Rapid manufacturing of plastic aspheric optical lens

This paper presents a new process to rapid manufacture the plastic aspheric optical lens. A bridge tooling was developed for fabricating the mold inserts of an aspheric lens using silicone rubber materials. Epoxy‐based composites were used to fabricate mold inserts of an aspheric optical lens. Z‐axis shrinkage error was investigated after plastic injection molding and compensated to the designed aspheric lens. In comparison with conventional method for fabricating a pair of mold inserts of a new plastic lens, a cost reduction of 75.02% and a time saving of 77.78% can be achieved. The deformation improvement percentage is about 92.48%. This technology can be used to compensate the z‐axis deformation efficiently due to shrinkage error of plastics in molding aspheric lens. Aspheric optical lens can be produced rapidly and cost‐effectively.     

The evolution of manufacturing processes for micro‐featured epoxy resin mold

Micro‐injection molding or micro‐hot embossing is a highly effective process for fabricating micro‐devices with microfeatures in polymer. Based on the strong demand on the precision components in the precision machinery industrial, two major concerns are the time and expense required for producing a precision mold for microfabrication. To enhance the competitiveness in the market of micorcomponents, this study presents six approaches for manufacturing precision epoxy resin molds with microfeatures. Evolutions manufacturing processes are described experimentally. Characteristics and applications of micro‐featured epoxy resin mold are introduced in detail.     

Development of bridge tooling for fabricating mold inserts of aspheric optical lens

A bridge tooling is developed for fabricating the temporary mold inserts of aspheric lens using silicone rubber materials. Prototype material of the aspheric lens is not recommended as quartz due to low successful rate in the fabrication process. This technology provides a fast, low cost, and high successful rate for fabricating the epoxy‐based composites mold inserts of plastic aspheric optical lens.     

Modeling and experimental analysis in lifespan of a precision epoxy resin mold

Micro‐hot embossing is a highly effective process for fabricating micro‐devices with microfeatures in polymeric materials. One of the most troublesome problems in precision machinery industry is the time and expense needed to produce a mold for microreplication. Epoxy resin mold has been successfully employed for microreplication using micro‐hot embossing. However, the junction of the groove and sprue of the backing plate has serious local stress concentration, leading to the reduction of lifespan of a precision epoxy resin mold during the micro‐hot embossing molding. This work presents an effective method for enhancing the lifespan of a precision epoxy resin mold using reduction of local stress concentration. The numerical models were developed for predicting the maximum stress using ANSYS software. The ANSYS simulations have been carried out and the predicted results show good agreement with experimental tests. The junction of the groove and sprue of the backing plate was machined with chamfer to revaluate lifespan of the epoxy resin mold using micro‐hot embossing molding. Micro‐hot embossing verification test showed that the lifespan of epoxy resin mold with chamfer is about 2.2 times that of the conventional epoxy resin mold.     

A cost‐effective approach for rapid manufacturing a low pressure wax injection mold with high surface finish and high dimensional accuracy

Investment casting process is considered as an economic method for mass production of metal parts. Improvement of mold surface quality and geometric accuracy in the fused deposition rapid tooling is a major concern. In this paper, a new technique is proposed for rapid manufacturing a low pressure wax injection mold with high surface finish and high dimensional accuracy. Wax patterns produced from this mold have not only better dimensional accuracy but also better surface finish. The average relative error of dimension of wax patterns can be reduced from 1.76% to 0.66%. Surface roughness improvement rate of wax patterns of up to 85.71% can be achieved. Advantages of this technique include low manufacturing cost, simple manufacturing process and flexible process capability.     

Vorhersage der Mikrostruktur und mechanischen Eigenschaften geschmiedeter Bauteile durch FEM‐Simulation

Prediction of microstructure and mechanical properties of forged parts with the aid of FE‐analysis The FEM‐simulation permits to predict final state variables of the workpieces and to visualize internal stress states. Thereby the simulation promotes the reduction of time and cost. Especially for complex precision forging processes with subsequent heat treatment, for instance the manufacturing of gears, the FEM‐simulation is successfully established as an effective tool for simulation aided design and planning in the early stage of the construction process. Specially developed subroutines, which describe the evolution of microstructure during the whole process using macroscopic approaches, were implemented in a commercial FE‐Code. This paper presents the results of experimentally validated FEM‐Simulations using the developed subroutines. Furthermore, this study includes simulation results of a precision forged gear in respect of the microstructure evolution as well as the mechanical properties of the finished part.     

High‐Speed 3D Printing of Millimeter‐Size Customized Aspheric Imaging Lenses with Sub 7 nm Surface Roughness

Advancements in three‐dimensional (3D) printing technology have the potential to transform the manufacture of customized optical elements, which today relies heavily on time‐consuming and costly polishing and grinding processes. However the inherent speed‐accuracy trade‐off seriously constrains the practical applications of 3D‐printing technology in the optical realm. In addressing this issue, here, a new method featuring a significantly faster fabrication speed, at 24.54 mm³ h^?1, without compromising the fabrication accuracy required to 3D‐print customized optical components is reported. A high‐speed 3D‐printing process with subvoxel‐scale precision (sub 5 µm) and deep subwavelength (sub 7 nm) surface roughness by employing the projection micro‐stereolithography process and the synergistic effects from grayscale photopolymerization and the meniscus equilibrium post‐curing methods is demonstrated. Fabricating a customized aspheric lens 5 mm in height and 3 mm in diameter is accomplished in four hours. The 3D‐printed singlet aspheric lens demonstrates a maximal imaging resolution of 373.2 lp mm^?1 with low field distortion less than 0.13% across a 2 mm field of view. This lens is attached onto a cell phone camera and the colorful fine details of a sunset moth's wing and the spot on a weevil's elytra are captured. This work demonstrates the potential of this method to rapidly prototype optical components or systems based on 3D printing.     

Carbon‐MEMS‐Based Alternating Stacked MoS2@rGO‐CNT Micro‐Supercapacitor with High Capacitance and Energy Density

A novel process to fabricate a carbon‐microelectromechanical‐system‐based alternating stacked MoS₂@rGO–carbon‐nanotube (CNT) micro‐supercapacitor (MSC) is reported. The MSC is fabricated by successively repeated spin‐coating of MoS₂@rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis. MoS₂@rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC. The fabricated MSC exhibits a high areal capacitance of 13.7 mF cm^?2 and an energy density of 1.9 µWh cm^?2 (5.6 mWh cm^?3), which exceed many reported carbon‐ and MoS₂‐based MSCs. The MSC also retains 68% of capacitance at a current density of 2 mA cm^?2 (5.9 A cm^?3) and an outstanding cycling performance (96.6% after 10 000 cycles, at a scan rate of 1 V s^?1). Compared with other MSCs, the MSC in this study is fabricated by a low‐cost and facile process, and it achieves an excellent and stable electrochemical performance. This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems.     

Precise Patterning of Organic Single Crystals via Capillary‐Assisted Alternating‐Electric Field

Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low‐cost and high‐performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high‐throughput, high‐precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary‐assisted alternating‐electric field method for the large‐scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm². The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible–blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high‐integration, high‐performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals.     

Pencil‐Drawing Skin‐Mountable Micro‐Supercapacitors

In this study, integrated plaster‐like micro‐supercapacitors based on medical adhesive tapes are fabricated by a simple pencil drawing process combined with a mild solution deposition of MnO₂. These solid micro‐supercapacitors not only exhibit excellent stretchability, flexibility, and biocompatibility, but also possess outstanding electrochemical performances, such as exceptional rate capability and cycling stability. Hence they may act as skin‐mountable and thin‐film energy storage devices of high efficiency to power miniaturized and wearable electronic devices.     

Effect of As,Cu and Sb impurities on performance of Pb‐Ca‐Sn grids of lead‐acid batteries

The performance of Pb‐Ca‐Sn grids of lead‐acid batteries made from recycled lead in 4 M H₂SO₄ in the absence and presence of traces of Cu, As and Sb, as potential impurities in the recycling process at 0.1% level, is investigated by electrochemical methods. The study includes the effect of each impurity and impurities combined on the alloy corrodibility, the efficiency of PbO₂ formation, the rate of the self‐discharge and the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The results show that individual impurity enhances the corrosion resistance but increases the anode corrosion and the self‐discharge rate. Impurities play opposite effects on hydrogen evolution reaction and oxygen evolution reaction either individually or combined. Concerning water loss problem, the harmful effect of individual impurity on increasing oxygen evolution reaction is compensated by their suppression of hydrogen evolution reaction. The impurities combined suppress effectively both hydrogen evolution reaction and oxygen evolution reaction relative to alloy without any impurity. Sb has the highest harmful effects on oxygen evolution reaction and the self‐discharge but it is the best in the suppression of hydrogen evolution reaction. The impurities combined relatively improve the general corrosion resistance, the anode corrosion resistance and the self‐discharge. The study supports higher tolerance levels of Cu, As and Sb in Pb‐Ca‐Sn grids, especially when present combined, than the recommended levels in the industry standards.     

High yield spray forming of small diameter tubes using pressure‐gas‐atomization

The economy of the spray forming process is restricted by the generation of overspray, which in many cases cannot be re‐introduced into the process by re‐melting or co‐injection. Especially for small deposits, such as small diameter tubes (diameter <100 mm), the amount of overspray can become large in conventional spray‐forming processes. In this work, an alternative process with a pressure‐gas‐atomizer operating at low melt flows is presented. Tubes with diameters of 50 mm and 90 mm were spray‐formed and analyzed regarding yield and porosity. It was found that yields up to 96% can be achieved with porosities below 1% if proper process parameters are identified and used. An evaluation of the yield and the corresponding achievable porosity is conducted to identify resource‐efficient sets of parameters.     

Charakterisierung von Randentkohlungsvorgängen bei der Austenitisierung des Wälzlagerstahls 100Cr6. Teil 1: Korrelation zwischen Randschichteigenschaften und Kohlenstoff‐Tiefenverlauf

Characterization of Decarburisation Processes During Austenitising of the Rolling Bearing Steel 100Cr6. Part 1: Correlation between Rim Zone Properties and Carbon Concentration Profile The influence of a decarburisation process during austenitising of the through‐hardenable rolling bearing steel 100Cr6 (SAE 52100) on the rim zone properties of the martensitic through‐hardened material was investigated by means of material analysis and diffusion calculations. For this purpose, two specimens were prepared under defined heat treatment conditions, and the near‐surface carbon distribution was determined micro‐chemically by using secondary ion mass spectrometry (SIMS). In part 1 of the present work, these concentration profiles are compared with the depth variation of the micro‐hardness and with the distance curves of the residual stresses and the line broadening ({211} α'‐Fe diffraction line) both measured by X‐ray diffraction (XRD). In addition, microstructure investigations were performed. In part 2, a refined kinetics model of a diffusion‐controlled reaction based on the finite element method (FEM) will be applied to the decarburisation process in order to describe the carbon distributions obtained.     

Simultaneous Fabrication of Very High Aspect Ratio Positive Nano‐ to Milliscale Structures

A simple and inexpensive technique for the simultaneous fabrication of positive (i.e., protruding), very high aspect (>10) ratio nanostructures together with micro‐ or millistructures is developed. The method involves using residual patterns of thin‐film over‐etching (RPTO) to produce sub‐micro‐/nanoscale features. The residual thin‐film nanopattern is used as an etching mask for Si deep reactive ion etching. The etched Si structures are further reduced in size by Si thermal oxidation to produce amorphous SiO₂, which is subsequently etched away by HF. Two arrays of positive Si nanowalls are demonstrated with this combined RPTO‐SiO₂‐HF technique. One array has a feature size of 150 nm and an aspect ratio of 26.7 and another has a feature size of 50 nm and an aspect ratio of 15. No other parallel reduction technique can achieve such a very high aspect ratio for 50‐nm‐wide nanowalls. As a demonstration of the technique to simultaneously achieve nano‐ and milliscale features, a simple Si nanofluidic master mold with positive features with dimensions varying continuously from 1 mm to 200 nm and a highest aspect ratio of 6.75 is fabricated; the narrow 200‐nm section is 4.5 mm long. This Si master mold is then used as a mold for UV embossing. The embossed open channels are then closed by a cover with glue bonding. A high aspect ratio is necessary to produce unblocked closed channels after the cover bonding process of the nanofluidic chip. The combined method of RPTO, Si thermal oxidation, and HF etching can be used to make complex nanofluidic systems and nano‐/micro‐/millistructures for diverse applications.     

Non‐isothermal ‘2‐D flow/3‐D thermal’ developments encompassing process modelling of composites: flow/thermal/cure formulations and validations

In the manufacturing process of large geometrically complex components comprising of fibre‐reinforced composite materials by resin transfer molding (RTM), the process involves injection of resin into a mold cavity filled with porous fibre preforms. The overall success of the RTM manufacturing process depends on the complete impregnation of the fibre mat by the polymer resin, prevention of polymer gelation during filling, and subsequent avoidance of dry spots. Since a cold resin is injected into a hot mold, the associated physics encompasses a moving boundary value problem in conjunction with the multi‐disciplinary study of flow/thermal and cure kinetics inside the mold cavity. Although experimental validations are indispensable, routine manufacture of large complex structural geometries can only be enhanced via computational simulations, thus eliminating costly trial runs and helping the designer in the set‐up of the manufacturing process. This study describes the computational developments towards formulating an effective simulation‐based design methodology using the finite element method. The specific application is for thin shell‐like geometries with the thickness being much smaller than the other dimensions of the part. Due to the highly advective nature of the non‐isothermal conditions involving thermal and polymerization reactions, special computational considerations and stabilization techniques are also proposed. Validations and comparisons with experimental results are presented whenever available. Copyright © 2001 John Wiley & Sons, Ltd.     

Inkjet‐Printed High‐Performance Flexible Micro‐Supercapacitors with Porous Nanofiber‐Like Electrode Structures

Flexible planar micro‐supercapacitors (MSCs) with unique loose and porous nanofiber‐like electrode structures are fabricated by combining electrochemical deposition with inkjet printing. Benefiting from the resulting porous nanofiber‐like structures, the areal capacitance of the inkjet‐printed flexible planar MSCs is obviously enhanced to 46.6 mF cm^?2, which is among the highest values ever reported for MSCs. The complicated fabrication process is successfully averted as compared with previously reported best‐performing planar MSCs. Besides excellent electrochemical performance, the resultant MSCs also show superior mechanical flexibility. The as‐fabricated MSCs can be highly bent to 180° 1000 times with the capacitance retention still up to 86.8%. Intriguingly, because of the remarkable patterning capability of inkjet printing, various modular MSCs in serial and in parallel can be directly and facilely inkjet‐printed without using external metal interconnects and tedious procedures. As a consequence, the electrochemical performance can be largely enhanced to better meet the demands of practical applications. Additionally, flexible serial MSCs with exquisite and aesthetic patterns are also inkjet‐printed, showing great potential in fashionable wearable electronics. The results suggest a feasible strategy for the facile and cost‐effective fabrication of high‐performance flexible MSCs via inkjet printing.     

Effect of heat treatment on the hardness of micro deep drawn cups of Al‐2Sc

Continuous miniaturisation of products e. g. for the automotive or the microelectronic sector necessitates process chains, which allow the manufacturing of microscopically small components in high quantities. The development of required processes and technologies is the aim of the Collaborative Research Centre (CRC) 747 “Micro Cold Forming” of the German Research Foundation. Besides micro cold forming another necessary step in the manufacturing process chain is the heat treatment process that enables the adjustment of materials properties being suitable for cold forming. Finally the application properties also have to be adjusted e. g. by precipitation hardening of aluminium alloys to increase the strength above the strain hardened level. Within the CRC an advanced Al‐Sc alloy with 2 mass‐% Scandium was developed to achieve particular properties. According to the very high Sc content dissolved a greater number of fine and homogeneously distributed precipitates causing a significant strengthening effect will be formed during artificial ageing. To meet the requirements of a high production rate the ageing of the micro deep drawn cups (1 mm in diameter) was performed in very short time in a drop‐down tube furnace. Before and after ageing the cups were characterised by ultra micro hardness measurements.     

Fabrication of modeling platform for fused deposition modeling using vacuum casting

This study presents a cost‐effective approach for rapid fabricating modeling platforms utilized in fused deposition modeling three‐dimensional printing system. A small‐batch production of modeling platforms about 20 pieces can be obtained economically through silicone rubber mold using vacuum casting without applying the plastic injection molding. The air venting systems is crucial for fabricating modeling platform using vacuum casting. Modeling platforms fabricated can be used for building rapid prototyping model after sandblasting. This study offers industrial value because it has both time‐effectiveness and cost‐effectiveness.