International Journal of Precision Engineering and Manufacturing-Green Technology最新文献

This paper presents a material-efficient multimaterial projection micro-stereolithography (PμSL), a digital light processing (DLP) additive manufacturing process for printing microstructures. We present a droplet-based resin supply system to address the issue of excessive material waste of the multimaterial PμSL. By depositing droplets of different liquid resins, 3D printing of a microstructure can still be performed without the need for a traditional vat while printing materials can be switched with minimal material consumption. Precise control of small droplet volume is obtained by pressure control of the resin injection nozzles, exact opening times of fluid valves, and appropriate surface coatings in order to portion droplets so that just enough material is brought to the build area. Since PμSL enables micro 3D printing (in-plane resolution of 76 μm), PμSL using droplet-based resin supply module provides multimaterial micro 3D printing with low material consumption. Also reported is that material bleeding, which degrades the printing resolution during multimaterial printing, can be minimized by using a cleaning droplet system. We present 3D printing of highly complex multimaterial 3D microstructures using three different photocurable polymers, demonstrating a material efficiency of 11.4%, which is 500 times higher than that of a previously reported PμSL process using dynamic fluidic control.

In order to cope with the global challenge of climate changes, which transcends national boundaries, it has become a global consensus to vigorously promote carbon emissions reduction. This will bring extensive and profound changes to the manufacturing industry. As an advanced manufacturing technology, additive-subtractive integrated hybrid manufacturing (ASIHM) is not only suitable for manufacturing complex parts but also offers significant advantages in terms of material utilization and production efficiency. In this paper, carbon emission modeling and a case study are conducted to assess the carbon emission characteristics of ASIHM quantitatively. Firstly, the research system boundary was delineated based on the life cycle theory. Secondly, the precise model of carbon emissions was established according to the equipment operating status and process characteristics. Then, the carbon emissions of the ASIHM process were analyzed, and comparative research on the carbon emissions in material and energy consumption was also carried out with the conventional subtractive manufacturing (CSM) process. The results have revealed that ASIHM has the highest proportion of carbon emissions during the additive forming stage, reaching over 54%. Compared to conventional milling, ASIHM has an 80% lower carbon footprint.

Fuel cell hybrid electric vehicles (FCHEVs) are being developed as eco-friendly vehicles, but one of the technical challenges is the short lifespan of the fuel cell system. Frequent starting and load changes of the fuel cell system are key factors that degrade the lifespan. To address this issue, we propose an infinity-horizon cost-based power management controller that reduces fuel cell degradation while minimizing battery degradation and hydrogen consumption. The proposed controller considers the expected cost incurred over an infinite horizon, which reduces unnecessary start/stop cycles of the fuel cell and optimizes the battery and fuel cell operation. We present three different controllers with infinity-horizon expected costs, which were and validated through multiple simulations. Our results demonstrate that the proposed controller is effective in minimizing fuel cell degradation and improving overall system efficiency in FCHEVs. The key contribution of this paper is that our proposed controller can minimize the fuel cell degradation and hydrogen consumption in both short-and long-term horizon by leveraging the concept of the infinity-horizon expected cost to short time horizon controllers.

In the field of metal 3D printing, in which metal powder is repeatedly layered by melting, decrease in strength and durability due to defects (pores, etc.) occurring in the layered metal is a major obstacle to commercialization. In this study, friction stir processing (FSP) was applied as a means to remove defects such as pores generated inside cast aluminum alloys fabricated using direct energy deposition, and to improve the microstructure. The AlSiMg alloy used in this study is commonly utilized for general casting parts in industry and is widely employed in the aviation and automobile industries where weight reduction is desired. FSP was performed using two types of tools with different shoulder shapes and their effect on the defects, microstructure, and hardness of the FSPed area was evaluated. Further, the effect of FSP on defect removal was studied. Prior to FSP treatment, many spherical pores (defects) with a diameter of 500 μm or less were formed in the deposited material. A larger stir zone area was formed on the cross section of the FSPed specimen treated with Tool 2 (open grooves on the shoulder) compared to that treated with Tool 1 (closed grooves on the shoulder). In addition, the maximum depth of the thermo-mechanically affected zone was greater in the former, but the decrease rate with increasing feed rate was smaller. For each tool, the change in the microstructure of the material for each feed rate was observed, and the stirred part, the part subjected to heat and mechanical change, and the part only subjected to heat were classified by examining the alloyed Si content through FE-EPMA. In addition, the removal or deformation of defects under the influence of FSP was observed microscopically, and the results were shown. Changes in hardness at each location were also measured and displayed. The results shows that FSP of DEDed cast aluminum is effective for removing defects, such as pores, and improving the microstructure. And Tool 2 with open grooves on the shoulder exhibits a relatively better stirring performance and is more stable.

This study aims to compare the microstructural and biotribological behavior of additively manufactured and commercially available stainless steel 316L (SS 316L) implants under simulated body fluid. The surface integrity, microstructures, and micro-hardness characterizations were performed. FESEM micrographs and 3D surface profiles dictate that the specimen is manufactured using a bi-directional 67º rot-scanning strategy. Further, the microstructure, XRD, and micro-hardness outcomes dictate that the selective laser melted (SLMed) sample has an anisotropic fine-grained (18.49 µm) gamma austenite phase with an improved hardness of 280.35HV_0.05, which is 146% higher compared to casted counterpart. In-vitro state biotribological results indicate that the SLMed part has a minimum coefficient of friction (COF: 0.287) value under simulated body fluid, which is 58% less than the casted part (COF: 0.494), and an improved volumetric wear loss at different loading conditions was also observed. The obtained outcomes dictate that selective laser melting is a better processing route to manufacture SS 316L permanent implants with enhanced microstructural, mechanical, and biotribological behavior.

Solid oxide fuel cells (SOFCs) have attracted significant attention as a highly efficient type of fuel cell. Recent research proposes the use of co-doped scandium-stabilized zirconia with Gd and Ce (denoted as 10Sc0.5Gd0.5CeSZ) and Yb and Bi co-doped gadolinium-doped ceria (denoted as GYBC) as promising materials for the electrolyte and buffer layers, respectively. 10Sc0.5Gd0.5CeSZ exhibits excellent structural stability and ionic conductivity, which can be attributed to the doping of Ce for enhanced stability and Gd for improved ionic conductivity. On the other hand, GYBC demonstrates good sinterability and ionic conductivity due to the ability of Bi to lower the sintering temperature and the high ionic conductivity of Yb. To evaluate the feasibility of 10Sc0.5Gd0.5CeSZ and GYBC at the single cell level. X-ray diffraction (XRD) peaks and Rietveld refinements show good structural stability with slight increase in the lattice parameter by doping. The particle morphologies, size distributions, and BET surface areas are evaluated for the basic material characterizations. Then, lanthanum strontium cobalt ferrite (LSCF)–gadolinium-doped ceria (GDC) was selected as cathode material with 10Sc0.5Gd0.5CeSZ and GYBC. Finally, a single cell composed of Ni-Yttria stabilized zirconia (YSZ)/10Sc0.5Gd0.5CeSZ/GYBC/LSCF-GDC (6.5:3.5) is fabricated by sequential 3-layer co-tape casting technique, and it shows good open circuit voltage of > 1.0 V, high electrochemical performance of 0.73 W/cm² and low ohmic resistance of 0.17 Ωcm² at 750 °C. Then, the electrochemical characteristics and long-term durability of this single cell are evaluated over 500 h without degradation issues. Based on these results, it is concluded that 10Sc0.5Gd0.5CeSZ and GYBC are promising candidate materials for SOFCs.

Optical metasurfaces consisting of two-dimensional nanostructures have rapidly developed over the past two decades thanks to their potential for use as optical components, such as metalenses or metaholograms, with ultra-compact form factors. Despite these rapid developments, major challenges for the commercialization of metasurfaces still remain: namely their mass production and use in real-life devices. A lot of effort has been made to overcome the limitations of electron beam lithography which is commonly used to fabricate metasurfaces. However, a breakthrough in mass production is still required to bring the cost of metasurfaces down into the price range of conventional optics. This review covers deep-ultraviolet lithography, nanoimprint lithography, and self-assembly-based fabrication processes that have the potential for the mass production of both cost-effective and environmentally friendly metasurfaces. We then discuss metalenses and future displays/sensors that are expected to take advantage of these mass-produced metasurfaces. The potential applications of mass-produced optical metasurfaces will open a new realm for their practical applications and commercialization.

There is an urgent demand to reduce the plastic mass as it has become a serious environmental concern. Plastic bottles made of PET (polyethylene terephthalate) have been widely used for water, milk, and other beverages packaging. PET blow molding process has sought researchers’ attention for the fabrication of light weight PET bottles with reduced cost. In this study, lightweight PET bottles were fabricated by reducing the weight of PET, usually used for manufacturing PET bottle in industry. Here, initially computer simulation was performed for designing the preform with reduced weight and the stretch blow molding process was used to fabricate carbonated soft drink PET bottles. The computer simulation was performed under the same conditions as the experiment using non-isothermal models to analyze the blowing phenomena, velocity, temperature, thickness distributions, and stretch ratio through stretching path of PET bottles. Experimental and simulation results were compared with existing PET bottle to confirm that the stretch blow molding simulation was significant for designing and fabricating of weight reduced PET bottle through the stretch blow molding process.

In this study, the change in the mechanical properties of glass fiber-reinforced thermoplastic (GFRTP) according to the recycled material content was evaluated. The recycled material was polypropylene, with short glass fiber reinforcement, dry blended with virgin polypropylene and additional glass fiber, and injected into its final shape. It is known that during the recycling process, the length of the glass fibers decreases, which leads to the deterioration of the mechanical properties. Therefore, to compensate for the fiber length shortening, long glass fibers were introduced, and changes of the length distribution of the glass fiber and mechanical properties were investigated. Variation of key short- and long-term mechanical properties by introducing long fibers was measured and investigated by performing tensile test, Izod impact test, essential work of fracture (EWF) test, and fatigue test. Most of the mechanical properties showed a linear relationship with the long glass fiber content, but the percent elongation at break and the resistance to the crack initiation were significantly improved immediately after the long fiber was introduced. In addition, the distribution of fiber length was measured and analyzed, and it was found that significant fiber breakage occurred during the injection process and the recycling process including the chopping of recycled material. Finally, through the observation of fracture surfaces, it was validated that the ductile-to-brittle fracture mechanism transition was mainly caused by the poor compatibility between virgin and recycled materials.