• Composites Research
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• v.28 no.2
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• pp.46-51
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• 2015

In this study, structural design and analysis of the automobile bonnet is performed. The flax/vinly ester composite material is applied for structural design. The Vacuum Assisted Resin Transfer Molding-Light (VARTML) manufacturing method is adopted for manufacturing the flax fiber composite bonnet. The VARTML is a manufacturing process that the resin is injected into the fly layered-up fibers enclosed by a rigid mold tool under vacuum. A series of flax/vinyl ester composite panels are manufactured, and several kinds of specimens cut out from the panels are tested to obtain mechanical performance data. Based on this, structural design of the automobile bonnet is performed.

• Design & Manufacturing
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• v.12 no.3
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• pp.19-24
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• 2018

Fused deposition Modeling (FDM) is one of the most widely used for the prototype of parts at ease. The FDM 3D printing method is a lamination manufacturing method that the resin is melted at a high temperature and piled up one by one. Another term is also referred to as FFF (Fused Filament Fabrication). 3D printing technology is mainly used only in the area of prototype production, not in production of commercial products. Therefore, if FDM 3D printer is applied to the product process of commercial products when considered, the strength and dimensional accuracy of the manufactured product is expected to be important. In this study, the mechanical properties of parts made by 3D printing with FDM method were investigated. The aim of this work is to examine how the mechanical properties of the FDM parts, by changing of processing FDM printing direction and the height of stacking layer is affected. The effect of the lamination direction and the height of the stacking layer, which are set as variables in the lamination process, by using the tensile specimen and impact specimen after the FDM manufacturing process were investigated and analyzed. The PLA (Poly Lactic Acid) was used as the filament materials for the 3D printing.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.7 s.184
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• pp.101-107
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• 2006

Cold gas dynamic spray or cold spray is a novel manufacturing method for coatings. Cold spray is a high rate and direct material deposition process that utilizes the kinetic energy of particles sprayed at high velocity (300-1,200m/s). In this research, a technique to repair the damaged mold by cold spray deposition and mechanical machining was proposed. An aluminum 6061 mold with three-dimensional surface was fabricated, intentionally damaged and material-added by cold spray, and its original geometry was re-obtained successfully by Computer Numerical Control (CNC) machining. To investigate deformation of material caused by cold spray, deposition was conducted on thin aluminum plates ($100mm{\times}100mm{\times}3mm$). The average deformation of the plates was $205{\sim}290{\mu}m$ by Coordinate Measurement Machine (CMM). In addition, the cross section of deposited layer was analyzed by scanning electron microscopy (SEM). To compare variation of hardness, Vickers hardness was measured by micro-hardness tester.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.323-327
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• 1993

Mold-making industry demands currently to reduce the tooling costs and time in mold making, and to improve the productivity and quality in injection molding process. These problems can be easily removed by laminated injection mold which is made with metal sheets prepared by laser cutting and bonded by brazing. Comparing withthe conventional mold making technology which mainly depends on the machining, this new technologyenables an arbitary design of cooling circuit without anyrestrictions of geometry. So it brings about high production rates of the injection molding processes. This paper estimate the conventional and laminated injection mold making process with a simple molding, and also the cooling efficiencyof thoes two kinds of mold with the filling and cooling analysis. The results show that the laminated injectionmold has much shorter tooling time, uniform mold temperature, and shorter cooling time in injection molding process.

• Composites Research
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• v.12 no.1
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• pp.37-46
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• 1999

In this study, the vibration analysis and modal tests of cylindrical composite shells which are manufactured with various stacking sequences in present laboratory were conducted under the free-free and clamped-clamped boundary conditions. Natural frequencies and mode shapes of these specimens were experimentally obtained and their results are compared with theoretical and FEM results. Both results are in good agreement, which confirm the usefulness of proposed manufacturing method for cylindrical composite shells.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.191-198
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• 2006

Dieless CNC forming is an innovative technology which can form various materials with complex shape by numerically controlled incremental forming process. In this paper, a method of NC tool path generation based on an STL file for dieless CNC forming is proposed. Tool trajectory adopts the principle of layered manufacturing in rapid prototyping technology, but it is necessary to consider STL offset because of the ball shaped tool with a radius. Vertex offset method which enables to compute offset STL directly is engaged for STL offset. The offseted STL is sliced by cutting planes to generate contouring tool path. Algorithm is implemented on a computer and experimented on a dieless CNC forming machine to show its validity.

• Design & Manufacturing
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• v.16 no.3
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• pp.58-65
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• 2022

Micro-fluidic chip has been fabricated by lithography process on silicon or glass wafer, casting using PDMS, injection molding of thermoplastics or 3D printing, etc. Among these processes, 3D printing can fabricate micro-fluidic chip directly from the design without master or template for fluidic channel fabricated previously. Due to this direct printing, 3D printing provides very fast and economical method for prototyping micro-fluidic chip comparing to conventional fabrication process such as lithography, PDMS casting or injection molding. Although 3D printing is now used more extensively due to this fast and cheap process done automatically by single printing machine, there are some issues on accuracy or surface characteristics, etc. The accuracy of the shape and size of the micro-channel is limited by the resolution of the printing and printing direction or layering direction in case of SLM type of 3D printing using UV curable resin. In this study, the printing direction and thickness of each printing layer are investigated to see the effect on the size, shape and surface of the micro-channel. A set of micro-channels with different size was designed and arrayed orthogonal. Micro-fluidic chips are 3D printed in different directions to the micro-channel, orthogonal, parallel, or skewed. The shape of the cross-section of the micro-channel and the surface of the micro-channel are photographed using optical microscopy. From a series of experiments, an optimal printing direction and process conditions are investigated for 3D printing of micro-fluidic chip.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.461-467
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• 2021

Among the defect factors that can occur when a wafer-level lens is molded using a thermosetting material, the mold sticking problem of a molded lens during the release process can damage the molded substrate and deform the substrate at the wafer level. An experiment was conducted to examine the factors affecting the demolding force in the lens forming process. The demolding force was examined according to the coating material of the molds. The mold was surface-treated with ITO and Ti, followed by plasma treatment in an O2 atmosphere. A DLC coating was then performed, and the curing and releasability were examined. A coating method for the pull-off experiment was selected based on the results. To measure the demolding force according to the curing process conditions, a method of curing at a constant pressure and a method of curing at a constant position were applied. As a result, the TiO2 surface treatment reduced the release force. When cured by controlling the location, curing shrinkage can reduce the adhesion energy of the interface during curing, resulting in better demolding.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.10-14
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• 2014

Laser aided Direct Metal Tooling(DMT) process is a kind of Additive Manufacturing processes (or 3D-Printing processes), which is developed for using various commercial steel powders such as P20, P21, SUS420, H13, D2 and other non-ferrous metal powders, aluminum alloys, titanium alloys, copper alloys and so on. The DMT process is a versatile process which can be applied to various fields like the mold industry, the medical industry, and the defense industry. Among of them, the application of DMT process to the mold industry is one of the most attractive and practical applications since the conformal cooling channel core of injection molds can be fabricated at the slightly expensive cost by using the hybrid fabrication method of DMT technology compared to the part fabricated with the machining technology. The main objectives of this study are to provide various characteristics of the parts made by DMT process compared to the same parts machined from bulk materials and prove the performance of the injection mold equipped with the conformal cooling channel core which is fabricated by the hybrid method of DMT process.

• Journal of Powder Materials
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• v.24 no.3
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.