Ho-Chan Kim

Reduction of post-processing for stereolithography systems by fabrication-direction optimization

The surface of stereolithography parts become rough due to the stair-stepping effect and burrs from the support structure. Therefore, most parts need some finishing work for further applications. Because post-processing operations are performed by skilled workers and require additional time and cost, the reduction of post-processing time and cost is a high priority. Basic approaches to minimizing post-processing are investigated. Surface roughness is analyzed through theoretical models and experiments developing an interpolation method to predict the behavior of the roughness under various equipment conditions and fabrication styles are conducted. Part orientation is optimized by a post-processing objective function. To accelerate the optimization, a model mapping method is developed and verified. An expert system is implemented by the suggested algorithms and examined by several models in real a workshop.

Development of a Fused Deposition Modeling System for Low Melting Temperature Metal Alloys

This research focused on extending the applications of fused deposition modeling (FDM) by extrusion and deposition of low melting temperature metal alloys to create three-dimensional metal structures and single-layer contacts which may prove useful for electronic interconnects. Six commercially available low melting temperature solder alloys (Bi36Pb32Sn31Ag1, Bi58Sn42, Sn63Pb37, Sn50Pb50, Sn60Bi40, Sn96.5Ag3.5) were tested for the creation of a fused deposition modeling for metals (FDMm) system with special attention given to Sn–Bi solders. An existing FDM 3000 was used and two alloys were successfully extruded through the systems extrusion head. Deposition was achieved through specific modifications to system toolpath commands and a comparison of solders with eutectic and non-eutectic compositions is discussed. The modifications demonstrate the ability to extrude simple single-layer solder lines with varying thicknesses, including sharp 90 deg angles and smooth curved lines and showing the possibility of using this system for printed circuit board applications in which various connections need to be processed. Deposition parameters altered for extrusion and the deposition results of low melting temperature metal alloys are introduced.

STL file generation from measured point data by segmentation and Delaunay triangulation

Abstract For the generation of the models in RP, a laser scanner is currently used a lot due to the fast measuring speed and high precision. Direct generation of STL file from the scanned data has a great advantage in that it can reduce the time and error in modeling process. The reduction of the number of point data is important while generating STL file directly from the measured point data with maintaining their precision. A new approach is addressed to reduce the amount of data by segmentation and Delaunay triangulation. Basic experiments are performed to apply the algorithm developed to real models. Different results are incurred by user-defined criteria, and some dominant output characteristics according to the user input are reviewed and analyzed. The program developed in the research generates an STL files efficiently with automated data reduction. Several criteria are specified in order to maintain the characteristics of the feature and satisfy the needs in real workshops.

Direct-Write Stretchable Sensors Using Single-Walled Carbon Nanotube/Polymer Matrix

There have been increasing demands and interests in stretchable sensors with the development of flexible or stretchable conductive materials. These sensors can be used for detecting large strain, 3D deformation, and a free-form shape. In this work, a stretchable conductive sensor has been developed using single-walled carbon nanotubes (SWCNTs) and monofunctional acrylate monomers (cyclic trimethylolpropane formal acrylate and acrylate ester). The suggested sensors have been fabricated using a screw-driven microdispensing direct-write (DW) technology. To demonstrate the capabilities of the DW system, effects of dispensing parameters such as the feed rate and material flow rate on created line widths were investigated. Finally, a stretchable conductive sensor was fabricated using proper dispensing parameters, and an experiment for stretchability and resistance change was accomplished. The result showed that the sensor had a large strain range up to 90% with a linear resistance change and gauge factor ∼2.7. Based on the results, it is expected that the suggested DW stretchable sensor can be used in many application areas such as wearable electronics, tactile sensors, 3D structural electronics, etc.

Determination of Fabrication Direction to Minimize Post-machining in FDM by Prediction of Non-linear Roughness Characteristics

Rapid Prototyping (RP) is a technology that generates physical objects directly from CAD data. As a prototype can be rapidly built by using this technology, the product cycle is remarkably reduced in manufacturing. However, the surface quality of RP processed parts is not sufficient for general mechanical parts because of the use of the layered manufacturing process. Therefore, additional post-machining processes are required such as grinding and coating. But, these processes are time-consuming and detrimental to the original part’s geometry. In this paper, a methodology for determining fabrication direction which aims to minimize the post-machining process in FDM (Fused Deposition Modeling) is proposed. In order to enhance the accuracy and the computational speed in determining the fabrication direction, a surface roughness model that is considered even non-linear surface roughness characteristics is presented. And, a required post-machining volume is newly introduced as a objective function. Also, a genetic algorithm is applied to obtain a reliable solution. Finally, it is verified that the proposed approach can be very efficient with the developed system.

Scheduling and process planning for multiple material stereolithography

Purpose – To operate a multiple material stereolithography (MMSL) system, a material build schedule is required. The purpose of this paper is to describe a scheduling and process‐planning software system developed for MMSL and designed to minimize the number of material changeovers by using low‐viscosity resins that do not require sweeping.Design/methodology/approach – This paper employs the concept of using low‐viscosity resins that do not require sweeping to minimize the number of material changeovers required in MMSL fabrication. A scheduling and process‐planning software system specific to MMSL is introduced that implements four simple rules. Two rules are used to select the material to be built in the current layer, and two rules are used to determine at which layer a material changeover is required. The schedule for the material to be built depends on the material properties stored in a user‐defined materials library. The developed algorithm produces sliced loop data for each material using the pred...

Simulation of micro-patterns engraved by grinding process with screw shaped wheel

Abstract Grinding is an important means of realizing precision and ultra-precision machining of workpiece surface. The surface patterning of workpiece directly affects its mechanical properties such as friction, wear, contact stiffness, fitting property. Therefore, prediction of the geometry of the workpiece surface is very important to evaluate the workpiece quality to perform mechanical function accurately. In this paper using MATLAB simulation, prediction for the geometry pattern of the workpiece according to the developed shape of the grinding wheel dressed by thread cutting was studied. The model for the geometry of the grinding wheel surface was first developed and subsequently, a new simulation model for surface pattern by grinding process was established. The simulation results could be used to optimize the grinding process and to improve the workpiece surface quality or predict the surface pattern by given grinding parameters.

Feature of nozzle for manufacturing flexbile tactile sensor skin

Recently, robot technologies are applying to the multidisciplinary fields of study due to the development of robot technology. To operate like a human being, many robot technologies need devices that can receive exterior stimulus, temperature, visual data, and the sense of smell, etc. The robots hand needs the sensor devices that can receive exterior stimulus to operate like a human skin. The flexible tactile sensor for the robot has to be manufactured alike to a shape of human skin. This research studied characteristics of synthesis of photopolymer resin which has an electric conductivity and nozzle for the development of the sensor.

Effect of foreign exchange management on firm performance using genetic algorithm and VaR

Management of foreign exchange risk is considered to be as important as trading results in firm performance when international trading and transaction of different kind of currencies are getting popular. Most previous researches on this issue have been based on the foreign exchange market and financial investing and accounting, focusing on theoretical point of view. And it is difficult to apply these research results to each company, since all companies in industry have different financial circumstances. In this paper, the solution for the foreign exchange management is proposed using GA and VaR which is very practical to export-oriented companies. The developed software enables a user to specify the criteria for the foreign exchange trading condition, constraints on dealing amount, GA operator and penalty, and variables in VaR. This approach is useful for managing foreign exchange holdings of a company in a practical way, analyzing past exchange rate trend with dealing results.

Development of Hybrid Fused Deposition Modeling System for Three-Dimensional Circuit Device Fabrication

은 일련의 유체에 직접 압력을 가하여 노즐을 통해 직접 분출되게 하고, 노즐의 위치를 이송시스템을 통하여 직접 제어하여 원하는 형상의 패턴을 성형하는 기술이다. 직접주사 기술은 패턴을 성형하는데 있어서 다른 기술들에 비하여 시스템 구성이 간단하다는 장점이 있다. 따라서, 임의형상 제작기술과 직접주사 기술을 통합한 다중재료를 적용한 임의형상 제작기술을 이용하면 기존의 2 차원 PCB(printed circuit board)와는 전혀 다른 형태의 Key Words: 3-Dimesional Circuit Device(3 차원 회로 장치), Direct Writing(직접주사), Solid Freeform Fabrication(임의형상 제작기술), Fused Deposition Modeling(용융압출 적층 조형) 초록: 임의형상 제작기술을 이용하면 원하는 형상을 빠르게 제작할 수 있다. 하지만 임의형상 제작기술을 직접 제품을 생산하기 위한 제조기술에 적용하기 위해서는 문제점들이 있다. 이에, 하나의 대안으로써 다중재료 임의형상 제작기술이 주목 받고 있다. 특히 다중재료 임의형상 제작기술을 이용하면 기존의 2 차원 PCB 와는 다른, 회로 소자의 배열 및 외부 형상의 제약이 적은 3 차원 회로 장치를 제작 할 수 있다. 본 연구에서는 3 차원 회로 장치 제작을 위하여 FDM 방식과 직접주사 방식을 통합한 장치를 설계하고, 이 장치를 이용하여 3 차원 회로장치를 제작하였다. 즉, LED 와 조도센서를 이용한 3 차원 회로 장치를 제작하여 작동을 확인하였으며, 자동화된 3 차원 회로 장치의 제작을 위한 임의형상 제작 기술과 직접주사 기술이 통합된 시스템 개발에 대한 기초연구를 수행하였다. Abstract: It is possible to fabricate a three-dimensional (3D) shape using the solid freeform fabrication (SFF) technology. However, there are several problems in applying conventional SFF technologies to the direct manufacturing of a product. Hence, multimaterial SFF is gaining attention. Moreover, a 3D circuit device that is different from a conventional two- dimensional PCB can also be fabricated using multimaterial SFF. In this study, a hybrid system using fused deposition modeling and direct writing was designed for 3D circuit device fabrication.