• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.264-265
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• 2006

The directions of further developments in the modeling of sintering are pointed out, including multi-scale modeling of sintering, on-line sintering damage criteria, particle agglomeration, sintering with phase transformations. A true multi-scale approach is applied for the development of a new meso-macro methodology for modeling of sintering. The developed macroscopic level computational framework envelopes the mesoscopic simulators. No closed forms of constitutive relationships are assumed for the parameters of the material. The model framework is able to predict the final dimensions of the sintered specimen on a global scale and identify the granular structure in any localized area for prediction of the material properties.

• Journal of Powder Materials
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• v.19 no.1
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• pp.19-24
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• 2012

The consolidation results of fine tungsten powders, W-Cu composite and W/Cu FGM by using a novel method combining resistance sintering with ultra high pressure have been reviewed. The densification effects of the consolidation parameters, including pressure, input power and sintering time, have been investigated. The sintering mechanism of this method was quite different from other sintering methods. Particle rearrangement, sliding, distortion and crushing due to the ultra high pressure are the dominant mehanisms at the initial stage, then the dominant sintering mechanisms are transient arc-fused processes controlled by the input power.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.280-281
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• 2006

Powder grades pre-alloyed with 1.5-3 wt% chromium can be successfully sintered at the conventional temperature $1120^{\circ}C$ although well-monitored sintering atmospheres are required to avoid oxidation. Mechanical properties of the Cr-alloyed PM grades are enhanced by a higher sintering temperature in the range $1120-1250^{\circ}C$, due to positive effects from pore rounding, increased density and more effective oxide reduction. Astaloy CrM (Fe-3 wt% Cr-0.5 wt% Mo) with 0.6 wt% graphite added obtains an ultimate tensile strength of 1470 MPa and an impact strength of 31 J at density $7.1\;g/cm^3$, after sintering at $1250^{\circ}C$ followed by cooling at $2.5^{\circ}C/s$ and tempering.

• Journal of Powder Materials
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• v.19 no.2
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• pp.127-133
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• 2012

The sintering behaviors and process parameters of some compounds (carbides, oxides, sulfides, borides) were investigated experimentally. These compounds were successfully consolidated and showed high densities. Some unique phenomena such as retardation of grain growth, suppression of thermal decomposition and maintenance of initial non-equilibrium phases, were observed by the proper control of process in spark sintering.

• Journal of Powder Materials
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• v.5 no.4
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• pp.299-302
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• 1998

Dimensional accuracy is one of the most important issues in the production of sintered parts. The iron-copper-carbon system is commonly used alloys in sintered structural parts production. The dimensional control of these alloys, however, is not easy because of their complex sintering behavior. This study is an effort to clarify the influence of common factors on dimensional change of Fe-Cu-C sintered structural parts. We determined the effect of such various parameters as chemical composition, particle diameter, compact density, sintering temperature and sintering time on dimensional changes. Consequently, we obtained a useful formula to predict the final dimension in function of these parameters. The effect of typical impurities in copper powder on the dimensional change of sintered parts has also been described.

• Korean Journal of Computational Design and Engineering
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• v.13 no.6
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• pp.421-428
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• 2008

This article investigates the fabrication of polycaprolactone (PCL) composites filled with different volume fractions (10-30%) of tricalcium phosphate (TCP) by selective laser sintering (SLS) for tissue engineering scaffolds. Optimal processing parameters for each composition were developed by design of experiments (DOE). Specimens for compressive testing for each composition were fabricated and tested. The results showed that the compressive modulus increases as a function of TCP volume fraction. The experimentally measured compressive moduli were compared with moduli predicted by Halpin's theoretical model and were found to be in excellent agreement. This result proved that experimentally determined processing parameters for each composition were well optimized.

• Transactions of Materials Processing
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• v.18 no.3
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• pp.262-267
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• 2009

Selective laser sintering is a kind of rapid prototyping process whereby a three-dimensional part is built layer wise by laser scanning the powder. This process is highly influenced by powder and laser parameters such as laser power, scan rate, fill spacing and layer thickness. Therefore a study on fabricating Fe-Ni-Cr powder by selective laser sintering has been performed. In this study, fabrication was performed by experimental facilities consisting of a 200W fiber laser which can be focused to 0.08mm and atmospheric chamber which can control atmospheric pressure with argon. With power increase or energy density decrease, line width was decreased and line surface quality was improved with energy density increase. Surface quality of quadrangle structure was improved with fill spacing optimization.

• Journal of Powder Materials
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• v.27 no.4
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• pp.293-299
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• 2020

W₂C is synthesized through a reaction-sintering process from an ultrafine-W and WC powder mixture using spark plasma sintering (SPS). The effect of various parameters, such as W:WC molar ratio, sintering temperature, and sintering time, on the synthesis behavior of W₂C is investigated through X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis of the microstructure, and final sintered density. Further, the etching properties of a W₂C specimen are analyzed. A W₂C sintered specimen with a particle size of 2.0 ㎛ and a relative density over 98% could be obtained from a W-WC powder mixture with 55 mol%, after SPS at 1700℃ for 20 min under a pressure of 50 MPa. The sample etching rate is similar to that of SiC. Based on X-ray photoelectron spectroscopy (XPS) analysis, it is confirmed that fluorocarbon-based layers such as C-F and C-F2 with lower etch rates are also formed.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.183-190
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• 2006

Digital 3D Real Object Duplication System (RODS) consists of 3D Scanner and Solid Freeform Fabrication System (SFFS). It is a device to make three-dimensional objects directly from the drawing or the scanning data. In this research, we developed an office type SFFS based on Three Dimensional Printing Process and an industrial SFFS using Dual Laser. An office type SFFS applied sliding mode control with sliding perturbation observer (SMCSPO) algorithm for control of this system. And we measured process variables about droplet diameter measurement and powder bed formation etc. through experiments. In case of industrial type SFFS, in order to develop more elaborate and speedy system for large objects than existing SLS process, this study applies a new Selective Dual-Laser Sintering (SDLS) process and 3-axis Dynamic Focusing Scanner for scanning large area instead of the existing f lens. In this process, the temperature has a great influence on sintering of the polymer. Also the laser parameters are considered like that laser beam power, scan speed, and scan spacing. Now, this study is in progress to evaluate the effect of experimental parameters on the sintering process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.408-411
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• 2004

The electrical stability against surge stress of ZPCCY-based varistors were investigated at different sintering times. Sintering time decreased the varistor voltage and nonlinear exponent from 279.6 to 179.1 and from 52.5 to 24.9, respectively. On the contrary, the leakage current and dielectric dissipation factor increased from 1.2 to 9.8 ${\mu}A$ and from 0.0461 to 0.0651 with increase of sintering time. For all varistors, the variation rates of V-I characteristic parameters against surge stress were affected in order of varistor voltage$\rightarrow$nonlnear exponent$\rightarrow$leakage current. On the whole, the electrical stability against surge stress increased with increasing sintering time. Conclusively, it is assumed that the varistor sintered for 2 h exhibited comparatively good characteristics, in view of overall characteristics.