• Title/Summary/Keyword: Powder forming

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Characterization of Direct Laser Metal Forming Technology for the Restoration of Mold Surface (레이저 직접금속성형기술을 이용한 금형재 표면보수 특성 연구)

  • Son, Young-Myung;Jang, Jeong-Hwan;Joo, Byeong-Don;Yim, Hong-Sup;Moon, Young-Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.7
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    • pp.681-686
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    • 2009
  • Direct laser metal forming technology was applied to restore the damaged mold surface. In order to estimate melting characteristics of the $20{\mu}m$ Fe-Cr-Ni powder, single layer experiments were performed at various levels of heat input. The process window of the $20{\mu}m$ Fe-Cr-Ni powder provided feasible process parameters for the smooth regular surface. The cross hatching scanning strategy on the multiple layer experiment was performed to reduce the thickness non-uniformity of edge portions compared with the one direction scanning. To estimate the coherence between the melted powder and the basematal, the tendency of hardness distribution has been observed. The hardness of the melted and the remelted zone was distributed from 400HV to 600HV. It is over 2 times compared of the hardness of the basemetal. Experimental results show that the mold restoring process using direct laser metal forming can be successfully applied in the mold repair industry.

Microstructural Evolution of Thick Tungsten Deposit Manufactured by Atmospheric Plasma Spray Forming Route (Plasma Spray Forming 공정에 의해 제조된 텅스텐 성형체의 미세조직 형성 거동)

  • Lim, Joo-Hyun;Baik, Kyeong-Ho
    • Journal of Powder Materials
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    • v.16 no.6
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    • pp.403-409
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    • 2009
  • Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

Fabrication and Magnetic Process of 13Cr-1.5Nb-Fe Stainless Sensors (13Cr-1.5Nb-Fe 스텐레스 센서재료의 제조 및 연자기특성)

  • 윤성호;김택기;조용수
    • Journal of the Korean Magnetics Society
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    • v.8 no.3
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    • pp.125-130
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    • 1998
  • 13Cr-1.5Nb-Fe alloy powder was fabricated by water atomization method, and ring-shape specimen of this composition was fabricated by oil press, and then sintered in the vacuum furnace. Powder shape, size distribution, composition (C, N, O, S) analysis and saturation magnetization of as-prepared 13Cr-1.5Nb-Fe alloy powder were investigated. Ac permeability and power loss was measured after forming and sintering process. Saturation magnetization and contents of oxygen of the alloy powder is160 emu/g and about 6000 ppm, respectively. 50 % volume fraction indicate particle size of 70$\mu$m. The ac permeability of sintered specimen increases with increasing sintering temperature and forming pressure. The power loss is 107 W/cc at sintering temperature of 1200 $^{\circ}C$, 12 ton/$\textrm{cm}^2$ forming pressure, and 20 KHz. It is the lowest among the prepared specimen.

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Advanced Powder Processing Techniques of Ti Alloy Powders for Medical and Aerospace Applications

  • Miura, Hideshi
    • Journal of Powder Materials
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    • v.20 no.5
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    • pp.323-331
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    • 2013
  • In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 ${\mu}m$ FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

Viscosity Study to Optimize a Slurry of Alumina Mixed with Hollow Microspheres

  • Bukhari, Syed Zaighum Abbas;Ha, Jang-Hoon;Lee, Jongman;Song, In-Hyuck
    • Journal of the Korean Ceramic Society
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    • v.52 no.6
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    • pp.403-409
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    • 2015
  • Porous alumina ceramics are involved in many industrial applications due to the exceptional properties of these products. This study addresses the preparation of porous alumina ceramics using hollow microspheres as a pore-forming agent and slip casting as a green-body-forming technique. A uniform distribution of pores is a basic requirement of a porous material. This study investigates three different slurry systems, i.e., as-prepared alumina slurry, alumina slurry electrostatically dispersed by hydrochloric acid (HCl), and slurry dispersed by the commercial dispersant 'Darvan C-N'. At a low viscosity, the hollow microspheres in the slurry tend to float, which causes a non-uniform pore distribution. To avoid this phenomenon, the viscosity of the slurry was increased to the extent that the movement of hollow microspheres ceased in the slurry. As a result, a uniform pore distribution was achieved.

Fabrication of Porous W by Heat Treatment of Pore Forming Agent of PMMA and WO3 Powder Compacts (기공형성제 PMMA와 WO3 분말 성형체의 열처리를 이용한 W 다공체 제조)

  • Jeon, Ki Cheol;Kim, Young Do;Suk, Myung-Jin;Oh, Sung-Tag
    • Journal of Powder Materials
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    • v.22 no.2
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    • pp.129-133
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    • 2015
  • Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and $WO_3$ powder compacts. The PMMA sizes of 8 and $50{\mu}m$ were used as pore forming agent for fabricating the porous W. The $WO_3$ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at $1200^{\circ}C$ in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about $400^{\circ}C$ and $WO_3$ was reduced to metallic W at $800^{\circ}C$. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.