• The Journal of Advanced Prosthodontics
• /
• v.6 no.4
• /
• pp.266-271
• /
• 2014

PURPOSE. The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS. Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets ($25.0{\times}3.0{\times}0.5mm$) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (${\alpha}=.05$). RESULTS. The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION. In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength.

• Journal of Korea Foundry Society
• /
• v.17 no.6
• /
• pp.538-544
• /
• 1997

• 제어로봇시스템학회:학술대회논문집
• /
• 1986.10a
• /
• pp.145-148
• /
• 1986

To perform the marking on metal with high speed and non-contact using the laser beam of high energy, laser marking system is designed and fabricated applying the galvanometer scanner capable of high speed-precise beam positioning controlled by microprocessor. Laser is a Q-switched Nd:YAG producing multi-mode, wavelength, 1060nm. Optical system is composed of beam expander, scanning mirror and flat field lens. Consequently, the laser marking is satisfactorily achieved regardless of kinds of metal.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.24 no.6
• /
• pp.980-985
• /
• 1987

The thin metal films of Cr, Al, Mn and were made in various evaporation rates with 100\ulcornerthickness under 2x10**-9 bar vacuum level. We analized and discussed the relationships between changes of structure, morphology and sheet resistance, light transmittance for the corresponding evaporation rates. As the evaporation rates were decreased at higher rates, grain sizes of all film were decreased, however both of the sheet resistance and light transmittance were increased. At lower evaporation rate, films of Cr and Cu porduced non-stoi-chiometric oxides but Al an Mn showed up amorphous structures.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1995.06a
• /
• pp.64-73
• /
• 1995

The forging limit curves of sintered porous metals have been calculated, in terms of the two principal strains, by the Lee-Kuhn initial imperfection model. The various yield functions for porous metal have been applied to the initial imperfection model. When the value of initial imperfection ratio equals the value of initial relative density of the sintered porous metals, the calculation values are in good agreement with the measured data. The slopes of the forging limit curves are about 0.5 as in the case of non-porous metals.

• Transactions of Materials Processing
• /
• v.8 no.5
• /
• pp.449-453
• /
• 1999

Sheet metal forming process is a non-linearity problem which is affected by various process variables, such as geometric shape of punch and die, frictional characteristic, etc.. Therefore, the knowledge of the influence of the process variables is needed in the design of sheet metal working processes. In this paper, cylindrical cup drawing tests for blank holding force, punch speed and lubrication between sheet material and tool were carried out to investigate the influence upon sheet formability. Experimental results were discussed about the defects on the deformation behaviors during the forming process.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.7
• /
• pp.2149-2155
• /
• 2012

A metal-free and efficient procedure for the oxidation of alcohols into the corresponding carbonyl compounds has been described using ammonium nitrate in the presence of silica sulfuric acid under mild and heterogeneous conditions. The use of non-toxic and inexpensive materials, simple and clean work-up, short reaction times and good yields of the products are among the advantages of this method.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.5
• /
• pp.656-673
• /
• 2003

Statement of problem : Long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused to metal (PFM) restoration could affect mechanical strength of dental porcelain if the restoration is refired. Purpose : This work was performed to verify the effect of water on the mechanical strength in aged dental porcelain. Material and method : 63 specimens(Vintage Metalbond opaque and opal powder) were distributed to three experimental groups ; non-water immersed control, immersed and pedried, and immersed and non-predired groups. The changes in flexural strength and fracture toughness after specimen refiring related to Fourier Transform Infrared (FT-IR) spectroscopy. Results : 1. The FT-IR reflectances assigned to molecular bonds of $H_2O$ were noted as significantly different between the first-fired group and three refired groups and between two water-immersed groups and control group after refiring(p<0.05). They were also significantly different between predried group and non-predried group after refiring(p<0.05) 2. For opal specimens, FT-IR absorbances for hydrogen bond of $H_2O$ and silanols were significantly higher in non-predried group than in predreid group(p<0.05). 3 Predried opal group showed the highest mean flexural strength(p<0.05). Non-predried group indicated higher mean flexural strength than control group(p<0.05). 4. The mean fracture toughness for predired group was higher than non-predried group(p<0.05). 5. The difference of leucite crystal size is noted between control group and water-immersed, predried group in scanning electron microscopic study(${\times}10000$).

• Journal of Periodontal and Implant Science
• /
• v.52 no.5
• /
• pp.411-421
• /
• 2022

Purpose: In this study, we aimed to evaluate the degree of heat generation when a novel drill design with an irrigation slot was used with metal sleeve-free (MF) and metal sleeve-incorporated (MI) surgical guides in an environment similar to that of the actual oral cavity. Methods: A typodont with a missing mandibular right first molar and 21 bovine rib blocks were used. Three-dimensional-printed MF and MI surgical guides, designed for the placement of internal tapered implant fixtures, were used with slot and non-slot drills. The following groups were compared: group 1, MI surgical guide with slot drill; group 2, MI surgical guide with a non-slot drill; and group 3, MF surgical guide with a slot drill. A constant-temperature water bath at 36℃ was used. The drilling was performed in 6 stages, and the initial, highest, and lowest temperatures of the cortical bone were measured at each stage using a non-contact infrared thermometer. Results: There were no temperature increases above the initial temperature in any drilling procedure. The only significant difference between the non-slot and slot groups was observed with the use of the first drill in the MI group, with a higher temperature in the non-slot group (P=0.012). When the heat generation during the first and the second drilling was compared in the non-slot group, the heat generation during the first drilling was significantly higher (P<0.001), and there was no significant difference in heat generation between the drills in the slot group. Conclusions: Within the limitations of this study, implant-site preparation with the surgical guide showed no critical increase in the temperature of the cortical bone, regardless of whether there was a slot in the drill. In particular, the slotted drill had a cooling effect during the initial drilling.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2007.11a
• /
• pp.179-180
• /
• 2007