• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1338-1345
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• 2009

Although rock excavation is necessary for the effective utilization of urban space, most conventional rock excavation methods, including the blasting method, cause high noise and vibration. Meanwhile, if a high pressure waterjet system is applied to excavate underground spaces in urban areas, the public grievance can be reduced by low noise and vibration. In this study, an abrasive waterjet system is designed and developed to study the influence of various performance parameters such as jet pressure, nozzle traverse speed, stand-off distance, or abrasive feed rate on waterjet excavation performance in laboratory. Using the developed waterjet system, rock drilling characteristics are identified by measuring drilling depths as a function of the jet exposure time. The drilling depth linearly increases with increasing the jet exposure time(under 60sec). Rock cutting characteristics are also obtained with various jet pressures(1600~3200kg/$cm^2$) and nozzle traverse speeds(1.9~14.1mm/s): The cutting depth is nonlinearly related to the jet pressure and traverse speed. Indeed, the cutting depth increases with an increase in the jet pressure and a decrease in the nozzle traverse speed. This trend can be explained by energy transferring/loss mechanism.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.271-280
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on optical microstructure, hardness and wear characteristics of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite appear in outermost surface layer with fine martensite in inside hardened zone. Hardness measurements have revealed that the range of maximun hardness value is $Hv=650{\pm}15$ and as the power density increases and the traverse speed decreses, the depth of hardened zone increases due to as increase in input power density. Wear test has exhibited that wear rasistance of laser surface hardened specimen is superier compared to that of untreated specimen under the condition of same load at a given sliding distance, showing that absorption results of an wxidized substance due to a heavy abrasion appear in untreated specimen. The amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load decreses with increasing traverse speed at a given power density and with increasing power density at a given traverse speed.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.289-299
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on the microstructure, hardness and residual stress of AISI 4140 treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite in outermost surface layer and fine lath martensite in inner surface hardened layer are formed under the condition of a given power density and traverse speed. Hardness measurements have revealed that as the power density increases at a given 2.0m/min of the traverse speed, the maximum hardness values of outermost surface hardened layer is increased from Hv=635 to Hv=670. X-ray analysis for residual stress has exhibited that low compressive residual stress values are obtained in center point of the cress section of surface hardened layer with in mid point between the edge and the center point, about 1.5mm from the center point, due simply to a difference in self-quenching rate. It has been shown that the higher the power density at a given traverse speed and the olwer the traverse speed at a given power density, the more the compressive residual stress values are increased due to an increase in the input heat of laser beam.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.104-111
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• 2009

This paper shows the behaviors of macro- and micro-structures and mechanical properties for specimen's welding region welded by FSW. according to welding conditions with 5mm thickness aluminum 5083O alloy plate. It apparently results in defect-free weld zone in case traverse speed was changed to 32 mm/min under conditions of anti-clockwise direction and tool rotation speed such as 800 and 1250 rpm with tool's pin diameter of 5 ${\Phi}mm$ and shoulder diameter of 20 ${\Phi}mm$, pin length of 4.5 mm and tilting angle of $2^{\circ}$. The ultimate stress of ${\sigma}_T=331$ MPa and the yield point of 147 MPa are obtained at the condition of the travel speed of 32 mm/min with the tool rotation speed of 1250 rpm. There is neither voids nor cracks on bended surface of $180^{\circ}$ after bending test. The improvement of toughness after impact test was found. The lower rotating and traverse speed became, the higher were yield point, maximum stress and elongation(%) with the stresses and the elongation(%) versus the traverse speed diagram. Vickers hardness for cross section of welding zone were also presented. The typical macro-structures such as dynamically recrystallized zone, thermo-mechanically affected zone and heat affected zone and the micro-structures of the transverse cross-section were also showed. However, the author found out that the region of 6mm far away from shoulder circumference was affected by friction heat comprehensively, that is, hardness softened and that part of micro-structures were re-solid-solution or recrystallized, the author also knew that there is no mechanically deformation on heat affected zone but there are the flow of plastic deformation of $45^{\circ}$ direction on thermo-mechanically affected zone and the segregation of Al-Mg on nugget. The solid solution wt(%) of parent material as compared against of friction stir welded zone was comprehensively changed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.3
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• pp.1-7
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• 2004

Abrasive water-jet(AWJ) machining can cut various materials such as metal, glass and plastics. However, the AWJ machining has some troubles including kerf, rounding and side taper. In this study, we experimently investigated the correlation between the traverse speed of the abrasive water-jet and the dimensional error of the workpiece according to the thickness and the types of the material. The specimen was the stainless steel and the mild steel and the predetermined contour cutting was conducted. A comer radius error, an uncut width and a kerf were measured and evaluated.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.3
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• pp.169-181
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• 1995

This study has been performed to investigate some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and fatigue resistance of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that the dissolution of graphite flakes and the coarsening of lath martensite tend to increase with a small amount of retained austenite as the power density increases under the condition of a given traverse speed. Hardness measurements have revealed that as the power density increases, hardness values of outermost surface layer increases from Hv=620 to Hv=647 in case of traverse speed of 2.0m/min at gray cast iron. Fatigue test has exhibited that the fatigue strength of laser surface hardened specimen is superier compared to that of untreated specimen, showing that values for the fatigue strength at $N_f=10^7$ of gray cast iron laser-surface-hardened at a low power density of $4076w/cm^2$ and a high power density of $8153w/cm^2$ under the condition of a given traverse speed of 2.0m/min are $15kg_f/mm^2$ and $20kg_f/mm^2$, respectively, whereas the fatigue strength of untreated specimen is $11kg_f/mm^2$. Under high stress-low cycle condition a noraml brittleness fracture appears, whereas a ductile fracture with beach mark is observed in the specimen tested under low stress-high cycle condition.

• Tunnel and Underground Space
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• v.4 no.2
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• pp.92-101
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• 1994

Water jet has been employed in extraacton of minerals for many years but the applications of low pressure jent s ar emodfined to some fields. With increasing strength of equipment it is possible to consider the use of high speed water jets for cutting hard rock. The high speed water jet technology is applied to various engineering fiels such as precessing rocks, quarrying rocks, mechanical fracturing as wel as rock excavation under the sea. For slot cutting in rocks with high speed water jets it is necessary to establish the empirical formula for estiamation of the cutting depth. The cutting depth is influenced by cutting parameters such as driving pressure, traverse speed, standoff distance, and shape and diameter of nozzel. Tests were carried out with a variety of cutting parameters on three types of granite. Nozzle pressures ranged from 1,200 to 2,800 bar, traverse speeds from 0.45 to 10.38 cm/min, standoff distances from 4.5 to 13.5 mm, and three types of nozzle diameter were used.

• Korean Journal of Computational Design and Engineering
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• v.2 no.3
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• pp.186-194
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• 1997

This paper describes new methods to minimize the cutting time in zigzag milling operation of two dimensional polygonal surfaces. Previous works have been focused on mainly experimental approaches by considering some machining parameters such as, spindle speed, depth of cut, cutter traverse rate, cutter diameter, number of teeth, tool wear, life of tool, and so on. However, in this study, we considered two geometrical factors one by one in order to see the effect separately, which are the length of cut and the number of cutter traverse. In an N-sided concave or convex polygon, an algorithm has been developed which minimize the total length of cut. Also, a heuristic approach was used to minimize the number of cutter traverse.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.24-32
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• 2007

Laser surface hardening is beneficially used for surface treatment of structural steel. Due to very rapid heating and cooling rates, structural low-alloy steel(SCM4) can be hardened as self quenching. The aim of this research project is to improve the influence of the process laser parameters: laser power, spot size, surface roughness, and traverse speed. The laser beam is allowed to scan on the surface of the workpiece at the constant power(1095W), varying the traverse speed at 0.3m/min, 0.5m/min and 0.8m/min. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with uniform hardness. From the results of the experiment, it has been shown that the stable hardness is about 600$\sim$700Hv, when the laser power, focal position and the traverse speed are P=1095W, z=0mm and v=0.3m/min.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.585-590
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• 2002

Abrasive water-jet(AWJ) machining is a new cutting technology. The AWJ can cut various materials touch as metal, glass and stone. However, the AWJ machining makes troubles including kerf, rounding and side taper. In this study, we investigated the correlation between parameters of abrasive water-jet machining arid cutting characteristics. The machining parameter were the material thickness and the traverse speed. The experiment was conducted to cut the stainless steel(STS41) and the mild steel(SS41) specimens. The results of the experiment weirs presented as the relation between cutting conditions and trouble of a dimension error, a conner error, an uncut width and a kerf.