• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.240-245
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• 2000

This paper presents the experimental study of drilling for duralumin A2024 with intermittently decelerated feed rate. It is achieved through a programmed periodic increase and decrease in the feed rate using a machining center. The following experimental result were performed with the objective of solving chip to disposal problems. In conventional drilling of aluminum, long continuous chips are produced that wind around the drill causing difficulties in eliminating chips from the cutting zone. In order to acquire the basic data necessary to regulate the chip profile, the relationship between cutting variables and chip shape was investigated. The following conclusions are established from the experimental results. At a suitable feed fluctuation ratio, intermittently decelerated feed drilling proved successful in breaking chips to appropriate lengths while maintaining stable cutting. Thus, it is an effective method for improving chip disposal. The amplitude of the dynamic component of cutting force in intermittent feed frilling is influenced by the feed fluctuation ratio.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.217-228
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• 2024

During deep drilling, confined aquifers can present various challenges such as the inability to remove cuttings, rapid groundwater influx, and mud loss. Particularly in flowing well conditions, it is essential to apply the suitable mud density since the aquifer can generates an overpressurized condition. This paper proposes a method for determining the suitable mud density while drilling (SMD) through confined aquifers using mud window analysis and applies it to a case study. The minimum mud density at each depth, which represents the lower limit of the mud window, is determined by the equivalent mud density pore pressure gradient (or by adding a trip margin) at that depth. The pore pressure gradient of a confined aquifer can be calculated using the piezometric level or well head pressure of the aquifer. As the borehole reaches the confined aquifer, there is a significant increase in pore pressure gradient, which gradually decreases with increasing depth. The SMD to prevent a kick can be determined as the maximum value among the minimum mud densities in the open hole section. After entering the confined aquifer, SMD is maintained as the minimum mud density at the top of the aquifer during the drilling of the open hole section. Additionally, appropriate casing installation can reduce the SMD, minimizing the risk of mud loss or invasion into the highly permeable aquifer.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.177-182
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• 1997

The purpose of this study is to analyze how tools, guide bush type and the change of cutting speed have effects on the diameter of cutting hole, surface roughness of workpiece and roundness during the deep hole machining of SM55C with solid BTA drill by using BTA drilling system through experiment. Conclusion reached is as follows. (1) The diameter was expanded for 25${\mu}{\textrm}{m}$ at the first section and then was reduced 0${\mu}{\textrm}{m}$ and 15${\mu}{\textrm}{m}$ respectively at the 10m and 20m section comparing to the diameter of tool with respect to the variation of cutting length. (2) It was proved that roughness was below 12S for the whole section of cutting length. (3) The roundness has been below 12${\mu}{\textrm}{m}$. Regarding the polygon phenomenon, it has bee proved that not only uneven number of angle but also even number (quadrilateral, elliptical) of angle were made. (4) Variation of diameter, surface roughness of workpiece and roundness turned out to ve the best at 70m/min of cutting speed, 0.15mm/rev of feed.

• The Journal of Engineering Geology
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• v.24 no.4
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• pp.455-461
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• 2014

The Honam-Jeju, Korea-Japan, and Korea-China subsea tunnel construction projects have drawn significant attention since the early 2000s. These subsea tunnels are much deeper than most existing natural shallow sea tunnels linking coastal areas. Thus, the need for developing new technologies for the site selection and construction of deep subsea tunnels has recently emerged, with the launch of a research project titled "Development of Key Subsea Tunnelling Technology" in 2013. A component of this research, an analysis of deep subsea geological structure, is currently underway. A ground investigation, such as a borehole or geophysical investigation, is generally carried out for tunnel design. However, when investigating a potential site for a deep subsea tunnel, borehole drilling requires equipment at the scale of offshore oil drilling. The huge cost of such an undertaking has raised the urgent need for methods to indirectly assess the local geological structure as much as possible to limit the need for repeated borehole investigations. This study introduces an indirect approach for assessing the geological structure of the seafloor through a submarine bathymetry analysis. The ultimate goal here is to develop an automated approach to the analysis of submarine geological structures, which may prove useful in the selection of future deep subsea tunnel sites.

• Economic and Environmental Geology
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• v.49 no.6
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• pp.479-490
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• 2016

Seabed drilling system has recently been used to drill seafloor mineral resources. This case report highlights the procedure and result of sea-trial of seabed drilling system at off-shore of Japan on March, 2016 as well as briefs an international-technical trend of seabed drilling system. In case of having less than 100 m drill depth, seabed drilling system is favorable for seafloor mineral deposits which are mostly distributed within a narrow district and situated between 1000~3000 m water depth, compared with vessel-mounted drilling system. The system is featured by the remotely-operated drill gear, which has top drives, drill strings and mud system on it. The core samples are generally recovered to ship with seabed driller after a dive. In this sea-trail, recovery rate of core samples averagely shows about 55% and the recovered rocks mostly correspond to fresh and/or weak-altered basalt. In case of drilling hydrothermal ore deposit, the recovery rate would be lower than 55% because of the fragile nature of ores. Alternatively it is used to collect cutting chips through riser or bins in order to increase the recovery rates. Recently a reverse circulation method is taken considered to acquire the better cutting-chips. Three-leg type outrigger system and four-leg type leveling system are the competing landing-instruments of seabed drill system. However the landing efficiency using these gears has to be further monitored due to lack of case reports.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.170-175
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• 1998

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.543-553
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• 2013

As the deep deck plate has the shape of open cross section, It can cause structural problems such as bending torsions due to instability of the section. There are a number of fasteners types which are frequently used on light gage steel diaphragms such as bolts, rivets, welds, and screws. In this study, the structural capacity of the self drilling screw connection between the deep deck and the reinforced cap plate was evaluated by experimental variables such as the arrangement method, numbers of screw, pitch of screw, and head plate thickness.

• Korean Journal of Construction Engineering and Management
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• v.6 no.4 s.26
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• pp.152-163
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• 2005

Pile driving work causes a vibration problem in the construction site using pile foundation and often causes civil affairs by construction noise around the construction site. For the vibration and noise problems, the driving after drilling method rather than the direct driving method is being generalized for reducing vibration and noise. However, this method also causes civil affairs when the driving work is operated in adjacent area. This study suggests a criterion for evaluating an optimal allowed distance for pile driving work by the driving after drilling method. Actual surveys of vibration and noise for pile driving work in seven construction sites were used for developing regression analysis equations. The results can be a standard to estimate the allowed distance to avoid vibration and noise problems in pile driving work for deep foundation.

• Tunnel and Underground Space
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• v.25 no.6
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• pp.534-542
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• 2015

Round trip activity occurs discretely due to the abrasion of drill bit in the deep drilling project. Round trip has great impact on the drilling performance because it takes more time to change a drill bit as the depth goes deeper. Therefore, a reliable prediction technology of the round trip should be secured for feasibility analysis and effective management of the drilling project. Lee et al. (2013) developed the TOSA (round trip occurrence simulation algorithm) which can analyze the depth and timing of round trip occurrence at each abrasion state of bit. However, TOSA has weakness that it takes long time for simulation because the number of simulation increase exponentially as increasing the number of simulation section. This study developed the TOSA based round trip performance prediction module using genetic algorithm for simulating in a short time and verified simulation results.

• Laser Solutions
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• v.12 no.1
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• pp.14-18
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• 2009

Ripple formation of femtosecond laser in stainless steel is investigated using 184 fs pulses with a center wavelength of 785 nm. The effect of the laser polarization relative to the translation direction is observed. For drilling with a certain aspect ratio, reflections at the hole walls take place, leading to a non-uniform intensity distribution deep inside the formed hole. Finally, it is shown that a circular polarization during the drilling process significantly improves the quality of the produced holes.