• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.15-21
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• 2004

Composite materials are widely used to make all kinds of machine parts, internal and structural materials of cars, aerospace industries, building structures, ship materials, sporting goods and others. It is worth the while to use composite materials as various substitutions when compared with others. But the use is limited in the field of the mechanical processing because of its difficulties in processing. Thus, it is proved that the surface is rough in and out of the hole processing the GFRP with HSS drill in the vertical machining center.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.7
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• pp.36-44
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• 1996

Drilling tests were carried out austempered ductile cast iron(ADI) to clarify the factors influencing the drilling characteristics of ADI material. The machinability of material was evaluated using high speed steel drill and cobalt contained drill of 6mm diameter. The spheroidal graphite cast iron materials were austemized at 900 .deg. C for 1 hour and then wear was kept at 375 .deg. C for 2 hours. Austempered ductile cast iron contains a great deal of retained austenite which contribustes to an improvement of impact strength. In this paper, machinability of ADI was invastigated by drilling experimentation. The results obtained are as follows:a) Flank wear incresses logarithmically with the increases of cutting time and proportionally with the increases of cutting force. b) Drilling hole number of about 2 times can be educed more step feed than ordinary feed due to the high hardness of ADI material and hardness increasing ascribed to the martensite of retained austenite.

• Journal of the Korean Society for Precision Engineering
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• v.3 no.2
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• pp.91-101
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• 1986

This paper deals with the effect of static and dynamic cuttig force and the behaviour of drill life in drilling process. The experiments are performed with cemented carbide drills and high speed steel drills of 10mm in diameter and in an annealed SM45C. The conclusions are as follows (1) Dynamic cutting force is varied with the dept of hole. (2) Dynamic cutting forces of torque and thrust are increase with the increase in feed and cutting speed. (3) Chipping influence the dynamic cutting force of thrust than torque, and in the case of thrust, the amplitude is 3-7 times large than ordinary cutting state. (4) Prediction of drill life can be obtained from more easily the amplitude of static cutting force than that of dynamic cutting force.

• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.20-26
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• 2023

Fiber-reinforced composite materials with carbon, glass, and aramid fibers are widely applied to industrial field structures due to their excellent properties. However, carbon fibers are vulnerable to external impacts, whereas aramid fibers degrade when exposed to water. This study evaluated carbon/aramid fiber composites degraded and damaged by high-temperature saline environments using acoustic emission (AE). The test specimen was molded using an autoclave and immersed in seawater at 70 ℃ for 224 days. In order to imitate the damage, a 3-mm-diameter hole was drilled using a diamond drill. Additionally, the specimen with the perforation was repaired by patch attachment processing. Three-point bending was used to conduct the flexural experiment, and an AE sensor with a 150-kHz resonance frequency was attached to evaluate the damage and the effect of patch attachment. AE accumulative counts obtained at the maximum load were 69.2, 67.1, and 91.2 for a high-temperature seawater deteriorated condition, a hole specimen, and a repaired patch specimen, respectively. Furthermore, the maximum amplitude of AE was detected at low values of 28 dB, 31.3 dB, and 30.3 dB.

• Journal of Korean Neurosurgical Society
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• v.37 no.4
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• pp.282-286
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• 2005

Objective: Symptomatic chronic subdural hematoma(CSDH) is a well-known neurosurgical entity and most of the lesion is managed by surgical treatment. The authors analyze the surgical indication and the treatment results of twist drill craniostomy with closed-system drainage(TDD) for the symptomatic CSDH. Methods: From March 2001 through December 2003, 31 patients who were treated with TDD for the symptomatic CSDH and followed more than 6months were included. The radiologic criteria of TDD in this study were 1) homogeneous density of hematoma on computed tomography(CT), 2) no septation of hematoma on magnetic resonance imaging(MRI), and 3) thicker hematoma more than twice thickness of skull. Surgical procedures were performed on the maximum thickness of hematoma on CT/MRI. Short and long Steinman pins were used to penetrate the skull and hematoma membrane. As the 5L catheter was inserted through the drill hole, it was kept for 1 - 7days for the drainage of CSDH. The patients of CSDH were followed with clinical symptoms and CT studies. Results: Most of all the 31 patients were improved. However, one patient was suffered from postoperative epidural hematoma and the other patients have received the secondary operation because of the recurrence of CSDH on 3 months after initial surgery. Conclusion: TDD is safe procedure for the symptomatic CSDH if the patients are selected appropriately.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.79.1-84
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• 1995

The thermal analysis method containing micro drilling characteristic is proposed for the first time. There are such problems in thermal analysis of micro hole drilling as the thermal modeling complexity of drilling process and the undesirable micro drilling characteristic. Especially, the undesirable micro drilling characteristic prevents our using conventional thermal modeling. To model the thermal behavior of the micro drilling process, the finite different method, where heat source vectors are distributed by the measured rhrust and torque, is proposed. This method agrees with thermal behavior of the real system. And, it enable to predict the temperature field near the drill during. The validity of this method is verified in comparing with experimental results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.4
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• pp.117-122
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• 1998

Glass fiber epoxy composite material is widely used in the structures of aircrafts, robots and other machines because of their high specific strength, high specific stiffness and high damping. In order for the composite materials to be used in the aircraft structures or machine elements, accurate surfaces for bearing mounting or joint must be provided, which require precise machining. In this paper, the machinability of the glass fiber epoxy composite material was experimentally investigated. The results can be summarized as follows : 1. The entrance of hole is very good manufacturing existing, but exit come to occur sever surface exfoliation. 2. The cutting force in drilling of the glass fiber epoxy composite material is decreased as the drilling speed increased. 3. If the glass fiber epoxy composite material is drilling by the standard twist drill, then the hole recommand cutting condition is spindle speed 400∼600rpm, feed 40∼50mm/min.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.823-826
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• 2000

Burr formed in drilling are classified into three types. no burr, burrs with cap, teared burr. To control burr size in drilling. the second type burrs with cap are to be formed because it is small and uniform. It is necessary to understand the mechanism of cap formation to derive the burr formation into second type burr with cap. In several materials, second type burrs are formed in drilling by changing cutting conditions. It is observed that cap is formed as a result of the plastic deformation along the outside of exit hole. According to the tension behavior of the material in concentrated region between hole and drill outside edge, the geometry of burr with cap is determined.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.6
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• pp.103-110
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• 2000

Experimental study of drilling for duralumin A2024 was conducted with intermittently accelerated and decelerated feedrate. It is achieved through a programmed periodic increase and decrease in the feedrate using a machining center. The following experimental results were performed with the objective of solving chip to disposal problems. In conventional drilling of aluminum, long continuous chips are produced with winding around the drill and 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 investigate. The following conclusions are established from the experimental results. At a suitable feed fluctuation ratio, intermittently decelerated feed drilling proved successful in braking 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 drilling is influenced by the feed fluctuation ratio.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.70-78
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• 1999

오늘날 기계공업 현장에서 심공드릴가공은 광범위한 응용과 양호한 생산성으로 인하여 그 요구가 증가 되고 있다. 그러므로, 본 연구는 난삭재인 SKD11고합금공구강을 여러가지 절삭조건하에서 BTA드릴가공하여 얻은 실험결과(표면조도, 진직도, 진원도, 원통도, 구멍확대량, 등)를 다루었으며 이들의 이론적 배경과 실험을 비교 분석하였다. 프레스금형 부품과 기계부품으로 사용되고 있는 SKD11고합금공구강은 기계가공이 힘든 난삭재료로서 그 어려움이 크므로 본 연구는 생산현장에 보다 나은 심공드릴가공결과와 관련 지식을 제공 할수 있다고 사료된다.