• 대한기계학회논문집A
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• 제24권8호
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• pp.2059-2064
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• 2000

The measurement of residual stresses by the hole-drilling method has been commonly used to evaluate residual stresses in structural members. In this method, one of the source of error is due to the misalignment between the drilling hole and strain gage center. This paper presents a finite element analysis of the influence of such misalignment for the uniaxial residual stress field. The stress error increases proportionally to hole eccentricity. The correction equations which easily obtain the residual stress taking account of the hole eccentricity are derived. The stress error due to the hole eccentricity decreases by approximately one percent using this equations.

• Journal of Welding and Joining
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• 제6권3호
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• pp.37-42
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• 1988

The Hole Drilling Method(HDM) is widely used to measure residual stresses in the welded structures. The purpose of this study is to evaluate the accuracy fo measuring residual stresses when drilling the hole by Air-abrasive Jet machine(AJM). Simulated residual stresses wre introduced by applying known stresses to steel bars. These known streses were then compared with measured stresses relaxed from hole drilling. the obtained results are summarized as follows; 1) It was possible to obtain well defined holes with the nozzle designed for this study. 2) If the hole shape is not cylindrical, critical may occur. 3) In the uniaxial strain field, the measurement error of the maximum principal stress was within .+-.10 percent. The orientation angle of the maximum principal stress was within 8.deg. from the given directioin. 4) meausrements were made varying hole depths. Little or no change of stresses occurs since holse were drilled more than the depth of the 0.6 times diameter. 5) The air-abrasive jet machining for drilling holse does not cause appreciable apparent stresses which si critical to measure residual stresses.

• 반도체디스플레이기술학회지
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• 제14권2호
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• pp.47-52
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• 2015

In this paper, the performance of uncoated- and Titanium nitride aluminium TiAlN-PVD coated- carbide twist drills were investigated when drilling aluminium alloy, Al 6061. This research focuses on the optimization of drilling parameters using the Taguchi technique to obtain minimum surface roughness and thrust force. A number of drilling experiments were conducted using the L9 orthogonal array on a CNC vertical machining center. The experiments were performed on Al 6061 material l blocks using uncoated and coated HSS twist drills under dry cutting conditions. Analysis of variance(ANOVA) was employed to determine the most significant control factors. The main objective is to find the important factors and combination of factors influence the machining process to achieve low surface roughness and low cutting thrust force. From the analysis of the Taguchi method indicates that among the all-significant parameters, feed rate are more significant influence on surface roughness and cutting thrust than spindle speed.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.263-268
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• 1999

The most important things to the tube the of the heat exchanger are the precision of t hole position and the quality of the drill face. Nowadays, 6 and 12 spindle multi-drilling machine controlled by CNC or used to drill holes of the tube sheet. The drilling of 12 axes can offer high speover three times as fast as the drilling of axis. However, the drilling of 12 axes h difficulty in controlling many motors to d spindles and assigning a corresponded numbe accurately to each axis. In the past, conventional method to inspect the code the drilling was machining holes on a thin plate previously which resulted in the productivity because it required a h production cost by machining and weldin time. In this thesis, there are two drilling codes different from CNC code. M code is used to control many motors and S code is used to assign a correspondent number for each axis. For increasing the productivity by removing process, this paper is intended to take simulation of the drill machining c including 6 and 12 axis on the persona computer.

• 대한기계학회논문집A
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• 제39권6호
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• pp.575-581
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• 2015

드릴비트는 암반에 직접적으로 타격력과 회전력을 전달함으로써 연속적으로 암반을 파쇄, 분쇄하는 천공기의 핵심 구성요소이다. 일정한 속도로 회전하는 동시에 회전축 방향으로 타격하며 암반을 파쇄하기 때문에 암반 파쇄효율을 높이기 위해서는 드릴비트의 배열 최적설계가 필요하다. 그러므로 본 연구에서는 버튼배열 최적화를 수행하기 위한 선행연구로써 버튼배열의 성능을 정량적으로 평가할 수 있는 방법에 대한 연구를 수행하였다. 버튼의 중복타격 면적, 비 타격 면적, 천공편향 모멘트와 같은 평가지표를 활용하여 버튼배열의 파쇄 효율성을 평가하였으며, 더불어 제안된 평가방법을 활용하여 기존 드릴비트 버튼배열의 파쇄 효율성을 검토함으로써 제안한 배열성능 평가방법의 적합성을 확인하였다.

• Journal of Periodontal and Implant Science
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• 제53권1호
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• pp.85-95
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• 2023

Purpose: In recent years, guided implant surgery has been widely used for the convenience of patients and surgeons. Further streamlining the surgical procedure would make implant surgery more convenient. Low-speed water-free conditions are often used in guided implant surgery. Therefore, in this study, we attempted to confirm once again whether drilling was safe at a low speed without water. The main purpose of this study was to evaluate whether a simplified drilling protocol that omits some intermediate steps in the drilling process was safe from the viewpoint of heat generation. Methods: D1 density artificial bone blocks were drilled under 50 rpm, 10 N·cm water-free conditions, and the surface temperature was measured using a digital infrared camera. First, drilling was performed with the sequential drilling method, which is the most widely used technique. Second, for each drill diameter, the temperature change was measured while performing simplified drilling with omission of the previous 1, 2, or 3 steps. Results: In sequential drilling, the heat generated during drilling at all diameters was less than the critical temperature of osteonecrosis (47℃) except for the ⌀2 drill. Statistical significance was observed in all groups when comparing sequential and simplified drilling in the ⌀3.2, ⌀3.8, and ⌀4.3 drills (P<0.001). However, in the simplified drilling procedures, the temperature was below the osteonecrosis threshold temperature (47℃) except for the ⌀4.3 drill with the omission of the previous 3 steps (⌀3.0, ⌀3.2, and ⌀3.8). Conclusions: In general, drilling under low-speed, water-free conditions has shown stable results in terms of heat generation. Simplified drilling showed statistically significantly greater heat generation than sequential drilling. However, most of the diameters and omitted steps seem to be clinically acceptable, so it will be useful if an appropriate selection is made according to the patient's clinical condition.

• 한국지열·수열에너지학회논문집
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• 제17권1호
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• pp.14-22
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• 2021

Drilling equipment is an essential part used in various fields such as construction, mining, etc., and it has drawn increasing attention in recent years. The drilling method is generally divided into three types. There are a top hammer method that strikes on the ground, a DTH (Down-The-Hole) method that directly strikes a bit in an underground area, and a rotary method that drills by using rotational force. Among them, the DTH method is most commonly used because it enables efficient drilling compared to other drilling methods. In the conventional DTH hammer, the valve between the piston and the bit is opened and closed using a face to face method. In order to improve the power of the DTH hammer, a DTH hammer with foot valve which is capable of instantaneous opening and closing is used in the drilling field. In this study, we designed a lab-scale DTH hammer with the foot valve, and manufactured an evaluation device for the experiment of the DTH hammer. In addition, we analyzed the performance of the DTH hammer adopted with foot valve according to the pressure range of 3-10 bar. As a result, the internal pressure distribution in the DTH hammer was experimentally analyzed, and then, the movement of the piston according to the pressure was predicted. We believe that this study provides the useful results to explain the performance characteristics of the DTH hammer with the foot valve.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1491-1498
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• 2000

In recent years, CFRP composite materials have been increasingly used in various fields of engineering because of a high specific strength and stiffness properties. Drilling is one of the most impo rtant cutting processes that are generally carried out on CFRP materials owing to the need for the structural integration. However, delamination are often occurred as one of the drilling damages. Therefore, there are needs studying for the relationships between CFRP drilling and delamination in order to avoid low strength of the structures and inaccuracies of the integration. In this study, AE signals and thrust forces were used for the evaluations of the delamination from a drilling process in [0/900]s CFRP materials. And the drilling damage processes were observed and measured by a real time monitoring technique with a video camera. From the results, we found that the relationships between the delamination from drilling and AE characteristics and drill thrust forces for [0/900]s CFRP composites. Also, we proposed the monitoring method for a visual analysis of drilling damages.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.287-290
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• 2002

Stainless steel used widely in various fields of industry have the characteristics of difficulty-to-cut. This difficulty comes from its peculiarity, for example work hardening, vibration, etc. And these peculiarity on the cutting process have an effect on tool wear or life shortness of tools. To solve these problems several method have been developed. Hot-machining is one way of these method. when a material is heated, organization of material is soften. So cutting process becomes easy. When such a hot-machining method applies on drilling process and then heated material is processed, cutting force is less than usual drilling process cutting force. In this paper, cutting force is compared heated SUS 304 with usual SUS 304. And shape of chips is also compared.

• 한국정밀공학회지
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• 제18권8호
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• pp.96-106
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• 2001

As the drilling depth increases, the cutting torque increases and fluctuates, which can lead to the machine tool vibration, severe tool wear, and catastrophic tool breakage. Hence, cutting torque control is very important to improve productivity in drilling. In this paper, a PID controller was designed to control the drilling torque. The plant including the feed drive system, cutting process and spindle drive system was modeled for controller design. The Ziegler-Nichols method was used to determine the controller gain and control action times and the root locus plot was used to tune the controller gain for a certain cutting condition. Also, suggested was a simple method to obtain the tuned controller gain for an arbitrary cutting condition not using the Ziegler-Nichols method and the root locus plot. The performance of the designed controller and the effect of controller gain tuning were verified from experiments.