• Journal of the Korean Society for Nondestructive Testing
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• 제33권1호
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• pp.73-79
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• 2013

In this study, NIMAX material has been processed using the three-dimensional measuring instrument and white light interferometer. they were tested to roundness and surface roughness and results are as follows: As for a cutting characteristic, it indicated that F4 showed a lower result than 2F showed due to the high hardness of the material and showed a good result when spindle rotation speed and tool feed were low. As for the measurement of roundness through 3-Dimensional measuring machine, it indicated that 4F showed a good result like the condition of cutting component and that roundness showed a good result when spindle rotation speed of 1,700 rpm and tool feed speed of 85 mm/min were applied. As for the surface roughness of processing surface, Surface roughness showed better 4F than 2F and conditions of spindle rotation speed 1,700 rpm, tool feed rate 55 mm/min showed good results in the Ra $0.4025{\mu}m$.

• Transactions of Materials Processing
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• 제19권6호
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• pp.337-343
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• 2010

Current need of weight reduction in automotive part increases the application for high strength steel (HSS). The various types of high strength steels have been used to produce chassis part, control arms and trailing arms for weight reduction and increasing of fatigue durability such as dual phase steel (DP) and ferrite bainite steel (FB). But, DP and FB steels have proven to show inferiority in durability as well as press formability. Edge cracking occurred often in flange forming and hole expansion processes is the major failure encountered. This paper discussed the behavior of edge stretchability of high strength steel of DP and FB steels. Experimental works have been conducted to study the effect of punch clearance and burr direction on hole expansion ratio (HER). Also finite element simulation (FEM) has been preformed to clarify the mechanism of flange crack and support the experimental results on HER of DP and FB steels. It was simulated the whole process of blanking process following by hole expansion process and ductile fracture criterion named the modified Cockcroft-Latham model which was used to capture the fracture initiation. From the hole expansion tests and FEM simulation studies it was concluded that ferrite bainite steel showed better stretch-flangeability than dual phase steel. It was attributed to the lower work hardening rate of ferrite bainite steel than dual phase steel at the sheared edge.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제12권6호
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• pp.132-141
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• 2013

Robotic Drilling Systems(RDSs) set the standard for the factory automation systems in aerospace manufacturing. With the benefits of cost effective drilling and predictive maintenance, RDSs can provide greater flexibility in the manufacturing process. The system can be easily adopted to manage very complex and time-consuming processes, such as automated fastening hole drilling processes of large aircraft sections, where it would be difficult accomplished by workers following teaching or conventional guided methods. However, in order to build an RDS based on a CAD model, the precise calibration of the Tool Center Point(TCP) must be performed in order to define the relationships between the fastening-hole target and the End Effector(EEF). Based on the kinematics principle, the robot manipulator requires a new method to correct the 3D errors between the CAD model of the reference coordinate system and the actual measurements. The system can be called as a successful system if following conditions can be met; a. seamless integration of the industrial robot controller and the IO Level communication, b. performing pre-defined drilling procedures automatically. This study focuses on implementing a new technology called iGPS into the fastening-hole-drilling process, which is a critical process in aircraft manufacturing. The proposed system exhibits better than 100-micron 3D accuracy under the predefined working space. Based on the proposed EEF fastening-hole machining process, the corresponding processes and programs are developed, and its feasibility is studied.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제18권10호
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• pp.8-19
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• 2019

In this study, the spray pattern of a centrifugal fertilizer distributor with two shutter holes was analyzed and an effective driving width that satisfies proper spray uniformity was derived. The centrifugal fertilizer distributor was mounted on a tractor with a rated power of 23.7 kW and static and dynamic spray pattern tests were performed according to the standard procedure proposed by the American Society of Agricultural and Biological Engineers Standard ASAE S341.5. The height of the fertilizer distributor was 80 cm from the ground and the PTO (power take-off) shaft speed of the tractor was fixed at 540 rpm. The fertilizer scattered in space was collected using 275 evenly spaced collectors at shutter opening ratios of 25%, 50%, 75%, and 100%. The spray pattern was analyzed via the amount of sprayed fertilizer at each collector location and the coefficient of variation was used as an indicator of spray uniformity. Using the analyzed spray pattern, the effective driving width that satisfied less than 15% of the coefficient of variation was derived for different tractor driving patterns (race track mode, back and forth mode). From the results, spray uniformity increased as the shutter opening ratio decreased. The largest effective driving width was 8 m at a shutter opening ratio of 25% for both driving patterns.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2000년도 제14회 학술강연논문집
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• pp.32-32
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• 2000

잠입노즐은 로케트 추진기관의 길이 및 중량을 감소시켜 체계설계의 관점에서 볼 때 많은 이점을 제공한다. 본 연구에서는 3단형 과학로케트 원지점 차넣기 모타(apogee kick motor)에 적용하기위한 잠입노즐의 기초기술 개발에 주안점을 두었다. 고고도에서 저속으로 회전하며 비행하는 원지점 차넣기 모타를 제작하기위해서 체계 요구성능에 의해 예상된 실물형의 50% 크기에 해당하는 축소형 잠입노즐을 제작하였다. 잠입노즐은 잠입부의 내외부가 고온의 추진제 연소가스에 노출된 상태에서 노즐 내부 압력 외에 연소실압에 의한 외부압력이 작용하므로 이를 고려한 열 및 구조설계가 중요하다. 본 연구에서는 노즐 수렴부와 목부에 일체형 그라파이트 소재를 적용하고 확장부 내열재 및 잠입부 배면내열재에 탄소/페놀 복합재를 노즐 내열재로 사용하였다. 그리고 이들의 구조적 지지를 위해 스틸구조물을 적용하였다. 적용된 스틸구조물에는 K형 열전쌍을 이용해 내열재와 구조물 온도를 측정할 수 있는 관통구멍 및 나사부를 구조물 외변에 가공하였다. 열전쌍은 노즐 목직경의 2, 4배 되는 확장부 내열재 단면위치의 2mm와 4mm 깊이와 구조물 내면 및 외면의 4개소에 열전쌍을 부착하여 지상연소시험시 노즐 내열재와 구조물의 온도분포를 관찰한다. 그리고 노즐 조립시 확장부 내열재와 구조물에 각 각 반원형 홈을 내어 여분의 접착제가 원형 홈에 밀려들어가 경화되어 노즐 기밀유지와 체결력을 향상시킬 수 있는 원형공간 접착제 충전 공법을 적용하여 실제모타에 대한 적용가능성을 지상연소시험을 통해 확인한다.

• Transactions of the Korean Society of Machine Tool Engineers
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• 제12권3호
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• pp.8-16
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• 2003

Monitoring of the drill wear :md hole quality change is conducted during the drilling process. Cutting force measured by tool dynamometer is a evident feature estimating abnormal state of drilling. One major difficulty in using tool dynamometer is that the work-piece must be mounted on the dynamometer, and thus the machining process is disturbed and discontinuous. Acoustic transducer do not disturb the normal machining process and provide a relatively easy way to monitor a machining process for industrial application. for this advantage, AE signal is used to estimate the abnormal fate. In this study vision system is used to detect flank wear tendency and hole quality, there are many formal factors in hole quality decision circularity, cylindricity, straightness, and so of but these are difficult to measure in on-line monitoring. The movement of hole center and increasement of hole diameter is presented to determine hole quality. As the results of this experiment AE RMS signal and measurements by vision system are shorn the similar tendency as abnormal state of drilling.

• Transactions of the Korean Society of Automotive Engineers
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• 제1권1호
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• pp.14-21
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• 1993

The effect of coolant flow pattern on the metal temperature of the combustion chamber was studied in 1.5L and 1.8L gasoline engines. One of the main important points in the design of the water jacket is the increase of the coolant flow velocity. In this paper, the water jackets of the cylinder head and the cylinder block were visualized for the purpose of improving the coolant flow pattern. By the use of this technique, the optimal design of the size and th location of the water transfer fole was possible. And, to lower the metal temperatures of the thermally critical parts, the drilled water passages were employed. To investigate of effect of the improved flow pattern and the drilled water passages, the metal temperatures of the combustion chamber were measured. As a result of the temperature measurement, it was found out that both the change of flow pattern and the drilled water passages have significant effect on the reduction of the peak metal temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.842-846
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• 1997

Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gaining increased attention in a wide spectrum of precision production industries. Alternative methods such as EDM, laser drilling, etc. can sometimes replace mechanical micro-hole drilling but are not acceptable in PCB manufacture because they yield inferior hole quality and accuracy. The major difficulties in micro-hold drilling are related to wandering motions during the inlet stage, high aspect ratios, high temperature,etc. However, of all the difficulties, the most undesirable one is the increase of drilling force as the drill penetrates deeper into hold. This is caused mainly by chip related effects. Peck-drilling is thus widely used for deep hole drilling despite the fact that it leads to low productivity. Therefore, in this paper, a method of cutting force regulation is proposed to achieve continuous drilling. A proportional plus derivative (PD) and a sliding modecontrol algorithm will be implemented for controlling the spinle rotational frequeency. Experimental results will show that sliding mode control reduces the nominal cutting force and its variation better than the PD control, resulting in a number of advantages such as an increase in drill life, fast stabilization of the wandering motion, and precise positioning of the hole.

• Transactions of the Korean Society of Mechanical Engineers
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• 제19권5호
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• pp.1176-1181
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• 1995

Microdrilling is one of the most difficult operations because of the poor chip discharge and the weakness of tool. This study is concerned about the development of a microdrilling monitoring system that is useful for minimizing the tool breakage and enhancing the machinability in the air spindle based microdrilling. The system is composed of a drilling state detection unit and an adaptive step-feed control unit that controls the micro-stepping motor driven spindle axis. Drilling states such as overload, tood breakage are recognized by the change of the air spindle speed which is measured via the reflective photo sensor. Based on the monitoring results, the adaptive step-feed control algorithm adjusts the step increment to keep the decrease of spindle speed within a specified range. The results of evaluation tests have shown that the developed system is very effective to prevent the breakage of microdrill and improves the productivity in comparison with the conventional microdrilling.

• Composites Research
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• 제26권1호
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• pp.42-47
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• 2013

In this study, an economical and effective processing technique to form multiple dimples on the surface of a composite part, which are known to be useful to improve aerodynamic performance and heat dissipation. Forming dimples on the surface using molds is an expensive processing because forming multiple tiny positive spheres on the surface of the mold requires much time and effort. In this study, plates with multiple round holes are utilized as a core to form dimples on the carbon/epoxy composite skin covering the core. A vacuum bagging process is used to apply pressure on the surface while curing. Composite parts which have multiple dimples on the surface can be utilized in the field which needs high aerodynamic performance and heat dissipation ability such as high speed sports car bodies.