• 터널과지하공간
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• 제22권4호
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• pp.284-295
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• 2012

본 연구에서는 암석 절삭 장비의 마모에 직접적인 영향을 주는 인자인 암석의 마모도(abrasiveness) 측정에 관한 연구를 수행하였다. 몇 가지 방법 중 세르샤 마모 시험(Cerchar abrasiveness test)을 통하여 암석의 마모도에 영향을 미치는 인자를 확인하고 효율적인 시험을 수행하기 위한 조건들을 연구하였다. 국내 19종 암석에 대한 시험 결과를 통하여, 세르샤 마모 지수(CAI, Cerchar Abrasiveness Index)에 영향을 미치는 암석의 역학적 물성(단축압축강도, 간접인장강도, 탄성계수, 포아송비, 공극률, 쇼어경도)과의 상관관계를 찾아보았고 X선 회절 분석을 통하여 암석의 구성 광물 중 마모도에 가장 큰 영향을 미치는 석영 함량, 등가 석영 함량과의 관계도 확인하였다. 그 결과로 암석의 입자 결합 특성보다 광물의 특성이 CAI에 영향을 더 미치는 것으로 관찰되었고, 단축압축강도와 등가 석영함량의 함수로 CAI를 예측하는 모델을 제시하였으며 핀의 경도가 커질수록 CAI값이 선형적으로 작아짐을 확인하였다. 수치해석적 연구를 통해 세르샤 마모 시험을 모사한 결과 초기 긁힘 거리에서 대부분의 마모가 발생함을 확인하였고 하중이 증가할수록 CAI값이 증가함을 확인하였다.

• 한국정밀공학회지
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• 제5권1호
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• pp.84-93
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• 1988

The on-line detection of the chip flow is one of the most important technologies in com- pletly automatic operation of machine tool, such as FMS and Unmanned Factories. This problem has been studied by many researchers, however, it is not solved as yet. For the recognition of chip flow in this study, the dynamic cutting force components due to the chip breaking were measured by dynamometer of piezo-electric type, and the frequency components of cutting force were also analyzed. From the measured results, the effect of cutting conditions and tool geometry on the dynamic cutting force component and chip formation were investigated in addition to the relationships between frequency of chip breaking (fB) and side serrated crack (fC) of chip. As a result, the following conclusions were obtaianed. 1) The chip formations have a large effect on the dynamic cutting force components. When chip breaking takes place, the dynamic cutting force component greatly increases, and the peridoic components appear, which correspond to maximum peak- frequency. 2) The crater wear of tool has a good effect on the chip control causing the chiup to be formed as upward-curl shape. In this case, the dymamic cutting force component greatly increases also 3) fB and fC of chip are closely corelated, and fC of chips has a large effect on the change of the situation of chip flow and dynamic cutting force component. 4) Under wide cutting conditions, the limit value (1.0 kgf) of dynamic cutting force component exists between the broken and continuous chips. Accordingly, this value is suitable for recognition of chip flow in on-line control of the cutting process.

• 한국정밀공학회지
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• 제4권3호
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• pp.44-51
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• 1987

In metal cutting various types of chips are produced in consequence of cutting conditions. Flow-type chips have been studied in most cases because they are easier to be analyzed, but the actual surfaces of chips are not smooth, but crushed. This paper deals with saw-toothed chips, special types of flow-type chips, which have deep concaves and high convexes and sharp angles on the free surface. I tried to establish the theory of saw-toothed chip mechanism through experimental observation, that is, the mathmatical model of the cutting energy and cutting mechanism through the geometrical observation of the chips by using a microscope. The results obtained are as follows: 1. The mechanism of saw-toothed chips is diffenent from that of general flow-chips. 2. In the case of saw-toothed chips, the shear angle must be measured by the hypotenuse angle and the rake angle, and the shear angle is more affected by the rake angle than by the hypotenbuse angle. 3. The friction angle is represented by .beta. = . pi. /4+ .alpha./ sub n/- .phi. which is different from Merchant's equation. 4. The pitch and the slip are greatly influenced by depth of cut, but the influence of the rake angle on it is small. 5. The normal stress and the shear stress on the shear plane decrease with the increase of the cutting depth, and they are almost independent on the variation of a rake angle. 6. The unit friction energy on the tool face, the unit shear energy on the shear plane, and the total cutting energy per unit volume decrease with the increase of rake angle and cutting depth.

• 한국소음진동공학회논문집
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• 제20권7호
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• pp.665-671
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• 2010

To improve the gear noise quality, gear tooth grinding machine are widely used in automotive industry. While using the gear profile grinding machine to improve the gear tooth quality of the transmission, several defects such as chattering, tooth waves that cause the gear noise occasionally happened. But it is very difficult to solve that problem, because there is no one who knows the setting up the optimal grinding condition appropriately. The abnormal manufacturing conditions which make the gear noise make the engineer to spend a lot of time, effort, and money. Due to demands for solving the serious abnormal gear noise happened in the automatic transmission in the mass product stage, the vibration checking process in the worm wheel axis, work rotation and fixed axis of the grinding machine were adapted to find the root causes. As a result, gear profile wave are affected by the work rotation axis's unbalance which is caused by worm wheel feeding speed. And a primary and the secondary grinding feeding speed, cutting oil, work fixed forces are also proved as the important factors. After setting up the grinding condition reported in this paper, it was adapted successfully to the grinding machine to manufacture the new automatic transmissions' gear. The gear noise was dramatically disappeared and the process and the results will offer good guides to the engineers who manufacture the gear with the grinding machine.

• Design & Manufacturing
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• 제13권1호
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• pp.5-12
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• 2019

In this paper, we studied the micro tool deflection, micro cutting with low temperature, and deformation of micro ribs caused by cutting forces. First, we performed an integrated machining error compensation method based on captured images of tool deflection shapes in micro cutting process. In micro cutting process, micro tool deflection generates very serious problems in contrast to macro tool deflection. To get the real images of micro tool deflection, it is possible to estimate tool deflection in cutting conditions modeled and to compensate for machining errors using an iterative algorithm correcting tool path. Second, in macro cutting fields, the cryogenic cutting process has been applied to cut the refractory metal but, the serious problem may be generated in micro cutting fields by the cryogenic environment. However, if the proper low temperature is applied to micro cutting area, the cooling effect of cutting heat is expected. Such effect can make the reduction of tool wear and burr formation. For verifying this passibility, the micro cutting experiment at low temperature was performed and SEM images were analyzed. Third, the micro pattern was deformed by the cutting forces and the shape error occurred in the sidewall multi-step cutting process were minimized. As the results, the relationship between the cutting conditions and the deformation of micro-structure during micro cutting process was investigated.

• Design & Manufacturing
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• 제13권2호
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• pp.54-59
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• 2019

CNC(Computer Numerical Control) machine tools are being used in various industrial fields such as aircraft and automobiles. The machining conditions used in the mold industry are used, and the simulation and the experiment are compared. The tool used in the experiment was carried out to increase the reliability of the simulation of the cutting machining. The program used in the 3D-FEM (finite element method) was the AdvantEdge and predicted by down-milling. The tool model is used 3D-FEM simulation by using the cutting force, temperature prediction. In this study, we carried out the verification of cutting force by using a 3-axis tool dynamometer (Kistler 9257B) system when machining the plastic mold Steel machining of NAK-80. The cutting force experiment data using on the charge amplifier (5070A) is amplified, and the 3-axis cutting force data are saved as a TDMS file using the Lab-View based program using on NI-PXIe-1062Q. The machining condition 7 was the most similar to the simulation and the experimental results. The material properties of the NAK-80 material and the simulation trends reflected in the reverse design of the tool were derived similarly to the experimental results.

• 한국산학기술학회논문지
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• 제22권6호
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• pp.60-66
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• 2021

광물자원의 개발 적합성을 가늠하기 위하여 굴착 장비로 지반 굴착을 통하여 코어를 채취한다. 코어를 채취하기 위해서는 시추장비의 가장 앞부분에 굴착을 위한 비트를 설치하여 직접지반을 굴착한다. 굴착을 진행 중에 드릴 비트는 지반과 직적접인 마찰로 인하여 국부에 응력을 받게 된다. 또한 마찰로 인하여 드릴 비트의 파손이 발생할 수 있기 때문에 지반의 조건에 따라 적합한 비트의 사용이 요구된다. 따라서 본 논문에서는 시추장비에 일반적으로 사용되는 세립비트를 기준으로 현재 개발 되어있는 비트의 모델을 이용하여 각각 이종재료와 동종재료의 보강재를 삽입한 새로운 비트 모델의 형상 및 재질을 비교·분석하였다. 그리고 세립비트의 형상을 각각의 형태로 모델링하여 절삭에 필요한 경도 및 항절력을 이론적 수식을 이용하여 계산하여 적합성을 확인하였다. 또한 기존의 모델과 새로운 형태의 설계모델을 Amsys Program을 이용하여 FEM해석을 실시하여 응력과 변형률을 계산한 결과, 응력이 1.92E+7Pa, 변형율 9.6E-5m/m인 응력과 변형율이 최소화된 새로운 모델을 설계하였고 그에 따른 세립비트 형상 및 구조의 최적화 설계를 진행하였다.

• Design & Manufacturing
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• 제15권2호
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• pp.42-48
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• 2021

In this paper, when manufacturing large/multi-mold parts (more than 30 core parts),A mold manufacturing (tolerance) management system was established through design-processing linkage.The mold manufacturing (tolerance) management system is a design-based measurement shape/measurement position determination system, M/C processing-linked measurement drive system,It is composed of four parts: CAD-linked measurement result analysis system and manager mold part quality management system.In addition, the constructed system was applied to the field and the effect of system construction was evaluated by comparing it with the existing process.As a result of the evaluation, the measurement precision is within 0.02mm, and the time it takes to measure after the end of processing is shorter than that of the existing process.(12 hours → 2 hours) It was shortened to 16.7%.In addition, it was confirmed that the time required for reprocessing after measurement was reduced by 25% (4 hours → 1 hour) compared to the existing process.

• 한국주조공학회지
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• 제41권2호
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• pp.139-143
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• 2021

타이타늄 합금 중 페로-타이타늄은 철강 업계에서 철강과 스테인리스강을 생산하는데 사용되는 주요 첨가물이다. 본 연구에서는 고품질의 페로-타이타늄 합금을 주조하기 위해 경제적인 면을 고려한 저비용 타이타늄 스크랩을 활용하고자 하였다. 먼저 재활용 타이타늄 스크랩의 표면에 형성되어 있는 절삭유 및 불순물을 제거하기 위한 최적의 전처리 공정을 연구하였다. 일반적인 세척 방법인 산이나 유기용제는 세척이 용이하나 환경적으로 문제가 되므로 친환경적인 방법을 고안하여 적용하고자 하였다. 또한, 타이타늄 스크랩을 활용하여 고품질의 페로-타이타늄 잉곳을 제조하고 성분 분석을 통해 불순물과 특성을 상용 소재 규격과 비교 분석하였다.

• 터널과지하공간
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• 제32권6호
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• pp.478-490
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• 2022

TBM의 주요 절삭도구인 디스크커터는 과다하게 마모되거나 손상된 경우 적절한 시기에 교체되어야 한다. 일반적으로 커터의 교체여부를 판단하기 위해서 작업자가 커터헤드 챔버의 내부로 접근하여 디스크 커터의 상태와 마모량을 계측하고 있다. 하지만 커터헤드(cutterhead) 챔버(chamber) 내부는 작업자에게 열악한 조건일 경우가 많아 작업자의 안전과 관련한 이슈가 있으며, 인력에 의해서 계측이 이루어짐에 따라 계측치의 오차도 발생하는 것으로 보고되고 있다. 이러한 한계점을 극복하고자 현재 해외에서는 디스크커터의 마모정도를 계측센서를 통해 굴착 중에 실시간으로 측정하기 위한 기술의 개발이 활발하게 이루어지고 있으며, 본 연구에서는 현재까지 해외의 문헌을 통해 보고되고 있는 TBM 디스크커터의 마모량 계측에 관한 연구현황에 대하여 소개하고자 하였다. 여러 형식의 센서가 디스크커터의 마모계측을 위해 활용되고 있으며, 향후 국내에서도 유사한 기술의 개발이 이루어지는 경우에 유용한 참고자료가 될 수 있을 것으로 판단된다.