온간 스파이더 표면결함 개선과 금형수명 향상에 관한 연구

강종훈(Jong-Hun Kang) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.5

Due to the complicated shape of the spider, the production method was changed from cold to warm forging. Finite element analysis was performed to predict the forging load and shape using the enclosed hydraulic die set. As the forging load increases due to the spider die volume, die stress analyses were performed to optimize the die design in order to reduce the die stress in various conditions. Large deformation while producing the complicated forging parts induces high forging load, which is one of the main parameters of the forging surface defects. The forging process was analyzed to find out the root cause of the surface defects generated during the spider production for various parameters, thereby revealing that the radius of die in the defect zone influenced the air trap depth, being the root cause of the surface defect. It was verified that die life was increased and the surface defect was eliminated by changing the die design during the mass production test.

객체 탐지 기술을 통한 휠 너트 제품의 단조 공정에서 불량 검출

김창대,백승욱,정완진,이창환 한국정밀공학회 2024 한국정밀공학회지 Vol.41 No.4

This study developed a defect-detecting system for automotive wheel nuts. We proposed an image processing method using OpenCV for efficient defect-detection of automotive wheel nuts. Image processing method focused on noise removal, ratio adjustment, binarization, polar coordinate system formation, and orthogonal coordinate system conversion. Through data collection, preprocessing, object detection model training, and testing, we established a system capable of accurately classifying defects and tracking their positions. There are four defect types. Type 1 and type 2 defects are defects of products where the product is completely broken circumferentially. Type 3 and type 4 defects are defects are small circumferential dents and scratches in the product. We utilized Faster R-CNN and YOLOv8 models to detect defect types. By employing effective preprocessing and post-processing steps, we enhanced the accuracy. In the case of Fast RCNN, AP values were 0.92, 0.93, 0.76, and 0.49 for types 1, 2, 3, and 4 defects, respectively. The mAP was 0.77. In the case of YOLOv8, AP values were 0.78, 0.96, 0.8, and 0.51 for types for types 1, 2, 3, and 4 defects, respectively. The mAP was 0.76. These results could contribute to defect detection and quality improvement in the automotive manufacturing sector.

선박용 축류 단조품 냉각공정 평가

박상철(Sang-Chul Park) 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.9

본 연구는 선박용 디젤엔진 부품인 축류 단조품을 단조작업에 의하여 제작하는 과정에서 발생하는 품질문제를 해결하기 위하여 수행되었다. 1차, 2차 가열 및 열간 단조를 거쳐 완성된 단조품은 최종 후열처리공정을 거치게 되는데 이 과정에서 발생하는 것으로 알려진 내부 결함문제를 해결하기 위하여 냉각공정을 평가하였다. 자유단조작업을 거쳐 제작된 축류 단조품에는 2차 열간 단조작업 후 냉각과정에서 소재 내부에 존재하고 있던 잔류 수소가 기공이나 미세균열, 입계, 계면 등으로 확산, 집적됨으로써 균열을 유발하여 내부 결함이 발생하는 것으로 알려져 있으며 실제 작업현장에서 균열발생 사례가 보고되고 있다. 이러한 문제를 해결하기 위하여 수치해석 전용 프로그램인 ANSYS를 사용하여 열전달 수치해석을 수행하였으며, 해석모델은 축류 단조품의 특성상 축대칭요소를 사용하여 구성하였고 단조품 초기 온도 1250 ℃에서 단조작업 완료 후 냉각과정에서 시간이 경과함에 따른 온도변화를 평가하였다. 주어진 4종류의 축류단조품에 대하여 온도이력을 평가한 결과 단조품 내부에 수소유기균열 발생이 예상되는 250 ℃까지 냉각되는데 소요되는 시간을 알 수 있었으며, 이러한 냉각시간은 추후 열처리 작업의 작업표준으로 적용함으로써 축류 단조품 제작 시 품질과 생산성을 높일 수 있다는 것을 알 수 있다. This study was performed to solve the quality problems of forging propeller shaft components in the marine diesel engines during the final cooling process and provide reasonable guidelines to increase the production of forging products. Residual hydrogen existing on the inside of forging products begins to diffuse and accumulates at the pores, micro-fissures, and grain boundaries as the temperature of forging products begins to decrease and reaches a critical temperature range, and finally transforming into internal defects. These defects were easily found near the surface of products after milling the surface of forging products. In this work, four types of forging products (shaft flange, shaft journal, thrust shaft, and propeller shaft) were chosen to evaluate the temperature history of products during the cooling process, employing non-linear numerical analyses with the ANSYS program. The times elapsed to reach 250 ℃ after cooling were approximately 9 ~ 23 hours for each forging product. These times can be used as cooling process guidelines on the quality and productivity of products after heat treatment.

A Relationship between UT Reported Sizes and Actual Sizes of Defects in Rotor Forgings

Seong, Un-Hak,Kim, Jeong-Tae The Korean Society for Nondestructive Testing 2005 한국비파괴검사학회지 Vol.25 No.6

The relationship between the EFBH (Equivalent Flat-Bottom Hole) size measured by non-destructive method and the actual size by destructive method in many rotors manufactured at Doosan Heavy Industries & Construction Co. Ltd. was investigated. In this investigation. "the Master Curve" compensating the differences between UT reported sizes and actual sizes of defects in our rotor forgings were obtainable. The applicability of this "Master Curve" as a way of calculating the actual defect size was also investigated. For the evaluation of rotor forgings, it is expected that this "Master Curve" may be used to determine the accurate actual sizes of defects.

Failure Analysis of the Defect-Induced Blade Damage of a Compressor in the Gas Turbine of a Cogeneration Plant

윤완노,최병호,강명수,정남근,김준성 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

Gas turbine engines are being widely used for power generation recently because of their high efficiency and versatility. However, it is occasionally reported that a gas turbine under normal operation fails even though careful inspections were scheduled. In this paper, the recent failure of the gas turbines of a cogeneration plant is analyzed by focusing mainly on the crack initiation mechanism of blade fracture. Damage of several blades of the compressor was observed after a gas turbine was disassembled, and the root causes of the damage were investigated in detail by scanning electron microscopy as well as optical microscopy. The defects observed at the crack initiation site have been characterized by comparison with previous studies. The fracture of the blade was supposed to be initiated by a crack due to concentrated stresses around a preexisting defect which was possibly formed before the turbine was operated, e.g., a forging defect during the three-step forging process for blades manufacture.

유한요소법을 이용한 냉간 개방 압출 공정의 성형 한계 예측

Qiu Yuangen,박승철(Seung Chul Park),조해용(Hae Young Cho) 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.6

냉간 개방 압출은 소재의 일부는 금형에 구속시키고 나머지는 금형 밖으로 노출시킨 후 압출하는 금속성형법이다. 과도한 단면 감소율로 냉간 개방 압출 시 베럴링 결함이 발생할 수 있다. 베럴링 결함이 발생하지 않는 최대 단면 감소율을 성형 한계라 한다. 볼트와 같은 체결용 부품은 다단 단조 공정을 통해 생산된다. 생산 효율을 높이고 생산 비용을 줄이기 위해 다단 단조 공정의 단수를 줄여야 한다. 이를 위해 성형 한계가 요구된다. 따라서 본 연구에서는 상용 유한요소 해석 프로그램은 DEFORM-3D를 이용하여 설계 변수에 따른 냉간 개방 압출 시뮬레이션을 하였고, 실험과 비교 및 분석하여 냉간 개방 압출 공정의 성형 한계를 제시하였다. The open-die extrusion is performed in state the billet is not entirely guided in the die. Cold open-die extrusion of Excessive reduction of area causes barreling defects. The maximum reduction of area at which no barreling defects occur is called the forming limit. Fasteners such as bolts are produced through a multi-stage forging process. In order to increase production efficiency and reduce production cost, the number of stages of multi-stage forging process should be reduced. Therefore, forming limits are required. In this thesis, predictions of forming limits in cold open-die extrusion process has been simulated by using commercial FEM code DEFORM-3D. the simulated results were compared with experimental ones.

유한요소법을 이용한 냉간단조에서 발생하는 주요 결함 사례 분석(2)

이성원(S. W. Lee),변우성(W. S. Byeon),차상렬(S. R. Cha),김봉수(B. S. Kim),전만수(M. S. Joun) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10

In this paper, case study on shape defects in cold forging is carried out using a finite element method. The representative defects are found from the related literature or industries. Two different materials, i.e., ESW105 with negligible strain hardening capability SCM435 with typical strain hardening behiviors, are tested for the same problem. The predictions of defect formation are seen through metal flow lines or state variables including effective strain and damage.

Development of a Flange type Nut with Elliptic-shape pilot Optimized by Forging analysis tool

J.Y. Seol(설주연),D.S. Kim(김동수),J.Y. Seo(서재윤),J.H. Park(박종혁),K.H. Lee(이광희),J.Y. Kim(김진용) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10

단조산업의 품질비용 관리체계 개발 및 지속적 품질개선 방안에 관한 사례 연구

김강우(Kang-Woo Kim),차병철(Byung-Chul Cha) 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.9

소재 산업은 공정 기술을 활용하여 최종 제품에 적용되는 부품을 생산하며 완성품의 품질을 결정하는 중요한 기반 산업이다. 그러나 최근 시장 환경이 악화되고 3D 업종으로 인식되어 다른 소재 산업 국가에 비해 경쟁력을 잃어가고 있는 실정이다. 본 연구는 단조 기업의 특성을 분석하고 품질 비용 범위를 설정하여 해당 산업에 특화된 품질 비용관리 체계 및 지속적 품질 개선 방안에 대한 프로세스를 개발한다. 본 연구를 통해서 단조 산업의 세 가지 특성인 설비의존, 수주 위주, 현장 중심을 발견하고 내부 실패 비용과 외부 실패 비용을 품질 비용 범위로 설정하였다. 대형 단조업체인 A기업에 대해서 개발된 품질 비용 관리 체계와 지속적 품질 개선 프로세스를 적용하여 총 8개의 품질 과제를 발굴하였으며, 개선 활동 결과 전년 대비 약 63.3%의 품질비용 저감을 확인하여 그 실효성을 증명하였다. 본 연구는 단조 기업들이 체계적으로 품질 비용을 관리하고 분석하여 품질 경영전략 방향성을 수립할 수 있도록 도움을 줄 것으로 판단된다. The material industry is an important infrastructure industry that uses process technology in order to produce parts applied to the final product and determine the quality of the finished product. However, the market environment, which has been recognized as a 3D industry, has deteriorated recently and lost competitiveness compared to other material industry countries. This study analyzed the characteristics of forging companies and The study found that three characteristics of the forging industry, facility-oriented, order-based, and field-centered, and internal failure cost and external failure costs were set as the range of quality cost. A total of eight quality tasks were selected by applying the quality cost management system and continuous quality improvement process developed for large-scale A forging company, and improvement activity proved its effectiveness reducing quality costs by 63.3% compared to the previous year. The research helps forging companies establish a quality management strategy by systematically managing and analyzing quality costs.

Al-Si 합금 열간단조품 내부의 판상 결함의 초음파 특성

이석원,전만수,이준현 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.6

본 연구에서는 Al-Si 합금 열간단조품 내부 판상 결함을 탐지하기 위한 초음파평가 기법을 확립하였다. 이를 위하여 내부에 존재하는 여러 가지 판상 결함의 초음파 특성을 실험적으로 구하였으며, 펄스-반사법을 적응하여 초음파 탐상신호에 대한 내부 판상 결함의 각도 등이 초음파 수신신호의 형태에 미치는 영향을 평가하였다. 한편 결함위치에 따른 초음파 신호특성을 규명하기 위하여 단조품 가장자리 부위에 존재하는 내부 판상 결함의 초음파 수신신호 특성을 평가하였으며, 본 시험편에 대한 초음파 투과법 적용 한계에 대하여 고찰하였다. 나아가 500개 이상의 파단 실험을 통해 제시된 초음파 평가기법의 신뢰성을 확인하였다. A nondestructive evaluation technique for detecting internal defects of an hot forged Al-Si allyoy part is established in this study. Ultrasonic characteristics of various internal planar defects are investigated by experiments for establishing a reliable test procedure. The effect of the angle between ultrasonic energy propagation directions and planar defects on the ultrasonic signal configuration is evaluated in the pulse-echo technique. A characteristic of ultrasonic signal for the internal planar defect located near the edge is also evaluated. The applicability of the through-transmission technique is also discussed. Reliability of the presented approach is validated by the destructive testing for more than 50 specimens.