• Title/Summary/Keyword: 굽힘공정

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Investigation of Residual Stress Distributions of Induction Heating Bended Austenitic Stainless Steel (316 Series) Piping (유도 가열 굽힘된 316 계열 오스테나이트 스테인리스 강 배관의 잔류응력 분포 고찰)

  • Kim, Jong Sung;Kim, Kyoung Soo;Oh, Young Jin;Chang, Hyun Young;Park, Heung Bae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.7
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    • pp.809-815
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    • 2014
  • The induction heating bending process, which has been recently applied to nuclear piping, can generate residual stresses due to thermomechanical mechanism during the process. This residual stress is one of the crack driving forces that have important effects on crack initiation and propagation. However, previous studies have focused only on geometric shape variations such as the change in thickness and ovality. Moreover, very few studies are available on the effects of process variables on residual stresses. This study investigated the effects of process variables on the residual stress distributions of induction heating bended austenitic stainless steel (316 series) piping using parametric finite element analysis. The results indicated that the heat generation rate and feed velocity have significant effects on the residual stresses whereas the moment and bending angle have insignificant effects.

A Study on Improvement of Bending Quality of Hemmed Plates in Sheet Metal Forming (헤밍 (Hemming) 구조를 가진 박판의 굽힘품질 개선에 관한 연구)

  • Kim, Pan Gun;Park, Sang Hu
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.12
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    • pp.1360-1367
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    • 2012
  • A bending process is considered as one of fundamental sheet metal forming processes, and it is widely used for fabrication of simple or complicated sheet metal products in industrial fields. Most of automobiles and electronics have many parts made by the bending process inside or outside of them. However, till now, there is few research reports on the bending process of hemmed plates. A hemmed plate has a locally different bending strength, so a waving shape occurs after bending. A poor outlook due to local uneven shape influences greatly on product competitiveness. To settle this problem, we studied the bending parameters of a hemmed plate and showed the major sensitive design-parameters on the bending quality.

An Experimental Study on the Bending Process of Stainless Steel Sheets (스테인리스 판재의 굽힘공정에 관한 실험적 연구)

  • Kim, Ho-Yoon;Hwang, Bum-Cheal;Bae, Won-Byong;Kang, Chung-Gil;Byun, Cheon-Deock
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.2 s.95
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    • pp.82-86
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    • 1999
  • An experimental study has been carried out to reduce bending load, surface roughness and springback in bending process of stainless steel sheets. A U-bending test has been performed to investigate appropriate process parameters for getting better surfaces and accurate dimensions of stainless steel products. In the test, selected process parameters are die material, lubricant, and die clearance. Die materials used in the test are STD11(HRC60), STD11(TiCN), and AMPCO. From the test results, we can suggest that AMPCO dies are most suitable for reducing bending load and surface roughness of stainless steel sheets. And STD11 dies are favorable for avoiding spring-back in the stainless steel sheet-bending.

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The Thinning Phenomena of the Wall Thickness during $360^{\circ}$ Cold Bending of Ti-6Al-4V Large-Diameter Seamless Tube (대 직경 이음매 없는 Ti-6Al-4V 합금 튜브의 $360^{\circ}$ 냉간 굽힘 시 벽두께 감소현상)

  • 허선무;박종승
    • Journal of the Korea Institute of Military Science and Technology
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    • v.3 no.1
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    • pp.231-236
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    • 2000
  • The wall thickness of the Ti-6Al-4V Large-Diameter Seamless Tube, which is supposed to be a very important parameter in a system design, was measured during $360^{\circ}$ cold bending processes. The factors or processes affecting the wall thickness include 1) primary bending, 2)secondary or finishing step of the $360^{\circ}$ bending, 3)cleaning processes in CERO TRUTM(CT)process. But thinning effects of the wall thickness during the cleaning processes are negligible compared to those during the formers. The variations in the percentages of the change in wall thickness were found to be from -14% to +16%.

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A Numerical study on Spring-back Phenomenon of a Rebar for Manufacture (철근 공장가공화를 위한 철근 스프링 백에 대한 수치적 연구)

  • Choi, Chang-Hwan;Kim, Jin-Ho;Lee, Sung-Kyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.8
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    • pp.3638-3643
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    • 2013
  • These days, workers in a construction site conduct a rebar bending process with a machine. This bending process has some problems such as long processing time and bad quality of the rebar. In order to manufacture a rebar having precision and machinability, we should study on Spring-back phenomenon. This phenomenon affects a shape of rebar after unloading due to restoration ability of material and it is influenced by bending angle, bending radius and a rebar diameter. The change of spring-back ratio according to the change of the parameters are analyzed by FEM. Consequently, Spring-back increases around $0.1^{\circ}$ as bending angle increases $10^{\circ}$. and it also increases around $0.6^{\circ}$ as diameter of rebar increases from ${\varphi}$ 10mm to ${\varphi}$ 16mm. while we can confirm that it decreases around $0.2^{\circ}$ as bending angle increases $10^{\circ}$.

Development of a Process Sequence Determination Technique by Fuzzy Set Theory for Electric Product with Piercing and Bending Operations (퍼지셋을 이용한 퍼어싱 및 굽힘공정을 갖는 전기제품의 공정순서 결정기법 개발)

  • Kim J.H.;Kim Chul
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.9 s.174
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    • pp.137-146
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    • 2005
  • This paper describes a research work to develop a computer-aided design for the product made by progressive working of bending and piercing. An approach to the system for progressive working is based on the knowledge-based rules. Knowledge for the system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer and is composed of three main modules, which are input and shape treatment, flat pattern layout, strip layout modules. The system is designed by considering several factors, such as piercing and bending sequences by fuzzy set theory, complexities of blank geometry, punch profiles, and the availability of a press equipment. Strip layout drawing generated in the strip layout module is presented in 3-D graphic forms, including piercing and bending sequences with punch profiles divided into for external area. Results obtained using the modules enable the manufacturer for progressive working of electric products to be more efficient in this field.

Experimental estimation of effective strain on strength of hydroformed engine cradle (액압성형공정을 적용한 엔진크레들의 변형률에 따른 강도변화의 실험적 연구)

  • Lee, S.M.;Park, H.K.;Yim, H.S.;Kim, K.S.;Moon, Y.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.05a
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    • pp.503-506
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    • 2008
  • 본 연구에서는 하이드로포밍 공정을 적용한 엔진크레들 제품에 대해 최종 제품의 강도를 평가하고자 하였다. 먼저 적용 판재인 370과 440 소재에 대해 인장시험을 수행하여 소재의 경도와 강도의 상관관계를 분석하여 경도와 강도의 변환식을 도출하였다. 그런 다음 예비굽힘, 예비성형, 최종성형된 제품의 각 공정에 따른 유효변형률을 측정하고 같은 위치에서의 경도를 측정하였다. 측정된 경도는 앞서 도출한 경도와 강도의 변환식에 대입하여 각 공정을 마친 제품의 강도를 예측하고 결국 하이드로포밍된 엔진 크레들 제품의 유효변형률에 따른 강도를 예측식을 실험으로 도출하였다. 그 결과 예비굽힘, 예비성형, 최종성형을 마친 엔진 크레들 제품에 대해 유효변형률이 $24{\sim}72%$로 변하였고 이때 HF370의 경우에는 유동응력값이 $375{\sim}500MPa$로 증가하여 원소재에 비해 성형 후 $25{\sim}66%$의 강도증가량을 보였고, HF440의 경우에는 $470{\sim}565MPa$로 증가하여, 원소재에 비해 $17{\sim}41%$로 강도가 증가하는 것으로 나타났다. 그리고 이와 같은 변화값을 이용하여 유효변형률과 강도의 상관관계를 도출하였다.

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Effect of various surface roughness of steel sheet on characteristic of surface friction in stamping (판재의 표면 거칠기에 따른 표면 마찰 특성 변화)

  • 조상헌;허보영;아라이히로시;주상응;김상열;이용진;문만빈;이영수;고흥석
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.03a
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    • pp.24-24
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    • 2003
  • 최근 자동차 산업이 발달함에 따라 철강업계와 자동차 회사에서는 전에 많이 사용하던 내연 무도금강판 대신 부식에 저항력이 강한 도금강판을 사용한 이후로 냉연강판의 가공 시에 야기되지 않았던 많은 문제점들이 나타났다 자동차용 강판의 경우 판재의 체적에 비하여 금형과 판재의 접촉면적이 큰 프레스 공정에서는 판재의 표면에 작용하는 마찰력의 크기가 판재의 스탬핑 성형성에 큰 영향을 미친다. 이는 마찰특성이 비록 재료고유의 성형한계에서는 영향을 미치지 못하나 스탬핑 공정에 있어서 금형과의 접촉면에서 마찰력의 크기가 패널의 변형률분포를 변화시켜 스탬핑 성형성에 큰 영향을 주는 것이다. 따라서 본 연구는 자동차용 도금강판의 표면 거칠기에 따른 판재의 표면 마찰 특성 변화를 알아보았다. 소재의 기계적 특성 측정은 UTM을 사용하였고, 도금층은 XRD, SEM을 이용하여 상분석 하였으며, 표면 거칠기는 AFM(Atomic Force Microscope), SJ-400(Mitutoyo)을 사용하여 표면 거칠기를 측정하였다. 또 드로잉 하중을 비드부에서의 굽힘-굽힘 풀림 소성변형에 의한 변형력 성분과 마찰력 성분으로 분리하여 강판의 쿠롬 마찰계수를 DBS(Draw bead simulation)로 측정하였다.

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