고속 성형의 성형성 향상 입증을 위한 실험 및 이론적 성형한계선도 획득 및 비교

김민석,장윤호,김정 한국소성∙가공학회 2024 소성가공 : 한국소성가공학회지 Vol.33 No.2

The current study aims to prove that high-speed forming has better formability than conventional low-speed forming. Experimentally, the quasi-static forming limit diagram was obtained by Nakajima test, and the dynamic forming limit diagram was measured by electrohydraulic forming. For the experiments, the LS-DYNA was used to create the optimal specimen for electrohydraulic forming. The strain measurement was performed using the ARGUS, and comparison of the forming limit diagrams confirmed that EHF showed better formability than quasi-static forming. Theoretically, the Marciniak-Kuczynski model was used to calculate the theoretical forming limit. Swift hardening function and Cowper Symonds model were applied to predict the forming limits in quasi-static and dynamic status numerically.

Evaluation and Prediction of Forming Limit of Boron (22MnB5) sheet metal in a Hot Press Forming Process

아루무감(Arumugam S),홍성훈(S. H. Hong),뚜안(D. T. Nguyen),마니반난(Manivannan R),김영석(Y. S. Kim) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5

At presence the industrial practice demands a reliable determination of forming limits which assures the prediction of properly selecting the forming process in a digital environment. Therefore, technological limits defined with the forming limit diagrams (FLDs) have to be known. The experimental evaluation of FLDs for sheet metal is time consuming and demands expensive equipment. Hot press forming (HPF) is an advanced sheet metal forming methodology which can able to produce high strength final product by forming the part with high temperature and also cooling the part rapidly inside dies, it’s an one of the most successful forming process which can produce a component with complex geometric shape, high strength and minimum spring back. For conventional sheet metal forming processes the forming limit diagram (FLD) is primarily applied as failure criterion in the automotive industry regarding a FE-based process design. This works deals with the prediction of formability of sheet metal during the hot press forming. In order to predict the FLD at high temperature, we used Marciniak-Kuczynski flat punch for equi-biaxial and round punch for uniaxial and plane strain for In-plane deformation test. However, thermo-mechanical coupled simulation carried out by using DEFORM-3D for forming and predicting the failure by using Normalized Cockcroft-Latham failure criterion model. By applying the above failure criteria in DEFORM-3D FLD simulation, we need to determine the critical damage values (C?) calculated from out of plane deformation test for uniaxial and plane strain experiments carried out at 25℃ (RT), 500℃ and 700℃. In addition, the formability of the simulation results in a hot press formed part is compared with the experimental ones to confirm the validity of the proposed simulations.

FE Analysis of Forming Limit Diagram of 22MnB5 Sheet Using Fracture Energy Theory

Dae Young Ahn,Ok Dong Lim,Min-Sik Lee 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.10

A forming limit diagram (FLD) is used to define the strain limit of a material fracture during sheet formation. Owing to its usefulness in the FE analysis of hot stamping, numerous studies have been conducted regarding the FLD based on temperature. There have been few studies on the forming limit of martensite, which must be investigated to measure the impact characteristics and impact toughness to evaluate the safety of car components. Moreover, the need for FLDs of hot press products to evaluate the collision characteristics of automobile parts is increasing. In this study, a stretch test is performed to measure the forming limit of 22MnB5 steel before and after hot press forming. To minimize the error between the experimental data and FE simulation, fracture energy theory was applied to the damage evolution technique to enhance the accuracy of the fracture results. Accordingly, an FE analysis of the FLD was performed using the ABAQUS software, and the method for minimizing the error compared to the actual data of FLD is examined. The results were validated between an experiment and FE analysis by applying forming limit analysis data to the FE analysis of the tensile test.

Experimental evaluation of coating delamination in vinyl-coated metal forming

Young-ki Son,Chan-joo Lee,Jung-min Lee,Sang-doek Byoen,Soen-bong Lee,Byung-MinKim 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.10

In this paper, a new evaluation and prediction method for coating delamination during sheet metal forming is presented. On the basis of the forming limit diagram (FLD), the current study evaluates the delamination of PET coating by using a cross-cut specimen, dome test, and rectangular-cup drawing test. Dome test specimens were subjected to biaxial, plane strain, and uniaxial deformation modes. Rectangular cup- drawing test specimens were subjected to the deep-drawing deformation mode, and compression deformation mode. A vinyl-coated metal (VCM) sheet consists of three layers of polymer on the sheet metals: a protective film, a PET layer and a PVC layer. The areas with coating delamination were identified, and the results of the evaluation were plotted according to major and minor strain values, depicting coating delamination. The constructed delamination limit diagram (DLD) can be used to determine the forming limit of VCM during the complex press-forming process. ARGUS (GOM) was employed to identify the strain value and deformation mode of the delaminated surface after the press forming. After identifying the areas of delamination, the DLD of the PET coating can be constructed in a format similar to that of the FLD. The forming limit of the VCM sheet can be evaluated using the superimposition of the delamination limit strain of the coating onto the FLD of VCM sheet. The experimental results showed that the proposed test method will support the sheet metal forming process design for VCM sheets. The assessment method presented in this study can be used to determine the delamination limit strain under plastic deformation of other polymer coated metals. The experimental results suggested that the proposed testing method is effective in evaluating delamination for specific applications.

고속박판성형을 위한 AHSS 차체강판의 성형한계도

임성준(S. J. Lim),김석봉(S. B. Kim),허훈(H. Huh) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5

In this paper, forming limit diagrams of DP780, DP980, TRIP590 and TRIP780 steel sheets were investigated for high-speed sheet metal forming. The static and high speed forming limit tests were conducted with the aid of punch stretch tests with arc-shaped and square-shaped specimens. The width of arc-shaped specimen was changed to compose the uniaxial tension region of FLD and the friction condition was also varied to obtain the biaxial tension region of FLD. A high speed crash testing machine with a specially designed high speed forming jig was used in order to realize the high speed forming condition. The forming speed of each test condition was determined by comparing the results of the finite element simulation and the experimental results.

Forming limit diagram of aluminum AA6063 tubes at high temperatures by bulge tests

Seyed Jalal Hashemi,Hassan Moslemi Naeini,Gholamhossein Liaghat,Rooholla Azizi Tafti,Farzad Rahmani 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.11

A free bulge test and ductile fracture criteria were used to obtain the forming limit diagrams (FLD) of aluminum alloy AA6063 tubesat high temperatures. Ductile fracture criteria were calibrated using the results of uniaxial tension tests at various elevated temperaturesand different strain rates through adjusting the Zener-Holloman parameter. High temperature free bulge test of tubes was simulated infinite element software Abaqus, and tube bursting was predicted using ductile fracture criteria under different loading paths. FLDs whichwere obtained from finite element simulation were compared to experimental results to select the most accurate criterion for prediction offorming limit diagram. According to the results, all studied ductile fracture criteria predict similarly when forming condition is close tothe uniaxial tension, while Ayada criterion predicts the FLD at 473 K and 573 K very well.

Comparison of plastic strains on AA5052 by single point incremental forming process using digital image processing

Mugendiran V.,A. Gnanavelbabu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

In this study, a surface based strain measurement was used to determine the formability of the sheet metal. A strain measurement mayemploy manual calculation of plastic strains based on the reference circle and the deformed circle. The manual calculation method has agreater margin of error in the practical applications. In this paper, an attempt has been made to compare the formability by implementingthree different theoretical approaches: Namely conventional method, least square method and digital based strain measurements. As thesheet metal was formed by a single point incremental process the etched circles get deformed into elliptical shapes approximately, imageacquisition has been done before and after forming. The plastic strains of the deformed circle grids are calculated based on the nondeformedreference. The coordinates of the deformed circles are measured by various image processing steps. Finally the strains obtainedfrom the deformed circle are used to plot the forming limit diagram. To evaluate the accuracy of the system, the conventional, leastsquare and digital based method of prediction of the forming limit diagram was compared. Conventional method and least square methodhave marginal error when compared with digital based processing method. Measurement of strain based on image processing agrees welland can be used to improve the accuracy and to reduce the measurement error in prediction of forming limit diagram.

친환경 자동차용 고강도 알루미늄 신소재(Almag6) 성형성 평가

이상민(Sangmin Lee),레 쫑 다이(Le Trong Dai),홍석무(Seokmoo Hong) 한국산학기술학회 2022 한국산학기술학회논문지 Vol.23 No.10

최근 자동차 배기가스로 인한 환경오염을 줄이기 위한 환경규제로 경량화에 관한 연구들이 활발하게 이뤄지고 있으며, 최근 사용하는 소재를 스틸에서 알루미늄으로 변경되고 있다. 알루미늄은 철에 비해 비중이 1/3로 경량화에 효과적이지만 철강소재에 비해 최대강도가 낮고, 연신율 또한 낮은 단점이 존재한다. 본 연구에서 사용한 Almag6은 이러한 단점을 개선하기 위해 기존 5000계열 소재에 마그네슘 함유량을 높여 강도를 향상시키고 특수 열처리를 통해 연신율을 향상시킨 신소재이다. 본 연구에서는 Al5052-H32 소재와 Almag6 신소재의 강도 및 연신율 특성을 비교하기 위해 인장시험과 성형한계도 시험을 수행하였다. 연신율이 낮고 강도가 높은 소재의 경우 성형한계도 시험 중 그립부 파단 현상이 발생하기 쉽기 때문에 본 연구에서는 소재에 작용하는 응력비에 따라 새로운 인장시편을 사용하여 인장시험기로 성형한계도 2사분면을 완성하였다. 또한 DIC(Digital Image Correlation)를 적용하여 네킹 및 파단 시점의 국부변형률을 측정함으로 해서 성형한계도의 네킹에서 파단까지의 범위를 도시할 수 있게 되었다. 따라서 기존 보수적인 네킹 발생 시 성형한계도를 작성한 경우 보다 파단에 근접한 제품 설계까지 판단 근거를 제시할 수 있을 것으로 기대된다. Recently, studies have been conducted on weight reduction to reduce environmental pollution caused by vehicles. Aluminum has 1/3 the weight of steel and is effective in reducing weight, but it has a disadvantage of low strength and elongation. Almag6 is a new material with increased magnesium content in compared to 5000 series material, which improves the strength and elongation through heat treatment. A tensile test and forming limit test were conducted to compare the strength and elongation characteristics of Al5052-H32 and Almag6. For materials with low elongation and high strength, it is easy to fracture a gripped part during the forming limit test, so a two-quarter forming limit was completed with a tensile tester using a new tensile specimen depending on the stress ratio applied to the material. In addition, we applied Digital Image Correlation to measure the local strain at the time of necking and fracture to show the range from necking to fracture of the forming limit diagram. It is expected that it will be possible to present a basis for determining product designs that are closer to breakage than before.

Infuence of Evolution in Anisotropy During Strain Path Change on Failure Limits of Sheet Metals

Kaushik Bandyopadhyay,Shamik Basak,Hongjin Choi,Sushanta K. Panda,Myoung‑Gyu Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

Effects of evolution in anisotropy during plastic deformation under strain path changes on the formability and failure wereinvestigated in the present study. The evolution in anisotropic property of the extra deep drawing steel was considered byimplementing the non-quadratic anisotropic yield function Yld2000-2d as a function of effective plastic strain, and the correspondingforming behaviour in two-step forming processes was analysed. For the strain path effect, pre-strain was appliedunder biaxial mode using Marciniak in-plane stretch forming set-up, followed by the secondary deformation using the outof-plane stretch forming tool. For failure prediction of the proposed two-step forming, different failure limit approaches wereinvestigated. First, a strain based forming limit diagram (FLD), proposed as the Marciniak–Kuczynski model was modifiedto include the evolution in anisotropic yield function. The dynamic shift in FLD was also determined by taking strain pathchange into consideration. In addition, the influence of evolution of yield function on the strain path independent failure limitcriteria was also assessed in terms of stress based forming limit diagram. Finally, the prediction accuracy of the failure limitcriteria was compared among different models in terms of failure location and limiting dome height (LDH). It was observedthat the incorporation of evolution in anisotropic yield surface improved the prediction of formability in terms of the LDHand strain distribution for the investigated material.

연소기 노즐목부 내피 벌징공정에 대한 소성불안정이론 기반 성형성 평가

허성찬(Seongchan Heo),유철성(Chulsung Ryu),이금오(Keumoh Lee),최환석(Hwanseok Choi) 한국추진공학회 2019 한국추진공학회 학술대회논문집 Vol.2019 No.5

재생냉각형 로켓 엔진용 연소기 노즐목부 내피의 다단벌징공정에 대한 성형성 평가를 수행하였다. 가공경화재료 거동을 가정한 동합금 내피에 대한 성형성 평가 기준으로 소성불안정 이론을 기반으로 한 이론적 성형한계변형률선도를 이용하였다. 다단벌징공정에 대한 수치해석을 수행하였으며 성형한계선도에 적용하기 위한 주변형률 분포를 도출하였다. 상기 결과로부터 스피닝 공정을 통해 제작된 내피는 벌징공정에 있어서 이론적 성형한계 대비 충분한 안전여유를 갖는 것으로 확인되었다. In this article, formability evaluation for the multi-stage bulging process of a nozzle throat inner liner used in the combustion chamber of a regenerative cooling type rocket engine had been carried out. Theoretical forming limit strain diagram based on the plastic instability theory with the assumption on work-hardening material behavior of the copper alloy was adopted as a formability evaluation criterion. Numerical simulation of the bulging process was conducted and the principal strain distribution was obtained for application to the forming limit diagram. From the result, it was verified that the inner liner manufactured through the spinning process had enough safety margin with regard to the forming limit during the forming process.