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.

점진성형에서 형상 정밀도에 영향을 미치는 공정 변수

강재관(Jae Gwan Kang),정종윤(Jong Yun Jung) 한국산업경영시스템학회 2015 한국산업경영시스템학회지 Vol.38 No.4

Incremental sheet metal forming is a manufacturing process to produce thin parts using sheet metals by a series of small incremental deformation. The process rarely needs dedicated dies and molds, thus, preparation time for the process is relatively short as to be compared to conventional metal forming. Spring back in sheet metal working is very common, which causes critical errors in dimensions. Incremental sheet metal forming is not fully investigated yet. Hence, incremental sheet metal forming frequently produces inaccurate parts. This paper proposes a method to minimize dimensional errors to improve shape accuracy of products manufactured by incremental forming. This study conducts experiments using an exclusive incremental forming machine and the material for these experiments are sheets of aluminum AL1015. This research defines a process parameter and selects a few factors for the experiments. The parameters employed in this paper are tool feed rate, tool diameter, step depth, material thickness, forming method, dies applied, and tool path method. In addition, their levels for each factor are determined. The plan of the experiments is designed using orthogonal array L8 (27) which requires minimum number of experiments. Based on the measurements, dimensional errors are collected both on the tool contacted surfaces and on the non-contacted surfaces. The distances between the formed surfaces and the CAD models are scanned and recorded using a commercial software product. These collected data are statistically analyzed and ANOVAs (analysis of variances) are drawn up. From the ANOVAs, this paper concludes that the process parameters of tool diameter, forming depth, and forming method are the significant factors to reduce the errors on the tool contacted surface. On the other hand, the experimental factors of forming method and dies applied are the significant factors on the non-contacted surface. However, the negative forming method always produces better accuracy than the positive forming method.

Two-stage forming approach for manufacturing ferritic stainless steel bipolar plates in PEM fuel cell: Experiments and numerical simulations

Bong, Hyuk Jong,Lee, Jinwoo,Kim, Jong-Hee,Barlat, Fré,dé,ric,Lee, Myoung-Gyu Pergamon Press 2017 International journal of hydrogen energy Vol.42 No.10

<P><B>Abstract</B></P> <P>Multi-stage micro-channel forming by stamping, as a method for cost effective and efficient for mass production, was performed for ultra-thin ferritic stainless steel sheets with thicknesses of 0.1 and 0.075 mm, as a good substitute for traditional graphite bipolar plates of proton exchange membrane fuel cell. Attention was directed to enhance the final forming depth and minimize localized thinning, extremely important aspects of the micro-channel on bipolar plate, by the proposed forming process. A forming depth at the first forming stage was chosen as a process variable, and its effect on the formability of the micro-channel at the second forming stage was experimentally investigated. Finite element simulations for the two-stage forming process were conducted to optimize the punch radius and forming depth at the first stage for improving the formability. The comparative study between the simulations and the experimental results could validate improvements in the formability by the proposed approach. In particular, this study could support the existence of an optimum forming depth at the first forming stage. Based on the simulation results, a mathematical model was established to identify the dominant factor needed for formability improvement and to propose a methodology for the process optimization of the multi-stage forming.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formability of ultra-thin sheet is improved by two-stage forming. </LI> <LI> Finite element simulation is agreed well with the experiments. </LI> <LI> A simple phenomenological model is proposed for optimization of two-stage forming. </LI> </UL> </P>

Modeling, Testing and Numerical Simulation on Hot Forming of HSS

Ning Ma Ping Hu,Guozhe Shen Wenhua Wu 한국소성가공학회 2010 기타자료 Vol.2010 No.6

The thermal-mechanical-transformation coupled relationship of microalloy steel has important significance in forming mechanism and numerical simulation of hot forming. Tensile and quenching experiments are implemented at high temperature, and then the thermal-mechanical-transformation coupled constitutive models of hot forming are developed. Based these models, the nonlinear large-deformation dynamic explicit finite element equations are proposed. The phase transformation latent heat is introduced into the analysis of temperature field during the hot forming process. Based on the independently developed commercial CAE software for sheet metal forming, named KMAS (King-Mesh Analysis System), the numerical simulation module of hot forming is developed, which considers multi-field coupled models, nonlinear and large deformation analysis. Then the hot forming process of a reinforced beam inside the automobile door is simulated by the KMAS software, and compared with its hot forming experimental testing. The experimental results indicate the validity and efficiency of the present multi-field coupled constitutive models and numerical simulation software KMAS of hot forming.

AL1050 소재의 양·음각 점진성형 공법간 성형 정밀도 비교

이경부(Kyeong-Bu Lee),오현만(Hyun-Man Oh),강재관(Jae-Gwan Kang) 한국생산제조학회 2013 한국생산제조학회지 Vol.22 No.5

Incremental forming of sheet metal is a modern method of forming sheet metal, where parts can be formed without the use of dedicated dies. Existing experimental configurations for incremental forming can be broadly classified into two categories, i.e., negative and positive forming. In this paper, forming qualities such as shape accuracy and surface roughness of Al 1050 material were discussed for different forming methods. The formed and the corresponding opposing surfaces were measured with a three-dimensional scanner and a surface roughness tester. It was found that in terms of shape accuracy, the best opposing surface was obtained with positive forming, whereas the worst formed surface was obtained with negative forming; furthermore, the opposing surface is always better than the formed surface, regardless of the forming method used.

고압 튜브를 위한 전후방 유동성형에서의 성형력에 관한 연구

남경오(Kyoungo Nam),염성호(Sungho Yeom),홍성인(Sungin Hong) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

The flow forming, also known as tube spinning, has been used to produce long thin walled tube parts, with reduced forming force and enhanced mechanical and surface quality for a good finished part, compared with other method formed parts. As the tool is applied locally on the workpiece, the total forming forces are reduced significantly compared to other forming method. Spinning and flow forming techniques are used frequently in automotive, aerial, space, defense industry. In flow forming, forward and backward flow forming methods are classified in accordance to their direction of axial flow during the process. For forward flow forming, the material flows in the same direction as that of the traversing rollers. This method is suitable for making high precision thin walled cylinders, such as hydraulic cylinders, high-pressure vessels, launcher tubes and combustion chamber. For backward flow forming, spun material flows under the roller in the opposite direction of the roller towards the unsupported end of the mandrel. In this paper, finite element method analysis of three-roller forward and backward flow forming for high pressure tube is carried out to study effects of forming depth and feed rate on forming force. The axial and radial forming forces of forward flow forming on several forming depth and feed rate conditions are compared with those of backward flow forming.

Crash Simulation of Roll Formed Parts by Damage Modelling Taking Into Account Preforming Effects

Edwin T. Till,Benjamin Hackl,Hermann Schauer 한국소성가공학회 2011 기타자료 Vol.2011 No.8

Complex phase steels of strength levels up to 1200 ㎫ are suitable to roll forming. These may be applied in automotive structures for enhancing the crashworthiness, e. g. as stiffeners in doors. Even though the strain hardening of the material is low there is considerable bending formability. However ductility decreases with the strength level. Higher strength requires more focus to the structural integrity of the part during the process planning stage and with respect to the crash behavior. Nowadays numerical simulation is used as a process design tool for roll-forming in a production environment. The assessment of the stability of a roll forming process is quite challenging for AHSS grades. There are two objectives of the present work. First to provide a reliable assessment tool to the roll forming analyst for failure prediction. Second to establish simulation procedures in order to predict the part’s behavior in crash applications taking into account damage and failure. Today adequate ductile fracture models are available which can be used in forming and crash applications. These continuum models are based on failure strain curves or surfaces which depend on the stress triaxiality (e. g. Crach or GISSMO) and may additionally include the Lode angle (extended Mohr Coulomb or extended GISSMO model). A challenging task is to obtain the respective failure strain curves. In the paper the procedure is described in detail how these failure strain curves are obtained using small scale tests within voestalpine Stahl, notch tensile?, bulge and shear tests. It is shown that capturing the surface strains is not sufficient for obtaining reliable material failure parameters. The simulation tool for roll-forming at the site of voestalpine Krems is Copra® FEA RF, which is a 3D continuum finite element solver based on MSC.Marc. The simulation environment for crash applications is LS-DYNA. Shell elements are used for this type of analyses. A major task is to provide results of the roll forming simulation as initial conditions for the crash model, taking over the shell thickness, the variation of the plastic strain and the damage parameter over the profile. This is realized by a python [13] interface program. Profiles are manufactured by the roll forming facility in Krems with a complexphase steel grade of 980 ㎫ strength. The final samples are manufactured using the profiled parts with cover plates fixed to them by spotwelds. Axial crash experiments are carried out using the inhouse horizontal crash test facility. It is observed that the component shows good folding behavior with some minor failure sites at edges where there is extensive forming during roll-forming. Simulation runs are made with LS-DYNA using the GISSMO damage model. The results match reasonably well with the experimental results. The simulation tool seems to be useful in order to assess not only the integrity of the roll-forming process but also to adequately predict the crash behavior of roll-formed components. Some suggestions are made in order to improve the simulation of the evolution of damage after initiation in the future.

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.

Deformation analysis and shape prediction for sheet forming using flexibly reconfigurable roll forming

Yoon, J.S.,Kim, J.,Kang, B.S. Elsevier 2016 Journal of materials processing technology Vol.233 No.-

<P>Demand for three-dimensional (3D) curved sheet metals for the manufacture of the skin structures used in various industrial fields continues to increase. Three-dimensional curved sheet metals have generally been manufactured using conventional die forming (CDF) processes, which can ensure forming quality and productivity. However, they are not economically efficient since they incur the additional production costs associated with the development and maintenance of the forming tools. For these reasons, many investigations into alternative flexible forming technologies have been conducted. Flexible forming technologies requiring only one forming die enable the manufacture of 3D curved components while simultaneously resolving the limitations of CDF processes. In this paper, a progressive forming process called 'flexibly reconfigurable roll forming' (FRRF), which utilizes adjustable punches and reconfigurable rollers as forming tools, is discussed, together with its detailed mathematical methodology. Using this methodology, curved shapes as well as arcs can be created by adopting conic section curves. This method is superior to existing flexible forming technologies. In this process, the formed shapes are not intuitively predictable since two-dimensional design lines corresponding to the reconfigurable rollers produce a 3D curved surface. To alleviate this limitation, a new predictive model for predicting the deformed shapes of the sheet metal, as derived from the mechanics of plastic deformation considering the law of volume constancy, is described with detailed techniques using a geometrical relationship. The experimental results also demonstrate that the predictive model for the FRRF process can be used to successfully ascertain the deformed shapes of the sheet metal. (C) 2016 Elsevier B.V. All rights reserved.</P>

Al6061 판재성형에서 핫 포밍 퀜칭의 성형성 및 기계적 특성 평가

고대훈(Dae Hoon Ko),김재홍(Jae Hong Kim),이찬주(Chan Joo Lee),고대철(Dae Cheol Ko),김병민(Byung Min Kim) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.4

알루미늄 소재의 냉간 판재성형에서는 낮은 성형성과 성형 후 과도한 스프링백에 의한 치수정밀도가 저감되는 문제가 있다. 이에 본 연구에서는 기존 제조공법의 문제점을 개선하기 위해 새로운 제조공법인 Hot forming quenching(HFQ)을 제시하고자 한다. HFQ 은 용체화처리 온도로 가열된 알루미늄 판재를 열간성형하고, 다이 내에 설치된 냉각채널에 의해 퀜칭하여 열간성형과 열처리를 동시에 함으로써 성형성 향상, 스프링백 저감 효과를 얻을 수 있다. 기존의 냉간성형 대비 HFQ 의 성형성 향상효과를 에릭슨 시험을 통해 평가하였다. 스프링백 특성을 파악하기 위해 V-beding 시험에 HFQ 를 적용하여 굽힘 성형된 제품의 치수정밀도를 기존의 냉간성형과 비교하였다. 또한 강도 및 경도를 측정하여 기존 냉간 성형에 의한 값들과 비교함으로써 알루미늄 제품 성형에 HFQ 을 적용하기 위한 타당성을 평가하였다. In aluminum sheet metal forming, the conventional forming methods of T4 or T6 heat-treated sheets result in low formability and dimensional accuracy. This study suggests a new forming method for aluminum sheets called as hot forming quenching (HFQ) that solves the problems faced in the conventional method. HFQ combines the heat treatment and forming processes through the forming die during the quenching of a solid solution. To evaluate the application of HFQ to the sheet forming of aluminum, an Erichsen and V-bending test are performed in this study to measure the dimensional accuracy and formability, which are then compared with those of the conventional forming method. Furthermore, the strength and hardness of the products formed by HFQ are measured to confirm the degradation in mechanical properties compared with the conventional forming method, which shows the validity of the application of HFQ to aluminum sheet metal forming.