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.

Smart Roll Forming Based on Real-Time Process Data

Jae-Hwan Son(손재환),Dong-Hyun Cho(조동현),Chul-Hong Kim(김철홍) 한국기계가공학회 2018 한국기계가공학회지 Vol.17 No.5

Roll forming refers to the production of long plate-molded products, such as panels, pipes, tubes, channels, and frames, by continuously causing the bending deformation to thin plates using rotating rolls. As the roll forming method has advantages in terms of mass production because of its excellent productivity, the size of the roll forming industry has been continuously increasing and the roll forming method is increasingly being used in diverse industrial fields as a very important processing method. Furthermore, as the roll forming method mainly depends on the continuous bending deformation of the plate materials, the time and the cost of the heterogeneous materials developed in the process are relatively large when considered from the viewpoint of plastic working because many processes are continuously implemented. The existing studies on roll forming manufacturing have reported the loss of large amounts of time and materials when the raw materials or product types were changed; further, they have stated that the use of this method can hardly guarantee the uniformity of the formed shapes and the consistency in terms of size and cannot detect all the defects occurring during the mass production and related to the dimensions. Therefore, in this research, a real-time process data-based smart roll forming method that can be applied to multiple products was studied. As a result, a roll forming system was implemented that remembers and automatically sets the changes in the finely adjusted values of the supplied quantities of individual heterogeneous materials so that the equipment setting changing time for heterogeneous material replacements or changes in the products being produced can be shortened. It also secures the uniformity of the products so that more competitive and precise slide-rail products can be mass-produced with improvements in the quality, price, and productivity of the products.

Analysis of a Micro Pattern Forming on the Thin Sheet Metal for Electronic Device

Sung-Hoon Cha,Jong-Bong Kim,Jong-Ho Kim,Hye-Jin Lee 한국소성가공학회 2010 기타자료 Vol.2010 No.6

Roll-to-roll forming process is one of important metal processing technology because the process is simple and economical. These days, roll-to-roll forming process is tried to be employed in manufacturing the circuit board, barrier ribs and electric device panel. However, it is difficult to apply the roll-to-roll forming into the forming of micro scale or sub-micro scale cavities. In this study, the roll-to-roll forming process for the forming of micro scale cavities is designed and analyzed. The electric device panel may have thousands of cavities in periodic arrays. In this case the analysis of forming considering all the cavities is impossible due to the computational costs. Therefore, analyses are carried out for various numbers of cavity arrays. Based on the analysis results, the optimum analysis conditions are found that guarantee the analysis results and computational efficiency. Then the cavity shape is designed in viewpoint of formability. The formability of the designed cavity is predicted in terms of filling ration and damage value. The optimum pitch distance and draft angle are decided considering the Cockcroft-Latham damage value and under-fill defects.

해석을 이용한 마이크로 박판 미세 패턴 성형 설계

차성훈(S.-H. Cha),신명수(M.-S. Shin),김종호(J.-H. Kim),이혜진(H. J. Lee),김종봉(J.-B. Kim) 한국소성가공학회 2009 금형가공 심포지엄 Vol.2009 No.11

Roll-to-roll forming process is one of important metal processing technology because the process is simple and economical. These days, with these merits, roll-to-roll forming process is tried to be employed in manufacturing the circuit board, barrier ribs and solar cell plate. However, it is difficult to apply to the forming of micro scale or sub-micro scale pattern. In this study, the roll forming processing for the micro scale is designed and analyzed. The forming of micro pattern for photovoltaic plate of a solar cell by incremental roll forming process is analyzed. The solar cell plate may have millions of patterns, and the analysis of forming considering all the patterns is impossible due to the computational costs. In this study, analyses are carried out for various numbers of patterns and the results are compared. It is shown that the analyses results with four row patterns and twelve row patterns are same. So, it is considered that the analysis can be carried out for only four rows of pattern for the design of incremental roll-to-roll forming process. Also formability is analyzed for various protrusion shapes at various forming temperatures.

Characterization of the longitudinal bow during flexible roll forming of steel sheets

Woo, Young Yun,Han, Sang Wook,Hwang, Tae Woo,Park, Ji Yeong,Moon, Young Hoon Elsevier 2018 Journal of materials processing technology Vol.252 No.-

<P>Flexible roll forming is an advanced sheet metal forming process that allows for the production of variable cross-section profiles. Longitudinal bow is one of the major shape defects found in roll-formed products. To characterize the degree of longitudinal bow during flexible roll forming, experiments were conducted on three different blank shapes: trapezoid, convex and concave. Symmetric U-sections with variable cross-sections were roll formed using the three sheet materials with different strengths from each blank shape. The effects of process variables on the longitudinal strain and longitudinal bow were analyzed both experimentally and by using finite element simulations based on ABAQUS-Implicit 6.14. The results show that the transversal nonuniformity of the longitudinal strain is one of the fundamental causes of longitudinal bow in roll-formed products. The bow height as a function of blank shape increases in the order of concave, trapezoid, and convex. The bow characteristics on the basis of blank shapes and material parameters provides a better understanding of the non-uniform longitudinal strain and bow height during flexible roll forming with high reliability. Furthermore, to reduce the longitudinal bowing, leveling roll is introduced. The effect of leveling roll on longitudinal bowing was investigated experimentally. The results show that longitudinal bowing was reduced with the use of three blank shapes when leveling roll was applied to a flexible roll forming process.</P>

Research on roll forming process and springback based on five-boundary condition forming angle distribution function

Chunjian Su,Jiazhen Liu,Zexuan Zhao,Shumei Lou,Rui Wang,Longyun Yang 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.12

In the present study, a five-boundary conditional distribution function of the forming angle is proposed. The stress, strain, and springback of a sheet in roll-forming process under three different angle distribution functions are studied. Furthermore, effects of forming angle increment, sheet thickness, and material yield strength on stress, strain distribution, and springback of sheet during roll forming are studied under optimized forming angle. The results demonstrate that stress, strain, and springback of each pass based on increment of forming angle under five-boundary condition during roll forming are less than those achieved by other forming angle distribution methods. The stress and strain in the bending zone increase with increase in the sheet thickness. After roll forming, the springback angle decreases with the increase of sheet thickness, increases with the increase of forming angle and material yield strength. However, springback angle can be effectively reduced by increasing the number of passes or correction rolls.

가변 단면 성형 롤의 반경 증가에 의한 롤 간섭 제거

김광희(Kwang-Heui Kim),윤문철(Moon-Chul Yoon),곽재섭(Jae-Seob Kwak) 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.2

In this study, we investigated whether the interference occurring in forming roll surfaces could be eliminated by increasing the radius of the variable section forming rolls. The surfaces of the rolls capable of forming products with different flange heights and bend angles with the bend line tilted at an angle of 1° from the longitudinal axis were created using the general CAD software CATIA. Roll interferences were determined for the change in the forming roll radius. The minimum gaps between the upper and lower roll surfaces were measured for the change in the forming roll radius, and the roll interferences were calculated from the difference between the measured value and the thickness of the product. It was observed that the thickness of the product had a slight effect on the roll interference when the thickness was between 0.8 and 1.2 mm. It was also observed that the roll interference could be eliminated by increasing the roll radius.

FLEXIBLE ROLL FORMING PROCESS DESIGN FOR VARIABLE CROSS-SECTION PROFILE

B. D. Joo,S. W. HAN,S. G. R. Shin,문영훈 한국자동차공학회 2015 International journal of automotive technology Vol.16 No.1

Roll forming is a continuous bending operation in which a long strip of sheet metal is passed through sets of rolls mounted on consecutive stands, each set performing only an incremental part of the bend, until the desired cross-section profile is obtained. Roll forming technology has been widely used in the automotive industry due to its various advantages, such as high production speed, reduced tooling cost and improved quality. Recently, flexible roll forming process which allows variable cross sections of profiles by adaptive roll stands was developed. In this study, profile design for the hat-channel has been analytically performed on the basis of established longitudinal strain during the flexible roll forming. The effect of geometrical parameters such as base section width, side wall height and flange width on the longitudinal strain was analyzed. The analytical analysis was experimentally verified by lab-scale flexible roll forming machine. The results show that the profile design method preformed in this study is feasible and the parts with variable cross sections can be successfully fabricated with flexible roll forming process.

다단 성형 기술을 이용한 차체 부품 개발

김동규(D. K. KIM),한상욱(S. U. HAN),전형준(H. J. JEON),천세환(S. H. CHEON),문영훈(Y. H. MOON) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5

In roll forming process, a sheet metal is continuously progressively formed into a product with required cross-section and longitudinal shape, such as a circular tube with required diameter, wall-thickness and straightness, by passing through a series of forming rolls in arranged in tandem. In this process, each pair of forming rolls installed in a forming machine play a particular role in making up the required cross-section and longitudinal shape of the product. In recent years, that process is often applied to the Car body part in the automotive industries. In this study, a optimal Sill Side manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle. And also effects of the process parameters on the final shape formed by roll forming defects were evaluated.

롤 포밍 공정에서의 길이방향 변형률 및 직진성 예측

정상화(Sang-Hwa Jeong),이상희(Sang-Hee Lee) 한국기계가공학회 2007 한국기계가공학회 춘추계학술대회 논문집 Vol.2007 No.-

Cold roll forming can be described basically as a process where a metal sheet is continuously formed in the transverse direction into a product with a desired cross-sectional profile by passing a series of pairs of forming rolls. However, process analysis is very difficult because deformation procedures are quite complex and have many variable. The cold-roll forming has been mostly developed through the experimental knowledge. In order to overcome this difficulty, the roll forming process for manufacturing the under rail is analyzed using a new computational method based on the rigid-plastic finite element. In this paper, the roll forming process of the lower member at under rail is simulated using simulation software. Tensile test is performed about SCP-1 to obtain material properties and curve fitting is executed to set up the flow stress equation. The lower member is designed using the constant arc length forming method and the constant radius forming method for excellent design. The longitudinal strain is estimated on the basis of simulation results. In addition, the numerical magnitudes of camber and bow are predicted from the results of the simulation