A NUMERICAL STUDY OF PARAMETERS GOVERNING AN INHERENT DEFORMATION DATABASE OF PLATES FORMED BY LINE HEATING Adan Vega, Hisashi Serizawa, Sherif Rashed and Hidekazu Murakawa Joining and Welding Research Institute, Osaka University, Ibaraki, Osaka, Japan Key Words: Plate forming, Line heating, inherent deformation database, FEM. INTRODUCTION An automatic plate bending process which has been successfully used in ship plates forming was proposed by [1]. However, to fully automate this process and minimize the work and re-work, accuracy improvements are necessary. As an overall strategy to improve the accuracy of the forming process, the authors pay attention to those factors which may influence the inherent deformation of plates formed by line heating. In order to identify those factors, we numerically analyze the inherent deformation produced by single heating lines and compare it with that obtained by different combination of multi-heating lines under different heating and cooling condition and applied over plates with different geometries. Based on acknowledge obtained from this study, the influential factors on inherent deformation are identified and its influence clarified. LINE HEATING INHERENT DEFORMATION Generally, plate deformation is classified into longitudinal shrinkage (δ xx ), transverse shrinkage (δ yy ), longitudinal bending (θ xx ) and transverse bending (θ yy ). These four components of inherent deformation can be determined as follows, ∫ = h / dydz p xx xx ε δ (1) ∫ = h / dydz p yy yy ε δ (2) ∫ − = dydz z p xx xx ) 12 / h /( ) 2 / h ( 3 ε θ (3) ∫ − = dydz z p yy yy ) 12 / h /( ) 2 / h ( 3 ε θ (4) Where h is the plate thickness. PREDICTION OF INHERENT DEFORMATION THROUGH FEM In order to create an accurate inherent deformation database, it is important to evaluate the effect of each influential factor on prediction accuracy. However, the influences of these factors are not so simple that they can be linearly related. Also, it is difficult to obtain these influences by experiments because of the large scatter in test results. It is necessary to understand the relationship between applied heat, influential factors, and plate deformation in order to develop a fully automated line heating. To achieve this, numerical simulation of the line heating processes is indeed necessary. Using FEM, the line heating process can be precisely simulated. Meanwhile, we can conveniently study the influence of above mentioned factors on plate deformation. On the other hand, thermal-elastic- plastic FEM requires very long computation time and large memory. To overcome this problem, an in-house three dimensional thermal elastic-plastic finite element code based on an iterative substructure method [2] is employed in this research. INFLUENTIAL FACTORS AFFECTING INHERENT DEFORMATION Heat-induced deformation is affected by many complex and uncertain factors that make it difficult to obtain accurate predictions required by automatic forming systems. In order to identify important factors affecting inherent deformation, first let us analyze the example of analysis results shown in Figure 1 which presents the inherent transverse shrinkage distribution along the heating line. A primary factor influencing inherent deformation is the heating method. The four components of inherent deformation are strongly related to variables such as the heat input, size of the heating zone and the heating source speed. Inherent deformation almost proportionally increases with the heat input and decreases with the heating source speed. Cooling method is another important factor. Inherent deformation is directly dependent on the rate of cooling. Rate of cooling can be increased by using water leading to an increase of transverse shrinkage and a slight decrease of longitudinal shrinkage. The location and area of application of water cooling affects all 4 components of inherent strain. Also, increasing the rate of cooling, the variation on inherent deformation along the heating line decreases. As shown Fig. 1, inherent transverse shrinkage varies along the heating line. At and near both the entrance and the exit edges (regions L 1 and L 3 ), inherent deformation is smaller than that in the middle region of the plate (L 2 ). The same tendency can be observed in the other three components of inherent deformation. The variation of inherent deformation at and near the edges from the maximum inherent deformation near the middle of the plate is another important factor known as the edge effect. When the same heating line is applied close to one side of the