Key Engineering Materials Vols. 340-341

Abstract: This paper describes the effect of tool modeling accuracy on the accuracy of springback simulation in sheet metal forming. Simulations of a two-dimensional draw-bending process are carried out by using the polyhedral tool model and the model whose surface is smoothed by quadratic parametric surfaces proposed by Nagata [1]. It is found that the tool modeling, especially the normal vector accuracy in the present model, plays an important role in the prediction not only of deformation but also of stress distribution. The simulated results show that the tool model based on the so-called Nagata patch enables a more accurate and efficient simulation.

Abstract: Resistance heating performance in some shaped blanks of high-strength steel sheet is examined by experiment and FE simulation, and the feasibility and effectiveness of the application of resistance heating to the hot press forming of high-strength steel sheet are discussed. The followings are made clear through this study. (1) A uniformly distributed current density is essential to uniform blank heating. (2) For a certain shaped blank, no matter how the electrodes are disposed, uniform blank heating is difficult. (3) A blank shape suitable for uniform heating by a single pair of parallel electrodes is restricted to a rectangle.(4) In case a uniformly heated blank is required, two-piece simultaneous forming with point-symmetric die layout is recommended from the viewpoint of material utilization.

Abstract: During lumber rolling, a fixation device is typically installed just behind the work roll to set up the delivery thickness and to fix the thickness reduction. However, the accompanying resistance force into the fixation device can cause slippage between the roll and material, indicating a bound for the rolling conditions. Slippage can be avoided by decreasing the resistance force or by adding a pushing force on the lumber from the entry side of the rolling mill. This paper experimentally investigated the effects of these horizontal forces on the rolling force and roll torque. From these results, the roll torque was found to be directly affected by the horizontal forces, but the rolling force was not affected. Secondly, a new parameter μeq was introduced and a condition of non-slippage, in which μeq must be less than the coefficient of static friction to avoid slippage, was proposed. This condition was then used to predict and to protect against slippage by identifying when this condition was violated and then applying a horizontal force to decrease μeq.

Abstract: The wall thickness around an inner corner in 3-stages formed cups with a flange was increased by means of conical punches in the 1st and 2nd stages. Since the strength of the formed cups is greatly improved by the increase in wall thickness, the weight of the formed products is reduced by an optimum distribution obtained from the increase in wall thickness. The increase in thickness around the inner corner is obtained by compressing the side wall and conical bottom of the cup in the 3rd stage. As the punch angle increases, the increase in thickness at the inner corner becomes large. The amount of compression is expressed by a drawn volume after the 2nd stage. A maximum 9% increase in wall thickness around the inner corner was successfully obtained for the punch angle of 25º.

Abstract: In this study, a new simulation-based design technique for multi-stage metal forming process is developed with special emphasis on reduction of stages in the process. The developed design technique is an iterative design optimization, which is based on response-surface-based numerical optimization and finite element analysis of the process. The design procedure starts with the initial rough process design. To eliminate one stage in the multi-stage process, the new optimum process design is determined based on the former process design by using numerical optimization in conjunction with FE simulation. This design optimization step is repeated, reducing the stages one by one, until the possible minimum number of stages is reached. The developed design technique is applied to stage reduction of a 3-stage axisymmetric forging process of aluminum billet. We can confirm that a new 2-stage process design is determined successfully and the developed design optimization technique is effective to reduce stages in multi-stage forming process.

Abstract: A forming sequence of one-piece automobile steel wheels without welding was designed. In this forming process, the one-piece wheel was formed from a circular blank only by multi-stage stamping operations, and a deeply drawn cup was formed into the wheel. Two humps of the rim flange for fixing the tire were formed in the flaring and flanging stages. The humps of the rim in the opening and outer side were formed by buckling the inner flange of the rim, and by swelling the outer flange with an upper die having a short land, respectively. In addition, the number of stages was considerably reduced from 16 stages to only 9 stages by combining the deep drawing and ironing stages and by adding a holding die in the flaring stages. The forming sequence of the one-piece wheels was evaluated by both finite element simulation and miniature experiment.

Abstract: Dynamic recrystallization, on which grain size of the final forging depends mainly, is one of the most important microstructure evolution processes in moderate-to-low stacking fault energy metals. In this paper, the process of dynamic recrystallization is simulated by numerical method. The paper first gives a visco-plastic model considering dynamic recrystallization in detail; secondly gives the applied finite element formulation and compiles an finite element program in Visual Fortran 6.5 based on the updated Lagrangian formulation rigid-plastic finite element; thirdly the material parameters are identified through inverse analysis, based on the compiled finite element program and the developed global optimization method; at last, the compiled finite element program is applied to simulate the microstructure evolution caused by dynamic recrystallization, the calculated result agrees with the experimental result relatively well.

Abstract: Recently it has been demonstrated that the classical Prandtl/Reuss theory based on the additive split of the deformation rate contrary to what is believed so far is possible to establish a consistent Eulerian rate formulation for finite elastoplasticity. Here, we attempt to place this Eulerian formulation on the thermodynamic grounds by extending it to a general case with thermal effects.

Abstract: The mi c ros copi c pl as t i c de format ion behavior of pol yc r ys t al l ine aluminum shee t dur ing uni axi al t ens ion i s exper iment al l y inves t iga t ed b y a confoc al l a s e r - s canning mi c ros cope. The gr ain rot at ion i s me asur ed f rom images of spec imen sur fa c e be fore and a f t e r deformat ion i s propos ed. Digi t al image proc es s ing t e chnique i s appl i ed to the sur f a c e gr ain image t aken by the CCD c ame ra . The exper iment al dat a obt ained f rom man y gr a ins a re s t a t i c al l y proce s s ed. I t i s shown that the gr ain rot at ion i s l a rge when the shape of gr ain i s clos e to a ci r cl e. Di s cus s ions a r e made on the r el at ion be twe en gra in rot at ion, s t ra ins of gr ains and va r ious f a ctor s af f e ct ing them, such as gr ain s i z e, gra in shape and s l ip- l ine angl e.