Kunihiro Hashimoto

Pressing Control Design Based on Analysis of Metal Temperature and Flow in Sand Mold Press Casting

The sand mold press casting method is a novel iron casting process, which has developed by our group in recent years. The proposed method can cast iron into complex shapes with a high yield over 90% and produces high-quality products by filling control of molten metal during pressing motion. However, molten metal inside mold is cooled down by heat transfer to the molds and atmosphere, and often causes solidification before the end of press. Then, the pressing movement of the upper mold is blocked by the solidified metal. Therefore, to avoid the solidification during pressing sand mold, metal temperature must be heated properly to estimate the filling temperature decrease behavior based on analysis results of CFD simulator, FLOW-3D. The necessary condition not to solidify molten metal before the end of press has been found. It was made clear that the mold must be heated up to the necessary temperature beforehand in the pressing process. Furthermore, optimum velocity reference with specified pressure constraints has been designed to prevent casting defect such as penetration and also to minimize the temperature decrease. In this paper, optimum velocity control of servo cylinder considering the both of allowable pressure of molten metal and starting time of solidification is proposed by using a theoretical approach of Model Predictive Control: MPC method. The effectiveness of the proposed control system has been demonstrated by computer simulation and experiments using a laboratory scale machine with molten metal of casting iron.

Molten Metal Pressure Control for Defect Prevention with Generalized Predictive Control in Rapid Press Casting

Abstract This paper presents a technique for controlling the pressure of molten metal when using a new type of the iron production method called greensand mold press casting to realize high productivity and obtain high-quality castings. In this method, molten metal is poured into a lower mold first, and the after upper mold is moved down toward the lower mold, then both molds are matched. Casting defects such as metal penetration are often caused by the high pressure in the high-velocity pressing process. Therefore, we proposed a pressure control method with a mathematical model of molten metal pressure, and with it we achieved confirmation simulation of the successful pressing production at the different pressing condition such as mold shape. Results show that the proposed pressing production considering the generalized predictive control: GPC can realize sound, penetration-free casting production under the pressure constraint for defect prevention. Here a simple simulation of model predictive pressing control and water pressing experiment using feed-forward motion input calculated by off-line GPC are presented. Discussions of the theoretical control design for the process as well as its practical confirmation result of water pressure behavior in pressing experiment are concluded.

Sand Mold Press Casting with Metal Pressure Control System

A new casting method, called the press casting process, has been developed by our group in recent years. In this process, the ladle first pours molten metal into the lower (drag) mold. After pouring, the upper (cope) mold is lowered to press the metal into the cavity. This process has enabled us to enhance the production yield rate from 70% to over 95%, because a sprue cup and runner are not required in the casting plan [1]. In the casting process, mol‐ ten metal must be precisely and quickly poured into the lower mold. Weight controls of the pouring process have been proposed in very interesting recent studies by Noda et al. [2]. However, in the pressing part of the casting process, casting defects can be caused by the pattern of pressing velocity. For example, the brake drum shown in Fig. 1 was produced with the press casting method. Since the molten metal was pressed at high speed, the prod‐ uct had a rough surface. This type of surface defect in which molten metal seeps through sand particles of the greensand mold and then solidifies, is called Metal Penetration. Metal penetration is most likely caused by the high pressure that molten metal generates, and it necessitates an additional step of surface finishing at the least. Thus, the product quality must be stabilized by the suppression of excess pressure in the high-speed press. For shortcycle-time of production, a high-speed pressing control that considers the fluid pressure in the mold is needed. Pressure control techniques have been proposed for different casting methods [3-4]. In the injection molding process, the pressure control problem has been suc‐ cessfully resolved by computer simulation analysis using optimization technique by Hu et al. [5] and Terashima et al. [6]. Furthermore, a model based on PID gain selection has been proposed for pressure control in the filling process. Although the pressure in the mold must be detected in order to control the process adequately using feedback control, it is difficult

Modelling and Control of Pressurized Molten Metal in Press Casting

Abstract This paper presents a modeling and control of molten metals pressure in a pressing process using an innovative iron casting developed by our group. In this method, molten metal is directly poured into the lower mold, and then pressed to fill the cavity by the upper mold being lowered down. For the complex liquid flow during pressing, the liquids pressure change inside vertical path with various contraction and expansion geometries is newly modeled via the unstationary Bernoulli equation. The mathematical model is derived for a control design of pressing. To conduct the pressing velocity design algorithm, an unknown parameter of proposed model considering viscous flow is identified by using CFD: Computational Fluid Dynamics model with heat flow calculation. Control performance using a multi-switching velocity pattern is confirmed as an effective control design using the pressure model, because the pressure fluctuation has discontinuous variation points. Substituting detailed information for mold shape, poured volume and initial temperature into a developed control input generator, an optimum pressing velocity design and a robust design for defect-free production are proposed by the design algorithm based on the construction of an inverse system comprised of the sequential switching from higher to lower speed. Consequently, the effectiveness of the pressing control with reasonable pressure suppression has been demonstrated through the CFD simulation.

Optimum Pressure Control of Molten Metals for Casting Production Using a Novel Greensand Mold Press Casting Method

This paper presents a novel method of sand mold press casting. In this process, molten metal is poured into a drag mold, and then the cope mold is placed on top of the drag mold, and the two molds are matched. The mold design for casting, the pouring control and the velocity control of the press have been previously clarified as key factors in the manufacture of sound products. This paper presents methods for modeling and control of the molten metal’s pressure for novel sand press casting technique. Substituting detailed information for the complex mold shape, the poured volume and initial temperature into a developed control input generator, an optimum pressing velocity design and a robust design for defect-free production are proposed by the sequential control algorithm based on the construction of an inverse system comprised of a sequential switching from higher to lower speed. The effectiveness of adaptive press casting is demonstrated by using CFD model simulations.

Pressing Velocity Control Considering Liquid Temperature Change in Press Casting

Abstract To newly create the sand casting method to drastically improve productivity and casting quality, authors group has actively developed advanced control technology in foundry. In high-speed filling of the press casting process using greensand mold, some defects are caused by increased pressure of molten metal, such as metal penetration which the solidified molten metal flows into between the sand particles. Hence, we will propose controlling the pressing velocity in order to suppress increasing pressure. Considering pressure constraint for a defect-free product, control velocity pattern is then derived by using proposed mathematical model of molten metals pressure in the mold. The simple pressure model is derived by considering the wall shearing stress depended on molten metals temperature to accurately represent actual pressure behavior during pressing. Analytical results for the liquid temperature decrease during filling and its consideration for the pressing control are mentioned in this paper. The effectiveness of control result using the model is checked by CFD: Computational Fluid Dynamics simulations. In near future, experimental examinations will be carried out by practically using water and molten metal.