Formability of Al Alloy Sheets in Actual Autobody Stamping

(Received on September 8, 1994)

Naotake YOSHIHARA, Kenji ARAKI, Hajime FUKUMOTO and Tadashi FURUBAYASHI

The relation between formability and mechanical properties of Al alloy sheets for autobody panels is investigated by means of a stamping test conducted on an actual front fender and the following results are obtained. (1) Wrinkling is controlled by yield stress a y, i.e., a lower yield stress leads to a lower critical blank holder force for wrinkling. (2) Fracture is controlled by tensile strength ƒÐ t, i.e., a higher tensile strength leads to a higher critical blank holder force for Fracture. (3) The range of blank holder force in which a perfect panel is obtained can be evaluated from the yield ratio ƒÐ y/ ƒÐ t, and it was found that a lower yield ratio leads to a wider range of blank holder force. (4) Shape fixability of aluminum alloy sheets is dependent on the yield stress; better shape fixability results from a lower yield stress. (5) Springback in bending is caused by a nonuniform stress distribution in the thickness direction. This however does not relate to the shape fixability in our examination on fender panels both of aluminum alloy and steel sheets. Instead the effect of in-plane elastic recovery should be taken into account. (6) The ratio of flow stress or K at point K of the panel where springback is measured, to elastic modulus E ( ƒÐ K/E) is a suitable measure of springback for both Al alloy and steel sheets. These results are taken into consideration in the forming of Al alloy automotive body panels.

Keywords:sheet metal forming, nonferrous metal, aluminum alloy, formability, shape fixability, wrinkle,fracture.



Flow Behavior of Zirconia and Stainless Steel Powder- Binder Compounds in Extrusion

(Received on October 27, 1995)

Zhongchun CHEN, jian-Xin XIE, Tadasu MURAKAMI and Keisuke IKEDA

The flow behavior and the relationship between flow and forming load in the extrusion of powder- binder compounds are investigated. The flow is observed using a split tool assembly. ZrO2 and stainless steel (SUS304L) powders with different particle sizes are used, and the binder is water-soluble hydroxypropyl methylcellulose (HPMC). For ZrO2 powder-binder compounds, the extrusion load increases abruptly before extrusion because the powders are compacted. When a critically densified state is approached, the shear increases rapidly and macroscopic slip occurs. Because of this flow behavior, there is a peak in the load vs. stroke curve for the extrusion of ZrO2 powder-binder compounds. For SUS304L powder-binder compounds, at the initial stage of extrusion, flow begins in a restricted area near the die exit before the formation of a dead zone, and the flow range is gradually broadened as extrusion continues. It is shown that the serration in the load vs. stroke curves results from macroscopic discontinuous slip inside the compound and friction between the billet and the tools in contact with the billet. Disordered flow occurs near the die exit, and inhomogeneous flow is promoted if a short die land is used. Therefore, it is necessary to use a longer die land for powder extrusion than for metal extrusion in order to obtain sound extrudates.

Keywords: extrusion, forming, flow, ZrO2, stainless steel, powder, binder.



Effect of Particle Size Distribution on Extrusion Characteristics of Stainless Steel Powders Containing Binder

(Received on October 27, 1995)

Zhongchun CHEN, jian-Xin XIE, Tadasu MURAKAMI and Keisuke IKEDA

The effect of particle size distribution on the extrusion characteristics of stainless steel powders (SUS304L) containing a binder is investigated. The mean particle sizes of the SUS304L powders are 5, 9 and 36 ƒÊm and water-soluble hydroxypropyl methylcellulose (HPMC) is used as the binder. It is shown- that the extrusion pressures in both conventional rod extrusion and multi-billet extrusion are lower for bimodal mixed powders with wider particle size distributions, than for individual coarse or fine powders. For a given binder content, the extrusion pressure is a minimum and the green density is a maximum at a composition of approximately 50% fine powder. In addition, the bigger the particle size ratio in a bimodal mixed powder, the lower the extrusion pressure. The results suggest that it is possible to obtain sound extrudates with a small amount of binder in the extrusion of mixed powders. However, the amount of binder needed in the multi-billet extrusion process is higher than that in the rod extrusion process, due to the different forming conditions of the two processes and the higher extrusion pressure in multi-billet extrusion. Although bimodal mixing can improve the green density, the sintered density and linear shrinkage are smaller than those of fine powders.

Keywords:extrusion, multi-billet, particle size distribution, bimodal mixing, stainless steel powder, binder.



Forging Die Design Using Forging Simulator

(Received on April 1, 1995)

Yasuhiko SATO, Kazuhito YAMAMOTO, and Shigefumi KIHARA

The Steam turbine blades require high precision in manufacture. The load and the metal flow pattern in the forging process have to be predicted in order to find the optimum die design. A new CAD/CAM and CAE system for forging die design was developed. The system is very user-friendly and yields a reliable solution without the need for a highly specialized technique for obtaining numerical convergence and accuracy. We describe the advantages of this system based on a particle flow model arid show an example of applying die design in titanium steam turbine blade forging.

Keywords: forging,titaninum turbine blade, particle flow model, CAD/CAM, CAE, die design



Elimination of Longitudinal Curvature of Product Formed by Press Brake

(Received on August 21, 1995)

Hiroshi ONA

When a narrow steel sheet is formed into a V shape by a press brake, the formed products have defects termed "longitudinal curvature". A few methods to correct the curvature are adopted in press brake apparatus. These methods, however, are not sufficient to obtain products without longitudinal curvature. In this work a new experimental apparatus which can control the curvature is proposed and tested. The experimental results are as follows. (1) The principle of this new apparatus consists of moving the die in the longitudinal direction during the forming process. (2) Moving the die results in friction force on the plate surface, and positive curvature of the products is corrected by a negative bending moment given by the product of the friction force and thickness of the plate. (3) Both the arrangement of the split die and the magnitude of displacement affect the curvature and the flange bend angle of products.

Keywords: press brake, reduction of longitudinal curvature, split die, improvement of press brake.



Ultrasonic Welding of Glass-Fiber-Reinforced Thermoplastic and Its Application

(Received on October 17, 1995)

Shin-ichi MATSUOKA

The characteristics of glass-fiber-reinforced plastic are influenced greatly by the type of matrix, the type or shape of the fiber and the method of reinforcement. We report the possibilities of ultrasonic welding, the characteristics of the joint strength and the workability of the welded products. Two kinds of fiber-reinforced plastic produced by different manufacturing processes are compared. The author has studied the effectiveness and characteristics of ultrasonic welding of glass-fiber- reinforced plastics produced by the paper-making method and the impregnation method, having obtained good indications that quick and easy welding is possible using this method, and that the welding process can be applied to other materials. In both of the materials investigared, the welding time can- be shortened by increasing the welding pressure while maintaining a constant amplitude. In the present tests, the weld strength can be increased to some extent by increasing the amplitude, without significantly charging other characteristics. The weldability is good and the weld strength is stable when using material produced by the paper-making method.

Keywords:Joint, Ultrasonic welding, Glass-fiber-reinforced plastic, Bending, Weld strength, Paper-making method, Impregnation method.