Z.R. Wang

Mechanical analysis on the cylinder-crown integrated hydraulic press with a hemispherical cylinder

As a new press, cylinder-crown integrated hydraulic press (CCIHP) is analyzed firstly in this paper. The hydraulic cylinder consists of a hemispherical shell, which also functions as a main proportion of press crown. Compared with the conventional hydraulic press which has a hydraulic cylinder mounted in the press crown, the structure and force distribution of CCIHP are significantly different. First, the section modulus of the hemispherical crown is much larger than that of the conventional rectangle crown because the hydraulic cylinder and press crown are manufactured into a solid part and have a higher geometry centroid. Therefore, the hemispherical crown has lower tensile bending stress and a higher safety factor from the strength point of view when the same bending moment is applied. Second, under the conditions of same value in terms of the allowable stress, internal pressure and internal radius, the wall thickness of hemispherical hydraulic cylinder could be much thinner than that of the conventional hydraulic cylinder. Both of the reasons mentioned above can result in a weight reduction of the press. Also, the cylinder and the press crown can be reinforced by each another, as a result, the material strength capacity is better utilized. As a prototype, the 6300 kN CCIHP with hemispherical hydraulic cylinder, which is the first one of this kind press designed and manufactured by Harbin Institute of Technology (HIT) is introduced in this paper. Finite element analysis for CCIHP has shown that both the stress and displacements on the press during the loading process are allowable, even if eccentric force is loaded. Finally the priority application range of CCIHP has also been proposed.

Research on hydroforming tubular part with large perimeter difference

The tube hydroforming process for manufacturing the tubular part with large perimeter difference was studied by means of experiments and FE simulation. It is an asymmetrical one and the expansion ratio is 70 percent. The part is successfully hydroformed by applying the useful wrinkles to accumulate sufficient metal in the area with large expansion ratio. The thickness distribution is analyzed, and the maximum thinning ratio of the part is 21.6 percent. It is shown from the experiment and simulation results that the tubular part with large perimeter difference, long expansion area and asymmetrical shape can be obtained in one step, applying the useful wrinkles. Typical failure modes were analyzed.

A Graphic Representation of Traction for a 3D Elastic/Plastic Stress State

The stress ellipsoid is often used to describe the variation scope of total stress of one stress state. But the direction of one vector from the original point to the ellipsoid surface is not always the one of the corresponding acting plane. A 3D graphic representation of total stress for an elastic/plastic stress state is given in this paper for the first time. The magnitude of the total stress on one plane can be described by the projection along the corresponding normal direction. The real direction of the total stress can be given directly. In a principal axes system, the figure is symmetric about the three principal axes. As for a plastic stress state, the stereograph of total stress has its own characters because the yield criterion must be obeyed. From the total stress figure, it is easy to get the magnitude of total stress acting on a certain plane. It is very helpful in understanding the concept of the stress ellipsoid and the variation of total stress across different acting planes.

A study on the bending of a trough-shaped profile using a roller and PUR pad

In bending with PUR pad, profile with different curvature radius can be manufactured. Experiment of trough-shaped profile was carried out to investigate the effect of section shape, penetration depth, roller radius and PUR pad thickness. Results show that both the position of neutral surface and section moment of bending have significant effect on curvature radius. Profile with bigger section moment of bending is difficult to bend. Curvature radius of bent profile decrease sharply when penetration depth increase. Change of roller radius has similar effect as the position of neutral surface. PUR pad thickness has big effect under small penetration depth.