A servo-type press machine or a servo-type press brake with no energy accumulation device as a flywheel has recently been used for sheet metal bending. Thus, the energy needed for sheet metal bending is an important characteristic for the design and selection of such a bending machine. The purpose of this study is to clarify the energy characteristic of sheet metal bending. In this report, the energy characteristic of air bending in V-bending, which is the most basic sheet metal bending method, was examined. The following results were obtained. As the die groove width wd and the punch top radius rp increase, the air bending energy Ea slightly decreases. As the sheet metal thickness t increases,Ea increases quadratically, and as the sheet metal tensile strength σB increases, Ea increases linearly. The energy Ea required for air bending in sheet metal V-bending was calculated to be about 0.9-fold of the basic energy E0, which is calculated as the product of the punch travel S0 up to the bottom dead center and the maximum bending load Pa at the stage of air bending.
In this study, we attempted to manufacture wood-based products of arbitrary shapes and high strengths by allowing cryptomeria powders to flow and harden in a metal mold without using a binder. Experimental results show that wood powders have good liquidity owing to the maintenance of their moisture using the metal mold that remains sealed in a hot press. The metal mold was filled with the wood powders and a good product was obtained under the following processing conditions : a molding temperature of 160°C, a moisture content of 10%, and a temperature hold time of 60 min. The density of the obtained good product is 1.38 g/cm3, and the average Vickers hardness is 24.1HV0.05. In addition, the product obtained at a molding temperature of 160°C and a sealing time of 30 min or more does not facilitate shape recovery even if it boils in water.
Two different torsional vibration modes growing under operation were observed. One is the in-phase mode of top and bottom rolls normally found at plate impact, and the other is an out-of-phase mode, not found in hot rolling mills. To identify the cause of vibration, field measurement and vibration analysis were performed. As a result, the vibratory divergence was found to depend on self-excited vibration and the high gain of speed control was found to show a strong possibility for this phenomenon. From evaluation results, the verification test was carried out to validate a vibration cause and a stable operation was realized.
The effect of the quality of a sheared edge on the formability of hole expansion of an ultra high strength steel sheet having low ductility was examined. The quality of the sheared edge in piercing was changed by the clearance between the punch and the die, and thus the formability of hole expansion after piercing was influenced. From a tensile test on a specimen having pierced holes, it was observed that cracks are initiated around the large macroscopic roughness of the sheared edge owing to the notch effect. The limiting expansion ratio of the pierced ultra high strength steel sheet was influenced by the roughness and not by microscopic roughness. In addition, the limiting expansion ratio decreased with an increase in the hardness of the fracture surface. Thus the finishing of a sheared edge with a conical punch is effective in improving the formability of the hole expansion of ultra high strength steel sheets.
In this study, a three-dimensional finite element (FE) modeling of multistage incremental tube burring was carried out to confirm a significantly crucial process path for the bar-tool-assisted incremental tube burring process proposed in our former study. The tube burring model of an aluminum alloy tube, A5083-O, of 400 mm diameter and 6.0 mm thickness using a bar tool of 65 mm diameter was used in the simulation and analyzed using an explicit dynamic FE code. A ductile fracture damage analysis of the process is also performed in the simulation. The distributions of thickness reduction ratio, forming force at each stage and final burring height are compared with the experimental results. The simulation results are in good agreement with the experimental results, and the validity of this analysis model is confirmed.
A hot gas bulging process for an aluminum alloy tube with resistance heating in a forming machine was developed. The tube was rapidly heated by electrifying to increase its formability and to decrease its flow stress. Since the tube was bulged by thermally expanding air sealed in the tube without controlling internal pressure during forming, the control became easy. The hot gas bulging of an aluminum alloy tube without and with axial compression was performed. The effects of the initial internal pressure and current on the expansion ratio of the tube were examined. The decrease in temperature around the contact with the electrode was prevented by inserting a stainless steel ring with low thermal conductivity and high heat generation between the copper electrode and the tube, and thus, the bulging length increased. The formability of the aluminum alloy tube was markedly improved, i.e., the expansion ratio at the onset of bursting for hot gas bulging was 130%, whereas that for cold hydroforming was 20%. It was found that hot gas bulging is effective in increasing the formability of aluminum alloy tubes.
Combined extrusion forging is effective in decreasing load and process simplification. However, combined forging is not used widely. The reason for this seems to be the load and metal flow being difficult to assume. Many research studies have been conducted to solve this problem. Although it is considered that extrusion load and metal flow are affected by the shape ratio of a billet (ho/do), research on this subject is insufficient. In this study, the effect of the shape ratio of a billet on extrusion load was examined by experiment and analysis. The extrusion load in both single extrusion and combined extrusion increases with the shape ratio of a billet. When the shape ratio is 1.5, the combined extrusion load corresponded to either of the forward extrusion load or the backward extrusion load, smaller. When the shape ratio is 0.4, the combined extrusion load was smaller than both of the forward extrusion load and the backward extrusion load. When the diameter and height of the billet based on the size of the product were given, the method of predicting a combined extrusion load was proposed.
A micro-dimple forming process using a forming tool was developed to improve the antiseizing properties of sliding surfaces of mechanical components and to reduce frictional resistance. This process combines a roller-burnishing process and a ball-burnishing process. The features of the process are as follows. A regular alignment of dimples can be achieved at a high speed using conventional machines such as lathes, milling machines and drilling machines. The alignment of dimples formed on the inner wall of metal pipe can be controlled by varying tool geometry and process conditions. This process is applicable to metals with a hardness lower than 400HV, including steel, aluminum and copper alloys. Bump-free dimples can be formed because roller burnishing after ball burnishing flattens bumps around the dimples. The thin layer of the processed surface is work-hardened with compressive residual stress.