Clinching is a mechanical joint for fastening sheet metal components. With its increasing applications to the automobile manufacture and construction, joint strength has become an important subject in guaranteeing structural strength and structural integrity. In this study, tensile test is carried out on clinched joints of an A6063-T5 aluminum alloy sheet to investigate their tensile-shear strength. The thickness range of the sheet examined is 1.5mm-3.8mm. The tensile-shear stress of clinched joint A, for which the shearing surface of the joint is perpendicular to the tensile-shear load, is also equal to the shearing stress of the base metal. The tensile-shear stress of clinched joint B, for which the shearing surface of the joint is parallel to the tensile-shear load, is about 0.4 times of the ultimate tensile strength of the base metal. It is found that the tensile-shear strength of the clinched joint is proportional to the thickness of the sheet. Empirical equations of tensile-shear strength for two types of clinched joint are established.

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Clinching is a mechanical joint for fastening sheet metal components. In this paper, fatigue tests are carried out on clinched joints of a 6063-T5 aluminum alloy sheet to investigate the fatigue strength of clinched joints. Two types of clinched joint, which differ in the orientation of the shearing surface of the clinched joint relative to the direction of the tensile-shear load, are examined. Comparisons of fatigue strength have been made between clinched joints and a base metal. It is found that for a sheet thickness of 1.5mm, the fatigue strength of a clinched joint is smaller than that of the base metal, and for a sheet thickness range of 1.9mm-3.8mm, the fatigue strength of a clinched joint is almost similar to that of the base metal. Empirical equations of fatigue strength for two types of clinched joint are established.

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In recent years, a decrease in tool life has been observed in the manufacturing of small screws for precision instruments by cold heading because of the complication of the head shape and hard workpiece material. Thus, remarkable cost saving and high productivity could be achieved by increasing the tool life used in the cold heading of screws such as an M2 pan head screw made of SWCH16A. The prevalent methods of improving the tool life are related to the wear or stiffness enhancement of the tool. In the present study, we propose a method of improving the tool life related to the elastic strain energy absorbed by the tool. First, we analyzed the heading tool for forming the M2 pan head screw, which had a structure configuration for reducing stress in the tool, using the finite element method (FEM) code. Second, the dimensions of the structure configuration of the tool with a hollow section were optimized by FEM analysis. Then, the tool life was increased successfully. The tool life of the developed heading tool was increased 3.7 times compared with that of a conventional heading tool.

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In plastic metalworking, a lubricant is usually applied between the metal surface and the tool surface to reduce friction. The reduction in friction prevents seizing, improves the forming limit and decreases the energy that the process requires. Therefore the use of a lubricant is extremely important. Oil-based lubricants and phosphate coatings which have a high environmental load have mainly been used as conventional lubricants before and after the working process. However with the recent trend in environmental protection lubricants should be pollution-free materials. In this project we aim to develop and evaluate new lubricants based soap and detergents. These materials are good lubricants and have little environmental load. The performance of the new lubricants was evaluated by the Erichsen test and cold bar drawing. The results of the experiments and elastic-plastic FEA were compared to determine the coefficient of Coulomb friction. It was clarified that an appropriate mixture of soap and a mild detergent is superior to lubricants on the market. In particular, the soap-based lubricant mixed with washing powder shows excellent performance. In addition, these lubricants are easily removed by water. Guidelines for the development of environmentally friendly lubricants and the application of such lubricants to metalworking were obtained.

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Dry press forming, which means press forming without lubricants, is an attractive forming technique for the zero emission of lubricants. As one of the dry press forming techniques, the application of dies coated with a CVD diamond film in forming tools has been proposed for their high tribological properties, abrasion resistance and heat resistance. In this study, using diamond-coated dies AZ31 magnesium alloy sheets were dry-deep-drawn and ironed to investigate the tribological properties of diamond-coated dies and the formability of magnesium alloy sheets. A friction test was conducted to confirm the tribological property of the diamond-coated dies, and the friction coefficient of the diamond-coated dies was compared with using the lubricants. Dry deep-drawing ironing tests were carried out under the following experimental conditions: 10% ironing ratio at a die temperature of 200°C. In addition, the forming limit using diamond-coated dies was compared with that using noncoated dies with a conventional lubricant. From the results, the deep-drawing ironing process was feasible using diamond-coated dies. Moreover, a 20% reduction in drawing force was confirmed in comparison with the use of a traditional lubricant (MoS₂). Furthermore, it was observed that the surface roughness of a wall part of the formed-cup using the diamond-coated dies was 0.38μmRz. From these results, the feasible use of the diamond-coated dies was suggested.

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The formability of hole expansion for punched ultra high strength steel sheets with low ductility was improved by smoothing the sheared edge of the sheet. In the smoothing process, the notch effect of the macroscopic roughness in the fracture face was eliminated using a conical punch. The effects of the smoothing conditions on the limiting expansion ratio were investigated. Setting the angle of the conical punch in the smoothing to the same angle as the fracture face was effective in improving the limiting expansion ratio. The clearance ratio in the punching influenced the limiting expansion ratio, thus the optimum clearance ratio resulted in a maximum limiting expansion ratio after the smoothing. The smoothing of the sheared edge was effective in improving of the formability of hole expansion for ultra high strength steel sheets.

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Magnesium alloys have poor ductility and it is difficult to manufacture magnesium alloy parts at room temperature. In this study, to form magnesium alloy sheets without heating using energy sources such as furnaces, torches and laser beams, a new forming process, called the friction stir incremental forming process, was developed. AZ31-O magnesium alloy sheets of 0.5mm thickness were formed into a frustum of pyramid shape. Tool rotation rate, tool feed rate, and the half apex angle of the pyramid were changed. Not only microstructure observation but also the investigation of formability was carried out. Formability by the developed method was compared with that by the conventional hot incremental forming method. From the experimental results, the AZ31 sheet of 0.5mm thickness was formed into a frustum of pyramid shape with a minimum half apex angle of 25° by the developed method and the sheet showed 137% elongation at room temperature. The degree of springback decreased when suitable working conditions were employed. The formability by the developed method was higher than that by the conventional hot incremental forming method.

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A square steel pipe is reshaped from a welded round pipe by roll forming. The effect of roll diameter on the cross-sectional size of the square steel pipe was investigated by experiment and three-dimensional finite element simulation. When the diameter of the top roll is larger than that of the side roll, the width of the cross section of the formed pipe is smaller than the height. To make the width and height equal, it is necessary to perform finishing forming in the last stage. When the diameter of the top roll is larger than that of the side roll, the width of a corner part of the formed pipe is larger than the height. The difference between the width and height of a corner part of a product is greater than that of a half-finished pipe. The difference becomes so large that the ratio of the diameter of the top roll to that of the side roll becomes large. The square steel pipe was formed by offsetting the small roll to the upstream side. The offset method is effective in making the width and height of a corner part equal.

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