Hypereutectic Al-Si alloy has excellent properties such as high temperature strength and high wear resistance owing to the presence of dispersed Si particles. However, its ductility and formability are reduced by such precipitates. To solve this problem, the microstructure refinement and homogeneous dispersion of a fine Si phase are necessary. The authors have investigated the microstructure refining method for hypereutectic Al-Si alloy by compressive torsion processing (CTP). It is an effective severe plastic deformation process which entails the simultaneous application of compressive and torsional loading to a cylindrical work piece. In this study, the effects of compressive torsion processing temperature and torsion number on the microstructure refinement of hypereutectic Al-Si alloy are dealt with. When CTP was applied on Al-Si alloy, primary Si and eutectic Si were refined more effectively at lower temperatures but they were dispersed more uniformly at higher processing temperatures. As torsion number increased, primary Si and eutectic Si were refined not only near the upper and lower dies but also inside the specimen.
In peen forming, though the amount and depth of plastic strain near the surface introduced by shot impinging are key parameters affecting the deformation of the whole part, they are not well understood theoretically or even in the computer simulation. In this study, the computer simulation of shot impinging by the finite element method (FEM) is performed to obtain fundamental information on plastic strain introduced by shot peening. In the first step, the simulation of shot impinging with both the static implicit and dynamic explicit methods is conducted to verify the precision of the simulation. It is clarified that simulation by the static implicit method can provide sufficiently precise results for the simulation of shot impinging. As results of the simulation using a single shot, it is found that the diameter of the plastic strain area in the material is about two fold larger than that of shot indent on the surface. Also, the simulation using multiple shots shows that the distance of each shot affects the each plastic strain profile at 0.75 R or less (R is the shot radius).
In piercing, a smooth shearing surface can be obtained by reducing the clearance between the punch and the die. However, continuous piercing in a small clearance is difficult during mass production, since adhesion may easily occur. A Press Working punch (PW punch) is a punch for piercing a steel plate developed on the basis of cold backward extrusion technology. However, the dimensions of the PW punch were not evaluated accurately. In this study, we evaluated the adhesion resistance of the PW punch when used for the fine piercing of a steel plate. Experiments on continuous piercing using a PW punch with a 10 mm diameter and 0.5 % clearance are performed on a hot-rolled steel plate having a thickness of 4.5 mm. Experiments using a conventional right angle punch are also performed for comparison. A mirrorlike shearing surface was obtained using a ceramic-coated PW punch without causing adhesion in 600 continuous piercings. As a result, the PW punch was found to be highly advantageous for the piercing of steel plates.
The large quantity of lubricant waste has become a very serious environmental issue. To realize zero emission of lubricants, dry deep drawing is attractive, but it is very difficult to apply to metal sheets. As one of the most promising methods without lubricant, the use of ceramic tools was proposed because of their high tribological properties. However, the workability of ceramics in tool preparation is inferior to that of alloy tool steel. Therefore, the forming of complex shapes is difficult. We propose the use of electroconductive ceramics for the tool in this study. The electroconductive ceramics can be formed by electrical discharge machining (die-milling electric discharge, etc). Therefore, the shape of the press die can be easily molded. In the previous paper, 10,000 repetitions of dry cylindrical deep drawing were achieved with the electroconductive ceramic tool. In this study, deep drawing of a rectangle, which is a more complex shape, was examined. As a result, 10,000 repetitions of dry rectangular deep drawing were achieved. The surface roughness of a dry-deep-drawn cup was equal to or better than that of a non-dry (oil)-deep-drawn cup. Moreover, it was confirmed that a complex shape of the press die could be easily molded.
Oxidation in hot stamping of quenchable steel sheets heated in an electrical furnace was prevented by coating the sheets with an oxidation preventive oil. Although the strength of the hot-stamped parts is increased by quenching with tools, the oxidation of the surface becomes remarkable. A solid film is generated on the surface of the sheet by drying the coated sheet, and the film changes into a liquefied film having an oxidation barrier at elevated temperatures. The degree of oxidation under natural cooling of the heated sheet without forming was first evaluated. Next, hot hat-shaped bending of the coated sheet was performed to examine the properties of the products. For the bent products, the oxidation preventive oil was effective, the shape accuracy was very high and the hardness increased to a level of 1.5GPa in tensile strength. The layer remaining on the surface of the formed product could be removed by means of phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of high strength steel products.
A small flywheel can be formed directly from a cylindrical workpiece by cold axisymmetric upsetting with lateral extrusion. The authors found that an effective material flow for fulfilling a die cavity in the above die forging can be generated by placing a stepwise cavity on the bottom die plane at the peripheral section. When the dimensions of the hollow plane formed on the disk product by the above die configuration are optimized in the shape and die designs of a flywheel, the net shape forging of a flywheel can be achieved by semi-core forging with the above improved material flow. The advantage of the above forming technology is that no severe increase in punch load, observed in core forging at the final stage of the forming process, occurs, and die life can be elongated in net shape forging. The surface condition and inner strain condition of the product were also investigated by observing the products and FEM, and sufficiently good conditions were confirmed
The endless hot rolling concept was introduced to meet the demand for diverse hot-rolled steel sheet products produced by a cost-effective process compared with the conventional batch-type process. Endless rolling involves joining the head and tail ends of two bars following their rough rolling. Previously, induction welding and laser welding have been employed in a hot mill line, nevertheless, these joining methods require a longer line space because of the long welding time. By applying solid-state joining utilizing the high temperature of the joined materials for endless hot rolling, a new joining technology was proposed to instantaneously obtain a sound and uniform joint as the base metal using relatively simple equipment. This report presents the friction joining method, in which one joined surface slides over the other surface to reduce the surface scale and each material is upset with friction to obtain a sound joint. In laboratory tests, the joint strength was approximately half that of the base metal and the joint area was very narrow. Obtaining a wide joint area without excessive scale is another problem that remains to be overcome.
The endless hot rolling concept was introduced to meet the demand for diverse hot-rolled steel sheet products produced by a cost-effective process compared with the conventional batch-type process. Endless rolling involves joining the head and tail ends of two bars following their rough rolling. By applying solid-state joining utilizing the high temperature of the joined materials for endless hot rolling, a new joining technology was proposed to instantaneously obtain a sound and uniform joint as the base metal using relatively simple equipment. This report presents the super deformation joining method, which was developed from a study on remedying the friction joining method. In this method overlapped materials are sheared incompletely to obtain a sound joint. In laboratory tests, in the presence of scale on the overlapping surface, the joint strength was approximately half that of the base metal, and the joint area was about 60 %, although the joint strength was approximately the same as that of the base metal when there was no surface scale. Obtaining a sound joint under actual hot rolling conditions, in the presence of scale on the overlapping surface remains a problem to be overcome.