Jun Yanagimoto

Springback of high-strength steel after hot and warm sheet formings

The springback of high-strength steel after hot and warm sheet formings is investigated. Environmentally friendly vehicles will promote the increasing usage of high-strength steel sheets, however, a large amount of springback after sheet forming is one of the major drawbacks. A series of hot and warm sheet forming experiments on high-strength steel sheets are conducted using a hot compression testing machine, and the effect of forming temperature on the amount of springback is evaluated. The springback is markedly reduced when the forming temperature is higher than 750K, which is approximately the critical temperature for the recrystallization of ferrite grains.

Flow Stress, Yield Criterion and Constitutive Equation of Mushy/Semi -Solid Alloys

Abstract New mathematical models of yield criterion and constitutive equations of mushy/semi -solid alloys (hereinafter described as semi -solid alloys) are proposed in order to investigate their flow features and deformation characteristics in various forming and shaping processes. First, a large number of uniaxial compression tests of semi -solid alloys are carried out and their stress -strain curves are measured. Through the tests, the remarkable drop of their flow stress is observed when their solid fraction decreases from 100%. The second, a new formula of yield criterion of semi -solid alloys is proposed. It can express the drop of their flow stress in semi -solid state. In addition, so -called constitutive equations, which describe flow and deformation of such alloys in forming and shaping processes, are derived from the formulated yield criterion. At the last stage, the obtained constitutive equations are introduced to 3D FEM simulation of upsetting of billets.

Application of mushy/semi-solid joining—Part 3

Abstract A process to join glass or stone onto base metal alloys is proposed. The process characteristics allow using various kinds of glasses or stones, such as craft glass, beads, tile, amethyst, agate and hematite with different shapes and sizes. The process utilizes excellent and active join ability of mushy or semi-solid alloy’s properties. In this study, the mechanism of the joining was investigated and some applications were showed. The process itself has several useful properties like: (1) easy-to-operate, (2) ability to get good joining condition, and (3) applicability to a continuous production system. Through the study, it is found that the mushy joining is a useful and valuable manufacturing method for developing and manufacturing glass/metal or stone/metal composites. The mushy joining process is different from the existing cloisonne and enameling process.

Effects of heat treatment on the microstructures and mechanical properties of a new type of nitrogen-containing die steel

Nitrogen can increase the strength of steels without weakening the toughness and improve the corrosion resistance at the same time. Compared with conventional nitrogen-free die steels, a new type of nitrogen-containing die steel was developed with many superior properties, such as high strength, high hardness, and good toughness. This paper focused on the effects of heat treatment on the microstructures and mechanical properties of the new type of nitrogen-containing die steel, which were investigated by the optimized deformation process and heat treatment. Isothermal spheroidal annealing and high-temperature quenching as well as high-temperature tempering were applied in the experiment by means of an orthogonal method after the steel was multiply forged. The mechanical properties of nitrogen-containing die steel forgings are better than the standard of NADCA #207-2003.

Recycling of Minute Metal Scraps by Semisolid Processing: Manufacturing of Design Materials

As a new attempt to recycle minute metal scraps, the possibility of manufacturing design materials by semisolid extrusion processing was shown. A design material with an intended shape, such as a character or petal shape, was manufactured using minute metal scraps. Similarly, a design material with an intended color pattern for each metal, such as red copper in a white aluminum matrix, resembling grainlike wood, was manufactured by mixing two or more types of minute metal scrap. In addition, secondary design materials, which have engraved patterns on the surface of the target metal made by an electric discharge machine using the above primary design material as an electrode, were manufactured.

Characterization of Three-Dimensional Metal Flow in Extrusion Process

Abstract This paper presents a rigid- plastic FEM code and describes its application to flew simulation during extrusion with aims to obtain knowledges and information usable for eliminating geometrical defects of products. The effects of some variables like the aspect ratio of products cross section, the bearing length and the position of die opening on the metal flow are studied. Results on the average extrusion pressure and the metal flow characteristics in terms of the velocity distribution profiles in the bearing section and the streamline patterns are presented. From them it is possible to predict the geometric defects of the product and find out the method to reduce them by modification of the die geometry, e.g., bearing length. The extrusion simulation of rectangular and angle sections is chosen to show the applicability.

Refining and Recycling of Metal Scraps by Semisolid Processing

In this study, the authors propose a new refining process different from the rheorefining (a screen method) or the melt zone method. This new refining process is based on the gradient of solidification speed of the molten metal poured into a container. The molten metal in the cylindrical container firstly solidifies to columnar crystals from the wall of the container and a liquid phase gradually changes to semisolid state and progresses to the central portion of the container. After an intended semisolid state is achieved, a backward extrusion is carried out to extract the liquid phase component. The liquid component is known to contain a lot of impurity substances. For the refining trials, three aluminium alloys were selected: wrought aluminium alloy A2011, cast aluminium alloy AC4C and aluminium beverage can scraps. Backward extrusion (extraction) was applied twice, and the amount of pure Al increased from 90.59 % in the initial ingot to 96.34 % in the refined material. This new refining process can easily achieve the purification level of the rheorefining or the melt zone method.

Mashy Metal/Alloy Joining a New Process for Manufacturing New Products

Abstract A new process to join metal and ceramics components on to aluminum, copper and magnesium alloys was proposed. The process is based on joinability of mashy (mushy/semi-solid) alloys. This paper shows the obtained results regarding two types of joinings as follows. (1) Multi wire fins (pins) were joined on to base blanks of an aluminum alloy, (ex. Wire fin type heat-sinks were made.) (2) Multi sheet fins were joined on to base blanks of an aluminum alloy (ex. Sheet fin type heat-sinks were made.). The effects of process parameters on the shear strength of interfaces between joined fins and base blanks and their internal structures were investigated. Through the study, it is found that the mashy-state joining makes it possible to join various materials together which can not be joined by other processes such as welding and soldering.

APPLICATION OF DAMAGE MODEL WITH MATERIAL FLOW EVALUATION TO HIGH TEMPERATURE COMPRESSION PROCESSES

Mechanisms of ductile failure in a compression process are studied, based on micro-structural considerations, with analytical and experimental investigations performed on a cylindrical specimen. Geometrical softening is able to occur by void if the shear band is generated inside of materials. The original Gurson model is used to analyze tensile deformation, and a modified Gurson model is proposed, which incorporates damage accumulation under shear and compression. This modified Gurson model is also applied to the void closure of sintered material under compression loading. However, the compressed materials must be considered in both the void nucleation and closure, because the void is nucleated and closed at a specific angle. The results of individual analyses of nucleation and closure do not agree with observations, but the analysis considered here, of both the nucleation and closure of a void, corresponds well with experimental results.

Mechanical properties and drawing process of multilayer carbon-fiber-reinforced plastic sheets with various prepreg thicknesses:

In this study, multilayer carbon-fiber-reinforced plastic sheets with various pre-impregnated thicknesses were developed. Specimens were fabricated by the hand lay-up process from standard and thin-ply unidirectional carbon fiber/epoxy resin prepreg sheets, which were also cured in an autoclave. Tensile tests from room temperature to 120°C and interlaminar shear strength tests at room temperature were first conducted to investigate the mechanical behavior of the laminated carbon-fiber-reinforced plastic sheets. Furthermore, with a view to increase the formability, in this study, a state-of-the-art drawing process for laminated carbon-fiber-reinforced plastic sheets at an elevated temperature was investigated, and the drawing ratio was also determined for the case of elliptical cup drawing. To achieve this, the relation between the punch load and stroke, and the distribution of thickness were determined by measurement. To clarify the forming behavior in this case, evaluation of the effect of increasing the number of drawing steps was performed to investigate the deformation history. The microstructures showed reduced delamination with increasing radius of the punch. The experimental results obtained in this study are expected to help designers perform the press forming of multilayer carbon fiber/epoxy resin sheets.