It is important to elucidate preforming processes such as tube bending and crushing carried out prior to tube hydroforming. Although tube bending affects the formability of the subsequent hydroforming, the study of prebending remains limited. To investigate the deformation behavior of tube bending, experiments and FEM simulations were carried out for rotary draw bending with the mandrel and wiper at three continuous portions for TS390MPa class steel tubes. The results are as follows: (1) Thinning and thickening behaviors in regions outside and inside the bend respectively are markedly affected by a change in the circumferential stress of a tube during the material pass through the mandrel. (2) The shear strain observed from the outside to the inside of the bend results from the difference between the longitudinal strain distributions inside and outside the bend. (3) In multiple bending whose areas are consecutive, the deformation properties of the prior bending affect those of the subsequent bending.
Shot peening is a surface treatment that improves the performance of engineering components. In conventional shot peening, the medium consists of small spheres, which are usually made of high-carbon cast steel; the diameter of the spheres is in the range from 0.3 to 1.2 mm. More recently, however, a new type of microshot has been developed to enhance the peening effect. The diameter of the spheres in the new medium is in the range from 0.02 to 0.15 mm. In this study, the effects of microshot peening on the surface characteristics and fatigue strength of cold tool steel were investigated. The projective method of the microshot was of the compressed air type. The peening microshots of 0.1 mm diameter were cemented carbide, and the workpiece used was the commercially cold tool steel JIS-SKD11. The surface roughness, hardness, compressive residual stress and fatigue strength of the peened workpieces were measured. The surface layer of the workpieces was sufficiently deformed by microshot peening. A high hardness or residual stress was observed near the surface. Also, the process improved the fatigue life of the workpieces at all stress amplitudes. The use of hard microshots such as cemented carbide was found to cause a significantly enhanced peening effect for cold tool steel.
The formation of an Fe-Al intermetallic compound film on carbon steel by shot lining and heat treatment was investigated. In the experiment, a centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial medium, namely, the carbon steel S45C, and the sheet was commercially available pure aluminum. The shot lining process of carbon steel with an aluminum sheet was carried out at 300 °C in air using a peening machine. Heat treatment was performed at diffusion temperatures from 600 to 1050 °C in vacuum. The lined substrates exhibited a harder layer of aluminum-rich intermetallics, such as Fe2Al5, in the diffusion temperature range of 650 to 900 °C. When the temperature of the lined substrates was more than 930 °C, the surface was covered with thicker and highly anticorrosive layers of iron-rich intermetallics, such as FeAl and Fe3Al. We found that the present method could be used for the formation of functional films on carbon steel.
In recent years, low-weight magnesium alloy parts have been widely applied to automobile manufacture. When functional rotating parts such as scroll rotor were made of magnesium alloys, remarkable weight saving and low moment of inertia of the rotating parts were achieved. However, the net shape forging of a scroll rotor using magnesium alloys has not been developed. In the present paper, we proposed a net shape forging process and an apparatus for forming a scroll rotor with a boss part using the magnesium alloy AZ31 at a low temperature such as 200 or 250°C in terms of the available forming temperatures. First, we analyzed the proposed forging process of AZ31 scroll rotor using rigid-plastic FEM program. Then, details of the forging process and apparatus were determined by experiments. One of the advantages of the proposed apparatus is that a uniform height of the scroll vane can be achieved using an air vent; hence, the use of a conventional backpressure adding system could be eliminated. Finally, we confirmed that a net-shaped AZ31 scroll rotor could be formed using the proposed forging process and apparatus.
The joinability of mechanical clinching for high strength steel sheets with a low ductility and an aluminum alloy A5052 sheet was improved. For the upper steel sheet, a fracture was observed around the punch corner. For the lower steel sheet, cracks appeared around the die corner. To prevent the fracture and cracks of the steel sheets, the concentration of deformation was relaxed by modifying the shape of the die. The effect of the die shape on the deforming behavior of the sheets was investigated by finite element simulation and experiment. The joinability for high strength steel and aluminum alloy sheets was improved by modifying the depth and diameter of the die. The strength of the joined sheets was measured by a cross-tension test. The fracture in the test appeared at the aluminum alloy sheet. As the tensile strength of the steel sheet increased, the strength of the joined sheets decreased because of the small interlock of the joined sheets.
The forgeability and machinability of lead-free free-cutting brass containing graphite particles were examined by standard compression tests and machinability tests. Compression tests were performed on specimens containing 0∼5 wt% graphite particles at RT and 600∼800°C and results revealed the flow stress and limit upsetting ratio of the material. In particular, under hot compression test, characteristic voids were observed in brass matrix. In the machinability test, a novel testing method has been proposed and its machinability features were investigated. With FEM simulation, extrusion and forging processes were analyzed and a characteristic correlation between nominal strain and graphite morphology was found.