For mashy-state forging of aluminum alloy using resistance heating, which was devised to eliminate the mashy-state billet handling indispensable to the current process, the influence of forging conditions upon the product condition was investigated by experimental gear forging using an A357 aluminum alloy prepared for mashy-state forging applications. Forging experiments were conducted by varying the operational variables of input electric energy and forging pressure, under the resistance heating conditions favorable to preventing sparks and realizing homogeneous billet heating. The product condition was examined by optical microstructure observation and hardness measurements, and the following findings were obtained. (1) The experimental mashy-state gear forging using resistance heating was successful under suitable operating conditions. (2) Rapid resistance heating prevented the growth of primary α grains. (3) For die-cavity filling, a lack of forging pressure was compensated with an increased input of electric energy to augment the liquid phase. (4) The eutectic phase and α phase tended to be dense in the periphery of the forged gear and near the electrodes, respectively. (5) The periphery of the forged gear that comes into contact with the metallic die was solution-conditioned by rapid cooling from the mashy state, and through natural aging, it became harder than the center.
A surface-coated die that can reduce the ejection force needed to obtain green compact has been developed to produce powder metallurgical parts constantly without the occurrence of scuffing or cracking. A plasma CVD (Chemical Vapor Deposition) method, which is able to be performed at temperatures below 823K, was applied to shrinkage-fit dies. Optimal conditions for the surface-finishing treatment of the die and die holder were examined. For a shrinkage-fit die composed of a die holder made of a steel tempered at a temperature equal to or higher than the PCVD treatment temperature, there was little effect of the PCVD treatment on the shrink-fitting force and the hardness of the die holder. However when a die holder made of a steel tempered at 453K was used for the shrinkage-fit die, the shrink-fitting force was increased and the hardness of the die holder was decreased by the PCVD treatment. Taking these results into consideration, a surface-coated die having an optimal combination of the die and die holder materials was devised and its performance was evaluated. The ejection force exhibited by the surface-coated dies decreased in the following order: non-coated die>TiN>TiCN>DLC-coated dies. That is to say, all surface coatings examined were found to be effective in reducing the ejection force.
Micro/nano imprinting or hot embossing is of interest in the industrial production of microdevices. In fluidic MEMS (micro electro mechanical systems) applications, polymer materials have been employed, because of their low cost in the fabrication of economical products. However glass is much more suitable for higher temperature applications or strong chemical environments. In optical MEMS as well, glass is a good candidate materials because of their better optical properties. Si or Ni molds, usually employed for polymer forming, can not be used for glass forming because of their poor heat resistance and the difficulty of removal arising from cohesion between the mold and the glass. Glassy carbon (GC) is thus a suitable material for high-temperature embossing. In this study, FIB (focused ion beam) machining was employed for micro/nano 3D-structuring of GC materials, the machining characteristics are summarized as follows. 1) Machining depth is proportional to machining time, 2) nanomachining of 0.3μm resolution is possible, 3) smooth surface with maximum roughness of Ra=30nm after is formed 20μm deep machining, 4) implanted Ga ions precipitate up on 350°C annealing, but disappear after annealing in vacuum at elevated temperatures. Finally a Pyrex-glass embossed structure is successfully fabricated by hot embossing with a good fidelity of 10x10x7μm in size and with a 0.3 μm line and space pattern and 0.4 μm depth.
The peen forming process has been applied to aerospace wing skin parts since the 1960s because there is no other suitable method for forming of wing skins that have both gentle and complex curvatures. However, it is very difficult to determine the forming parameters; in fact, numerous trial-and-error forming tests have been conducted before production. Therefore, the development of a simulation method for the peen forming process is necessary for decreasing the development duration and total cost of aerospace parts. The objective of this work is to develop a simulation method for the peen forming process. In this study, the peen forming test and FEM impact analysis of a single shot are performed for obtaining fundamental information on shot peening. From the results, it is found that the diameter and depth of indentation increase with the energy of shot peening, and the profile of the diameter has a normal distribution. Also, the FEM simulation model for peen forming with a shell element, which has a total strain estimated from impact analysis near the surface layer, is developed. The simulation results of peen forming are in good agreement with the forming test results.
Branched tubing is an important component of piping systems. Welding structure type branched tubing has the disadvantages of low productivity and low flexibility due to difficulty in automatic welding, low reliability and low quality assurance. In this study, a new incremental burring process for manufacturing branched tubing without welding is developed to enhance the formability, product quality and process flexibility of large branched tubing. A crucial process history using a bar tool is proposed and is based on the forming characteristics of conventional forming processes, the rigid plug pull-out and T-drill methods. The effectiveness and merit of the proposed incremental burring process history is confirmed through an experiment using A5083-O aluminum alloy tube of 100mm in diameter and 1.0mm in thickness. The experimental results imply that the new incremental burring process is suitable for achieving a better wall thickness distribution of branched parts, and that a bar tool is superior to a roller tool for roundness and a wide range of applicable tube sizes.
The injection-compression molding of large-size molded products requires an extensive consideration of multigate designing and adjustment to control resin filling balance, although stable molding is still difficult if waste or composite plastics are used as materials, which have unstable fluidity. Our research aims to realize flexible resin filling flow control by die tilting in injection-compression molding. In this study, the effectiveness of die tilting is verified in an actual molding machine, and the effects of tilting angle and resin fluidity on filling balance are examined in a testing machine. It is found that flow balance varies linearly with tilting angle and is independent of fluidity.
The formability and the occurrence of surface cracks in the hot shear spinning of cast aluminum alloys were investigated. To eliminate their coarse microstructure and shrinkage holes, cast aluminum alloys were generally processed by hot shear spinning. The effects of ironing ratio, forming temperature, roller feed speed and tip radius on the formability and microstructure of and surface cracks in the alloys were examined. The occurrence of fractures was prevented by heating the alloys above 400 °C. The coarse microstructure of and shrinkage holes in the alloys were successfully eliminated by hot shear spinning. Surface cracks caused by a large shear deformation were reduced by decreasing roller feed speed and increasing roller tip radius. It was found that hot shear spinning is effective in improving the formability of cast aluminum alloys and the strength of the formed products.
The die quenching of ultrahigh-strength steel sheets in hot stamping using rapid resistance heating was experimentally investigated. A 1.2 mm-thick steel sheet with an ultimate tensile strength of 980 MPa was used as an experimental material. A test piece 130mm long and 20mm wide was resistance-heated at various temperatures above the Ac1 point with an AC power supply and, immediately after the completion of the electrification, the heated test piece was quenched by sandwiching with cold steel blocks 115mm long, 65mm wide and 30mm thick and holding for a predetermined time. The quenched test piece was evaluated by optical microstructure observation and hardness and tensile tests. The influence of material conditions on the quenching performance of the annealed sheets was also examined. Our findings are as follows. (1) The sheets resistance-heated above the Ac3 point and properly die-quenched showed a high hardness value of 495 HV, which is 1.6 times as large as the 312 HV of the original sheet, and an ultimate tensile strength of above 1400 MPa. (2) The use of an annealed sheet with coarse grain structures is not suitable for die quenching using rapid resistance heating. (3) The die quenching conducted on a trial basis in hot hat-shaped bending was successful and the hardness of the formed part increased by approximately 1.6 times that of the blank sheet.
A sheet stamping simulator with a segment blank holder is developed to carry out the variable control of distributed blank holder force (BHF) for forming irregular-shape parts. This simulator is designed to study the in-process intelligent control of BHF distribution in sheet stamping experimentally. The blank holder has 108 segments and is composed of 36 hydraulic actuator modules, which can be flexibly assembled with each other to easily construct a blank holder for forming a wide variety shapes. In this paper, basic performances with regard to the response and the accuracy of the hydraulic BHF control system are evaluated in a square-cup deep-drawing process. It is suggested that the in-process control of sheet stamping can be conducted in the simulator considering flange draw-in as a process variable. In conclusion, the stamping simulator developed possesses a fundamental performance that can realize distributed BHF control. The application of the module blank holder to nonaxisymmetric stamping is also suggested.
A process control algorithm of blank holder force (BHF) distribution to realize intelligent sheet-stamping in irregular shape stamping is proposed. The development of the algorithm involves the generalization of evaluation functions for detecting the risks of fracture and wrinkling from material flow-in, and simplification by applying a simple BHF control model of a circular-cup deep-drawing process to each cell of the segment blank holder. The architecture of the control algorithm is described for a square-cup deep-drawing process, in which the present algorithm is realized as a fuzzy model for a segmented blank holder. To verify the effectiveness of the algorithm, virtual stamping simulation, in which the BHF distribution of a segment blank holder is controlled by the algorithm, is conducted. From the simulation results, it is found that an appropriate binder force distribution can be obtained. A result of ductile fracture damage estimation using Oyane's ductile fracture criteria shows that the control method can improve drawability as indicated by a previous experiment using a sheet-stamping simulator.
The frictional behaviour of magnesium alloy AZ31B (Mg-3%Al-1%Zn) is evaluated by a tapered plug penetration test under dry conditions. The cemented tungsten carbide (WC) plugs, polished to exhibit a mirror-like surface, are coated with diamond-like carbon (DLC) and TiAlN by physical vapor deposition (PVD). The cylindrical hollow billets of AZ31B heated to a temperature of 200 °C are penetrated by the tapered plugs. Coating a tool with DLC is effective in preventing AZ31B from adhering to the tool surface. To examine the deformation behaviour of the billet during plug penetration, finite element simulation is carried out. From the simulation and experimental results, the coefficients of shear friction of WC-AZ31B and DLC-AZ31B are estimated to be about 0.30 and 0.25, respectively.