In this study, we investigated the possible use of an aluminum alloy mold for high-cycle production in injection molding by carrying out comparative tests on an aluminum alloy mold and an S55C mold. The ABS resin used during injection has lower temperatures when using the aluminum alloy mold. However, the difference in mold material does not affect the amount of temperature increase during injection. The pressure in the mold is lower and the weld depth is larger when using the aluminum alloy mold. The aluminum alloy mold showed smaller warpage. When comparing warpage, the aluminum alloy mold achieved a smaller warpage at shorter cooling times. It is clarified that the aluminum mold is a good candidate for reducing cycle time.
Hot ring rolling is a useful process for producing large seamless rings such as bearing races for ships, airplanes and windmills. Ring rolling is classified into two types, i.e., two-roll-type and three-roll-type, by roll layout. A two-roll-type ring rolling mill is generally used for manufacturing processes. On the other hand, a three-roll-type ring rolling mill has fewer applications, and therefore has been less studied. In this study, the deformation characteristics in both types of ring rolling were investigated experimentally. It is found that the deformation characteristics near the center of the width of the ring in three-roll-type ring rolling are similar to those observed under plane strain compression. In this region, fiber flow toward the outer side is observed. It is also found that three-roll-type ring rolling shows less lateral spread and more uniform deformation than the two-roll-type process without axial rolls.
Hot ring rolling is a useful process for producing large seamless rings. Ring rolling mills are classified into two types, i.e., two-roll-type and three-roll-type, by roll layout. In our previous study, the deformation characteristics in three-roll-type ring rolling were investigated experimentally. It was found that the deformation characteristics near the center of the width of the ring are similar to those observed under plane strain compression. In this region, fiber flow toward the outer side was observed. In this study, numerical simulation was performed by FEM together with the ALE method for each process. FEM together with the ALE method can simulate deformation for the two types of ring rolling process. In the three-roll-type process, effective strain distributes uniformly and hydrostatic stress shows a compression state on the RD cross section. On the other hand, in the two-roll-type process, effective strain concentrates at the corner of the ring and hydrostatic stress shows less compression or tensile state. The elongation efficiency at the center of the width also shows uniform deformation in the three-roll-type ring rolling process. These results show the advantage of the three-roll-type ring rolling process for preventing internal voids and surface cracks.
The shaping of spur gears by cold extrusion through the expansion of the inner diameter of a workpiece is examined experimentally. A workpiece is set with its inner diameter in the front part of a stepped mandrel, which is placed in a container. Then, it is extruded with the expansion of its inner diameter, by passing through the tooth part of the die. The specifications of gear examined are as follows: module m=1.25-2.0 mm, pressure angle 20 deg, number of teeth Z=18-16, and whole depth h=2.25 module. The material used is the low-carbon steel, JIS S15C. The criterion for the shaping of complete teeth is discussed in terms of reduction in area, expansion ratio of the inner diameter of the workpiece and other factors. This method can produce spur gears of much better shape, i.e. having complete teeth, than the former proposed extrusion method, without reducing the outer diameter of the workpiece. Especially, a gear having a relatively medium-to-large sized bore can also be well shaped by the present method. The needed pressure of the punch, mandrel, and die is far below the strength of the punch and die materials.
For the high-cycle production of carbon-fiber-reinforced plastic, the press forming of carbon fiber sheets filled with thermoplastic is investigated. In this process, carbon fiber sheets with thermoplastic are prepared before the pressing. In the first step, the prepared sheets, laminated between silicon rubber sheets, are compressed and heated using heater plates. In the second step, laminated sheets are pressed by cold dies with silicon rubber sheets. The production time of the total two steps is within 1 minute. The deformation of the carbon fiber and plastic during the press forming is investigated with relation to punch and die cushion loads. The cross section of the formed material is also observed to investigate the arrangement of carbon fibers and their contact situation with the plastic.
In this study, we aim to quantitatively evaluate ductile crack initiation with equivalent plastic strain and stress triaxiality on cold upsetting. An investigation into the behavior of cracking on the surface in the cold upsetting of typical cold-forged steels of S45C was carried out with a crank press. To apply various amounts of stress and strain histories, the shape of the test specimen was changed. The stress and strain histories were calculated by the finite element method (FEM). The result shows that ductile crack initiation was determined by equivalent plastic strain and stress triaxiality. The workability limit was predicted by comparing the criteria for ductile crack initiation to the history of the equivalent plastic strain and stress triaxiality to determine the final forging from the material by cold forging.
A forming experiment on a titanium alloy sheet of Ti-6Al-4V was carried out to study the features of incremental forming using a bar tool and high-frequency induction coil set beneath a blank sheet. A sheet heated by the induction coil was formed such that it had less than half the thickness of the original blank under certain conditions. The formed article was straightened by creep forming under argon gas pressure in a hot die. Finally, effective forming conditions were analyzed, and the forming of an article was completed successfully resulting in good quality. It was found that the combination of incremental forming and creep forming is comparable to superplastic forming (SPF) in formability and quality, and that this working process has advantages in low-temperature working condition and non-strict facility requirement, by comparison with SPF. It is expected that the process will become more widely used in the forming of titanium alloy sheets as a new working method in small production industries.
To reduce the forging load of the proposed large deformation forging technology, a new type of forging system is proposed. In this forging system, the contact length between forging dies and a work can be reduced by adjusting the swing motion of the dies during forging. This swing motion results in load reduction because contact length is a dominant factor of the load for this type of forging. Also, this forging technology is relatively stable when using lubrication because of its basic up-and-down motion. In this study, load reduction effect with the newly proposed forging system and lubrication are examined by laboratory-scale experiments and FE analysis. It appears that a nearly 30% load reduction can be achieved by the swing-type forging compared with the flying-type forging under the condition of a large thickness reduction. Width spread is also reduced by the swing type forging because contact length has a large influence on a material's lateral flow. Moreover, another 20% to 30% load reduction is confirmed and seizure on the forging dies was prevented by lubrication.