A both-sided ironing process can iron the inner and outer surfaces of a can at the same time using inner and outer dies. The limiting ironing ratio of the both-sided ironing process is lower than that of the one-sided ironing process. In the case of an ironing die profile radius of 10mm, the limiting ironing ratio of the both-sided ironing process is 27%, and that of the one-sided ironing process is 36%. This characteristic depends on the difference in the forming mechanism. The limiting ironing ratio of the both-sided ironed can is found to be influenced by the combination of different die profiles for inner and outer dies, the lubrication on both sides of the can. The limiting ironing ratio increases with increasing the profile radius of the inner die. The limiting ironing ratio is slightly affected more by the lubrication of the outer side rather than that of the inner side. The limiting ironing ratio decreases when the outer side is not lubricated.
Deformation of a steel tube was investigated when its outside diameter was cold-reduced through a die. Numerical analyses by axi-symmetric elastic-plastic finite element analysis (FEA) were carried out. When a conventional die with a single die angle was used, the outside diameter of the top portion of the tube became slightly larger, and the wall thickness became thinner than the middle portion. The influences of the wall thickness of the tube and the die angle were investigated. To check the validity of the result, an experiment was carried out. Then, numerical investigation by FEA was carried out to determine the optimum geometry of a die that would decrease the degree suppress this phenomenon followed by an experiment to check validity. The optimum die geometry happened to have the same geometry as that proposed by the authors for suppressing the undershooting phenomenon and the bending phenomenon. It is able to decrease the different level of deformation between the top and the main portion of the tube.
Shave joining with a screw was experimentally confirmed as very promising for forming a single lap joint between sheets such as mild steel, aluminum, plastics, and fiber-reinforced plastics. Here, an external screw of hard steel serves as a rivet, but its threads shave a machined bore of lapped sheets into an internal screw. The press insertion force is much smaller than that of riveting, resulting in a decrease in working noise. The joint surface can be flat when using a flat-headed screw. Although the engagement between screw and bore is tight through lapped sheets, its joint can essentially be disassembled, when required. The strength of the lap joint under tensile stress is markedly improved as the screw pitch decreases or screw number increases. Furthermore, the value becomes maximum using a headed screw, thereby upsetting the stem bottom. Such effects are successfully caused by control of specimen curling or screw pullout in testing. The screw should be harder than sheets to be joined. Softening of plastics and its composites by a heated screw is utilized to fasten the screw and bore wall closely.
Though the demand is increasing for high-strength sheet steel products made by press working, high-strength sheet steels have several disadvantages, including cracking due to the press workings and their lower shape-fixing ability due to springback. Press workings at high temperature are investigated as a countermeasure to these disadvantages. In this case, it is important to obtain the material property data at high temperatures. However, it is often difficult to measure many specimens because a special furnace and sensors must be used. In this paper, a new simple measurement method is proposed. Using a three-point bending test apparatus and a PID-controlled infrared heater, a specimen is heated and cooled to the various cyclic temperatures to acquire bending flow load data related to the temperature. Investigation results showed that the proposed simple measurement method is practical for obtaining high-temperature properties of sheet steel. The method of estimation of springback is described as an example of the application of this method.
The authors have previously proposed a two-step cold extrusion method for shaping spur gears. This time, the method was applied to shape helical gears. A specially designed die was used for shaping helical gears in two steps. The specifications of helical gears examined were as follows: module m=1.5, number of teeth Z=18 and helix angle β=20°. The tested material was low-carbon steel, S15C. The inner diameter of the workpiece was varied in order to examine the effect of reduction in area. For this purpose, three types of experiment were carried out, namely, 1) using a mandrel of equal diameter to the inner diameter of the workpiece, 2) using a mandrel of smaller diameter than the inner diameter of the workpiece and 3) without using a mandrel. It was shown that almost all the shaping conditions examined resulted in complete teethed helical gears with even only a 7 percent area reduction under a low punch pressure.
The methods for the prevention of fracturing due to seizure on the die surface in the press-forming of pure titanium sheets are experimentally investigated by applying various kinds of lubricants. First, a commercial liquid that includes carbon particles that is used for masking in the spray coating of metal is found to be a good antiseizure lubricant even when common tool steel (SKD11) is used as the die material. Then, new lubricants are contrived. Carbon-graphite and/or carbon-black are added to a press-forming oil or a liquid that includes glycerin and/or water in various mixing ratios. The die material is tungsten carbide (G5) or tool steel (SKD11). Press-forming oil with these additives is found to be inappropriate for performing consecutive forming. However, glycerin with carbon-graphite is found to be effective for forming with a tungsten carbide die. Water and glycerin with larger mixing ratios of carbon-graphite and carbon-black also allow us to perform the drawing process consecutively even when common tool steel (SKD11) is used. This lubricant is also confirmed to be appropriate for a consecutive 4-stage drawing process.
The feasibility of hot stamping of high-strength steel sheet with resistance heating was examined. Resistance heating and hot stamping experiments were conducted using rectangular blanks of high-strength steel sheet, SPFC980Y, 1.2mm thick, 80mm wide and 130mm long. The blanks were resistance-heated between a pair of parallel electrodes placed 120mm away from each other, with an AC power supply, and heating temperature was measured by thermography. The function of input energy control adopted for heating temperature control and the performance of blank holders with multiple pins designed for eliminating unequal contact of the blank with electrodes and achieving stable and homogeneous blank heating were tested. It was concluded that hot stamping with resistance heating is highly feasible, from the experimental results as follows. (1) The rectangular blank was resistance-heated up to 900°C in approximately 2.5s at an average current density of 65A mm-2 in effective value. (2) The input energy control functioned well because of the rapidness of the resistance heating. (3) The designed blank holders worked well. (4) Hot stamping, whose controller is linked to the resistance heating controller, performed successfully.
Effects of coated-layer cracks on a coated layer on a change in friction coefficient are examined. Experimental results indicate that sliding distance influences friction coefficient rather than the cracks on a coated layer. To express the change in friction coefficient due to sliding, a frictional work parameter ω, which is derived as a summation of products of sliding distance and normal pressure, is proposed. In addition, it is demonstrated that ω is a state variable of friction coefficient, which has a sliding-history independence. It is shown that the subsequent friction coefficient during a sequential sliding test can be expressed in terms of two state variables, ω and normal pressure. Finally, a polynomial expression for the evolution of friction coefficient is introduced in contrast to a constant value typical for the Amontons-Coulomb laws.
Steady-state analyses of helical rolling of tubes were carried out by the three-dimensional rigid-plastic finite element method. The analysis results were validated by comparison with hot rolling experiments on steel tubes. Using the calculated velocity field and distribution of equivalent strain rate, equivalent strain and Cockcroft's damage factor were integrated along the streamline. The maximum equivalent strain occurred on the outer surface of the rolled tube and the minimum one occurred at the center of its thickness. The maximum damage factor occurred on the inner surface of the tube. The experimental result for Ni-base alloy tubes showed small cracks on the inner surface. This large damage factor was mainly accumulated just in front of the region of contact with the mandrel, because the wall of the tube bulged out in the radial direction between rolls. The analysis results showed that the increase in drawing velocity and t1/D1 (t1 and D1 denote the thickness and diameter of the rolled tube, respectively) makes the maximum damage factor decrease. There were no cracks on the inner surface of the Ni-base alloy tube that was rolled under the proposed forming condition.