Backward extrusion is the most common method of forming bosses within product cases. However, backward extrusion requires a very large forming load, and has the disadvantage of producing dimple defects when forming thin sheets. To overcome this disadvantage, we developed a method of bottom compression drawing to replace backward extrusion. Bottom compression drawing is a technique in which, during normal drawing, back pressure from the counter punch that opposes the drawing punch applies a load on the blank, so that compressive force acts on the bottom face of the blank. Bosses are formed at the same time as the case is formed as a result of this drawing. Backward extrusion and bottom compression drawing were compared using both FEM analysis and experiment in the formation of solid bosses. The results showed that bottom compression drawing could form a piece with about 50% of the forming load used in backward extrusion because the radial compression stress in the bottom material is reduced by the tension in the bottom compression drawing.
Backward extrusion is the most common method of forming bosses within product cases. However, backward extrusion requires a very large forming load. To overcome this disadvantage, we developed bottom compression drawing to replace backward extrusion in our previous study. In this study, the formability and boss forming limit in bottom compression drawing are investigated by a series of experiments and finite element analysis. The results showed that the failure at the punch shoulder occurs when the radial tensile stress at the punch shoulder reaches the tensile strength of the sheet metal. With increasing surface roughness of the counterpunch, the formable zone of a solid boss expands. Adhesion on the counterpunch surface can be observed with repeated forming cycles under a dry condition, but the irregularity in the product configuration converges to a befitting level after a few forming cycles.
A number of reduction gear units with small electric motors as power sources are used in automobiles. Smaller units with a low energy consumption are required for future electric vehicles. Although worm gears are widely used in units with a large gear ratio, their efficiency is too low. Therefore, only large motors can be applied in cases where a large torque is required. Even cylindrical gear pairs and/or face gears with a large gear ratio could enable reduction gear units to have a higher efficiency and a lower energy consumption. For this purpose, helical gears with a small number of teeth and a large helix angle are necessary. In the present paper, cold form rolling for forming such gears was proposed. The tooth form accuracy of form-rolled gears was compared with those cut using a hob. Furthermore, the efficiency and service life of the gears were examined. The results show that cold form rolling can be used to form helical gears with a small number of teeth and a large helix angle.
Hot ring rolling is a useful process for producing large seamless rings. The ring rolling mills are classified into two types, i.e., two-roll-type and three-roll-type by roll layout. In our previous studies, the deformation characteristics in the three-roll-type ring rolling process have been investigated experimentally and numerically. In this study, a numerical simulation of the asymmetric product was performed by FEM together with the ALE method. The relative velocity between the ring and the rolls in the three-roll-type ring rolling process is low compared with that in the two-roll-type ring rolling process because of the roll layout. The reduction in the relative velocity improves the surface condition of the material and roll life. In the three-roll-type ring rolling mill, the rotation axes of the two main rolls lean from the horizontal axis. Therefore, the circumferential velocity of the main rolls has a transverse component in the roll bite. This velocity component introduces ring deformation toward the z-direction in the roll bite. In the production of asymmetric products, three-roll-type ring rolling has an advantage of formability over the two-roll-type ring rolling.
A skinpass rolling experiment using a dull-finished work roll of commercial-scale diameter has been performed on cold rolled strips with various steel grades to clarify the characteristics of roll force behavior and the transcription of material surface roughness. The effects of elongation, tension, lubrication and work roll diameter on rolling load and material surface roughness have been investigated for various steel grades, elongations given by rolling, lubrication conditions of rolling, entry and delivery tensions, and work roll diameters. The results show that steel grade, elongation, tension, especially delivery tension, and work roll diameter have significant effects on rolling load.The effect of lubrication conditions becomes notable for 1% elongation or more. The transcription of roll surface roughness to a material surface is enhanced with higher rolling load and larger elongation. Hence,if sufficient elongation is given by rolling, the control of the surface roughness of high-strength materials becames easier.
A square steel pipe is reshaped from a welded round pipe by roll forming. The effect of ellipse preforming on the cross-sectional size of the square steel pipe was investigated by experiment and three-dimensional finite element simulation. When designing a roll-forming machine for a square steel pipe, the diameter of the paired top and bottom rolls is usually set larger than that of the side roll pair, thereby avoiding interference between the roll axes driven by electric motors. When the diameter of the top roll is larger than that of the side roll, the width of a corner part of the formed pipe is larger than the height. A square pipe was formed from a preformed elliptical pipe to make the width and height of the corner part equal. As a result of ellipse preforming, the peripheral length of a square product increases and the size of the corner part of that product decreases. Therefore, elliptical preforming is effective in forming square pipe with a sharp corner. However, excessive preforming causes a hollow at the flat surface of a square product.
Magnetic pulse welding is effective for lap-joining similar and dissimilar sheet metals such as Al/Al, Cu/Cu, and Al/Cu. A discharge circuit is used for the seam welding. It is composed of a flat one-turn coil and an energy-storing capacitor bank. The coil is an important component to obtain a high-density magnetic flux, and is made of one copper alloy plate, instead of a winding. The influence of the seam length of a sheet metal has been confirmed by welding an aluminum sheet to another aluminum sheet. It has been clarified that magnetic pulse welding is suitable for joining a sheet metal with increasing seam length, because the effective inductance increases with increasing seam length. As a result of investigating the transfer quantity of the electric energy from a capacitor to a coil, it has been found that magnetic pulse welding with a high energy efficiency can be used to join sheet metals if the transfer coefficient is large. On the basis of the experimental results, the influence of the remaining inductance on the transfer coefficient is calculated. A decrease in the remaining inductance adds to the welding capability of equipment and reduces the electric energy consumption.
To obtain fine and uniform microstructures, appropriate forging conditions were examined using high-speed large-reduction forging. Swing-type forging equipment was employed in hot-forging experiments using low-carbon steel (0.14%C-0.64%Mn). Also, a microstructure analytical system was developed by combining thermomechanical FE analysis with microstructural analysis to discuss the metallurgical phenomena occurring during forging. It was observed that coarse austenite grains can be refined to 20-30 μm uniformly using the proposed forging technology in the case of 59% reduction in thickness at 1273 K. In this case, dynamic recrystallization is a dominant factor for obtaining fine and uniform austenite grains. In the case of 43% reduction in thickness, the recrystallization is inhomogeneous, resulting in an inhomogeneous microstructure. Thus, about 60% reduction in thickness is necessary to obtain fine and uniform microstructures using the proposed technology when applied to the roughing of hot strip mills.