The so-called “thick piece” revolving body means that the thickness h is greater than or equal to the radius R (i.e. H / D ≥ 0.5, where D is the diameter of the workpiece), and the workpiece that will not produce plastic hinge in the rolling process. The rotary rolling forming ofbelongs to the rolling of thick parts. It is worth mentioning that the situation of rotary rolling bevel gear is similar to that of rotary rolling rough cylinder. Therefore, in order to simplify the problem and facilitate the discussion, the situation of rotary rolling bevel gear is often discussed by using the situation of rotary rolling tender and thick cylinder.
The deformation of thick parts during rolling can be divided into the following three types, as shown in the figure:
1,When the H / D of the workpiece is large and the relative feed q is small, the contact area of the conical die is small, the total pressure is small, the lower surface of the workpiece is almost close to the plane, and the contact area of the lower die is much larger than that of the upper die, so that the pressure per unit area at the lower end of the workpiece is less than the yield strength without plastic deformation. At the same time, the active deformation area is equivalent to a wedge, and its shape is wide at the top and narrow at the bottom Therefore, the wedge wedge has a greater impact on the upper part of the workpiece than on the lower part; in addition, due to the rolling or rolling + sliding of the cone die on the workpiece in the rolling process, its friction effect on the workpiece is much smaller than that of the general forging method, which makes the metal on the workpiece surface easier to flow. Therefore, the workpiece surface close to the swing head is easy to yield, and the deformation energy decays too fast from top to bottom along the workpiece, resulting in the deformation of the upper part Large, small deformation at the lower part, forming an upper mushroom shape, as shown in figure (a);
2.When the relative feed rate q is large, the contact area of the conical die is large, so the friction between the die and the workpiece is large, which will seriously affect the metal flow. Therefore, when rolling starts, the upper contact area will undergo plastic deformation, and then the workpiece will adhere to the upper die and become an extension of the die, the lower die contact area will begin to undergo plastic deformation. However, the friction between the lower die and the workpiece is small and easy to be rolled Form lower mushroom shape, as shown in figure (b);
3.When the workpiece is in one of the following two situations, it is easy to form pulley shape, as shown in figure (c) In one case, the H / D of the workpiece is small. During rolling, the workpiece produces axial bending, which reduces the contact area of the lower die, so that the pressure per unit area reaches the yield strength of the material, resulting in plastic deformation, forming the upper and lower plastic deformation areas corresponding to the upper and lower dies. In the other case, the relative thickness of the workpiece at the beginning is large, so there is only the upper contact area In both cases, the active deformation zone is equivalent to “wedge splitting” If the two plastic deformation areas formed at this time cannot be connected, or only part of them are connected, the metal in the upper and lower contact areas will have both tangential flow and obvious radial flow, but the deformation in the middle of the height direction is less than that at both ends, so a pulley shape is formed.