Application of conical plate upsetting in forging of large forgings (figure)

Ingot upsetting is an important forming method in forging of large forgings. Due to the inevitable defects such as shrinkage, porosity, segregation and inclusions in the ingot, if the deformation and mechanical conditions are not correct during the upsetting process, it is easy to develop into a crack at the initial stage of deformation, resulting in the scrapping of the entire ingot. This is an important reason for the occurrence of waste in the forging of large forgings, which brings huge economic losses to the country.

How to create favorable mechanical conditions and prevent the ingot from cracking during the upsetting process is a subject of great theoretical significance and significant economic value. Many experts and scholars have done a lot of research work and proposed the use of spherical plates and dish-shaped plates for upsetting (Figure 1).

Figure 1 Three forms of thick plates
(a) flat plate (b) spherical plate (c) dish plate

The author believes that the use of spherical plates and dish-shaped plates can improve the hydrostatic pressure inside the ingot, improve the plasticity of the material and prevent the occurrence of cracks, but there will be a large range of difficult-to-deform regions near the spherical plate and the dish. As a result, the fracture of the as-cast crystal grains in the region is incomplete, the internal pores are difficult to forge, and the mechanical properties of the material cannot be improved, which also makes the forging quality not reach the standard.

The literature [1] proposes to use a conical plate upsetting, which is a novel idea. This new process has been successfully applied in production to effectively prevent cracks. According to the conventional point of view, the conical plate is easier to crack the ingot than the plate upset. Why is it true that the use of a conical plate is thick and can indeed inhibit the generation of cracks? This paper theoretically analyzes this.

Using the principal stress method, it can be inferred that when the plate is upset (Fig. 2), the positive pressure σz on the contact surface is:

Figure 2 slab upset

The tapered plate is upset (Fig. 3) and the stress σz on the contact surface is:

Where k1=tanα+tanβ

K2=-k1s+τ(2+tan2α+tan2β)

The examples are illustrated below.

Example: A round blank having a diameter d and a height h is set up between the flat plate and the tapered plate. Assuming frictional force τ = 0.5S, cone angle α = β = 20°, and setting h = d / 2, these data are substituted into equations (1) and (2), respectively, and the rough normal stress of the plate is:

Its distribution curve is shown in Figure 2, which is a linear distribution.

The taper plate upset normal stress σz is:

Its distribution curve is shown in Figure 3, distributed in a logarithmic curve. Comparing Fig. 2 and Fig. 3, it can be seen that the normal stress of the upset of the tapered plate is obviously smaller than the normal stress of the upset of the flat plate, so the hydrostatic pressure is correspondingly reduced, the plasticity of the material is reduced, the internal defects are easily developed, and the ingot is easily cracked. . This is why people are reluctant to use the tapered plate.

Figure 3 Conical plate upset (late)

Why is the literature [1] proposed, and it has been proved by practice that the use of conical plate upsetting can suppress the internal crack of the ingot? Comparing the difference between the plate upset and the conical plate upset, it can be found that when the plate is upset, the circle The end face of the blank is in contact with the flat plate at the same time, and the inside and the outside of the billet are simultaneously subjected to upsetting deformation. The radial compressive stress σr due to the friction of the contact surface is not very large.

The conical plate is different in thickness (Fig. 4). The conical plate first contacts the end surface of the round billet with the center taper tip, and then the contact taper surface is gradually enlarged, and the corresponding upset deformation zone is gradually enlarged from the inside to the outside. At the periphery where the end face is not in contact with the tapered plate, the upset deformation is not started, but is radially outwardly flowed under the expansion of the internal upsetting metal. Therefore, the entire round blank can be divided into two zones, and the outer zone is relatively thickly walled by internal pressure, and the inner zone is tightly hooped. The inner zone is equivalent to upsetting under high side pressure. Let the maximum radius of the contact cone at a certain moment in the deformation process be ρ (Fig. 4), then the side pressure is:

Figure 4 Conical plate upset (previous period)

The axial stress σz of the inner zone is:

Substituting (6) into it gives:

It can be seen from the equations (6) and (7) that when the upset is started, ρ = 0, and the side pressure q is the largest until the end faces of the round billet are all in contact with the tapered plate, at this time ρ = d / 2 and the side pressure q = 0. It can be seen that the internal upset before ρ=d/2 is the upset with the side pressure q, the hydrostatic pressure is high, and the material plasticity is good. Therefore, the generation of internal cracks can be suppressed, which is advantageous for the forging of internal defects. After ρ=d/2, the upset has entered the late stage, the defects have been closed, the material properties have been improved, and the possibility of cracking is greatly reduced. Of course, if the angles α and β of the tapered plate are appropriately selected according to the height and diameter of the ingot, the effect of suppressing crack generation is also better.

The use of a tapered plate for upsetting is simple and effective, and will play an important role in the large forging forging industry.

references

[1] Liu Zhubai. New plastic forming technology and its mechanical principle. Beijing: Mechanical Industry Press, 1995.

[2] Wang Danian. Principle of metal plastic forming. Beijing: Mechanical Industry Press, 1985.

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