JPH0450092B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a stepped forming method for shaft members.

[Prior Art] Generally, when a shaft member is stepped, a cut is made in the stepped portion of the shaft member using a back cutting tool, and then a reduced diameter portion is forged and formed.

That is, as shown in FIG. 2, a pair of back cutting tools 2 are pressed against both sides of the stepped portion of the forged shaft material 1, and the back cutting tools 2 are pushed in with the anvil 3 to cut the stepped portion of the shaft material 1. After making a cut to an appropriate depth, the shaft material 1 is rotated by a predetermined angle and the above-mentioned cutting operation is repeated again using the back cutting tool 2, thereby cutting the entire circumference of the stepped portion of the shaft material 1. Add. At this time, the axial center portion of the shaft member 1 may expand and deform under the action of the tensile stress in the axial direction, resulting in defects. This defect is usually discovered only after the forging, heat treatment, etc. processes have been completed, and by ultrasonic flaw detection after grinding, and the shaft material becomes a defective product that cannot be recycled. Furthermore, since it takes several weeks to several months to manufacture large steel forgings, for example, the occurrence of defects during forging poses a serious hindrance in terms of process control, production efficiency, yield, and the like.

Therefore, the present applicant proposed a stepped forming method for preventing the occurrence of defects in the stepped forming described above, in the patent application filed in 1983-
This has already been proposed in No. 158966 (Japanese Unexamined Patent Publication No. 61-37342). This stepped forming method, which has already been proposed,
Back cutting ratio t/R of a pair of back cutting tools [t is the limit cutting amount of the back cutting tool in the radial direction of the shaft material, R is the diameter reduction part of the shaft material before the cutting process by the back cutting tool radius] is set below the allowable back cutting ratio (0.08+6/θ) [θ is the wedge angle (degrees) of the back cutting tool] without causing defects in the shaft material.

That is, according to the stepped forming method already proposed above, when forming a shaft material with a large step, a cut within the above limit is added, the reduced diameter part is temporarily formed, and then the cut is made again. By repeatedly molding the diameter-reduced portion with a small amount of material, it is possible to prevent defects from occurring.

[Problems to be Solved by the Invention] However, in the stepped forming method already proposed above, the limit depth of cut without causing defects determined by the allowable back cut ratio is relatively small. small. Therefore, it takes time to form the temporary reduced diameter portion, the temperature of the forged shaft material decreases, and in some cases, it becomes necessary to increase the number of times the forged shaft material is heated.

An object of the present invention is to make it possible to expand the limit cutting depth of a back cutting tool without causing defects in the shaft material.

[Means for Solving the Problems] The present invention provides a stepped forming method for a shaft material, in which a cut is made in the stepped portion of the shaft material using a back cutting tool, and then a diameter-reduced portion is forged and formed. , the preparation added to the stepped section is
A back cutting tool with a wedge angle θ is used to cut only from one side of the stepped part, and the limit cutting depth t is set to the radius R of the shaft material before cutting, t/R≦0.15+(7.5 /θ) 25 degrees≦θ≦50 degrees.

[Function] According to the present invention, as shown in FIG. 1, the axial center of the shaft material 1 is cut by cutting only from one side of the stepped portion of the forged shaft material 1 using the back cutting tool 2. It becomes possible to significantly reduce the axial tensile stress generated in the axial direction, and also to reduce the axial elongation strain. Therefore,
Even when the cut by the back cutting tool 2 is set deeper within the range of the above-mentioned limit cut amount, defects will not occur in the shaft material 1. That is, it becomes possible to expand the limit cutting depth of the back cutting tool without causing defects in the shaft material.

[Example] Hereinafter, the basis for establishing the present invention will be explained in detail.

The integral value of the strain that occurs in the axial center of the shaft material during stepped forming using the back cutting tool can be measured as the axial elongation of the material due to the cutting depth of the back cutting tool. Therefore, the diameter
Make a white plasticine billet of 100 mm and length 145 mm, mark the circumferential surface with gauge lines with an axial gauge interval of 85 mm, and mark the wedge angle (apex angle) θ in the center.
Add a cut around the billet with a 45 degree back cutting tool,
The elongation was measured. The growth is shown in Figure 3.
Here, the ○ mark in the figure is the result when cutting with a pair of back cutting tools as in the conventional method, while the ● mark is the result when using the method of the present invention, and the difference from the conventional method is The point is that there is only one back cutting tool. That is, as shown in FIG.
In this method, a triangular spine cutting tool 2 is placed on top of the triangular cutting tool 2 to make a cut, and the shaft member 1 is rotated slightly and the cutting is repeated until the cut is made to a predetermined depth.
According to the method of the present invention, it is recognized that the elongation in the axial direction is smaller than that of the conventional method, that is, the amount of elongation and strain in the axial center portion is small.

In addition, a small pressure detector with a diameter of 6 mm was embedded in the axial center of a billet of the same size, and the axial stress at the time of cutting was measured. The results are shown in FIG. Here, the ○ marks in the figure are the results obtained by the conventional method, and the ● marks are the results obtained by the method of the present invention. Although the axial tensile stress increases with the increase in the depth of cut in both the conventional method and the method of the present invention, it is recognized that the tensile stress in the case of the method of the present invention is low.

That is, in the case of the method of the present invention, although the axial center part expands and deforms under the action of a lower stress when making a cut with the back cutting tool, the amount of elongation is smaller than that of the conventional method, and therefore the axial center part It is clear that defects are less likely to occur.

By the way, the stress and elongation mentioned above that occur when cutting with a back cutting tool are due to the so-called wedge effect of the back cutting tool, so if the wedge angle θ is made smaller, the stress and elongation will become smaller, and even if the cut is made deeper, defects will not occur. This means that there will be no occurrence of Here, we will explain in detail how to use the triangular back cutting tool.
As shown in Fig. 5A, in order to make a step on the left side of the shaft material 1, a cut is made with one wedge surface of the back cutting tool 2 whose wedge angle θ is approximately 45 degrees, and then the right step is made. Add a cut for the attachment part, but at this time, see Figure 5A.
As shown in , rotate the back cutting tool 2 90 degrees and make a cut with the other wedge surface. Therefore, we used a triangular back cutting tool 2 with a triangular cross section to reduce the wedge angle θ (θ<
45 degrees), only one wedge surface can be used as shown in Fig. 5B, and in order to form the left and right stepped parts as shown in Fig. 5A, the direction of the oblique side is symmetrical to that of Fig. 5B. It is necessary to replace it with another triangular spine cutting tool, and since the contact width with the anvil 3 is narrow, it is unstable and may rotate during cutting. However, this problem can be solved by using an L-shaped back cutting tool 2 having an L-shaped cross section as shown in FIGS. 5C and 6. That is, according to this L-shaped back cutting tool 2, it is stable even if the wedge angle is small, and moreover, by utilizing both wedge surfaces, it is possible to perform deeper and more efficient cutting operations according to the present invention. .

Next, the limit depth of cut of the back cutting tool in the present invention will be explained based on specific implementation results.

(Execution result 1) Outer diameter (2R) 1500mm uniformly heated to 1250℃,
For a shaft material made of Ni-CrMoV steel with a length of 3000 mm, in order to form reduced diameter parts with an outer diameter of 1000 mm on both sides of the shaft center length of 2000 mm, a back cutting tool with a wedge angle θ of 50 degrees was used. A stepped molding method according to the present invention was carried out. That is, the shaft material extracted from the heating furnace was placed on a flat anvil, and one triangular back-cutting tool was placed on top of the shaft material, and it was pressed down with a press to make a cut. The depth of cut is t=225mm, so the back cut ratio is t/
R=225/750=0.3. After making the cuts, it was forged and stretched with a flat anvil until it reached an outer diameter of 1000mm. After heat treatment and cooling, this forged shaft material was subjected to ultrasonic flaw detection over its entire length in the axial direction, and as a result, no defects were detected from the axes of both stepped portions. The results are shown in FIG. 7 in comparison with the conventional method disclosed in Japanese Patent Application No. 59-158966. In other words, in the conventional method, defects were observed when cutting to a depth of cut t = 225 mm, that is, a back depth ratio t/R = 0.3, with a pair of triangular back cutting tools (wedge angle θ = 45 degrees). . (X mark at θ=45 degrees in Figure 7).
Therefore, in the conventional method, the limit depth of cut is t/R=0.08
+6/θ or less, and when the wedge angle θ = 45 degrees, the above t/R = 0.21, so the depth of cut t = 150 mm
(t/R=0.2) to temporarily machine the reduced diameter part to an outer diameter of 1200 mm, and then cut again to form a reduced diameter part with an outer diameter of 1000 mm. (○ mark at θ = 45 degrees in Figure 7). In this way, in the conventional method, the cutting is performed in two steps, but according to the method of the present invention, the depth of cut in one cut by the back cutting tool, that is, the limit depth of cut, is set as t/R= No defects were observed up to 0.3.

(Execution result 2) In order to form reduced diameter parts with an outer diameter of 600 mm on both sides of the center 1550 mm of a 3% Cr steel ingot with an outer diameter (2R) of 1200 mm that was uniformly heated to 1180 °C, a wedge angle θ of 25 degrees was used. A cut was made using an L-shaped back cutting tool according to the present invention. Place the shaft material on a flat anvil, place an L-shaped back cutting tool on top of it, and press down with a press to make cutting depth t=
The depth of cut was added to 270mm. During the cutting process, the back cutting tool did not rotate unstablely, and the cutting process was carried out as smoothly as the conventional triangular back cutting tool with a wedge angle θ of approximately 45 degrees. Thereafter, it was molded to an outer diameter of 600 mm using a flat anvil, then heat treated and cooled. Thereafter, the entire length in the axial direction was subjected to ultrasonic flaw detection, and no defects were found. In this case, the back-cut ratio is t/R=270/600=0.45, and the results are shown in FIG.

(Implementation Result 3) Figure 8 shows the results of implementation showing the relationship between the wedge angle θ and the allowable back cutting ratio t/R of a wider range of back cutting tools. This indicates that an ultrasonic defect of 1.0 mm or less was present.

Regarding the appropriate range of the wedge angle θ of the back cutting tool, the following was confirmed through experiments.

As the wedge angle θ of the back cutting tool increases beyond 50 degrees (θ>50 degrees), the drooping deformation of the shaft material during cutting increases, and the sharpness of the back cutting tool deteriorates.

From the point of view of preventing defects in the shaft material, the smaller the wedge angle θ of the back cutting tool, the better. However, if the wedge angle θ is smaller than 25 degrees (θ < 25 degrees), the cutting edge of the back cutting tool will become thinner. This results in deformation and cracking of the cutting edge during hot working.

That is, the above (implementation result 1), (implementation result 2),
According to (implementation result 3), the limit depth of cut of the back cutting tool in the present invention is defined as the area shown by the mesh line in FIG. When the radius of the material is R, it is recognized that it can be extended to the range determined by t/R≦0.15+(7.5/θ)...(1) 25 degrees≦θ≦50 degrees...(2).

Therefore, according to the present invention, by adding a depth of cut with one back cutting tool, the limit depth of cut can be made deeper than when cutting is performed with a pair of triangular back cutting tools in the conventional method. becomes possible. This makes it possible to omit the process of cutting to the limit depth of cut and temporarily forming a reduced diameter part, which is required in conventional methods, when the amount of steppedness to be formed on the shaft material is large. In some cases, it becomes possible to reduce the number of times the shaft material is heated.

[Effects of the Invention] As described above, the present invention provides a stepped forming method for a shaft material, in which a cut is made in the stepped portion of the shaft material using a back cutting tool, and then a diameter-reduced portion is forged and formed. In this case, the cut into the stepped part is made only from one side of the stepped part using a back cutting tool with a wedge angle θ, and the limit cutting depth t is set as the radius R of the shaft material before cutting. t/R≦0.15+(7.5/θ) 25 degrees≦θ≦50 degrees. Therefore,
It becomes possible to expand the limit cutting depth of the back cutting tool without causing defects in the shaft material.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the state of implementation of the present invention;
The figure is a front view showing the conventional method, Figure 3 is a diagram showing the relationship between billet depth of cut and axial elongation, and Figure 4 is a diagram showing the relationship between billet depth of cut and axial tensile stress. , Figures 5A to 5C are schematic diagrams showing how the back-cutting tool is used, Figure 6 is a front view showing the L-shaped back-cutting tool, and Figure 7 is a diagram showing the wedge angle of the back-cutting tool and the allowable back-cutting ratio. FIG. 8 is a diagram showing the relationship between the wedge angle of the back cutting tool, the allowable back cutting ratio, and the presence or absence of defects. 1... Shaft material, 2... Back cutting tool.

Claims (1)

[Scope of Claims] 1. In a stepped forming method for a shaft material in which a cut is made in a stepped portion of a shaft material using a back cutting tool, and then a diameter-reduced portion is forged and formed, the stepped portion is The additional preparation is performed only from one side of the stepped part using a back cutting tool with a wedge angle θ, and the limit cutting depth t is set as t/R≦ with respect to the radius R of the shaft material before cutting. 0.15+(7.5/θ) A stepped forming method for shaft material characterized by setting 25 degrees ≦ θ ≦ 50 degrees.