JPH0542483B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses a die having a conical processing portion at the tip to cut the hole edge of a circular hole where stress concentration of a transmission shaft is subjected to bending or torsional loads, etc. This method relates to a method for strengthening transmission shafts with circular holes, which increases the strength of the shaft as a whole and increases the permissible load of the transmission shaft by strengthening the parts. (including a driving shaft, a driven shaft, and a connecting shaft).

(Prior art) Crankshafts, propeller shafts, and other types of power transmission shafts are provided with circular holes through which fluid passes for lubrication, cooling, etc. When a load or the like is applied, stress concentration occurs, and therefore, the hole edge portion where the stress concentration is present must be strengthened.

That is, (1) Stress generated at the edge of the oil hole (circular hole), that is, at the edge of the hole due to bending load.When a bending moment M acts on a shaft member of diameter D that has a circular hole of diameter d shown in Fig. 6. , a large stress is generated due to stress concentration at point A, which is located somewhat in the center of the circular hole. Figure 7 shows the degree of stress concentration. Now the diameter of the circular hole d = 0.1・
If D, the stress concentration rate α=2.4, and a stress of 2.4·M/Z is generated near point A on the inner edge of the circular hole. However, M: moment applied to the axis, Z: section modulus of the round bar (=πD ³ /32). Generally, the diameter of the oil hole attached to the shaft material is 0.1 to 0.2・D.
Therefore, it is inevitable that stress concentration of about 2.0 to 2.4 will occur near point A.

(2) Stress generated on the edge of the oil hole (circular hole) due to torsional load As shown in Figure 8, when the torque shown in the figure is applied to the shaft material with the circular hole, the stress in the axial direction
The maximum tensile stress σmax occurs at the 45° inclined point AA, and the maximum compressive stress σmin occurs at the BB point. Also, on the axis 0-x, 0-y on the shaft skin, there is a maximum stress of 1.33·τ ₀ at points E and F, which are 0.73·r away from points C and D (√ ³ ·r from the center of the circular hole). occurs. Here, r: radius of the circular hole, τ ₀ : shear stress generated on the shaft skin (=16·T/π·D ³ , where T: torsional moment, D: diameter of the shaft).

As shown in FIG. 8, the stress generated at points A and B reaches its maximum at a point that is slightly closer to the center than the edge of the circular hole. Maximum stress points A1 and B1 on the inner wall of the circular hole
The distance between the hole and the edge of the circular hole is about 0.4·r.

FIG. 9 shows the relationship between the stress concentration ratio and d/D (or 2.r/D) at points A, B, A', B', and E, F. Among the three, the stress concentration ratio α A ′, B ′ at points _A ′ and _B ′ is the largest, and considering the case where the hole diameter ratio d/D = 0.1 to 0.2, which is normally drilled as an oil hole, α _A ′, _B
' = 2.15 to 2.30, and a large shear stress is generated around the oil hole. For this reason, in shaft materials with oil holes, A
Also, a crack (cross mark) tilted at 45 degrees to the axis from point B may occur and breakage may occur.

When a circular hole such as an oil hole is drilled in a transmission shaft in this way, the inner surface of the oil hole (hole edge) will have a stress of 2.0% of the standard stress under either bending or torsional stress conditions.
The following countermeasures have been taken in design and construction to avoid stress that is ~2.5 times as large. However, the use of high-strength materials and increased man-hours cannot avoid an increase in manufacturing costs or design inconveniences.

That is, (a) the design has been improved and no oil hole for supplying lubricating oil is provided on the transmission shaft;

(b) Increase the diameter of the transmission shaft or increase the material strength to withstand stress concentration around the oil hole.

(c) Carefully take care of the edge of the oil hole so that no bite marks remain and the stress concentration factor does not become large.

From this technical background, conventional methods for strengthening oil hole holes include pressing a flat or convex plate (see Figure 10a), as shown in Figure 10, or methods used to strengthen bolt holes. (Figure 10b),
A method has been proposed, such as pressing a punch with a cone angle α of about 90° at the tip. In experiments using small test pieces, these methods increased the fatigue limit by more than 50% and are considered to be an effective method for strengthening shaft members with circular holes, but they have not been put to practical use at all. This is because the previously proposed methods of strengthening oil holes by pressing them are difficult to put into practical use, or contain the following basic defects that prevent them from being put into practical use even if they are attempted to be put into practical use.

(Problems to be Solved by the Invention) The conventional example shown in FIGS. 10a and 10b has the following problems.

(a) As mentioned earlier, the maximum stress part of the circular hole edge is 0.4r from the circular hole edge (hole edge) as shown in Figure 6.
It will be in a position closer to the center. In the case of small-diameter shafts, as shown in Figure 5a, simply pressing a flat plate onto the circular hole edge will have a reinforcing effect on the area of maximum stress, but for medium-sized and large-diameter shafts used industrially, the circular hole Even if a flat die is pressed against the chopsticks, no effective strengthening effect can be obtained.

(b) If the circular hole of a rotating shaft is pressed with a flat die, the circular hole will be deformed, and the roundness of the shaft itself will deteriorate, making it unusable for practical use as a rotating shaft.

(c) As shown in Figure 10b, simply pressing with a conical punch does not easily cause plastic flow in the contact area, so an effective strengthening effect cannot be obtained unless the conical punch is pressed with a strong pressure. Therefore, if the method shown in FIG. 10b is used, the shaft will be bent, so it is difficult to put this method into practical use for shaft members.

(Means for solving the problem) The present invention was devised based on the above technical background to solve the problems of the conventional example, and includes:
This method uses a die with a conical shaped part at the tip to strengthen the edge of a circular hole where the stress concentration of the transmission shaft is subjected to bending or torsional loads. Using a first die in which convex portions are formed at predetermined intervals in the circumferential direction along the generatrix, press the conical processing portion against the hole edge portion of the circular hole, and use the convex portion to radially cut only the corresponding portion. A plastic flow is generated outward in the direction, and then a conical processing portion of another second die in which no convex portion is formed is pressed against the hole edge portion of the circular hole.
Provided is a method for strengthening a power transmission shaft with a circular hole, characterized in that a portion not processed by the first die is caused to undergo plastic flow radially outward by a conical processing portion of the die. It is.

(Function) As shown in Fig. 1, the first convex part has a conical processing part at the tip and four convex parts 7-1 to 7-4 along the generatrix on the outer peripheral surface of this processing part. Dice 7-
5, 7-5' are pressed against the circular hole edge (hole edge), and plastic flow is caused in the 45° direction A, B, C, and D portions of the circular hole edge to strengthen it. Next, the second upper and lower dies 7-6, 7-6' having conical processing parts are pressed against the circular hole edge, and the E, F, G and By creating plastic flow in the H section to strengthen it and returning the circular hole edge to a smooth circular shape, the edge of the circular hole where stress is concentrated is strengthened, increasing the strength of the transmission shaft as a whole. This means that the allowable load on the shaft can be increased.

(Example) An example of the present invention will be described in order of steps with reference to FIG.

In FIG. 1, reference numeral 8-10 is a transmission shaft, which in this example has a circular hole 8-9 passed through in the transverse direction.

7-5 and 7-5' have a conical processing part 8- at the tip.
2 and 8-2', respectively, and each of the processing parts has a convex part 7-2 along the generatrix.
1, 7-2, 7-3, 7-4 (the lower die has a common part with a dash), and each convex part is equally spaced in the circumferential direction. In this example, the outer circumferential surface of each convex portion is rounded, and the space between each convex portion is a rounded concave portion.

Therefore, as shown in FIG. 1a, first, the convex portion 7-1
The first conical dies 7-5 and 7-5' having sizes 7-4 and 7-4 are pressurized from above and below the circular hole edge, and the direction (A,
Points B, C, and D (see Figure 1 b) are pressurized to cause plastic flow radially outward and strengthened.
As shown in Fig. 1c, another second die 7-6, 7-6' which does not have the above-mentioned convex part in the conical processing part is pressed against the circular hole edge from above and below, and 45 The protrusions between points A, B, C, and D in the ゜ direction (see Figure 7b), points E, F, G, and H are pressurized to cause plastic flow in the radial direction and strengthened. In addition to eliminating the unevenness of the circular hole edge and making it smooth, the axial direction where the maximum bending stress occurs is strengthened by pressure.

The tip angle α of the conical die (see Figure 1) is 20°~
90° is appropriate. The selection is based on the position of the maximum stress part shown in FIG.
and the ratio of R of the circular hole edge/diameter of the circular hole d. If the diameter of the circular hole is small (approximately 15 mm or less), consider the d/D and R/d ratios, determine the optimal tip angle α ₁ , and pressurize only with a die with this tip angle α ₁ . , the hole diameter is 15mm or more, especially
When the diameter exceeds 20 mm, it is recommended to use dies with two or three types of tip angles α ₁ , α ₂ or α ₁ , α ₂ , α ₃ to pressurize and strengthen the area around the maximum stress area. good.

A specific example of the pressure processing apparatus will be described with reference to FIG.

In FIG. 2, 8-1 is a fixed frame, on which a lower die 7-5', a pressurizing cylinder 8-3 and a movable frame 8-4 are attached.
It is attached via pins 8-5 and 8-6. An upper die 7-5 is attached to the movable frame 8-4 via a spherical seat 8-8, and the spherical seat 8-8 connects the axis of the circular hole 8-9 with the upper and lower dies 7-5, Even if the lines connecting the centers of 7-5' do not match, no strain will occur due to the pressure applied by the upper and lower dies. To take out or insert the shaft member 8-10 from the pressurizing jig, remove the pin 8-5 and move the movable frame 8-4 to the pressurizing cylinder 8-
This is done by removing it from 3.

The die pressing force P is first calculated using equation (1).

P=k・π・d・√・・sinα/2・Ym ...(1) where k: Constant determined by processing method Method according to the present invention k=0.6 Method using conical die k=1.0 d: Circular hole Diameter mm R: Radius of the circular hole edge mm α: Die cone tip angle Ym: Yield point of material Kg/mm ² The circular hole edge is The maximum deformation rate of the circular hole diameter is Δd/di, however, the symbols used are as shown in Figure 3, and are 0.02.
Adjust the die pressing force to ~0.03. This is one of the values that form the basis of the present invention, as the reinforcing effect is greatest when the maximum deformation rate is 0.02 to 0.03, as shown in FIG.

When the maximum deformation rate is 0.02 to 0.03, the die contact length h (see FIG. 3) is approximately expressed by equation (2).

h〓0.28～0.35・√・ ...(2) Here, d: Diameter of the circular hole mm R: Radius of the circular hole edge mm In actual operation, it is convenient to take the length of the die contact part as the standard. The quality of the operation can be determined by comparing the value of h calculated by equation (2) with the measured value of the length of the die contact portion measured after the operation.

According to the first and second pressurizing jigs shown by the upper and lower dies, in the machining process of pressing the upper and lower dies 7-5, 7-5' against the circular hole chopper, the shaft member 8-
No bending or other loads are applied to 10. Additionally, dies 7-5, 7-5' having four convex portions and second conical dies 7-6, 7- having no convex portions are used.
Since the pressure machining of the circular hole chopper is performed in two parts (6'), as is clear from equation (1), the pressure around the circular hole is 40% lower than when using a simple conical die. is reinforced to the desired strength, and the shaft material 8-10
Almost no bending occurs.

FIG. 5 shows an example of the use of the present invention. FIG. 5a relates to the oil hole openings 11-1 and 11-2 of the crankshaft. When a bending load is applied to the crankshaft, maximum stress occurs in the pins and the journal fillets 11-3, 11-4. When a torsional load is applied, the oil hole openings 11-1, 11-2
Maximum shear stress occurs at Although pins and journal fillets can be strengthened by cold rolling, a method for strengthening oil hole openings has not yet been developed.

The permissible transmission torque of the crankshaft depends on the stress around the oil hole, so in response to the recently developed energy saving requirements, the shaft diameter of the crankshaft that satisfies the requirements for low rotational speed and large torque transmission, such as in engines, is I had to make it bigger. However, when the oil hole opening is strengthened by the strengthening method of the present invention, it becomes possible to reduce the shaft diameter or use a low-strength material.

FIG. 5b relates to the control oil introduction opening 11-5 of a variable pitch propeller (CPP).
CPP requires a control oil introduction hole for pitch change, but the diameter of the shaft 11-6 on which the control oil introduction hole opening 11-5 is provided is made large to prevent stress near the opening from increasing. There is. However, if the method of strengthening circular hole chopsticks according to the present invention is applied, there is no need to increase the shaft diameter, making it possible to reduce the cost.

In addition, in power transmission shafts used in general industrial machinery, it is sometimes difficult to provide oil holes from the viewpoint of strength, but when the strengthening method of the present invention is used, it is difficult to select the position of the oil hole opening. There are almost no restrictions.

Note that the circular hole in the present invention includes an air hole in addition to an oil hole, and may be a circular hole with a bottom. If there are, the number is not limited to four.

(Effects of the Invention) The effects of the present invention are that, by using a small die pressing force, the fatigue limit of the shaft material with a circular hole can be set to the same value as that without a circular hole, without causing dimensional changes such as bending in the shaft material with a circular hole. The goal lies in the fact that it can be raised to the highest level.

The effects will be explained below using examples.

1 The fatigue limit of the conventional method proposed so far for S45C, shaft material with a shaft diameter of 20 mm and no circular hole was 30 Kg/ ^mm2 , but if a circular hole of 3.5 mm in diameter was added to this, the fatigue limit The weight decreases to 18Kg/mm ² (approximately 60% of that without the circular hole). When a load of 10 tons is applied to the hole part of this shaft material with a circular hole using a flat die (the method shown in Figure 10a), the fatigue limit increases to 26 kg/ ^mm2 , which is almost the same as that without a circular hole. Restore to strength. However, when a load of 10 tons is applied, the shaft material deforms significantly, making it impossible to put it to practical use. This is because, as shown in Figure 11, the maximum stress area is located slightly in the center of the circular hole edge, so in order to obtain a strengthening effect only by pressurizing the circular hole edge with a flat die, it is necessary to This indicates that a large pressure force must be applied to the circular hole chopper, making it almost impossible to apply the reinforcement method using flat dies to large shafts used industrially.

2 Strengthening effect by the present invention Similar to the above test, a diameter 100 mm made of S45C material
A circular hole with a diameter of 10 mm was drilled in the center of the mm shaft member, and a radius of 5 mm was made on both edges to prepare a plane bending fatigue test piece.

After pressurizing this circular hole edge (hole edge portion) using dies with conical tip angles of 22.5° and 45° according to the present invention at pressing forces of approximately 1000 kg and 1800 kg, a plane bending fatigue test was conducted. Fatigue limit is 28
It was measured as Kg/ ^mm2 . This value is 20 as mentioned in section 1.
This is slightly lower than the fatigue limit of 30Kg/mm ² for a shaft with a diameter of mm, but this is due to a dimensional effect, and the fatigue limit of 28Kg/mm ² is lower than that of a 100mm shaft without a circular hole. Almost equal to the fatigue limit.

As described above, according to the technology for strengthening circular hole chopsticks of the present invention, even if a circular hole such as an oil hole is made in the shaft material, the circular hole chopstick can be strengthened by applying a pressure of about 2000 kg. It is reinforced and has almost the same fatigue limit as without the hole. Furthermore, although the examples described in this section are only related to the plane bending fatigue limit, it is generally understood that the relationship shown in equation (3) holds between the plane bending fatigue limit (σw) b and the torsional fatigue limit τw. Since τw = (σw)b/√3...(3) It is highly inferred that the torsional fatigue limit, like the bending fatigue limit, will increase to the value when there are no holes.

Even if a metal material is subjected to an equal pressure such as hydrostatic pressure on its entire surface, it will hardly harden, and almost no residual stress will be generated. In order to harden and strengthen metal materials through pressure working, plastic flow must occur. The present invention uses the processing jig shown in Fig. 2, and uses a conical die having four protrusions in orthogonal directions, with the protrusions tilted at 45 degrees with respect to the axis of the circular hole chopper. Apply pressure in the direction of
The areas where the maximum shear stress occurs due to torsional load under processing conditions where plastic flow is likely to occur are strengthened, and then the convex part of the circular hole edge (the area where the conical die did not touch in the previous process) is strengthened. Pressure-processed using another conical die that does not have a convex part,
The parts where the maximum stress occurs under bending load are strengthened, and the circular hole edges are formed smoothly. In this way, by pressurizing the die contact surface under conditions that facilitate plastic flow, a large strengthening effect can be obtained with a small pressurizing force.

[Brief explanation of the drawing]

Figures 1 a, b, c, and d are a plan view and a cross-sectional view showing an embodiment of the present invention in the order of steps, Figures 2 a and b are an elevational view and a view indicated by arrow A of an example of the same device, and Figure 3 4 is an explanatory diagram showing the symbol of the die contact part, FIG. 4 is an explanatory diagram showing the relationship between hole diameter expansion rate and fatigue limit increase rate, and FIGS. 5 a and b are front views showing two usage examples of the present invention. Figure 6 is an explanatory diagram showing the state where bending stress is applied, Figure 7 is a graph showing the stress concentration rate of the circular hole edge (hole edge) when bending moment is applied, Fig. 8 is an explanatory diagram of the state in which torsional torque is applied, Fig. 9 is a graph showing the stress concentration rate of the circular hole edge when torsional torque is applied, and Fig. 10 a and b show two conventional examples. The explanatory diagram, FIG. 11, is an explanatory diagram showing the maximum stress part of the circular hole chopstick. 7-1, 7-4... Convex portion, 7-5, 7-5'...
...First die, 7-6, 7-6'... Second die, 8-2, 8-2'... Conical processing part, 8-
9...Circular hole, 8-10...Transmission shaft.

Claims (1)

[Scope of Claims] 1. A method of strengthening the hole edge portion of a circular hole where the stress concentration of a transmission shaft that is subjected to bending or torsional loads is performed using a die having a conical shaped portion at the tip, the die having a conical shape. Using a first die in which convex portions are formed on the outer circumferential surface of the processed portion along its generatrix at predetermined intervals in the circumferential direction, the conical processed portion is pressed against the hole edge portion of the circular hole, and the conical portion is pressed against the hole edge portion of the circular hole. Plastic flow is caused only in the portion corresponding to the hole in the radial direction outward, and then the conical processing portion of another second die in which no convex portion is formed is pressed against the hole edge portion of the circular hole.
The conical processing portion of the second die
A method for strengthening a power transmission shaft with a circular hole, which is characterized by causing plastic flow in the portion that has not been machined with a die radially outward.