JPH0270341A - Manufacture of driving shaft made of steel pipe - Google Patents

Abstract

PURPOSE:To make a product light in weight and to improve its reliability by using a difference thickness steel pipe which has a thickness increased part at an equal interval in the longitudinal direction of the pipe and whose wall thickness ratio of the thickness increased part and a usual wall thickness part is above a specific value, as a stock, cutting the thickness increase part to a short pipe, and performing connection use spline working to both pipe and parts. CONSTITUTION:A difference thickness steel pipe in which a usual part 1 and a thickness increased part 2 in the pipe longitudinal direction are formed, and a wall thickness ratio of the thickness increased part and the usual part is >=2 is used as a stock. Said steel pipe is cut to a short pipe in the center of the thickness increased part 2, and thereafter, a driving shaft is manufactured by forming a spline 3 on the outside periphery of both end parts by machining. the driving shaft which is obtained in such a way scarcely causes a variance of a fatigue service life, and has an excellent fatigue strength. Also, as another method, the difference thickness steel pipe having the thickness increased part is cut in the center of the thickness increased part 2, and to both ends of the steel pipe which is obtained, a stem part which is prepared separately is brought to friction welding. A welding burr generated in the outside periphery of a friction weld zone is cut by machining. In such a way, the driving shaft is made light in weight, and also, the fatigue strength of the driving shaft and the reliability of a product can be improved.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a drive shaft such as a drive shaft used in an automobile using a steel pipe as a material.

[Conventional technology]

Drive shafts used in automobiles have traditionally been manufactured mostly from steel bars, but recently, consideration has begun to switch from steel bars to steel pipes. First, by switching from steel bars to steel pipes,
The weight can be reduced, and vehicle dynamic performance such as acceleration performance can be improved. The second reason is that the natural frequency can be changed outside the engine speed range, resonance phenomena can be avoided, and vibration and noise can be reduced. There are two main methods for manufacturing such steel pipe drive shafts as follows. One method is to use an integrally molded steel pipe drive shaft as shown in FIG. 5, in which the end of the steel pipe a is drawn, and then the drawn part C is splined. The other case is a welded assembly type steel pipe drive shaft as shown in Fig. 6, in which a stem e with a pre-splined constriction part C is welded to both ends of the steel pipe a (f indicates the welded part). It is something. [Problems to be Solved by the Invention] Among these manufacturing methods, those that manufacture integrally molded steel pipe drive shafts suffer from slight angular deviation and uneven wall thickness in the circumferential direction, which are difficult to avoid in manufacturing. This may be increased by end drawing and become a noticeable flaw. Such flaws become starting points for fatigue cracks due to repeated torsional loads during use.
This causes the problem of reducing the fatigue strength of the drive shaft. On the other hand, in the method of manufacturing a welded assembly type steel pipe drive shaft, the end of the pipe is not drawn, so the angularity and uneven wall thickness of the raw steel pipe are not promoted, but the heat generated during welding As a result, a softened area called a heat-affected zone occurs, and the fatigue strength of this area decreases. Further, although this is a problem especially in the case of a thin wall, the welded portion may not have sufficient strength due to misalignment between the axes of the steel pipe f and the stem e. The decrease in fatigue strength mentioned above has a significant impact on the reliability of the product, especially when it is applied to the drive shaft of an automobile.
This is a serious obstacle to the practical application of steel pipe drive shafts. An object of the present invention is to provide a method for manufacturing a steel pipe drive shaft that eliminates the problems related to fatigue strength caused by the prior art while considering manufacturing cost reduction. [Means for Solving the Problems] A first manufacturing method of the present invention is a method for manufacturing a drive shaft using a steel pipe, in which thickened portions are provided at equal intervals in the longitudinal direction of the pipe, and Normally, a differential thickness steel tube with a wall thickness ratio of 2 or more is used as a raw material, and after the differential thickness steel tube is cut into short tubes at the thickened portion, spline processing for connection is performed on both tube ends. A second manufacturing method of the present invention is a method for manufacturing a drive shaft using a steel pipe, in which a differential thickness steel tube having thickened portions at equal intervals in the longitudinal direction of the tube is used as a material, and the differential thickness steel tube is formed at the thickened portions. After cutting a short tube, the stem portion is joined to both ends of the tube by friction welding. [Function] In the first manufacturing method of the present invention, since the thick-walled tube end is splined, the fatigue strength of the drive shaft is improved. Furthermore, since the entire tube is not thickened, weight reduction is also achieved. Furthermore, since a differential thickness steel pipe having thickened portions at regular intervals in the pipe longitudinal direction is used as the raw pipe, a process can be omitted, unlike increasing the wall thickness through post-processing. In the first method of the present invention, the reason why the wall thickness ratio between the thickened part and the normal part of the differential thickness steel pipe is set to 2 or more is to ensure the fatigue strength of the thickened part where splines are formed in a later process. . It goes without saying that in order to further ensure fatigue strength, it is better to increase the wall thickness ratio, but increasing the wall thickness ratio unnecessarily will hinder weight reduction, so the wall thickness ratio should be 2 or more. Select by range. Table 1 shows the constant load bidirectional torsional fatigue tests conducted on differential thickness steel pipes with various wall thickness ratios, which were cut into short tubes at the thickened part and then machined to form splines in the thickened part. The results are shown below. As a differential thickness steel pipe, the dimensions of the normal part are 50 m in outer diameter and 2 in wall thickness.
．． 51all STKM16C equivalent material was used. The spline shape was trapezoidal with a tooth height IIm. It can be seen from Table 1 that the fatigue life improves as the wall thickness ratio increases, and is saturated at a value of 2 or more. Further, when the wall thickness ratio is less than 2, fatigue cracks occur in the spline portion, but when the thickness ratio is 2 or more, fatigue cracks do not occur in the spline portion, but fatigue cracks occur at the boundary between the thickened portion and the normal portion. From this, it can be seen that if the wall thickness ratio is 2 or more, even if a spline is formed in the thickened part, sufficient fatigue strength can be ensured in this part. Table 1 In the second manufacturing method of the present invention, since the stem is welded to the thick walled portion of the tube end, the fatigue strength of the drive shaft is reduced compared to the case where the stem is welded to a steel tube with the normal wall thickness. improves. Furthermore, since the entire raw pipe is not made thicker, weight reduction is also achieved. Furthermore, since a differential thickness steel pipe having thickened portions at regular intervals in the pipe longitudinal direction is used as the raw pipe, a process can be omitted, unlike increasing the wall thickness through post-processing. The reason why friction welding is adopted in the second method of the present invention is that friction welding has the highest productivity among various welding joints, enables manufacturing cost reduction, and is a welding method suitable for circumferential welding of steel pipes. be. Furthermore, since the drive shaft is a rotating body, rotational balance is a problem, but in friction welding, the bead amount of the welded part is the same at any position in the circumferential direction, and the amount of eccentricity is extremely small. Therefore, the rotational balance after welding is also excellent. [Example] Hereinafter, an example of the present invention will be specifically described based on the drawings. Fig. 1 is a cross-sectional view showing an example of a steel pipe with a different thickness used in the manufacturing method of the present invention. This is a tube in which thickened parts 2 with small thicknesses are alternately formed at a predetermined pitch. Such steel pipes are usually made from steel pipes with uniform wall thickness and manufactured by special cold drawing. As an example of the first method of the present invention, the pipe has a normal part l with an outer diameter of 50 cm and a wall thickness of 2.51 m, and has a pipe length of 500 g+ in the longitudinal direction.
After cutting a short pipe at the center of the thickened part 2 for a steel pipe of different thickness with a length of 150mm and a thickened part 2 of 150 mm in length at a pitch of 150 mm, the outer periphery of both ends is cut as shown in Fig. 2. A spline 3 was formed by machining to produce a drive shaft with a total length of 500 m. Figure 3 shows the results of a constant load double-sided torsional fatigue test performed on the drive shaft manufactured in this way. A steel pipe made of the same material (outside diameter 50mm, wall thickness 2.5mm+) is used as a raw material, and the pipe end is drawn, and then the drawn part is splined. This is the result. The drive shaft according to the present invention has excellent fatigue strength with little variation in fatigue life. On the other hand, in comparative products, as mentioned above, flaws may occur due to the mouth drawing process, and those in which fatigue cracks occur starting from these flaws have a reduced fatigue life. For this reason, the fatigue life of comparative products varies widely. From the above, it can be seen that the drive shaft according to the present invention has sufficient fatigue strength to withstand practical use. Next, as an example of the second method of the present invention, the normal part 1 has an outer diameter of 75 as, a wall thickness of ff+, 6+n+w, and the thickened part 2 has a length of 50 m, a wall thickness of 2.5 m, and a length of 500 m in the longitudinal direction of the pipe. *The differential thickness steel pipe formed with pitch was cut at the center of the thickened part 2. Then, separately prepared stem parts were friction welded to both ends of the obtained steel pipe with a total length of 500 mm under the conditions of a friction pressure of 8 kgfZ, an upset pressure of 12 kgf7m, and an absent time of 4 seconds.The outer periphery of the friction welded part The weld burrs that were generated in the process were cut by machining.The results of a constant load double-oscillating torsional fatigue test performed on the drive shaft manufactured in this way are shown in Figure 4.The solid line in Figure 0 indicates that the drive shaft according to the present invention was For comparison, the dashed line is a steel pipe made of the same material without the thickened part (outer diameter 75 m, wall thickness P'!, 1
．． 6 wh and 2.5 ■) were used as materials and polished under the same conditions.
! This is the case of a drive shaft manufactured by J welding and cutting the outer weld bead. Among the comparison products, the outer diameter is 75m and the wall thickness is 1.6m.
- is called comparative product A, and the one with an outer diameter of 75 m and a wall thickness of 2.5 m is called comparative product B. According to this figure, the drive shaft according to the present invention has the same fatigue strength as comparative product B, which has a thick wall, and has significantly improved fatigue strength compared to comparative product A, which has a thin wall. Recognize. Note that the fact that the drive shaft according to the present invention and comparative product B showed equivalent fatigue strength corresponds to the fact that they both have the same wall thickness at the ff friction weld, which is the starting point of fatigue cracks. Table 2 also shows the drive shaft according to the present invention, comparative product A.
The weight ratios of Comparative Product B and Comparative Product B are shown. From this table, it can be seen that the drive shaft according to the present invention is slightly heavier than comparative product A, but much lighter than comparative product B, which has the same fatigue strength. Table 1 shows that the rotational balance of the drive shaft according to the present invention is excellent. Table 3 also shows the drive shaft according to the invention described above, comparative product A.
Vibration experiments were conducted on Comparative Product B and Comparative Product B, and the natural frequencies of bending vibration were investigated. There are no adverse effects due to the use of steel pipes with different thicknesses, and the natural frequencies are approximately the same for all three.
The frequency is approximately 800 Hz in the first mode. It can be seen that this value is higher than the rotational speed of the automobile drive shaft, and no resonance phenomenon occurs. On the other hand, regarding rotational balance, when we measured the balance according to the regulations of JIS BO905, the drive shaft of the present invention had a rotational speed of 15aus/
S, when a drive shaft with the same dimensions as the drive shaft according to the present invention is manufactured by arc circumferential welding, it is 31 mm/S.From the above, the drive shaft according to the second method of the present invention has high fatigue strength and It can be seen that the shaft has excellent strength and reliability. In addition, weight reduction has been achieved, and even though welding is used, rotational balance is excellent, and vibration reduction effects can be fully expected. [Effects of the Invention] As is clear from the above explanation, the method for manufacturing a steel pipe drive shaft of the present invention uses a differential thickness steel pipe having a thickened portion from the steel pipe stage, so it is not necessary to increase the thickness by post-processing. Unlike conventional products, it is possible to omit the process, making it economical, and also makes the drive shaft lighter, improving the fatigue strength of the drive shaft despite the lighter weight, and increasing the reliability of the product. Furthermore, the second aspect of the present invention
Although the method uses welding, it can be expected to have a sufficient vibration reduction effect.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional view of the differential thickness steel pipe used in the present invention, FIG. 2 is a partial vertical cross-sectional view of a drive shaft manufactured from the differential thickness steel pipe,
Fig. 3 is a graph showing the results of the torsional fatigue test, Fig. 4 is a graph showing the results of the torsional fatigue test in other examples, Fig. 5 is an explanatory diagram of the drive shaft of the conventional integrally molded type, Fig. 6 is an explanatory diagram of a conventional welded assembly type drive shaft. In the figure, 1: normal part, 2: thickened part, 3 varnish spline. Figure Number of torsional charge repetitions (times) Figure Figure Number of torsional R east repetitions (times) Figure Figure

Claims (1)

[Scope of Claims] 1. A method for manufacturing a drive shaft using a steel pipe, wherein the pipe has thickened portions at regular intervals in the longitudinal direction of the pipe, and the wall thickness ratio between the thickened portion and the normal thick portion is 2 or more. A method for producing a drive shaft made of a steel pipe, which is made of a steel pipe of different thickness, which is cut into short pipes at a thickened part, and then splined for connection at both ends of the pipe. 2. In a method of manufacturing a drive shaft using a steel pipe, a steel pipe of different thickness having thickened portions at equal intervals in the longitudinal direction of the pipe is used as the material,
A method for manufacturing a steel pipe drive shaft, which comprises cutting the differential thickness steel pipe into short pipes at the thickened part, and then joining stem parts to both ends of the pipe by friction welding.