JPH06270810A - Method for improving fatigue strength of rolling stock truck frame welding portion - Google Patents

Abstract

PURPOSE:To improve fatigue strength by forming a melted metal through a process of making MAG welding of each welding portion of a truck frame, adding compression remaining stress by applying shot peening process to the whole surface of the smelted metal after improving the surface shape of a welding start end portion by means of TIG welding. CONSTITUTION:A rolling stock truck frame is formed by applying fillet welding 4 to left and right lateral beams 1, 2 and a lateral beam 3 provided in the center portion between those beams. In this instance, a melted metal 5 is formed by making MAG welding of each welding portion 4 and the surface shape of a welding start end portion is improved by means of TIG welding, and then compression remaining stress is added by applying shot peening process to the whole surface of the melted metal 5. As a result, care work by means of a grinder is not needed, and the fatigue strength of each welding portion 4 is improved in high productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the fatigue strength of a bogie frame welded portion for railway vehicles.

[0002]

2. Description of the Related Art Tensile residual stress generally occurs in the vicinity of a welded portion of a welded joint of a welded structure. Therefore, if repeated stress is applied to the welded joint for a long period of time, the welded structure may be fatigue fractured. As a mechanical treatment for improving the fatigue strength of such a welded joint, a hammer peening method is generally used (Japanese Patent Laid-Open No. 4-21).
No. 717, etc.).

On the other hand, a bogie frame for a railway vehicle is shown in FIG.
As shown in A and B, left and right side beams 1 and 2 and a lateral beam 3 provided in the center between them are formed by fillet welding 4, and the welded joints are defined by JIS E 4207. For example, a standard stress of 11 Kgf / mm ² is required. Conventionally, as shown in FIG. 2, the surface portion of the weld metal 5 formed by fillet welding by the MAG welding method was trimmed by a grinder to improve the shape and at the same time improve the fatigue strength. The weld metal between the MAG welding surface 6 shown by the two-dot chain line and the grinder finishing surface 7 shown by the solid line in the figure is scraped off by the grinder.

However, the maintenance work by the grinder is
This is the most important example of 3K work, and automation and mechanization are urgent tasks. However, even if the grinder work is automated or mechanized, it is not suitable because the processing speed is slow and the productivity is poor.

[0005]

As described above, in order to improve the fatigue strength of the bogie frame welded portion for railway vehicles, it is not desirable in terms of production to perform maintenance work with a grinder.

[0006] The present invention provides a method for improving the fatigue strength of a bogie frame welded portion for a railway vehicle, which does not require maintenance work by a grinder, in order to eliminate the drawbacks found in the above conventional method.

[0007]

In order to achieve the above object, a method for improving fatigue strength of a bogie frame welded part for a railroad vehicle according to the present invention is to perform MAG welding on a welded joint part of a bogie frame for a railroad vehicle and then perform TIG welding. Then, the shape of the weld toe is improved, and further shot peening is applied to add compressive residual stress.

[0008]

In general, TIG is used to improve fatigue strength.
A method of improving the shape by welding and a method of applying a compressive residual stress by shot projection are known. However, since the method for improving the shape by TIG welding has many variations in the fatigue strength improvement due to the skill of the operator and the shape of the bead of the base, the fatigue strength value due to the grinder maintenance work may be lower than this method alone. In addition, the method of applying compressive residual stress by shot peening is because the weld toe has a sharp buildup shape and it is difficult to apply a shot uniformly to the weld toe. Not enough effect.

Therefore, as shown in FIG. 3, according to the present invention, the welded joint portion of the bogie frame for railway vehicles is MAG welded to form the weld metal 5, and then the surface shape of the weld toe portion is TIG welded. By performing shot peening on the entire surface of the deposited metal 5, it is possible to stably improve the fatigue strength of the welded joint.

[0010]

EXAMPLE As shown in FIGS. 1A and 1B, left and right side beams 1, 2
When manufacturing a bogie frame for a railway vehicle constituted by fillet welding 4 of a horizontal beam 3 and a transverse beam 3 provided in the center between them, as shown in FIG. After forming, the surface shape of the weld toe was improved by TIG welding, and further shot peening was performed on the entire surface of the deposited metal 5.

In order to confirm the effect of improving the fatigue strength of the welded joint according to the embodiment of the present invention, a test piece 8 of a rib cross welded joint in which the four corners are fillet welded 4 was prepared as shown in FIGS. 4A and 4B. Then, the improvement of the shape of the weld toe portion by TIG welding was investigated. The results are shown in FIGS. 5A and 5B. A shows a state in which MAG welding is performed as it is, and the radius R1 of the weld toe is 1.5 mm. On the other hand, in the case of TIG welding of the weld toe shown in B, the radius R2 of the weld toe is 14 mm, and it can be seen that the shape of the weld toe is improved. However, due to poor melting of the base bead, a portion having a radius of 1.5 mm may remain as R3. Therefore, it is necessary to apply residual stress by shot peening.

Next, the difference in residual stress due to the difference in the processing condition of the welded joint was investigated. The results are shown in Table 1 below.
From the results shown in Table 1, with TIG welding alone, as-welded +4.1 Kgf / mm ² , it is -4.2 Kgf / mm ^2.
The residual stress has occurred. However, when TIG welding and shot peening according to the embodiment of the present invention are performed, a residual stress of −22.1 Kgf / mm ² occurs. From this result, it is understood that the present invention is effective in improving the fatigue strength of the welded joint.

[0013]

[Table 1]

Further, the result of measuring the fatigue strength is shown in FIG.
Fig. 3 shows a SN diagram under each processing condition of the welded joint.
From this figure, the fatigue strength when performing TIG welding and shot peening according to the present invention is 32 Kgf /
mm ² and 29 Kgf / m due to grinder maintenance
It can be seen that it is higher than m ² .

[0015]

EFFECTS OF THE INVENTION It is possible to further improve the fatigue strength of a welded joint with high productivity without requiring maintenance work by a grinder.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a bogie frame for a railroad vehicle constructed according to an embodiment of the present invention, in which A is a plan view and B is a front view.

FIG. 2 is an explanatory view of a case where a welded joint portion of a bogie frame for a railway vehicle is finished by a grinder maintenance by a conventional method.

FIG. 3 is an explanatory view in the case where the welded joint portion of the bogie frame for a railway vehicle is finished by TIG welding and shot peening by the method of the present invention.

FIG. 4 is a test piece of a rib cross joint according to the method of the present invention, in which A is a plan view and B is a front view.

FIG. 5 is an explanatory view showing a comparison of the shapes of the weld toe portion due to the difference in processing, where A is the state of MAG welding as it is and B is the state of MA.
The state in which the shape is improved by TIG welding after G welding is shown.

FIG. 6 is an N- of the test piece of the rib cross joint shown in FIG.
It is an S diagram.

[Explanation of symbols]

 1, 2 Side beam 3 Horizontal beam 4 Fillet weld 5 Weld metal 6 MAG welding surface 7 Grinder finishing surface 8 Test piece

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location B61D 17/00 C C21D 7/06 Z 7412-4K

Claims (1)

[Claims] 1. A MAG for a welded joint portion of a bogie frame for a railway vehicle.
After welding, TIG welding is performed to improve the shape of the weld toe, and shot peening is further applied to add compressive residual stress. A method for improving fatigue strength of a bogie frame welded portion for a railway vehicle.