JPS638875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for forming grooves or depressions on the surface of a pipe material using electrical resistance heat generation. For example, in a strut-type shock absorber for a vehicle, in order to prevent the connecting part between the outer shell and the nutcle from rotating and coming off, a groove is formed by mechanical cutting on a part of the outer periphery of the outer shell, and a groove is formed by mechanical cutting to prevent bolts, pins, etc. The contact friction force was increased. In order to prevent the strength of pipe materials from decreasing due to mechanical cutting, grooves are sometimes formed by press forming. A technology has also been developed that molds grooves while heating. According to this method, distortion and residual stress in the machined part can be reduced, and the thickness of the machined part can be kept the same, so that the strength is satisfactory. However, in this method, both electrodes are placed opposite each other and the pipe material is clamped from the outside, so there is a risk that thin-walled pipe material may deform as a whole during processing, and the outer circumferential surface of the pipe material may be deformed. Burns are likely to occur due to electrical discharge at the contact area with the electrode.
Furthermore, the grooves do not exactly match the shape of the pressed electrode, and sagging inevitably occurs at the edges of the grooves, making it difficult to process sharp grooves. From this point of view, the present invention places a pressing electrode on the outer surface of the pipe material, a pressure receiving electrode on the inner surface, and clamps the pipe material.
It is an object of the present invention to provide a method and apparatus for instantaneously forming grooves using resistance heat generation, thereby solving the above-mentioned problems. The present invention will be explained in detail below. First, in Figures 1 and 2, resistance welding machine 1
comprises an upper moving electrode 2 and a lower fixed electrode 3. The upper electrode 2 is connected to the cylinder 5 with respect to the arm part 4.
The lower electrode 3 is attached to a fixed support arm 6 and clamps the pipe material 7 with a predetermined pressure during processing. A current from a high current power source (not shown) is applied between the electrodes 2 and 3, causing the pipe material 7 held between them to generate heat. As shown in FIG. 3, the externally pressed electrode 2 is provided with a convex portion 9 at its tip that matches the groove shape formed in the pipe material 7, and a cooling water passage 10 is formed inside. The electrodes are cooled. On the other hand, the pressure receiving electrode 3A inserted into the inside of the pipe material 7 functions as a so-called core electrode, and as shown in FIG. , has a concave portion 12 corresponding to the concave groove shape as described above, and has a shaft portion 13 at the base end.
It is attached to the support arm part 6 via. Alternatively, as shown in FIG.
A, 16B are provided, the cooling water passage 17 is penetrated therein, and the pressure receiving surface of the pressure receiving electrode 2 is sequentially rotated, thereby making it possible to extend the life of the electrode 3B. However, in the case of the electrode 3A shown in FIG. 4, since it is easy to extract it from the pipe material 7, the semicircular curvature of the insertion part 11 is brought as close as possible to the inner circumferential surface of the pipe material 7, so that contact with the pipe material 7 is avoided. Although the energization state can be stabilized by increasing the area, in Fig. 5, considering the application to pipe materials 7 with different inner diameters, it is necessary to reduce the outer diameter of the insertion portion 15 in advance for the sake of extraction. The contact area becomes smaller. After forming both electrodes 2 and 3 in this manner, the positions of the electrodes are determined based on the relationship with the pipe material 7. When the pressure-receiving (core) electrode 3 is inserted into the pipe material 7 and the pressure electrode 2 is applied with a predetermined pressure while being energized, the pipe material 7 centering around the part that contacts the convex part 9
is heated, and the pipe material 7 is heated so as to fit into these irregularities between the concave portions 12 (16A, 16B).
is deformed and a groove is formed. At this time, since the insertion portion 11 (15) of the pressure-receiving electrode 3 is in close contact with the back surface (inner surface) of the pipe material 7, the shape of the molded groove portion 20 (see Fig. 6) is exactly that of the molded material. A sharp groove with no sag is formed which coincides with the convex portion 9 and the concave portion 12. Particularly, in the case of preventing rotation of the shock absorber outer shell described above, if the shape of the recessed groove portion 20 loses its sharpness as shown by the dotted line in FIG. 6, the rotation prevention function deteriorates, which is extremely undesirable. In the present invention, such problems can be solved. Further, even if the pipe material 7 is formed of a relatively thin member, no overall deformation occurs, and therefore,
Compared to the conventional method, this method has the advantage of being able to perform groove processing with high accuracy even on pipes with considerably thinner walls. Furthermore, burns caused by sparks during welding do not occur on the outer surface of the pipe. Next, examples of the present invention will be described. Example 1 Pressure-receiving electrode (diameter of insertion part) as shown in Fig. 2
38.5φ) and aim for a groove depth of 1.6mm. The pipe material to be used is one with a diameter of 45φ and a thickness of 2.6mm. When the pressing force (Kg) and current (A) are changed as shown in the table below, the required energization time is determined, and the required amount of heat at that time is roughly estimated. In addition, the bottom column of the table also shows the experimental results (one example) conducted using the conventional device.

【table】

[Table] From the above, it can be seen that machining time can be shortened by increasing the current value while keeping the pressing force constant. In that case, the characteristic is that the required energy does not increase much. If the pressing force is increased at the same time, the processing time can be further shortened, so it is preferable to increase the pressing force within a range that does not cause problems in terms of the durability of the electrodes 2 and 3. In addition, when experimenting under other conditions, especially when the current value was increased to 15000A or more, electrode 2,
There was a tendency for flow diversion to occur more easily in relation to 3.

[Brief explanation of the drawing]

FIG. 1 is an overall side view of the device of the present invention, FIG.
The figure is an enlarged sectional view of the main part, Figures 3A and B are a front view and a sectional view of the pressure electrode, Figures 4 and 5 are a side view and a sectional view showing an example of the pressure receiving electrode, respectively, and Figure 6 is a side view and a sectional view of the pressure receiving electrode. FIG. 3 is a cross-sectional view showing an example of a grooved pipe material. 1...Resistance welding machine, 2...Press electrode, 3,3
A, 3B...Pressure receiving (core) electrode, 4, 6... Arm portion, 7... Pipe material, 9... Convex portion, 10...
Cooling water passage, 11...insertion part, 12...recessed part,
15...insertion part, 16A, 16B...concave part.

Claims (1)

[Scope of Claims] 1. A convex outer electrode that matches the shape of a groove formed on the outer surface of the pipe material, and a concave inner electrode that matches the shape of this groove, in which the wall of the pipe material is sandwiched. A method for molding a pipe material, which comprises applying pressure while generating heat by applying electricity between electrodes in the state of the pipe material, thereby forming grooves on the outer surface of the pipe material. 2. One pressure electrode of the resistance welding machine is provided with a convex part that matches the groove shape to be machined on the outer surface of the pipe material, and the other fixed side pressure receiving electrode is provided with an insertion part with a diameter smaller than the inner diameter of the pipe material. , and a concave portion matching the shape of the concave groove is formed in the insertion portion. 3. Claim 2, wherein the insertion portion has a semicircular cross section, and a single concave portion is formed in the circular portion.
A pipe material forming apparatus as described in Section 1. 4. The pipe material molding apparatus according to claim 2, wherein the insertion portion has a circular cross section and a plurality of concave portions are formed around the insertion portion.