JPS6144574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides pilot holes at predetermined positions in a material,
This relates to a burring process in which the periphery of a hole is raised to form a flange, and this burring process is particularly applied to the bearings of suspension arms and disc wheels in the automobile industry.

As is well known, in the automobile industry, it is currently a major problem to reduce the decline in fuel efficiency due to measures against automobile exhaust gas pollution, and one effective means of dealing with this problem is to make the steel plates used in vehicles thinner. One example of this is aiming to reduce the weight of the vehicle body.

In order to reduce the thickness of a steel plate, it is necessary to increase the rigidity of the steel plate. However, high-rigidity steel sheets sometimes undergo work hardening and have a low elongation rate, and the height of the flange is limited even during burring, which increases the risk of cracks and cracks in the processed area, so high flanges are not recommended. The forming process, so-called deep drawing process, is difficult. Conventionally, methods have been used to improve moldability by heating the processed portion, or to replace only the processed portion with a high-grade material with good moldability. However, the former method has the disadvantage that thermal distortion occurs in the material and scale adheres to the material surface as a result of high-temperature treatment, while the latter method does not have a uniform appearance and only reduces its commercial value. Or, because high-quality materials are used in the processing parts, material costs are high.

The object of the present invention is to provide a burring method that allows smooth deep drawing without using high-grade materials and while preventing the occurrence of thermal distortion and scale. The material flow during processing is averaged by reducing the heat capacity by thinning the wall, softening the end surface of the processed part by heating to an extent that does not cause thermal distortion or scaling, and creating a circular curved surface due to surface tension. The main purpose of this is to prevent cracks from occurring in the processed parts.

In other words, the burring method of the present invention includes Step 1 of opening a pilot hole at a predetermined position in a material, and forming a thin wall part on the peripheral edge of the pilot hole by applying a slight burring to the peripheral edge of the pilot hole or without burring. step 2 of providing a circularly curved end surface, step 3 of heating and softening the end surface of the thin wall part to form a circularly curved surface due to surface tension, and step 4 of finally applying burring to the peripheral edge of the prepared hole whose end surface is a circularly curved surface. It is characterized by

The present invention will be explained in detail below in the order of the above steps.

Shown in the figure is one embodiment of the present invention.

In step 1, a hole 10 is punched out at a predetermined position in a material 1 having a thickness of t, which is a steel plate, by, for example, a press. At this time, the peripheral end surface 10A of the hole 10 lacks smoothness and is in a state where cracks and cracks are likely to occur.

In step 2, the periphery of the hole 10 is slightly burred to form an initial flange 2 with a height ΔH, and the tip of the initial flange 2 (periphery of the hole 10)
For example, a thin wall portion 3 having a thickness of t−△h is formed by pressing, but at this time, the tip of the initial flange 2 is
It may be thinned from the outside as shown in the figure, it may be thinned from the inside as shown in FIG. 4, or it may be thinned from both sides, although not particularly shown.

In step 3, the end surface 3A of the thin portion 3 is heated and softened, for example, by high frequency induction heating.
Thus, the end surface 3A of the thin portion 3 forms a circularly curved surface 4 as shown in FIG. 5 due to surface tension. In this way, the end surface 3A of the thin wall portion 3, which was not smooth, is smoothed.

In step 4, the periphery of the hole 10 is finally burred to a sufficient height H as shown in Figure 6.
The flange 5 having the flange 5 is raised up. Since the conical surface 4A of the thin wall portion 3 is smooth and uniform, the machining force at this time is less likely to be concentrated, and is evenly distributed over the entire processed portion, so that cracks and cracks are less likely to occur.

Next, a second embodiment of the present invention will be described.

Step 1 is similar, but in Step 2, the initial flange 2 is not formed and the peripheral edge of the hole 10 has a thickness t
The thin part 13 of Δh is provided, but the thin part 13 is the seventh
Of course, the thickness may be thinned from the top as shown in the figure, or from the bottom, or even from the top and bottom. However, in step 3, the thin portion 13
The circular curved surface 14 is formed by heating and softening the end surface 13A. In step 4, when the periphery of the hole 10 is finally burred, the flange 5 having a sufficient height H as shown in FIG. 6 is erected.

In the present invention, as described above, when a pilot hole is opened at a predetermined position in the material and the periphery of the pilot hole is burred to erect a flange, a thin portion is provided at the periphery of the pilot hole, so that the heat capacity of the processed portion is Therefore, gentle heating that does not generate thermal distortion or scale can be applied. Such heating softens the end face of the thin wall part and makes it a circular curved surface due to surface tension, so the peripheral end face when drilling the pilot hole is softened. The non-smoothness has been eliminated and smoothness has been achieved, and since burring is applied to such processed parts, the processing force is not concentrated but is evenly distributed, which effectively prevents the occurrence of cracks and cracks even during deep drawing processing. It is prevented.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention. FIG. 1 is a central sectional view in step 1, FIG. 2 is a central sectional view in step 2 with an initial flange formed, and FIG. 3 is a central sectional view in step 2. FIG. 4 is a central sectional view of the thin portion formed from the outside, FIG. 4 is a central sectional view of the thin portion formed from the inside in process 2, FIG. 5 is a central sectional view of process 3, and FIG. 6 is process 4. 7 and 8 show other embodiments, FIG. 7 is a center sectional view in step 2, and FIG. 8 is a center sectional view in step 3. In the figure, 1... Material, 10... Hole, 10A... Peripheral end face, 2... Initial flange, 3, 13... Thin wall portion, 4, 14... Circular curved surface, 5... Flange.

Claims (1)

[Claims] 1. Step 1 of opening a prepared hole in a predetermined position of the material.
and Step 2 of providing a thin wall portion at the peripheral edge of the pilot hole with or without burring a little, heating and softening the end face of the thin wall portion to form a circular curved surface due to surface tension. A burring method comprising step 3 and step 4 of finally burring the peripheral edge of the prepared hole whose end surface is a circular curved surface.