JPH10251743A - Method for strengthening bolt or rivet hole of steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively improve fatigue strength of a structural material by executing the irradiation of laser beam on the surface of a steel plate on the outer periphery of opening end part of a bolt or rivet hole bored in the steel plate and forming the annular quenched part. SOLUTION: The steel plate 10 is fastened with the other parts with the bolt 14. The bolt hole 12 or the rivet hole is formed with ordinarily punching work or by machining with a drill but the crack is easily developed from the opening hole edge of the bolt hole 12 on the surface of the steel plate 10 caused by stress concentration with burr or sharp edge. The annular quenching part on the outer peripheral point containing the opening hole edge of the bolt hole 12 is formed with the irradiation of the laser beam. This quenching part is desirable to form continuously over the whole periphery in the circular direction. The development of the crack on the opening hole end edge of the bolt hole 12 is prevented by this quenching part and also, the fatigue strength can be improved by developing the compressive residual stress on the quenched part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reinforcing a bolt or rivet hole in a steel sheet.

[0002]

2. Description of the Related Art A chassis frame of a truck or the like has a pair of left and right side rails extending in the front-rear direction of the vehicle and having a U-shaped cross section, and is disposed so as to extend in the vehicle width direction and each end is provided with a bolt or a bolt. A plurality of cross members are fixed to the side rails by rivets, and the side rails and the cross members are usually made of a steel plate.

In the underframe, bolt holes or rivet holes for inserting the bolts or rivets are formed in side rails, cross members, and reinforcing accessories such as reinforcing gussets and stiffeners. These bolt holes or rivet holes are formed by punching using a punch and a die or turning using a drill.

[0004] When the above-mentioned bolt hole or rivet hole is machined, the above-mentioned bolt is formed by burrs and sharp edges generated at the opening end of the hole and fretting of the steel plate surface which comes into contact with the bolt head due to a strong tightening axial force of the bolt. Holes or rivet holes tend to be weak points on the strength of the chassis frame,
This is one of the important factors that reduce the fatigue strength of the chassis frame.

As a method of increasing the fatigue strength of the chassis frame to improve the durability, a method of manufacturing components such as side rails and cross members from a high-strength steel plate material,
Alternatively, a conventional steel plate is used, but a method of increasing the thickness of the steel plate is considered.However, the use of a high-tensile steel plate is expensive because the material itself is expensive, and the press formability deteriorates. When a crack occurs, it has a problem that the speed of its growth is high and it can be destroyed immediately.On the other hand, increasing the thickness of a conventional steel sheet naturally leads to an increase in weight, which leads to an increase in fuel efficiency and running of the vehicle. There is a drawback that adversely affects performance and the like.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a structure, such as a truck underframe, made of a steel plate material and having components connected by bolts or rivets. The fatigue strength of
It is effectively improved without problems such as deterioration of press formability, increase in weight, and large increase in material cost,
It is an object of the present invention to provide an inexpensive method that can improve durability and reliability.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of irradiating a laser beam to a bolt formed in a steel plate, a bolt in a rivet hole, or a steel plate surface around an opening end on a rivet head side. The present invention proposes a method for strengthening a bolt or rivet hole of a steel plate material, wherein an annular quenched portion is formed.

According to the above method, the bolt or the rivet head is brought into contact with the outer periphery of the open end of the bolt or rivet hole.
By forming a local quenched portion by performing laser quenching with a remarkable rapid quenching effect, it is possible to increase the hardness and generate a compressive residual stress, so that a bolt or a bolt which conventionally formed a weak point portion on strength The rivet hole can be effectively strengthened. The annular quenched portion is formed on the outer periphery of the opening end of the bolt or the rivet hole. The quenched portion is formed continuously over the entire circumference in the circumferential direction. A quenched portion having a point-like or arc-shaped quenched portion is formed in the shape of a ring.

In the method of the present invention, it is preferable to form a ring-shaped quenched portion by irradiating a laser on the outer peripheral portion of the opening end on both the front and back surfaces of the bolt or rivet hole formed in the steel plate. According to this method, when the steel plate is fastened to another steel plate by bolts or the like, not only the outer peripheral portion of the opening end on the side where the bolt head or the like abuts the bolt hole or the like, but also to the other steel plate or the like. Since a hardened hardened layer is also formed on the outer peripheral portion of the opening end such as the bolt hole on the contact side,
Further improvement in durability is achieved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, in the first embodiment shown in FIGS. 1 and 2, reference numeral 10 denotes an arbitrary part of a chassis frame in a truck, for example, a steel plate material forming a cross member (only a part of which is extracted and shown). The steel plate 10 is provided with a bolt hole 12. The steel sheet 10 is fastened to another part of the chassis frame, for example, a steel sheet (not shown) forming a side rail, by a bolt 14 shown by a one-point acute line in the cross-sectional view of FIG.

The bolt hole 12 is usually formed by punching using a punch and a die or turning by a drill. However, due to stress concentration due to burrs and sharp edges, the steel plate 10 of the bolt hole 12 is formed. Cracks are easily generated from the opening edge on the surface. Therefore, an annular quenched portion 16 is formed on the outer peripheral portion including the opening edge of the bolt hole 12 by laser irradiation. The annular quenching part 16 includes:
As shown in FIG. 1, it is most preferably formed continuously over the entire circumference in the circumferential direction. However, a point-shaped or arc-shaped quenched portion is formed on concentric circles at appropriate intervals in the circumferential direction. The quenching part 16 which is formed and has an annular shape as a whole may be provided. The provision of the quenched portion 16 allows the bolt holes 12
Cracking at the opening edge of the opening is effectively prevented, and the compressive residual stress is generated in the quenched portion 16, whereby the fatigue strength is improved.

Next, in a second embodiment shown in FIGS. 3 and 4, a bolt hole 1 formed in a steel plate material 10 similar to that described above is used.
A flange portion 14b formed integrally with the head portion 14a of the flange bolt 14 at an outer peripheral portion of the opening end
An annular quenched portion 16 is formed by laser irradiation on the surface where the outer peripheral portion abuts and the adjacent portion thereof.

When the steel plate 10 is fastened to another steel plate or the like using the flange bolt 14, a large compressive force acts near the outer peripheral portion of the flange portion 14b based on the axial force of the bolt.
Since breakage due to fretting is likely to occur, the annular quenched portion 16 is provided in this portion to prevent breakage due to fretting and to improve fatigue strength based on the compressive residual stress of the quenched portion 16. .

In the third embodiment shown in FIGS. 5 and 6, the head 1 of the flange bolt 14 extends radially outward from the opening edge of the bolt hole 12 formed in the steel plate 10.
An annular quenched portion 16 is formed by laser irradiation in a wide range up to an adjacent portion beyond the outer peripheral portion of the flange portion 14b provided in 4a. According to this configuration, in a structure in which the steel plate 10 is tightened to another steel plate or the like by the flange bolt 14, usually, the opening edge of the bolt hole 12 where defects such as cracks easily occur, and the flange portion of the bolt 14. 14b is in contact with the bolt and the tightening axial force of the bolt acts, so that it is possible to simultaneously prevent breakage of the seat surface where defects due to fretting are likely to occur, and to achieve improvement in fatigue strength due to compressive residual stress generated in the quenched portion 16. Is done.

Further, in the fourth embodiment shown in FIGS. 7 and 8, a steel plate 10 having a bolt hole 12 formed therein and a bolt hole 1 having substantially the same diameter as the bolt hole 12 are formed.
When tightening the other steel plate material 10 ′ in which the 2 ′ is drilled by the flange bolt 14 and the nut 18 screwed to the bolt, even at the contact surface where the steel plate materials 10 and 10 ′ abut each other, Since the tightening axial force of the bolt 14 acts on the outer peripheral portions of the open ends of the bolt holes 12 and 12 ′, annular hardened portions 20 and 20 ′ are added to the open edges of the bolt holes 12 and 12 ′ and the outer peripheral portions thereof. It is provided. On the other hand, on the surface of the steel plates 10 and 10 'on the side where the bolt head 14a and the nut 18 are in contact, the annular quenched portion 16 and the annular hardened portion 16 substantially similar to the third embodiment shown in FIGS. 16 'is formed.

According to this configuration, the steel plates 10 and 10 '
Surface of the side which comes into contact with the bolt head 14a and the nut 18;
In addition, defects and breakage of the outer peripheral portions of the opening ends of the bolt holes 12 and 12 ′ in the contact surfaces of the steel plates 10 and 10 ′ are effectively prevented, and the hardened portions 16, 16 ′ and
The fatigue strength is improved based on the compressive residual stress generated at 20 and 20 '.

In all of the first to fourth embodiments, the bolt holes 12 formed in the steel plates 10 and 10 'are formed.
Annular hardened portions 16, 16 ', 20 and 20' formed on the outer peripheral portions of the open ends of the opening portions 12 and 12 'are formed by a laser irradiation apparatus whose conceptual configuration is shown in FIG. In the figure, reference numeral 22 denotes a laser oscillator, and 24 denotes a processing head 2 while changing the direction of a laser beam generated by the laser oscillator 22 through a laser mirror (not shown) as necessary.
6 is a laser path leading to 6. As the laser oscillator 22, a CO ₂ laser oscillator which is widely used when large heat energy is required, such as welding or quenching of a metal, can be advantageously used.

The processing head 26 is attached to an output end of a three-dimensional processing machine or a working machine (not shown) widely used for robots and the like, and is drilled in steel plates 10 and 10 'as works as shown. Bolt holes 12, 12 '
After changing to the desired radial position R on the outer peripheral portion of the opening end of the above, the desired hardening is performed by rotating around the center line OO of the bolt holes 12, 12 '(usually one rotation), It is provided so that it can sequentially move to the outer peripheral portion of the other bolt holes 12, 12 ', or return to the standby position for the next operation.

A focusing lens 28 is provided in the processing head 26, and an assist gas supply passage 32 for allowing the assist gas to flow out from a tapered opening 30 having a nozzle shape is connected. An assist gas is supplied from a gas source 34 to the assist gas supply passage 32. As the assist gas, argon, nitrogen gas, or the like suitable for shielding the high-temperature quenched portion from the outside air is appropriately used.

In FIG. 9, the laser parallel beam is
8, the processing head 26 is focused so as to be focused on the surface of the steel plate 10, 10 ', so that the energy of the laser beam is concentrated in a narrow area of the surface of the steel plate 10, 10'. Although it is arranged, if necessary, the processing head 26 is displaced upward or downward from the position shown in the drawing to separate the focal position upward or downward from the surfaces of the steel plates 10 and 10 ′. The light beam can be adjusted to illuminate a desired wide range.

In order to verify the effects of the above embodiments,
A test piece having a thickness of 5 mm was prepared using a hot-rolled steel plate for automobile structure SAPH440 used for a chassis frame of a conventional truck and the like, and a test result obtained by irradiating a laser beam under various conditions on the test piece is described below. Laser irradiation conditions were 2 kW laser output, and the flow rate of argon as an assist gas was 2
0 L / min.
5, 2.0, and 5.0 (m / min) were performed, and quenched portions were respectively formed. FIG. 10 shows the result of measuring the hardness of the quenched portion. As is clear from FIG. 10, the hardness of the base material is about 150 to 160 in HV, whereas the feed speed is 5.0 m / mi on the surface of the quenched part.
HV at 300 n, feed rate 0.5 m / mi
It was confirmed that HV at n and 2.0 m / min was significantly increased up to 450.

The increase in hardness of the quenched portion and the generation of a sufficient compressive residual stress based on local rapid heating and quenching by laser irradiation confirmed from the above test results are due to the quenched portion 16 of the first to fourth embodiments. And 16 'occur substantially in the same manner, and as already described for each embodiment, the opening edges of the bolt holes 12 and 12' and the seat surface peripheral portion where the head 14b of the bolt 14 abuts. Obviously, it is possible to prevent the occurrence of defects and effectively prevent breakage due to fretting, thereby improving the fatigue strength, and thus achieving the improvement in durability and reliability.

Although the present invention has been described with respect to bolt fastening in which a large axial force acts as a member for fastening a steel plate to another steel plate or the like, the present invention can also be applied to a fastening structure using rivets. Further, the output and the irradiation speed, that is, the energy density of the laser applied to the outer peripheral portion of the opening end of the bolt or the rivet hole are appropriately selected depending on the type of the steel sheet, the thickness, the pattern (width and depth) of the quenched portion, and the like. And a CO ₂ laser is most suitable for practical use,
Other gas lasers and solid state lasers can also be used.
Further, the present invention is not limited to a chassis frame or a cab frame of a truck or the like, but can be widely applied to a steel plate structure fastened by bolts or rivets. Ordinary hexagon head bolts may be used.

[0024]

As described above, the method for strengthening a bolt hole or a rivet hole of a steel sheet according to the present invention is directed to a bolt or a rivet hole of a steel sheet or an outer periphery of a rivet head side opening end. Laser irradiation is performed on the steel sheet surface to form an annular quenched part, which reduces the fatigue strength of the steel sheet structure, such as deterioration of press formability, increase in weight, and large increase in material cost. There is an advantage that it is possible to provide an inexpensive method that can be effectively improved without accompanying problems and improve durability and reliability.

In the above invention, the steel plate is fastened by irradiating a laser to the outer peripheral portions of the open ends on both the front and back surfaces of the bolt or rivet hole formed in the steel plate material to form annular hardened portions. Therefore, it is possible to effectively prevent the defect or breakage of the bolt or rivet hole outer peripheral portion at the contact portion with the mating part, and thus there is an advantage that the durability and reliability of the steel plate structure can be further improved.

[Brief description of the drawings]

FIG. 1 is a partial plan view showing a first embodiment of the method of the present invention.

FIG. 2 is a sectional view taken along a center line of a bolt hole in FIG. 1;

FIG. 3 is a partial plan view showing a second embodiment of the method of the present invention.

FIG. 4 is a sectional view taken along a center line of a bolt hole in FIG. 3;

FIG. 5 is a partial plan view showing a third embodiment of the method of the present invention.

FIG. 6 is a sectional view taken along the center line of the bolt hole in FIG. 5;

FIG. 7 is a partial plan view showing a fourth embodiment of the method of the present invention.

FIG. 8 is a sectional view taken along the center line of the bolt hole in FIG. 7;

FIG. 9 is a conceptual configuration diagram of a laser irradiation device used for carrying out the method of the present invention.

FIG. 10 is a diagram illustrating a surface hardness measured in a direction perpendicular to a quenched portion formed by laser irradiation on a test piece made of a SAPH440 steel plate material.

[Explanation of symbols]

10 and 10 ': steel plate material, 12 and 12': bolt hole,
14 bolt, 14a bolt head, 14b flange part, 16 and 16 'hardened part, 18 nut, 20 and 20' hardened part, 22 laser oscillator, 26 processing head.

Claims (2)

[Claims] An annular quenched portion is formed by irradiating a laser on a surface of a bolt or a rivet hole bolt or a rivet head side opening end outer periphery of a steel plate material. Bolt or rivet hole reinforcement method. 2. The steel sheet according to claim 1, wherein an annular quenched portion is formed by irradiating a laser beam on the outer peripheral portion of the opening end on both the front and back surfaces of the bolt or rivet hole formed in the steel sheet material. Bolt or rivet hole reinforcement method of material.