JP7529630B2 - Laser hole formation method - Google Patents

Description

The present invention relates to a laser hole forming method in which a laser beam is irradiated onto steel material to form a round hole.

In general, steel structures are produced by transporting components that have been processed in factories to the construction site and assembling them by connecting them with bolts or welding. High-strength bolts are used for the bolt connections of the main components.
There are strict standards for holes for high-strength bolts, and conventionally, holes for high-strength bolts have been formed in steel materials by drilling (see Non-Patent Document 1). However, drilling equipment is different from laser cutting equipment, and drilling work requires work such as transportation and setting between processes and redundant cleanup, which increases the process load and costs, and improvements were required.

To solve this problem, attempts have been made to drill holes using a laser using the same laser cutting equipment. However, when ordinary laser drilling is performed on steel, a notch-shaped scratch called a melting notch is generated on the wall surface of the circular hole at the meeting point of the cutting start end and the cutting end end on the hole circumference (see Non-Patent Documents 2 and 3). In other words, when a part of the steel other than the circumferential path to be cut into a circular hole is used as the cutting position, cutting is performed from the cutting position to the cutting start end on the circumferential path, and a full circle is cut from the cutting start end and cut away from the cutting end end. In this case, the distance close to the already cut line becomes long in the area where the cutting line enters just before the cutting end end, or the distance close to the already cut line becomes long in the area where the cutting line comes out when cutting away from the cutting end end, causing the temperature of the circular hole wall surface (cut surface) on the product side around the area where the cutting start end and the cutting end end overlap, and the temperature rise causes a melting notch to be generated on the wall surface of the circular hole at the meeting point of the cutting start end and the cutting end end on the hole circumference on the product side. In this way, it has been found that when a melting notch occurs on the wall surface of a circular hole at the meeting point of the cut start end and cut end on the hole circumference, the accuracy of the hole diameter deteriorates and the fatigue life is reduced depending on the direction of the load (see Non-Patent Document 3).

Here, various loads act on joints using high-strength bolts, and joint performance that can withstand them is required. The loads acting on normal structures are the structure's own weight, live load, earthquake load, wind load, etc., but depending on the application, some structures are subject to repeated loads. For example, crane girders in factories and bridge beams. Joints using high-strength bolts in these crane girders and bridge beams are required to be able to withstand repeated loads, and the holes formed in the steel for the high-strength bolts need to have fatigue properties equivalent to those of drilling.

In order to repair the erosion notch that has occurred on the wall of the circular hole at the joining position of the cut start end and the cut end on the hole circumference, it is conceivable to repair the erosion notch by overlaying it with welding. However, this overlaying by welding is not recommended because it not only creates a short bead but also becomes a breeding ground for new defects (see Non-Patent Document 2).
On the other hand, in order to eliminate the erosion notch, a method has been proposed in which the cutting start and end are not joined together, but rather a protrusion is left uncut (see Non-Patent Document 2). However, leaving the protrusion causes a problem that the hole diameter becomes smaller and it becomes more difficult to insert high-strength bolts during the construction stage than usual. To avoid this problem, it is possible to remove the protrusion that is left uncut using a grinder, but there is a problem that it takes a lot of effort to process all the holes with a grinder.

When performing annular laser cutting on a thick plate (steel material), a laser cutting method has been known in the past to suppress the occurrence of recesses that tend to occur on the inner surface of the annular hole in the cutting end area, as shown in, for example, Patent Document 1.
The laser cutting method shown in Patent Document 1 uses oxygen as an assist gas, and defines a position A where the circular path to be cut from the piercing position is reached, and a position a predetermined distance from position A in the direction of laser cutting is defined as position B. Also, a position a predetermined distance from position A in the opposite direction to the laser advancement direction is defined as position C. In this case, when performing laser cutting from position A to position C via position B, and then performing laser cutting from position C to position B via position A, the laser output is reduced relative to the laser output and cutting speed from position A to position C, and the cutting speed is slowed down to perform laser cutting from position C to position B, and the laser output is set to zero at position B.

According to the laser cutting method shown in Patent Document 1, when performing annular cutting on a workpiece, the laser cutting proceeds from the position where the laser cutting starts along the annular cutting path, and the laser output is reduced and the laser cutting speed is controlled to a low speed before reaching the laser cutting start position. As a result, when the cut piece is tilted and comes into contact with the annular inner surface, the laser light reflected from the cut piece to the inner surface has a low output, and it is possible to prevent a large recess from being formed on the inner surface.

Furthermore, a laser drilling method disclosed in, for example, Patent Document 2 is known as a method capable of realizing high-quality laser drilling even in steel plates having a relatively large thickness, for example, 9 mm.
The laser drilling method shown in Patent Document 2 is a laser drilling method in which a laser beam generated by a laser oscillator is irradiated onto a workpiece to drill a hole, and the laser beam output condition parameters, namely the laser output and pulse duty, and the processing condition parameters, namely the cutting speed and processing gas pressure, are simultaneously controlled to appropriate values according to the drilling cutting position to perform the hole drilling process.
The laser drilling method shown in Patent Document 2 makes it possible to eliminate chipping on part of the inner circumference of the hole, or conversely, to prevent protrusions on part of the inner circumference of the hole due to uncut areas, thereby enabling processing aimed at improving the quality of drilling in relatively thick steel plate, for example 9 mm.

JP 2012-115899 A Japanese Patent Application Publication No. 4-33788

Architectural Institute of Japan, Standard Specifications for Building Construction JASS6 Steel Construction, 2018 Architectural Institute of Japan, Technical Guidelines for Steel Construction - Factory Production, pp. 263-264, January 2018 Japan Society of Civil Engineers, Slip Resistance and Fatigue Strength of High-Strength Bolted Friction Joints with Laser-Drilled Holes, Journal of Structural Engineering, Vol. 55A, March 2009

However, in neither of the laser cutting method shown in Patent Document 1 nor the laser drilling method shown in Patent Document 2 is sufficient consideration given to the length of the distance that the cutting line approaches the already cut line in the area just before the cut end and the length of the distance that the cutting line approaches the already cut line in the area where the cutting line emerges when cutting away from the cut end, and neither method is able to sufficiently avoid a rise in temperature on the wall surface (cut surface) of the circular hole around the product side around the area where the cut start end and the cut end overlap, and is unable to sufficiently avoid the occurrence of a melting notch on the wall surface of the circular hole at the meeting point of the cut start end and the cut end on the product side.
Therefore, an object of the present invention is to provide a method for forming a hole using a laser, which can improve the accuracy of the hole diameter by avoiding the occurrence of a melting notch on the wall surface of a circular hole formed in a steel material at the meeting point of the cutting start end and the cutting end end on the circumference of the hole.

In order to solve the above problems, one aspect of the present invention is a laser hole forming method that irradiates a steel material with a laser beam to form a round hole, and the method includes the steps of: setting a portion of the steel material other than the circumferential path to be cut into the round hole as a cutting position; cutting out from the cutting position, cutting into a first point on the circumferential path with an arc having a radius of 1.0 mm or less; cutting from the first point around the circumferential path to the first point; and then cutting out from the first point with an arc having a radius of 1.0 mm or less.

In another aspect of the present invention, a laser hole forming method is a laser hole forming method in which a laser beam is irradiated onto a steel material to form a round hole, and the method includes cutting out a portion of the steel material other than the circumferential path to be cut into the round hole as a cutting position, cutting in a straight line from the cutting position, cutting into a first point on the circumferential path at a right angle to a tangent to the first point, cutting from the first point around the circumferential path to reach the first point, and then cutting out so as to exit the first point along an arc having a radius of 1.0 mm or less.

Furthermore, a laser hole forming method according to another aspect of the present invention is a laser hole forming method in which a laser beam is irradiated onto a steel material to form a round hole, and the method includes the steps of: setting a portion of the steel material other than the circumferential path to be cut into the round hole as a cutting position; cutting in a straight line from the cutting position; cutting into a first point on the circumferential path at a right angle to a tangent to the first point; cutting from the first point around the circumferential path to the first point; and then cutting out from the first point at a right angle to the tangent to the first point.

The laser hole forming method of the present invention can provide a method for forming holes using a laser that can improve the accuracy of the hole diameter by shortening the length of the proximity to the already cut line in the area where the cutting line enters just before the cut end, and shortening the length of the proximity to the already cut line in the area where the cutting line emerges when cutting away from the cut end, thereby avoiding a temperature rise on the circular hole wall surface (cut surface) around the hole circumference around the area where the cut start end and cut end overlap, and avoiding the occurrence of a melting notch on the circular hole wall surface at the meeting point of the cut start end and cut end on the hole circumference due to the temperature rise.

As a result, by drilling holes in steel using the laser hole formation method of the present invention in the same laser cutting equipment as the laser cutting equipment that cuts the outside of the steel, duplicated work such as transportation, setup, and cleanup between processes when used in combination with drill hole drilling is eliminated, and the occurrence of melting notches caused by laser drilling is avoided and the accuracy of the hole diameter is improved, solving the problem that high-strength bolts are more difficult to insert than usual without grinding, and it is possible to obtain laser holes with fatigue life equivalent to that of bolt holes drilled regardless of the load direction. This reduces the cost of bolt joints, shortens construction time, and saves labor, contributing to strengthening the competitiveness of steel structures and improving productivity.

1 is a schematic diagram of a laser drilling device to which a laser hole forming method according to first to third embodiments of the present invention is applied; FIG. 2 is a diagram for explaining the basic configuration of the laser drilling device shown in FIG. 1 . 3A to 3C are diagrams illustrating a hole forming method using a laser according to the first embodiment of the present invention. 1A to 1C are diagrams for explaining a first reference example of a hole forming method using a laser. 13A to 13C are diagrams for explaining a second reference example of a hole forming method using a laser. 13A to 13C are diagrams for explaining a third reference example of a hole forming method using a laser. 6A to 6C are diagrams illustrating a hole forming method using a laser according to a second embodiment of the present invention. 13A to 13C are diagrams illustrating a hole forming method using a laser according to a third embodiment of the present invention. FIG. 1 is a plan view for explaining a sample (steel material) created in an example for verifying the effects of the present invention. 11A and 11B are diagrams for explaining a method for measuring the inner diameter of a circular hole formed in a sample based on coordinates. FIG. 13 is a diagram for explaining a method for measuring the inner diameter of a circular hole formed in a sample based on a melting notch standard. FIG. 13 is a diagram for explaining the squareness when measuring the inner diameter based on the coordinate system and the inner diameter based on the erosion notch of a round hole formed in a sample. 1 is a graph showing the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of round holes formed by the hole forming method of Example 1 for each sample having a steel plate thickness of 6 mm, 9 mm, and 12 mm. 13 is a graph showing the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of round holes formed by the hole forming method of Example 2 for each sample having a steel plate thickness of 6 mm, 9 mm, and 12 mm. 13 is a graph showing the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of round holes formed by the hole forming method of Example 3 for each sample having a steel plate thickness of 6 mm, 9 mm, and 12 mm. 1 is a graph showing the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the corrosion notch standard of round holes formed by the hole forming method of Example 1 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 1 is a graph showing the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the corrosion notch standard of round holes formed by the hole forming method of Example 2 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 13 is a graph showing the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the corrosion notch standard of round holes formed by the hole forming method of Example 3 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 1 is a graph showing the measurement results of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) based on the corrosion notch standard of round holes formed by the hole forming method of Example 1 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 1 is a graph showing the measurement results of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) based on the corrosion notch standard of round holes formed by the hole forming method of Example 2 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 1 is a graph showing the measurement results of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) based on the corrosion notch standard of round holes formed by the hole forming method of Example 3 for each sample of steel plate thicknesses of 6 mm, 9 mm, and 12 mm. 11A to 11C are diagrams for explaining a hole forming method according to Comparative Example 1. 13A to 13C are diagrams for explaining a hole forming method according to Comparative Example 2. 13A to 13C are diagrams for explaining a hole forming method according to Comparative Example 3.

Hereinafter, a hole forming method using a laser according to an embodiment of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is not limited to the following embodiments in terms of the material, shape, structure, arrangement, etc. of the components.
In addition, the drawings are schematic, and therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual ones, and the drawings also include parts in which the relationship and ratios of dimensions differ from each other.

(Configuration of laser drilling device)
FIG. 1 shows a schematic configuration of a laser drilling apparatus to which the laser hole forming methods according to the first to third embodiments of the present invention are applied, and FIG. 2 shows the basic configuration of the laser drilling apparatus shown in FIG. 1.
The laser drilling device 1 shown in FIG. 1 and FIG. 2 irradiates a steel material S with a laser beam LB to form a round hole H. The laser drilling device 1 includes a pair of X-axis direction moving members 3 that can run in the X-axis direction on a pair of rails 2 installed on the outside of both ends of the steel material S to be drilled, a Y-axis direction extension member 4 that connects the pair of X-axis direction moving members 3, and a laser processing head 5 that can move in the Y-axis direction along the Y-axis direction extension member 4. The laser processing head 5 moves in the X-axis direction as the X-axis direction moving members 3 run along the X-axis direction, moves in the Y-axis direction as the Y-axis direction extension member 4 moves, and can also move in the Z-axis direction. The laser drilling device 1 also includes a control box 6 that includes a control device that controls the travel of the X-axis direction moving members 3 in the X-axis direction and the movement of the laser processing head 5 in the Y-axis direction and the Z-axis direction, and controls the output of a laser oscillator 7, which will be described later.

2, the laser processing head 5 of the laser drilling device 1 focuses the laser light LB oscillated from a laser oscillator 7 by an internal focusing lens 8 and irradiates the laser light LB onto the steel material S. The laser processing head 5 is also connected to an assist gas supplying means 9 for injecting assist gas into the steel material S when forming a round hole in the steel material S. The laser oscillator 7 is a _CO2 laser oscillator or a fiber laser oscillator. The assist gas is oxygen.

First Embodiment
Next, a laser hole forming method according to a first embodiment of the present invention, in which a laser beam LB is irradiated onto a steel material S to form a round hole H using the laser drilling device 1 shown in FIGS. 1 and 2, will be described with reference to FIG. 3.
The thickness of the steel material S to be drilled is not particularly limited, but is set to about 6 mm to 16 mm in this embodiment. The material of the steel material S is not particularly limited, and may be carbon steel, stainless steel, or the like.
When the laser beam LB is irradiated onto the steel material S to form the round hole H, the movement of the laser processing head 5 in the X-axis direction, the Y-axis direction, and the Z-axis direction is controlled to cut as follows.
First, a portion of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as a cutting position CP.

Next, the cutting is performed by cutting out in a straight line from the cutting position CP so as to enter and be tangent to the first point P1 on the circumferential path 11 with an arc 13 having a radius R1 of 1.0 mm or less. In this embodiment, specifically, the cutting is performed so as to enter and be tangent to the first point P1 with an arc 13 having a radius R1 of 1.0 mm.
Next, the cutting is performed from the first point P1 around the circumferential path 11 until the cutting returns to the first point P1.
Then, the cut is made so as to come out in a straight line from the first point P1 at a circular arc 16 having a radius R2 of 1.0 mm or less. In this embodiment, specifically, the cut is made so as to come out from the first point P1 at a circular arc 13 having a radius R2 of 1.0 mm.

As a result, a round hole H (a through hole penetrating the steel material S as shown in FIG. 2) is formed in the steel material S.
The cutting lines from the cut-out position CP to the end in forming this round hole H are a straight cutting line 12 from the cut-out position CP to the arc 13, the arc 13, a cutting line 14 from the first point P1 to a specified point 180° along the circumferential path 11, a cutting line 15 from this specified point to the first point P1, the arc 16, and a straight cutting line 17 from the end of the arc 16 to the end.

The cutting speed of the laser beam LB is appropriately determined according to the thickness of the steel material S, and in this embodiment, cutting is performed at a constant speed (e.g., 1200 mm/min) from the cutting at the cutting position CP to the final cutting. The output of the laser oscillator 7 is constant (e.g., 3000 kW) from the cutting at the cutting position CP to the final cutting. The frequency of the laser oscillator 7 is constant (e.g., 1000 Hz) from the cutting at the cutting position CP to the final cutting. The duty ratio of the laser oscillator 7 is constant (e.g., 60%) from the cutting at the cutting position CP to the final cutting. The gas pressure of oxygen as the assist gas is constant (e.g., 27 KPa) from the cutting at the cutting position CP to the final cutting.

In this way, the portion of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cutting position CP, and it is cut in a straight line from the cutting position CP, and cut so that it enters and touches the first point P1 on the circumferential path 11 with an arc 13 having a radius R1 of 1.0 mm or less. Then, it cuts from the first point P1 around the circumferential path 11 once to reach the first point P1, and then cuts away so that it exits and touches the arc 16 having a radius R2 of 1.0 mm or less from the first point P1.

This shortens the distance between the cut line 12 and the arc 13 in the area where the cut line 15 enters just before the cut end (first point P1), and shortens the distance between the cut line 14 and the area where the arc 16 and the cut line 17 exit when cutting away from the cut end (first point P1). This prevents a temperature rise on the circular hole wall surface (cut surface) around the circumference of the circular hole H in the area where the cut start end (first point P1) and the cut end end (first point P1) overlap, and prevents a melting notch from occurring on the circular hole wall surface at the meeting point of the cut start end and the cut end on the product side due to the temperature rise, thereby improving the accuracy of the hole diameter.

As a result, by drilling holes in steel material S using the laser hole formation method according to the first embodiment in the same laser cutting equipment as the laser cutting equipment that cuts the outside of steel material S, duplicated work such as transportation, setup, and cleanup between processes when used in combination with drill hole drilling is eliminated, and the occurrence of melting notches due to laser drilling is avoided and the accuracy of the hole diameter is improved, solving the problem that high-strength bolts are more difficult to insert than usual without grinding, and it is possible to obtain laser holes whose fatigue life is as excellent as that of bolt holes drilled regardless of the load direction. This makes it possible to reduce costs, shorten construction periods, and save labor for bolt joints, contributing to strengthening the competitiveness of steel structures and improving productivity.

Here, if the cutting is performed from the cutting position CP so that the arc 13 with a radius R1 of 1.0 mm or more touches the first point P1 on the circumferential path 11, the distance over which the cutting line 15 from the specified point to the first point P1 is in close proximity to the cutting line 12 and the arc 13 from the cutting position CP to the arc 13 that have already been cut will be long. Therefore, a self-burning phenomenon occurs around the cutting end (first point P1) due to a sudden rise in temperature, and melting notches and unevenness occur on the cut surface on the outside (product side) of the cutting line 15, significantly reducing the roughness of the cut surface. For this reason, the cutting is performed from the cutting position CP so that the arc 13 with a radius R1 of 1.0 mm or less touches the first point P1 on the circumferential path 11.

In addition, if the cut is made so that the arc 16 with a radius R2 of more than 1.0 mm is tangent from the first point P1 to the cut line 14, the distance over which the arc 16 and the linear cut line 17 from the end of the arc 16 to the end are in close proximity to the cut line 14 from the first point P1 to a specified point 180° along the circumferential path 11, will be longer. This makes it easier for melting notches to occur, and the thermal effect on the inner wall of the hole on the outside (product side) of the cut line 14 will be greater, damaging the surface shape. For this reason, the cut is made so that the arc 16 with a radius R2 of 1.0 mm or less is tangent from the first point P1 to the cut line 14.

Next, a hole forming method using a laser according to a first embodiment of the present invention shown in FIG. 4 will be described.
In the case of the hole forming method by laser according to the first reference example, first, a portion of the steel material S other than the circumferential path 11 to be cut into the circular hole H is set as a cutting position CP.
Next, the cutting is performed in a straight line from the cutting position CP so as to enter a point P11 on the circumferential path 11 at a predetermined distance in the traveling direction from the first point P1 described above, so as to be tangent to a circular arc 112 of a comparatively large radius.
Next, the cutting is performed from point P11 around the circumferential path 11 until it reaches point P12, which is a predetermined distance away in the reverse direction from the first point P1.
Thereafter, the arc 115 having a relatively large radius is cut from the point P12 to make a tangent and exit in a straight line.

In the case of the laser hole forming method according to the first reference example, as shown in Fig. 4, overlap between the periphery of the cutting start end (point P11) and the periphery of the cutting end end (point P12) on the circumference of the round hole H is avoided, so that no melting notch is generated on the wall surface of the round hole H on the circumference. However, since a protrusion 116 is formed between the arcs 112 and 115, it is necessary to remove the protrusion 116 after the hole is formed by the laser. If the protrusion 116 is to be removed by a grinder or the like, it would be very laborious to process all the holes with the grinder.
In contrast, in the case of the laser hole forming method according to the first embodiment, no protrusions remain on the inner surface of the round hole H after the round hole H is formed, so there is no need to remove them with a grinder or the like.

Next, a hole forming method using a laser according to a second embodiment of the present invention will be described with reference to FIG.
In the case of the laser hole forming method according to the second reference example, first, a portion of the steel material S other than the circumferential path 11 to be cut into a circular hole H, which is on the opposite side of the traveling direction from the first point P1 described above, is set as the cutting position CP.
Next, the cutting is performed in a curved line from the cutting position CP so as to enter a point P13 on the circumferential path 11 at a predetermined distance in the traveling direction from the first point P1 described above, so as to be tangent to a circular arc 118 having a comparatively large radius.
Next, the cutting is performed from point P13 around the circumferential path 11 to point P14, which is a predetermined distance away in the reverse direction from the first point P1.
Thereafter, the vehicle makes a curved cut to come into contact with a circular arc 121 of a comparatively large radius from point P14 and exits toward the traveling direction toward the first point P1.

In the case of the laser hole formation method according to the second reference example, as shown in FIG. 5, overlap between the periphery of the cut start end (point P13) and the periphery of the cut end (point P14) on the circumference of the round hole H is avoided, so no melting notches are formed on the wall surface of the round hole on the circumference of the round hole H. However, since a protrusion 122 is formed between the arcs 118 and 121, it is necessary to remove the protrusion 122 after the hole is formed by the laser. If this protrusion 122 is to be removed with a grinder or the like, it would be very laborious to process all the holes with the grinder.

Next, a hole forming method using a laser according to a third embodiment shown in FIG. 6 will be described.
In the case of the hole forming method by laser according to the third reference example, first, a portion of the steel material S other than the circumferential path 11 to be cut into the circular hole H is set as a cutting position CP.
Next, the cutting is performed in a straight line from the cutting position CP so as to enter at a right angle, which is an arc having a radius of 0 mm, at the first point P1 on the circumferential path 11 described above.
Next, the cutting is performed from the first point P1 around the circumferential path 11 until it reaches a point P15 that is a predetermined distance away from the first point P1 in the reverse direction, and then the cutting is completed.

In the case of the laser hole forming method according to the third reference example, as shown in Fig. 6, overlap between the periphery of the cutting start end (first point P1) and the periphery of the cutting end end (point P15) on the circumference of the round hole H is avoided, so that no melting notch is generated on the wall surface of the round hole H on the circumference. However, a protrusion 126 is formed between the first point P1 and point P15, and this protrusion 126 needs to be removed by tapping. A great deal of work is required to tap and remove the protrusion 126 for all holes.
In contrast, in the case of the laser hole forming method according to the first embodiment, no protrusions remain on the inner surface of the round hole H after the round hole H is formed, so there is no need to remove them with a grinder or the like.

Second Embodiment
Next, with reference to FIG. 7, a laser hole forming method according to a second embodiment of the present invention will be described, in which laser light LB is irradiated onto steel material S to form a round hole H using the laser drilling device 1 shown in FIG. 1 and FIG. 2.
The plate thickness and material of the steel material S to be drilled are similar to those of the steel material S to be drilled in the laser hole forming method according to the first embodiment.
When the laser beam LB is irradiated onto the steel material S to form the round hole H, the movement of the laser processing head 5 in the X-axis direction, the Y-axis direction, and the Z-axis direction is controlled to cut as follows.
First, in the same manner as in the laser hole forming method according to the first embodiment, a portion of the steel material S other than the circumferential path 11 to be cut into the circular hole H is set as a cutting position CP.

Next, the cutting is performed in a straight line from the cutting position CP to a first point P1 on the circumferential path 11 so as to enter at a right angle to a tangent line 30 that is in contact with the first point P1.
Next, the cutting is performed from the first point P1 around the circumferential path 11 until the cutting returns to the first point P1.
Then, the cut is made so as to come out in a straight line from the first point P1 along the arc 21 having a radius R3 of 1.0 mm or less. In this embodiment, specifically, the cut is made so as to come out from the first point P1 along the arc 21 having a radius R3 of 1.0 mm.

As a result, a round hole H (a through hole penetrating the steel material S as shown in FIG. 2) is formed in the steel material S.
The cutting lines from the cut-out position CP to the end in forming this round hole H are a straight cutting line 18 from the cut-out position CP to the first point P1, a cutting line 19 from the first point P1 to a specified point 180° along the circumferential path 11, a cutting line 20 from this specified point to the first point P1, an arc 21, and a straight cutting line 22 from the end of the arc 21 to the end.

Regarding the cutting speed by the laser light LB, cutting is performed at a steady speed (e.g., 1200 mm/min) from the cut-out position CP to the first point P1. This steady speed is appropriately determined according to the thickness of the steel material S. Then, the cutting speed is decelerated from the steady speed from the first point P1 (e.g., decelerated by about 90% ≒ decelerated to 110 mm/min) to cut from the first point P1 to the second point P2, which is a predetermined distance (e.g., about 2 mm) in the direction of travel on the circumferential path 11. Thereafter, the cutting speed is accelerated from the second point P2 to the aforementioned steady speed to cut around once to the first point P1, and then the cutting is performed at the aforementioned steady speed.

The output of the laser oscillator 7 is constant (e.g., 3000 kW) when cutting at a steady speed and when cutting at a decelerated speed. The frequency of the laser oscillator 7 is constant (e.g., 1000 Hz) when cutting at a steady speed and is constant (e.g., 10 Hz) when cutting at a decelerated speed. The duty ratio of the laser oscillator 7 is constant (e.g., 60%) when cutting at a steady speed and is constant (e.g., 25%) when cutting at a decelerated speed. The gas pressure of oxygen as the assist gas is constant (e.g., 27 KPa) when cutting at a steady speed and is constant (e.g., 35 KPa) when cutting at a decelerated speed.

In this way, the part of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cutting position CP, and it is cut in a straight line from the cutting position CP to the first point P1 on the circumferential path 11 so as to enter at a right angle to the tangent line 30 that touches the first point P1. Then, it is cut from the first point P1 around the circumferential path 11 to the first point P1, and then it is cut away so as to touch the arc 21 with a radius R3 of 1.0 mm or less from the first point P1 and exit.

This shortens the distance between the cut line 20 and the already cut line 18 in the area just before the cut end (first point P1), and shortens the distance between the cut line 20 and the already cut line 19 in the area where the arc 21 and the cut line 22 exit when cutting away from the cut end (first point P1). This prevents a temperature rise on the circular hole wall surface (cut surface) around the circumference of the circular hole H in the area where the cut start end (first point P1) and the cut end end (first point P1) overlap, and prevents a melting notch from occurring on the circular hole wall surface at the meeting point of the cut start end and the cut end on the product side due to the temperature rise, thereby improving the accuracy of the hole diameter.

As a result, by drilling holes in steel material S using the laser hole formation method of the second embodiment in the same laser cutting equipment as the laser cutting equipment that cuts the outside of steel material S, duplicated work such as transportation, setup, and cleanup between processes when used in combination with drill hole drilling is eliminated, and the occurrence of melting notches due to laser drilling is avoided and the accuracy of the hole diameter is improved, solving the problem that high-strength bolts are more difficult to insert than usual without grinding, and it is possible to obtain laser holes whose fatigue life is as excellent as that of bolt holes drilled regardless of the load direction. This makes it possible to reduce costs, shorten construction periods, and save labor for bolt joints, contributing to strengthening the competitiveness of steel structures and improving productivity.

Here, cutting is performed from the cut-out position CP to the first point P1 on the circumferential path 11 at a right angle to the tangent line 30 that touches the first point P1, so that the cut line 20 from the predetermined point to the first point P1 has almost no distance in close proximity to the cut line 18 from the cut-out position CP to the first point P1. Therefore, the self-burning phenomenon due to a sudden increase in temperature does not occur around the cut end portion (first point P1), and the occurrence of melting notches and unevenness on the cut surface on the outside (product side) of the cut line 20 is avoided, and the roughness of the cut surface does not decrease significantly.
It is preferable to cut the first point P1 on the circumferential path 11 at a right angle to the tangent 30, but a slightly acute or obtuse angle may also be acceptable.

In addition, if the cut is made so that the arc 21 with a radius R3 of more than 1.0 mm is tangent from the first point P1, the distance over which the arc 21 and the linear cutting line 22 from the end of the arc 21 to the end are in close proximity to the cutting line 19 from the first point P1 that has already been cut to a specified point 180° along the circumferential path 11 will be long. This makes it easier for melting notches to occur, and the thermal effect on the inner wall of the hole on the outside (product side) of the cutting line 14 will be large, damaging the surface shape. For this reason, the cut is made so that the arc 21 with a radius R3 of 1.0 mm or less is tangent from the first point P1.

In addition, in the laser hole forming method according to the second embodiment, cutting is performed at a steady speed from the cut-out position CP to the first point P1, and unlike the laser hole forming method according to the first embodiment, the cutting speed is decelerated from the steady speed from the first point P1 to cut to the second point P2, which is a predetermined distance from the first point P1 in the direction of travel on the circumferential path 11. This has the effect of suppressing poor cut surface quality caused by a sudden change in speed when transitioning from a primary stop state of the machine to cutting.

In addition, the deceleration speed in cutting from the first point P1 to the second point P2 is preferably decelerated to 5.0% to 10.0% of the steady speed in cutting from the cut-out position CP to the first point P1. When decelerating to more than 10.0%, the duty ratio of the laser beam is lowered at the same time as decelerating to reduce the amount of heat applied to the steel plate, resulting in a disadvantage that the amount of heat is insufficient compared to the speed, and the quality of the cut surface deteriorates. On the other hand, when decelerating to less than 5.0%, the difference from the normal cutting speed becomes large, and the speed difference when accelerating to the normal cutting speed becomes larger, resulting in an increased risk of deterioration of the quality of the cut surface when switching.
In the hole forming method using a laser according to the second embodiment, the cutting speed is accelerated from the second point P2 to a steady speed, goes around once to cut to the first point P1, and then the cutting speed is reduced to the steady speed.

Third Embodiment
Next, a laser hole forming method according to a third embodiment of the present invention will be described with reference to FIG. 8, in which a laser drilling device 1 shown in FIG. 1 and FIG. 2 is used to irradiate a steel material S with laser light LB to form a round hole H.
The plate thickness and material of the steel material S to be drilled are similar to those of the steel material S to be drilled in the laser hole forming method according to the first embodiment.
When the laser beam LB is irradiated onto the steel material S to form the round hole H, the movement of the laser processing head 5 in the X-axis direction, the Y-axis direction, and the Z-axis direction is controlled to cut as follows.

First, in the same manner as in the laser hole forming method according to the first embodiment, a portion of the steel material S other than the circumferential path 11 to be cut into the circular hole H is set as a cutting position CP.
Next, the cutting is performed in a straight line from the cutting position CP to a first point P1 on the circumferential path 11 so as to enter at a right angle to a tangent line 30 that is in contact with the first point P1.
Next, the cutting is performed from the first point P1 around the circumferential path 11 until the cutting returns to the first point P1.
Thereafter, the cut is made so as to exit in a straight line from the first point P1 at a right angle to a tangent line 30 that touches the first point P1.

As a result, a round hole H (a through hole penetrating the steel material S as shown in FIG. 2) is formed in the steel material S.
The cutting lines from the cut-out position CP to the end in forming this round hole H are a straight cutting line 23 from the cut-out position CP to the first point P1, a cutting line 24 from the first point P1 to a specified point 180° along the circumferential path 11, a cutting line 25 from this specified point to the first point P1, and a straight cutting line 26 from the first point P1 to the end.

Regarding the cutting speed by the laser beam LB, the cutting is performed at a steady speed (e.g., 1200 mm/min) from the cut-out position CP to the first point P1. This steady speed is appropriately determined according to the plate thickness of the steel material S. Then, the cutting speed is decelerated from the steady speed from the first point P1 (e.g., decelerated to about 90% ≈ 110 mm/min) to cut from the first point P1 to a second point P2 that is a predetermined distance (e.g., about 2 mm) in the traveling direction on the circumferential path 11. Thereafter, the cutting speed is accelerated from the second point P2 to the aforementioned steady speed to cut around once to the first point P1, and then the cutting is performed at the aforementioned steady speed.

The output of the laser oscillator 7 is constant (e.g., 3000 kW) when cutting at a steady speed and when cutting at a decelerated speed. The frequency of the laser oscillator 7 is constant (e.g., 1000 Hz) when cutting at a steady speed and is constant (e.g., 10 Hz) when cutting at a decelerated speed. The duty ratio of the laser oscillator 7 is constant (e.g., 60%) when cutting at a steady speed and is constant (e.g., 25%) when cutting at a decelerated speed. The gas pressure of oxygen as the assist gas is constant (e.g., 27 KPa) when cutting at a steady speed and is constant (e.g., 35 KPa) when cutting at a decelerated speed.

In this way, the part of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cutting position CP, and it is cut in a straight line from the cutting position CP to the first point P1 on the circumferential path 11 so as to enter at a right angle to the tangent line 30 that touches the first point P1. Then, it is cut from the first point P1 all the way around the circumferential path 11 to the first point P1, and then it is cut out so as to exit in a straight line from the first point P1 at a right angle to the tangent line 30 that touches the first point P1.

This shortens the distance between the cut line 25 and the already cut line 23 in the area just before the cut end (first point P1), and shortens the distance between the cut line 25 and the already cut line 24 in the area where the cut line 26 leaves when cutting away from the cut end (first point P1). This prevents a temperature rise on the circular hole wall surface (cut surface) around the circumference of the circular hole H in the area where the cut start end (first point P1) and the cut end (first point P1) overlap, and prevents a melting notch from occurring on the circular hole wall surface at the meeting point of the cut start end and the cut end on the product side due to the temperature rise, improving the accuracy of the hole diameter.

As a result, by drilling holes in steel material S using the laser hole formation method of the third embodiment in the same laser cutting equipment as the laser cutting equipment that cuts the outside of steel material S, duplicated work such as transportation, setup, and cleanup between processes when used in combination with drill hole drilling is eliminated, and the occurrence of melting notches due to laser drilling is avoided and the accuracy of the hole diameter is improved, solving the problem that high-strength bolts are more difficult to insert than usual without grinding, and it is possible to obtain laser holes whose fatigue life is as excellent as that of bolt holes drilled regardless of the load direction. This makes it possible to reduce costs, shorten construction periods, and save labor for bolt joints, contributing to strengthening the competitiveness of steel structures and improving productivity.

Here, cutting is performed from the cut-out position CP to the first point P1 on the circumferential path 11 at a right angle to the tangent line 30 that touches the first point P1, so that the cut line 25 from the predetermined point to the first point P1 has almost no distance in close proximity to the cut line 23 from the cut-out position CP to the first point P1. Therefore, the self-burning phenomenon due to a sudden rise in temperature does not occur around the cut end portion (first point P1), and the occurrence of melting notches and unevenness on the cut surface on the outside (product side) of the cut line 25 is avoided, and the roughness of the cut surface does not decrease significantly.
It is preferable to cut the first point P1 on the circumferential path 11 at a right angle to the tangent 30, but a slightly acute or obtuse angle may also be acceptable.

In addition, since the cut is made so as to extend in a straight line from the first point P1 at a right angle to the tangent line 30 tangent to the first point P1, there is almost no distance over which the straight cutting line 26 from the first point P1 to the end is in close proximity to the cutting line 24 from the already cut first point P1 to a predetermined point 180° along the circumferential path 11. For this reason, melting notches are unlikely to occur, and the thermal effect on the inner wall of the hole on the outside (product side) of the cutting line 24 is reduced, so that the surface shape is not damaged.
Here, it is preferable to cut away from the first point P1 so as to exit in a straight line perpendicular to a tangent line 30 that touches the first point P1, but it does not matter if the angle is a slightly acute or obtuse angle.

In addition, in the laser hole forming method according to the third embodiment, cutting is performed at a steady speed from the cut-out position CP to the first point P1, and unlike the laser hole forming method according to the first embodiment, the cutting speed is decelerated from the steady speed from the first point P1 to cut to the second point P2, which is a predetermined distance from the first point P1 in the direction of travel on the circumferential path 11. This has the effect of suppressing poor cut surface quality caused by a sudden change in speed when the machine transitions from a paused state to cutting.

The deceleration speed during cutting from the first point P1 to the second point P2 is preferably 5.0% to 10.0% of the steady speed during cutting from the cut-out position CP to the first point P1. When decelerating to more than 10.0%, the duty ratio of the laser beam is lowered at the same time as the speed is reduced to reduce the amount of heat applied to the steel plate, resulting in a disadvantage that the amount of heat is insufficient compared to the speed, and the quality of the cut surface deteriorates. On the other hand, when decelerating to less than 5.0%, the difference from the normal cutting speed becomes large, and the speed difference when accelerating to the normal cutting speed becomes even larger, resulting in a disadvantage that the risk of the cut surface quality deteriorating when switching speed increases.

In the laser hole forming method according to the third embodiment, the cutting speed is accelerated from the second point P2 to a steady speed, and cutting is performed once to the first point P1, and then the cutting is continued at the steady speed.
Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made.
For example, the cutting speed, the output of the laser oscillator 7, the frequency of the laser oscillator 7, the duty ratio of the laser oscillator 7, and the gas pressure of oxygen as the assist gas are not limited to the examples described above.
Furthermore, in the laser hole forming methods according to the second and third embodiments, the steady-state speed is decelerated from the first point P1 to the second point P2, which is a predetermined distance in the traveling direction on the circumferential path 11 from the first point P1, but cutting may be performed at the steady-state speed from the first point P1 to the second point without decelerating the cutting speed.

In order to verify the effects of the present invention, for each steel material S having a material quality of standard SS400, a plate width W of the steel material S of 150 mm, a plate length L of the steel material S of 300 mm, and a plate thickness T of the steel material S of 6 mm, 9 mm, and 12 mm, samples (three in total) were created in which two round holes were formed by the hole forming method of Example 1, two round holes were formed by the hole forming method of Example 2, and four round holes were formed by the hole forming method of Example 3, as shown in FIG. 9 .
In each sample, the surface treatment remained black.

In addition, the round holes formed by the hole forming method of Example 1, the hole forming method of Example 2, and the hole forming method of Example 3 were perfect circles with a hole diameter of Φ21.65 mm, and a _CO2 laser cutting machine was used as the laser drilling device.
The hole forming method according to Example 1 corresponds to the laser hole forming method according to the first embodiment (see FIG. 3), and first, a portion of the steel material S other than the circumferential path 11 to be cut into a round hole H is set as a cut-out position CP, and then cut in a straight line from the cut-out position CP, and cut so as to enter and touch a first point P1 on the circumferential path 11 with an arc 13 having a radius R1 of 1.0 mm. Then, the cut goes around the circumferential path 11 from the first point P1 to the first point P1, and then cuts out so as to exit and touch a circular arc 16 having a radius R2 of 1.0 mm from the first point P1 in a straight line.

In the hole forming method according to Example 1, the cutting speed by the laser beam LB was 1200 mm/min from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 6 mm, 1100 mm/min from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 9 mm, and 1000 mm/min from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 12 mm. The output of the laser oscillator 7 was 3000 kW from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 6 mm, 3000 kW from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 9 mm, and 3200 kW from the cut-out position CP to the final cut-out in the sample with a plate thickness T of 12 mm. The frequency of the laser oscillator 7 was 1000 Hz from the cutting at the cutting position CP to the final cutting run-off for samples with a plate thickness T of 6 mm, 9 mm, and 12 mm. The duty ratio of the laser oscillator 7 was 60% from the cutting at the cutting position CP to the final cutting run-off for samples with a plate thickness T of 6 mm, 65% from the cutting at the cutting position CP to the final cutting run-off for samples with a plate thickness T of 9 mm, and 65% from the cutting at the cutting position CP to the final cutting run-off for samples with a plate thickness T of 12 mm. The gas pressure of oxygen as the assist gas was 27 KPa from the cutting at the cutting position CP to the final cutting run-off for all plate thicknesses T of 6 mm, 9 mm, and 12 mm.

The hole forming method according to Example 2 corresponds to the laser hole forming method according to the second embodiment (see FIG. 7), in which the portion of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cut-out position CP, cut in a straight line from the cut-out position CP, and cut into the first point P1 on the circumferential path 11 at a right angle to the tangent line 30 tangent to the first point P1. Then, the cut goes around the circumferential path 11 from the first point P1 to the first point P1, and then cuts out so as to come out in a straight line from the first point P1 to an arc 21 with a radius R3 of 1.0 mm or less.

In the hole forming method of Example 2, the cutting speed of the laser light LB for a sample with a plate thickness T of 6 mm was 1200 mm/min from the cut-out position CP to the first point P1, then the cutting speed was decelerated to 110 mm/min from the first point P1 to cut to the second point P2 a predetermined distance (2 mm) in the direction of travel on the circumferential path 11 from the first point P1, and then accelerated from the second point P2 to the aforementioned 1200 mm/min to make one full revolution and cut to the first point P1, after which the cutting was completed at 1200 mm/min. In addition, for a sample with a plate thickness T of 9 mm, the cutting was performed from the cut-out position CP to the first point P1 at a steady speed of 1100 mm/min, and from the first point P1 the cutting speed was decelerated to 95 mm/min and the cutting was performed from the first point P1 to the second point P2, which is a predetermined distance (2 mm) in the traveling direction on the circumferential path 11, and from the second point P2 the cutting speed was accelerated to the aforementioned 1100 mm/min to make one revolution and cut to the first point P1, and then the cutting was performed at 1100 mm/min. Also, for a sample with a plate thickness T of 12 mm, the cutting speed was reduced to 75 mm/min from the first point P1 to cut to the second point P2, a predetermined distance (2 mm) along the circumferential path 11 from the first point P1, and the cutting speed was accelerated from the second point P2 to the aforementioned 1000 mm/min to make one revolution and cut to the first point P1, after which the cutting was stopped at 1000 mm/min.

In addition, the output of the laser oscillator 7 was 3,000 kW when cutting at a steady speed and when cutting at a decelerated speed for samples with plate thicknesses T of 6 mm and 9 mm, and was 3,200 kW when cutting at a steady speed and 3,200 kW when cutting at a decelerated speed for a sample with plate thickness T of 12 mm.
The frequency of the laser oscillator 7 was 1000 Hz when cutting at a steady speed and 10 Hz when cutting at a decelerated speed when the plate thickness T was 6 mm, 9 mm, and 12 mm. The duty ratio of the laser oscillator 7 was 60% when cutting at a steady speed and 25% when cutting at a decelerated speed when the plate thickness T was 6 mm, and 65% when cutting at a steady speed and 25% when cutting at a decelerated speed when the plate thickness T was 9 mm and 12 mm. The gas pressure of oxygen as the assist gas was 27 KPa when cutting at a steady speed and 35 KPa when cutting at a decelerated speed when the plate thickness T was 6 mm, 9 mm, and 12 mm.

The hole forming method according to Example 3 corresponds to the laser hole forming method according to the third embodiment (see FIG. 8), in which the portion of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cut-out position CP, cut in a straight line from the cut-out position CP, and cut into the first point P1 on the circumferential path 11 at a right angle to the tangent line 30 touching the first point P1. Then, the cut goes around the circumferential path 11 from the first point P1 to the first point P1, and then cuts out so as to exit in a straight line from the first point P1 at a right angle to the tangent line 30 touching the first point P1.

In the hole forming method of Example 3, the cutting speed of the laser light LB in a sample with a plate thickness T of 6 mm was such that the cutting speed was 1200 mm/min steady-state cutting speed from the cut-out position CP to the first point P1, the cutting speed was decelerated to 110 mm/min from the first point P1 to cut to the second point P2 a predetermined distance (2 mm) in the direction of travel on the circumferential path 11, and the cutting speed was accelerated from the second point P2 to the aforementioned 1200 mm/min to make one full revolution and cut to the first point P1, after which the cutting was completed at 1200 mm/min. In addition, for a sample with a plate thickness T of 9 mm, the cutting was performed from the cut-out position CP to the first point P1 at a steady speed of 1100 mm/min, and from the first point P1 the cutting speed was decelerated to 95 mm/min and the cutting was performed from the first point P1 to the second point P2, which is a predetermined distance (2 mm) in the traveling direction on the circumferential path 11, and from the second point P2 the cutting speed was accelerated to the aforementioned 1100 mm/min to make one revolution and cut to the first point P1, and then the cutting was performed at 1100 mm/min. Also, for a sample with a plate thickness T of 12 mm, the cutting was performed from the cut-out position CP to the first point P1 at a steady speed of 1000 mm/min, the cutting speed was decelerated from the first point P1 to 75 mm/min, and the cutting was performed from the first point P1 to the second point P2, which is a predetermined distance (2 mm) in the direction of travel on the circumferential path 11, and the cutting speed was accelerated from the second point P2 to the aforementioned 1000 mm/min, and the cutting was performed once around the first point P1, and then the cutting was performed at 1000 mm/min.

The output of the laser oscillator 7, the frequency of the laser oscillator 7, the duty ratio of the laser oscillator 7, and the gas pressure of oxygen as the assist gas are the same as those in the hole forming method according to the second embodiment.
Then, for each sample of steel material S having plate thicknesses T of 6 mm, 9 mm, and 12 mm, the inner diameters A (front), B (front), A (rear), and B (rear) based on the coordinate system of the round holes formed by the hole forming method of Example 1, the round holes formed by the hole forming method of Example 2, and the round holes formed by the hole forming method of Example 3 (see FIGS. 10 and 12), the front inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the corrosion notch standard, and the rear inner diameters C (rear concave), C (rear convex), D (rear), E (rear), and F (rear) based on the corrosion notch standard (see FIGS. 11 and 12).

Table 1 and Figure 13 show the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of the round hole formed by the hole forming method of Example 1 for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 1 and Figure 13 show the average values of the inner diameters A (front), B (front), A (back), and B (back) for each sample with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Table 2 and Figure 14 show the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of the round holes formed by the hole forming method of Example 2 for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 2 and Figure 14 show the average values of the inner diameters A (front), B (front), A (back), and B (back) for each sample with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Table 3 and Figure 15 show the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of the round holes formed by the hole forming method of Example 3 for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 3 and Figure 15 show the average values of the inner diameters A (front), B (front), A (back), and B (back) for each sample with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Table 4 and Figure 16 show the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the erosion notch standard of the round holes formed by the hole forming method of Example 1 for each sample of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 4 and Figure 16 show the average values of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) for each sample having a plate thickness T of 6 mm, 9 mm, and 12 mm.

Table 5 and Figure 17 show the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the erosion notch standard for round holes formed by the hole forming method of Example 2 for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 5 and Figure 17 show the average values of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) for each sample with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Table 6 and Figure 18 show the measurement results of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the erosion notch standard for round holes formed by the hole forming method of Example 3 for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 6 and Figure 18 show the average values of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) for each sample with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Furthermore, the measurement results of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) based on the erosion notch standard of the round holes formed by the hole forming method of Example 1 for each sample of steel material S having plate thicknesses T of 6 mm, 9 mm, and 12 mm are shown in Table 7 and Figure 19. The measurement results in Table 7 and Figure 19 show the average values of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) for each sample having plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Table 8 and Figure 20 show the measurement results of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) based on the erosion notch standard of the round holes formed by the hole forming method of Example 2 for each sample of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm. The measurement results in Table 8 and Figure 20 show the average values of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) for each sample having a plate thickness T of 6 mm, 9 mm, and 12 mm.

Furthermore, the measurement results of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) based on the erosion notch standard of the round holes formed by the hole forming method of Example 3 for each sample of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm are shown in Table 9 and Figure 21. The measurement results in Table 9 and Figure 21 show the average values of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) for each sample having a plate thickness T of 6 mm, 9 mm, and 12 mm.

Table 10 shows the squareness (average value) and roundness (average value) of the round hole calculated from the measurement results (Table 1, Figure 13) of the inner diameters A (front), B (front), A (back), and B (back) of the round hole formed by the hole forming method of Example 1 based on the coordinate standard, the surface side corrosion notch depth (average value) calculated from the measurement results (Table 4, Figure 16) of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) of the round hole formed by the hole forming method of Example 1 based on the corrosion notch standard, and the back side corrosion notch depth (average value) calculated from the measurement results (Table 7, Figure 19) of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) of the round hole based on the corrosion notch standard.

Table 11 also shows the squareness (average value) and roundness (average value) of the round hole calculated from the measurement results (Table 2, Figure 14) of the inner diameters A (front), B (front), A (back), and B (back) of the round hole formed by the hole forming method of Example 2 based on the coordinate standard, the surface damage notch depth (average value) calculated from the measurement results (Table 5, Figure 17) of the front side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) of the round hole formed by the hole forming method of Example 2 based on the corrosion notch standard, and the back side corrosion notch depth (average value) calculated from the measurement results (Table 8, Figure 20) of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) of the round hole based on the corrosion notch standard.

Furthermore, for each sample of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm, the squareness (average value) and roundness (average value) of the round hole formed by the hole forming method of Example 3 calculated from the measurement results of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate standard (Table 3, Figure 15), the surface side corrosion notch depth (average value) calculated from the measurement results of the surface side inner diameters C (front concave), C (front convex), D (front), E (front), and F (front) based on the corrosion notch standard (Table 6, Figure 18) of the round hole formed by the hole forming method of Example 3, and the back side corrosion notch depth (average value) calculated from the measurement results of the back side inner diameters C (back concave), C (back convex), D (back), E (back), and F (back) based on the corrosion notch standard (Table 9, Figure 21) of the round hole are shown in Table 12.

(Inner diameter measurement results based on coordinate system)
As shown in Table 10, the squareness (average value) of the round hole calculated from the measurement results (Table 1, FIG. 13) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of the round hole formed by the hole forming method of Example 1 was in the range of −0.13 mm to +0.05 mm for samples of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm. In addition, the roundness (average value) of the round hole calculated from the measurement results (Table 1, FIG. 13) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system of the round hole formed by the hole forming method of Example 1 was in the range of −0.06 mm to 0.00 mm for samples of steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm.

As shown in Table 11, the squareness (average value) of the round hole formed by the hole forming method of Example 2, calculated from the measurement results (Table 2, Figure 14) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system, was in the range of -0.09 mm to +0.02 mm for samples of steel material S with thicknesses T of 6 mm, 9 mm, and 12 mm. The roundness (average value) of the round hole formed by the hole forming method of Example 2, calculated from the measurement results (Table 2, Figure 14) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate system, was in the range of -0.05 mm to +0.02 mm for samples of steel material S with thicknesses T of 6 mm, 9 mm, and 12 mm.

Furthermore, as shown in Table 12, the squareness (average value) of the round hole formed by the hole forming method of Example 3, calculated from the measurement results (Table 3, Figure 15) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate standard, was in the range of -0.11 mm to +0.05 mm for samples of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm. Furthermore, the roundness (average value) of the round hole formed by the hole forming method of Example 3, calculated from the measurement results (Table 3, Figure 15) of the inner diameters A (front), B (front), A (back), and B (back) based on the coordinate standard, was in the range of -0.06 mm to +0.05 mm for samples of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Therefore, the absolute value of the squareness (average value) of the round holes formed by the hole forming methods of Examples 1 to 3 was 0.13 mm or less, and the absolute value of the circularity (average value) of the round holes was 0.06 mm or less. The squareness and circularity of the round holes were both sufficiently small, and there was little variation in the overall measurement results of the flat portion of the inner diameter on both the front and back sides.

(Inner diameter measurement results based on the corrosion notch standard)
(1) Surface Side As shown in Table 10, the depths (average values) of the surface-side corrosion notches calculated from the measurement results (Table 4, FIG. 16) of the surface-side inner diameters C (surface concave), C (surface convex), D (surface), E (surface), and F (surface) based on the corrosion notch standard of the round holes formed by the hole forming method of Example 1 were in the range of 0.00 mm to +0.05 mm for each of the samples having plate thicknesses T of the steel material S of 6 mm, 9 mm, and 12 mm.

As shown in Table 11, the depth (average value) of the surface corrosion notch calculated from the measurement results (Table 5, Figure 17) of the surface inner diameters C (concave surface), C (convex surface), D (surface), E (surface), and F (surface) based on the corrosion notch standard for round holes formed by the hole forming method of Example 2 was in the range of -0.04 mm to +0.06 mm for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Furthermore, as shown in Table 12, the depth (average value) of the surface corrosion notch calculated from the measurement results (Table 6, Figure 18) of the surface inner diameters C (concave surface), C (convex surface), D (surface), E (surface), and F (surface) based on the corrosion notch standard for round holes formed by the hole forming method of Example 3 was in the range of -0.04 mm to +0.06 mm for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Therefore, the depth of the erosion notch on the surface side of the round hole formed by the hole forming method of Examples 1 to 3 was in the range of -0.04 mm to +0.06 mm, and the depth of the erosion notch was sufficiently small, with little variation in the overall measurement results of the inner diameter. According to the JASS6 standard, the erosion notch depth meets the standard at ±0.50 mm or less, and the erosion notch depth meets the standard at 1.00 mm or less when measured with a positive/negative gauge.

(2) Back side As shown in Table 10, the depths (average values) of the corrosion notches on the back side calculated from the measurement results (Table 7, FIG. 19) of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) based on the corrosion notch standard of the round holes formed by the hole forming method of Example 1 were in the range of −0.05 mm to +0.07 mm for each sample of the steel material S having a plate thickness T of 6 mm, 9 mm, and 12 mm.

Also, as shown in Table 11, the depth (average value) of the corrosion notch on the back side calculated from the measurement results (Table 8, Figure 20) of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) based on the corrosion notch standard of the round holes formed by the hole forming method of Example 2 was in the range of -0.07 mm to +0.07 mm for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Furthermore, as shown in Table 12, the depth (average value) of the corrosion notch on the back side calculated from the measurement results (Table 9, Figure 21) of the back side inner diameters C (concave back), C (convex back), D (back), E (back), and F (back) based on the corrosion notch standard of the round holes formed by the hole forming method of Example 3 was in the range of -0.07 mm to +0.07 mm for each sample of steel material S with plate thicknesses T of 6 mm, 9 mm, and 12 mm.

Therefore, the depth of the erosion notch on the back side of the round hole formed by the hole forming method of Examples 1 to 3 was in the range of -0.07 mm to +0.07 mm, and the depth of the erosion notch was sufficiently small, with little variation in the overall measurement results of the inner diameter. According to the JASS6 standard, the erosion notch depth meets the standard at ±0.50 mm or less, and the erosion notch depth meets the standard at 1.00 mm or less when measured with a positive/negative meter.

In addition, in order to verify the effect of the present invention, six round holes (two cut with a radius R4 of 3 mm in FIG. 22, two cut with a radius R4 of 4.5 mm, and two cut with a radius R4 of 6 mm in FIG. 22) were made by the hole forming method according to Comparative Example 1 for a steel material S having a standard of SS400, a plate width W of the steel material S of 150 mm, a plate length L of the steel material S of 300 mm, and a plate thickness T of the steel material S of 12 mm, and six round holes (two cut with a radius R4 of 3 mm in FIG. 22, two cut with a radius R4 of 4.5 mm, and two cut with a radius R4 of 6 mm in FIG. 22) were made by the hole forming method according to Comparative Example 2. In the comparative example 2, two samples were cut at a radius R5 of 3 mm, two samples were cut at a radius R5 of 4.5 mm, and two samples were cut at a radius R5 of 6 mm, and six samples (nine samples in total) were formed by the hole forming method according to Comparative Example 3 (two samples were cut at a radius R6 and a radius R7 of 3 mm, two samples were cut at a radius R6 and a radius R7 of 4.5 mm, and two samples were cut at a radius R6 and a radius R7 of 6 mm in FIG. 24).
In each sample, the surface treatment remained black.

In addition, the round holes formed by the hole forming method according to Comparative Example 1, the hole forming method according to Comparative Example 2, and the hole forming method according to Comparative Example 3 were perfect circles with a hole diameter of Φ18 mm, and a _CO2 laser cutting machine was used as the laser drilling device.
The hole forming method according to Comparative Example 1 is shown in FIG. 22. First, a portion of the steel material S other than the circumferential path to be cut into a round hole H is set to the cutting position CP, and then the steel material S is cut in a straight line from the cutting position CP so as to enter and touch a first point P1 on the circumferential path with an arc of radius R4 of Rmm (3 mm, 4.5 mm, 6 mm). The steel material is cut from the first point P1 around the circumferential path to reach the first point P1, and then cut out so as to exit in a straight line perpendicular to the tangent line to the first point P1 (the tangent line to the first point P1 is omitted in FIG. 22).

In the hole forming method according to Comparative Example 1, the cutting speed by the laser light LB was 1050 mm/min from the cutting at the cutting position CP to the final cutting run-off. The output of the laser oscillator 7 was 3600 kW from the cutting at the cutting position CP to the final cutting run-off. The frequency of the laser oscillator 7 was 1000 Hz from the cutting at the cutting position CP to the final cutting run-off. The duty ratio of the laser oscillator 7 was 60% from the cutting at the cutting position CP to the final cutting run-off. The gas pressure of oxygen as the assist gas was 36 KPa from the cutting at the cutting position CP to the final cutting run-off.

The hole forming method according to Comparative Example 2 is shown in FIG. 23, where the portion of the steel material S other than the circumferential path to be cut into the round hole H is set as the cutting position CP, cut in a straight line from the cutting position CP, cut at a first point P1 on the circumferential path 11 at a right angle to the tangent line to the first point P1, cut from the first point P1 around the circumferential path to the first point P1, and then cut away from the first point P1 so that it comes out in a straight line tangent to an arc with a radius R5 of R mm (3 mm, 4.5 mm, 6 mm) (the tangent line to the first point P1 is omitted in FIG. 23).

In the hole forming method according to Comparative Example 2, the cutting speed of the laser beam LB was 1050 mm/min from the cut-out position CP to the first point P1, the cutting speed was decelerated to 80 mm/min from the first point P1 to the second point P2, which is a predetermined distance (2 mm) from the first point P1 in the direction of travel on the circumferential path 11, and the cutting speed was accelerated from the second point P2 to the aforementioned 1050 mm/min to cut one revolution to the first point P1, and then cut away at 1050 mm/min. The output of the laser oscillator 7 was 3600 kW both when cutting at a steady speed and when cutting at a decelerated speed. The frequency of the laser oscillator 7 was 1000 Hz when cutting at a steady speed and 10 Hz when cutting at a decelerated speed. The duty ratio of the laser oscillator 7 was 60% when cutting at a steady speed and 25% when cutting at a decelerated speed. In addition, the gas pressure of oxygen used as the assist gas was 36 KPa when cutting at a steady speed and 37 KPa when cutting at a decelerated speed.

The hole forming method according to Comparative Example 3 is shown in FIG. 24, in which the portion of the steel material S other than the circumferential path 11 to be cut into the round hole H is set as the cutting position CP, cut in a straight line from the cutting position CP, cut so that it enters the first point P1 on the circumferential path with an arc of radius R6 of Rmm (3mm, 4.5mm, 6mm), cuts from the first point P1 around the circumferential path until it reaches the first point P1, and then cuts out so that it exits from the first point P1 in a straight line with an arc of radius R7 of Rmm (3mm, 4.5mm, 6mm).

In the hole forming method according to Comparative Example 3, the cutting speed by the laser light LB was 1050 mm/min from the cutting at the cutting position CP to the final cutting run-off. The output of the laser oscillator 7 was 3600 kW from the cutting at the cutting position CP to the final cutting run-off. The frequency of the laser oscillator 7 was 1000 Hz from the cutting at the cutting position CP to the final cutting run-off. The duty ratio of the laser oscillator 7 was 60% from the cutting at the cutting position CP to the final cutting run-off. The gas pressure of oxygen as the assist gas was 36 KPa from the cutting at the cutting position CP to the final cutting run-off.

The quality of the cut surface was investigated for each of six round holes formed by the hole forming method of Comparative Example 1 (two cut at a radius R4 of 3 mm in FIG. 22, two cut at a radius R4 of 4.5 mm, and two cut at a radius R4 of 6 mm), six round holes formed by the hole forming method of Comparative Example 2 (two cut at a radius R5 of 3 mm in FIG. 23, two cut at a radius R5 of 4.5 mm, and two cut at a radius R5 of 6 mm), and six round holes formed by the hole forming method of Comparative Example 3 (two cut at radii R6 and R7 of 3 mm in FIG. 24, two cut at radii R6 and R7 of 4.5 mm, and two cut at radii R6 and R7 of 6 mm).
The survey results are shown in Table 13.

As shown in Table 13, in Comparative Example 1 (where the cut is made so that the first point P1 on the circumferential path is tangent to an arc with a radius R4 of R mm (3 mm, 4.5 mm, 6 mm)) and Comparative Example 3 (where the cut is made so that the first point P1 on the circumferential path is tangent to an arc with a radius R6 of R mm (3 mm, 4.5 mm, 6 mm)), the radius of the arc is greater than 1.0 mm, and the area where the cutting line is located after one full cut (area A in Figures 22 and 24) is close to the existing cutting line by a long distance. As a result, the quality of the cut surface of the new cutting line on the product side becomes rough due to the temperature rise, and notches and burning occur, resulting in an evaluation of × or △.

In addition, in Comparative Example 2 (where the cut-off is made so that the cut-off line is a straight line that comes from the first point P1 and meets an arc of radius R5 of Rmm (3mm, 4.5mm, 6mm)) and Comparative Example 3 (where the cut-off line is made so that the cut-off line is a straight line that comes from the first point P1 and meets an arc of radius R7 of Rmm (3mm, 4.5mm, 6mm)), in the area where the cut line comes off after one revolution (area B in Figures 23 and 24), the radius of the arc is greater than 1.0mm and the distance close to the previously cut line is long, so although not as great as in area A, the temperature rise causes the quality of the cut surface on the product side of the previously cut line to become rough, and notches and burning occur, resulting in an evaluation of × or △.

The quality of the cut surface was evaluated as follows: ○ if the roughness and characteristics of the cut surface were WES2801 Grade 1 (50μ or less), △ if the roughness and characteristics of the cut surface were WES2801 Grade 2 (more than 50μ, less than 100μ), and × if the roughness and characteristics of the cut surface were more than 100μ or if it was a fractured surface.
Therefore, it was proven that in order to improve the quality of the cut surface at the circular hole H, the radius of the arc at the cut-out and cut-out needs to be sufficiently small, so in the present invention, the radius of the arc at the cut-out and cut-out is set to 1.0 mm or less.

REFERENCE SIGNS LIST 1 Laser drilling device 2 Rail 3 X-axis direction moving member 4 Y-axis direction extension member 5 Laser processing head 6 Control box 7 Laser oscillator 8 Condenser lens 9 Assist gas supply means 11 Circular path 12 Cutting line 13 Arc 14 Cutting line 15 Cutting line 16 Arc 17 Cutting line 18 Cutting line 19 Cutting line 20 Cutting line 21 Arc 22 Cutting line 23 Cutting line 24 Cutting line 25 Cutting line 26 Cutting line 111 Cutting line 112 Arc 113 Cutting line 114 Cutting line 115 Arc 116 Protrusion 117 Cutting line 118 Arc 119 Cutting line 120 Cutting line 121 Arc 122 Protrusion 123 Cutting line 124 Cutting line 125 Cutting line 126 Projection CP Cutting position H Round hole LB Laser light P1 First point P2 Second point P11 Point P12 Point P13 Point P14 Point P15 Point S Steel material

Claims (4)

A laser hole forming method for forming a round hole by irradiating a steel material with a laser beam, comprising the steps of:
a cutting position is a portion of the steel material other than a circumferential path to be cut into the round hole, the cutting position is a straight line, the cutting is made so that a first point on the circumferential path is tangent to an arc having a radius of 1.0 mm or less when the steel material is cut, the cutting is made from the first point around the circumferential path once to the first point, and then the cutting is made so that a first point is tangent to an arc having a radius of 1.0 mm or less when the steel material is cut. A laser hole forming method for forming a round hole by irradiating a steel material with a laser beam, comprising the steps of:
a cutting position being a portion of the steel material other than the circumferential path to be cut into the round hole, cutting in a straight line from the cutting position, cutting to a first point on the circumferential path so as to enter at a right angle to a tangent to the first point, cutting from the first point around the circumferential path once to reach the first point, and then cutting away from the first point so as to exit along an arc having a radius of 1.0 mm or less. A laser hole forming method for forming a round hole by irradiating a steel material with a laser beam, comprising the steps of:
a cutting position is set to a portion of the steel material other than the circumferential path to be cut into the round hole, the steel material is cut in a straight line from the cutting position, the cutting is performed so as to enter a first point on the circumferential path at a right angle to a tangent line tangent to the first point, the cutting is performed from the first point around the circumferential path to the first point, and then the cutting is performed so as to exit from the first point in a straight line at a right angle to the tangent line tangent to the first point ;
a cutting speed being reduced from the first point to a second point a predetermined distance in the direction of travel on the circular path from the first point, and a cutting speed being accelerated from the second point to the steady speed to cut once around the circular path to the first point, after which the cutting speed is increased again to the steady speed to cut around the circular path to the first point . 3. The method for forming a hole using a laser according to claim 2, characterized in that cutting is performed from the cut-out position to the first point at a steady speed, the cutting speed is decelerated from the steady speed from the first point to a second point a predetermined distance in the direction of travel on the circular path from the first point, the cutting speed is accelerated from the second point to the steady speed to make one revolution and cut to the first point, and then the cutting is performed at the steady speed.

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