JP2011251344A - Laser beam machining method and laser beam machining head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining method for executing the laser beam machining with a protective sheet being affixed to a surface of a material, the method which is capable of preventing the surface of the material from being damaged, and of suppressing any peeling and turning-up of the protective sheet.SOLUTION: In the laser beam machining method, a plate-like metal material with a protective sheet being affixed to a surface thereof is irradiated with laser beam while blowing assist gas to conduct cutting, boring or other machining. A nozzle opening diameter is set to satisfy the inequality D/G≥2, where G[mm] denotes the melting width of the protective sheet, and D[mm] denotes the nozzle opening diameter. The plate-like metal material and the protective sheet are machined with one time of laser beam irradiation.

Description

  The present invention relates to a laser processing method for cutting and drilling a plate-like metal material with a laser beam, and a processing head used in this processing method.

  Laser processing can process a wide range of materials from metals such as iron, stainless steel, aluminum and copper to ceramics, resins and wood. Among them, the metal material may be used as a design, and may be subjected to surface finish such as mirror finish or hairline finish. As described above, the material whose surface is finished for the purpose of design naturally loses its commercial value when the surface is scratched. Therefore, it is desirable that the metallic material for design is subjected to transportation, cutting, bending, or the like with a protective sheet attached to the front and back surfaces.

  In particular, laser processing is a complicated process in which a metal is melted by the heat of a laser beam, and an assist gas is blown into the metal to blow the melt away. The blown melt becomes fine sparks and the surface of the material. May adhere to the back. In addition, the material is laser processed in a state of being fixed on the processing table, but this processing table is not melted as much as possible by the laser beam, and so as not to be fused integrally with the material even if melted. Since the tip portion in contact with the material has a sharp shape so as to reduce the contact area with the material and the back surface of the material is very easily damaged, processing with the protective sheet attached is desirable.

  However, when laser processing is performed by attaching a protective sheet to the back surface (non-laser beam irradiated surface) of the material, the molten metal flow melted by the heat of the laser beam becomes slow due to the influence of the protective sheet. As a result, there is a problem that the molten metal adheres to the back surface of the material as dross. FIG. 10 shows the state of dross adhesion when laser processing is carried out using stainless steel (SUS304) with a thickness of 3 mm as a material, and a portion with a protective sheet attached and a portion not attached to the back surface. Is. As shown in FIG. 10, it can be seen that dross is attached only to the portion where the protective sheet is pasted on the back surface. Since this dross is very hard and requires a lot of time and cost to remove, usually the protective sheet on the back of the material is peeled off once and laser processing is performed, and after laser processing, the protective sheet is pasted again and bent. The work of performing processing was performed.

  Then, the processing method which prevents adhesion of the dross at the time of laser processing by sticking the process paper which has a releasable adhesion layer containing a heat resistant particle on the back of a metal material is disclosed (for example, patent documents) 1).

  On the other hand, when a protective sheet is attached to the surface of the material (laser beam irradiation surface), there is a problem that the protective sheet is peeled off and turned up by the assist gas sprayed vigorously. FIG. 11 is a diagram showing a state in which the protective sheet attached to the surface is peeled off from the material and turned up. If the protective sheet is peeled off from the material and turned up, it will naturally no longer play a role of protecting the surface from scratches. There is a problem that a sensor that controls the distance cannot measure an accurate distance, and causes a processing failure due to deviation from a predetermined distance, or the processing machine stops due to a processing error.

  Therefore, in order to prevent the protective sheet from peeling off and turning up, first remove only the protective sheet with a low laser beam power, return to the processing path again, and this time cut the material with a high laser beam power. There is a technique of “cutting twice” (for example, Patent Document 2).

  Also, in order to prevent the protective sheet on the material surface from peeling off and turning up, a first gas passage and a second gas passage are provided in the nozzle, and the pressure of the assist gas supplied to the second gas passage is supplied to the first gas passage. There is a technique for making the pressure higher than the pressure of assisting gas (for example, Patent Document 3). The material with the protective sheet attached to the surface is processed by the laser beam and the assist gas injected from the first gas passage, and the protective sheet is peeled off and turned up by the assist gas injected from the second gas passage. The protective sheet is pressed against the material surface with pressure so that there is no such problem.

JP-A-6-198461 JP-A-7-236984 JP 2001-212690 A

  In the technique disclosed in Patent Document 1, it is necessary to contain heat-resistant particles in the adhesive layer, and cost increase is inevitable. Since the protective sheet is a consumable part and needs to minimize the cost increase, it can be handled with an inexpensive protective sheet in which a normal adhesive layer is provided on a single resin material, which is commonly used for industrial products. However, when such a general protective sheet is used, dross adheres.

  Moreover, in the technique disclosed in Patent Document 2, since the processing path is traced twice, it goes without saying that the processing time is naturally increased, and the protective sheet is not peeled off and turned up. The removal width of the protective sheet to be removed first needs to have a certain width, and as a result, there is a problem that an exposed portion whose material surface is not covered by the protective sheet becomes large.

  Further, in the technique disclosed in Patent Document 3, more assist gas is required than that used in normal processing for the purpose of pressing the protective sheet against the material surface with pressure, and its running cost is more than doubled. End up. In addition, the cost is increased in that a special nozzle having two first and second paths is required. Furthermore, when the cutting is good, the gas sprayed from the nozzle passes through the cutting groove to the lower part of the workpiece, but when a cutting failure occurs when appropriate processing conditions and processing programs are not set. In some cases, the cutting groove is not formed. In such a case, the assist gas injected from the second gas passage set to the high pressure flows back into the first gas passage set to the low pressure. At this time, there is a problem that spatter generated by cutting (the molten metal flying up and becoming a spark) enters the inside of the nozzle together with the backflowing gas and contaminates the processed lens. Since the intrusion of the spatter and the adhesion to the processed lens occur very instantaneously, the method of detecting the backflow using a pressure gauge or a flow meter is slow and cannot be dealt with.

  The present invention has been made to solve the above-described problems, and enables laser processing to be performed while a protective sheet is stuck on the surface of a material.

  In the laser processing method according to the present invention, in the laser processing method in which cutting and drilling are performed by irradiating a laser beam onto a plate-shaped metal material having a protective sheet attached to the surface and blowing an assist gas, When the melt width is G [mm] and the nozzle opening diameter is D [mm], the nozzle opening diameter satisfying D / G ≧ 2 is set, and the plate-shaped metal material and the protective sheet are applied to the laser beam once. Processing is performed by irradiation.

  In the present invention, in the laser processing method in which laser processing is performed with the protective sheet attached to the surface of the material, it is possible to prevent the surface of the material from being scratched and to prevent the protective sheet from peeling off and turning up. In addition to providing the design of materials with surface finishes such as mirror finish and hairline finish, that is, providing them as products without impairing the product value, avoid problems such as re-pasting the protective sheet and processing defects. Can do.

It is a block diagram which shows the laser processing method based on the reference example 1 of this invention. It is an experimental result which shows the influence which the molecular weight of a protection sheet and the thickness of a protection sheet have on adhesion of dross. It is a block diagram which shows the laser processing method based on Embodiment 1 of this invention. It is an experimental result which shows the influence which the adhesive force of a protective sheet and the pressure of the assist gas to use have on the peeling of a protective sheet. It is an experimental result which shows the influence which the melt width of a protection sheet and the opening diameter of the nozzle to use have on the peeling of a protection sheet. It is explanatory drawing which shows the fusion width of a protection sheet. It is explanatory drawing which shows the cutting groove width for processing satisfactorily with each board thickness of SUS304. It is explanatory drawing which shows the relationship between the nozzle opening diameter and assist gas pressure for processing favorably with each board thickness of SUS304. It is a block diagram which shows the laser processing method based on Embodiment 2 of this invention. It is explanatory drawing which shows adhesion of the dross by the presence or absence of the conventional protective sheet. It is explanatory drawing which shows peeling of a protection sheet.

Reference Example 1
FIG. 1 shows a laser processing method in Reference Example 1 for carrying out the present invention. In FIG. 1, a laser beam 3 passes through a processing lens 5 in the processing head 2 and is irradiated onto a material 7 from a nozzle 6 at the tip of the processing head. Further, the assist gas 10 is also blown to the material 7 from the nozzle 6 at the tip of the processing head 2. The material 7 is a plate-like metal material, and a protective sheet 13 for the back surface is attached to the back surface. The material of the protective sheet 13 is a polymer organic material such as polyester. This reference example is characterized in that laser processing is performed while the protective sheet 13 is adhered to the back surface of the material 7.

  Here, when a protective sheet that is generally sold for industrial use is attached and laser processing is performed, the molten metal flow caused by the heat of the laser beam becomes slow due to the influence of the protective material, and the molten metal becomes dross. It will stick to the back of the material. As a result of experiments conducted by the inventors, the adhesion of dross when laser processing is performed with the protective sheet attached to the back surface of the material, the molecular weight of the material of the protective sheet used, and the thickness of the protective sheet used It was found that these two parameters are related.

FIG. 2 shows the results of an experiment for confirming the presence or absence of dross adhesion when the molecular weight of the material of the protective sheet applied to the back surface of the material and the thickness of the protective sheet are changed. The processing conditions in this experiment are as follows.
Processing condition 1
Material: Stainless steel (SUS304) t3mm
Processing lens: focal length 7.5 inch
Nozzle opening diameter: φ1.7mm
Laser beam output: 4000W
Laser beam wavelength: 10.6 μm
Processing speed: 4000 mm / min
Assist gas type: Nitrogen assist gas pressure: 1.2 MPa
Focus position: 3mm downward from the material surface
Nozzle-material distance: 1 mm
The above processing conditions are the same as the optimum conditions that do not cause dross when the protective sheet is not attached, and it is not necessary to change the processing conditions specially by attaching the protective sheet. In addition, the thickness of the protective sheet used in this experiment was set to 20 μm or more because the protective function of the material surface needs to be practical. Moreover, about the molecular weight of the raw material of a protective sheet, the thing of 50,000 or more is prepared, and the thing of molecular weight smaller than it is unconfirmed. Here, the molecular weight means an average molecular weight. The pressure-sensitive adhesive layer of the protective sheet is the same as the pressure-sensitive adhesive layer of the protective sheet that is generally sold for industrial use.

  In FIG. 2, the criterion for ◯ × is that when the laser processing is carried out with the protective sheet attached to the back surface, the dross height attached to the back surface of the material is less than 0.1 mm, and the back surface of the material is A case where the height of the attached dross was 0.1 mm or more was evaluated as x. In this experimental result, the maximum dross height at ○ is less than 0.1 mm, and the maximum dross height at × is 1 mm or more, and the difference between them can be judged very clearly. That is, in FIG. 2, it can be said that the difference between the ◯ mark and the X mark is a significant difference.

  As shown in FIG. 2, in the range where the thickness of the protective sheet is 20 μm or more, when the molecular weight exceeds 300,000, the region of “◯” was not obtained, and dross was always attached. Further, when the molecular weight was in the range of 50,000 or more, even in the range where the thickness exceeded 140 μm, a state where no region was attached, that is, no dross was attached, was not obtained. That is, it was found that in order to process satisfactorily without dross adhesion, it is necessary to reduce the molecular weight of the material of the protective sheet and reduce the thickness of the protective sheet. This is because, as the molecular weight of the protective sheet material is smaller and the thickness is thinner, it is more likely to vaporize by the heat of the laser beam, and the molten metal flow caused by the heat of the laser beam becomes slower due to the influence of the protective sheet. As a result, it is considered that the molten metal is unlikely to adhere to the back surface of the material as dross.

  Here, when the molecular weight is in the range of 50,000 to 300,000, the boundary between ○ and × is M × t = when the molecular weight of the material of the protective sheet is M and the thickness of the protective sheet is t [m]. It is a curve substantially satisfying 7.5, and the lower side of this curve is a circled region. Therefore, when the relationship between the molecular weight M and the thickness t [m] satisfies M × t ≦ 7.5 in the molecular weight range of 50,000 to 300,000, there is no adhesion of dross, that is, dross adhesion. The state can be realized. In general, protective sheets that are sold for industrial use usually have a thickness of 50 μm or more, and the material is made of polyethylene having a molecular weight of about 300,000. It can be said that it was difficult to perform laser processing without adhesion.

  Thus, in the laser processing method in which laser processing is performed with a protective sheet made of a polymer organic material having a molecular weight and a thickness satisfying the above relationship attached to the back surface of the material, the back surface of the material is scratched. In addition to preventing the occurrence of dross, it is possible to suppress the occurrence of dross, and as a product without sacrificing the design of the surface finish such as mirror finish or hairline finish, that is, the product value, and to remove dross Such enormous time and cost can be reduced. Moreover, since the molecular weight of the raw material of a protective sheet and the thickness of a protective sheet should just be made into an appropriate value, the cost increase of a protective sheet can also be suppressed.

  FIG. 2 shows the results of an experiment conducted on stainless steel (SUS304) t3 mm, but the same experiment was performed on those having a plate thickness of 1 mm and 2 mm, and similar results were obtained. Similar experiments were performed on aluminum and copper, which are other materials that place importance on design as well as stainless steel, and similar results were obtained. Therefore, it can be said that the processing method according to the present reference example can be applied regardless of the thickness of the metal material and the type of metal, and the above-described effects can be obtained.

Embodiment 1 FIG.
FIG. 3 shows a laser processing method according to Embodiment 1 for carrying out the present invention. The same parts as those in FIG. In FIG. 3A, a protective sheet 14 for the surface is attached to the surface of the material 7. The present embodiment is characterized in that laser processing is performed while the protective sheet 14 is stuck on the surface of the material 7. The material of the protective sheet 14 is the same as that generally sold for industrial use.

  Further, as shown in FIG. 3B, the assist gas 10 is not sprayed from a plurality of jetting ports or provided separately from the irradiation port of the laser beam 3, but a nozzle that is the irradiation port of the laser beam 3. It is characterized by ejecting from one of the six openings. Further, only the protective sheet is removed by the first laser beam irradiation, or the protective sheet is baked on the material so that the protective sheet is not peeled off or turned up, and then the cutting process is performed by the second laser beam irradiation. The method is characterized in that the material 7 and the protective sheet 14 attached to the material are subjected to processing such as cutting by one-time laser beam irradiation without using the method of “cutting”.

  Here, when a protective sheet that is generally sold for industrial use is attached and laser processing is performed, the protective sheet is peeled off and turned up by the assist gas sprayed vigorously. As a result of experiments conducted by the inventor, the pressure of the protective gas and the pressure of the assist gas ejected from the nozzle are used to peel off and turn over the protective sheet when laser processing is performed with the protective sheet applied to the surface of the material. The relationship between these two parameters was found to be important.

  FIG. 4 shows the results of an experiment for confirming whether the protective sheet is peeled or turned up by changing the adhesive strength of the protective sheet attached to the material surface and the pressure of the assist gas ejected from the nozzle. The processing conditions in this experiment are the same as the processing conditions 1 of Reference Example 1 except for the pressure of the assist gas.

In FIG. 4, the criteria for ◯ × is a region 3 mm or more away from the cutting groove of the material, where there is no peeling or turning of the protective sheet, and a little peeling or turning in the region 3 mm or more away from the cutting groove. Some things were marked as x. Basically, the protective sheet serves to protect the surface of the material, and the range where it does not come into contact with the nozzles is marked as ◯.
As shown in FIG. 4, it is necessary to increase the adhesive force of the protective sheet as the pressure of the assist gas ejected from the nozzle increases, and the relationship can be considered to be linear. Therefore, when the pressure of the assist gas ejected from the nozzle is P [MPa] and the adhesive strength of the protective sheet is F [N / 20 mm], when the laser processing is performed with the protective sheet attached to the surface of the material, In order to prevent the protective sheet from peeling off or turning over, the relationship between P and F only needs to be in the region of ◯ in FIG. 4, and the following relationship may be satisfied.
P / F ≦ 0.3 [MPa · 20 mm / N] (Formula 1)
In general, the pressure of the assist gas is determined by the processing conditions such as the material quality and the plate thickness. Therefore, if a protective sheet having an adhesive force that satisfies (Equation 1) with respect to the pressure of the assist gas is selected. Good.

  In addition, as a result of experiments conducted by the inventors, two parameters, adhesive strength of the protective sheet and nozzle opening diameter, are used to peel off the protective sheet when the laser processing is performed with the protective sheet attached to the surface of the material. It turns out that relationships are also important.

  FIG. 5 shows the results of an experiment for confirming whether the protective sheet is peeled or turned up when the melt width during processing of the protective sheet attached to the material surface and the opening diameter of the nozzle are changed. Here, the melt width of the protective sheet is a width from which the protective sheet is removed during processing. FIG. 6 shows the state of the material 7 that has been subjected to laser processing while the protective sheet 14 is stuck on the material surface. FIG. 6A is a photograph of the surface, and FIG. 6B is a schematic diagram of the AA cross section of FIG. As shown in FIG. 6, the protective sheet 14 is removed around the processed groove, and the protective sheet melting width is wider than the processed groove width. The melt width of the protective sheet is substantially determined by the cut groove width of the material, and is about 1.5 times the cut groove width of the material, depending on the thermal characteristics of the protective sheet. The processing conditions in this experiment are the same as the processing conditions 1 of Reference Example 1 except for the nozzle opening diameter.

In FIG. 5, the criterion for ◯ × is basically ◯ if the processed protective sheet plays a role of protecting the material surface from scratches and does not contact the nozzle. As for, the case where there was no peeling or turning at a distance of 3 mm or more from the cutting groove of the material was given as “◯”, and the case where peeling or turning at a distance of 3 mm or more from the cutting groove was even a little.
As shown in FIG. 5, in order not to peel off, it is necessary to increase the nozzle opening diameter as the melt width of the protective sheet increases, and the relationship can be considered to be linear. Accordingly, when the melt width of the protective sheet is G [mm] and the opening diameter of the nozzle to be used is D [mm], when the laser processing is performed with the protective sheet attached to the surface of the material, In order to prevent peeling and turning-up, the relationship between G and D only needs to be in the region of ◯ in FIG. 5, and the following relationship may be satisfied.
D / G ≧ 2 (Formula 2)
In general, since the melt width of the protective sheet is determined by the processing conditions such as the material and thickness of the material, a nozzle having an opening diameter that satisfies (Equation 2) with respect to the melt width of the protective sheet is selected. do it.

  Here, the following appropriate values exist for each processing parameter. The cutting groove width of the material has an appropriate value that can be satisfactorily processed depending on the material and plate thickness of the material. FIG. 7 is a graph showing an appropriate cutting groove width for satisfactorily processing each plate thickness of stainless steel (SUS304). Generally, as the plate thickness increases, the processed groove width needs to be increased. Further, if the assist gas pressure is constant, the nozzle opening diameter increases, and if the nozzle opening diameter is constant, the assist gas pressure increases, the flow rate of the assist gas to be ejected increases and the running cost increases. It is desirable that the nozzle opening diameter and the assist gas pressure be as small as possible. In addition, there is a relationship between the nozzle opening diameter and the assist gas pressure for good processing depending on the material and the plate thickness. FIG. 8 is a graph showing a relationship between the opening diameter of the nozzle and the assist gas pressure for satisfactory processing when each plate thickness of stainless steel (SUS304) is laser processed. Generally, as the plate thickness increases, it is necessary to increase the nozzle opening diameter and increase the assist gas pressure. And finally, since it is necessary to peel off the affixed protective sheet, it is desirable to make the adhesive strength of the protective sheet as small as possible in consideration of the ease of peeling at that time.

Therefore, by using (Equation 1) and (Equation 2) obtained from the experimental results of FIG. 4 and FIG. 5, an efficient laser with which the protective sheet is not peeled off or turned up and the running cost is minimized. Appropriate processing conditions for performing processing can be obtained.

  For example, consider a case where laser processing is performed with a protective sheet attached to the surface of a stainless steel (SUS304) t1 mm material. In this case, in order to process better than FIG. 7, the width of the cutting groove is 0.3 mm to 0.7 mm. Since the melt width of the protective sheet is larger than the cut groove width of the material and is experimentally found to be about 1.5 times the cut groove width of the material depending on the thermal characteristics of the protective sheet, .45 mm to 1.05 mm. Accordingly, considering the case where the melt width of the protective sheet is 1.05 mm, which is the largest, the nozzle opening diameter needs to be 2.1 mm or more from (Equation 2). Here, in order to suppress the running cost of the assist gas as much as possible, it is desirable that the opening diameter of the nozzle be as small as possible. Therefore, when a nozzle having an opening diameter of 2.1 mm is used, the pressure of the assist gas is 0.9 [ MPa] or more. Here, in order to suppress the running cost of the assist gas as much as possible, it is desirable that the pressure of the assist gas is as small as possible. Therefore, when an assist gas pressure of 0.9 [MPa] is used, the protective sheet to be attached from (Equation 1) The adhesive strength of 2.7 needs to be 2.7 [N / 20 mm] or more. As described above, since the protective sheet is finally peeled off, the adhesive strength of the protective sheet is preferably a value close to 2.7 [N / 20 mm].

  As described above, it is possible to derive a condition for processing a stainless steel (SUS304) t1 mm material without peeling or turning over while the protective sheet is attached to the surface and suppressing the running cost of the assist gas as much as possible. With respect to other materials and materials having the same thickness, it is possible to obtain processing conditions in which the protective sheet is not peeled off and the running cost is suppressed as much as possible with the same concept.

In this way, in the laser processing method in which laser processing is performed while being attached to the surface of the material, by appropriately setting the pressure of the assist gas and the adhesive strength of the protective sheet so as to satisfy the above-described relationship, the surface of the material As a product, the protective sheet can be prevented from being peeled off and curled up, and the design of the surface finish such as mirror finish or hairline finish, that is, the product value is not impaired. While providing, it is possible to avoid problems such as re-sticking of the protective sheet and processing defects.
Moreover, the same effect can be acquired by setting appropriately the melt width of a protective sheet, and the opening diameter of a nozzle so that the said relationship may be satisfy | filled.
Furthermore, due to the relationship between the material thickness, cutting groove width, melt width of the protective sheet, nozzle opening diameter, assist gas pressure and protective sheet adhesive force, the protective sheet does not peel off and the running cost is minimized. In addition, it is possible to obtain appropriate processing conditions for performing efficient laser processing.

Embodiment 2. FIG.
FIG. 9 shows a laser processing method according to Embodiment 2 for carrying out the present invention. The same parts as those in FIG. 1 and FIG. As shown in FIG. 9, the back surface protective sheet 13 described in Reference Example 1 is pasted on the back surface of the material 7, and the front surface protective sheet 14 described in Embodiment 1 is pasted on the front surface. The laser processing is carried out. Therefore, the characteristics of the protective sheet required on the back surface and the front surface are different, and on the back surface, the molecular weight of the material of the protective sheet and the thickness of the protective sheet must be set to predetermined values, and on the front surface, the adhesive strength of the protective sheet is set to a predetermined value. It is necessary to. Further, the processing conditions such as the assist gas pressure and the nozzle opening diameter may be set to appropriate values according to the contents described in the first embodiment.

  As a result, the front and back surfaces of the material can be prevented from being scratched, dross generation and peeling of the protective sheet can be suppressed, and the design of the material subjected to surface finish such as mirror finish or hairline finish, that is, the product It can be provided as a product without losing value, and the time and cost required to remove dross can be reduced.

  Also, prepare a protective sheet that satisfies all the parameters of molecular weight and thickness required for the protective sheet for the back surface and the adhesive force parameter required for the protective sheet for the front surface, and apply them to the back surface and the surface of the material. Even if laser processing is performed under predetermined processing conditions after being attached, it is possible to prevent the front and back surfaces of the material from being scratched, and to suppress the occurrence of dross and peeling of the protective sheet. In this case, since only one type of protective sheet is required, the manufacturing and distribution costs of the protective sheet can be reduced, and the occurrence of processing defects due to the wrong surface to which the protective sheet is attached can be prevented.

  The laser processing method and processing head according to the present invention are suitable for processing a material having a surface finish such as a mirror finish or a hairline finish.

2 Processing Head 3 Laser Beam 5 Processing Lens 6 Nozzle 7 Material 10 Assist Gas 14 Protection Sheet

Claims (3)

In a laser processing method in which processing is performed by irradiating a laser beam and spraying an assist gas from the same opening of a nozzle at the tip of a processing head on a plate-shaped metal material having a protective sheet attached to the surface.
When the melt width of the protective sheet is G [mm] and the opening diameter of the nozzle is D [mm], a nozzle opening diameter that satisfies D / G ≧ 2 is set,
A laser processing method, wherein the plate-shaped metal material and the protective sheet are processed by a single laser beam irradiation. In a laser processing method in which processing is performed by irradiating a laser beam and spraying an assist gas from the same opening of a nozzle at the tip of a processing head on a plate-shaped metal material having a protective sheet attached to the surface.
Obtaining an optimum cutting groove width from the material and thickness of the plate-like metal material; and
A step of obtaining a melt width of the protective sheet with respect to the obtained cutting groove width;
A step of obtaining a nozzle opening diameter satisfying D / G ≧ 2 when the melting width of the protective sheet is G [mm] and the opening diameter of the nozzle is D [mm] with respect to the obtained melting width of the protective sheet. When,
Obtaining an assist gas pressure for the obtained nozzle opening diameter;
A process for obtaining an adhesive force that satisfies P / F ≦ 0.3 when the adhesive force of the protective sheet is F [N / 20 mm] and the pressure of the assist gas is P [MPa] with respect to the obtained assist gas pressure. Then, a laser processing method characterized by obtaining a processing condition. Provided with an opening for laser beam irradiation and assist gas spraying,
The opening diameter of the opening is more than twice the melting width of the protective sheet when the plate-like metal material with the protective sheet attached to the surface is processed by one laser beam irradiation. A laser processing head characterized by being.