JP4709599B2 - Laser processing method, laser processing apparatus, and structural member manufactured by laser processing method - Google Patents

Description

  The present invention relates to a laser processing technique for irradiating a surface of a workpiece with a laser beam, and cutting or crushing the surface and a portion to be processed immediately below the surface. This technique is suitable for use in laser processing.

  In general, when removing and dismantling structural materials such as concrete and rock, it is often carried out by repeatedly cutting with a diamond saw or performing a small break that gives a physical impact. At that time, there was no machining method with high machining accuracy and sufficient machining efficiency because the work piece was outdoors, it was large and the degree of freedom in the machining approaching direction was small. In particular, in the repair work of existing buildings and structures, which have become important in recent years, there are cases where conventional diamond saws and processing methods using physical impact cannot be handled due to vibration and noise problems. .

  As a new structural material processing method, laser beam processing technology that can be applied outdoors and has almost no vibration and noise problems is attracting attention. For example, Patent Document 1 discloses a technique for increasing the energy density of a laser beam by condensing and irradiating the laser beam on concrete, thereby melting and cutting a processed portion of the workpiece. . Patent Document 2 discloses a technique for perforating a ceramic structure such as concrete or rock. However, since structural materials such as concrete are generally deep and there are many machining situations in which laser beams and gases do not penetrate the opposite surface, it is difficult to discharge dross, which is a molten structural material, from the vicinity of the workpiece. In many cases, the energy of the laser beam is not used effectively.

  In this case, in order to increase the processing efficiency (defined by the amount of processing removal per unit time), the molten dross that absorbs and reflects the laser beam (hereinafter referred to as dross) is efficiently removed, and the laser beam is It is always necessary to make direct contact with the new surface of the workpiece. For this reason, Patent Document 3 discloses various techniques such as dross removal by gas injection and reduction of dross viscosity by additive material to improve removal. However, there was a problem that the dross could not be completely removed and the machining efficiency of laser machining was poor compared to machining methods using diamond blades or physical impact fracture. On the other hand, as described in Patent Document 4, there has been an attempt to absorb a liquid (water) having a relatively high absorption rate in concrete and increase the laser energy contributing to processing. It was difficult to absorb all of them uniformly, and no significant improvement was obtained from the viewpoint of melting and removing concrete. In addition, the idea of increasing the laser output capacity and increasing the processing speed was not realistic considering the construction in the field.

Japanese Patent Laid-Open No. 10-18612 JP 2000-170473 A JP 2000-170475 A JP-A 64-15296

  In view of the problems of the conventional laser beam processing method when cutting or crushing a structural material made of an inorganic material or an organic material such as concrete or rock, or both, as a workpiece, the present invention The present invention provides a laser processing method and a laser processing apparatus for a structural material capable of high-speed processing with the energy utilization efficiency of the laser beam as high as possible, and also provides a structural member manufactured by the laser processing method. For the purpose.

  As a result of detailed examination of the crushing mechanism of structural materials such as concrete by laser processing using a laser beam, the present inventor has obtained the following knowledge. The conventional laser processing method is to increase the laser beam intensity and irradiate the part to be processed in order to increase the apparent crushing force. The main mechanism is the melting, high temperature softening, or evaporative removal of the structural material. It was processing. In addition to the need to use large amounts of laser beam energy to generate melting, high temperature softening, and evaporation, laser beam absorption, reflection, and scattering are found to be caused by molten or high temperature softening structures did. Therefore, when the laser beam is irradiated onto the workpiece, the workpiece is rapidly heated or rapidly cooled after heating while suppressing melting, high-temperature softening, or sublimation of the workpiece. A method of cutting or crushing at a higher speed and higher energy efficiency than the conventional method by generating a large thermal stress between the low temperature part and the nearby low temperature part and causing a crushing phenomenon due to the thermal stress in the work part. It came to invent. In the present invention, “fracturing due to thermal stress” means that the processing part is irradiated with a laser beam to raise the temperature, thereby causing fracture due to thermal stress generated inside the workpiece and cooling after the temperature rise. This includes both fracture due to thermal stress generated inside the workpiece.

The gist of the present invention is as described below.
(1) In the laser processing method of the present invention, a structural member made of concrete or rock is processed, and a laser beam is irradiated to a predetermined processing portion of the processing material to raise the temperature. A two-dimensional temperature distribution on the surface of the processed part so that the maximum temperature of the processed part is lower than the melting point or softening temperature of the workpiece by the laser beam irradiation. The measurement is performed using a radiation thermometer, and the laser beam power, the scanning speed, or the laser beam spot size shape on the processing portion is controlled .
(2) In the laser processing method of the present invention, in the invention described in (1 ), the laser beam is pulsed light, and the laser beam is irradiated while applying a cooling gas or a cooling liquid to the processing portion. And
(3) the laser processing method of the present invention is the invention described in (1), before Symbol laser beam is a pulsed light or continuous light, the laser by the beam irradiation, the maximum temperature of the working portion is the melting point of the workpiece , Softening temperature, thermal decomposition temperature, or sublimation point or less, and the temperature difference between the melting point, softening temperature, thermal decomposition temperature, or sublimation point and the maximum temperature of the processed part is within 300 ° C. It is characterized by controlling the power, the scanning speed, or the size and shape of the laser beam on the processing part.
(4) A structural member processed by the laser processing method according to any one of (1) to ( 3 ).
(5) The laser processing apparatus of the present invention uses a structural member made of concrete or rock as a workpiece, and condenses and irradiates a laser light source and a laser beam emitted from the laser light source onto a predetermined processing portion of the workpiece. A laser condensing optical system for scanning and a scanning device for scanning the laser beam on the workpiece, and the laser beam is focused on a predetermined processing portion of the workpiece to raise the temperature. And a laser processing apparatus for generating fracture due to thermal stress in the processed part, comprising a radiation thermometer for detecting a two-dimensional temperature distribution on the surface of the processed part, and for measuring temperature measurement data of the radiation thermometer. It is characterized in that the maximum temperature can be crushed at the melting point, softening temperature, thermal decomposition temperature, or sublimation point temperature of the workpiece .
(6) The laser processing apparatus of the present invention, (5) A laser processing apparatus according to, comprising a maximum temperature control unit for controlling the power of the laser beam on the basis of the temperature measurement data of the radiation thermometer The material can be crushed at a melting point, a softening temperature, a thermal decomposition temperature, or a temperature below the sublimation point of the workpiece.
(7) The laser processing apparatus of the present invention, (5) or in the laser processing apparatus according to (6), a suction nozzle for discharging the swarf generated in the previous SL machining unit, the workpiece the laser beam characterized by comprising a scanning device for scanning on wood.

  According to the present invention, in a laser processing method using a structural material as a work material, the work material is processed using a fracture phenomenon caused by thermal stress that suppresses melting, high-temperature softening, thermal decomposition, or sublimation of the work material. , Laser processing can be performed at high speed with high energy efficiency by suppressing energy loss of the laser beam. Therefore, it is possible to realize processing that has sufficient processing accuracy and energy efficiency, which is a feature of laser processing, and can be performed with a relatively small-capacity laser device, and has a remarkable industrially useful effect.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.
<First embodiment>
FIG. 1 is a schematic diagram showing an example of an embodiment of a laser processing method according to the present invention. FIG. 1 illustrates a cross section of the workpiece 3 along the laser processing line. In the vicinity of the processing point 7, a heating laser beam 1, an injection nozzle 4 for injecting gas or liquid, and a suction nozzle 6 for sucking powder are installed. A laser beam 1 is condensed and irradiated on a workpiece 3 by a condenser lens 2 which is a condensing optical system, the surface of the workpiece 3 is heated, and the vicinity of the surface of the workpiece 3 is partially expanded and generated. It crushes by the applied thermal stress. The crushed workpiece crushed material 5 falls spontaneously, but if it is removed from the processing part with an assist gas such as nitrogen gas for removing powder sprayed from the spray nozzle 4 or a liquid such as water, the workability is further improved. . Further, a part or all of the crushed material 5 may be removed by the suction nozzle 6. The above is a method of crushing by the thermal stress generated by heating and expanding the surface layer of the processed part, but the processed part heated by the laser beam 1 is cooled and partially contracted, The workpiece 5 can also be crushed by the thermal stress generated during the process. In that case, crushing may be performed by injecting a cooling gas or a cooling liquid to the vicinity of the processing point 7 from the ejection nozzle 4.

FIG. 2 schematically shows a temperature distribution in a processing portion near a processing point irradiated with a laser beam during the crushing. The vicinity of the processing point is heated by the laser beam 1 having a laser power P (W / cm ² ) and heated to a temperature θ described by the heat transfer equation (1). On the other hand, the conditions for occurrence of crushing only by induction of thermal stress occur when (A) the temperature of the workpiece 3 does not exceed the melting point, softening temperature, or sublimation point, and (B) when the temperature of the processed part is increased (2 The thermal stress σ expressed by the formula (1) exceeds the tensile strength or compressive strength σt of the physical property value of the workpiece 3. This is the crushing mechanism used in the present invention.
▽ ² θ− (1 / κ) (dθ / dt) = − P / ρ · C (1)
Where κ is the thermal diffusion constant of the workpiece, ρ is the density, and C is the heat capacity.
σ = α ・ Δθ ・ E (2)
Where α is the linear expansion coefficient of the workpiece, Δθ is the temperature gradient, and E Young's modulus.

In the laser processing method of the present embodiment, an example of laser irradiation conditions for realizing the crushing phenomenon by an actual laser beam will be shown taking concrete as an example. Figure 4 shows the model calculation using the finite difference method for the temperature distribution in the concrete when the machining point at the center of the laser beam is the origin when the moving speed of the laser beam is v = 50 (m / min). The temperature distribution inside the concrete calculated by The concrete used for the model calculation is called mortar, and its physical constants are thermal diffusion constant κ = 0.008 (cm ² / s), density ρ = 21.8 (g / cm ³ ), and heat capacity C = 0. 0.79 (J / g ° C.). The laser beam irradiation conditions were laser input power (continuous) P = 500 (W) and laser beam size = 3 mm × 3 mm. Under this condition, each point does not reach the material melting point of about 1700 ° C. or the softening point of 1500 ° C.

Thermal stress accompanying the above temperature rise occurs in the concrete. This thermal stress can be approximated using a simple model shown in FIG. Disk 1 to Diskn are divided in the depth direction into thicknesses that are considered to be sufficiently uniform in the disk in the direction perpendicular to the beam movement direction in the model used in the above model calculation, and the temperature of each Diskn is Tn ° C. To do. Since these disks are firmly fixed to the left and right with respect to the temperature rise (hatched portion), compressive stress is generated due to expansion accompanying the temperature rise. When the linear expansion coefficient of the mortar used is 1 × 10 ⁻⁵ (1 / ° C.) and Young's modulus E = 215 × 10 ³ (kg / cm ² ), the compressive strength σt is 100 (kg / cm ² ). From equation 2, it can be seen that crushing occurs when Δθ is 50 ° C. As a result, in the model shown in FIG. 4, the above-mentioned crushing occurs at a point of about 6 mm wide and a depth of 3.0 mm from the surface.

  FIG. 6 shows the calculation result of evaluating the removal processing amount by crushing by changing the moving speed of the laser beam on the concrete surface by the model calculation for the above concrete. In FIG. 6, the horizontal axis indicates the laser beam moving speed, and the vertical axis indicates the removal processing amount or the maximum temperature on the workpiece surface with respect to the moving speed. As a result, when the beam moving speed is slowed down to 32 (m / min) or less, the maximum temperature of the upper surface becomes 1500 ° C., which is the softening point, and phase change occurs, so that the processing efficiency is extremely deteriorated. It was. On the other hand, when the beam moving speed is increased, the temperature rise depth is gradually lowered and the efficiency is lowered. Therefore, it was found that the effective range of this processing method is that the maximum temperature of the surface layer is below the melting point and the melting point minus 300 ° C. or above is effective.

  As described above, according to the laser processing method of the present invention, since the point to be processed is not heated to the melting point as in the conventional laser processing method, the processing efficiency is greatly improved. For this reason, the capacity of the laser device necessary for heating the workpiece is small, and the capacity of ancillary equipment such as a power source is small. Therefore, the processing device can be moved by a truck, a freight car, or the like. Fig. 3 shows a schematic diagram of the equipment configuration when processing outdoors. The truck or freight car 11 is equipped with a laser oscillator for generating a laser beam, a cooling device, a power source, a compressor 10 for assist gas, and the like. A laser beam is guided from this oscillator through an optical fiber 11 and mounted on an aerial work vehicle 12. A laser focusing optical system, a nozzle for applying a cooling gas or a cooling liquid, a nozzle for discharging processing waste, Processing is performed by a laser processing head 14 provided with a scanning device for operating a laser beam.

<Second Embodiment>
Also, it is possible to create a negative temperature gradient Δθ by rapidly cooling the workpiece surface using a cooling medium, and it is industrially significant to protect the workpiece from thermal deformation. . For this reason, the laser beam is pulsed, and a cooling gas or a cooling liquid is applied from the nozzle between the pulses to exert this effect. At this time, if the minute area is repeatedly crushed, the machining shape accuracy can be easily improved.

<Third embodiment>
The laser processing method and the processing apparatus of the present invention are characterized in that the maximum temperature of the processed part during heating with a laser beam is lower than the melting point, softening temperature, thermal decomposition temperature, or sublimation point of the workpiece. In the present embodiment, as shown in FIG. 7, in order not to raise the temperature of the processing point 7 more than necessary, the two-dimensional temperature distribution near the processing point 7 is measured using a radiation thermometer 21 and is covered during laser processing. The temperature of the processing point 7 can be monitored so that the workpiece 3 is not melted, thermally softened, pyrolyzed, or sublimated, and when the temperature becomes too high, the power of the laser beam 1 can be lowered.

  Furthermore, the temperature of the processing point 7 is continuously extracted from the measurement data image of the above two-dimensional temperature distribution so that the temperature becomes a preset temperature below the melting point, softening temperature, thermal decomposition temperature, or sublimation point. A personal computer 22 for controlling the maximum temperature for controlling the power of the laser beam 1 is provided, so that the pulverization work by laser processing can be executed stably and at high speed. Commercially available products can be used as the radiation thermometer for two-dimensional measurement. Using commercially available image processing software, the highest temperature is detected from the highest luminance pixel in the luminance data of the two-dimensional temperature distribution of the measurement data. Based on the maximum temperature and a preset temperature, the power of the laser beam is controlled by, for example, proportional control or PI control. The signal processing and data processing for measurement and control are executed using the personal computer 22.

<Other embodiments>
It should be noted that if the work piece powder blocks the laser beam, the temperature rise process of the work is hindered, so it is effective to promote removal of the work piece powder using a suction nozzle.
As the laser beam used for this processing, a laser device with a small beam divergence parameter M ² that allows a large depth of focus is preferable because the density change of the laser energy is small even when the position from the lens changes during processing of thick materials. . Examples of such lasers include fiber lasers and DISK lasers.

  In addition, when the workpiece is thicker than the thickness that can be processed by a single beam scan, the workable thickness can be improved by swinging the beam in the traveling direction and repeatedly irradiating the processing point with the beam. An outline of this swinging method is shown in FIG. In the process in which the laser beam 1 is focused on the processing point through the condenser lens 2, the processing point is oscillated by a reflection mirror (beam scanning device 8) attached to a galvano motor that can be rotated in a reciprocating manner. By this swinging, it becomes possible to repeatedly perform processing as shown in FIG. Here, by adjusting the reciprocating rotation angle and setting the swing amount to the required swing amount 9 in the figure, the above-mentioned thick material can be realized.

  A first embodiment of the present invention will be described. The work material used was a columnar mortar material. The sample size is 1 mm wide, 1 m deep and 100 mm thick. The sample was cut in the thickness direction. The laser used was a continuous wave fiber laser with an output power of 500 W and a wavelength of 1070 nm, and was focused on a spot having a diameter of about 5.2 mm with a lens having a focal length of 1200 mm. The depth of focus at this time was about 200 mm. The laser was installed at an angle of 30 degrees with respect to the workpiece, and the galvano motor was scanned and processed so that the laser beam in the groove had a beam swing speed of 50 m / min. As assist gas, dry air was used and sprayed at a flow rate of 300 L / min from a nozzle having a diameter of 5 mm in the vicinity of the processing point. At this time, a dust collector was attached to the suction nozzle to remove the powder. When the laser was moved at a speed of 50 mm / min, a crushing phenomenon occurred, and it became possible to cut 100 mm thick concrete with a kerf width of about 6 mm.

  A second embodiment of the present invention will be described. The work material used was a columnar mortar material. The sample size is 1 mm wide, 1 m deep and 100 mm thick. The sample was cut in the thickness direction. The laser used was a pulsed fiber laser with an output power of 500 W and a wavelength of 1070 nm, a peak output of 1000 W, a repetition rate of 300 Hz, and a pulse duty of 50%. Condensation was performed on a spot having a diameter of about 5.2 mm with a lens having a focal length of 1200 mm. The depth of focus at this time was about 200 mm. The laser was installed at an inclination of 30 degrees with respect to the workpiece, and the galvano motor was scanned and processed so that the laser beam in the groove had a beam swing speed of 50 m / min. In order to remove the pulverized material, water was used and intermittently sprayed from a 5 mm diameter nozzle near the processing point at 20 L / min while the laser beam was not irradiated. At this time, a dust collector was attached to the suction nozzle to remove the powder. When the laser was moved at a speed of 30 mm / min, a crushing phenomenon occurred, and it became possible to cut 100 mm thick concrete with a kerf width of about 6 mm. At this time, the base metal after cutting had no heat storage and the cut surface had good properties.

  The present invention can be used in a laser processing technique for processing a workpiece using a laser beam.

It is the figure which showed the outline of one form of the laser processing apparatus of this invention along the laser processing cross section. 6 is a schematic diagram of a temperature distribution in the vicinity of a laser beam processing point. 1 is a schematic diagram of a configuration when implemented in the laser processing field of the present invention. It is an internal temperature distribution calculation result near the processing point using model calculation. It is the model schematic for showing the crushing mechanism by the temperature rising by the laser beam processing method. It is a figure which shows the relationship between process removal efficiency and the maximum surface temperature. It is one example of the laser beam processing apparatus of this invention, and is the whole schematic of the processing apparatus containing the maximum temperature control apparatus. It is a figure for demonstrating the repetitive processing method by laser beam rocking | fluctuation in one Embodiment of the laser beam processing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser beam 2 ... Condensing lens 3 ... Workpiece 4 ... Injection nozzle 5 ... Crushed work piece 6 ... Suction nozzle 7 ... Processing point 8 ... Beam scanning apparatus 9 ... Necessary amount of oscillation 10 ... Laser oscillator, cooling Equipment, compressor, power source 11 ... optical fiber 12 ... work vehicle 13 ... work piece 14 ... laser processing head 15 ... truck or freight car 21 ... radiation thermometer 22 ... personal computer 23 for maximum temperature control ... laser oscillator body

Claims (7)

A laser processing method in which a structural member made of concrete or rock is used as a workpiece , a laser beam is irradiated to a predetermined processing portion of the workpiece, the temperature is raised, and fracture due to thermal stress is generated in the processing portion. ,
Use a radiation thermometer to measure the two-dimensional temperature distribution on the surface of the processed part so that the maximum temperature of the processed part is below the melting point, softening temperature, thermal decomposition temperature, or sublimation point of the workpiece by the laser beam irradiation. And measuring a laser beam power, a scanning speed, or a laser beam spot size shape on a processing portion . The laser processing method according to claim 1, wherein the laser beam is pulsed light, and the laser beam is irradiated while applying a cooling gas or a cooling liquid to the processing portion . The laser beam is pulsed light or continuous light,
By laser beam irradiation, the maximum temperature of the processed part is below the melting point, softening temperature, thermal decomposition temperature, or sublimation point of the workpiece, and the maximum melting point, softening temperature, thermal decomposition temperature, or sublimation point of the processed part. The temperature difference from the temperature is 300 ° C
The laser processing method according to claim 1, wherein the laser beam power, the scanning speed, or the laser beam size and shape on the processing portion are controlled so as to be within the range . A structural member processed by the laser processing method according to claim 1. A structural member made of concrete or rock is used as a workpiece, a laser light source, a laser condensing optical system for condensing and irradiating a laser beam emitted from the laser light source onto a predetermined processing portion of the workpiece, and the laser A scanning device for scanning the beam on the workpiece, the laser beam is focused on a predetermined processing portion of the workpiece, the temperature is raised, and the processing portion is crushed due to thermal stress. A laser processing device for generating,
  A radiation thermometer for detecting a two-dimensional temperature distribution on the surface of the processed part;
  A laser processing apparatus, wherein the maximum temperature of the temperature measurement data of the radiation thermometer can be crushed at a melting point, a softening temperature, a thermal decomposition temperature, or a temperature below the sublimation point of the workpiece. The laser processing apparatus according to claim 5,
  A maximum temperature control unit for controlling the power of the laser beam based on temperature measurement data of the radiation thermometer;
  A laser processing apparatus characterized in that it can be crushed at a melting point, a softening temperature, a thermal decomposition temperature, or a temperature below a sublimation point of the workpiece. In the laser processing apparatus according to claim 5 or 6,
  A laser processing apparatus, comprising: a suction nozzle for discharging processing waste generated in the processing section; and a scanning device for scanning the laser beam on a workpiece.

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