Patent Application
20050230370
This application is based on Japanese Patent Applications No. 2004-120538 filed on Apr. 15, 2004, and No. 2005-36713 filed on Feb. 14, 2005, the disclosures of which are incorporated herein by reference.
The present invention relates to laser beam machining equipment and a method for machining by using laser beam.
A laser beam machining method is disclosed in, for example, Japanese Patent Application Publication No. S58-38689. The method is such that an object is irradiated with a laser beam, which is focused on the object by an optical system such as an object lens and the like, so that a part of the material of the object is evaporated and removed so that the object is machined. In this method, the focus of the laser beam is positioned on a predetermined position of the object. Here, the focus is a point, which has the maximum energy density. Thus, the predetermined position of the object is evaporated and removed. Then, the focus is shifted so that the predetermined position of the object is also displaced, and the object is machined, i.e., cut or drilled.
However, in the above method, a condenser lens is shifted up and down so that the focusing position is shifted. Therefore, when the laser beam is focused on a lower side of the object for machining the lower side of the object, the laser beam having a comparatively large energy density is absorbed on an upper side of the object in a large area of the object with a defocusing state of the laser beam. Accordingly, the upper side of the object, which is a part not to be machined, may be also evaporated and removed. Therefore, for example, a periphery of a through-hole to be machined is formed to be a tapered shape. Thus, an opening of the through-hole is tapered from a lower side to an upper side. Thus, the positioning accuracy and the machining accuracy of the through-hole is reduced.
To improve the above defocusing, another laser beam machining method is disclosed in, for example, Japanese Patent Application Publication NO. 2002-239769. In this method, when the focusing position of the laser beam is shifted from the upper side of the object to the lower side, an expanding angle of the laser beam becomes larger. The expanding angle has a vertex as the focusing position. Specifically, the focusing position is moved in a thickness direction of the object so that the expanding angle becomes larger. Accordingly, when the lower side of the object is machined with the laser beam, the energy density of the laser beam, which is defocused on the upper side of the object, can be reduced. Therefore, the upper side of the object is not substantially evaporated; and therefore, only the lower side of the object, which is to be machined, is evaporated and removed. Thus, the machining accuracy of the method is improved.
However, in the above method, the focusing position is continuously shifted so that the through-hole or the like is formed in the object in one process. Therefore, the focusing position of the laser beam may be shifted before the to-be-machined position of the object is completely evaporated and removed. In this case, the machining accuracy of the method is reduced.
In view of the above-described problem, it is an object of the present invention to provide laser beam machining equipment having high machining accuracy and a method for machining by using a laser beam with high machining accuracy.
A method for machining an object includes the steps of: forming a hole in the object by a laser beam in such a manner that the laser beam has a first focus point; and reforming the hole by the laser beam in such a manner that the laser beam has a second focus point, which is different from the first focus point. The first and the second focus points are disposed on a same light axis. In at least one of the step of forming the hole and the step of reforming the hole, the object is machined by a diffusion and a condensation of the laser beam in the object. The condensation is performed by reflection of the laser beam reflected on an inner wall of the hole.
By the above method, the object is machined with high machining accuracy. Specifically, the first focus point of the laser beam is changed once in the shape reform process. Thus, the difference of the width between the wide width portion and the narrow width portion is reduced. Accordingly, the hole having high straightness is obtained.
Preferably, the hole is machined to have a predetermined shape, which includes a narrow width portion and a wide width portion. The narrow width portion is formed by the laser beam switching from the condensation to the diffusion. The wide width portion is formed by the laser beam switching from the diffusion to the condensation. The narrow width portion and the wide width portion of the hole are disposed alternately in the object.
Preferably, in the step of reforming the hole, the hole is reformed multiple times with the laser beam having different focus points, which are different from the first focus point.
Further, laser beam machining equipment for forming a through-hole in an object includes: a laser beam output device for outputting a laser beam; a condenser lens for condensing the laser beam on the object; and a varifocal device for controlling a focus point of the laser beam coaxially. The varifocal device controls the laser beam to have a predetermined focus point so that a diffusion of the laser beam in the object and a condensation of the laser beam reflected on an inner wall of the through-hole are occurred for machining the through-hole having a predetermined shape. The varifocal device is capable of changing the focus point of the laser beam so that the through-hole is reformed.
The above equipment machines the object with high machining accuracy. Specifically, the focus point of the laser beam is changed once in a shape reform process. Thus, the difference of the width between the wide width portion and the narrow width portion is reduced. Accordingly, the hole having high straightness is obtained.
Preferably, the equipment further includes: a diameter controller for controlling a diameter of the laser beam outputted from the condenser lens; and an energy density controller for controlling an energy density of the laser beam. The laser beam is controlled by at least one of the diameter controller, the energy density controller and the varifocal device.
Preferably, the varifocal device changes the focus point of the laser beam a plurality of times to be different positions for reforming the through-hole.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
The equipment 100 includes a condenser lens 10, a varifocal lens device 20, a mirror 30 and a laser beam output device 40. The condenser lens 10 condenses a laser beam 60 to irradiate the laser beam 60 on an object, i.e., the metallic plate 50 to be machined. The varifocal lens device 20 is capable of changing a curvature of a lens surface so that the varifocal lens device 20 controls an incident angle of the laser beam 60 to be introduced into the condenser lens 10. The mirror 30 works as a reflection mirror. The laser beam output device 40 outputs the laser beam 60. Here, the object 50 as a to-be-machined work is disposed under the condenser lens 10. The above parts such as a condenser lens 10 are conventional parts, which is disclosed in, for example, Japanese Patent Application Publication No. 2002-239769.
The varifocal lens device 20 includes a lens portion 21 and a laminated type Piezoelectric actuator 22. The lens portion 21 controls a curvature of the lens portion 21. The actuator 22 is bonded to the lens portion 21 so that the actuator 22 actuates the curvature of the lens portion 22. An electric voltage is applied to the actuator 22. The voltage applied to the actuator 22 is controlled so that amount of variation of a Piezoelectric bimorph composing the actuator 22 is controlled. Specifically, the curvature of the lens portion 21 is controlled after the voltage is applied to the lens portion 21. Accordingly, the focus point of the laser beam is controlled.
The laser beam output device 40 outputs the laser beam 60 having a predetermined wavelength for drilling a through-hole in the object 50. The laser beam output device 40 outputs a SHG (i.e., second harmonic generation) laser as the laser beam 60. The SHG laser has a 532 nm wavelength, and is based on a primary YAG (i.e., yttrium aluminium garnet) laser having a 1064 nm wavelength. The equipment 100 can use another laser beam selected on the basis of a machining condition of the object 50 as long as a laser beam oscillator radiates the laser beam or it's harmonic generation laser.
The laser beam 60 outputted from the laser beam output device 40 is reflected with the mirror 30 toward the object 50. The, the laser beam 60 enters in the varifocal lens device 20. The laser beam 60 is outputted from the varifocal lens device 20 with a predetermined expanding angle in accordance with the curvature of the lens portion 21 in the varifocal lens device 20. Then, the laser beam 60 is condensed by the condenser lens 10 so that the laser beam 60 having a predetermined focus position is irradiated on the object 50. Thus, a part of the object 50 to be machined is evaporated and removed so that the through-hole is formed.
Here, the inventors have preliminarily studied about the laser beam machining. Specifically, the focus point of the laser beam 60 is fixed, and the laser beam 60 is irradiated on the object 50. Then, the through-hole formed in the object 50 is observed, i.e., the cross section of the through-hole in a thickness direction is observed. The SGH laser having an output power of 2 W, a frequency of 1 kHz is used. An output diameter of the laser beam 60 outputted from the condenser lens 10 is set to be 3 mmφ. The object 50 is made of chrome molybdenum steel (i.e., SCM), and the thickness of the object 50 is in a range between 0.5 mm and 1.5 mm.
A machining result of the above study is shown in
The cross section of the through-hole 51 formed in the object 50 has at least one wide width portion. The wide width portion is formed by an expansion and a condensation of the laser beam 60 in the object 50. The expansion of the laser beam 60 is performed in the object 50, and the condensation of the laser beam 60 is performed by a reflection of an inner wall of the through-hole 51. Therefore, the laser beam 60 does not continue to expand from the focus point 61 in the object 50. But, the laser beam 60 temporarily expands in the object 50, then the energy density of the laser beam 60 is reduced so that the laser beam 60 can not evaporate and remove a part of the object 50 any more in an expanding direction, and then, the laser beam 60 is reflected on the inner wall of the through-hole 51 so that the laser beam 60 is condensed. Here, the inner wall of the through-hole 51 has a mirror surface manufactured by evaporation and removal of a part of the object 50. Here, as shown in
As shown in
Next, the through-hole 51 having a predetermined shape is formed in the object 50 by the laser beam machining equipment 100. Specifically, the through-hole 51 shown in
Firstly, the through-hole forming process is performed so that an initial through-hole 51 is formed in the object 50. In this process, the focus point 61a of the laser beam 60 is set on the surface of the object 50, and then, the laser beam 60 is irradiated on the object 50. Thus, the through-hole 51 having at least one wide width portion is formed in the object 50. In
Thus, in the method for machining the object 50 according to the first embodiment, the focus point 61 of the laser beam 60 is changed in each process so that the object 50 is machined to be a predetermined pattern having the wide and the narrow width portions. Thus, the machining pattern in each process is overlapped finally so that the through-hoe 51 is formed to be a predetermined shape. Accordingly, the method of the first embodiment can perform to machine the object 50 with high machining accuracy, compared with a conventional method for machining an object. The conventional method is such that the focus position of the laser beam is continuously changed.
The shift distance of the focus position is in a range of one pitch between neighboring wide width portions or neighboring narrow width portions. Here, in the method shown in
However, in the method according to the first embodiment, firstly, at least one wide width portion is formed in the through-hole 51. Therefore, the displacement distance of the focus point 61 becomes shorter. Accordingly, the through-hole having a predetermined shape is formed in a time efficient manner. Further, after the through-hole is preliminarily formed, the focus point 61b is shifted to form another predetermined patter of the through-hole 51 having at least one narrow width so that the through-hole 51 having high straightness is provided.
The process for forming the through-hole 51 having at least one wide width portion depends on the material of the object 50, the thickness of the object 50, the wavelength of the laser beam 60 and the like. Specifically, as shown in
The distance between the wide width portion and the narrow width portion in the through-hole 51 formed by a process shown in
Similarly, the condensation angle becomes smaller as the focal distance becomes long. Thus, in this case, the distance between the wide width portion and the narrow width portion becomes longer. Further, the distance between the wide width portion and the narrow width portion becomes longer, as the energy density of the laser beam 60 becomes higher. This is because the thermal energy absorbed in the object 50 becomes higher when the energy density is high, so that the melting range of the object 50 expands in the radial direction. Thus, the diameter of the through-hole 51 becomes larger so that the distance between the wide width portion and the narrow width portion becomes longer. Here, if the energy density of the laser beam 60 becomes much higher, the laser beam 60 continue to diffuse in the object 50 without reflecting on the inner wall of the through-hole 50. For example, when the output power of the laser beam 60 is 4 Watts, the wide width portion is not formed in the through-hole 50, so that the cross section of the through-hole 50 becomes a horn shape. Specifically, the laser beam 60 is diffused from the focus point 61 without condensing in the object 50.
Thus, by controlling at least one condition among the diameter of the laser beam 60, the focal distance between the condenser lens 10 and the focus point 61 and the energy density of the laser beam 60, the cross section of the through-hole 51 is controlled effectively. Further, by controlling all of conditions of the diameter, the focal distance and the energy density appropriately, the cross section of the through-hole 51 can be controlled with high accuracy. For example, in the shape reform process, the focus point 61 of the laser beam 60 and the energy density of the laser beam 60 are changed simultaneously so that the cross section of the through-hole 51 is controlled appropriately. In the first embodiment, the laser beam machining equipment 100 has the varifocal lens device 20 so that the expanding angle of the laser beam 60 outputted from the varifocal lens device 20 is controlled. Thus, the energy density of the laser beam 60 and the diameter of the laser beam 60 outputted from the condenser lens 10 are controlled appropriately with high accuracy. Accordingly, the shape of the through-hole 51 is controlled with high accuracy.
Preferably, as shown in
In the first embodiment, the focus point 61 of the laser beam 60 is changed once in the shape reform process. The focus point 61 can be changed multiple times in the shape reform process so that the through-hole 51 having high straightness is obtained. Specifically, the laser beam 60 is controlled to have different multiple focus points 61 so that the shape reform process is performed. In this case, the inner wall of the through-hole 51 becomes much straight, i.e., more smooth, so that the accuracy of the shape of the through-hole is much improved. Specifically, the difference of the width between the wide width portion and the narrow width portion is reduced.
Although the focus point 61 of the laser beam 60 is set to be in the object 50, the focus point 61 can be set to be outside of the object 50. For example, at least one time, the focus point is set to be outside of the object 50, the through-hole can be formed with high accuracy in shape of the through-hole 50 even when the thickness of the object 50 is thick.
Although the equipment 100 includes the varifocal lens device 20, the equipment 100 can include no varifocal lens device. In this case, the condenser lens 10 or the object 50 is displaced so that the focus point 61 of the laser beam 60 is controlled. Here, if the object 50 is displaced, the object 50 may be oscillated so that the machining accuracy of the object 50 may be deteriorated. Further, when the weight of the object 50 is large, or the dimensions of the object 50 are large, the equipment for displacing the object 50 becomes larger. Therefore, it is preferred that the condenser lens 10 is displaced without displacing the object 50 for displacing the focus point 61 of the laser beam 60.
Although the object 50 is made of metallic plate, the object 50 can be made of any material such as resin. Here, in the method for machining by using the laser beam 60, the condensation and the diffusion of the laser beam 60 in the object 50 are utilized. Therefore, it is preferred that the inner wall of the through-hole 51 is mirror-finished. In case of resin composing the object 50, the inner wall of the through-hole 51 is difficult to finish with a mirror surface, compared with the case of metallic plate composing the object 50. Accordingly, it is preferred that the object 50 is made of metallic material.
In the first embodiment, the varifocal lens device 20 works as an energy density controller for controlling the energy density of the laser beam 60 and a diameter of laser beam controller for controlling the diameter of the laser beam 60 outputted from the condenser lens 10. Therefore, the focus point 61 of the laser beam 60, the energy density, and the diameter of the laser beam 60 can be controlled by the varifocal lens device 20. Here, the energy density of the laser beam 60 can be controlled by the laser beam output device 40. Further, the diameter can be controlled by a beam expander and a collimator together with the condenser lens 10.
Although the equipment 100 includes the mirror 30, the equipment 200 can have no mirror 30.
Although the equipment 100 machines the through-hole 51, the equipment 100 can machine other through-holes such as a through-hole having a cylindrical shape and a through-hole having a tapered shape. Further, the equipment 100 can machine a hole having a bottom.
Although the equipment 100 machines the through-hole 51 having the wide width portion and the narrow width portion in both of the through-hole forming process and the shape reform process, in at least one of the through-hole forming process and the shape reform process, the through-hole 51 having at least one wide width portion can be formed. For example, as shown in
Laser beam machining equipment 200 according to a second embodiment of the present invention is shown in
The equipment 200 can control the focus point 61 of the laser beam 60 automatically. The equipment 200 includes a detection portion 70 for detecting the laser beam 60 penetrating through the object 50 and a controller 80 for controlling the voltage applied to the varifocal lens device 20 on the basis of the detected laser beam 60 detected by the detection portion 70. Thus, the controller 80 controls the focus point 61 of the laser beam 60 on the same light axis on the basis of the detected laser beam 60. Accordingly, the equipment 200 has an automatic varifocal system.
The detection portion 70 can detect the laser beam 60 penetrating through the object 50 after the through-hole 51 is formed in the through-hole forming process. The detection portion 70 is formed of, for example, a photo diode. In this case, the equipment 200 has a simple construction. However, the photo diode does not detect the displacement of the focus position 61 of the laser beam 60. Therefore, the focus point 61 can not be controlled automatically even when it is necessary for the focus point 51 to displace another point after the through-hole 51 is formed in the object 50. However, in this case, the controller 80 controls the laser beam output device 40 to radiate the laser beam 60 in a predetermined interval. Thus, even after the through-hole 51 is formed, the focus point 61 of the laser beam 60 can be controlled on the basis of the detection of the laser beam 60 detected by the detection portion 70.
Further, the detection portion 70 can be composed of a laser beam profiler having a CCD (i.e., charge coupled device) camera. In this case, the machining state of the through-hole 51, the intensity of the laser beam 60 and the like are detected by the profiler in real time. Accordingly, even after the through-hole 51 is formed in the through-hole forming process, the focus point 61 of the laser beam 60 can be controlled on the basis of the detection of the laser beam 60 by the detection portion 70.
Thus, the controller 80 controls the voltage applied to the varifocal lens device 20 so that the focus point 61 of the laser beam 60 is displaced a different position automatically. Thus, the shape of the object 50 is reformed appropriately so that the through-hole 51 having high straightness and high accuracy of shape.
Specifically, the equipment 200 can displace the focus point 61 multiple times so that the inner wall of the through-hole 51 becomes much smooth. The accuracy of the shape of the through-hole 51 is much improved.
Although the varifocal system is provided by the detection portion 70 and the controller 80, the varifocal system can be provided by other constructions. For example, in a case where the equipment 200 has no varifocal lens device 20, at least one of the condenser lens 10 and the object 50 is displaced on the basis of the detection of the laser beam 60 by the detection portion 70 so that the focus point 61 is changed.
Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-120538 | Apr 2004 | JP | national |
| 2005-36713 | Feb 2005 | JP | national |
