DE19744368A1 - Ultra-short pulse laser beam micro-engineering for drilling symmetrical recess - Google Patents

Abstract

A work piece (8) is excavated with rotational symmetry by rotating the direction of polarization (P) of an ultra-short laser beam, relative to the work piece, during machining. An Independent claim is also included for the processing equipment. Preferred features: Relative rotation through 180 deg and preferably 360 deg occurs at least once, in a plane perpendicular to the beam. Rotation is continuous or stepwise, in one direction, and the work piece is held against transverse movement during operation. The work piece may be held fixed relative to the beam, of which the direction of polarization may be rotated, using a rotary optical delay plate, especially a half wave plate (6), being turned in the propagation path of the beam. During laser machining, the object is turned about an axis perpendicular to the plane of polarization. The beam has linear polarization with a quarter-wave plate optionally used for circular polarization and the laser may be pulsed, preferably an ultra short wave laser is used, pulsed in the pico- or femtosecond (4) region.

Description

The invention relates to a method in the upper Concept of claim 1 mentioned type and a pre direction of those mentioned in the preamble of claim 18 Type for micromachining workpieces using lasers radiation, especially for forming essentially rotationally symmetrical recesses in workpieces.

By Momma et al, "Using Precise Micromachining Femtosecond laser pulses ", lasers and optoelectronics 29 (3/1997), is a procedure of the type concerned knows the laser radiation from an ultrashort pulsed lasers, for example one every femtosecond pulsed laser area, aimed at a workpiece is used, for example, in the workpiece substantial rotationally symmetrical recess, for example a hole to form. The necessary for this che intensity distribution on the workpiece, for example wise with an essentially rotationally symmetrical Drilling a circular or ring-shaped intensity ver division, will map in the known method of geometry. Read with the known method work out in 100 µm thick workpieces, for example Drill steel holes that are rota are symmetrical.

There is a disadvantage of the known method but in that especially with thicker workpieces  with increasing machining depth the geometry of the formed recess of the desired geometry, for example a circular cross section gives way, so that with increasing depth the machining the processing uniformity deteriorate tert.

A device for loading is described in US Pat. No. 4,547,651 processing of a workpiece using laser radiation knows the direction of polarization of the laser radiation, for example when cutting a work piece by means of laser radiation, is changed in such a way that the direction of polarization of the laser radiation with the direction of the cut in the workpiece Right. However, the known device is for micro machining of workpieces, in particular for forming of essentially rotationally symmetrical recesses in one workpiece, not suitable.

Furthermore, US 4,908,493, US 5,057,664 and US 5 223 692 Devices for machining work known by means of laser radiation, in which the Direction of polarization of the laser radiation during the Machining process is changed. This also got However, devices are for micromachining Workpieces not suitable.

The object of the present invention is therein, a method or a device of the to specify the type in which the same the processing result is improved.

With regard to the method, this task by the teaching and with regard to claim 1 Lich the device specified in claim 18 ne teaching solved.

The basic idea of the teaching according to the invention be is the polarization direction of the laser beam to rotate during the machining process. It has surprisingly been shown to work in this way achieve particularly uniform machining results  to let. For example, it is by means of the invention according to the method and the device according to the invention possible, even in thicker workpieces bring in where the desired, essentially circular cross section of the holes over the entire Machining depth is retained without mentioning value deviations from the desired cross-section to step.

Another solution of the basis of the invention task is with regard to the procedure in the saying 11 and with respect to the device in claim 26 specified.

The basic idea of this teaching is zir to use kular polarized laser radiation. On this way can also be particularly uniform achieve machining results so that diesel ben advantages as in the inventive method or the device according to the invention, in which or at which the direction of polarization is rotated ben. The method according to the invention and the inventions device according to the invention, in which or in the circular polarized laser radiation is used is further simplified, since means for rotating the polarization direction of the laser radiation, such as in the use of linearly polarized laser radiation are avoided.

The method according to the invention is not only for Forming essentially rotationally symmetrical responses, but also diverse in other ways applicable, for example for cutting workpieces, for the production of micro components, for forming any recesses and in another way to Wed. co-machining of workpieces.

The method according to the invention is simple and can be carried out quickly. The device according to the invention is simple in construction and inexpensive to manufacture.

Furthermore, the method and according to the invention open up  the device according to the invention in new applications the micromachining of workpieces using lasers radiation in the known method due to the restrictions existing there with regard to not sufficient uniformity of the processing result nisses, especially with increasing processing depth, were not possible.

A particularly advantageous further training of the inventive method provides that the Polarisa direction during a machining operation, at for example when forming an essentially rota tionally symmetrical recess, at least once at least about 180 °, preferably at least about 360 ° to one to the plane of polarization essentially vertical axis is rotated. That way a particularly uniform processing result achieve.

The direction of polarization of the laser radiation can be rotated arbitrarily, for example randomly. A advantageous embodiment of the Ver However, driving provides that the direction of polarization and the workpiece is continuous relative to each other to be turned around. In this way, the uniformity the processing result further improved.

However, it is also possible to use the polarization direction tion and the workpiece gradually relative to each other to turn like this is another training he provides teaching according to the invention. For example wise possible when using a pulsed laser the direction of polarization after a laser pulse to rotate a predetermined angular step.

Basically, the direction of polarization and the workpiece is changing relative to each other Direction of rotation. However, it is advisable the polarization direction and the workpiece relative to each other in a constant direction of rotation. In this way, the implementation of the Invention  simplified procedure.

Another development of the invention The teaching stipulates that the workpiece during machining tion process against lateral displacements in one fixed to the plane parallel to the polarization plane is arranged. In this way, for example Avoid forming rotationally symmetrical recesses that that due to undesirable lateral displacement exercises of the workpiece during the machining process Deviations from the desired geometry of the recess occur.

Basically, you can achieve a rotation of polarization direction and workpiece relative to each other the polarization direction of the laser radiation is different and / or the workpiece during the machining process be rotated. An expedient embodiment However, the method according to the invention provides that the workpiece relatively during the machining process to the laser radiation is fixed and the pola direction of risk of laser radiation by means of Rotation of the polarization direction is rotated. At this embodiment is a rotation of the workpiece not required what to do the procedure simplified.

In the aforementioned embodiment, the bottom larization direction expediently by an im Propagation path of the laser radiation arranged, rotating drivable delay plate, in particular a λ / 2- Plate (half-wave plate) rotated. That way the implementation of the method according to the invention simplified.

However, it is also possible that during loading the polarization direction of the La radiation is fixed and the workpiece by one Polarization plane ge substantially vertical axis is rotated as this is another embodiment of the provides method according to the invention.  

Basically, the Ver drive any polarized laser radiation used become. However, one embodiment provides that li near polarized laser radiation is used.

In the embodiment of the Ver driving, with circularly polarized laser radiation is used, the laser radiation is more appropriate circularly polarized by means of a λ / 4 plate. This is how the procedure is carried out simply designed.

The laser radiation is expediently transmitted through generates a pulsed laser.

An extremely advantageous embodiment stipulates that the laser radiation by an ultra short pulsed, especially one in the pico and / or Femtosecond range pulsed laser, is generated. On this is an undesirable melting of the Workpiece in the machining area, which leads to a un uniform machining result could lead to reliably avoided.

The method according to the invention is diverse Suitable for micromachining workpieces, for example to form any shape in workpieces or to create micro- Components, such as micro gears. Expedient However, the method according to the invention is also used used in the workpiece by means of the laser radiation is essentially rotationally symmetrical Hole to form as this is an embodiment of the provides method according to the invention.

To generate a defined intensity ver division on the workpiece, for example a circular or ring-shaped intensity distribution, can at for example focusing or imaging processes be used. An extremely beneficial one Further development of the method according to the invention however, before that on the workpiece to be machined de  Finished intensity distributions with high efficiency are generated by means of diffractive optics. With help diffractive optics can be practically any very defined intensity distributions on the work piece surface without the appearance of for the ultra short laser pulses generate critical intermediate focus. In this way it is possible to define any structures free of melting and burrs in all materials, especially in metals, transparent and organic Create materials without the need for one Processing in a vacuum chamber.

A training of the aforementioned execution form provides that the diffractive optics holograms are. Such holograms can be varied Manufacture way easily and inexpensively.

The diffractive optics can be computer generated, etched or laser structured holograms be how this provides for a further embodiment.

According to another development of the execution shape with the holograms, the holograms are in transparent plastics, polymers, glasses, quartz or Salt or in reflective materials. In this way, the holograms are easy to handle.

A further development of the device according to the invention tion provides that the means for rotating the polar direction and the workpiece relative to each other the polarization direction and the workpiece relative to each other during a machining process, at for example when forming an essentially rota tionally symmetrical recess, at least once at least about 180 °, preferably at least about 360 ° essentially to the plane of polarization turn the vertical axis. In this way, one can achieve a particularly uniform machining result.

The means to rotate the direction of polarization and the workpiece relative to each other, the pola direction of risk and the workpiece relative to each other  rotate continuously or gradually like this expedient further developments of the invention provide direction.

Another development of the invention The device provides that the means for rotating the Direction of polarization and the workpiece relative to the workpiece and the direction of polarization relative to each other in a constant direction of rotation rotate. This embodiment is simple and costly cheap to manufacture.

The means for rotating the workpiece and the bottom Larization direction relative to each other can be in a lot be more wrinkled. One especially before partial development of the device according to the invention tion, however, provides that the means for rotating the Polarization direction and the workpiece relative to each other another by one in the path of the laser radiation arranged delay plate, in particular a λ / 2- Plate (half-wave plate) are formed around a axis of rotation perpendicular to the plane of polarization by means of a rotary drive device can be driven in rotation. The like delay plates are simple and inexpensive producible. This embodiment is also simple and robust in construction.

In the embodiment of the invention direction with the means for circular polarization these agents are expedient for laser radiation formed by a λ / 4 plate. With such a λ / 4 plate can be a particularly simple achieve circular polarization of the laser radiation.

According to another development of the invention according device are means for against lateral Ver shifts during the machining process in one plane substantially parallel to the plane of polarization non-displaceable mounting of the workpiece is provided. In this way there are undesirable lateral displacements workpiece during the machining process,  the deviations from the desired machining geometry can be reliably avoided.

Another embodiment sees a position nier device for positioning laser and work piece relative to each other. That way it is possible to position the workpiece relative to the laser To position the machining process precisely or at for example when cutting with laser radiation, wuh rend the machining process to achieve the ge to position the desired cut.

Another institution sees an institution to generate a certain intensity distribution on the workpiece to be machined.

According to a development of the aforementioned Aus management form is the device for generating a a diffractive op tik. In this way, practically any very defined intensity distributions on the work achieve piece surface without, for example ultra-short laser pulses are a critical intermediate focus occurs.

The diffractive optics is expediently one Hologram. Such holograms are simple and knockout inexpensive to manufacture.

The diffractive optics can also be converted into a trans parent material introduced hologram, such as this is another development of the embodiment with which provides diffractive optics. That way the hologram is easier to handle.

In the aforementioned embodiment, this can transparent plastic material, made of a poly always consist of glass, quartz or a salt.

However, the diffractive optics can also be integrated into one reflective material introduced hologram, as this is another development of the embodiment with the hologram.

According to another training, the dif  fractive optics and the workpiece relative to each other positionable. In this way it can be Adjust the working area of the workpiece precisely.

The invention is described below with reference to the beige added drawing, in which an embodiment is explained in more detail.

It shows

Fig. 1 shows a schematic side view of an inventive device from the management, for example for carrying out the OF INVENTION to the invention process,

Fig. 2 shows the intensity distribution on the workpiece using a donut-Ho logrammes,

Fig. 3 is a scanning electron micrograph of a radiation with the apparatus of Fig. 1 produced by the inventive method bore in a workpiece made of steel in the entry region of the laser,

Fig. 4 in the same representation as FIG. 3, the exit region of the laser radiation in the bore of FIG. 3,

Fig. 5 is a scanning electron microscope image of a hole produced with a method according to the prior art in steel of the same thickness as in Figs. 3 and 4 in the entrance area of the laser radiation and

Fig. 6 shows the outlet area of the laser radiation in the bore of FIG. 5.

In Fig. 1, an apparatus according to the invention is shown, which has a laser system 4 with an ultra-short pulsed laser, which generates laser pulses in the femtose customer area. In the path of propagation of the laser radiation generated by the laser system 4 in the direction of expansion behind the laser system 4 , a half-wave plate 6 is arranged, which is perpendicular to the plane of polarization of the laser radiation in FIG. 1 and into this and is symbolized by a line P. , is arranged in parallel and forms means for rotating the direction of polarization of the laser radiation and the workpiece relative to each other. The half-wave plate 6 can be continuously driven in rotation by means of a rotary drive device (not shown in FIG. 1) about an axis of rotation essentially perpendicular to the polarization plane P. The laser radiation generated by the laser system 4 is linearly polarized.

In the direction of propagation of the laser radiation behind the half-wave plate 6 , a diffractive optic is arranged in the path of propagation of the laser radiation, which forms a device for generating a certain intensity distribution on a workpiece 8 to be machined and is formed by a hologram 10 in this exemplary embodiment. The hologram 10 is attached to a positioning table, which is symbolized in FIG. 1 by an arrow 12 and serves to set the distance between the hologram 10 and the workpiece 8 to be machined.

The workpiece 8 is also arranged on a positioning table, which is symbolized in FIG. 1 by an arrow 14 and is used for precise adjustment of the area of the workpiece 8 to be machined.

In the embodiment shown in FIG. 1, the hologram 10 is a donut hologram, so that when operating the device 2 on the surface of the workpiece 8 to be machined, an annular intensity distribution 16 sets, as can be seen from FIG. 2.

In the following, the implementation of the method according to the invention by means of the device 2 will be explained in more detail using a machining process which consists in forming an essentially rotationally symmetrical bore in the workpiece 8 .

During the machining process, the laser radiation of the laser system 4 via the half-wave plate 6, and the hologram 10 on the piece to be machined 8 directed, so that the annular intensity distribution is adjusted to the surface of the workpiece 8 sixteenth During the machining process, the half-wave plate 6 is continuously driven in rotation by the rotary drive device, not shown, so that the polarization direction of the laser radiation is continuously rotated in the polarization plane P during the machining process in a uniform direction of rotation. The laser radiation removes 16 material from the workpiece in accordance with the annular intensity distribution, so that a bore 18 with a substantially circular cross section begins to form.

In Fig. 3, the entrance area 20 of the laser radiation at the bore 18 is shown.

During the machining process, material is then removed from the workpiece 8 until a break is formed and the laser radiation on the side of the workpiece 8 facing away from the entry region 20 emerges from the workpiece 8 in an exit region 22 .

From Figs. 3 and 4 it can be seen that the bore formed by means of the method according to the invention 18 with a good approximation, is rotationally symmetrical and that the ge desired circular cross-section is maintained in the outlet region 22 of the laser radiation. In this way, a particularly uniform machining result is achieved.

In comparison to this, in FIG. 5 the entry area 20 and in FIG. 6 the exit area 22 of a bore made with a method according to the prior art are provided in a material of the same thickness. It can be seen that the entry region 20 of the bore still has the desired circular cross section in wesentli, but that with a material thickness of one millimeter in the exit region 22, however, considerable deviations from the desired, essentially circular geometry of the bore 18 occur, so that the known method for forming precise holes is not suitable for material thicknesses of approximately 200 µm. In contrast, the method according to the invention is also suitable for forming bores in materials of greater thickness.

If circularly polarized laser radiation is used instead of linearly polarized laser radiation, then a stationary λ / 4 plate is used instead of the rotationally drivable half-wave plate 6 , which circularly polarizes the laser radiation.

Claims (36)

1. Method for micromachining workpieces by means of laser radiation, in particular for forming essentially rotationally symmetrical recesses in workpieces,
in which the laser radiation is directed onto the workpiece to be machined,
characterized by
that to generate a substantially rotationally symmetrical material removal on the workpiece, the polarization direction of the laser radiation and the workpiece are rotated relative to one another during the machining operation about an axis substantially perpendicular to the plane of polarization. 2. The method according to claim 1, characterized in that that the direction of polarization and the workpiece during a machining process, for example when forming an essentially rotationally symmetrical exception tion, at least once by at least about 180 ° preferably by at least about 360 °, one to the polar sationsplane essentially vertical axis relative are turned towards each other. 3. The method according to claim 1 or 2, characterized  records that the direction of polarization and the work pieces are rotated continuously relative to each other. 4. The method according to claim 1 or 2, characterized records that the direction of polarization and the work piece are rotated gradually relative to each other. 5. The method according to any one of the preceding claims, characterized in that the polarization direction and the workpiece relative to each other in a constant direction of rotation. 6. The method according to any one of the preceding claims, characterized in that the workpiece during the Machining process against lateral displacements in a plane parallel to the plane of polarization fastener is arranged. 7. The method according to any one of the preceding claims, characterized in that during processing the workpiece relative to the laser radiation is fixed and the direction of polarization Laser radiation by means of rotation of the Polarisa direction is rotated. 8. The method according to claim 7, characterized in that that the direction of polarization by a spread The path of the laser radiation is arranged, rotatable re delay plate, especially a λ / 2 plate (Half-wave plate) is rotated. 9. The method according to any one of claims 1 to 5, because characterized in that during the processing the direction of polarization of the laser radiation is firm and the workpiece is one for polarization plane is rotated substantially perpendicular axis.   10. The method according to any one of the preceding claims, characterized in that linearly polarized lasers radiation is used. 11. Method for micromachining workpieces by means of laser radiation, in particular for forming essentially rotationally symmetrical recesses in workpieces,
in which the laser radiation is directed onto the workpiece to be machined,
characterized,
that circularly polarized laser radiation is used to generate a substantially rotationally symmetrical material removal on the workpiece. 12. The method according to claim 11, characterized in net that the laser radiation using a λ / 4 plate is circularly polarized. 13. The method according to any one of the preceding claims, characterized in that the laser radiation by a pulsed laser is generated. 14. The method according to claim 13, characterized in net that the laser radiation by an ultrashort pulsed lasers, especially one in the pico and / or Femtosecond range pulsed laser, is generated. 15. The method according to any one of the preceding claims, characterized in that by means of in the workpiece the laser radiation is essentially rotationally symmetrical trical bore is formed. 16. The method according to any one of the preceding claims,  characterized in that on the to be processed Workpiece-defined intensity distributions with high Efficiency can be generated using diffractive optics. 17. The method according to claim 16, characterized in net that the diffractive optics are holograms. 18. The method according to claim 16, characterized in net that the diffractive optics computer-generated, are etched or laser structured holograms. 19. The method according to claim 17 or 18, characterized ge features the holograms in transparent art fabrics, polymers, glasses, quartz or salt or in right reflective materials are introduced. 20. Device for micromachining workpieces by means of laser radiation, in particular for forming essentially rotationally symmetrical recesses in workpieces,
with a laser,
marked by
Means for rotating the direction of polarization of the laser radiation and the workpiece ( 8 ) relative to each other during the machining operation about an axis perpendicular to the polarization plane (P) to achieve a substantially rotationally symmetrical removal on the workpiece ( 8 ). 21. The apparatus according to claim 20, characterized in that the means for rotating the direction of polarization and the workpiece ( 8 ) relative to each other, the direction of polarization and the workpiece ( 8 ) relative to each other during a machining operation, for example when forming a substantially rota tion-symmetrical recess, at least once by at least about 180 °, preferably at least about 360 °, about an axis perpendicular to the polarization plane (P) in Chen Chen wesentli axis. 22. The apparatus of claim 20 or 21, characterized in that the means for rotating the direction of polarization tion and of the workpiece (8) to one another, the polarization direction, and the workpiece (8) rotate relative to each other continuously relatively. 23. The apparatus of claim 20 or 21, characterized in that the means for rotating the direction of polarization and the workpiece ( 8 ) relative to each other, the direction of polarization and the workpiece ( 8 ) rotate relative to each other step by step. 24. Device according to one of claims 20 to 23, characterized in that the means for rotating the direction of polarization and the workpiece ( 8 ) relative to each other rotate the direction of polarization and the workpiece ( 8 ) relative to each other in a constant direction of rotation. 25. Device according to one of claims 20 to 24, characterized in that the means for rotating the direction of polarization and the workpiece ( 8 ) relative to each other by a radiation plate arranged in the propagation path of the laser radiation, in particular a λ / 2 plate (half-wave plate) ( 6 ), are formed, which can be driven rotatably about a axis of rotation perpendicular to the polarization plane (P) by means of a rotary drive device. 26. Device for micromachining workpieces by means of laser radiation, in particular for forming essentially rotationally symmetrical recesses in workpieces,
with a laser,
marked by
Means for circular polarization of the laser radiation. 27. The apparatus according to claim 26, characterized in net that the means for circular polarization of the Laser radiation are formed by a λ / 4 plate. 28. The device according to any one of claims 20 to 27, characterized by means for against lateral displacements during the machining process in a plane parallel to the polarization plane (P) substantially displaceable mounting of the workpiece ( 8 ). 29. Device according to one of claims 20 to 28, characterized by a positioning device for positioning the laser ( 4 ) and workpiece ( 8 ) relative to one another. 30. Device according to one of claims 20 to 29, characterized by a device for generating a specific intensity distribution on the workpiece ( 8 ). 31. The device according to claim 30, characterized net that the facility for generating a particular Intensity distribution is a diffractive optic. 32. Apparatus according to claim 31, characterized in that the diffractive optics is a hologram ( 10 ). 33. Apparatus according to claim 31, characterized in that the diffractive optics is a hologram ( 10 ) introduced into a transparent material. 34. Device according to claim 33, characterized net that the transparent plastic material, from a polymer, made of glass, quartz or a salt. 35. Apparatus according to claim 31, characterized in that the diffractive optic is a hologram ( 10 ) introduced into a reflecting material. 36. Device according to one of claims 31 to 35, characterized in that the diffractive optics and the workpiece ( 8 ) can be positioned relative to one another.