DE4209933A1 - Partial laser modification of surfaces - useful for shallow or deep engraving or inscription - Google Patents

Abstract

Partial surface modification of metallic or non-metallic bodies is carried out using a Q-switched continuous wave Nd:YAG laser having opt. a beam expander in the beam path, a beam deflector with a computer-controlled rotary deflection mirror, and a plane field objective for focussing the laser beam, the laser being moved over the surface along one or more reference lines present by the computer. The novelty is that the laser beam is moved within an outline (U1, U2) delimiting the surface portion (A) to be modified, along reference lines forming the grid lines (R1, R2, R3) of a grid field (N) and then the entire grid field (N) is shifted at least once by a certain amount, while maintaining the relative position of the outline (U1, U2) and the entire surface portion (A) is re-scanned by the laser beam along the grid lines (R1, R2, R3). During each scan, the operating time and the energy content level of the laser pulses are limited so that material evapn. is effected with minimal plasma formation. USE/ADVANTAGE - The process is useful in laser engraving or insorption processes carried out e.g. on metallic or plastic surfaces. It achieves the prescribed shallow penetration depth for prodn. of inscriptions, but can also produce deeper penetration depths to achieve relief-like material surface removal.

Description

The invention relates to a method for partial ver change of surfaces of metallic or non-metallic Body with a Q-switched continuously excited Nd: YAG laser according to the preamble of the claim 1. Devices that can work with similar procedures NEN, are known for example from DE-OS 39 39 866 been.

The well-known Nd: YAG lasers are mainly used for lasers engraving or laser marking process, at least for sol processes for the partial change of surfaces with which only burn-in depths of maximum 20 µm are achieved will. The limitation of this burn-in or penetration depth may be associated with metal workpieces to explain that ent in laser beam processing existing oxide layers have a deeper thermal impact  effect of the laser beam on the work underneath Prevent fabric area. Try thermoplastic Workpieces made of plastics resulted in application the known method - especially with a longer duration of action - just an untargeted melting or burning of the art fabric.

The guidance of the laser beam by means of an elec electronic computers containing, for example, digital ab steering system often happens in known methods, that the laser beam is "wobbled", i.e. H. run away in small the overlapping circular movements becomes.

The object underlying the invention is therein, the known method according to the preamble of claim 1 to change so that not only the front described low penetration depths for the production of Be writings, but also much higher input penetration depths can be achieved, which one in the broadest Senses deep, approximately relief-like, removal of the workpiece top allow area.

According to the invention, this object is ge has been resolved that the laser beam ver ver changing surface part delimiting outline along Ra Reference lines forming a grid of a grid is performed, whereupon the entire grid un ter maintaining the relative position of the outline at least one times offset by a certain amount and the surfaces part along the grid lines of the grid again is traversed together with the laser beam, with each Ab  drive the exposure time and the amount of energy in the the body surface is impacted by a laser pulses are limited in such a way that while minimizing a Plasma formation causes evaporation of the material.

According to the invention, the laser beam is internal half of an outline, which the one to be changed Delimited surface part. Here the laser beam is like this led that he covered the entire surface part along the Ra Lines of a grid are processed uniformly. As soon as the laser beam the grid lines of the grid as a whole has departed, this will determine the guidance of the laser beam mende, generated by a computer control around moved a certain amount. Here, however, the Outline which determines the surface part to be changed, maintained in its local relative position.

After the offset occurs by a certain amount the laser beam travels the grid lines of the grid again, reducing the machining density on the surface part to be changed is enlarged. If necessary derlich, an offset, possibly with the same be agreed amount, once or several times in succession follow, at least until a sufficient material is reached.

The offset according to the invention ensures that as few places as possible of the surface area to be changed ch are sometimes hit several times by the laser beam, in particular, an overlay of intersections is ver avoided. When scanning the grid with the laser beam care must be taken to ensure that the duration of exposure and the amount  the energy content of the body surface like a bullet laser pulses are limited such that at Minimizing plasma formation essentially only ver vaporization of the material occurs.

It is overall with the measures according to the invention has become possible, for example with a steel of the type 1.2311 a depth of cut in the order of millimeters to achieve. This advantageous large, not yet achieved Depth of cut can only be achieved through the strange inventions explain the proper guiding of the laser beam and thereby that practically while avoiding plasma formation according to Mög only evaporation of the material takes place. There through that the material under the action of the laser beam immediately evaporated and suctioned off can be used the method of the invention the depth of penetration of Laser beam obstructing oxide formation apparently largely be avoided.

It also appears important by limiting energy the content of the pulse in the manner of individual bullets the material impinging laser beam a plasma formation to be able to minimize it as far as possible in order to otherwise reducing the penetration depth of the laser beam to avoid sorption.

When using the method according to the invention Laser beam with the help of an acousto-optical modulator purpose moderately controlled with a frequency of approx. 10 kHz. That invented The grid according to the invention is therefore composed of grid line lengths composed of 10,000 each per second successive, line-like in a row  arranged, laser bullets exist. The middle The radiation power of the laser is about 50 W.

In a further embodiment of the invention, the offset of the grid generated by this by a be agreed circumferential angle, the angle of rotation, is offset.

According to other features of the invention, the Ra Sterfeld by a certain distance, if necessary additionally to a rotation, translationally offset.

In a further embodiment, the Er found out that the grid is a network Has line structure.

It is also in accordance with other features of the invention possible to run the grid lines parallel to each other leave to form a grid. The grid lines are expediently straight.

The predetermined offset, such as rotation angle or translato rical offset, is in a further embodiment of the invention depending on the material to be machined chooses. This also applies to the parallel spacing of the grid lines from each other.

When processing the aforementioned steel of the type 1.2311, for example, the angle of rotation can be 15 ° The parallel spacing of the grid lines from each other is approx. 50 µm is.

The method according to the invention will now be added with reference to ter drawings explained, this shows

Fig. 1 in more schematic form apparatus the construction of a laser used for practicing the method according to the invention,

Fig. 2 is a plan view of a workpiece and finally Lich

Fig. 3-5 detail enlargements substantially accordingly the encirclement designated III, IV and V in Fig. 2.

The heart of the laser device 10 in FIG. 1 consists of an Nd: YAG rod 11 .

Parallel to the Nd: YAG rod 11 is a Krypton arc lamp operated with direct current, the emission spectrum of which is suitable for exciting the optical states in the Nd: YAG rod.

The light generated by the krypton arc lamp enters the Nd: YAG rod. There, the laser beam L is generated together with the optical resonator consisting of end mirror 13 and decoupling mirror 14 .

An acousto-optic modulator 15 is installed between the Nd: YAG rod 12 and the decoupling mirror 14 and is positioned approximately as follows:

In a glass block, an ultrasonic wave is injected by a piezo element, which generates an optical grating in the glass block. The switching on and off of the grid is caused by a control part designated as a total of 17 , from which electrical control lines 16 lead to the acousto-optical modulator 15 .

Switching the optical grating of the acoustic stooptic modulator 15 on and off results in the laser beam L being switched on and off. This switching on and off, in the present case with a switching frequency of about 5 kHz, in connection with the Nd: YAG rod results in particularly high power peaks, which can be described overall by the term "technology of Q-switching".

By means of a scattering lens 18 and a converging lens 19 it then follows an expansion of the laser beam L. The expanded laser beam L is placed on a first rotating mirror 20 and is reflected by this onto a second rotating mirror 21 . The axes of rotation x, y of the two rotating mirrors 20 , 21 are orthogonal to one another. The axis of rotation y of the rotating mirror 20 extends z. B. perpendicular and the axis of rotation x of the rotating mirror 21 horizontally.

Both rotating mirrors 20 , 21 are driven by a so-called galvanometer scanner 22 , 23 corresponding to the rotary double arrows v, z. The galvanometer scanner 22 , 23 are connected via electrical control lines 24 , 25 to the control part 17 . The galvanometer scanners make it possible to generate rotations with defined angles of rotation. Typical values are +/- 8 degrees.

It should also be added that the krypton arc lamp 12 , the so-called "pump lamp", is supplied via two electrical lines 26 , 27 by the control unit 17 .

Before the laser beam, denoted continuously by L, reaches the workpiece W with which it is to interact, it is passed through a focusing lens, which is a plane field lens 28 , in order to be able to generate a high energy density on the workpiece W.

The workpiece W shown in Fig. 2 offers the viewer his engraving area G. The engraving area G should belong to the central component of a tool insert, which is used in the article-forming shaping within a mold for the production of plastic injection molded articles. The engraving area G contains a modified or worn area A and a raised area B. The contour of the raised area B has an arrow shape.

A net-like grid N can be seen from FIG. 2, which - in each case oriented differently - can also be partially seen in enlarged detail representations corresponding to FIGS. 3-5.

The grid N, which is to a certain extent on the engraving area G is projected is intended to illustrate how the laser beam L is guided to the removed area A to er testify.

The removed area A is on the inside of an outline U1, which corresponds to the contour of the arrow and the outside of one Outline U2 limited.  

The outline U1 and U2 practically represent an inner boundary and an outer boundary, which the laser beam on the workpiece W does not exceed. The contour lines U1 and U2 of the grid N are the result of the laser beam control, for which a programmable computer contained in the control unit 17 is decisive.

The grid N is made up of straight grid lines R1, R2 and R3 together. A number of grid lines R1, one another number of grid lines R2 and another number of grid lines R3 each run parallel with a par allelic distance p from each other.

The grid lines R1 and R2, like the grid lines R2 and R3, each enclose an angle of 60 °, so that, as can be seen from FIG. 3, small equilateral triangles result from the grid lines R1, R2 and R3.

In a first phase ( Fig. 3), the laser beam is now deflected by the movement of the rotating mirrors 20 , 21 initiated by the computer of the control device 17 and is guided in accordance with the outlines U1 and U2 in such a way that the surface of the workpiece W is machined along the lines of the grid field N takes place.

As soon as the grid N extending over the entire area A has been processed in accordance with the position shown in FIG. 3, the grid N is rotated to the left with an angle of rotation of 150 and at the same time shifted translationally to avoid that the grid line crossing points K according to FIG. 3 coincide with those according to FIG. 4.

Along the offset grid N according to FIG. 4, the entire area A, delimited by the outlines U1 and U2, is then again worked in total, which is then done once more after a further rotation to the left by 150 and a further analog translational shift takes place as shown in Fig. 5.

Each grid line R1, R2 and R3 consists of one Large number of small pulse-like laser beam bullets together, of which 10,000 / s take place. Here the work material, in the present case steel of type 1.2311, evaporates and suctioned off, so that overall the removed area A ent stands, which is a height difference compared to the raised surface B. limit on the order of millimeters.

During the offset (rotation and translational displacement) of the grid N according to the representations of FIG. 3 to FIG. 4 and FIG. 4 to FIG. 5, the local position of the outlines U1 and U2 remains unchanged.

Claims (10)

1. A method for the partial change of surfaces of metallic or non-metallic bodies with a Q-switched continuously excited Nd: YAG laser, with beam expansion optionally integrated into the beam path, with a beam deflection mirror controlled by a computer and having a rotatably driven deflection mirror, and with a flat field lens for focusing the laser beam, which leads along at least one reference line predetermined by the computer over the surface to be changed, characterized in that the laser beam (L) within a surface part (A) to be changed has a boundary outline (U1, U2 ) along grid lines (R1, R2, R3) of a grid (N) forming reference lines, whereupon the entire grid (N) is shifted at least once by a certain amount while maintaining the relative position of the outline (U1, U2) and the surface part (A) along the rest erlinien (R1, R2, R3) of the Ra sterfeldes (N) again in total with the laser beam (L) is abge, with each time the exposure time and the amount of energy in the body surface a shot-like laser pulses so limited who that the evaporation of the material is effected while minimizing plasma formation. 2. The method according to claim 1, characterized in that that the grid (N) by a certain circumferential angle, the Angle of rotation.   3. The method according to claim 1 or claim 2, characterized characterized in that the grid (N) around a certain Distance, possibly in addition to a turn, transla is moved torically. 4. The method according to any one of claims 1 to 3, characterized characterized in that the grid (N) is a network-like structure has. 5. The method according to any one of claims 1 to 4, characterized characterized in that raster lines (R1, R2, R3) parallel to each other other run. 6. The method according to any one of claims 1 to 5, characterized characterized in that the grid lines (R1, R2, R3) are straight are. 7. The method according to any one of claims 1 to 6, characterized characterized in that the predetermined offset, such as angle of rotation or translational offset, depending on the be working material is selected. 8. The method according to any one of claims 1 to 7, characterized characterized in that the parallel spacing (p) of the grid lines (R1, R2, R3) from each other depending on the situation delenden material is selected. 9. The method according to any one of claims 1 to 8, characterized characterized in that the angle of rotation when machining Type 1.2311 steel is approx. 15 °.   10. The method according to any one of claims 1 to 9, characterized characterized in that when machining steel of the type 1.2311 the parallel distance (p) of the grid lines (R1, R2, R3) is approximately 50 µm.