WO2011154379A1

WO2011154379A1 - Laser cutting system

Info

Publication number: WO2011154379A1
Application number: PCT/EP2011/059337
Authority: WO
Inventors: Stephan Geiger; Ludger Müllers
Original assignee: Rofin-Baasel Lasertech Gmbh & Co. Kg
Priority date: 2010-06-07
Filing date: 2011-06-07
Publication date: 2011-12-15
Also published as: TW201210730A

Abstract

A laser cutting system (10) includes a laser device providing a collimated laser beam,a multiple-axis laser scanner (16) causing the laser beam (L) to move along a path(P)within a working area and a gas-assisted nozzle (18) having a lens (39) and a nozzle orifice (42) wherein said nozzle orifice size is greater than said working area.

Description

Laser Cutting System

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates generally to laser cutting of materials and, more particularly, to a laser cutting system utilizing a multiple-axis indexing motion system, along with a multiple-axis scanner and a gas-assisted nozzle, to produce very accurate hole patterns on an article.

Discussion

In the mass production of thin wall metallic articles, where a large quantity of repetitive features must be cut out in a specified pattern on a flat or curved surface, a laser cutting machine having a multiple-axis motion system is one method often utilized. The motion system moves the focused spot of the laser beam over the stationary article and traces the hole pattern (for example an array of circular holes) while melting the metal away to form the arrangement of holes.

It is further known to augment this process by employing a jet of assist gas to blow away the molten material to assure that it is removed from the cut (also known as the kerf) before it resolidifies. The assist gas may include oxygen or other gases which react with the material to assist in the removal of the molten material. Due to the very small hole diameters (sub-millimeter, for example) , and the large number of holes per pattern (in the hundreds, for example) associated with a hole perforation application (such as might be required for generation of speaker or microphone interfaces), a large amount of process time per pattern may be incurred when utilizing the known process described above. This is due to the relatively large mass that must be moved at high speeds and accelerations to accomplish each hole feature in the pattern. In a high-speed production application, the large process time required to generate each hole pattern on an article becomes a significant factor in the economic decision-making process. The motion system as described above can cut material in a circular mo^¬ tion approximately 150-170 milliseconds (ms) per hole.

Another known approach used for cutting holes with a laser includes the use of a boring head with a trepanning feature. In such an example, the boring head includes dual rotating optical wedges causing the laser beam to rotate. A boring head system can cut material in a circular motion in approximately 75 - 100 milliseconds (ms) per hole.

For a conventional laser cutting process, a collimated laser beam passes through the center of a focusing lens, which im- ages the laser beam to a very small spot on or near the ar^¬ ticle surface. Just above the surface of the article a coaxial nozzle is positioned through which the focused laser beam passes. In the zone between the focus lens and the nozzle tip, a cover slide optic provides a sealing surface to protect the lens from the process gases and spatter. During the cutting, pressurized assist gas fills the volume between the cover slide and the nozzle outlet port (typically 0.5 to 1 mm in diameter) . In this way, a high flow concentrated stream of gas assists the laser cutting process by blowing through the hole of the article, or also known as the kerf. Use of a gas- assisted nozzle is necessary when using a laser to cut metals since the gas is needed to eject the molten metal created by interaction of the intense laser beam overcoming surface tension in the narrow kerf and leading to a precise, sharp and clean cut material edge. There are two conventional beam delivery processes relevant to the background of this invention. First, as described above, a laser cutting system which incorporates a focusing lens and a gas-assisted nozzle to produce the cut. Second, a laser process which produces a contour of a collimated beam on the surface of an article with use of a multi-axis scanner or also known as a galvo (short for the word galvanometer) . Scanners are typically used for marking, ablating, or other laser processes. However, a scanner has not been used for cutting metals since the scanning field of view required for a scanned beam exceeds the gas-assisted nozzle orifice.

It is therefore an object of the invention to provide an ex^¬ tremely fast laser cutting system able to cut or bore metallic articles having a pattern of multiple holes spaced on an ar- ticle surface. In addition to speed, another object of the present invention relates to providing a very high quality cut or bore.

SUMMARY OF THE INVENTION

A laser cutting system and method including a laser device providing a collimated laser beam. The laser beam is projected into a multiple-axis laser scanner causing the laser beam to move along a contour or cutting path within a working area. The laser beam is focused by a lens and the focused laser beam is projected into a gas-assisted nozzle having a nozzle ori- fice wherein said nozzle orifice size is greater than said working area. The laser beam is projecting onto or near an article surface at sufficient energy to melt the article ma^¬ terial while the gas is sent out of the nozzle orifice onto the article coincident with the shaped laser beam to cause the melted material to be removed from a predetermined kerf there^¬ by formed in the article.

Basic idea of the present invention is to combine two differ^¬ ent techniques when producing a lot of very small openings at precise determined positions into a workpiece by cutting the workpiece along narrow closed paths. The precise positioning of the laser cutting head above the workpiece at different positions is carried out with conventional linear positioning devices having a relatively high inertial mass whereas the movement of the laser beam during the cutting of the workpiece is done without moving the cutting head but only by a fast movement of the laser beam effected by a fast multiple-axis scanner within the stopped cutting head. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which:

FIGS. 1-3 show a laser cutting system; FIG. 4 shows a metallic article having a varying surface with a cut or bore extending therethrough;

FIG. 5 is a perspective view of a scanner or galvo for use in the laser cutting system;

FIG. 6 is a simplified sectioned side view of a nozzle for use in the laser cutting system; and

FIG. 7 is diagram showing the cutting path of the laser cutting system when cutting a circular bore through an article; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to FIGS. 1 - 3 of the drawings which depict preferred embodiments of the invention comprising a laser cutting system for cutting or drilling metallic ar- tides. Although this embodiment is disclosed for use with drilling metals, it should be realized that this embodiment and other embodiments of the invention can also be used in connection with cutting or perforating other materials besides just metallic materials.

A laser cutting system or laser cutting head is shown generally at 10 in FIGS. 1-3. The laser cutting system includes a beam of light provided by a laser through fiber-optic cable (hereinafter laser beam) 12, a collimator 14, a scanner (or as described above, also known as a galvo) 16 and a gas-assisted nozzle 18. In addition, the laser cutting system 10 includes a xy stage 20 having a rotary 22 mounted thereto and a z stage 24 all mounted to an outer surface of a fixture table 26. The xy stage 20 is provided for moving the article in both the x and y direction. The z stage 24 is provided with height sens^¬ ing in order to move up and down along the z-axis to maintain a constant distance between a focus lens and the surface of the article being cut. The laser beam 12 is preferred to be a fiber delivered beam with appropriate beam quality for cutting but it should be appreciated that other types of lasers may be utilized provided the appropriate intensity is provided in order to melt the article.

Also shown in FIGS. 1 - 3 a table 28 is leaned at a predeter^¬ mined angle against and fixed to the rotary 22. The article or articles 30, as best shown in FIGS. 2 and 3, to be cut or drilled are arranged on the table 28. The table 28 is fixed to the rotary 22 at an appropriate angle to the laser beam 12 depending on the varying surface of the article 30 and the pattern of holes to be cut or drilled on the article 30. The table 28 is rotatingly mounted to the rotary 22 such that during production cutting, the rotary 22 can be rotated, along with the xy stage 20 and the z stage 24, to provide for an appropriate amount of indexing of the articles 30. Again the indexing is determined based on the pattern of holes and the most efficient and effective manner of cutting the article 30 in a high-speed manner. The rotary 22, xy stage 20, and z stage 24 are all controlled by a preprogrammed production controller .

FIG. 3 shows the laser cutting system 10 having two scanners 16 and nozzle subassemblies 18 mounted into one fixture table not shown in FIG. 3. In this configuration, the laser cutting system 10 can be used in parallel with another system to cut multiple articles 30 at once including where the articles 30 may have varying patterns to be cut. Alternatively, although not shown, another embodiment includes the use of one fiber^¬ optic beam 12 having sufficient energy to be split into more man one beam and thereafter, projected into more than one scanner 16 and nozzle subassembly 18.

FIG. 4 shows an article 30 to be cut or drilled to produce a high quality bore having a smooth transition from the top surface through to a bottom surface of the article. The ar^¬ ticle 30 shown in FIG. 6 shows a circular bore 32 and a par^¬ tially square bore 34 both formed on a varying curved surface 36 of the article 30. It should be appreciated that many dif- ferent configurations of the bore shape can be provided with the prevent invention. Further, although this FIG. 4 only shows two bores, as described above, the present invention works best when a plurality of such bores are required to be cut or drilled in one operation and in a very fast manner such as at 10 - 30 milliseconds (ms) . In addition, and also as described above, the use of the xy stage 20 and the z stage 24 permit the bores to be cut or drilled on many different types of article surfaces including a varying radius type shape as shown in FIG . 4.

The laser scanner 16, also known as the galvo, shown in FIG. 5 consists of two small mirrors 37a, 37b which are mounted on associated galvanometers 38a, 38b. Galvos 38a, b can be thought of as very high speed, current sensitive, limited rotation electrical motors. The amount of rotation (within the rota^¬ tional limits of the galvo) is determined by the amount of current applied with the direction of the limited rotation controlled by the polarity of the current applied. Galvanome^¬ ters used with lasers comprise a rotatably arranged shaft to which the mirrors 37a, b are fixed, wherein the shaft is rota- tionally driven by a motor to spatially vary the beam trajec^¬ tory of a laser beam L impinging upon the mirrors 34, 36. An arrangement of two such galvanometers in series enables a two- dimensional deflection of the laser beam L. The laser beam L first encounters the x (horizontal) mirror 37a. This deflects the laser beam L at an angle to its line of travel and upwards onto the y mirror 37b. The deflected laser beam L passes a focusing lens 39 and is focused on the article 30. When the angle of the mirrors 37a, b is varied, the focused laser beam L moves along a path p over the stationary article 30. In other words: The center line of the laser beam moves along a trajec- tory or path defined by the variation of the angle of the mirrors 37a, b. As such, when the angle of each mirror 37a, b is changed, a different beam trajectory can be created. When moving along a closed path or trajectory, an opening is produced in the article. Such a two-dimensional, 2D- or two-axis scan system provided by Scanlab such as their hurrySCAN II product has been found to provide appropriate control.

In a further improvement a 3D- or three-axis scan system can be provided by additionally moving the focusing lens 39 in the direction of the arrows 53. In this case a shaping of the wall of the kerf is possible. In this way a conical side wall of the opening can be achieved which is inclined to the surface normal of the article. The gas-assisted nozzle 18 is shown in FIG. 6. The nozzle 18 has a substantially cylindrical shaped cutting tip 40 having a substantially conical outer surface 41 with a small orifice 42 at the apex. The cutting tip 40 is mounted to the end of a substantially cylindrical shaped nozzle body 44. The nozzle body 44 includes the focusing lens 39 provided to focus the laser beam L onto the article 30 after such beam L exits the small orifice 42. The nozzle body 44 further includes an inlet 48 extending to a hollow body 50 for permitting assist gas G to be injected into the hollow body 50 of the nozzle 18. In the zone between the focusing lens 39 and the nozzle orifice 42, a cover slide optic 52 provides a sealing surface to pro- tect the lens 46 from the process gases and spatter. During the cutting, pressurized assist gas G fills the hollow body 50 between the cover slide 52 and the nozzle orifice 42 to pro^¬ vide a high flow concentrated stream of assist gas G which thereby assists the laser cutting process by blowing through the hole of the article 30, or also known as the kerf.

In operation, the article 30 (which may include more than one article at a time) is arranged on the table 28. The xy stage 20, rotary 22 and the z stage 24 move to a position in close proximity to the first hole or bore to be cut. The collimated laser beam L is projected into the galvo where each mirror 34, 36 is rotating at a predetermined angle to the laser beam L such that a predetermined beam path is generated by the move^¬ ment of the mirror. The laser beam L is projected into a gas- assisted nozzle having a nozzle orifice 42 including a prede^¬ termined shape and size. The shape and size of the gas- assisted nozzle are important to permit the moving laser beam L to project through the nozzle orifice 42 while the appropri^¬ ate amount of assist gas G is permitted to exit the nozzle orifice 42. In other words: The shape and size of the nozzle orifice 42 is adapted to the effective angular scanning field or the working area of the laser beam L or vice versa. In FIG. 6 a laser beams L is shown which is deflected at a maximum possible angle a from a center axis 49. The working area of the laser beam L corresponds to an effective scan area which is determined by the diameter of the nozzle orifice 42, which is normally smaller than the whole scan area which could be covered by movement of the galvo mirrors 34, 36. As described above, it is important to permit the right amount of assist gas G to exit the nozzle orifice 42 proximate the beam shape in order to provide the correct amount of ejection of melted material.

FIG. 7 shows a diagram of the cutting path P of the laser beam L after exiting the nozzle orifice 42 and when cutting a shape 54 through the article 30. The opening or shape 54 to be cut or drilled can be any number of different shapes depending on, among other factors, the two-axis galvo arrangement and the nozzle orifice shape and size. More specifically, by varying the angle of the rotating galvo mirrors 37a, b, many different shapes can be cut or drilled into the article 30. In this embodiment, a closed circular path P is shown. As shown, the laser beam L first touches the article 30 inside of the shape 54 to be cut. Thereafter, by varying the angle of the galvo mirrors 37a, b, the laser beam L moves to the cutting edge of the shape 54 to cut the material in a rotational-like manner around the cutting edge of the shape 54. With use of the low mass, high-speed galvo mirrors 37a, b of the galvo, the accele^¬ rations and velocities to produce the bores are much higher than could be achieved through the conventional process, and hence lead to significant reduction in time per hole laser processing. Again, as provided above, the present invention works best when a plurality of such bores are required to be cut or drilled and in a very fast manner such as at 10 - 30 milliseconds (ms) . The method of cutting an article using the laser cutting sys^¬ tem according to the invention includes: (1) projecting a collimated laser beam through a two-axis scanning galvanometer having two rotatable mirrors attached to galvanometers to obtain a shaped laser beam; (2) projecting said rotating laser beam through a third optical lens; (3) projecting said rotat^¬ ing laser beam from said third optical lens through a nozzle orifice of a nozzle wherein the orifice size is a predeter^¬ mined amount greater than the working field of the laser beam; (4) injecting a gas into said nozzle proximate said nozzle orifice; (5) projecting said shaped laser beam onto an article surface at sufficient energy to melt the article material; and (6) directing said gas out of said nozzle orifice onto the article coincident with the shaped laser beam to cause the melted material to be removed from a kerf formed in the ar^¬ ticle . Aspects of the invention that minimize hole processing time include: 1) the ability to pierce through the material while moving the xy stage, rotary and the z stage (on the fly cut^¬ ting) ; 2) the ability of the workstation to support multiple processing laser cutting systems whereby multiple laser beams could produce the same hole pattern in parallel on multiple articles; 3) the ability to support multiple fiber-optic input laser beams; and 4) alternately the ability to support energy sharing configuration with a single fiber-optic input beam and multiple output beams.

The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifi- cations and variations can be made therein without departing from the true spirit and fair scope of the invention as de^¬ fined by the following claims. Accordingly it is of course not necessary to orient the center axis of the laser cutting head in a vertical direction or in a direction normal to the surface of the article. If more than one laser cutting heads are used, it is also possible to orient their center axes in dif- ferent directions.

Claims

Claims What Is Claimed is:

1. A laser cutting system including:

a laser device providing a collimated laser beam;

a multiple-axis laser scanner causing the laser beam to move along a path within a working area; and

a gas-assisted nozzle having a lens and a nozzle orifice wherein said nozzle orifice size is greater than said working area .

2. A method of laser cutting comprising the steps of:

projecting a collimated laser beam through a multiple-axis scanning galvanometer having two rotatable mirrors attached to galvanometers to obtain a laser beam moving along a path within a working area;

projecting said moving laser beam through a lens;

projecting said moving laser beam from said lens through a nozzle orifice of a nozzle wherein the orifice size is a greater than the working area;

injecting a gas into said nozzle proximate said nozzle orifice;

projecting said laser beam onto an article surface at suf^¬ ficient energy to melt the article material; and

directing said gas out of said nozzle orifice onto the ar^¬ ticle coincident with the shaped laser beam to cause the melted material to be removed from a kerf formed in the ar^¬ ticle .