Patent Application
20240424608
The present invention relates to a laser machining method and device, in particular for forming zero and/or predetermined taper machined cuts, cutouts and/or holes in a workpiece.
Machining a workpiece of hard and/or brittle material such as metals, like stainless steel, light metals such as titanium, magnesium and aluminum, or ceramic, cermet, tungsten carbide, PCD diamond, CVD diamond, PCBN, and the like, with or without coating is known to be difficult. For example, drilling in indexable inserts made of superhard material an insert hole arrangement comprising a hole with or without one or two countersinks for permitting the insert to be secured to a toolholder is a challenge. To process such workpieces laser machining methods and devices are generally known but less known for drilling zero taper holes in indexable inserts by using a scanner unit.
It is known to use drill or cutting lasers for making holes, including high precision bore holes, or cuts in these workpieces. Laser drilling or cutting is advantageous because it is fast and highly flexible and can drill through bore holes as well as bore holes with complex shapes or can make high precision cuts. Compared to customary drilling methods with twist drills, in the case of hard material and/or small diameters of the hole to be machined laser drilling or cutting is cheaper due to contact-free machining avoiding wear and tear of the machining tools.
In laser machining, a laser beam generation device is used in conjunction with an optical system to direct the laser beam onto a workpiece to be machined. The impingement of the laser beam on the workpiece locally melts, vaporizes, and/or ablates workpiece material to produce or extend a hole or cut in the workpiece. The location of the impingement point on the workpiece may be controlled by moving one or both of the laser beam and the workpiece relative to one another to thereby control the geometry of the hole or cut. It is known that laser machining of holes produces tapered holes, for which an entry diameter is greater than a ground diameter of the hole or even an outlet diameter in the case of a through hole.
High precision and deep laser drilling of holes can be performed by trepanning or helical drilling. Trepanning or helical drilling uses a special optic allowing to change an incident angle of the laser beam and to move the laser beam along a rotative path with high speed. The workpiece remains stationary. Both of these processes require a complex optical setup to control a taper angle of the hole. Therefore, laser machining holes with no taper angle by these methods includes specific and complex equipment and methods which can only be used for hole drilling but not for other laser machining processes. These well-known methods are generally implemented on dedicated devices and cannot be implemented on conventional laser machine devices using a scanner unit.
Another approach to avoid undefined or unselected tapered edges is to move the workpiece physically, in particular moving a holding or clamping device in which the workpiece is supported while keeping the laser beam at the same incident angle. This method needs high precision for translational and/or rotational movements of the workpiece by the laser machining device about usually 4 or even 5 axes and a sophisticated control software to achieve a zero tapered or a defined tapered edge. Furthermore, additionally, or as alternative the laser system, in particular the scanner unit, can be moved relative to the workpiece.
From US2014263212 laser systems and methods are known for machining features in a workpiece. In particular, a beam coordination is described to control taper of cuts or kerfs made in the workpiece. To generate desirable taper characteristics of a side wall of the kerf by a focused laser beam propagated along a beam axis, the angle of incidence and azimuth of the beam axis can be moved relative to the workpiece. During the cutting process the workpiece and the beam axis are both in relative motion while the laser beam is actively machining the workpiece, in particular irradiates the workpiece along a cutting path. According to this document, the machined spot is moved off center using two linear axes, which leads to a defined incidence angle of the beam on the machined surface. The machining speed is slow due to the slower speed of these axes compared to the speed of optical axes, and due to the need to move the machined workpiece over long distances in order to achieve the desired incidence angle.
From US20120132629 a method and device for reducing taper in a kerf generated by laser processing or scribing is known. The method is based on strategic laser positioning for reducing taper of scribes or cuts. Accordingly, the method comprises aiming the laser beam onto the surface of the substrate in a first cutting direction and tilting the laser beam at a beam tilt angle, further aiming the laser beam at the surface of the substrate in a second direction perpendicular to the first cutting direction and tilting the laser beam at the tilt angle. The cut is formed by applying the laser beam to the surface of the substrate while aiming the laser beam and cutting in the first cutting direction and applying the laser beam to the surface of the substrate while aiming the laser beam in the second direction and cutting in one of the first cutting direction and the second cutting direction opposite the first cutting direction. The described method requires a specific device for tilting the beam which means lost in flexibility and reduced machining speed.
Therefore, an object of the invention is to provide a laser machining method and device, with which defined cutouts, large and deep bores and/or cuts can be produced with zero and/or predetermined taper angle, in particular negative taper angle, in high quality components. The laser machining device can use a scanner unit, such that the machining capabilities and throughputs are high. Another object is to provide a laser machining method and device eliminating post machining and cleaning operations, improving repeatability, reliability, velocity, and accuracy, and therefore reducing costs of manufacturing. Furthermore such laser machining method provides process flexibility, high cutting rates and non-contact operation.
According to an aspect of the invention, there is provided a method for laser machining a defined cutout in a workpiece, comprising:
According to the invention the method uses a combination of at least two different machining strategies. With a first machining strategy a laser beam is shone with an incidence angle close to 0°, i.e. normal to the surface of the workpiece to be machined, i.e. to a top surface of the defined machining volume, resulting in a high material removal rate, however resulting in a tapered characteristic. With a second strategy the laser beam is shone with a great incidence angle, typically >80°. With this high incidence angle the material removal rate is lower than with the first strategy. However, a high surface quality is achievable and undesired taper angles resulting from the first strategy can be removed.
Furthermore, the method addresses the problems of taper angles resulting from laser machining using a scanning unit and of decreasing specific material removal rate by forming deep cutouts. By using multiple steps in the depthwise direction, the method allows controlling the scanned cutout characteristic for full material removal by repeating scans or repeating passes of the laser beam.
Achievable taper angles of cutting flanks using a scanning unit are typically >5°. This is due to the reduction in laser intensity when projecting onto the inclined ablation flank, as a result of which ablation stops at a critical angle. Unlike conventional laser drilling methods using a scanner unit, the method described herein can enable formation of cutouts having a predetermined taper angle and quality parameters such as entry geometry, ground, or outlet geometry, contour accuracy, and surface characteristics. With the proposed laser machining method, positively conical, i.e. positive tapered, cylindrical, and also negative conical, i.e. negative tapered, holes as well as bore funnels, hour-shaped bores or bores of Laval-nozzle shape can be created.
The laser machining method is configured preferably to laser machine a workpiece made of hard, superhard and/or brittle material for example such used for indexable inserts or including a multilayered substrate comprising a plurality of layers of different material and/or different heights.
According to an embodiment, the machined cutout or formation in the workpiece is a blind hole, a through hole, a through hole with a countersink or chamfer at one or both ends of the through hole or a cutout with constant or varying cross section. One example of such cutout is a through hole with or without countersinks as an insert hole arrangement for permitting the insert to be secured to a toolholder.
The laser beam used for laser machining is generated under laser process parameters by means of a laser system with a scanner unit as an optical system. The scanner unit can be configured as a movable unit. The laser beam can pass through a set of optics prior to reaching the scanner unit to shape it. The laser beam may be prolongated through the scanner unit along the scanner axis. The laser beam is focused onto a surface of the workpiece typically by means of a focusing lens, arranged between the scanner unit and the workpiece. The scanner unit is configured to move the focal point of the laser beam in one plane, in particular in 2D, or preferably in 3D and/or scanned across over a desired area of the workpiece. In this case the laser beam is refracted, diffracted and/or reflected by optical means of the scanner unit to realize its movement on a surface of the workpiece. The scanner unit may be configured to provide a largely free, three-dimensional orientation of the impingement point and/or focal point of the laser beam onto the workpiece and hence on the machining space.
Furthermore, the method includes that the workpiece is supported and held in the holder and is positionable relative to the scanner axis. Additionally or alternatively to the controlled movement of the laser beam by means of the scanner unit, the holder can be configured for moving the supported workpiece relative to the scanner axis about at least one rotary axis and/or along at least one translational axis in a controlled manner. The laser beam is focused on a spot, and therefore a relative motion between the laser beam and the workpiece to be machined is needed to process the workpiece. The location of the laser beam focal point at the workpiece may be controlled by moving one or both of the laser beam and the workpiece relative to one another. Since the movement of the laser beam by means of the movable scanner unit is faster than the movement of the holder by means of device axes, the relative motion during removal of material is performed preferably by controlled movement of the laser beam via the scanner unit.
Between machining steps, the workpiece can be moved into a newly defined relative position by drives of the laser machining device with motion in translational and/or rotational directions. Alternatively, a hybrid movement can be used with the laser beam scanning across the workpiece while moving the workpiece in sequence.
According to an embodiment, the workpiece is moved in a controlled manner about multiple axes of a laser machining device into the determined relative positions such as a rotary A-axis and B-axis and a translational Z-axis. The scanner unit includes preferably three optical axes, X-, Y, and Z-axis.
The laser machining method comprises step a) to define a machining volume of the workpiece. The machining volume may be determined by one or more properties such as the surface area, in particular an entry perimeter, a bottom or ground or outlet perimeter and the depth or height or by a lateral surface from entry perimeter to bottom or outlet perimeter. Hereinafter, the surface area characterizes a surface portion of the workpiece to be machined limited by a perimeter having a circle, oval, ellipse, rectangle, or polygon or any other closed form. The machining volume might have a cylindrical form or a cone form or any other suitable three-dimensional form. Particularly, the machining volume might have a varying perimeter value and/or form over the depth. The surface area can be seen as the surface portion which will be machined at least partially.
According to the invention, a first relative position between the machining volume and the scanner axis is determined. Preferably, the scanner axis in this step b) is orientated approximate perpendicular, i.e. normal to the surface of the machining volume. By relative motion the workpiece and/or the scanner axis are brought in the determined first relative position. Preferably, the workpiece is moved into the first relative position by controlled activation of the device axes.
In step c) of the laser machining method the laser beam is directed along the scanner axis approximate perpendicular to the surface area onto the workpiece within this surface area. One or both of the laser beam and the workpiece are moved relative to one another causing the laser beam moving along a first cutting path. In other words, the laser beam is scanned along the first cutting path within the surface area. The first cutting path can be configured so that the surface portion to be machined can be traversed by the laser beam in different ways by appropriate control of the relative motion. For instance, the laser beam can be scanned along a spiral shaped curve, or a path along regularly spaced parallel lines. Alternatively, the laser beam may be scanned along a curve or a series of parallel curves or series of concentric circles with a specific offset between adjacent paths. Typically, when machining a hole, the surface area is limited by a perimeter which is a closed curve and in the case of the machining of a cylindrical hole such perimeter curve is circular. According to the invention, the form of this curve can as well include irregular shapes in the case of a free formed perimeter. Other scan or cutting paths are also possible for this removal. Depending on the defined cutout and the strategy of machining a central portion of the surface area could remain unmachined.
The first cutting path and/or a second cutting path may be defined by its shape, by starting point and end point as well as by a direction in which the laser beam is scanned across the surface portion. Varying the cutting path enables optimizing the specific material removal rate and ensures high-speed machining.
For machining the machining volume as well as machining further volumes the laser beam may be scanned several times across the surface area of the cutout using various scanning movements, such that the machining volume and any further removable machining volume can be removed layerwise. Each subsequent scan of the laser beam could have an axial offset between the scans of typically 0.1 to 25 μm, depending on material removal. Each subsequent scan of the laser beam might have an additional lateral offset. In other words, the surface portion to be scanned by a subsequent scan is smaller than the preceding one. The lateral offset depends on the geometry properties of the formation to be machined. By controlling scan velocity, laser power and other parameters such as starting point and/or end point of the cutting path, the depth of material removal in any one scan can be controlled.
Resulting of step d) the cutout in the machining volume has a first taper characteristic. The first taper characteristic is influenced by the material properties, machining parameters, and the machining volume and is typically >5°. It can be determined experimentally. It can be beneficial to the overall machining duration to take this determinable taper characteristic in account when defining the machining volume, a so-called first machining volume.
The laser machining method according to the invention further comprises step e) defining a second machining volume comprising the first side wall with the first taper characteristic and stretching up to a second side wall with a predetermined characteristic. In the case that the first cutout is a hole, the second machining volume may have approximately a ring shape. The predetermined characteristic may include positive, zero and negative taper characteristic. Therefore, an entry diameter of the defined cutout to be machined, configured as a hole could be greater, equal, or smaller as a ground diameter or even an outlet diameter in the case of a through hole.
The defined second material volume is removed by relative positioning of the laser beam and/or the workpiece in a determined second relative position. Therefore, the laser beam may be directed under a predetermined tilt angle onto the second machining volume and irradiates this second machining volume while scanning the laser beam across thereof. Therefore, the laser beam is focused under laser process parameters at a surface portion of the second material volume to remove at least a portion of the second material volume to form the defined cutout with the predetermined characteristic. Machining of the second machining volume may be performed by successively removing layers of material by multiple scans of the laser beam with an axial and/or radial offset between scans.
By repeating the removal of the machining volume with the laser beam extending in the first direction perpendicular to the surface of the workpiece and then removing the second material volume with the laser beam orientated in another orientation as the first direction, in particular with a predetermined tilt angle, one can optimize the entire machining speed and ensures the predetermined characteristic of the side wall of the defined cutout.
Preferably, the predetermined tilt angle is greater than the radial laser beam divergence angle of the focused laser beam. The tilt angle depends on processing parameters and material properties and can be determined by experiments. Typically, the tilt angle is between 3 to 15°, preferably between 5° and 10°.
According to one embodiment, the laser machining method comprises that in step e) the second machining volume is divided into m sections and m is being m≥1. Preferably m is between 1 and 4. In step f) a relative position between one of the m sections and the scanner axis is determined and said section and/or the scanner axis is positioned in this relative position and that in step g) the scanner axis is oriented under the predetermined beam tilt angle onto said section, irradiating said section by scanning the laser beam along the second cutting path and removing material from said section to form the second side wall of said section. Therefore, each of these sections is machined until the predetermined characteristic of this section is achieved before machining a next section. In this strategy, the relative position between the scanner axis and the selected section stays at the previously determined relative position until the second side wall of this section has turned into the predetermined form. Then the relative position is newly determined and by relative motion of the workpiece and/or the scanner axis another of the m sections is positioned in the newly determined relative position to be machined. This procedure is repeated until each of the m sections is machined, and the defined cutout with the predetermined characteristic is finished.
Dividing the second machining volume into m sections enables processing each of the m sections separately until the second machining volume is removed which may result in a further optimized machining speed and quality. By selecting an appropriate number of sections, each of the section can be machined under a suitable tilt angle.
The selected and positioned section of the m sections is machined by scanning the laser beam along the second cutting path in one or multiple scans with a second specific offset. The second cutting path may comprise a number of laser lines with lateral offset between the lines and/or can comprise a second cutting pattern. Preferably, the second cutting path or pattern may be generated by offsetting the perimeter curve, or a part of the perimeter curve, multiple times with a fixed offset between each curve, wherein the surface of the to-be removed machining volume is scanned. Typically, when machining a hole, such path is made of a section of the hole perimeter, repeated, and offset in concentric manner.
According to another embodiment of the laser machining method the machining volume defined in step a) is subdivided into n layers, each layer has a surface area, i.e. an individual surface area limited by an individual perimeter and a thickness and with n being n≥1. Each of the n layers defines an individual machining volume to be removed by the two-step machining strategy described. The value of n, the number of the subdivisional layers, depends on the depth or height of the machining volume to be removed. Preferably, n lies between 2 and 10. The subdivision in n layers which are subsequently machined is advantageous in regard of material removal rate and thus machining time and of the side wall characteristic of the cutout.
Each of the defined first machining volumes are machined successively such that laser machining parameters can be adjusted individually to each of the n layers. Alternatively, each of the n layers can be processed under the same laser machining parameters. Adjustable process parameters for each of the n layers may ensure optimized machining through each of the n layers, in particular in the case of multilayered materials. The material of the first machining volume is removable in a sequence of machining steps from a top surface of the workpiece downwards.
The thickness of each of the n layer to be machined may be selected such to overcome the limitation on material removal rate which decreases as a function of depth into the workpiece. The thickness of each of the n layers may be typically between 0.1 and 2 mm depending on material properties and/or geometry properties of the defined cutout.
In the case the workpiece is a multilayered substrate, the thickness of at least one, or each of the n layers can correspond to the thickness of the at least one or each individual material layer. Alternatively, the thickness of at least one of the n layers can be determined by the change of material processed. In such case the thickness of the layer is determined by detecting the change of material to be processed, for example by an external inline or offline process control system. By selecting a suitable thickness for each of the n layers and/or by adjusting laser machining parameters according to detectable change of material the material removal rate can be kept maximized throughout the machining via optimizing the processing parameters for machining each material.
With the laser machining method the laser machining process can be optimized in regard to cycle time, throughput, flexibility, and higher process quality. In particular, scanning the laser beam across the workpiece along the first cutting path while directed in the first direction about perpendicular or normal to the surface area results in a specific high removal rate. However, a potentially undesired taper angle results, which can be adjusted by machining the second machining volume. Preferably, machining the first machining volume of the defined n layer and removing the second machining volume of each of the n layers before machining another of the n layers keeps the material removal rate approximately constant and at a high level. By removing the material of the taper it does not contribute to absorption of laser energy during machining deeper structures. Therefore, decreasing material removal rates due to scanning further downward in the same direction is avoided. Furthermore, with this method thermal effects can be reduced, improving the quality and repeatability of the machined cutouts.
In one embodiment, the machining of the defined cutout is performed from a top side and subsequently from a bottom side of the defined cutout, the cutouts from both sides join to form a single through cutout. This strategy of machining from both sides enables forming a cutout of curved and tapered and circular or freely formed wall structures. By this the machining velocity can be optimized due to further reduction of the overall depth and/or by adapting the first cutting path for each of the n layers.
A further step at the end of processing defined cutout can be performed for finishing the second side wall of the cutout by laser machining. This finishing step improves the overall quality of the machined surface over the entire cutout depth. According to an embodiment of the laser machining method, this finishing step includes subdividing the surface to be machined into multiple sectors and performing laser machining with a scanner axis orientated in a defined second tilt angle. Alternatively, the laser machining can be performed with the scanner axis orientated in another definable tilt angle.
Furthermore, the invention relates to a laser machining device for laser machining a defined cutout in a workpiece with the method according to the invention, comprising a laser system with a scanning unit used to move the laser beam in at least two coordinate directions and configured to generate a laser beam along a scanner axis and to direct the laser beam onto the workpiece approximate perpendicular to a surface area and to direct the laser beam onto the workpiece in a second cutting direction, a holder for supporting and holding the workpiece movable about at least one rotary axis and/or along at least one translational axis by means of drive units of the laser machining device, and at least one controller configured to scan the laser beam along a first cutting path and along a second cutting path and to control the drive units to move the workpiece to machine the defined cutout as well as to determine n layers successively machined by scanning the laser beam along the first cutting path and m sections machined by scanning the laser beam along the second cutting path. The controller can comprise a suitable processing unit for settings for controlling system hardware and processes, software and/or memory for operation of the laser machining device to perform the laser machining method.
The laser machining device may comprise one controller for controlled moving of mechanical axes related to the workpiece and optical axes related to the scanner unit. Alternatively, the laser machining device may comprise one controller configured for moving the workpiece about mechanical axes and another controller provided for moving optical axes of the scanner unit such that the laser beam is orientated towards the workpiece and scanned over a surface of the workpiece. Furthermore, the scanner unit of the laser machining device may be configured to be moved along and/or about mechanical axes while the workpiece is kept positioned during processing. Alternatively, the scanner unit may be kept positioned while the workpiece is moved along and/or about mechanical axes. Even furthermore, mechanical axes of the laser machining device may be provided to move the workpiece as well as the scanner unit for laser processing the workpiece according to the inventive method.
For a more complete understanding of the invention and the advantages thereof, exemplary embodiments of the invention are explained in more detail in the following description with reference to the accompanying figures, in which like reference characters designate like parts and in which:
According to one embodiment the motion stages 12 are configured for moving the workpiece. The motion stages 12 related to the holder 11 or chuck can be provided with rotary axes known as A-axis and/or B-axis and/or may comprise linear axis to move the workpiece into predetermined positions and/or to move the workpiece during laser machining. Any number of known designs can be used for motion stages 12 such that translational and/or rotational movements are included in laser machining device 1.
Additionally to the arrangement described in
Another option is that the holder 11 is mounted on a fixed base and the scanner unit 4 and/or the focusing optics 5 is movable by means of corresponding motion stages 13 (not shown), controlled by the controller 6.
According to
Preferably, the controller 6 is adapted to control the motion stages 12 and/or the other motion stages 13 in order to provide relative motion between the scanner unit 4 and the workpiece 10 and to control movement of the axes of the scanner unit 4 in order to control movement of the laser beam. According to another embodiment the control for the relative positioning of the scanner unit 4 and the workpiece 10 and the control of the movement of the axes of the scanner unit 4 are separated: the further controller 7 may be provided to control the axes of the scanner unit 4 in order to control movement of the laser beam, while the controller 6 controls only the motion stages 12 and/or motion stages 13.
As shown in
According to an example shown in
In the case that a through hole is machined in the workpiece 10 the laser beam 20 does not have to be scanned over the entire surface 21 of the machining volume to be removed, in order to have a faster machining process. A central portion can be kept which will be removed by falling out when the through hole is finished.
The second machining volume 26 can be removed by relative positioning the laser beam 20 and/or the workpiece 10 in a predetermined second relative position. The scanner axis 34 may be oriented under a predetermined tilt angle ß in order to machine the second machining volume 26 and irradiates the second machining volume 26 while scanning the laser beam 20 across thereof. After machining the first layer n1, a blind hole with zero taper results, as shown in
The method 100 further includes an operation 110 for defining the second machining volume 26 between the first side wall 24 formed in the operation 108 and the predetermined second side wall 27 corresponding at least partly to the side wall of the defined cutout to be machined. This operation 110 could include that the second machining volume 26 is virtually subdivided in m sections which could be machined subsequently.
Operation 112 includes determining a second relative position between the second machining volume 26 and the scanner axis 34 and rearranging the workpiece 10 and/or the scanner axis 34 in that second relative position. In operation 112 the laser beam 20 is directed under a predetermined tilt angle ß onto the second machining volume and laser process parameters could be adjusted based on the one or more properties of the method 100. In some embodiments the laser process parameters could include the laser power, a focal beam diameter, a focus height, a beam spot size, an offset of the laser beam 20 from precedent scans and/or a combination thereof.
The method 100 includes operation 114 in which at least a portion of the second machining volume 26 is removed under adjusted laser process parameters. According to method 100 each of the m sections of the second machining volume 26 are machined including rearrangement of the workpiece 10 and the scanner axis 34 such that optimal laser machining conditions are achieved for machining each of the sections. After the second machining volume 26 of the layer n1 is removed the method 100 includes repeating the operations 106 to 114 until the cutout of the workpiece 10 has reached the defined form. In one embodiment the method 100 further includes another operation 116 to finish the formed side walls of the cutout.
This invention is not limited to the embodiments described but may be varied in construction and detail.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23181014.4 | Jun 2023 | EP | regional |
