Patent Publication Number: US-2021170529-A1

Title: Apparatus for 3D Shaping of a Workpiece by a Liquid Jet Guided Laser Beam

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for three-dimensional (3D) shaping of a workpiece into a final part by material ablation. The material ablation is effected with a laser beam, preferably a pulsed laser beam, which is guided in a fluid jet onto the workpiece. The present invention relates further to a method for 3D shaping of a workpiece by material ablation with a laser beam coupled into a fluid jet. 
     BACKGROUND 
     A conventional apparatus for machining a workpiece with a laser beam that is coupled into a pressurized fluid jet is generally known. However, the “machining” of the workpiece with such a conventional apparatus is limited to through-cutting and -drilling. The machining process control of the apparatus is not sufficient to allow full 3D shaping of the workpiece into a final part. This is mainly due to the fact that the conventional apparatus at best knows, at which x-y-position of the workpiece the laser beam ablates material, but does not know the z-position at which material ablation occurs. As a consequence, the apparatus is also unable to determine how much material the laser beam actually ablates in z-direction (depth) of the workpiece. Therefore, the conventional apparatus cannot, for instance, precisely control a cutting depth or a drilling depth into the workpiece. 
     Conventional 3D shaping of a workpiece is either done by Additive Manufacturing (AM) or Subtractive Manufacturing (SM). While “AM” refers to a process which builds up a desired 3D shape of a final part by material deposition, typically layer-by-layer deposition, “SM” refers to a process which removes material from a workpiece (solid body), in order to obtain a desired 3D shape of a final part. For many practical applications SM is preferred over AM. This is, because many parts can be produced faster, more efficiently, and more economically with SM. 
     Further, laser SM, i.e. removing material from a workpiece with a laser beam, has the advantage that it can be combined with conventional machining techniques, e.g. milling, in order to achieve a more efficient overall shaping process. However, conventional laser SM is a relatively slow and rather imprecise process. 
     In view of the above, the present invention aims at improving conventional SM for producing parts with desired 3D shapes, particularly improving the process speed and precision. To this end, the invention intends to employ the advantages of an apparatus for machining a workpiece with a laser beam coupled into a fluid jet with SM. Accordingly, it is an object of the present invention to provide an apparatus and method for 3D shaping of a workpiece by material ablation with a laser beam that is guided by a fluid jet. In particular, the apparatus and method should be able to shape the workpiece into a final part having any desired 3D shape. The shaping process should be fast and accurate. Thereby, the apparatus and method of the invention should also make the SM process more efficient and economic than conventional SM. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are defined in the dependent claims. 
     In particular, the present invention proposes the use of a laser beam coupled into a fluid jet for 3D shaping of a workpiece by material ablation. The workpiece is shaped with the laser beam into a final part by removing material from the workpiece. In other words, the final part is obtained by SM. 
     A first aspect of the invention provides an apparatus for 3D shaping of a workpiece by material ablation with a laser beam, the apparatus comprising a machining unit configured to provide a pressurized fluid jet onto the workpiece and to couple the laser beam into the fluid jet towards the workpiece, a motion controller configured to set an x-y-z-position of the workpiece relative to the machining unit, a measuring unit configured to measure a z-position of the point of incidence of the pressurized fluid jet on the workpiece in the z-direction. 
     The motion controller allows moving the workpiece in three dimensions to effect the shaping of any 3D contours with the laser beam. The set x-y-z-position relates to a position of the workpiece in a predefined axis (coordinate) system with. respect to an original position (0-0-0-position). The x-y-z-position of the workpiece set by the motion controller may thereby be determined by the positioning of a movable machining surface, on which the workpiece is provided. The motion controller may further be able to move the workpiece along rotational directions (e.g. effect panning, tilting and rolling). The motion controller is preferably able to change the position of the workpiece with high speed and high accuracy. Thus, 3D shaping of the workpiece by material ablation is enabled in a speed and precision that does not exist today. Alternatively, the axis system moves the machining unit in all linear and rotary axes or in some of these axes. 
     During the 3D shaping process, the measuring unit functions as a depth sensor, and provides knowledge about the z-positon of the material ablation at any time and at any position, i.e. where fluid jet and laser beam impact on the workpiece. This z-position is usually different from the z-position of the material surface set by the motion controller. This z-position may change, for instance, if the fluid jet is moved along the workpiece surface or if the laser beam ablates material from the workpiece surface, i.e. machines into the workpiece. The latter moves the point of incidence deeper into the workpiece. One reason for setting also a z-position by the motion controller is to ensure a controlled shaping process. Preferably, the workpiece is positioned such that it is impinged by the fluid jet in a distance from the fluid jet creation point that is constantly within a determined range. Accordingly, the workpiece can always interact with the part of the fluid jet, which most efficiently guides the laser beam, even if more and more workpiece material is ablated from the workpiece in the z-direction. Notably, in this document the term “fluid jet” means the laminar fluid jet, able to guide a laser beam like a fiber. The fluid output by the apparatus forms a laminar fluid jet only over a certain length, and beyond that length the fluid jet becomes an unstable fluid flow that finally disperses into droplets. 
     In this document, “measuring” the z-position of the point of incidence of the fluid jet on the workpiece includes at least one active measurement of a physical quantity. For instance, it may include a measurement of a time difference between a time point of emitting waves from the measuring unit and a time point of receiving waves reflected from the workpiece by the measuring unit. As another example, it may include a measurement of a phase difference of different waves, if an interferometric principle is used. As another example, it may include an optical, electrical or capacitive measurement of a characteristic length of the fluid jet. “Measuring” the z-position does not merely mean estimating the z-position based on, for instance, some known dimensions of the apparatus, the workpiece and/or the final part. The measured z-position of the point of incidence of the fluid jet on the workpiece allows determining how much material the laser beam ablates in z-direction from the workpiece at a given x-y-position. This information is crucial for obtaining a full 3D shaping capability. The x-y-positions at which material ablation occur are derivable from the x-y-coordinates of the x-y-z-position set by the motion controller. Accordingly, the apparatus of the first aspect has full control and position information about the 3D shaping process of the workpiece. 
     Accordingly, the apparatus is advantageously configured to control the 3D shaping of the workpiece by material ablation based on the z-position of the point of incidence of the pressurized fluid jet on the workpiece. 
     In a preferred implementation form of the first aspect, the laser controller is configured to adjust the power or energy of the laser beam based on an x-y-z-position set by the motion controller and a z-position of the point of incidence of the pressurized fluid jet on the workpiece measured by the measuring unit. 
     Thus, a fast, precise, and fully controlled 3D shaping process of the workpiece is possible. 
     In a further preferred implementation form of the first aspect, the laser beam is pulsed, and the apparatus further comprises a laser controller configured to adjust individually the energy of each laser pulse based on an x-y-z-position set by the motion controller for that laser pulse and a z-position of the point of incidence of the pressurized fluid jet on the workpiece measured by the measuring unit before that laser pulse. 
     That means, the energy of each laser pulse can be individually adjusted by the apparatus to effect a certain amount of material ablation in the z-direction (depth) of the workpiece (at a given x-y-position of laser ablation). In particular, the ablation result of each laser pulse can be controlled in a fast and direct way. Consequently, a fast and precise 3D shaping process of the workpiece is possible. 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to determine an ablation result of each laser pulse at the z-position of the point of incidence of the pressurized fluid jet on the workpiece measured by the measuring unit after that laser pulse, and the laser controller is configured to adjust the energy of the next laser pulse based on the determined ablation result. 
     Thus, the apparatus gains knowledge about the amount of material that was ablated in z-direction with the last laser pulse, and can take this information into account when setting the energy for the next laser pulse. Two laser pulses may occur at different x-y-positions of the workpiece, in order to ablate a layer from the workpiece surface. Two laser pulses may, however, also occur at the same x-y-positon of the workpiece, in order to obtain a certain amount of material ablation or to correct an ablation result. Consequently, the apparatus is configured to control the ablation at each point on the workpiece, so that the 3D shaping of the workpiece can be carried out very accurately. 
     In a further preferred implementation form of the first aspect, the laser controller is configured to control the energy of each laser pulse by setting its width and/or amplitude and/or by setting a pulse rate and consequently a time delay between consecutive pulses and/or by executing a pulse burst. 
     Thus, the apparatus is provided with several means of controlling the laser beam ablation, which further improves the precision and efficiency of the 3D shaping process. 
     In a further preferred implementation form of the first aspect, the laser controller is configured to control the energy of each laser pulse such that it ablates in z-direction between 1-1000 μm depth of workpiece material at the x-y-z-position of the workpiece set by the motion controller for that laser pulse. 
     Thus, the apparatus is configured to set the ablation depth in z-direction individually at each x-y-position. Accordingly, the apparatus is configured to ablate one or more layers of workpiece material from the surface of the workpiece. Thereby, the ablated layers may have a uniform or non-uniform thickness between 1-1000 μm, preferentially 1-200 μm. 
     In a further preferred implementation form of the first aspect, the apparatus further comprises a laser source for generating the laser beam, the laser source including the laser controller and a fast switch, preferably a Q-switch, for modulating the laser pulses. 
     The laser source is included in the apparatus. The switch allows the apparatus to affect a fast modulation of the laser pulses, and thus to accurately and individually control their energy from 0 to 100%. Accordingly, a fast and precise 3D shaping process is supported. 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to measure the z-position of the point of incidence of the fluid jet on the workpiece within a time period between two subsequent laser pulses. 
     In this way, the measurement of the z-position carried out by the apparatus does not interfere with the material ablation induced by the laser beam pulses. The precision of the measurement of the z-position can consequently be increased. Controlling the 3D shaping process becomes easier as well. 
     In a further preferred implementation form of the first aspect, the motion controller is configured to step-wise or continuously change the x-y-z-position of the workpiece relative to the machining unit after each laser pulse. 
     Thus, the apparatus is able to pulse-wise ablate material at a determined x-y-position of the workpiece. As a consequence, a fully digital material ablation process is enabled. Layers or structures of material can be ablated from the workpiece surface. Ablated layers may cover the complete surface or only part of the surface. Thus, different regions of the workpiece surface may be ablated differently in the z-direction, thereby providing the ability to shape the workpiece in 3D. 
     In a further preferred implementation form of the first aspect, the motion controller is configured to accelerate or decelerate the changing of the x-y-z-position of the workpiece when moving the workpiece along a trajectory, and the laser controller is configured to increase or decrease a laser pulse frequency, respectively, such that a number of laser pulses per distance is constant along the trajectory. 
     The precision of the ablation process can thus be further improved. Notably, it is also possible for the laser controller to apply a higher or lower number of laser pulses during a certain phase of movement or in certain regions of the workpiece. For instance, if higher or lower precision (or more or less material removal is required), achievable with more or less laser pulses, is only needed locally. 
     In a further preferred implementation form of the first aspect, the motion controller is configured to repeatedly change the x-y-z-position of the workpiece such that the laser beam scans the workpiece surface in the x-y-plane. 
     For instance, the x-y-z-position may be change after each laser pulse. Thus, layers covering the complete workpiece surface (or only a part of the workpiece surface) can be ablated. This allows for a precise and flexible 3D shaping of the workpiece into the final part. 
     In a further preferred implementation form of the first aspect, the apparatus is configured to selectively activate or deactivate the laser beam during the scan of the workpiece surface depending on the x-y-z-positions given by the motion controller. 
     The laser beam may be selectively activated or deactivated by a fast switch of the laser source, for instance a Q-switch, during a continuous motion (“on the fly”). The motion controller may provide a signal at various x-y-z-positions to the laser controller during the motion, which may accordingly control the switch. As a consequence, the laser beam may be turned ON and thus ablates material at some x-y-z-positions set by the motion controller, and may be turned OFF and thus does not ablate material at some other x-y-z-positions set by the motion controller. In this way material ablation occurs only at some positions or in some areas on the workpiece surface depending on the position of the workpiece relative to the machining unit and the speed is constant, which also means that the ablation depth is constant. The apparatus has thus the advantage of faster processing. 
     In a further preferred implementation form of the first aspect, the apparatus is further configured to shape the workpiece by ablating, layer-by-layer, a plurality of layers of workpiece material with the laser beam. 
     As mentioned above, layers can be 1-1000 μm thick and can also have non-uniform thickness. Further, each layer may cover a different part of the workpiece surface. Accordingly, layer-by-layer a precise shaping of the workpiece into the desired 3D shape is possible. 
     In a further preferred implementation form of the first aspect, each of the plurality of layers takes an individually predetermined area in the x-y-plane and has an individually predetermined uniform or non-uniform thickness along the z-direction. 
     The area and thickness for each layer can be determined individually. Multiple layers ablated individually in this way lead to an overall ablated volume of workpiece material, yielding the final 3D part made from the remaining workpiece material. 
     In a further preferred implementation form of the first aspect, the apparatus further comprises a processing unit configured to calculate a layered representation of the to be ablated volume of the workpiece, wherein the apparatus is configured to shape the workpiece by ablating the plurality of layers of workpiece material based on the calculated layered representation. 
     The layered representation is calculated before or during the 3D shaping process and functions as a digital input that determines the overall volume and shape of the ablated workpiece material. 
     Accordingly, full and precise control is gained over the ablation process. The layered representation also allows making adjustments during the material ablation process. 
     In a further preferred implementation form of the first aspect, the laser controller is configured to control the energy of the laser beam based further on the layered representation received from the processing unit. 
     In particular, the laser controller may control the energy of each laser pulse based on the layered representation. The layered representation functions as a digital input or programming of the apparatus, and thus allows carrying out a precise and full 3D material ablation process. 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to feedback a measured z-position of the point of incidence of the fluid jet on the workpiece to the processing unit, and the processing unit is configured to recalculate the layered representation, particularly a number of layers of the layered representation, based on the feedback from the measuring unit. 
     In this way, the ablation process can be adjusted to increase its precision. For instance, if the material ablation intended at a certain position or with a certain laser pulse is not the same as the material ablation result, this deviation can be taken into account so as to compensate and guarantee the preciseness of the 3D shaping process. 
     In a further preferred implementation form of the first aspect, the processing unit is configured to recalculate the layered representation after each workpiece material layer that is ablated from the workpiece. 
     In this way, errors and deviations from the intended ablation result, like irregularities that occur during the shaping process, can be corrected in due time. As a consequence, the accuracy of the 3D shaping of the workpiece into the final part is improved. 
     In a further preferred implementation form of the first aspect, the measuring unit is further configured to determine a first inclination and/or surface irregularity of a lastly ablated workpiece material layer by scanning the workpiece surface in the x-y-plane and thereby measuring z-positions of a plurality of points of incidence of the fluid jet on the workpiece and a second inclination and/or surface irregularity on the surface of the workpiece, and the apparatus is configured to ablate at least a next layer or next layers based on the first inclination and/or surface irregularity determined by the measuring unit. 
     Any undesired inclination or irregularity occurring during the ablation process can thus be corrected with or starting from the next layer. One or several layers may be required to completely compensate for the inclination and/or irregularity. Consequently, it can be avoided that the deviation from the intended ablation result worsens over the process duration and—in the worst case becomes uncorrectable at some point. 
     In a further preferred implementation form of the first aspect, the laser controller is configured to adapt, for at least the next layer, individually the energy of each laser pulse and/or a trajectory of moving the workpiece by changing the x-y-z-position after each laser pulse based on the first inclination and/or surface irregularity determined by the measuring unit. 
     Due to the relative movement between the workpiece and the fluid jet, a change of the trajectory of movement of the workpiece means also a change of the trajectory of the fluid jet as it moves over the workpiece surface. Changing the trajectory of the workpiece movement may particularly include changing the direction of movement, the moving speed, the acceleration, and/or the radius of a curved movement. 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to measure the z-position of the point of incidence of the fluid jet on the workpiece by using an electromagnetic radiation or acoustic waves. 
     The electromagnetic radiation or the acoustic waves are preferably selected such that they do not cause any ablation of material from the workpiece. In this way, a precise determination of the z-position of the point of incidence of the fluid jet on the workpiece is enabled without interfering with the ablation process. 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to measure the z-position of the point of incidence of the fluid jet on the workpiece by measuring a characteristic length of the fluid jet. 
     For instance, the measuring unit may interferometrically measure a characteristic length of the fluid jet with the laser light guided in the fluid jet. The characteristic length may be defined by a certain measurement range. Changes of the measured characteristic length may provide a precise indication about, for instance, the complete length of the fluid jet between machining unit and workpiece, and thus about the z-position of the point of incidence of the fluid jet on the workpiece, 
     In a further preferred implementation form of the first aspect, the measuring unit is configured to measure the z-position of the point of incidence of the fluid jet on the workpiece through the fluid jet. 
     In particular, the measuring unit may for instance send electromagnetic radiation or acoustic waves through the fluid jet onto the workpiece. The electromagnetic radiation or acoustic waves are accordingly guided by the fluid jet precisely to the workpiece x-y-position of which the z-position is to be measured. The reflected electromagnetic radiation or acoustic waves may also be guided in the fluid jet back to the measuring unit. Based on, for instance, a time distance between sending and receiving the electromagnetic radiation or the acoustic waves, the z-position of the point of incidence of the fluid jet on the workpiece can be determined with high accuracy. Accordingly, a very precise ablation process is enabled. 
     In a further preferred implementation form of the first aspect, the measuring unit is integrated into the machining unit. 
     Thus, the apparatus becomes very compact and has the inherent ability to measure the z-position of the point of incidence of the fluid jet on any part of the workpiece. 
     A second aspect of the present invention provides a method for 3D shaping of a workpiece by material ablation with a laser beam, the method comprising providing a pressurized fluid jet onto the workpiece and coupling the laser beam into the fluid jet towards the workpiece, setting an x-y-z-position of the workpiece relative to the fluid jet, measuring a z-position of the point of incidence of the pressurized fluid jet on the workpiece. 
     Advantageously, the method further comprises adjusting the energy of the laser beam based on a set x-y-z-position and a measured z-position of the point of incidence of the pressurized fluid jet on the workpiece. 
     In a preferred implementation from of the second aspect, the method comprises coupling the laser beam pulsed into the fluid jet, setting the x-y-z-position of the workpiece for each laser pulse, measuring the z-position of the point of incidence of the fluid jet before each laser pulse, and adjusting individually the energy of each laser pulse based on the x-y-z position set for that laser pulse and the z-position of the point of incidence of the pressurized fluid jet on the workpiece measured before that laser pulse. 
     In a further preferred implementation form of the second aspect, the method comprises scanning the surface of the workpiece in the x-y-plane, and determining a profile of the surface by measuring z-positions of a plurality of points of incidence of the fluid jet on the workpiece, and setting individually the energy of each laser pulse and/or a trajectory of moving the workpiece by changing the x-y-z-position after each laser pulse based on the determined profile of the surface. 
     The method of the second aspect provides the same effects and advantages that are described above for the apparatus of the first aspect. Notably, the method of the second aspect may be developed with implementation forms according to the implementation forms described above for the apparatus of the first aspect. The method may be carried out by the apparatus of the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above-described aspects and preferred implementation forms of the present invention are explained in the following description of specific embodiments in relation to the enclosed drawings, in which 
         FIG. 1  shows an apparatus according to an embodiment of the present invention. 
         FIG. 2  shows possibilities to control the energy of a laser pulse by an apparatus according to an embodiment of the present invention. 
         FIG. 3  shows an adaption of a laser frequency and number of laser pulses to a movement velocity of the workpiece by an apparatus according to an embodiment of the present invention. 
         FIG. 4  shows an apparatus according to an embodiment of the invention. 
         FIG. 5  shows (a) an apparatus according to an embodiment of the invention, and (b) a measurement scheme of the z-position in between two laser pulses. 
         FIG. 6  shows a layered representation of the to-be-ablated volume as calculated in an apparatus according to an embodiment of the invention. 
         FIG. 7  shows the scanning of the workpiece surface with a laser beam coupled into a fluid jet performed in an apparatus according to an embodiment of the invention. 
         FIG. 8  shows a layer-by-layer ablation of workpiece material by an apparatus according to an embodiment of the invention. 
         FIG. 9  shows a correction of a surface inclination and/or irregularity performed by an apparatus according to an embodiment of the invention. 
         FIG. 10  shows a method according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an apparatus  100  according to an embodiment of the invention. In particular,  FIG. 1  shows an apparatus  100  that is configured to shape a workpiece  101  by material ablation with a laser beam  102  in up to three dimensions (full 3D shaping). To this end, the apparatus  100  comprises at least a machining unit  103 , a motion controller  105 , and a measuring unit  107 . Preferably, the apparatus  100  further comprises a laser controller  106  that controls a laser source  110  generating the laser beam  102 . Thereby, the laser source  110  is part of the apparatus  100 . The laser controller  106  and laser source  110  are shown in dotted lines in  FIG. 1 . 
     The machining unit  103  is configured to provide a pressurized fluid jet  104 , wherein the fluid is preferably water, onto the workpiece  101 , and to couple the laser beam  102  into the fluid jet  104  towards the workpiece  101 . The laser beam  102  is in particular a high-intensity laser beam that is suitable for cutting and shaping materials including but not limited to metals, ceramics, diamonds, semiconductors, alloys, superalloys, or ultra-hard materials. The laser beam  102  may exemplarily have a laser power of between 1-2000 W. 
     The motion controller  105  is configured set an x-y-z-position of the workpiece  101  relative to the machining unit  103 , i.e. to control movements of the workpiece  101  in three dimensions. To this end, the motion controller  105  may either move the workpiece  101  or the machining unit  103  or a combination of moving the workpiece  101  and the machining unit  103 . The workpiece  101  may be positioned on a machining surface, which may or may not be part of the apparatus  100 . In either case, the apparatus  100  is arranged such that it is able to machine the workpiece  101  disposed on the machining surface. As shown in  FIG. 1 , the motion controller  105  may provide the x-y-z-position that is to be set to a movable machining surface, on which the workpiece  101  is disposed, and the machining surface may then take this position within a pre-calibrated axis (coordinate) system. 
     The measuring unit  107  is configured to measure a z-position z p  of the point of incidence  108  of the pressurized fluid jet  104  (and thus also of the laser beam  102 ) on the workpiece  101  in the z-direction. The point of incidence  108  may be on the workpiece surface  109  or may lie beneath the workpiece surface  109  e.g. if the laser beam  102  has already ablated workpiece material at this x-y-position. That is, the point of incidence  108  can be in a trench or in an indentation  111  in the workpiece surface  109  as indicated in  FIG. 1 . The measuring unit  107  may be referred as a depth sensor, since the measured position z p  indicates the z-position of the material ablation, i.e. the depth at which the workpiece is machined by the laser beam  102 . The measuring unit  107  is preferably able to measure multiple positions z p  of points of incidence  108  in the z-direction, in particular if the fluid jet  104  is moved along the workpiece surface  109 . In this way the measuring unit  107  is able to measure a precise surface profile of the workpiece  101 . Notably, the propagation direction of the fluid jet  104  is preferably along the vertical direction, but can also be at an angle to the vertical direction. Since the fluid jet  104  is pressurized, the fluid jet  104  will always propagate linearly. The z-direction can be parallel to the vertical direction and/or to the propagation direction of the fluid jet  104 , but does not have to be. The x-y-plane is in general perpendicular to the z-direction. 
     The optional but preferred laser controller  106  is configured to provide the laser beam  102  to the machining unit  103 . The laser controller  106  is preferably provided with the x-y-z-position of the workpiece  101  set by the motion controller  105 . Furthermore, the laser controller  106  may be provided with the z-position of the most recently measured point of incidence  108  on the workpiece  101 . Preferably, the laser controller  106  may then adjust a laser power of the laser beam  102  based on the x-y-z-position set by the motion controller  105  and/or based on one or more z-positions z p  measured by the measuring unit  107 . 
     Advantageously, the laser beam  102  used by the apparatus  100  may be pulsed. To this end, the laser source  110  may be configured to provide a pulsed laser beam  102 , and preferably the laser controller  106  is configured to control pulse width, amplitude, rate etc. In this case, the laser controller  106  may preferably be configured to adjust the energy of each laser pulse  200  based on the x-y-z-position set by the motion controller  105  for said laser pulse  200 , and based on the z-position z p  of the point of incidence  108  of the pressurized fluid jet  104  on the workpiece  101  measured by the measuring unit  107  before said laser pulse  200 . In this way, the laser-induced ablation of workpiece material may individually be adjusted for each laser pulse  200 , particularly in a fast and direct way. Thus, precise 3D-shaping of the workpiece  101  is possible. In particular, if the laser controller  106  and the motion controller  105  both allow high-speed operation, very precise 3D contours can be generated in a speed and precision superior to any known technique. 
       FIG. 2  shows how the energy of one or more laser pulses  200  may be controlled by the apparatus  100 , particularly by means of the laser controller  106 .  FIG. 2( a )  shows that the laser controller  106  may be configured to set a laser pulse width. In  FIG. 2( a )  all the laser pulses  200  are shown having an amplitude of 100%, but the laser pulses  200  have different widths (i.e. durations), which are labelled τ 1 , τ 2  and τ 3 . Accordingly, the energy provided by each laser pulse  200  is different. 
       FIG. 2( b )  shows that the laser controller  106  may also be configured to set an amplitude of each laser pulse  200 . Again, three laser pulses  200  are shown. However, only the first laser pulse  200  has an amplitude A 1  of 100%, The other laser pulses  200  have a lower amplitude A 2  or A 3 , respectively. Accordingly, the laser pulse energy of each laser pulse  200  is different. 
       FIG. 2( c )  shows that the laser controller  106  may also control a pulse rate and in consequence a time delay between consecutive pulses  200 . Further, the laser controller  106  may even be configured to execute a pulse burst  201 . The first three pulses  200  (left-hand side of  FIG. 2( c ) ) compose a pulse burst  201  and have accordingly shorter time delays Δ 1  between the consecutive pulses  200 . The pulses  200  may all have an equal pulse width of τ 0 . In contrast, the second three laser pulses  200  (right-hand side of  FIG. 2( c ) ) have a larger time delay Δ 2  between the consecutive pulses  200 , i.e. the pulse rate for these laser pulses  200  is lower. Accordingly, different energies per time are provided by the laser beam  102  with the pulse burst  201  and the other pulses  200 , respectively. 
     Preferably, the motion controller  105  is further configured to change the x-y-z-position of the workpiece  101  relative to the machining unit  103 . In particular, if the laser beam is pulsed, the motion controller  105  may change the position of the workpiece  101  after each laser pulse  200 . Thereby, the workpiece position may be changed stepwise or continuously. It is also possible that the motion controller  105  accelerates or decelerates the changing of the x-y-z-position of the workpiece  101  while moving the workpiece  101  along a trajectory. This is shown in  FIG. 3 ( 1 ), wherein the velocity of the workpiece  101  movement changes over time. The workpiece may specifically be moved along the x-, y-, z-axis, or along rotational directions A, B, C. 
     The laser controller  106  may be configured to increase or decrease a laser pulse frequency (as shown in  FIG. 3 ( 2 )) such that a number of laser pulses  200  per distance is constant along the trajectory of movement (shown in  FIG. 3 ( 3 )). The motion controller  105  may therefore give information to the laser controller  106  that the number of pulses  200  along the trajectory should stay constant in any acceleration and deceleration phase of the axis system. However, the motion controller  105  could also inform or instruct the laser controller  106  to adapt the number of pulses  200  depending on the velocity, for example, to provide more pulses  200  when a rotational movement with a radius of e.g. less than 1 mm is carried out. The scheme of  FIG. 3  is further not only applicable with respect to the laser frequency (pulse rate), but also with the other options of adapting the laser energy that are shown in  FIG. 2 . 
     The apparatus  100  can also be configured in such a way with a fast laser switch control, that the axis system determines a surface scan of the workpiece  101 —as shown in and explained below with respect to  FIG. 7 —and the laser beam  102  for ablation is only activated in some areas of the surface scan in function of the actual position of the workpiece  101  versus the machining unit  103  during a continuous motion, This is possible thanks to a fast output of the x-y-z-position by the motion controller  105 . In the above manner, the apparatus  100  does not need to compensate the frequency of the laser and has the advantage to ablate material at constant speed (meaning constant depth) and to process faster. 
       FIG. 4  shows an apparatus  100  according to an embodiment of the invention, which builds on the apparatus  100  shown in  FIG. 1 , Same components in  FIG. 1  and  FIG. 4  have the same reference signs and function likewise. The apparatus  100  of  FIG. 4  also has the machining unit  103 , and has the laser source  110  that provides the laser beam  102  to the machining unit  103 . Thereby, the laser beam  102  may be provided from the laser source  110  to the machining unit  103  by means of an optical fiber  401 . In the machining unit  103 , the laser beam  102  may be coupled into the fluid jet  104  directly or preferentially by one or more optical elements  402 . This optical element  402  may be a lens or a lens assembly or any other suitable element to focus the laser beam into the fluid jet. The machining unit  103  may also contain other optical elements, for instance, a beam splitter, mirror, grating, filter or the like, in order to guide the laser beam  102  from the edge of the machining unit  103  to the at least one optical element  402 . The machining unit  103  may further include an optically transparent protection window (not shown), in order to separate the optical arrangement (here the optical element  402 ) from a fluid circuit and region of the machining unit  103  where the fluid jet  104  is produced. Typically, the fluid jet  104  is produced by a fluid jet generation nozzle that has a fluid nozzle aperture, and the produced fluid jet  104  is output from the machining unit  103  via the nozzle. 
     The laser source  110  includes the laser controller  106  and a laser resonator  403 . If the laser beam  102  is a pulsed laser beam, the laser source  110  may include a switch  400  for modulating the laser pulses  200 . In a preferred implementation, this switch  400  is a Q-switch for providing particular fast 0-100% modulation capabilities. The switch  400  is controlled by the laser controller  106 . 
       FIG. 5( a )  shows an apparatus  100  according to an embodiment of the invention, which builds on the apparatus  100  shown in  FIG. 1 . Same components in  FIG. 1  and  FIG. 5( a )  have the same reference signs and function likewise. Particularly,  FIG. 5( a )  shows the machining unit  103  of the apparatus  100 , and the fluid jet  104  that guides the laser beam  102  onto the workpiece  101 . The apparatus  100  of  FIG. 5( a )  has the measuring unit  107  advantageously integrated into the machining unit  103 . In this way, the measuring unit  107  may be configured to measure the z-position of the point of incidence  108  of the fluid jet  104  on the workpiece  101  through the fluid jet  104 . This allows for a compact apparatus  100  and at the same time for a precise and fast measurement of the z-position at a certain x-y-position of the workpiece  101 .  FIG. 5( a )  indicates that the z-position currently measured is in an indentation  111  in the workpiece surface  109 , i.e. it is below the workpiece surface  109  in the z-direction. However, the measuring unit  107  can likewise measure a z-position of a point of incidence  108  of the fluid jet  104  on the workpiece surface  109 . 
     The measuring unit  107  may be configured to measure the z-position by using electromagnetic radiation or acoustic waves. The measuring unit  107  may emit the electromagnetic radiation or the acoustic waves so that it is guided in the fluid jet  104  by means of total reflection onto the workpiece  101 . Likewise, the measuring unit  107  may receive a reflection of the electromagnetic radiation or the acoustic waves, respectively. These reflected signals may also be carried in the fluid jet  104  towards the measuring unit  107 . By evaluating, for instance, a time difference between the sending and receiving of corresponding signals, the measuring unit  107  can calculate the z-position of the point of incidence  108 . The measuring unit  107  may from this z-position also derive is a length of the fluid jet  104 , for instance the complete length l between the machining unit  103  and the workpiece surface  109  or indentation  111  in the workpiece surface  109  as shown in the figure. 
       FIG. 5( b )  shows at what point in time the measuring unit  107  is preferably configured to measure the z-position of the point of incidence  108  of the fluid jet  104  on the workpiece  101 , namely within a time period between two subsequent laser pulses  200  (see the dotted lines). In other words, the measuring unit  107  may measure the z-position after and before each laser pulse  200 , respectively. During providing a laser pulse  200 , preferably no measurement is carried out. In this way, the measurements performed by the measuring unit  107  do not interfere with the material ablation caused by the laser pulses  200 . 
     Notably, it is also possible that the measuring unit  107  scans and measures the complete workpiece surface  109  before the apparatus starts providing the laser beam  102  or the laser pulses  200  onto the workpiece  101  for ablating material. For instance, the apparatus  100  may be configured to shape the workpiece  101  by ablating layer-by-layer a plurality of layers of workpiece material with the laser beam  102 . In this case, the measuring unit  107  could be configured to scan the workpiece surface  109  with the electromagnetic radiation or acoustic waves before each layer, and thereby determine a surface profile. Based on the determined surface profile, the laser controller  106  may then adjust the energy of the laser beam  102  or individual laser pulses  200 , respectively, for controlled ablation of the next layer. 
       FIG. 6  shows a further advantageous unit, which may be included in an apparatus  100  according to an embodiment of the invention as shown in  FIG. 1, 4 or 5 ( a ). In particular, the apparatus  100  may further comprise a processing unit  600  configured to calculate a layered representation  601  of the to-be-ablated volume of the workpiece  101 , i.e. the volume of material represented by multiple layers that is to be removed from the initial workpiece  101  to reach the shape of the final part, The apparatus  100  may then generally be configured to shape the workpiece  101  based on the calculated layered representation  601 . For creating the layer representation  601 , a Computer-Aided Design (CAD) approach may be employed. The layered representation  601  includes a plurality of layers and a defined thickness of the layer, the sum of these layers yielding the volume that has to be ablated from the workpiece  101 . The layers can indicate the amount of material that is to be ablated with each complete surface scan of the workpiece  101 . The layered representation  601  can be provided by the processing unit  600  to the laser controller  106 , and the laser controller  106  may then be configured to control the energy of the laser beam  102  or of each individual laser pulse  200 , respectively, based on the layered representation  601  in order to achieve the defined thickness of each layer. 
       FIG. 7  shows how the apparatus  100  implements a surface scan of the workpiece  101  with the fluid jet  104  guiding the laser beam  102  (or not, if the surface  109  is to be measured while not ablating material). To this end, the motion controller  105  may be configured to change the x-y-position of the workpiece  101  such that the fluid jet  104  and/or laser beam  102  scans the workpiece surface  109  in the x-y-plane, which may be the horizontal plane. The surface scan may be carried out line-by-line, column-by-column or in any other suitable manner. In particular, the motion controller  105  may be configured to change the position of the workpiece  101  after each laser pulse  200  (in case that the laser beam  102  is pulsed), With each surface scan, material can be ablated from the workpiece  101  if the laser beam energy is set correctly. For instance, the laser beam  102  or each laser pulse  200  may be provided with energies such that 1-1000 μm depth of workpiece material is ablated in the z-direction at a given x-y-z-position of the workpiece  101 . In this way, each complete scan of the workpiece surface  109  can ablate a layer with a thickness of 1-1000 μm. The ablated layer may be uniform or non-uniform in its thickness along the z-direction. A surface scan may also be carried out without ablating material if the laser beam energy is set low enough or if the laser beam  102  is turned off. With such a scan, the measuring unit  107  may measure a profile of the workpiece surface  109 . 
       FIG. 8  illustrates how the apparatus  100  is configured to shape the workpiece  101  by ablating a plurality of layers  800  of workpiece material particularly layer-by-layer. The plurality of layers  800  may be identical to the calculated layered representation  601  shown in  FIG. 6 . Each of the plurality of layers  800  may have a predetermined area in the x-y-plane, which depends on the x-y-positions that the motion controller  105  sets. Preferably, the motion controller  105  sets the x-y-z-positon of the workpiece based on the layered representation  601 . Each layer  800  may have an individual uniform or non-uniform thickness along the z-direction, wherein the thickness depends on the laser energies that the laser controller  106  has set for each x-y-z-position of the workpiece  101  relative to the machining unit  103 . For each x-y-z-position of the workpiece  101 , the apparatus  100  is configured to determine the z-position of the point of incidence  108  of the fluid jet  104  on the workpiece  101 , and to adjust the laser power accordingly, so that at each workpiece position a certain depth of workpiece material is ablated in the z-direction. 
       FIG. 9  shows that the apparatus  100  according to an embodiment of the invention—as shown in  FIG. 1, 4 or 5 ( a ), is also able to correct inclinations and/or irregularities that unintentionally occur during ablating workpiece material. If such an inclination and/or irregularity is not corrected in time, the error can add up with each layer  800 , and can lead to an imprecise 3D shape of the final part. In particular, the measuring unit  107  is thus configured to determine an inclination and/or irregularity  901  of a lastly ablated workpiece material layer  900 . This can, for instance, be done by measuring the depth after each laser pulse or by scanning the workpiece surface  109  in the x-y-plane (e.g. without material ablation), and thereby determining z-positions of a plurality of points of incidence  108  of the fluid jet  104  on the workpiece  101 . Thereby, an inclination and/or surface irregularity  902  on the surface  109  of the workpiece  101  can be determined, from which the inclination/irregularity  901  can be calculated. This is shown in  FIG. 9( a ) . 
     The apparatus  100  may then be configured to ablate at least the next layer  800  based on the determined inclination and/or irregularity  901  of the last ablated layer  900 . Accordingly, the surface irregularity and/or inclination  902  can be removed with ablating at least the next layer  800 . To this end, the apparatus  100  is configured to adapt laser energies or trajectory of moving the workpiece  101 , the movement of the workpiece  101  being caused by repeatedly changing the x-y-z-position set by the motion controller  105 . This causes also an adaption of a trajectory, along which the fluid jet  102  moves over the workpiece  101 , for the ablation of at least the next layer  800 . In other words, the laser controller  106  may be configured to adapt the laser beam  102  energy for different x-y-positions or adapt individually the energy of each laser pulse  200 . Additionally (or optionally) the motion controller  105  may also adapt a trajectory of the pressurized fluid jet  104 , in order to remove material only or predominantly at certain positions on the workpiece surface  109 , for instance where a surface irregularity  902  is. The adaption of the laser energies and/or of the trajectory of moving the workpiece  101  and/or of the angle of incidence of the fluid jet  102  on the workpiece  101  is preferably carried out based on the determined inclination and/or irregularity  901  (or based on the surface inclination and/or irregularity  902  on the workpiece surface  109 ). The apparatus  100  can in this way remove the inclination and/or irregularity  902  starting with the next ablated layer  800 . It may take several layers  800  to remove the irregularity and/or inclination. After successful removal, the normal layer-by-layer ablation can continue. 
       FIG. 10  shows a method  1000  for 3D shaping of a workpiece  101  by material ablation with a laser beam  102 . The method  1000  contains a first step  1001  of providing a pressurized fluid jet  104  onto a workpiece  101 , and coupling a laser beam  102  into the fluid jet  104  towards the workpiece  101 . Further, the method  1000  includes a second step  1002  of setting an x-y-z-position of the workpiece  101  relative to the fluid jet  104 . Finally, the method  1000  at least includes a third step  1003  of measuring a z-position of the point of incidence  108  of the pressurized fluid jet  104  on the workpiece  101 . 
     The method  1000  may include further steps according to the above-described functions of the apparatus  100 . The method  1000  may particularly be carried out by the apparatus  100 . Preferably, the method  1000  includes providing a pulsed laser beam  102  and adjusting individually the energy of each laser pulse  200  based on the x-y-z-position set for said laser pulse  200  and the z-position of the point of incidence  108  of the pressurized fluid jet  104  on the workpiece  101  measured before said laser pulse  200 . 
     The present invention has been described in conjunction with various embodiments as examples as well as implementation forms. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, the description and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.