Process of treating a workpiece using a liquid jet guided laser beam
The invention concerns a process for treating a workpiece, preferably for shaping a workpiece by ablating material, by a liquid jet guided laser beam. The process comprises the following steps: Production of a liquid jet by a nozzle; impinging the liquid jet on a reference surface allocated to the workpiece, whereby an intersection of the liquid jet with the reference surface defines a liquid jet-footprint; effecting a displacement between the liquid jet and the reference surface, whereby the liquid jet-footprint evolves to a trace along a trajectory associated with the trace during the time frame, wherein the trace covers a trace-area; irradiating the workpiece at least during part of the time frame with a laser beam coupled into the liquid jet, preferably for ablating material such that the trace has at least one overlap-area, wherein each of the at least one overlap-areas is defined by an associated common area of an associated second length-section of the trace and an associated first length-section of the trace and wherein the workpiece is irradiated by the laser beam along at least one of the length-sections. It concerns further a computerized numerical control (CNC) program for controlling a liquid jet guided laser machining device and a computer readable medium containing such a CNC program. Further, it contains a computer program for generating the above mentioned CNC program. Finally the invention concerns a liquid jet guided laser machining device to perform the above mentioned process.
1. A process for shaping a workpiece by ablating material using a liquid jet guided laser beam within a time frame, comprising the following steps:
a. producing a liquid jet by a nozzle,
b. impinging the liquid jet on a reference surface allocated to the workpiece, whereby an intersection of the liquid jet with the reference surface defines a liquid jet-footprint,
c. effecting a displacement between the liquid jet and the reference surface, whereby the liquid jet-footprint evolves to a trace along a trajectory associated with the trace during the time frame, wherein the trace covers a trace-area, and
d. irradiating the workpiece at least during part of the time frame with a laser beam coupled into the liquid jet to ablate material, and
e. monitoring the remaining thickness of the workpiece while irradiating the workpiece with the laser beam; and
wherein the trace has in sequence a first advance-segment, a return-segment and a second advance-segment, wherein
i. the first advance-segment and the return-segment form a first and a second length-section of a first overlap area;
ii. the return-segment and the second advance-segment form a first and a second length section of a second overlap area;
iii. a common area of the first and the second overlap area are essentially superimposable with at least one of these two overlap areas; and
iv. the trajectory is shifted in a reference surface coordinate direction, such that center lines of the different segments are displaced with respect with each other in such a way that the common area is part of the first advance-segment, of the return-segment and of the second advance-segment.
2. The process according to claim 1 wherein one or more of the following parameters are changed within the time frame:
e) the impinging angle,
f) space coordinates of the centre-line,
g) a speed of displacement, and
h) laser parameters.
3. The process according to claim 1 , further comprising:
changing laser parameters, process parameters and/or liquid jet parameters based on an output of a measurement device by a Human-machine-interface program controlling and executing a CNC program.
4. The process according to claim 2 , whereby one or more of the parameters are changed when it is detected that a portion of the material is difficult to remove.
5. The process according to claim 3 , wherein:
the laser parameters comprise a laser pulse rate, a laser energy, or a laser radiation frequency; and/or
the liquid jet parameters comprise a pressure of the liquid jet, or a composition of the liquid.
6. The process according to 1 , wherein an amount of the ablated material and/or the remaining thickness of the workpiece is determined by:
analyzing, by a measurement device, reflections of a measurement laser coupled into the liquid jet or the laser beam coupled into the liquid jet, to measure a distance from the nozzle to the workpiece surface.
7. The process according to claim 1 , wherein an amount of the ablated material and/or the remaining thickness of the workpiece is determined by:
measuring, by a measurement device, a distance from the nozzle to the workpiece surface by using ultra-sound coupled into the liquid jet.