Electric heating – Metal heating – By arc
Reexamination Certificate
2001-05-09
2004-09-14
Edmondson, L. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121620, C219S121670, C219S121830, C427S008000
Reexamination Certificate
active
06791057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a method for processing workpieces by means of laser radiation, wherein the radiation is focused by a processing optic onto a processing site. The light radiation emanating from the workpiece is received utilizing the processing optic and is analyzed by a detector. An optical measurement with respect to a surface of the workpiece is performed by means of an external source of measuring light, utilizing measuring light reflected from the processing area.
A method comprising the aforesaid method steps is generally known. It is used, for example, for a form of welding processing of workpieces in which the process monitoring system performs keyhole monitoring of the processing site and a distance measurement is effected by means of the external measuring-light source in order to measure or regulate the distance between the processing optic and the workpiece. The light radiation emanating from the workpiece, specifically secondary or thermal radiation produced by the welding process, passes into the processing optic isoaxially with the high-energy or laser radiation and is decoupled there for the detector of the process monitoring system. However, distance measurement or contactless mapping with respect to the geometry of the workpiece is performed by means of receiving units installed outside the processing optic-Measuring systems located outside the processing optic cause problems, however, due to the contamination of optical systems that occurs in an industrial environment, and they hamper the processing head, which is less readily accessible and cannot be used as well with complex—especially three-dimensional—workpiece geometries. In general, it can be stated that methods of workpiece processing involving on-line monitoring of the workpiece have heretofore been performed only with special systems tailored to the job concerned.
2. Description of the Prior Art
The object of the invention, by contrast, is to improve a method comprising the method steps cited in the introduction hereto in such a way that a combination of process monitoring and additional monitoring measurements can be performed on the workpieces.
SUMMARY OF THE INVENTION
This object is accomplished by using the same processing optic for the light radiation used for process monitoring and the reflected measuring light used for optical measurement. It is of significance for the invention that the processing optic detects not only the light radiation used for process monitoring, but also the measuring light used for optical measurement that is reflected by the workpiece. This eliminates the need to install measuring systems for the measuring light on a measuring head or near the processing optic, such measuring systems being lens systems that can become contaminated during industrial operation and can limit the range of application of the workpiece processing operation.
The method is suitable for all types of laser-beam sources, for example CO
2
lasers, Nd:YAG lasers and diode lasers. The method is also suitable for all kinds of materials processing employing high-energy or laser radiation, such as welding, cutting or coating. Owing to the integration of plural measuring methods into the area of the processing optic, the method is suitable for all types of process and quality monitoring, especially in the areas of tailored blanks and 3D contour processing.
Integrating the measuring systems into the area of the processing optic has numerous advantages. Especially notable is compact construction in the region of the processing head. Components required for known methods are no longer needed. The result is a proportionate decrease in maintenance expenditure, since, for example, it is no longer necessary to clean additional optics. The procedures involved in processing a workpiece are simplified, since fewer structural components have to be attended to and the integration of the measuring steps simplifies analysis of the measurement results. The overall cost of the method is therefore decreased.
The method can advantageously be realized so that the light radiation used for process monitoring and the reflected measuring light are detected, utilizing the same processing optic, isoaxially or approximately isoaxially with the light radiation or axially parallel thereto. Such detection ensures that the processing optic and hence the processing head can be used without any major changes of the kind made necessary by overly large angles or oblique lines of sight, for example widening of the hole in a hole mirror.
The method is, in particular, universally applicable. It is suitable for all types of optical measurements relating to the workpiece during processing. This is of significance because quality assurance during processing demands an extremely wide variety of measurements with respect to the workpiece. To this end, the method can be performed so that the optical measurement performed with respect to the workpiece surface is a measurement of the distance between the processing optic and the workpiece and/or a mapping of the workpiece geometry before the processing site and/or a mapping of the seam geometry present after processing and/or a mapping of the melt produced at the processing site. Mapping of the distance between the processing optic and the workpiece is necessary, for example, in applications where the workpiece exhibits dimensional changes in the direction of the laser beam. Mapping of the workpiece geometry before processing serves to detect geometric defects such as edge displacement, gaps, etc., and permits seam tracking. Mapping of the seam geometry present after processing can be used to regulate process variables so as to maintain a given seam quality. Mapping of the melt produced at the processing site furnishes comparative data for comparison with reference values from processing operations having defined parameters, any discrepancies being evidence of processing errors. The foregoing optical measurements do not constitute an exhaustive list. They do, however, make it possible to simplify the most significant industrial methods in order to achieve the object stated in the introduction hereto.
The method can preferably be performed so that different zones I, II, III of the processing area of the workpiece are detected by means of the same detector. Metrologic sensing of different zones of the workpiece processing area serves to eliminate distortion from measurement tasks, since a larger area can be measured. This simplifies control of the processing operation. For example, the workpiece geometry can be detected at a greater distance from the processing site, malting it possible to take compensatory action, for example by the control of guide rollers positioning the workpiece. It is possible to work with different qualities of light at different locations in the processing area, for example with light of different intensities. All such measurement tasks can be performed with one and the same detector, making for considerable method integration.
The method can be performed so that the first zone of the processing area is taken to be the region of an interaction zone, the second zone, encompassing the first, is taken to be the region of the melt, and the third zone is taken to be the processing area as a whole. These zones of a workpiece processing area exhibit typical characteristic curves for the light radiation and typical geometrical characteristics that can be used to influence process control. For example, in a given processing task the melt has a typical shape and dynamics that can be mapped optically to draw conclusions regarding disturbances of the process.
The manner of proceeding is advantageously such that the sensing of different zones of the processing area takes place simultaneously. Performing all the measurement tasks simultaneously eliminates delays in the monitoring and control of the processing method, thus reducing the susceptibility to error of the processing operations.
The method can be performed so t
Abels Peter
Kaierle Stefan
Kratzsch Christian
Edmondson L.
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Pandiscio & Pandiscio
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