Electric heating – Metal heating – By arc
Reexamination Certificate
2000-03-17
2001-12-04
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121630
Reexamination Certificate
active
06326589
ABSTRACT:
The invention relates to a method involving procedural steps for treating materials by means of plasma-inducing radiation.
Treating materials with plasma-inducing high-energy radiation, such as laser or electron radiation, requires on-line regulation and monitoring for quality during its application. It is desirable to optimize the treatment process. Optical and acoustic signals from the treatment area have therefore long been used for purposes of quality control. For example, the degree of root penetration which can be a qualitative characteristic for the complete welding of a work piece can be determined by observing the underside of the work piece or by lateral observation of the treatment area. To do so, optical detectors are employed to determine center frequencies based on the optical intensity values, from which the degree of root penetration can in turn be inferred. However, both these methods are indirect and fraught with errors.
A method involving the procedural steps referred to initially is known from DE 44 34 409 C1. These steps relate to a direct process. The observation of the vapor capillary area of the work piece takes place in the axis of the inducing laser radiation. Based on the observation of the plasma radiation emission, a mean value of the intensity is determined and used as a measurement for the depth of penetration. This method makes it necessary to adjust the measuring device relative to the axis of the plasma-inducing laser radiation. Because a mean value is produced, the resulting observation results are of a summary nature so that the observational accuracy and its dependent analysis, as well as the process control of the material treatment which in turn is a function of the latter, appear in need of improvement.
The invention therefore is founded upon the objective of improving a method involving the procedural steps referred to initially in order to enhance the control of the material treatment process and to prevent process defects to a significant degree by means of direct and improved process observation.
In this invention, it is first of all important to dispense with the idea of forming a mean value when analyzing the intensities of the plasma radiation. It is, however, essential that the momentary plasma intensities be analyzed at several points of the observation area of the vapor capillaries. It has been shown that the plasma intensity observed at a measurement point is directly related to the formation of the vapor capillaries. In principle, it is thus possible to determine the momentarily appearing shape of the vapor capillaries or at least the parameters of this shape by observing the treatment area pixel-by-pixel or point-by-point. The plasma intensities are measured point-by-point and parallel to the axis of the inducing radiation. The shape of the vapor capillaries or their parameters, i.e. the capillary geometric parameters allow for an immediate assessment of the quality of treatment, inasmuch as a high-quality treatment is reflected by the shape of the vapor capillaries and/or the capillary geometric parameters. The capillary geometric parameters of predetermined treatment tasks are known for their predetermined treatment qualities. Conversely, based on the capillary geometric parameters measured it is thus possible to draw inferences as to the treatment quality that is actually present. This makes it unnecessary to constantly adjust the measuring device to the axis of the inducing radiation. The capillary geometric parameters obtained by this method are employed in the control of the material treatment process. In this way, a point-by-point analysis of the momentary plasma intensities facilitates at least a partial representation of the capillaries. Their formation and/or their extent is a measure for a treatment parameter—as is the laser radiation output or the rate of feed-which influences the control of the material treatment.
The ablation depression which results when materials are treated with plasma-inducing high-energy radiation essentially extends in the direction of the axis of the inducing radiation or parallel thereto. This is a necessary requirement if one is to penetrate as deeply as possible into the work piece. In order to obtain this desirable deep penetration, it is of advantage if the process is accomplished using a capillary depth as a capillary geometric parameter. The momentary depth of the vapor capillaries in all places of the treatment area is directly connected to the process parameters which determine the treatment quality. The treatment quality is deficient if, for example, the capillary depth is not as great as specified while a work piece is being treated.
The treatment result can be further enhanced by determining the shape of the vapor capillaries based on a great number of capillary geometric parameters, on which the control of the material treatment is then based. The comprehensive determination of the momentary shape of the vapor capillaries makes it possible to accurately predict the treatment quality. For example, when a direct and comprehensive observation of the momentary vapor capillaries is effected, treatment defects that have occurred or are in the process of developing can be directly observed. Melting bath ejections during laser beam welding of aluminum are but one example. Any partial closing of the vapor capillaries is shown directly, and if the geometrical data derived from this representation are correctly converted, the process can be controlled such that the particular treatment defect is prevented. It is possible to optimize this type of process control if the shape of the vapor capillaries is determined as a whole. However, if the vapor capillaries are determined only partially or if only a few capillary geometric parameters are determined, a correspondingly more limited process control is also possible.
The vapor capillary extends at different capillary depths, both in the axis of the inducing radiation and parallel thereto; radially to the aforementioned axis it has different radial measurements with different depth ranges. These, too, can be utilized as capillary geometric parameters; this is possible to best advantage especially when the shape of the vapor capillaries is fully determined. However, a simpler method results when the length of the opening of the vapor capillaries in the direction of the feed is used as a capillary geometric parameter. This length of the opening of the vapor capillaries in the feed direction is significant because, together with the capillary depth, it determines the aspect ratio, i.e. the ratio of the aforementioned length to the capillary depth. A sufficiently large aspect ratio permits the unobstructed escape of the vapor from the vapor capillaries into the environment, which stabilizes the process. Executing this procedure based on a predetermined length of the vapor capillary opening in the feed direction yields qualitatively sufficient treatment results if one proceeds on the premise that the welding depth remains constant in many treatment tasks and that it can be established by assigning a predetermined value to the linear energy, i.e., through the ratio between the laser beam output and the rate of feed. In a special case, the length of the vapor capillary opening in the direction of the feed obviously has a special significance as a capillary geometric parameter. This is because when a work piece is welded through, the capillary form immediately becomes significantly slimmer since a large part of the energy being beamed in penetrates the vapor capillaries and thus is no longer available to the fusing of materials. The aforementioned length is reduced accordingly, allowing any root penetration to be instantly determined by observation parallel to the axis of the inducing radiation.
In many material treatment process it is sufficient to determine the required energy, it being unnecessary to make adjustments while the treatment is in progress. To do so, the linear energy is determined, i.e. the ratio between the laser beam output and t
Beersiek Jorg
Schulz Wolfgang
Evans Geoffrey S.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Pandiscio & Pandiscio
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