DD221665A1 - METHOD FOR MONITORING AND CONTROLLING THE WELDING PROCESS - Google Patents

Abstract

The invention relates to a method for monitoring and controlling the welding process during arc welding or cutting. The aim is to determine with little effort temperature fields and from them measurement quantities, with which a control of the welding process can take place. The solution must be designed in such a way that process monitoring and control in real-time operation is ensured. It is characteristic that a recording optics, consisting of pinhole, polarization and narrow band filter, is arranged on the recording head so that the transmission of the optical image over fiber optic cable with direct coupling to the receiving tube of the television camera takes place that suppresses the interference radiation by filtering using a narrowband filter and polarization filter is that the circuit variant generates an equidensity signal and a contour signal as a function of the temperature and geometry of the welding bath and from this voltages are formed, which are related to the geometry of the temperature field and via an actual target comparison, a process control of the parameters welding speed, welding current and welding voltage occurs.

Description

For this 4 pages drawings

Field of application of the invention

Method for monitoring and controlling the welding process, in particular for detecting the weld zone in arc welding and cutting, using Bildlichtleiterh.

Characteristic of the known technical solutions

It is known that fusion welds in general only after their completion on quality and position of the weld and on any errors such. B, larger pores and leaking welded spots are checked. The test can be done visually or by X-rays, ultrasound or the like. For troubleshooting is often an extensive Nacharbeitervorlich. .

It is also known that from the measurement of the time interval in which the temperature of the weld metal passes through a certain range, for example 8OfJ ⁰ C to 500 ⁰ C, conclusions on the forming structure and related mechanical properties can be drawn. Cooling time measurement is conventionally carried out with thermocouples and time registration. The method has the disadvantages that no continuous measurement and no application in the production is possible. By melting the elements, a commercial control of the welding process is not possible. Extensive preliminary investigations are necessary to determine the welding parameters. Thermocouples are not suitable for arrangement in the melt itself. They disturb the welding process and influence the temperature field. It has also been attempted to computationally record the cooling interval from the given welding parameters and welding conditions. Since it is not possible to grasp the complexity of the welding process in this way, this method is bound to numerous simplifying assumptions and / or empirical adjustments. These can lead to considerable errors in the specific application. *

It is also known to pyrometrically monitor the fusion weld. However, only a local measurement can be carried out. If a partial or field scanning done, a complex mechanical deflection is necessary. Due to the inertia of the mechanical deflection system, the working frequency is low and limited. The scope of this method is limited to cases where one point or one line must be scanned. To protect the optics, a sufficient distance must be maintained. As a result, the surface considered in the visor characteristics of conventional pyrometer is correspondingly large, and thus the resolution is limited. The pyrometer must be exactly felt with the burner to always maintain the same position to the heat field.

It is also known that, when welding workpieces of the same composition, a different medium is introduced into the region of the root-side weld zone, the spectral lines of at least one selected as indicator element of this medium and controlled by changing the brightness of the respective spectral lines, the welding process by changing the welding conditions.

According to DDPS 157398, DE-AS 1284659, DE-AS 257/643 and SU-PS 567564, solutions are known which detect isotherms of a region of the weld zone which are evaluated by visual inspection or enable a manual readjustment of a welding process by electronic comparison. Furthermore, solutions with light guides according to DD-PS 152734 are known, which are based on brightness differences of the welding arc and the welding pool. The main disadvantages of these solutions are:

- Allocation camera welding torch often problematic.

- Camera must be carried along with the burner.

- In many cases (with complicated components), the camera can not "look" directly at the welding torch (corners / edges).

- High thermal, mechanical and dirt load on the camera.

- Signal acquisition is expensive - requires relatively high electronic effort.

- The digital office evaluation in real-time operation is problematic - there is no continuous control signal for process control.

Zksl dar invention

It is an object of the invention to determine with relatively little effort temperature fields during welding and from it continuous measured variables, with which a process control can be such that a consistently good weld quality is achieved.

The WmBn of the invention

The invention has for its object to develop a method and a control, where it is ensured that a Temperaturfeidermittlung is realized at any burner position and process monitoring and control is ensured in real-time operation.

According to the invention the object is achieved in that a recording optics consisting of pinhole, polarization and narrow band filter, the recording head is arranged so that the forwarding of the optical image via fiber optic cable with

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direct coupling to the recording tube of the television camera, that the interference by filtering means

Narrowband filter and polarization filter is suppressed that the circuit variant generates a Equidensitensignal and a contour signal depending on the temperature and geometry of the weld pool and from this voltages are formed, which are related to the geometry of the temperature field and an actual-target comparison, a process control of Parameters welding speed, welding current and welding voltage takes place.

It is thus a novel image recording and evaluation process, wherein signals are obtained from the temperature field during welding, which are used for process optimization.

Here, the image is taken by a recording head, which is located directly on the welding torch and contains a pinhole, which images the welding process on the image guide instead of a glass optics. The picture is transmitted via an image guide to the TV camera. The hole camera principle is an ideal solution due to the high light intensity available during welding and the less stringent image definition requirements. Thus, the small dimensions of the head and the direct arrangement on the welding torch are possible. The optical filters suppress the arc radiation and reflections. The correct image brightness is set by twisting the polarizing filters against each other. For image evaluation is a circuit that generates a displaceable in the TV screen gray wedge, for example, for temperature calibration, and provides a Equidensiten- and contour signal when the image signal exceeds or falls below an adjustable threshold. The television operations center provides a standard video signal (U _V id _eo ) as well as the required vertical (V), blanking (A) and sync pulses (S).

The V-pulse is delayed with the delay being adjustable to determine the wedge and a monostable

Multivibrator controls, which determines the wedge width. ^v >

The Α pulse synchronizes a sawtooth generator whose output voltage is used to generate the gray scale. The signal switching is done with a FET switch, which also connects the Equidensiten- or contour signal. To generate the equidensity and contour signal, the video signal is compared with a reference voltage (LT). A

logic circuit ensures that both the over-and falling below the reference voltage on;

Output pulse with defined width as a contour _signal (Uk _0n ,) is generated. A second logic circuit puts the '

Equidensitensignal U _aqui as long as high level, as U _V ideo is greater than the reference voltage (U ').

The signal switching is followed by a video amplifier, which compensates for signal attenuation and the gray wedge necessary

Sync pulses mixed, so that the output again ein.normgerechtes video signal with gray wedge and Equidensite or contour is applied.

The peculiarity of the developed circuit is that with very little effort (compared to commercial equipment, such as Densitron) the parameters set for the present application are met.

From U _kon , and U _aqui measured values (voltages) are generated according to the invention, which serve by an actual-target comparison for controlling the welding process.

An integration of the equidensity trace by an RC element results in a voltage value (U _b ) which is proportional to an area written bright on the monitor. By integration of the contour signal, a voltage value is obtained which is proportional to the length of the surface (U _a ), ie perpendicular to the line device or in the welding direction.

The simple division of both quantities by a logic circuit yields a value Ü _c which is approximately proportional to the width of the area.

These 3 measurands are in real time continuously at the output of the sensor system. They are sufficient for monitoring the process. By a downstream signal processing unit, the process can be controlled by actual-target comparisons

become. ''

The quantities U _a to Up are compared with voltages characteristic of the respective process. In case of over or

If the setpoint values are undershot, the signal processing unit initiates a welding parameter change. ,

Äosführungsfeeäsptel

The invention will be explained in more detail below using an exemplary embodiment. The accompanying drawings show:

Fig. 1: image conductor optics and block diagram.

Fig.2: Recording head and welding torch. ^:

Fig.3: Picture ladder with TV camera and Endikon. '

Fig.4: Scheme of the generated signals

According to FIG. 1, image acquisition takes place via an image conductor optics, wherein the recording head 2 according to FIG. 2 is arranged directly in the vicinity of the welding torch 1. According to the invention, a pinhole aperture 14 is used instead of a taking lens.

In front of it is a narrow band filter 12 UG 6 for IR radiation. Instead of a diaphragm for polarity adjustment two polarizing filters 13 are used, of which one is rotated ¹ against the other. To protect against radiant heat is

provided a water cooling. An exchangeable protective glass 11 and a gas stream introduced through the feed nozzle 10 protect the optics from contamination. The recording head 2 forms the temperature field 15 on the image guide 3, wherein the image guide is optically tightly coupled to the Endikon 9 a stationary television camera 4 according to Figure 3. As coupling medium silicone oils are used.

The monitor 5 is used to monitor the temperature field 15 during the welding process. The image guide 3 is so _; adjusted to the Endikon 9 that the temperature field 15 of the weld pool appears perpendicular to the monitor 5, ie

Welding direction perpendicular to the image line direction.

The television operations center with image analyzer 6 according to FIG. 1 generates the video signal (Uv; _de o) according to FIG

Equidensitensignal (U _aqui ) and the contour _signal (U _kont ) for a by the reference _voltage U 'selectable gray wave.'

The equidensit signal U _aqui is equal to zero when the video signal U <U 'and U _aqui = U _max when U>U', ie U _max is the

maximum video signal voltage for white. The contour _signal changes from 0 to U _max , if U _Vid80 exceeds or _{falls below} the value U ', remains at U _max for the time τ and then drops back to 0. The position of U 'is chosen so that the associated »contour of an isotherm T = 1500 ⁰ C = melting temperature of steel.

By integrating the signals U _kont and U _aqui , the voltages U ₈ and U _{b are} generated, which are used in the Signalverarbeitungseiiihoit 8 for an actual-target comparison. In addition, a voltage U _{c is} generated by dividing the voltages U _a and U _b in a Logikschaliung 7, with the also in the signal processing unit 8, an actual target comparison is performed.

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For the output voltages U _a to U _c then applies

(J _a proportional to the length of the bath .-.

Ub proportional to the melt pool size

U _c proportional to the seam width.

The voltages U ₈ to U _c are compared with predetermined setpoints. If U _c exceeds or falls below the setpoint value, then

the welding speed is increased or decreased. If U _b exceeds or falls below the nominal value, then the welding parameters U _s and Ij are to be lowered or increased.

Claims (1)

-1- 260 733 Invention claim: Method for monitoring and controlling the welding process, in particular for detecting the weld zone in arc welding and cutting using image light guides, characterized in that a pickup optical system consisting of pinhole (14), polarization and narrow band filter (12, 13), on the recording head ( 2) is arranged so that the transmission of the optical image via optical fiber cable with direct coupling to the recording tube of the television camera (4), that the interference is suppressed by filtering means of narrowband filter (12) and polarizing filter (13) that by the circuit variant a Equidensitensignal and a contour signal depending on the temperature and geometry of the welding pool is generated and from this voltages are formed, which are related to the geometry of the temperature field and an actual-target comparison, a process control of the parameters welding speed, welding current and welding voltage he follows.