DE3543681C2 - - Google Patents

Description

The invention relates to a device for production a weld with a weld head over the Weld seam arranged and relative to it in its longitudinal direction is displaceable, and with a sensing device, the signals of the welding process and an evaluation circuit feeds.

Known such devices commonly use a measuring head in which the sensing device is arranged, and the leading in front of the welding head over the weld is positioned. In a control circuit, those of recorded by a single sensor in the sensing device Signals used to weld the welding head in one plane parallel to the plane of the parts to be welded together Guide sheets over the weld.

This known device has indeed just ver proven welding seams. Once the weld but if there is a curvature, difficulties arise due to the constructionally necessary advance of the measuring head in front of the welding head. This advance is necessary around the measuring head from damage by the to protect heat generated during the welding process. Furthermore is to influence the measurement results by the lead can be avoided by the welding plasma.

Furthermore, it is disadvantageous in this known device weight that the quality of the weld seam cannot be controlled. One therefore has proportionality elaborate quality control procedures for such  Welds developed, but only after application and cooling the weld on the welded Workpiece can be carried out yourself. It will then If a fault is discovered in the weld seam, this leads usually to the reject of the workpiece in question.

From ZIS Mitteilungen 7/73, pp. 856, 857 is a Method for measuring the welding gap is known, in which by coupling ultrasound pulses into the distance between the two welding partners to the respective edge is measured. The sum of the measurement signals (Sum of the transit times of the two ultrasonic pulses) with an auxiliary voltage compared to the distance of the corresponds to both measuring heads. A difference this Sum signal to the auxiliary voltage is then a measure of the width of the welding gap and can be used for the night regulation of the welding power can be used.

The invention is based on the object propose a device of the type mentioned at the outset, with the help of a quality control of the Weld can be done, during of the welding process itself, and optionally a flawless one Position the welding head over the Weld seam enables, if necessary also with curved running weld.

To achieve this object, the invention is characterized in that that the sensor device two stationary the structure-borne noise assigned to the parts to be welded has sensing sensors, the output signals of the  Evaluation circuit are supplied, which are the quotients from the difference and the sum of the two output signals forms.

It is important that the sound transmitted through the air is not detected by the sensor, since this is no information about the position of the weld pool in relation to the weld seam contains. Such arrangements are from the literature already known FR-OS 21 94 521 and Welding Journal, Sept. 85, S-43-48).

The difference of the signals is zero if the Welding head correctly positioned over the weld seam is. If he moves towards one of the two sensors, so the difference signal becomes positive or negative. It can then in a control loop to readjust the Serve welding head.

The sum of the two output signals is a measure of that Strength of the power coupling into the weld seam and therefore provides quality control for the weld To illustrate, it should be mentioned that this sum is strong drops if, for example, the gap width is too large, the performance of the welding machine is too low or even if there is a local enlargement of the welding gap. The drop in the sum signal that occurs here is therefore a measure of the quality of the weld.

The evaluation circuit forms the quotient from the Difference and the sum of the output signals. Through the thereby normalizing the two signals won a signal that from hum, from machine vibrations,  which are transferred to both sheets or also largely of fluctuations in the power of the welding machine is independent.

For both possible uses of the invention Device, namely quality control of the weld seam and tracking of the welding head over the weld seam, it is preferred if the output signals of the evaluations circuit can be fed to a threshold switch, which then generates two different error signals (Welding intensity too small or joint gap too large or Sweat intensity too high), so with the help of this Error signals an incomplete or too welded Workpiece can be discarded. With multiple These errors can also occur throughout Welding system to be shut down.

You can run parallel to the weld on both sides Arrange several of the sensors or on the right and left of the Each weld seam is a band-shaped sensor that the Structure-borne noise signals of the weld pool. These Signals can be made using different principles working sensors can be detected. It is preferred but if the sensors act as acoustic vibration sensors are trained. In this embodiment there is a particularly simple coupling of the Signals in the feelers, whereby one also makes use of makes that during the welding process, especially with the laser welding, broadband noises are generated that So be well grasped by the vibration sensors can. When evaluating the vibration of these transducers emitted signals  one also takes advantage of the fact that the weld is still warm the sound waves are not well transmitted, so that interference be reduced from one sheet to another.

The invention is described below using exemplary embodiments explained in more detail. It shows

. Figure 1 shows schematically and in perspective, the production of a welded seam with an inventive device;

Fig. 2 shows the situation of Fig. 1 again in a simplified representation, but several of the sensors are arranged on both sides of the weld.

The device according to the invention can be particularly Use advantage with a laser welding device. Out For this reason, we will refer to such a system below Referred.  

When using high-power lasers for the production of Welding in workpieces of all kinds is a very precise one Compliance with the process parameters is necessary if optimal Results are to be achieved. Among others are the following parameters important:

• - laser power on the workpiece,
• - focusing distance,
• - Focal position relative to the weld joint.

The first two parameters determine the power density at the processing location. You can z. B. by observation check the welding plasma. In a commercial Such a monitoring device is executed by registering the plasma emitted UV light. The intensity of this UV radiation is one good measure of the coupled laser power and thus for the achieved welding depth.

Of particular importance when executing Laser welds also relate the location of the weld to the joint gap. That means the weld should ideally lie symmetrically on the joint gap. The ones to be followed Tolerances are in the 0.1 mm range, which affects the accuracy and stability of the joining and Positioning device places high demands.

These requirements can be met by automatic recording the focal position with tracking of the welding head be significantly mitigated. Such tracking systems are, as mentioned, with optical or inductive Scanning of the joining gap has already been implemented. they have the disadvantage that the measuring head at a certain distance must be mounted to the welding head in order to influence it to avoid by the welding plasma. The  Measurement is therefore generally leading, which in particular the tracking for curved weld seams of the welding head difficult.

The invention of a sweat described below seam sensor system was the task with one and same measuring arrangement both welding intensity (sweat seam depth) as well as the seam position on the joint gap capture and as separate signals for corresponding over to provide monitoring or control systems. In particular the measured value acquisition in the welding location itself respectively.

The solution to this problem can be found in the following illustrate preferred embodiment described.

First, for a better understanding, look at the kinetics of the welding process and the formation of the welding plasma enter into.

When welding by laser, sufficient is formed Power density in the melted material through a channel which the radiation can penetrate deeply and in which it is perfect is absorbed. The channel is closed by the pressure of the partially evaporating material kept open. The one out flowing steam is ionized and emits strongly in the UV Area. The ejection of the material from the welding channel does not take place continuously. Rather, they arise in rapid succession individual plasma balls that are directed towards of the incident laser beam. You absorb the radiation partly and expand through heating until the laser radiation penetrate fully again can. Then another is formed  Plasma balls with subsequent weakening of the radiation on the weld pool. The process is repeated with frequencies that go far into the kHz range. This alternating signal can be obtained from the observation of the UV light can be obtained as well by registration the resulting noise with a normal microphone.

It is particularly favorable to register the structure-borne noise transmitted in the material by means of one or more vibration sensors. The arrangement according to the invention of the vibration sensor shown in FIG. 1 can be assumed. The welding example shown is the production of an I-seam for connecting two sheets 1, 2 . The focal point of the laser beam moves along a joining gap 3 , which is shown here in an exaggerated manner in order to make a fault situation clear, which can also be detected with the design of a welding monitoring system according to the invention.

A welding plasma 4 is created above the processing point and is expelled intermittently from the steam channel. The recoil generates sound waves, which are detected with two vibration sensors 5, 6 on both sides of the joint gap.

The measurement signals enable the welding bath to be centered precisely on the joining gap 3 , since the strength of the sound coupling into the material depends on how much laser power strikes the edges of the parts to be welded. The signals from the vibration sensors are standardized as follows:

with SA 1 = signal of the vibration sensor 5 and SA 2 = signal of the vibration sensor 6 .

U is a position signal that can be used directly to control a control loop. It is zero when the ideal position is reached and varies from positive to negative values, depending on whether one or the other vibration sensor is more strongly excited. It does not depend on the overall power coupling strength. This is represented by the sum of the signals from the two sensors. The value SA 1 + SA 2 = P can therefore be used to monitor the power density impinging on the material. In addition, this value can also be used to check whether the joint gap is too large, since there is then less power coupling.

In a practical embodiment of the weld seam control system, depending on the length of the weld seam, a plurality of vibration sensors 5, 6 are required, which are expediently used in a holding-down device 7 used to clamp the sheets to be welded (see FIG. 2). Instead of this, a band-shaped vibration sensor can also be arranged on both sides of the weld seam 8 .

Adaptation of the process to other welding geometries is possible. So in the case of a circular weld only two sensors are required, either grinding on the involved welding workpieces can be contacted or be fixed in such a way that a flexible cable routing rotation of the workpiece is possible.

It can thus be seen that the signal (SA 1 + SA 2 ) corresponds to the signal from the UV welding monitor. In the ideal case, the signal (SA 1 + SA 2 ) must be approximately zero if the focal point of the laser beam is symmetrically above the joining gap 3 . If this is not the case, the signal (SA 1 + SA 2 ) becomes positive or negative if the focal point is more on sheet 1 or 2 . The weld seam is hot and weakens the sound waves at the more distant vibration sensor. By standardization: a position signal U is obtained which is largely independent of hum, machine vibrations that are transmitted to both sheets or power fluctuations (laser).

The laser welding head 9 can be tracked with the signal U. If the signal SA 1 + SA 2 falls below a fixed threshold, this means that either the joining gap is too large or the laser power is too small. Both lead to the committee. The vibration sensors 5, 6 must either be moved along with the laser head (with mechanical coupling of the sheets 1 or 2 ) or SA 1 or SA 2 = sum of all signals on this side. The individual vibration sensors are attached to the jaws of the press of the system.

Claims (1)

1. Device for producing a weld seam with a welding head, which is arranged above the weld seam and can be displaced relative to it in its longitudinal direction, and with a sensor device that receives acoustic signals of the welding process and feeds an evaluation circuit, characterized in that the sensor device is two stationary The sensor ( 5, 6 ) assigned to the parts to be welded and detecting the structure-borne noise, the output signals (SA 1 , SA 2 ) of which are fed to the evaluation circuit which forms the quotients from the difference and the sum of the two output signals. 2. Device according to claim 1, characterized in that the sensors ( 5, 6 ) are designed discreetly or as continuous sensor chains.