JP2023546637A - Method for inspection of welds, especially spot welds - Google Patents

Abstract

Inspection of welds, particularly spot welds, is not carried out by directly determining the properties of the weld itself, but rather by determining the area around the weld whose surface optical properties are The area unaffected by the welding process is heated, then the spatial distribution of the time course of the heat radiation from the surfaces within the weld area is measured and the measured values are determined for a sufficiently high quality weld. Determines whether it falls within a range of default values. [Selection diagram] Figure 1

Description

The invention relates to a method for inspecting welds, in particular spot welds, and in particular to a method for inspecting products in which a plurality of spot welds occur.

Currently, spot welds are inspected using both destructive and non-destructive methods. Non-destructive and non-contact methods include methods based on the use of infrared radiation and heat transfer processes. They measure the temperature response of the front or back side of the weld in response to a heat source. The heat sources used are flash lamps, halogen lamps or infrared lasers. In each case the surface is heated in the area of the weld. The thermal processes during and after the action of the heat source are measured by infrared detectors or thermal imagers.

A series of recorded infrared images are computer-processed using sophisticated algorithms that highlight small temperature differences and look for differences with the characteristics of high-quality welds.

Although these methods have unique advantages over other methods, they also have a number of drawbacks. A fundamental drawback, which in principle complicates the distinction between high-quality and low-quality welds, is the action of the heat source on the surface of the material of the weld, and in the weld area the absorption of thermal radiation is caused by the previous welding process. be influenced in various ways by The original homogeneous photothermal properties of the surface are disturbed by the formation of oxide layers, deposited impurities, and mechanical stress. The result is an irregular spatially heterogeneous absorption of a spatially homogeneous heat source. These phenomena in the thermal process overlap with the thermal phenomena caused by poor weld quality, and as a result, the automatic evaluation of poor quality welds is significantly hindered.

Another shortcoming of the current state of affairs is the use of flash lamps with short excitation heat pulses and small temperature differences in the controlled weld, which means expensive cooled infrared cameras and spatial algorithms that require processing time and data volume. is the necessity of using. When using lasers, the main problem is to achieve spatial homogeneity of heating over a larger area and a controlled dependence of the heat flux density on the distance of the heat source from the surface.

The invention provides that the inspection of welds, particularly spot welds, is carried out not by directly determining the properties of the weld itself, but by determining the optical properties of the area around the weld and its surface. The area unaffected by the previous welding process is heated, then the spatial distribution of the time course of the heat radiation from the surfaces within the weld area is measured and the measured values are of sufficiently high quality. It is based on the fact that the determination is made whether it falls within the range of predetermined values for the weld.

The area around the weld is the closest closed area whose surface optical properties are not affected by the previous welding process, for example the closest intermediate ring, i.e. its inner circle outside the weld. The ring is spaced within a range of 0.5 mm to 25 mm from the boundary.

The area around the weld is the closest open area whose surface optical properties are unaffected by the previous welding process, and this open area is centered on the weld to be inspected. Encloses more than 270 degrees of a circle. This open area may also consist of more parts.

The surroundings of the weld are preferably heated in a non-contact manner and the spatial distribution of the time course of the heat radiation from the surfaces in the area of the weld is preferably measured in a non-contact manner by radiometry.

Preferably, the spatial distribution of the time course of the heat radiation from the surface in the area of the weld is measured within a range of 0.01 seconds to 10 seconds.

That the value falls within predetermined values for sufficiently high quality welds is determined from samples of high quality welds or by computer simulation.

A fundamental advantage of the method of quality control of welds according to the invention is that the heating acts in the vicinity of the weld, the optical properties of whose surfaces are not influenced by previous welding steps. This ensures spatially homogeneous heating within one controlled weld and reproducibility of the absorbed power within different welds of the same type.

In the current state of the art, the surfaces containing the weld itself are also heated, and therefore there is significant non-uniformity and non-reproducibility of the heating of the measured area due to impurities that regularly occur on the surface of the weld itself. .

The process of inspecting welds avoids heating the surface of the weld itself, which is often influenced in a variable and irregular manner by previous welding operations, and thus detects the same type of damage occurring on the same welded part. Significantly simplifies the process of automating the inspection of welds.

The advantage of the method according to the invention is that it makes it possible to achieve larger temperature differences with additional heating times and thus instead of faster and more expensive photon thermal imagers that require additional active cooling. It is possible to use a type of bolometric uncooled thermal imager that is orders of magnitude cheaper. With the current state of the art, the heating process that creates temperature differences between welds with different defects occurs only for a small portion of the total inspection time. The problem of differentiating weld processes, automating machine evaluation, and processing large data can be solved by using continuous laser action and by reducing the temperature during the heating phase instead of the cooling phase after a short heating pulse. By using evaluations carried out to

The advantage of the method of quality control of welds according to the invention is that it makes it possible to define the different power, time and space effects of the non-contact heat source and thus the different welds that normally occur on one welded part. It becomes possible to solve the optimal parameters for the control of

The method of inspecting welds according to the invention allows overall simpler and cheaper components to be used for inspecting welds, so that the investment requirements of the overall inspection station are significantly reduced.

Certain illustrative embodiments of the invention are illustrated in the accompanying drawings.

1 schematically depicts an apparatus for carrying out a weld inspection method and the heat fluxes associated with the heating step and temperature response measurement step; FIG. 2 schematically shows a plan view of the welded portion in FIG. 1 and its surroundings. Indicates the heat flux within the welded material being inspected. Figure 3 shows the spatial heat flux on the material surface in the area of the weld and its surroundings. The spatial temperature distribution on the material surface is shown in the weld section. The time course of the heat flux action is shown divided into a heating phase and a cooling phase. Figure 3 shows the time course of the surface temperature in the weld zone and its vicinity; Figure 3 shows an evaluation of the weld quality by the measured surface temperature in the weld area. The inspection of spot welds is schematically shown. The inspection of a line weld is schematically shown. Fig. 3 schematically shows the inspection of a spatially distinctive weld. 2 schematically shows an embodiment of an optical mechanical member using a lens or an aperture. 1 schematically shows an embodiment of an opto-mechanical element with mirrors using a scanning head; 1 schematically depicts a weld testing device ensuring positioning of the measurement system and the weld to be inspected in the desired relative position;

The inspection of welds according to the invention can be carried out on the device shown schematically in FIG. The heating process is provided by a laser source 1, an infrared detector system 2 is used to measure the temperature response, and control, communication, evaluation and display is provided by a control unit 3. The welded part to be inspected consists of the upper plate 4, the lower plate 5, and the actual joint, which is the weld nugget 6. The test device includes opto-mechanical elements that ensure a defined spatio-temporal action of the laser beam in the vicinity of the weld.

The surface around the weld nugget 6 is shown in FIG. A heating heat flux 7 acts on the heated area 14 of the upper plate 4 and provides heating around the weld. However, in the context of the invention, the heating heat flux 7 is the welding zone when most of the power of the laser source 1 should act in the vicinity of the weld, whose optical properties are unaffected by the previous welding process. It can also affect the area of the body. A radiant heat flux 8 is sensed by an infrared detector system 2 from a measured area 15 including the weld area and its vicinity.

The heat flux of the material during the heating process is shown in FIG. A heating heat flux 7 acts around the weld. The laser beam is absorbed by the surface of the material, causing an increase in temperature around the weld. Subsequently, the heat is mainly conducted through the upper plate 4 to the weld area and dissipated through the weld nugget to the lower plate 5. This tells us that the thermal process causes heating of the weld area surface, where the temperature is significantly influenced by the thermal properties of the welded joint.

The spatial distribution of the heat flux on the surface of the material in the weld area and its vicinity and the heat flux time curve are shown schematically in FIGS. 4 and 5. Preferably, the heating heat flux 7 acts spatially on the heated area 14 around the weld nugget 6, and that the heating heat flux 7 does not act on the area of the weld nugget 6 itself.

The process of operation of the laser source in terms of time can be seen from FIG. It is divided into a heating phase 16, during which the laser beam hits the surface around the weld and heats the surface, and a cooling phase 17, during which the surface of the material cools down after the laser source has been switched off.

The spatial and temporal temperature profiles on the surface of the material in the area of the weld are shown schematically in FIGS. 6 and 7.

The spatial distribution of the surface temperature of the material in the measured area 15 in the weld section at time t _T during the heating process is shown in FIG. There is a maximum temperature 10 in the heated area 14 around the weld nugget 6, the value of which is most influenced by the laser power and the thermal properties of the upper plate 4.

At the location of the weld nugget 6, the level of the surface temperature 11 is mainly influenced by the thermal properties of the weld nugget 6, which are indicative of the quality of the weld. FIG. 7 then shows the time course 12 of the temperature in the laser-heated area x _p around the weld, i.e. in the vicinity of the weld nugget 6, and in the weld, i.e. in the area x _T of the weld itself. 13 is schematically shown, and basic evaluation of the quality of the weld is performed using it.

A method for evaluating the quality of a weld using the measured surface temperature in the weld area is shown in FIG. A suitable temperature zone 20 is determined using experimental calibration or using a computer simulation of the weld variant. For given welding parameters, in particular the thickness of the upper plate 4 and lower plate 5 and the size of the weld nugget 6, and given heating parameters, in particular the power of the laser source 1 and the size of the area on which the heating heat flux 7 acts. The area corresponds to high quality welds. This area is marked "OK" in FIG. 8 and corresponds to the temperature of the high quality weld 18.

If the temperature is higher, a high temperature zone 21 will be reached, which means a low-quality weld in which less heat is dissipated through the weld nugget 6 and the lower plate 5 than in a high-quality weld. suggest. If the temperature were lower, a low temperature zone 22 would be reached and the result of the test would therefore still be unsatisfactory, marked "NOK" in FIG. This is due to the fact that heating could not be carried out. These areas represent the temperature of the poor quality weld 19.

Surface temperature is generally measured non-contact using an infrared detector that primarily detects the intensity of the radiant heat flux 8 emitted by the surface of the material. Temperature is evaluated by quantifying the radiative processes involved, including emissivity values of the surface being measured, temperature values of the radiant environment, and transmittance values of the atmosphere. Therefore, the method for determining weld quality is the same whether temperature values or source signal values of the measured heat flux are used for its evaluation.

Inspection of welds by the method according to the described invention can be used for welds of different shapes and sizes produced by various techniques. This is shown schematically in FIGS. 9 to 11. These may be spot welds formed by resistance welding techniques, as shown in Figure 9, or line welds, formed by laser technology with a technical head, as shown in Figure 10. It can be a spatially characterized weld formed by so-called remote laser technology using a scanning head as shown in FIG.

The shape of the heated area 14, on which the laser beam acts, corresponds to the shape and size of the weld nugget 6 to be inspected, and likewise to the shape and size of the welded part to be inspected, i.e. edges of the material or other welds. It also corresponds to existence. The spatial distribution of the heat flow in this heated area 14 is not homogeneous and may be related to the above-mentioned properties of the weld under test. The heated area 14 need not simply be in the immediate vicinity of the weld, nor does it need to be a closed area, but it is always necessary for the heating process and temperature response measurements to distinguish between high quality and low quality welds. It must serve to meet the needs of precision and reproducibility.

The technical implementation of the opto-mechanical element 9, which ensures the spatial and temporal action of the laser beam on the surface around the weld, can be carried out in various ways, as shown schematically in FIGS. 12 and 13. It can be carried out with This may involve the principle of shaping the laser beam by a lens 23 or aperture 24 in FIG. 12, or positioning the laser beam using mirrors, for example by a scanning head in FIG. 13.

It is usually necessary to inspect several different welds located at spatially different locations on one welded part.

In such cases, it is necessary to ensure the desired relative position of the measuring system and the welded part to be inspected. As shown in FIG. 14, the attachment of the measurement system 26 is installed on the arm of the industrial robot 28 or on the gantry manipulator, and the arm is attached to the attachment 27 of the welded part to be inspected. This can be determined by moving the measuring part of the device around the statically positioned part to be welded using the The opposite method is also technically possible, in which case the welded part to be inspected is positioned with respect to a stationary measuring system using an industrial robot or another conveyor.

The invention can be used, inter alia, for workshops where multiple spot welds are performed and the quality of those welds needs to be inspected quickly and efficiently.

1 Laser source 2 Infrared detector system 3 Control unit 4 Upper plate 5 Lower plate 6 Welding nugget 7 Heating heat flux 8 Radiant heat flux 9 Optical and mechanical components 10 Maximum temperature 11 Surface temperature 12 Around the weld Temperature over time 13 Temperature over time in the weld 14 Area to be heated 15 Area to be measured 16 Heating phase 17 Cooling phase 18 Temperature of high quality weld 19 Temperature of low quality weld 20 Appropriate temperature range 21 High temperature Band 22 Low temperature zone 23 Lens 24 Aperture 25 Mirror 26 Attachment of measurement system 27 Attachment of welded part to be inspected 28 Industrial robot

Claims (9)

In a method for inspecting welds, especially spot welds,
An area around the weld, the optical properties of whose surface is unaffected by the previous welding process, is heated, followed by a temporal adjustment of the thermal radiation from the surface within the weld area. A method characterized in that the spatial distribution of the progress is measured and it is determined whether the measured value falls within a range of predetermined values for a sufficiently high quality weld. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
A method characterized in that the area around the weld is the closest closed area, the optical properties of the surface being unaffected by the previous welding process. A method for inspection of welds, in particular spot welds, according to claim 2, comprising:
The area around the weld is the closest intermediate ring, the optical properties of the surface of which are unaffected by previous welding steps, and whose inner circle extends from the outer boundary of the weld. A method characterized in that the rings are separated by 0.5 mm to 25 mm. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
The area around the weld is the closest non-closed area, the optical properties of the surface being unaffected by the previous welding process, and this non-closed area is the closest non-closed area to the inspection. A method characterized by enclosing more than 270 degrees of a circle centered on the target weld. A method for inspecting welds, in particular spot welds, according to claim 4, comprising:
the non-closed area, the optical properties of the surface of which are unaffected by previous welding steps, and which enclose more than 270 degrees of a circle centered on the weld to be inspected; A method characterized in that the area consists of at least two parts. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
A method characterized in that the area around the weld is heated in a non-contact manner. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
Method, characterized in that the spatial distribution of the time course of the thermal radiation from the surface in the weld area is measured non-contact by radiometry. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
The method characterized in that the spatial distribution of the time course of the thermal radiation from the surface in the area of the weld is measured in the range from 0.01 seconds to 10 seconds. A method for inspection of welds, in particular spot welds, according to claim 1, comprising:
The method characterized in that said value falling within a predetermined range of values for sufficiently high quality welds is determined from a set of high quality welds or by computer simulation.

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