Method for inspecting welds, particularly spot welds - Patents.com

Abstract

Inspection of welds, particularly spot welds, is not performed by directly determining the properties of the weld itself, but rather by heating an area around the weld whose surface optical properties are not affected by the previous welding process, and then measuring the spatial distribution of the thermal radiation over time from the surface within the weld area, and determining whether the measured value falls within a predetermined range of values ​​for a weld of sufficiently high quality.

Description

[Technical field]

[0001] The invention relates to a method for inspecting welds, particularly spot welds, and more particularly to a method for inspecting products in which multiple spot welds occur. [Background technology]

[0002] Currently spot welds are inspected both destructively and non-destructively. 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 surface of the weld in response to a heat source. The heat sources used are flash lamps, halogen lamps or infrared lasers. In all cases 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.

[0003] The series of recorded infrared images are then computer-processed by sophisticated algorithms that highlight small temperature differences and seek out those that are characteristic of a quality weld.

[0004] These methods have their own advantages over other methods, but also have many disadvantages. A fundamental disadvantage that 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, where the absorption of thermal radiation is influenced in a variety of ways by the previous welding process. The original homogeneous photothermal properties of the surface are disturbed by the formation of oxide layers, adherent impurities, and mechanical pressure. The result is an irregular, spatially inhomogeneous absorption of a spatially homogeneous heat source. These phenomena in the thermal process overlap with the thermal phenomena caused by poor weld quality, as a result of which the automatic assessment of low-quality welds is significantly hindered.

[0005] Another drawback of the current state of the art is the use of flash lamps with short excitation heat pulses and small temperature differences in the controlled weld, which means the need to use expensive cooled infrared cameras and spatial algorithms that require processing time and data volume.When using lasers, the main problem is to achieve spatial homogeneity of heating over larger areas and the dependence of the heat flux density on the distance of the heat source from the controlled surface. Summary of the Invention [Means for solving the problem]

[0006] The invention is based on the fact that inspection of welds, in particular spot welds, is not carried out by directly determining the properties of the weld itself, but rather an area around the weld, the optical properties of whose surface are not affected by the previous welding process, is heated, and then the spatial distribution of the time course of the thermal radiation from the surface in the weld area is measured and it is determined whether the measured values ​​fall within a predefined range of values ​​for a weld of sufficiently high quality.

[0007] The area around the weld is the nearest closed area whose surface optical properties are not affected by the previous welding process, for example the nearest intermediate ring, i.e. the ring whose inner circle is separated from the outer boundary of the weld within a range of 0.5 mm to 25 mm.

[0008] The area around the weld is the closest open area whose surface optical properties have not been affected by a previous welding process, and which encompasses more than 270 degrees of a circle centered on the weld being inspected. This open area may consist of more parts.

[0009] The periphery of the weld is preferably heated in a non-contact manner and the spatial distribution over time of thermal radiation from the surface in the area of ​​the weld is preferably measured non-contact by radiometry.

[0010] The spatial distribution of the time course of the thermal radiation from the surface in the area of ​​the weld is preferably measured within a range of 0.01 to 10 seconds.

[0011] That the value falls within a predetermined range of values ​​for a sufficiently high quality weld is determined from a sample of high quality welds or by computer simulation.

[0012] A fundamental advantage of the method for quality control of welds according to the invention is that the heating is applied in the vicinity of the weld, whose surface optical properties are not affected by previous welding steps, which ensures spatially homogeneous heating within one controlled weld and reproducibility of the absorbed power within several different welds of the same type.

[0013] In the current state of the art, the surface including the weld itself is also heated, and therefore there is significant non-uniformity and non-repeatable heating of the measured area due to impurities that constantly occur on the surface of the weld itself.

[0014] The process of inspecting welds significantly simplifies the process of automating the inspection of the same type of weld occurring on the same welded part by avoiding heating the surface of the weld itself, which is often affected in different and irregular ways by previous welding processes. Effect of the Invention

[0015] The advantage of the method according to the invention is that it makes it possible to realize larger temperature differences with further heating times and thus to use bolometric uncooled thermal imagers of the order of magnitude cheaper type instead of faster and more expensive photonic thermal imagers that require additional active cooling. In the current state of the art, the heating process that creates temperature differences between welds with different defects only occurs for a small part of the total inspection time. The process of differentiating welds, the automation of the machine evaluation and the problems of processing large data are significantly simplified by using continuous laser action and by using an evaluation carried out on the temperature during the heating phase instead of a cooling phase after a short heating pulse.

[0016] The advantage of the method for quality control of welds according to the invention is that it makes it possible to define the effects of different powers, times and spaces of non-contact heat sources and thus to solve the optimal parameters for the control of different welds that usually occur on one welded part.

[0017] The method of weld inspection according to the invention allows simpler and less expensive components to be used to inspect welds overall, thereby significantly reducing the capital requirements of the overall inspection facility.

[0018] Certain exemplary embodiments of the invention are illustrated in the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 illustrates a schematic diagram of an apparatus for performing a weld inspection method and heat fluxes associated with the heating and temperature response measurement steps. [Diagram 2] FIG. 2 is a schematic plan view of the welded portion and its surroundings in FIG. 1; [Diagram 3] 1 shows the heat flux within the welded material being inspected. [Figure 4] 1 shows the spatial heat flux on the material surface in and around the area of ​​the weld. [Diagram 5] The spatial temperature distribution on the material surface is shown in the cross section of the weld. [Figure 6] 1 shows the time course of the heat flux action divided into heating and cooling phases. [Figure 7] 4 shows the time course of the surface temperature in and near the weld area. [Figure 8] 1 shows an assessment of the weld quality by the measured surface temperature in the weld area. [Figure 9] 1 shows a schematic diagram of inspection of spot welds. [Figure 10] 1 shows a schematic diagram of inspection of a line weld. [Figure 11] 1 shows a schematic of inspection of a spatially featured weld; [Figure 12] 1 shows a schematic representation of an embodiment of an opto-mechanical component using a lens or an aperture. [Figure 13] 1 shows a schematic representation of an embodiment of a mirror-based opto-mechanical component using a scanning head; [Figure 14] 1 shows a schematic of a weld testing device that ensures that a measurement system and a weld to be inspected are positioned in a desired relative position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The inspection of a weld according to the invention can be carried out on a device which is shown diagrammatically in Figure 1. 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 are provided by a control unit 3. The welded part to be inspected consists of an upper plate 4, a lower plate 5 and the actual joint which is the weld nugget 6. The testing device contains optical-mechanical elements which ensure a defined spatial-temporal action of the laser beam in the vicinity of the weld.

[0021] The surface around the weld nugget 6 is shown in Fig. 2. A heating heat flux 7 acts on the heated area 14 of the upper plate 4, providing heating around the weld. However, in the context of the invention, the heating heat flux 7 may also act on the area of ​​the weld, as most of the power of the laser source 1 should act on the vicinity of the weld, whose optical properties are not affected by the previous welding process. A radiant heat flux 8 is sensed by the infrared detector system 2 from a measurement area 15 that includes the weld area and its vicinity.

[0022] The heat flux of the material during the heating process is shown in Fig. 3. A heating heat flux 7 acts around the weld. The laser beam is absorbed by the surface of the material and causes an increase in temperature around the weld. The heat is then mainly transferred 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.

[0023] The spatial distribution of heat flux on the surface of the material in and near the weld zone and the heat flux time curves are shown diagrammatically in Figures 4 and 5. The heating heat flux 7 acts spatially on the heated zone 14 around the weld nugget 6, and preferably does not act on the region of the weld nugget 6 itself.

[0024] The process of the action of the laser source from a time point of view can be seen in Fig. 5. It is divided into a heating phase 16, during which the laser beam hits the surface around the weld and heats it up, and a cooling phase 17, during which the material surface cools down after the laser source is switched off.

[0025] The spatial and temporal temperature profiles on the surface of the material in the area of ​​the weld are shown diagrammatically in FIGS.

[0026] At time t during the heating process TThe spatial distribution of the material surface temperature in the measured area 15 at the weld cross section in is shown in Figure 6. In the heated area 14 around the weld nugget 6 there is a maximum temperature 10, the value of which is most influenced by the laser power and the thermal properties of the upper plate 4.

[0027] 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. Next, FIG. 7 shows the laser heating zone x around the weld, i.e., in the vicinity of the weld nugget 6. p The temperature profile 12 in the weld, i.e. the area x of the weld itself, T 13 and the temperature profile over time at 14 are shown diagrammatically, with which a basic assessment of the weld quality is made.

[0028] A method for assessing the quality of a weld using measured surface temperatures in the weld zone is shown in FIG. 8. Using experimental calibration or using computer simulations of weld variants, an appropriate temperature zone 20 is determined. For given welding parameters, in particular the thickness of the upper and lower plates 4 and 5 and the size of the weld nugget 6, and for given heating parameters, in particular the power of the laser source 1 and the size of the zone acted upon by the heating heat flux 7, an area corresponds to a high-quality weld. This area is marked "OK" in FIG. 8 and corresponds to the temperature of a high-quality weld 18.

[0029] Higher temperatures would result in high temperature zones 21, which are indicative of a poor weld where less heat is dissipated through the weld nugget 6 and bottom plate 5 than a high quality weld. Lower temperatures would result in low temperature zones 22, and thus the inspection result would also be unsatisfactory, marked as "NOK" in FIG. 8, primarily due to failure to achieve the required heating around the weld. These areas represent the temperatures of poor quality welds 19.

[0030] Surface temperatures are typically measured non-contact using infrared detectors that primarily detect the intensity of the radiative heat flux 8 emitted by the surface of the material. Temperature is assessed by quantification of the radiation processes involved, including values ​​of the emissivity of the measured surface, the temperature of the radiating environment, and the transmittance of the atmosphere. Thus, the method of determining weld quality is the same whether temperature values ​​or source signal values ​​of the measured heat flux are used for the assessment.

[0031] The inspection of welds by the method according to the described invention can be used for welds of different shapes and different sizes produced by various techniques, as shown diagrammatically in Figures 9 to 11. These can be spot welds produced by resistance welding technique as shown in Figure 9, or line welds produced by laser technique using a technological head as shown in Figure 10, or spatially featured welds produced by so-called remote laser technique using a scanning head as shown in Figure 11.

[0032] The shape of the heated zone 14 where the laser beam acts corresponds to the shape and size of the weld nugget 6 to be inspected, as well as the shape and size of the welded part to be inspected, i.e., the presence of edges of material or other welds. The spatial distribution of heat flow in this heated zone 14 is not homogenous and may be related to the above-mentioned characteristics of the weld to be inspected. The heated zone 14 does not have to be merely the immediate vicinity of the weld, nor does it have to be a closed zone, but must always serve to ensure that the heating process and temperature response measurements meet the need for precision and repeatability to distinguish between high quality welds and low quality welds.

[0033] The technical implementation of the optical-mechanical member 9 ensuring the spatial and temporal action of the laser beam on the surface around the weld can be performed in various ways, as shown diagrammatically in Figures 12 and 13. This can involve the principle of shaping the laser beam by means of a lens 23 or an aperture 24 in Figure 12, or the principle of positioning the laser beam using mirrors, for example by means of a scanning head in Figure 13.

[0034] It is usually necessary to inspect several different welds located at different spatial locations on a single welded part.

[0035] In such a case, it is necessary to ensure the desired relative position of the measurement system and the welded part to be inspected. This can be ensured by mounting the attachment of the measurement system 26 on the arm of an industrial robot 28 or on a gantry manipulator, as shown in Figure 14, and the arm moves the measurement part of the device around the statically positioned welded part using the attachment 27 of the welded part to be inspected. The reverse method is also technically feasible, in which case the welded part to be inspected is positioned with respect to the stationary measurement system using an industrial robot or another conveyor. [Industrial Applicability]

[0036] The invention can be used, inter alia, for work sites where multiple spot welds are performed and the quality of the welds needs to be inspected quickly and efficiently. [Explanation of symbols]

[0037] 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 Temperature profile around the weld 13 Temperature profile at welds over time 14 Heated area 15 Area to be measured 16 Heating Phase 17 Cooling Phase 18 High quality weld temperature 19 Temperature of poor quality welds 20 Appropriate temperature range 21 High temperature zone 22 Low temperature zone 23 Lens 24 Aperture 25. Mirror 26 Measurement system attachments 27 Attachment of the welded part to be inspected 28 Industrial Robots

Claims

1. A method for the inspection of welds, in particular spot welds, comprising: a method comprising heating an area around the weld, the optical properties of whose surface are not affected by a previous welding process that produced the weld being inspected, followed by measuring the spatial distribution of the time course of thermal radiation from said surface in the weld area, and determining whether said measured value falls within a predetermined range of values ​​for a weld of sufficiently high quality.

2. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of: The method, characterized in that the area around the weld is the closest enclosed area whose optical properties of the surface are not affected by the previous welding process that created the weld being inspected.

3. 3. A method for inspection of welds, in particular spot welds, according to claim 2, comprising the steps of: wherein the area around the weld is the nearest intermediate ring, the optical properties of the surface of which are not affected by the previous welding process that created the weld being inspected, and the inner circle of which is separated from the outer boundary of the weld by 0.5 mm to 25 mm.

4. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of: the area around the weld is the nearest non-closed area whose surface optical properties are not affected by a previous welding process that created the weld being inspected, and the non-closed area encompasses more than 270 degrees of a circle centered on the weld being inspected.

5. 5. A method for inspection of welds, in particular spot welds, according to claim 4, comprising the steps of: the non-occluded area, the optical properties of the surface of which were not affected by a previous welding process that created the weld being inspected, and which circumscribes more than 270 degrees of a circle centered on the weld being inspected, is comprised of at least two portions.

6. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of: wherein the area around the weld is heated in a non-contact manner.

7. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of:

5. The method of claim 1, wherein the spatial distribution of the time course of the thermal radiation from the surface within the weld area is measured non-contact by radiometry.

8. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of: wherein the spatial distribution of the time course of the thermal radiation from the area of ​​the weld is measured within a range of 0.01 seconds to 10 seconds.

9. 2. A method for inspection of welds, in particular spot welds, according to claim 1, comprising the steps of: The method of claim 1, wherein the value falls within a predetermined range of values ​​for a sufficiently high quality weld is determined from a set of high quality welds or by computer simulation.

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