CN115628710A - Thermal wave imaging coating detection device and method - Google Patents
Thermal wave imaging coating detection device and method Download PDFInfo
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- CN115628710A CN115628710A CN202110754044.3A CN202110754044A CN115628710A CN 115628710 A CN115628710 A CN 115628710A CN 202110754044 A CN202110754044 A CN 202110754044A CN 115628710 A CN115628710 A CN 115628710A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
- G01B21/085—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness using thermal means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
- G01B15/02—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons for measuring thickness
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- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Length Measuring Devices With Unspecified Measuring Means (AREA)
- Investigating Or Analyzing Materials Using Thermal Means (AREA)
Abstract
The invention relates to a thermal wave imaging coating detection device and a method, wherein the device integrates a reference test piece, is positioned in a field of view of a thermal imager together with a tested piece, simultaneously carries out thermal excitation and thermal wave imaging detection, and corrects the initial detection value of the tested piece by using the measurement result of the reference test piece with known coating parameters to obtain the accurate result of the tested piece.
Description
Technical Field
The invention relates to a device and a method for detecting coating thickness based on a thermal wave imaging technology, belonging to the technical field of infrared nondestructive testing.
Background
With the rapid development of scientific technology, the application of the coating is more and more extensive, and the industry has raised higher requirements for measuring the thickness and defects of the coating, such as the requirements of online, non-contact, real-time detection and the like. The conventional means used for detecting the thickness of the coating at present mainly comprise eddy current, ultrasound, X-ray, probe method, optical method and the like, but the methods cannot completely meet the requirements of modern industry on the detection of the coating, such as the eddy current method has the requirements on the properties of a substrate material and must have electromagnetic properties; the ultrasonic method requires a coupling agent and cannot effectively measure thin coatings; x-ray requires that the sample can be detected by transmission and has special safety protection requirements; the probe method belongs to contact detection and has damage to a sample; optical methods require that the film layer be a transparent medium and have a high finish, and the like. At present, most coatings have the characteristics of thin thickness, non-transparency, fragility, easy damage and the like, so that more advanced technical means are required to meet the measurement requirement of the films.
The thermal wave imaging technology is a nondestructive testing means developed recently, and the basic principle of the nondestructive testing method is that a thermal excitation source is adopted to heat the surface of a test piece, so that a thermal pulse is generated and is transmitted to the interior of the test piece, when thermal waves encounter defects or the thermal impedance changes in the interior of the test piece, a part of the thermal energy is generated and is reflected back to the surface of the test piece, and dynamic temperature distribution is formed on the surface of the test piece. And recording information of the surface temperature of the test piece along with time by using a thermal infrared imager, and correcting, processing and analyzing thermal wave signals by image processing to realize detection of the thickness of the film layer. Compared with the traditional nondestructive detection means, the thermal wave imaging technology has unique advantages, such as non-contact, large-area rapid imaging, suitability for non-transparent coating, sensitivity to the thermal property of the material and the like, and can meet the requirement of film thickness detection in modern industry.
However, the thermal wave imaging technique is an indirect measurement method, and the result is obtained by comprehensively measuring and calculating various physical parameters, so that the system is susceptible to system drift caused by various external factors, such as aging of parts, changes in environmental conditions, and changes in operation methods. These all affect the accuracy of detection and require compensation corrections. In addition, when the coating is detected by thermal wave imaging, the relation between the detected signal and the thickness of the coating is complex, and the calculation cannot be carried out by using a simple formula, so that the difficulty is brought to the accurate measurement of the thickness of the coating.
Disclosure of Invention
The invention aims to provide a novel detection device and a novel detection method aiming at the defects of the current thermal wave imaging coating detection technology.
For the detection of the thickness of the coating, the reference test pieces adopt the coating which is the same as or similar to the coating of the tested piece, the thickness is distributed in a certain range, the range comprises the thickness of the coating of the tested piece, the reference test pieces are detected, and the detection result is fitted to obtain a relation curve reflecting the thickness of the coating and the measured value of the thermal wave imaging. Thus, when the tested piece is detected, the corresponding coating thickness can be obtained on the relation curve by using the obtained measured value.
Drawings
FIG. 1 is a schematic view of an apparatus of the present invention;
FIG. 2 is a schematic diagram of the thermal wave imaging detection principle;
FIG. 3 is a three-dimensional schematic view of an apparatus of the present invention;
FIG. 4 is a schematic view of a thermal imager field of view and a reference test strip;
FIG. 5 is a schematic diagram of system drift detection calibration using a reference strip;
FIG. 6 is a schematic diagram of a plurality of reference test strips for detecting the coating thickness of a test piece.
Detailed Description
In order that the features of the invention may be better understood, the invention will now be further described with reference to the following specific drawings and examples.
First, the basic principle of thermal wave imaging is described, and as shown in FIG. 2, a thermal excitation source 11 heats the surface of a test piece 14, which may be in the form of high energy short pulses, or intensity modulated so-called phase lock. The generated thermal wave 21 propagates towards the interior of the tested piece, when meeting the interface 23 between the coating 15 and the substrate, one part of the transmitted thermal wave 24 continues to propagate towards the interior of the sample, the other part of the reflected thermal wave 22 will be reflected back to the surface of the sample, and the time, intensity and the like of the reflected thermal wave are related to the thickness of the coating and the physical properties of the coating and the base material. By detecting the time-varying relation of the thermal wave signal, the information such as the thickness of the coating can be obtained.
In the detection process of thermal wave imaging, the temperature of the surface of the tested piece is determined by thermal excitation energy, surface light energy absorptivity, material heat capacity, density, thermal diffusion coefficient, ambient temperature and the like. The surface temperature and the thermal excitation energy are in a direct proportion relation and are in a linear relation with the system drift, so that the data can be normalized by a method for simultaneously detecting the reference test piece and the tested piece, and the influence generated by the thermal excitation energy and the system drift can be eliminated.
Fig. 1 is a schematic diagram of the system of the present invention, which is composed of a thermal imager 10, a thermal excitation source 11, a support frame 12, a reference test piece 13, a signal acquisition and processing module 16, a thermal excitation driver 17, and the like. The thermal imager 10 is fixed at one end of the support frame 12, and the reference test block is fixed at the lower portion of the support frame 12 near the other end of the test piece and within the field of view of the thermal imager 10. The reference strip may be one or more, and has two functions, namely, it is used to correct the system drift, such as the intensity variation of the excitation source, or the aging of the components used in the apparatus, and the change of the ambient temperature and humidity. The reference strip may be of a material slightly different from that of the test piece, but preferably has similar physical properties. Another function of the reference strip is to calibrate the coating thickness, and the reference strip should be as identical as possible to the substrate and coating material of the tested piece, so that reliable measurement results can be obtained.
Fig. 3 is a schematic perspective view of the device of the present invention, wherein a test piece holder 18 for holding a reference test piece 13 is disposed at the bottom of the supporting frame 12, the test piece holder 18 is in the field of view, and plays a role of supporting and fixing the reference test piece 13, and simultaneously plays a role of protecting and hiding the reference test piece 13, i.e. the reference test piece is not visible from the outside. Fig. 4 shows the spatial relationship between the test piece tray 18, the reference test piece 13, the outer frame 25 of the support frame 12, and the field of view 24 of the thermal imager 10, where the reference test piece 13 is located at the edge of the field of view 24 of the thermal imager 10, and when the detection result is presented, the tray area in the field of view is hidden by the software, so that the reference test piece 13 is not shown in the image of the detection result.
Usually, when the system drifts, including the change of environmental conditions, the same ratio of the influence is generated on the reference test strip 13 and the tested object 14, as shown in fig. 5, since various parameters of the reference test strip 13 are known, when the measurement result changes, usually caused by the change of external conditions, the same influence is generated on the tested object 14. The measured value of the tested object 14 is corrected by using the measured value of the reference test piece 13, so as to obtain the correct value of the tested object 14.
When coating thickness measurements are made, the measurements and the coating are related to a number of physical parameters of the substrate material, as these physical parameters are often not accurately known. In addition, various factors cannot be sufficiently taken into consideration, and therefore, it is difficult to directly measure the coating thickness. For this purpose, a calibration curve method can be used, as shown in fig. 6, several reference test pieces 13 with different thicknesses are used, the thermal wave signal values of these reference test pieces 13 with different thicknesses are measured, and numerical fitting is performed on the coordinates of the thermal wave signal corresponding to the thickness of the coating layer, so as to obtain a calibration formula. When the tested piece 14 is detected, the obtained thermal wave signal is substituted into the calibration formula, so that the coating thickness of the tested piece 14 can be obtained. Usually, the reference test piece 13 is made of the same or similar material as the tested object 14, and the coating thickness of the reference test piece 13 is distributed around the coating thickness range of the tested object 14, so as to obtain better detection accuracy.
Based on the thermal wave imaging detection device, the method for correcting the drift caused by the change of the system and the environment during the detection of the coating comprises the following steps:
A. thermally exciting the to-be-tested piece and the reference test piece by a thermal excitation source at the same time;
B. simultaneously acquiring the changes of the surface temperatures of the piece to be tested and the reference module along with time by adopting a thermal imager;
C. analyzing the time-varying curves of the surface temperatures of the test piece to be tested and the reference test piece by the data processing device to obtain a preliminary measurement result;
D. the method comprises the steps of comparing a preliminary detection result of a reference test piece with a detection result of the reference test piece during system calibration to calculate the drift amount of the result, and correcting the preliminary detection result of the tested piece by using the drift amount, thereby eliminating the influence of a thermal excitation source, a detection system or environmental condition change on the detection result of the tested piece.
Also, a method for detecting a coating thickness of the present invention includes the steps of:
A. selecting a plurality of reference test pieces with known thickness, and placing the reference test pieces in a visual field of a thermal imager;
B. thermally exciting the to-be-tested piece and the reference test piece by using a thermal excitation source;
C. simultaneously acquiring the changes of the surface temperatures of the test piece to be tested and the reference test piece along with time by adopting a thermal imager;
D. calculating the detection results of a plurality of reference test pieces with different coating thicknesses, and performing numerical fitting on the detection results to obtain a calibration formula of the relation between the detection signal and the coating thickness, wherein the calibration formula for fitting can adopt a physical formula based on theoretical derivation or simply adopts a polynomial;
E. and comparing the detection signal of the tested piece with the calibration curve to obtain the coating thickness of the tested piece.
The thermal excitation source may be actuated in a variety of ways, such as by pulsing, i.e., by a short pulse of high energy, typically a flash lamp. The thermal imaging system collects the variation curves of the surface temperatures of the reference test piece and the tested piece along with time, and obtains the information of the thickness of the coating and the like by analyzing the characteristics of the variation curves. For another example, a phase-locked method is adopted, that is, a periodically modulated thermal excitation mode is adopted to generate periodically-changed temperature distribution on the surfaces of the reference test piece and the tested piece, and the information such as the thickness of the coating is obtained through calculation by analyzing the phase change of the periodic temperature of the surface.
The invention is mainly applied to the measurement of the thickness of a coating, and comprises a single-layer or multi-layer structure, but can also be applied to the detection of other physical parameters of the coating, such as the thermal characteristics, the mechanical parameters, the bonding quality and the like of the coating and a substrate material.
The foregoing description of the invention is illustrative, but not limiting, and it is intended that the invention be modified, varied and equivalents within the scope of the claims appended hereto as fall within the scope of the invention.
Claims (9)
1. A thermal wave imaging coating detection device, comprising:
the thermal excitation source is used for exciting thermal waves on the surface of the tested piece;
the thermal imager is used for acquiring a thermal wave signal of the surface of the tested piece;
the signal acquisition processing module is used for analyzing and processing the acquired thermal wave image;
the supporting frame is used for bearing the thermal imager and keeping the working distance between the thermal imager and the tested piece;
and the reference test piece is arranged on the supporting frame and close to the part of the tested piece, is positioned in the field of view of the thermal imaging instrument and is used for providing a correction basis for the detection result of the tested piece.
2. The device according to claim 1, comprising a plurality of reference test strips distributed in different areas within the field of view of the thermal imager.
3. The device according to claim 1, wherein the reference strip has a coating and a base material with the same or similar thermal and mechanical properties as the tested piece.
4. The plurality of reference test strips of claim 2 having different coating thicknesses, the thickness ranges being distributed in the regions adjacent to the coating thickness of the test strip.
5. The device according to claim 1, wherein the bottom of the supporting frame has a test piece support platform parallel to the detection plane for receiving the reference test piece.
6. A thermal wave imaging coating detection method is characterized by comprising the following steps:
thermally exciting the to-be-tested piece and the reference test piece by a thermal excitation source at the same time;
simultaneously acquiring the surface temperature changes of the test piece to be tested and the reference module by adopting a thermal imager;
analyzing the surface temperature changes of the test piece to be tested and the reference test piece by using a data processing device to obtain a measurement result;
and correcting the coating detection result of the tested piece by using the drift amount of the detection result of the reference test piece, and eliminating the influence of the thermal excitation source, the detection system or the environmental condition change on the detection result of the tested piece.
7. A thermal wave imaging coating detection method is characterized by comprising the following steps:
selecting a plurality of reference test pieces with known thickness, and placing the reference test pieces in a field of view of a thermal imager;
thermally exciting the to-be-tested piece and the reference test piece by a thermal excitation source at the same time;
simultaneously acquiring the changes of the surface temperatures of the test piece to be tested and the reference test piece along with time by adopting a thermal imager;
carrying out numerical fitting on the detection results of the reference test pieces with different coating thicknesses to obtain a calibration formula of the relation between the detection signal and the coating thickness;
and substituting the detection signal of the tested piece into the calibration formula to obtain the coating thickness of the tested piece.
8. The method for detecting thermal wave imaging coating according to claim 6 and 7, wherein the thermal excitation source adopts a pulse excitation mode and adopts a polynomial fitting to the surface temperature change curve along time.
9. The thermal wave imaging coating detection method as claimed in claims 6 and 7, wherein the thermal excitation source adopts a periodic modulation mode, the data processing adopts a phase locking method, and the phase of the periodic temperature change of the surface is calculated.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110754044.3A CN115628710A (en) | 2021-07-04 | 2021-07-04 | Thermal wave imaging coating detection device and method |
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| CN202110754044.3A CN115628710A (en) | 2021-07-04 | 2021-07-04 | Thermal wave imaging coating detection device and method |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117367344A (en) * | 2023-09-14 | 2024-01-09 | 深圳市汇天益电子有限公司 | Coating thickness measuring system and method based on infrared nondestructive testing technology |
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2021
- 2021-07-04 CN CN202110754044.3A patent/CN115628710A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117367344A (en) * | 2023-09-14 | 2024-01-09 | 深圳市汇天益电子有限公司 | Coating thickness measuring system and method based on infrared nondestructive testing technology |
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