Automated non-destructive weld evaluation method and apparatus

• US 20020134817A1
• Filed: 01/05/2001
• Published: 09/26/2002
• Est. Priority Date: 01/06/2000
• Status: Active Grant

• Current Assignee: Thermal Wave Imaging, Inc.
• Original Assignee: Thermal Wave Imaging, Inc.
• Inventors: Shepard, Steven M.
• Granted Patent: US 6,585,146 B2
• Time in Patent Office: Days
• US Class Current: 228/105
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

A method and apparatus for automated, non-destructive evaluation of spot welds includes a device for heating a sample containing a spot weld, an infrared camera for detecting changes in the surface temperature of the weld, and a computer to acquire and analyze data from the camera. In one embodiment, the sample is heated on one side and the time-temperature characteristic is monitored as the heat travels through the sample and the spot weld. The computer generates a histogram that represents the relationship between a particular time-temperature characteristic and the number of pixels exhibiting that characteristic, thereby representing the quality and size of the weld nugget. By generating a histogram corresponding to weld quality, the inventive apparatus and method provides an objective weld quality indicator and allows automation of the evaluation process.

Claims

1. An apparatus for non-destructive evaluation of a weld in a sample, comprising:

a heater that heats a surface of the sample;

a heat-detecting camera that collects temperature data from the sample over a selected time period; and

a computer coupled to the heat-detecting camera to monitor a time-temperature characteristic from the temperature data and to compare the time-temperature characteristic with a predetermined standard indicating weld quality.

2. The apparatus of claim 1, wherein the heater is selected from the group consisting of a flashlamp, pulsed laser, optical fiber, and light source coupled with a focusing lens.

3. The apparatus of claim 1, wherein the sample has a first surface and a second surface, and wherein the heater is disposed opposite the first surface and the heat-detecting camera is disposed opposite the second surface.

4. The apparatus of claim 3, wherein the heater heats the first surface of the sample and the heat-detecting camera monitors the temperature of the second surface, and wherein the computer measures a time interval between the initiation of the heating and the time at which at least a portion of the second surface reaches a predetermined temperature level.

5. The apparatus of claim 4, wherein an image generated by the heat-detecting camera is made of a plurality of pixels, and wherein the computer generates a histogram representing the thermal flux through the weld region.

6. The apparatus of claim 5, wherein the histogram reflects a half-max time for each pixel in the image, which indicates the time at which the temperature for the pixel reaches half its maximum temperature.

7. The apparatus of claim 6, wherein the computer evaluates the weld by comparing at least one of a peak time and a peak amplitude indicated in the histogram to at least one threshold value.

8. The apparatus of claim 1, further comprising a mirror that reflects visible light but passes infrared light, wherein the heat-detecting camera and mirror are disposed opposite a first surface of the sample and wherein the heater is disposed to reflect the visible light onto the first surface of the sample.

9. The apparatus of claim 8, wherein the heater heats the first surface of the sample and the heat-detecting camera monitors the temperature of the first surface, and wherein the computer measures a time interval between the initiation of the heating and the time at which at least a portion of the first surface cools to a predetermined temperature level.

10. The apparatus of claim 9, wherein an image generated by the heat-detecting camera is made of a plurality of pixels, and wherein the computer generates a histogram representing the thermal flux through the weld region.

11. The apparatus of claim 10, wherein the histogram reflects a half-max time for each pixel in the image, which indicates the time at which the temperature for the pixel reaches half its maximum temperature.

12. The apparatus of claim 11, wherein the computer evaluates the weld by comparing at least one of a peak time and a peak amplitude indicated in the histogram to at least one threshold value.

13. The apparatus of claim 1, wherein an image generated by the heat-detecting camera is made of a plurality of pixels, and wherein the computer generates a histogram representing the time-temperature characteristic for each pixel in the image and evaluates the weld by comparing the time-temperature characteristic with an objective threshold.

14. The apparatus of claim 13, wherein the computer evaluates at least one of a maximum amplitude, ascending slope, descending slope, and maximum time of the time-temperature characteristic to evaluate the weld.

15. The apparatus of claim 1, further including a conical snout disposed between said heater and said sample for concentrating the heat generated by the heater upon the surface of the sample.

17. The method of claim 16, wherein the heating and capturing steps include the steps of:

heating a first surface of the sample; and

capturing a plurality of infrared images of a second surface of the sample over time.

18. The method of claim 17, wherein the comparing step includes comparing at least one time-temperature characteristic selected from the group consisting of thermal flux through the weld region, a maximum amplitude, an ascending slope, a descending slope, maximum time value of the time-temperature history with the threshold.

19. The method of claim 16, wherein the heating and capturing steps include the steps of:

heating a first surface of the sample; and

capturing a plurality of infrared images of the first surface of the sample over time.

20. The method of claim 19, wherein the comparing step includes comparing at least one time-temperature selected from the group consisting of a maximum amplitude, an ascending slope, a descending slope, and maximum time of the time-temperature history.

21. The method of claim 16, wherein the determining step includes the steps of:

obtaining a time-temperature characteristic for each pixel in the plurality of images;

creating at least one histogram based on all of the time-temperature characteristics from the obtaining step.

22. The method of claim 21, wherein the time-temperature characteristic is a half-max time.

23. The method of claim 21, wherein the time-temperature characteristic is a half-max time, wherein the creating step includes the step of generating a first histogram indicating a peak time, which corresponds to the half-max time associated with the greatest number of pixels;

and

generating a second histogram indicating a peak amplitude, which corresponds to a total number of pixels having a half-max time less than or equal to a selected half-max time.

24. The method of claim 23, wherein the selected half-max time for determining the peak amplitude is the peak time.

16. A method for non-destructive evaluation of a weld in a sample, comprising the steps of:

heating the sample;

capturing a plurality of infrared images of the sample over time;

determining a time-temperature history of the sample; and

comparing a time-temperature characteristic in the time-temperature history with a threshold value to evaluate the weld.