Cracks Detection Based On Laser Scanning Thermography

Cracks and other forms of defects often occur in products and equipment in the industrial field.With the continuous improvement of quality requirements,defect detection has become an indispensable link during industrial production and product service.Non-destructive testing technology has gradually become the main detection method for crack defects.In recent years,infrared non-destructive testing technology has developed rapidly,a variety of testing methods have continuously emerged,and considerable progress has been made in defect detection.However,the current infrared non-destructive testing technology is mostly in the form of surface excitation.After thermal excitation,the surface heat wave of the object does not have lateral propagation characteristics,and it is not sensitive enough to crack defects of the object,so it does not have advantages in crack defect detection.Combining heat conduction theory and radiation measurement theory,this paper studies infrared thermal wave imaging nondestructive testing technology using line laser scanning excitation,discusses its advantages and disadvantages in crack defect detection,and develops and builds a laser scanning infrared thermal imaging nondestructive testing system.When the line laser scanning is used to excite the object,the thermal wave on the surface of the object has a lateral propagation characteristic,so that it has a strong sensitivity to crack defects on the surface of the object or shallow surface.In this paper,the laser scanning infrared non-destructive testing system has a light path adjustment system that can focus and output a linear laser beam with a submillimeter width level,which enhances the light intensity of the laser beam within a unit length.This paper proposes a combining method combining grating mirror and polarization combining to realize four-way laser coupling,which greatly enhances the intensity of the beam in a unit area,and reduces the difficulty of debugging the actual system compared to the spatial combining method.The cylindrical micro-lens structure is used to greatly enhance the uniformity of the Gaussian beam in the optical path after the beam is homogenized in the direction of the line diameter,and improve the uniformity of excitation in the detection plane.The various light path adjustment structures enhance the system's ability to detect crack defects.In this paper,the laser scanning stitching algorithm technology is proposed by analyzing the synchronization relationship between the laser scanning speed and the acquisition speed of the thermal imager.Improved the convenience of later defect judgment.Through experiments,the laser scanning infrared non-destructive testing system designed in this paper can realize the detection of crack defects with a width of micrometer level.In actual detection,the upper computer control software module can realize automatic detection,the detection does not require complicated steps,and the process is simple;through the upper computer image processing software module,the post-processing time of the laser scanning system is very short,so the detection of the laser scanning system The period only depends on the speed of the scanning speed.Compared with the traditional lock-infrared detection technology,the detection time is greatly shortened.The detection time of the laser scanning detection is almost equivalent to the detection time of the pulse excitation method.At the same time,in the scanning area,the spatial uniformity of thermal radiation after laser scanning excitation is very high,which avoids the difficulty of adjusting the spatial uniformity of excitation by the pulse excitation method.