SLITWIS: Smart Laser-assisted Lock-in Thermography Weld Inspection System

The Laser-assisted Lock-in Thermography-based weld inspection system is a non-contact, intelligent non-destructive evaluation technique used to identify and classify subsurface defects in welds. It combines a modulated laser heat source with a synchronised infrared (IR) camera to detect and identify anomalies such as cracks, pores, and lack of fusion.

The value proposition of a Laser-Assisted Lock-in Thermography weld inspection system lies in its unique ability to provide high-speed, non-contact, and subsurface quality assurance, which conventional methods like visual or ultrasonic testing cannot achieve simultaneously.

• Good and bad quality weld can be detected in welded assemblies in a non-contact manner.
• Laser heating gives better penetration; defects can be detected with better accuracy.
• Effect of surface finish is less; No special surface treatment of the test specimen is necessary for capturing thermal images

By analyzing phase shifts in heat flow, the technique detects subsurface micro-cracks and other hidden defects regardless of surface-induced emissivity variations, uneven lighting and non-uniform heating. AI-based model integrated into the system, trained to identify defects such as blowholes, porosity, and lack of fusion (LOF), enhances the system's utility for quality assessment of welded assemblies.

• Laser-based modulated excitation
  Precisely controlled periodic heating using a laser source enables targeted and repeatable inspection.
• Lock-in thermography analysis
  Extraction of amplitude and phase images enhances defect visibility and suppresses noise.
• AI-driven defect detection
  Integration of machine learning enables automatic identification, classification, and sizing of weld defects.
• High sensitivity to subsurface flaws
  Capable of detecting defects such as lack of fusion, cracks, and porosity beneath the surface.
• Non-contact, non-destructive inspection
  No physical interaction with the component, ensuring safe inspection of hot or moving parts.
• Real-time data acquisition and processing
  Enables online/inline monitoring in manufacturing environments.
• Full-field imaging capability
  Simultaneous inspection of large weld areas instead of point-by-point scanning.
• Adaptive frequency control
  Ability to tune excitation frequency for different depth profiling and material properties.
• Minimal surface dependency
  Phase-based analysis reduces effects of emissivity variations and surface roughness.

• Non-contact & non-destructive – no surface damage or couplants required
• High sensitivity – detects both surface and subsurface weld defects
• Improved accuracy – lock-in processing enhances signal-to-noise ratio
• Wide applicability – works on various materials and weld geometries
• Minimal preparation – less affected by surface condition
• Full-field imaging – covers large areas quickly
• Automation-ready – supports AI-based defect detection and reporting