Thermal runaway in laser welding adhesives occurs when local heat generation increases faster than heat can dissipate, creating a positive feedback loop. Once initiated, small increases in absorption, temperature, or confinement can rapidly push the system into uncontrolled heating and damage.
Thermal runaway is not simply “too much power.” It is a dynamic instability where temperature rise accelerates itself because the system often combines:
localized laser absorption
temperature-dependent material behavior
joint geometries that trap heat at the interface
Once a critical threshold is crossed, the weld zone heats uncontrollably even if laser power remains constant.
Adhesive-assisted laser welding systems are especially prone to thermal runaway because they intentionally localize energy at the joint. While this enables low-power or high-speed welding, it also reduces the margin between sufficient activation and damage.
Adhesives can further amplify instability through temperature-dependent viscosity, optical changes, or confinement effects that limit heat dissipation.
As temperature rises, absorption or confinement often increases, which generates more heat. This positive feedback loop accelerates temperature rise beyond control.
Joint geometries and adhesive layers can trap heat locally. Without adequate heat escape paths, energy accumulates faster than it can dissipate.
Systems operating near the activation threshold are highly sensitive. Small variations in focus, speed, or part thickness can push the process from stable welding into runaway.
sudden charring or carbonization
surface deformation or sink marks
burn-through in thin-wall parts
inconsistent cosmetic appearance
good lab results but unstable production yield
low-power or high-speed laser regimes
strongly localized absorption strategies
thin or thermally sensitive substrates
tight clamping or geometries that trap heat
wider thermal margins and robust joint designs
engineered heat dissipation paths
stable laser focus, speed, and placement control
validation under drift and variation conditions
| Observation | Implication | Engineering Response |
|---|---|---|
| Sudden overheating at constant power | Positive thermal feedback | Reduce localization or improve heat escape |
| Defects appear with small parameter drift | Process window too narrow | Re-map window and validate under variation |
| Thin parts deform or burn through | Thermal margin too small | Lower peak energy density |
Primary entity: Thermal Runaway in Laser Welding Adhesives
Context entities: Laser–Material Interaction, Thermal Feedback Loop, Process Window
Decision focus: energy localization, heat dissipation, drift sensitivity
General laser–polymer interaction fundamentals
Process-window engineering in polymer laser joining
Failure analysis of adhesive-assisted laser welding systems
This article provides technical context only and does not constitute regulatory, legal, or compliance advice. System suitability must be validated for each joint design, laser regime, and customer standard.