Introduction
Some users may notice that laser marking results become inconsistent during long production runs. Typical symptoms include:
● Marking gradually becoming lighter or darker
● Inconsistent engraving depth
● Loss of detail or sharpness
● Blurry text or graphics
● Different results between the beginning and end of a job
● Results improving after the machine cools down
These symptoms are often related to thermal effects within the laser system or the material being processed.
This article explains the most common thermal-related issues and provides practical recommendations to improve processing stability.
1. Thermal Lensing
Typical Symptoms
● Marking quality gradually decreases during continuous operation.
● Fine details become blurry.
● Engraving depth becomes inconsistent.
● Refocusing the machine temporarily restores the original result.
● Performance returns to normal after the machine cools down.
What Causes Thermal Lensing?
When optical components such as the field lens absorb heat, their optical properties can change slightly.
As the temperature increases:
● The focal position may shift.
● The laser spot size may increase.
● Beam quality may decrease.
This phenomenon is called Thermal Lensing.
Thermal lensing becomes more noticeable during:
● Long continuous operation
● High average power processing
● Large filled areas
● Dirty or contaminated lenses
How to Check
When the issue appears:
1. Stop the process.
2. Refocus the material.(as the lens may swell due to overheat and then the focal lengh changes)
3. Run the same marking again.
If the result improves significantly after refocusing, thermal lensing may be present. Please also record how and how far the focal distance changed.
2. Thermal Drift
Typical Symptoms
● Marking becomes progressively lighter during operation.
● Focus adjustment does not significantly improve the result.
● Performance improves after cooling down.
● The problem becomes more noticeable during long production runs.
What Causes Thermal Drift?
Thermal drift can occur inside:
● Laser sources
● Galvanometer scanners
● Electronic control systems
As internal temperatures rise, system performance may gradually change.
In some cases, the laser output power remains constant while beam quality changes.
In other cases, actual laser output decreases as the system heats up.
How to Check
Observe whether:
● The problem only appears after extended operation.
● Refocusing does not restore performance.
● Different fill angles produce different results.
If changing the fill angle significantly changes the marking quality, thermal drift within the laser source or scanner system may be involved.
3. Process Heat Accumulation
Typical Symptoms
● The material becomes hotter during processing.
● Results gradually change even though the machine is operating normally.
● The issue is material-specific.
● Quality improves after allowing the material to cool.
What Causes Heat Accumulation?
Heat accumulation occurs when energy is deposited into the material faster than it can dissipate.
Common examples include:
● Deep metal engraving
● Large filled areas
● High-frequency marking
● Slow scanning speeds
● Multiple overlapping passes
The material itself becomes hotter and responds differently to the laser over time.
How to Check
Try:
● Increasing scanning speed
● Reducing power
● Allowing cooling time between jobs
If the problem improves, process heat accumulation is likely contributing.
4. Why Thermal Issues Occur
Thermal-related issues are usually caused by one or more of the following:
● High average laser power
● Long continuous operating time
● Large filled areas
● High pulse frequency
● Long pulse width
● Dirty optical components
● Poor ventilation
● Insufficient cooling
● Heat-sensitive materials
In many cases, multiple factors are involved simultaneously.
5. Recommended Parameter Adjustments
The goal is not simply to reduce power.
The goal is to reduce thermal load while maintaining the desired processing result.
Recommendation 1: Increase Speed and Use Multiple Passes
Instead of:
● High power
● Low speed
● Single pass
Consider:
● Lower power
● Higher speed
● Multiple passes
This often produces:
● Better consistency
● Lower material temperature
● Reduced thermal accumulation
● More stable long-term operation
Multiple lighter passes allow heat to dissipate between scans.
This reduces thermal accumulation in both the material and the optical system, leading to more stable and repeatable results.
Recommendation 2: Avoid Running at Maximum Power Continuously
Most industrial users operate below maximum output during long production runs.
Maintaining a power reserve of approximately 10–30% can help reduce:
● Thermal lensing
● Thermal drift
● Optical heating
● Long-term component stress
Recommendation 3: Optimize Frequency Settings
Higher frequency generally means:
● More pulses
● More heat accumulation
When possible, test lower frequencies and compare results.
Many applications achieve similar marking quality while reducing thermal load.
Recommendation 4: Use Cross-Hatch Fill Patterns
Instead of repeatedly using a single fill angle:
● 0°
● 45°
● 90°
or cross-hatch patterns
can distribute heat more evenly across the material.
This often improves consistency during long runs.
Recommendation 5: Keep Optical Components Clean
Contaminated lenses absorb significantly more heat than clean lenses.
Regular inspection and cleaning of:
● Field lenses
● Protective lenses
● Mirrors
● Lens on the laser output head
● Cooling fans on the laser souce
can greatly reduce thermal-related issues.
If thermal-related issues are observed, please provide:
● Machine model and serial number
● Laser source model and serial number
● Field lens type and size
● Material type
● Processing parameters
○ Power
○ Speed
○ Frequency
○ Pulse width (if applicable)
○ Fill angle
○ Hatch setting (DPI and fill angle)
○ Passes count
● Photos of the marking results
● Videos showing the issue
● Results of the focus recovery test (How and how far the focal distance changes)
● Results of the fill angle comparison test
This information helps determine whether the issue is caused by:
● Thermal lensing
● Thermal drift
● Process heat accumulation
● Optical contamination
● Parameter settings
Conclusion
Thermal lensing, thermal drift, and process heat accumulation can produce similar symptoms, but their root causes are different.
In many cases, processing stability can be significantly improved through parameter optimization, including:
● Increasing speed
● Reducing peak power
● Using multiple passes
● Optimizing frequency
● Alternating fill angles
● Maintaining clean optics
These adjustments often improve consistency, reduce thermal stress, and provide more reliable results during long production runs.
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