The influence of optical system contamination of the laser welding machine on welding quality

I. Introduction

Laser welding technology is widely used in lithium battery sealing, consumer electronics, medical device manufacturing, and metal processing due to its high energy density, welding precision, and low deformation. However, during long-term operation, the optical system of a laser welding machine is prone to contamination by smoke, spatter, oil, and moisture, which affects beam transmission quality and ultimately reduces welding stability. Optical contamination has become a potential hidden factor that affects welding quality and should be addressed from both process and maintenance perspectives.

II. Role of the Optical System in Laser Welding Machines

A typical optical system mainly consists of:

Laser output window

Collimator/beam expander

Scanning galvanometer (if applicable)

Focusing lens or F-Theta lens

Protective lens (to shield optical components)

The core function of the optical system is to transmit and precisely focus high-energy laser beams onto the welding area. Therefore, the cleanliness and transmittance of optical surfaces are critical for efficient energy coupling during welding.

III. Main Sources of Optical Contamination

Optical contamination mainly originates from the following sources:

Smoke and vapor condensates
Metal vapor produced by high-temperature welding condenses into particles and deposits on optical surfaces.

Molten spatter adhesion
During deep penetration welding or unstable processing, molten droplets may adhere to protective lenses.

Moisture and oil films
Originating from oily air compressors, water chiller leakage, or ambient humidity, forming low-transmittance thin films.

Fingerprints and cleaning residues
Human contact or improper solvents can cause secondary contamination on optical surfaces.

These contaminants may appear in the form of dust, oil films, solid particulates, or burn marks.

IV. Mechanisms by Which Optical Contamination Affects Welding Quality

Optical contamination mainly affects welding quality in the following ways:

1. Laser Energy Attenuation

Contamination reduces beam transmission efficiency, causing insufficient welding energy. Common manifestations include:

Insufficient weld penetration

Lack of fusion or weak welds

Darkened or discontinuous weld seams

Narrowed process window

Materials that are sensitive to energy levels (e.g., aluminum, copper, battery tabs) are more significantly affected.

2. Beam Distortion and Focal Shift

Contamination changes beam propagation characteristics, causing focal drift or uneven energy distribution, which may lead to:

Inconsistent weld widths

Weld path deviation

Increased molten pool fluctuation

Reduced welding stability

In high-precision welding, a focal shift of several tens to hundreds of microns can significantly affect yield rates.

3. Increased Risk of Thermal Damage to Optical Components

Contaminants absorb laser energy and generate localized heat, potentially causing:

Protective lens burn marks or coating delamination

Burn spots on beam expanders or scanning lenses

Damage to the laser output window

Optical damage is usually irreversible and requires component replacement, which increases cost.

4. Welding Process Abnormalities and Instability

Optical contamination may lead to:

Uneven molten pool boiling

Increased porosity

Rough weld seams or undercuts

System alarms or energy fluctuation

In automated production lines, such issues directly affect consistency and throughput.

V. Material Sensitivity Differences (Without Comparison Charts)

Different welding materials exhibit varying sensitivity to optical contamination, for example:

Aluminum: High reflectivity and highly sensitive to insufficient energy; even slight contamination may cause lack of penetration or undercutting.

Copper or battery tabs: Requires highly stable energy; contamination leads to weak welds, affecting conductivity and battery cycle performance.

Stainless steel: Contamination results in rough weld surfaces, darkened weld seams, and inconsistent penetration.

Carbon steel: Produces more spatter and contaminates optics rapidly, increasing protective lens consumption and process instability.

These risks can be sufficiently described in text without charts or visual comparisons.

VI. Detection and Evaluation Methods

Optical contamination can be identified through the following approaches:

Visual inspection: Use angled lighting to observe deposits on lens surfaces

Energy attenuation monitoring: Track output power deviations over time

Weld quality feedback: Check penetration and surface formation

Process alarm logs: Observe welding energy stability alarms

Advanced facilities may also utilize coaxial vision or laser power monitoring equipment for diagnostics.

VII. Prevention and Maintenance Strategies

Optical contamination can be controlled through process management and preventive maintenance:

Use protective lenses and replace them regularly

Add side-blowing or coaxial shielding gas

Use high-purity auxiliary gases (argon/nitrogen)

Install fume extraction systems to reduce deposition

Optimize process parameters to minimize spatter

Use specialized alcohol and optical wipes for cleaning

Establish optical transmittance tracking and component life management

These practices are essential for industries with high consistency requirements, such as battery manufacturing.

VIII. Conclusion

Optical system contamination is a key hidden factor that leads to degraded laser welding quality. It exhibits characteristics of being concealed, accumulative, and destructive. By enhancing contamination monitoring, optimizing process parameters, and establishing maintenance protocols, the lifespan of optical components can be extended and welding stability and consistency can be improved. As laser technology continues to expand into precision manufacturing fields, optical contamination management will become a critical element influencing yield rate and cost control.