Dust and Fume Collection for Laser Welding

In LBW applications, the laser provides a highly concentrated heat source that produces a neat, narrow weld by melting the edges of both pieces of material together. The concentrated energy from the laser heats up both sides of the joint in milliseconds, melting the material and fusing the sides together. Different types of lasers have different welding characteristics and applications; laser welding can be broadly characterized as either “keyhole laser welding” or “conduction limited laser welding,” depending on the power density and penetration depth of the laser. Lasers may be solid-state, gas or fiber. 

While manual laser welding does exist, the vast majority of laser welding applications are robotic. Laser welding is typically automated using computer-aided design (CAD)/computer-aided manufacturing (CAM).

What Are the Health Risks of Laser Welding Emissions?

The fumed particles created by the laser are very tiny, often in the sub-micron range. These tiny particles can be breathed deeply into the lungs, where they can become lodged in lung tissue or even migrate into the bloodstream and throughout the body. The health hazards associated with laser welding fumes depend on the materials used, but may include cancer, lung damage, neurological damage and kidney disease. 

• Breathing in microplastics generated by welding plastic can lead to asthma and other lung diseases. When fumed plastics make their way into the bloodstream, plastic exposure is associated with neurological, cardiovascular and immunological problems. Plastic fumes are also considered to be carcinogenic (cancer-causing). 
• Laser welding of metals produces toxic particulates similar to those produced by resistance welding. Depending on the base materials used and coatings present, laser welding emissions may include fumed metal particles and metal oxides of iron, lead, aluminum, cadmium, cobalt, copper, chromium, zinc, manganese, beryllium, molybdenum and other toxic elements. Many metals and metal oxides are associated with dangerous conditions, including metal fume fever, manganism (a neurological disease similar to Parkinson’s Disease), kidney and nervous system damage, stomach ulcers and lung disease. Metallic weld fume is carcinogenic and has been associated with cancers of the lung, urinary tract and larynx. Welding galvanized or coated materials or using fillers produces a higher volume of fume and more hazardous emissions. 

How Do Laser Welding Emissions Impact Equipment and Weld Seam Quality? 

Dust and fumes from laser welding can cause problems with production equipment. Robotic laser welding is typically conducted within an enclosure. Uncontrolled weld fumes can build up in the enclosure and interfere with the laser mechanism. A high dust concentration will cause refraction of the laser beam, which diffuses the beam. That means the beam hitting the material will be less energetic and less precise, which results in a lower quality weld. If interference is high enough, the resulting weld may not meet quality criteria for weld strength and precision. Laser welding emissions may also damage the laser welder. Dust can build up on the optical lens or in the diaphragm or shutter mechanisms, impacting laser performance or causing unexpected shutdowns. An efficient dust collection solution for laser welding will help prevent problems with equipment performance and weld seam quality.

OSHA PELs for Laser Welding 

OSHA sets Permissible Exposure Limits (PELs) for weld fume as a whole as well as specific components commonly found within weld fume. These are expressed as a Time-Weighted Average (TWA) over an 8-hour shift. The OSHA PEL for weld fume concentration is 5 mg/m3 when welding mild steel, iron or aluminum. PELs for specific elements and compounds found in weld fumes may be much lower. Some of these include: 

• Zinc oxide: 5.0 mg/m3 (for zinc oxide fume or respirable dust) 
• Lead: 50 μg/m3 (PEL)/action limit 30 μg/m3
• Hexavalent chromium: 5 μg /m3
• Nickel: 1.0 mg/m3
• Cadmium: 0.005 mg/m3
• Manganese: 5.0 mg/m3 
• Cobalt: 0.1 mg/m3 
• Mineral oil mists: 5.0 mg/m3 
• Benzine: 1 part per million (5 ppm for short-term exposure limit)
• Triphenyl phosphate (a phosphate ester): 3.0 mg/m3 

Laser weld fume composition and volume vary greatly depending on the materials used and the volume of welding conducted. For this reason, it is often advisable to conduct an analysis of laser welding emissions to determine the exact concentrations of hazardous elements and compounds in the weld fume. Understanding the composition of your weld fumes will ensure that you stay in compliance with all national and local worker health and safety regulations. 

EPA Regulations for Manufacturers using Laser Welding 

If laser welding fumes are exhausted to the outside, it may put the facility out of compliance with the EPA Clean Air Act. Manufacturers are responsible for ensuring that emissions do not exceed EPA regulations for known air pollutants, including lead and lead oxides and other hazardous emissions that may be found in laser welding fumes. For this reason, an air filtration system is recommended for facilities using laser welding. 

Laser welding emissions fall under EPA rules for Metal Fabrication Hazardous Air Pollutants (MFHAP), which covers emissions containing ±0.1% cadmium, nickel, lead or chromium or ±1% manganese.  EPA regulation 40 CFR 63.11516(f)(2) states:  

You must implement one or more of the management practices specified in paragraphs (f)(2)(i) through (v) of this section to minimize emissions of MFHAP, as practicable, while maintaining the required welding quality through the application of sound engineering judgment.  (i) Use welding processes with reduced fume generation capabilities; (ii) Use welding process variations which can reduce fume generation rates; (iii) Use welding filler metals, shielding gases carrier gases, or other process materials which are capable of reduced welding fume generation; (iv) Optimize welding process variables to reduce the amount of welding fume generated and (v) Use a welding fume capture and control system.

Combustible Dust Regulations 

Metallic dust produced during resistance welding may be combustible. Combustible dusts are regulated under OSHA’s General Duty Clause (Section 5(a)(1)) with additional requirements under the Hazardous Locations (§1910.307), Hazard Communication (§1910.1200) and Housekeeping (§1910.22) standards. In addition, manufacturers dealing with combustible dusts must follow National Fire Protection Association (NFPA) standards for prevention of fires and explosions. If you are not sure whether your dust is combustible, it may be advisable to conduct a Dust Hazard Analysis (DHA). Read more: Are Weld Fumes Combustible?

• Where possible, robotic laser welding should be conducted within a hood or enclosure that is ducted to a dust collector for source capture of laser welding emissions. In addition to a clean air environment, laser welders require light-tight enclosures to prevent lasers from escaping the weld area and causing harmful effects to the plant and workers. 
• Since the enclosure is essentially sealed, source capture welding ventilation systems should be integrated with each laser welding enclosure to prevent weld fume accumulation. Several laser welding stations can be ducted to a centralized dust collector for weld fume extraction, or smaller collectors may be used for each station. In most cases, a centralized dust collection system is more efficient and easier to maintain. It must be sized to provide adequate airflow (CFM) to maintain appropriate capture velocities for all stations. The laser welding dust collection system should provide a 10- to 15-second turnover rate for air at the point of welding to ensure a clean enough environment.
• The laser welding dust collection system should incorporate filters designed specifically for capturing the ultra-fine particles created by laser welding and removing them from the air before it’s returned to the plant environment. That will typically mean a dry filter with a MERV rating of MERV15 or above. 
• Paints and coatings on welded materials may create gases, aerosols or oil mists during laser welding. Welding plastics can also release toxic gases and volatile organic compounds (VOCs). Where possible, ensure that materials are clean before welding. If the resulting fume is oily, an oleophobic filter media may be required. Gaseous fumes may, in some cases, be vented to the outside. If this is not possible or puts the facility out of compliance with environmental regulations, an activated carbon after-filter may be used to collect VOCs, gases and odors not captured by the dry cartridge filter. 
• Depending on the volume and combustibility of fumes collected by resistance welding, the dust collector may need to be equipped with a deflagration system. This system may include explosion vents for safe venting of the energy from a dust collector explosion, isolation valves and a rotary airlock to prevent dust in the collection bin from being used to fuel an explosion. 
• If conducting manual laser welding, the source capture solution (e.g., fume arm or backdraft plenum) must be positioned to pull weld fume up and away from the welder’s breathing zone and have high enough CFM to enable effective capture of fume as it is created. Fume guns are not used for laser welding.