Welding Digest

With the technological advancement in high-power pump diodes and fiber lasers, the cost of ownership for laser welding machines has been reduced. The air-cooling method makes laser welding devices more portable and affordable. Also, the benefits of excellent welding quality and minimal postweld finish work with handheld laser welding devices have drawn interest in the past few years.

Although lasers have gained popularity in the welding industry over the last three decades, most are used in automation processes in a more controlled environment and high-end manufacturing segments. With the proliferation of handheld laser welding devices into the more traditional handheld welding market and putting a few kilowatts of laser power in a human’s hand, laser safety is more critical than ever.

What Challenges Do Handheld Laser Operators Encounter?

A laser with output power exceeding 500 mW is considered a Class 4 laser, which has the potential to be the most hazardous. The major potential hazards handheld laser welding operators must contend with include eye injury, skin burns, and welding fumes.

Eye Hazards

Most handheld lasers on the market are fiber lasers, which produce wavelengths near 1070 nm. This wavelength is in the infrared spectrum and is invisible to the human eye. It won’t trigger the human corneal reflex. Humans may not notice the immediate damage to their vision if exposed to laser energy without proper protection.

Figure 1 shows a simplified human eye diagram, including the cornea, lens, and retina. If proper personal protection equipment (PPE) is not utilized, the visible and invisible laser light will pass through the cornea and be focused by the lens onto the retina. The invisible laser light can permanently damage the retina. The cornea will absorb UV light and can cause temporary symptoms.

An example calculation of laser intensity on the retina is made to better understand the laser energy level compared to visible light. Figure 2 shows the light intensity on the retina of a light bulb and a fiber laser with a beam divergence of 32.4 mrad at 100 W from 1 m away. The light intensity on the retina of a fiber laser is 952 times that of a light bulb. Scaling this model up for a 2-kW handheld laser, the light intensity is almost 20,000 times that of a 100-W light bulb. Even at significant distances, invisible energy can pose a hazard to individuals who are not properly protected.

Skin Hazards

Another possible hazard of handheld laser welding is skin injuries. These would include thermal burns typically associated with traditional welding processes and photochemical skin injuries. If the skin is directly exposed to the laser, it can cause severe skin burns with deep penetration. Thermal burns also include skin contact with hot workpieces and welding sparks. The main photochemical skin hazard in laser welding comes from the UV light of welding plasma. UV light can cause sunburn (Ref. 1).

Respiratory Hazards

Laser welding produces fumes, but generally at a much lower level than traditional arc welding processes. According to some research work characterizing the welding fumes of different processes, fume particles tend to agglomerate due to their small size and large surface tension. It was found that laser fume agglomeration has structures similar to arc welding fumes. However, the laser fume agglomeration particles are generally slightly smaller than arc welding particles (Refs. 2, 3).

Hierarchy of Laser Safety Controls

OSHA’s hierarchy of controls — detailing elimination, substitution, engineering controls, administrative controls, and PPE — ranks and identifies safeguards (osha.gov/safety-management/hazard-prevention).

Engineering Controls

Many types of laser welding machines and handheld laser welding devices are on the market. Below are examples of basic engineering.

-Key switch is a method of limiting operations only to those with proper training.

-An emergency stop button is a method of stopping the laser welding operations in an emergency.

-External interlocks prevent someone from being exposed to the laser when they unexpectedly open the door and enter the laser-controlled area (LCA).

Some handheld laser welding devices include more advanced engineering controls, such as the following:

-A safety work sense clamp to ensure the torch is connected to the workpiece when the emission is on.

-A two-level trigger to prevent unintentional laser emissions.

-A plasma sensor, a photo sensor inside the welding torch, monitors the welding plasma. If insufficient plasma light is created after the start of a weld, the laser will automatically shut off.

-A back reflection sensor monitors for excessive reflected laser energy coming back toward the torch and/or the operator.

In a manufacturing environment, the handheld laser device should only be placed in an LCA, a designated space for laser use, where access and activity are controlled and supervised. Typically, the LCA can be a laser enclosure with laser-blocking panels or a laser room with concrete walls, an access door with an interlock switch, and an area warning device. Proper room ventilation or local exhaust ventilation is important in any LCA. A filter with a MERV rating above 15 is recommended for laser welding.

Administrative Controls

Administrative controls will be required when engineering controls cannot fully mitigate all associated risks. They include training, monitoring, procedures, and warning signs. 

Before using the laser welding device in your facility, ensure an LCA is set up properly and at least one laser safety officer is on staff. They are responsible for evaluating, monitoring, and enforcing laser safety control.

There are some basic safety rules when handheld laser welding: Never look directly into any laser beam, do not attempt to view the part from or place any body part within the expected beam reflection zone, do not place any body part behind the weld joint, and do not point the laser torch at others.

PPE

The PPE for handheld laser welding includes laser safety eyewear, a laser welding helmet, welding gloves, welding apparel, and welding boots. When selecting eyewear and a helmet, you need to ensure the glasses are designed to protect the specific wavelength of the laser with an adequate optical density level. It is recommended to use laser safety eyewear under the laser welding helmet.

What Standards/Regulations Can Apply to Handheld Laser Welding?

Several safety standards can apply to handheld laser welding, including AWS Fact Sheet No. 46 (aws.org/standards-and-publications/free-resources), ANSI Z136.1, Safe Use of Lasers, and the OSHA Technical Manual, Section III: Chapter 6, Laser Hazards.  

References

1. Gupta, A., et al. 2013. Low-level laser (light) therapy (LLLT) in skin: Stimulating, healing, restoring. Seminars in Cutaneous Medicine and Surgery 32: 41–52.

2. Berlinger, B., et. al. 2011. Physicochemical characterization of different welding aerosols. Anal Bioanal Chem 399: 1773–1780.

3. Noskov, A., et. al. 2020. Characterization of ultrafine particles emitted during laser‑based additive manufacturing of metal parts. Scientific Reports 10: 20989.

This article was written by Shuang Liu, PhD (project manager – Miller Electric Laser Welder, Appleton, Wis., and a member of the AWS C7C Subcommittee on Laser Beam Welding and Cutting) for the American Welding Society.