No matter how confident you are in a welding process, it is sometimes necessary to certify it – and laser welding is no exception. Whether you need to satisfy internal quality control standards or put a customer’s mind at ease, the benefits of laser welding sometimes take a back seat when welding to codes like AWS D1.6, AWS D1.1, and AWS D1.2.
Fortunately, certifying handheld laser welding to code is possible. And fabricators are already doing it.
Self-certifying a laser process and creating a laser Welding Procedure Specification (WPS) is similar to self-certifying your arc welding process, with a few key differences.
This guide details the critical differences in welding parameters and equipment specifications you need to know to achieve code compliance.
Laser Welding WPS: What is Different?
A laser welding WPS serves the same function as an arc welding WPS by providing a specific recipe for a repeatable, high-quality weld. As a result, a laser welding WPS does not look significantly different from the WPSs you may already be used to seeing.
Sample laser welding WPS qualified to D1.6 provided by the Handheld Laser Institute.
Here are the primary differences (highlighted and numbered above):
(1) Process Designation: List the welding process as “Laser Beam” and record the welding mode.
(2) Equipment Specifications: Laser welding equipment requires documentation of optical and beam-delivery specs that do not apply to arc welding machines.
(3) Welding Parameters: The inputs that define the welding procedure (like wobble and pulse frequency) differ significantly from ones like voltage and amperage.
Now it’s time to break those differences down into what you need to know and how to use that knowledge to start laser welding to code.
Defining Process & Mode
The simplest part of creating a laser welding WPS is designating the process. For laser welding, this is simply recorded as “Laser Beam”. That’s one thing checked off.
Mode can be slightly more complicated (but it’s usually not). Handheld laser welding falls into one of two categories that are defined by the behavior of the weld pool: Keyhole or Conduction.
Keyhole Welding
Keyhole welding is by far the most common mode of operation for handheld laser welding applications.
- Overview: High power density creates a deep, narrow vapor-filled channel, allowing for deep weld penetration.
- Identification: Keyhole welding can usually be easily identified by a distinct sizzling sound.
- Profile: In a cross-section test the weld profile is significantly deeper than it is wide. The weld should be performed with a wobble width of zero. Fortunately, a cross-section test is rarely necessary.
Conduction Welding
Conduction mode is uncommon in handheld laser welding applications, although conduction welding may occur when the wattage is very low.
- Definition: Heat is absorbed at the surface and transferred via thermal conduction into the material, resulting in a wide and shallow weld pool.
- Identification: Conduction welds can be identified by a much quieter sizzling sound.
- Profile: In a cross-section test, a conduction weld’s profile is wider than it is deep. Again, while rarely necessary, a test weld should be performed with a wobble width of zero.
Critical Laser Equipment Specifications
Laser welding machines have different key specifications than arc welding machines. You can typically locate the necessary information in your equipment’s product documentation or by contacting the manufacturer.
Here’s a high-level overview of what each key spec is and how you may be able to identify them.
Wavelength: Most handheld laser welders emit an infrared wavelength of approximately 1070 nm. This can vary somewhat by brand so it’s worth confirming your machine’s officially listed wavelength spec.
Spot size: Spot size refers to the width of the laser spot (typically measured in microns) on the target material. The exact measurement of this spot varies both by brand and from machine to machine. The easiest way to find this exact measurement is to request it from your machine’s manufacturer.
Fiber Diameter: Most handheld laser welders are fiber lasers, meaning an optical fiber delivers the light to the torch. “Fiber Diameter” refers to the diameter of this optical fiber’s core.
Collimator Length: Collimators are beam shaping optics held within the welding torch. This length is a static, hardware-specific value.
Focal Length: Focal length is a key property of a laser welder’s beam that is determined by optics within the torch. This spec can be adjusted to alter the laser’s focus to achieve different results.
If you have never adjusted your machine’s focal length, refer to your equipment’s documentation first.
Extension Tube Length: This is a physical dimension of the nozzle at the end of your torch. This dimension can be measured by hand or you can refer to product documentation to find it.
Nozzle Tip Part Number: This is just the identifier or SKU for the nozzle tip you are using for your welding process. This one should be simple but, if you have any problems, the manufacturer should be able to help.
Dialing in Laser Welding Parameters
Understanding how laser welding parameters differ from arc welding parameters is the most important part of laser welding to code.
You will need to specify the following parameters (some unique to laser welding and some not) on your WPS. Consult this guide to learn more about how to dial in your parameters to achieve your desired results.
Note: Different machines may present certain parameters slightly differently (e.g. using percentage for power rather than watts). Adjust your WPS as necessary.
Number of passes: Most laser welds are made with a single pass, meaning this number will usually be “1”. However, it is possible to take advantage of multi-pass welding to achieve code compliance, enhance joint strength, or even refine the metallurgical properties of the weld.
Program number: Some laser welding machines include factory preset parameters designed to address common materials and thicknesses. These machines also allow users to create custom parameter presets and save them for future use.
As an example, “F1” is one preset program number used by LightWELD machines — this preset is designed to maximize weld quality in 5000 series aluminum alloys and requires only that the user adjust the power for different thicknesses.
Mode (Continuous Wave vs. Pulsed): Laser welding machines, by default, fire the laser beam in a steady stream of continuous power, referred to as Continuous Wave or CW. Many machines also allow the welder to automatically and rapidly pulse this output to control heat input and influence weld quality.
In a WPS the former would be recorded as “Continuous Wave” and the latter would be recorded simply as “Pulsed”.
Power & power compensation: Power is most often measured in wattage (and sometimes percentage) and is generally increased to achieve deeper weld penetration and welding speeds. If your process uses one kilowatt of power, you would record this on a WPS as “1000 W”. If your process uses a specific percentage, record that number instead.
Used sparingly and by advanced users, power compensation is represented by a percentage and automatically adjusts a laser’s output power along the beam’s travel path (when using wobble welding). Machines with this functionality enable users to fine tune their weld profiles.
Pulse length & frequency: If using a pulsed welding mode, the behavior of the pulse can be adjusted to fine tune your results.
Pulse length refers to how long the laser beam remains on during each pulse. This is measured in milliseconds and can be expressed, for example, as “25 ms”.
Pulse frequency refers to how often the laser pulses are fired. This parameter is measured in Hertz and may be written in a WPS as something like “200 Hz”.
If you are not using pulsed welding, these parameters will simply be “N/A”.
Wobble length & frequency: A laser welding machine’s wobble feature automatically directs the beam side to side along the weld path, similar to a “wobbling” motion. This behavior is sometimes built into a machine’s application-specific presets.
Wobble length governs how far the beam travels left and right and is typically expressed in millimeters (ex: “4 mm”). Wobble frequency, which governs the speed of the wobbling motion, is expressed in Hertz (ex: “150 Hz”).
Wire feed speed: Laser welding can be performed without wire (a.k.a. autogenously) or with standard MIG wire. The specifics of the filler wire are the same as a typical arc welding WPS but, in the case of laser welding, the wire feed speed must be specified.
The ideal wire feed speed is primarily governed by other laser welding parameters, similar to weld travel speed. This parameter can be adjusted directly by users and is typically expressed in centimeters per minute (ex: “40 cm/min”).
Gas pre-flow & post-flow: Laser welding is typically performed with gas pre-flow and post-flow. The gas used is determined by the material (nitrogen for steels and copper, argon for aluminum and titanium). It’s usually unnecessary to adjust the pre-flow and post-flow durations – you will typically record “1 second” for both.
Travel speed: The ideal travel speed is governed by parameters like power, mode, and wire feed speed. Travel speed is typically nearly 1:1 with wire feed speed and is measured in a range of centimeters per minute (ex: “40-45 cm/min”).
Heat input: Heat input can be measured in Joules per millimeter (ex: “98 J/mm”) by dividing the laser’s output power (watts) by the travel speed (millimeters).
Things are trickier if you are using a pulsed welding process. Determining the laser’s average power while in pulsed mode requires the use of a laser power meter – you can buy your own or reach out to your machine’s manufacturer for assistance.
Laser Welding Procedure Qualification Records (PQR)
As with arc welding, every WPS requires a supporting Procedure Qualification Record.
To generate a laser welding PQR, you must conduct mechanical and metallurgical tests as specified by the relevant code (e.g. AWS D1.6 for stainless steel) using a preliminary WPS. This typically involves visual inspection, tensile testing, bend testing, and macro-etching.
For more information, consult AWS C7.4 (Process Specification and Operator Qualification for Laser Beam Welding).
A note on the strength of laser welds
While qualifying laser welds to AWS D1.6, tensile tests have produced ultimate loads of nearly 18,000 lbs, with visual inspection, macro-etching, and bend testing also meeting and exceeding the code’s standards.
Similarly positive results have been achieved in accordance with other AWS codes like D1.2 as well as codes like Section IX of ASME’s Boiler and Pressure Vessel Code (BPVC).
How to Get Started
Trying to self-certify so you can laser weld to code? Whether you are laser welding with LightWELD or not, don’t hesitate to reach out – we’re happy to help you get started, provide specifications, or direct you to helpful resources.
Haven’t started your handheld laser welding journey yet? Click here to learn more about LightWELD, try it yourself, or even send us a sample part for testing.
