Lasers are used in diverse manufacturing processes, and in recent years the spectrum has become increasingly wider. Whether VCSELs in sensor technology, blue and green lasers for welding battery cells, powerful fiber lasers in additive manufacturing, or quantum cascade lasers in medical technology, laser technology is currently revolutionizing numerous industries. But one thing stands out—even in modern production plants, the opportunity to make laser-based processes more sustainable by measuring the laser system itself is often neglected.
There are many new technologies and instruments that contribute to increased production quality in laser-based processes while simplifying documentation and conserving resources. Today, it is even possible to characterize the entire beam caustics with cycle-time-neutral, fully automated measurements during the very short loading of a robot cell or in a sealed construction chamber in additive manufacturing.
A Paradox With Risks
For many years there was a persistent belief that a laser beam, per se, is “maintenance-free,” since it never “dulls” as a tool. Even now, there are still companies that invest in state-of-the-art production facilities but measure the laser far too rarely and using outdated measurement technology. The reality is that laser processes change over time. People in industry are starting to realize how important it is to check the focused laser beam. In addition to increasing demands on component quality and the economic pressures faced by many firms, sustainability is becoming a crucial decision factor. But here, laser technology and environmental awareness should go hand-in-hand. The objectives are straightforward:
Reduced material consumption;
Lower energy consumption;
Minimization of rework.
When designing processes, one thing must be kept in mind: a laser only works as well as its beam delivery. And its builtin components do wear out and get dirty over time. This often causes either the focus diameter to grow larger overall or the focus position to shift, which also results in a larger beam diameter. In either case, this reduces the power density at the processing level. If these changes go unnoticed, additional costs will arise – material wasted in defective parts and/or time and labor wasted in troubleshooting the problem. To compensate for the change in the process without actually fixing the source, users resort to reducing processing speed and/or increasing laser power. Both lead to higher consumption of energy and process gases. In other words...not something anyone wants or can afford these days!
Focus Quality and Unit Cost
To increase the sustainability of the laser process, one can start at a couple of different entry points. First, it is paramount to know how the beam focus behaves overall and how any changes in laser power and focus position will affect the process. These investigations are usually conducted during development.
Once the laser process is put into operation, however, a measurement can tell whether the laser still works in the production environment as it did in development. As the operation continues, essential maintenance tasks include checking the optical lenses and protective windows – and replacing them as necessary. If errors and rejects are occurring, it is recommended to have a clear measurement strategy that defines how to quickly get the laser system back up and operating again.
The following procedure usually produces good results:
- Check the beam adjustment at the cutting nozzle (if relevant).
- Replace the protective window.
- Check the beam path adjustment.
- Check the laser’s output beam for its power and beam profile.
The central parameters to be measured are laser power, focus diameter, focus position (x, y, z), focus shift, beam profile and divergence, beam quality M2, as well as BPP (beam parameter product). However, for all these measurements, the question of which measuring technology to use should not be decided solely based on laser power; it is essential to also know laser power density.
Laser power density is defined as the power per unit area (watt/cm2). A change in the focus diameter – for example, due to an incorrectly cooled lens or a dirty protective window – exerts a direct influence on the power density of the laser beam and can have multiple consequences:
The travel speed may have to be reduced.
The quality of the machined part in the cutting or welding process may suffer.
Production times and power consumption can increase, as can the need for expensive gases used in processing.
The heat-affected zone (HAZ) will be larger, requiring more post-process finishing like straightening, deburring, or polishing. Under certain circumstances, an undetected loss in product quality can lead to diminished strength – a defect that, once recognized, may result in costly recalls.
These technical effects inevitably take a significant toll on costs and sustainability. The greater the deviation in the beam quality at the processing point, the more spent on energy and process gases.
Efficient Power Measurement
Even with these clear correlations, critics often claim that measuring the laser beam is too expensive and the instruments too fragile. But new technologies are available that are optimally adapted to industrial applications.
MKS Instruments, for instance, recently introduced a new power gauge that not only covers a wide range of laser applications, but is also quite small, compact, and robust. The Ophir Ariel determines laser power up to 8 kW based on a quick measurement of the energy. Even in continuous mode, power levels up to 500W can be measured. Different wavelength ranges — 440-550nm, 900-1100nm, 10.6 μm and 2.94 μm — can be calibrated and measured with one device. The included diffuser can be easily attached so that the instrument also works with high power densities, such as when the beam diameter is small.
Given the kinds of industrial settings in which laser measurement is used, the system design needs to be robust; preferably shockproof, dustproof and splashproof; with no need for cooling with water or air. This allows for measurements in closed construction chambers, as is often the need in additive manufacturing or robot cells. Measurements should be readable via Bluetooth using an app or on a PC, and shown directly on a high-resolution display. Alternatively, they can be stored in the internal memory and transferred over a USB-C interface. Developers, operators and service technicians can get a first impression of the process quality by quickly determining the laser power with such compact instruments.
For performance measurement in automated laser production systems, there are also compact and robust systems available that operate without the need for water cooling. Such systems measure the laser beam quickly and reliably, and they transmit the data to a central data storage system via an appropriate network interface. Such systems include a standard RS232 interface. More modern systems, such as the Ophir Helios Plus, also have a Profinet or an Ethernet/IP interface. Using a thermal measurement method, such devices can determine laser powers up to 10 kW or more in just a few seconds.
Even in very complex processes, such as welding battery packs or manufacturing a fuel cell, the proactive measurement of laser power can be both fast and precise. However, it should be noted that measuring the laser power provides only a first glimpse into more complex processes.
In order to draw reliable conclusions about the laser beam caustics, one requires either a camera-based measurement system or a non-contact method for measurement. Figure 3, left, shows a camera-based measuring device that must be moved along the z-axis in order to find the focus position by means of the determined beam profiles. Rapid changes in the focus position are therefore difficult to detect. On the right is a schematic representation of a non-contact measurement technology, which shows that the caustic of the entire beam is recorded at once. Here, a change in the focus position shows up immediately and is resolved in space and time.
Especially in the field of automated production, non-contact measurement of the laser beam proves to have a bright future. In sensitive areas, such as the manufacture of gearboxes or battery packs, new products combine multiple measurement methods in a single system. In the Ophir BeamWatch Integrated system, for example, beam caustics can be recorded using non-contact measurement technology; a water-cooled measuring head for high-power lasers determines the laser power; and the measurement data is passed on to the production network via integrated interfaces (Profinet, Ethernet/IP, CC-Link, GigE). Different welding heads and parameters can also be tested. By capturing the beam at video frame rates, focus shift can be detected in near real time, as shown in Figure 4. Here, a dirty protective window was to blame for the shift in focus.
Laser systems are central to a variety of complex manufacturing processes. Thanks to new innovations in measurement technologies, manufacturers and users now have a wide range of options for proactively measuring the laser beam. Key laser parameters can be recorded and adjusted quickly and accurately. This ensures that the process runs under optimal conditions, that there are no additional costs due to wasted energy and materials, and that the products manufactured meet the highest quality requirements. Measurement technology for the laser thus contributes significantly to sustainable production.
This article was written by Christian Dini, Director Business Development, Ophir (North Logan, UT). For more information, visit here .