Laser myths: What fabricators don’t know can hurt the process

Lasers often are used for joining applications in automotive manufacturing. Monitoring the laser system helps ensure consistent and high-quality joining processes.

Application of high-powered lasers is becoming more commonplace in industrial environments, such as sintering in additive manufacturing, joining of body components in the automotive industry, and drilling and cutting of aerospace components. As more applications of these lasers are discovered and developed, more manufacturers are realizing how reliable and repeatable industrial laser systems can be.

Like any other machine tool, the technologies surrounding the laser system have advanced significantly over the past several decades. However, many myths surrounding the employment, operation, and maintenance of an industrial laser still exist. Separating fact from fiction is critical to ensuring a high-quality laser process.

The use of a laser as an industrial tool can be traced almost as far back as the advent of the laser itself. The CO2 laser used to be the workhorse of laser manufacturing with its raw horsepower, relatively inexpensive operating costs, and ease of maintenance. Hundreds of thousands are still in use today.

The 1980s saw the introduction of the fiber laser as an industrial tool, and it has changed the landscape of industrial laser manufacturing. The fiber laser brought several benefits, such as increased wall-plug efficiency, improved beam quality, and decreased maintenance, compared to the well-established CO2 lasers. But the early generations of the fiber laser were expensive, did not produce the wattage necessary for industrial laser applications, and were difficult to maintain. Fiber laser manufacturers have overcome most of these hurdles and now are providing sources and systems that are more practical.

As high-quality and reliable as today's laser systems have become, the user might be tempted to neglect the fact that the system is still made of physical parts with physical properties. Laser systems comprise mechanical and electrical components that degrade or fail after periodic use. When these lasers are used in harsh industrial environments filled with process debris, degradation and failure of components are multiplied, resulting in decreased efficiency and increased operational costs.

System designers have gotten creative in their management of process debris. However, without measuring laser system performance, the user cannot understand the full effects of these system component degradations or how and when to take action to maximize the system's efficiency.

Laser systems require significant financial investments to produce parts as quickly and as efficiently as possible. Periodic maintenance on the system is necessary, but the obvious desire to maximize return on investment (ROI) means minimizing the time that it takes to maintain the system. A laser performance measurement system can provide a quick indication of how the laser is performing and help in the development of a more comprehensive laser maintenance routine.

In CO2 laser applications, when a laser starts to drift from its optimized process, a laser user might be tempted to turn up the power to keep processing parts without addressing why the laser is losing efficiency. What might be happening is an increased thermal effect on the laser system caused by an aged, damaged, or contaminated optic, usually close to the process. The thermal effect causes the focused spot to shift upwards, resulting in decreased power density.

Beam profiling instrumentation allows end users to tune their laser processes to achieve a precise irradiance that is enough for the task, but not too intense that a weld, for example, overheats and renders less optimum results. Today's laser measurement tools help users understand the performance of their laser light and to optimize the operation and maintenance of their systems.

On a related note, manufacturers should know the major difference between CO2 lasers and fiber lasers. CO2 lasers operate at a very forgiving 10.6-µm wavelength. The optics for these lasers are robust, less susceptible to damage from surrounding process debris, and easier to maintain. Modern-day fiber, disc, and diode lasers operate near a 1-µm wavelength. The optics used in these lasers are more susceptible to damage from the debris produced in their harsh industrial environments and must be handled with extreme care when being replaced. Some laser operators rely on the legacy practice of changing CO2 laser optics, but these practices ultimately can damage the processing heads of their 1-µm wavelength lasers.

Laser-based additive manufacturing systems require precise output powers and focused spot sizes at the process to produce quality parts consistently.

This myth that the ROI with a laser measurement system is low is rooted in the misconception that these systems are expensive and difficult to set up and use. Also, many manufacturers think that, while laser measurement equipment is nice to have, it might not provide information that is useful or relevant to the application.

Historically, the cost to purchase laser measurement systems was high. When electronic laser measurement products began to come on the scene in the 1970s, they were mostly used in scientific laboratories and highly controlled environments. The information that they supplied was particularly useful, but the cost of ownership allowed only well-funded organizations to have these tools.

Today, with the advancements in camera technologies, optical components, networking, and communication technologies, as well as computing power and software, laser measurement products are smaller, faster, and cheaper. Laser power meters and beam profiling products have evolved into cost-effective maintenance tools that can integrate directly into laser workcells. For example, it is increasingly common for automotive manufacturers to integrate an industrial combination power measurement and beam profiling device into their workcells to monitor laser performance for trend analysis, process traceability, and smarter maintenance prediction.

In addition to cost improvements, several advancements allow for easier operation of these products. Today's laser measurement systems take into consideration the needs of system integrators, operators, and maintenance personnel. For instance, they employ industry-standard communication protocols and are designed with rugged industrial hardware connections. They also include safety enhancements to protect against damage from process debris and overheating. Laser power meters and beam profiling products are used widely in scientific and research arenas and often are designed for those environments. These products also are being applied in industrial arenas because of the relevant laser performance information they supply. Because of this, their designs have been adapted to more harsh production environments.

It is not uncommon to hear laser personnel in industry say, "This laser process is so robust, there's rarely anything that goes wrong with it" or "This laser is welding sheet metal, so why would I care about its performance?" In some cases, a laser application is developed and deployed, and performance is simply assumed to remain consistent until something goes wrong. That's not the best way to manage a process. Also, it is especially troubling to hear these statements made by people in high-precision applications, such as automotive manufacturing, that place such an emphasis on safety and quality.

The reality of the manufacturing world, however, is that the push for safety and quality is counterbalanced with the constant drumbeat to reduce operating costs. But this can sometimes be difficult, especially for laser applications, such as welding highly reflective materials, in which achieving a consistent laser process isn't always easy. To ensure that the laser is performing consistently over time, key performance measurements must be taken, analyzed, and acted upon. When these laser parameters are unknown, the process can drift and ultimately result in scrapped parts. For instance, if the focused spot in a copper welding application shifts from its designed position, loss of weld penetration can occur from the beam size increasing at the process point. If the focus shift on the laser system is tracked, this drift can be avoided.

Sustainability is a major consideration as well. Manufacturing companies are seeking ways to consume resources more wisely to reduce the impact on the planet. Anyone who has been involved in these initiatives knows that every little improvement to a process helps.

Measuring, tracking, and analyzing laser performance, and taking action to maintain consistent laser performance, can support sustainability. A properly maintained laser system consumes less power and maximizes throughput, which is not only good for reducing operating costs, but also good for the planet.

The "don't fix what isn't broken" philosophy is alive and well in manufacturing. For example, some laser service personnel still use very simple tools for maintaining and troubleshooting laser problems. Laser "power pucks," acrylic mode blocks, and phosphor-coated fluorescent plates are quick and easy to use, but these legacy products paint an incomplete picture of how the laser is performing at any given point in time.

With these primitive methods, a laser is fired into a bulk thermal device for several seconds, which produces a single number corresponding to output power. The laser beam is imaged into an acrylic block or fluorescent plate and analyzed subjectively without any trending data or industry standards of measurement. Today's electronic laser measurement products provide time-based measurements, which allow for short- or long-term trend analysis of laser performance. They are calibrated against NIST-traceable standards and use ISO-compliant methods of beam measurement. This provides the user with a more comprehensive analysis of laser characteristics and confidence in the accuracy of the measurements.

In this age of Industry 4.0, the demand for feedback from machine tools is proving very valuable to improving industrial processing. The laser, when viewed as a machine tool, is no exception. Products now can provide information about the laser's performance characteristics with a couple of different approaches. In-process or "in-situ" measurement can provide real-time feedback on how the laser is operating, but often only analyzes part of the laser system, which limits the information that can be supplied. On the other hand, at-process measurement products provide a more complete analysis of how the laser is performing at the point of processing; however, these products must be used between part runs, so the resulting information is not in real time. Either way, having information about the laser's performance is always better than no analysis when considering process improvement.

The job of the laser operator is challenging enough without access to laser performance data. Measuring, tracking, and analyzing long-term performance trends can help them better operate and maintain their laser systems and quickly troubleshoot problems when they arise.