Abraham Lincoln, the 16th President of the United States, once said: "You can fool all the people some of the time, and you can fool some of the people all the time, but you cannot fool all the people all the time."[11The same is true when monitoring the performance of lasers integrated into a system. In industrial production, the entire system can be monitored for a period of time, or part of the system can be monitored all the time, but it is impossible to monitor the entire system all the time. In the era of Industry 4.0, that is, the era of smart manufacturing, it is very important to understand the difference between the two.
Industry 4.0 is changing the manufacturing situation in all walks of life. Technological advances are helping manufacturers to conduct industrial production more efficiently, faster, and smarter. To properly apply smart machines, it is necessary to collect various data, analyze and filter them to improve the process. Too little data will hinder process improvement, but at the same time, too much data may be counterproductive.
Laser processing systems have their own set of operating characteristics and related issues. Too much data about laser performance can be counterproductive, as it can be overwhelming and overwhelming.
When to measure laser performance metrics?
There are four ways to measure laser performance. The first approach is what most laser system operators prefer, which is scheduled maintenance. In this approach, laser performance metrics are measured based on scheduled downtime of the laser, usually quarterly, semi-annual, or annually. During this time, laser performance metrics are measured and compared to previous measurements to analyze laser operating trends.
The second method is to measure during process failures. For example, if the weld quality is degraded during laser welding, or if the cutting fails or cannot be performed during laser cutting, the performance of the laser can be measured to restore the laser system to the designed operating parameters.
The third and fourth methods are exactly what this article will discuss - in-process monitoring and at-process monitoring. Both methods have their advantages and disadvantages. Operators must be clear about the advantages and disadvantages of these two methods while mastering the optimal processing method of the laser. In addition, operators must also understand which laser indicators are critical to measure during industrial production processes.
How does the laser process materials?
According to high requirements, no matter what processing technology the laser is used for, operators must understand how the laser processes materials. For example, to know which type of laser is suitable for welding, you even have to understand how the laser welds the door frame of an automobile. The easiest way to understand this is through laser power density.
The definition of power density refers to the laser power irradiated to a unit area of material. Power density is usually expressed in W/cm2, where "W" stands for power "watt". For continuous (CW) lasers, its value is the power value: for pulsed lasers, it is its average power value. "cm2" represents the area of the laser spot on the working plane. For example, 100 W laser focused to a spot size of 100 mm has a power density of 1.27x103kW/cm2.
The power density of a laser is affected by changes in the laser power or light size applied to the material. Laser operators must measure, analyze, and understand these two variables to ensure the efficient operation of the laser process.
Important laser performance indicator measurements
The measurement of laser light is usually achieved by a power meter. A power meter is a sensor that collects laser light and converts it into an electrical signal, then infers the power or energy produced by the beam, and finally provides the reading to a meter or computer for analysis. This process usually takes only a few seconds, but it can vary depending on the technology used. These measurements are very important for data collection and analysis, especially in the production stage of the laser, because the data allows users to understand how the performance of the laser changes and how these changes affect the application of the laser in the processing process.
In addition, the diameter of the laser beam must be measured. There are many ways to calculate the beam diameter, such as the D40 method, the 13.5% peak method, and the 10/90 knife edge method, and the calculation results of different methods vary greatly. People from different industries, backgrounds, and experiences use corresponding calculation methods according to their application scenarios.
When calculating the beam diameter, the roundness or ellipticity value of the beam must be considered. It is important to understand the shape of the beam and how the energy is distributed in the beam profile. Is it a Gaussian beam or a flat-top beam? When trying to understand how the laser is used in the process, the measurement of laser beam parameters should be completed by an industry-standard beam wheel measurement system.
In addition to beam diameter, beam quality must also be considered when selecting a laser, developing a laser application, and integrating or debugging a laser source into a system. In most cases, once a laser is put into production, its beam quality is generally no longer analyzed, so it is very important to complete the beam quality analysis before the laser leaves the factory.
Beam quality can be expressed by the M2 value, and an M2 value of 1.0 indicates that the laser beam quality is optimal. The beam parameter product (BPP=0xw, where 0 is the half angle of the beam far-field divergence angle and w is the beam waist radius) and the K value (1/MM2) can also be used to express laser beam quality. The beam quality and efficiency of laser sources have improved. When it comes to different processing processes, different laser sources have their own advantages.
It is important for users to understand the changes in the performance indicators of the laser during the processing process. Measuring laser power, beam size, and how and why they change over time is critical to fully understanding system performance and ensuring more stable long-term performance.
In-process monitoring vs. at-process monitoring
Today, data input is required as close to real-time as possible. This requires a technique commonly referred to as "in-process monitoring," which involves monitoring laser performance measurements while the laser process is in progress. In the field of additive manufacturing, this technique is called "in-situ monitoring."
The counterpart to "in-process monitoring" is "at-process monitoring," which measures laser performance between processes. Both monitoring methods have their own advantages and disadvantages.
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In-process monitoring or in situ monitoring measures part of the performance of the laser during operation and production. A dedicated test subsystem is set up in the laser system to only measure the performance of part of the laser and analyze it in real time.
In-process monitoring has significant advantages. First, since the subsystem is integrated with the entire system, the two can communicate easily. Real-time feedback on laser performance is delivered continuously, so adjustments to the entire system can be made quickly if needed. Second, these subsystems are often designed specifically for the system they are integrated into and are often simple, providing only the feedback required by the customer. The information they collect can be easily presented on a human-machine interface seen by the laser operator. This data can also be stored and analyzed, and warnings can be issued based on the analysis results to ensure the safety of the system and users, or to reduce the scrap rate.
The main disadvantage of in-process monitoring is that these subsystems can only measure a portion of the laser performance of the entire laser system. A portion of the sample is collected before the laser reaches the processing area and analyzed during processing. Unfortunately, many problems that arise during processing are often caused by functional degradation of components close to the processing area after the laser measurement sample has been collected. If a component in the system degrades or fails during processing, the sample used for laser measurement may miss the degradation or failure, providing false feedback to the system.
Another disadvantage of in-process monitoring is the difficulty in calibrating the optical measurement components. Because subsystems are integrated with the overall system, it is often difficult or impossible to remove components for recalibration. Power measurement components must be calibrated frequently (Ophir recommends calibration every 12 months) to ensure measurement accuracy.
Such measurement subsystems also provide additional sensory feedback to the laser system to indicate laser performance without relying on actual measurements of laser performance. For example, a temperature monitor is installed on the cover glass close to the processing area to protect the laser components. When there are too many processing debris on the cover glass and the debris absorbs the laser energy, causing the temperature to rise, the temperature monitor It will remind laser users and provide valuable information to the system and users.
At-process monitoring
At-process monitoring typically uses a separate set of products to take measurements in the laser processing area and analyze the entire laser system. These monitoring systems can be composed of separate products for measuring laser power, energy and beam quality analysis, or they can be composed of products that can test these parameters simultaneously (see Figure 2). These inspection systems can be interdependent or independent of each other, integrated into the overall system, or the system can be regularly maintained between processes.
Similar to in situ monitoring, at-process monitoring has its pros and cons. The main benefit of at-process monitoring is a more complete assessment of the entire laser performance within the system. 100% of the laser beam is collected for power or energy measurement, and the focused spot can also be analyzed to provide the user with a comprehensive analysis of the laser's performance at that point in time. This data can be saved, stored, or logged throughout the system, and then accessed for trend analysis to ensure system recovery after a failure and maintain original system efficiency. Collecting data using this method ultimately gives the user a complete picture of the laser's use, but it does come at a cost.
The most obvious disadvantage of at-process monitoring is downtime. Since the measurement is performed on the entire laser, the laser must be removed from production to perform the measurement. If the laser measurement system is integrated into the machine, it is usually not a big deal, but time is money. However, while integrating a laser measurement system into the overall system is convenient, it can be costly and sometimes even considered unnecessary. If not integrated into the overall system, laser measurement products can be used as maintenance tools. However, the laser must be taken out of production to make the measurements, and when maintenance personnel are not familiar with the operation of the laser tool, the measurements are very time-consuming, which may result in less frequent measurements or even no measurements at all.
In addition, there are other products that can provide users with information about the process. For example, several companies offer products that can analyze the welding process in real time using a variety of technologies. These systems implement "go/no-go" or "pass/no-go" limits on the welding process, allowing users to know when the system may have problems, ensuring the production of higher quality products and reducing scrap rates.
Ensuring that the laser performs stably throughout its life cycle is critical to maximizing and maintaining the consistency and efficiency of the process, extending the life of the laser, and improving the return on investment of the system. Only by measuring the performance of the laser in the field at the job site can users know exactly how the laser is working.
Both in-process and at-process measurement methods have their own advantages and disadvantages, but both methods can provide important laser processing information. Products that measure laser performance indicators are constantly evolving, becoming easier to operate, and more durable. By measuring multiple key performance indicators of the laser, users will find it easier to understand the working principle of the laser and perform long-term performance maintenance of the laser.
