October, 2022- Face Time with TOM KUGLER, a fiber systems manager at Laser Mechanisms. Tom explains why proper laser beam monitoring during additive manufacturing is so important—especially given the high value of the parts

October, 2022 - TOM KUGLER, fiber systems manager at Laser Mechanisms, explains why proper laser beam monitoring during additive manufacturing is so important—especially given the high value of the parts

Q:Why is it important to monitor the laser beam during additive manufacturing?

A: Selective laser melting (SLM) additive manufacturing’s deposition quality depends upon monitoring four main aspects of the system—atmosphere quality; quality and consistency of the delivery of the deposition alloy; the speed and path accuracy of the beam motion system; and the laser power, focus position and focus spot size of the laser beam. Laser beam monitoring can provide quality control of all aspects of the laser beam and also path accuracy information. A laser beam’s path through focus is similar to an hourglass. Any variation in the focus position relative to the part being produced will change the spot size on the material and create a melt zone that can be too large or too small, which will change the track width, track height or surface finish of the deposition. A scanning system’s accuracy requires that the focus plane of the optics matches the surface plane of the material being melted. If the focus plane is above the material plane, then the angles from scanner will offset the beam and melt zone away from the center of the scanner. This dimensional error increases with increasing distance away from center. The synchronization of the laser with the scanner also is vital to accurate parts since incorrect synchronization can change the scale and accuracy of the deposition. Finally, the size of the focus spot will determine the material interaction and the consistency of layer bonding.

Q:What are some typical questions customers have about laser beam diagnostics?

A: Some customers believe that beam diagnostics must be real-time measurements or require a long time for a measurement and, therefore, need water cooling. Also, many customers believe that the beam diagnostic devices won’t fit into their build chambers or require cabling to be routed out of the sealed chamber. Modern beam diagnostic hardware can measure laser power very quickly, requiring only a few seconds for a power check and no need for water cooling. Also, beam analyzers have been engineered to fit inside build chambers and communicate via a wireless WLAN network.

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Q:How can companies determine where their issues are coming from?

A: Build consistency in terms of deposition layer thickness, width and dimensional tolerances of the build are where most laser beam issues will become apparent. Loss of deposition width and thickness, or bonding to the previous layer, are telltale signs of a possible laser power issue or a focus position issue. Surface finish on the sides of the deposition can be a sign of focus spot size variations. Dimensional issues with the build in X and Y are signs of positional accuracy issues related to the focus plane in the Z axis being at a different position than the material plane. Also, scanner/motion path accuracy and synchronization of the laser to the scanner will shift the dimensions and affect build tolerances. Finally, if a system has more than one scanner for the same build area, alignment accuracies between the scanner fields will create dimensional variations in the parts. Laser Mechanisms distributes the Primes line of beam analysis equipment. The Primes ScanFieldMonitor can measure beam diameter, X-Y-Z position of the laser beam, scanner speed and synchronization of the laser and scanner, as well as thermal focus shift of the optics. The unit is designed to be installed inside the build chamber of scanner-based SLM systems and communicates with a WLAN wireless interface. For very fast power measurement, the Primes Cube M is an even smaller unit designed to work inside or outside chambers and deal with beams near the focus plane for fast power measurement where space is at a premium.

Q:What benefits can be realized from proper laser beam monitoring?

A: Consistent beam analysis checks are just like any other quality control checks. By measuring the system consistently, there is a baseline and history of data on the laser-related components in the system. Lenses and fibers can be replaced. Even laser sources can be replaced over time. It is very important to know that the laser beam is consistent throughout these changes and regular maintenance. Given the high value of many of the parts manufactured by these systems, it is vital to keep all quality records and to measure the system before and after the build. MM

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Tom Kugler is fiber systems manager at Laser Mechanisms (lasermech.com 248/474-9480). He is a physicist and has spent 38 years working with laser applications, systems and beam delivery.