Date of Award

2025-12-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Francisco Medina

Abstract

The technology of Laser-Based Power Bed Fusion of Metals (PBF-LB/M) has been one of the most common in the industry among the others Additive Manufacturing technologies due to its ability to create complex designs in a variety of powder metallic materials. PBF-LB/M systems are composed of various subsystems that are essential for the machine to perform its functions properly. The subsystem reviewed in this work is the laser source subsystem, which is one of the most indispensable in the machine, as it represents the power source that fuses the powder material into manufactured functional parts. Given its role as the primary energy source, the study of the laser beam is fundamental to the reliability and quality of the system. PBF-LB/M commonly uses a Gaussian beam laser, which is composed of several key characteristics. To ensure the laser remains in optimal condition to effectively fuse the material and provide high-quality end-use parts, it is crucial to maintain a constant inspection of the characteristics. These characteristics, such as beam waist, Rayleigh length, and divergence, among others, need to follow and meet the standards and criteria for laser health to consider an ideal healthy Gaussian beam to be able to complete its designated goal. The laser has been designed to focus the melting point position on the build plate, concentrating its energy on the smallest spot, known as the beam waist of the Gaussian beam, thus creating an ideal melting pool. The primary objective of this study is to detect the beam waist focal shift phenomenon, commonly observed in lasers, known as thermal lensing. The thermal lensing shifts the beam waist on the z-axis and defocuses the laser, preventing the correct energy deposition on the powder, which creates distortions in the manufactured parts. The thermal lensing prevents the laser source from fulfilling its purpose. Experiments conducted on the machines, designated as laser beam measurements, are described below. The machines primarily involved in this study were AconityMIDI+, SLM 280HL, EOS M290, and Renishaw 500Q Flex. These experiments provided an understanding of the laser characteristics through recording data, enabling the diagnosis and prevention of laser abnormalities, like thermal lensing phenomenon. The primary objective of this work is to detect thermal lensing in the laser beams and monitor the laser health, thereby preventing potential issues in machine performance that the laser can cause, such as permanent damage to the laser source subsystem. To achieve this, it was necessary to identify the most suitable device among various commercially available options capable of measuring thermal lensing and the key characteristics of a Gaussian beam. The selected device supported the development of a standardized and reliable measurement process, enabling consistent evaluation across different machines and ensuring confidence in the collected data and the analyses. Commercially available camera analyzers for laser beam measurement are designed to measure the laser beam and collect its characteristics, helping the user determine the laser beam's health status. After the camera has provided the data, the user will be able to analyze the beam characteristics data across time. However, not all analyzers operate the same, and each records different characteristics or presents data differently, potentially leading to variations. This thesis presents a comparative evaluation of two such devices: the BeamWatch® AM and BWA-CAM®. The analysis includes a discussion of the advantages and limitations of each system. The BeamWatch® AM provides real-time, two-dimensional cross-sectional profiles of the laser beam along the X and Y axes. In contrast, the BWA-CAM® displays real-time spot-based representations of the laser’s cross-section along its propagation axis, in addition to having adjustable mirrors that are adapted to any laser possible. Based on a comprehensive assessment of functionality, data output, and suitability for the research objectives, the BWA-CAM® was selected as the most appropriate tool for this study. The BWA-CAM® (BWA-CAM®, Haas Laser Technologies, Inc., Flanders, NJ) provides the laser beam characteristics, allowing this research to analyze the data given in accordance with ISO 11146, ISO 13694, and ISO/ASTM 52941 standards. Following the requirements of these standards organization's, a laser measurement protocol was developed to ensure that measurements were conducted correctly and consistently. This standardized procedure enabled the collection of reliable and repeatable data. Each laser of each system was evaluated at three different power levels 100, 200, and 300 Watts in four different machines: Renishaw 500Q flex, SLM 280HL, EOS M290, and AconityMIDI+. As a result of prevention of thermal lensing, this thesis introduces a user-friendly software application interface created and designed to help user analyze BWA CAM® data easily and assess the quality of their lasers. This tool promotes continuous observation of the Gaussian laser beam health and simplifies the interpretation of measurement results. In addition to the measurement protocol, custom-built plate fixtures were designed and fabricated to ensure precise alignment with the laser beam, facilitating a faster and more repeatable measuring process. These fixtures were made from polycarbonate, selected for its lightweight in sufficient thickness to reach the required measurement height specified in the protocol each fixture includes an alignment space designated for the BWA-CAM® analyzer positioned beneath each laser in the machine studied. This setup improves both measurement accuracy and efficiency through the experimental process. Once the data was collected from the trust process, the key goal was to achieve a result understandable to any user. This thesis presents a user-friendly method for implementing data, enabling users to identify anomalies in their laser systems easily. The general objective of this work is to provide a practical and accessible solution based on a reliable and validated process that enables users to inspect their Gaussian beam lasers and detect thermal lensing efficiently and accurately. The results presented in this thesis are based on monthly laser beam measurements for 35 seconds each in different power levels, using the standardized protocol developed for this study, enabling the constant inspection of the laser characteristics. Additionally, the machines tested underwent a decommissioning and recommissioning process by the Original Equipment Manufacturer due to the relocation of the laboratory to new facilities. The machines were measured before and after the move to observe any change to the system. The analyzed data, visualized in plots, illustrates the focal shift of the beam waist position (in millimeters) per second observed at different power levels for each machine evaluated. To expand the dataset, measurements were also conducted on a PBF-LB/M machine located at a different facility, the AconityMIDI. This system is similar to the AconityMIDI+ available in the laboratory, but it features smaller physical dimensions and a lower-powered laser, providing comparative data among the same original manufacturer but different commercial machines. As well as demonstrating the real consequences of poor laser quality or laser-related issues in actual manufactured parts. Offering this study the opportunity to understand laser beam behavior across AM technologies. This work highlights the importance of maintaining consistent documentation of laser behavior to track laser health over time effectively.

Language

en

Provenance

Received from ProQuest

File Size

196 p.

File Format

application/pdf

Rights Holder

Paola Almaraz

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Available for download on Sunday, December 31, 2028

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