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A holistic, closed-loop system provide inline quality control of laser sintering and direct metal deposition manufacturing processes. (Credit: University of Michigan)

Additive manufacturing techniques have great potential to improve productivity and energy efficiency during part fabrication. Even small defects in fabricated parts can have a large impact on performance and safety, which is why manufacturers need to be on the lookout for several types of defects, including inaccuracies in part dimensions and composition, microscale cracks, porosity, and others.

A number of methods exist for postmortem part analysis and inspection, but they are time- and labor-intensive, and some lack the desired degree of accuracy. They also forego a key opportunity offered by additive manufacturing: the chance to make layer-by-layer corrections while part fabrication is underway rather than after the fact.

Building on decades of research in materials processing and laser-aided manufacturing, researchers have developed and demonstrated a holistic, closed-loop system for inline quality control of laser sintering and direct metal deposition manufacturing processes.

The in-situ optical diagnostics system, dubbed the Smart Optical Manufacturing System (SOMS), is helping establish a new paradigm, “certify as you build.” The SOM system includes a number of optical sensors to detect defects and diagnose composition inconsistencies and other problems, including phase transformation. A fast-response optical sensor, based on optical emission spectroscopy, uses the plasma created by laser-aided additive manufacturing to detect pinholes, porosity and tiny cracks within milliseconds.

Analyzing the laser-induced plasma also provides valuable information about material composition. Similarly, using algorithms to analyze the relationship between spectral lines from different materials alerts inspectors to possible phase changes taking place as the metals are heated to high temperatures.

The SOMS also includes sensors to monitor temperature in order to determine, and control, the cooling rate of materials. The approach incorporates technologies in a seamless way that yields capabilities greater than the sum of the individual parts. This includes identification of problems in less than a second, rather than the hours or days of conventional approaches. Identifying defects quickly enables manufacturers to course correct and prevent defects from worsening.

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