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The relationship between In-Process Quality Metrics & Computational Tomography (CT) in Additive Manufacturing of Metal Parts

Executive Summary

What if manufacturers using additive technologies like 3D printing could see and analyze the structure of a part while it was being made? They would have a high degree of confidence in the manufacturing process, as would their customers. They could also make real-time adjustments to the manufacturing process that would further assure the quality of the process.

This, in turn, could reduce the cost of manufacturing said parts, as well as ultimately reduce the cost of complimentary quality assurance testing. Sigma Labs has developed a method to do just that, with results comparable and complementary to – and in some cases better than – CT testing.

Manufacturers fabricating parts for high-risk, demanding industries like aerospace and the military, need to be sure that these parts have been accurately made and to have confidence that the parts will not fail. The consequences of failure can be expensive. More importantly the consequences can be deadly.

There are two ways to certify that a part made using additive manufacturing meets quality assurance standards: destructive testing and computed thermography (CT). Each has drawbacks. Destructive testing may indeed find a part meets specifications, but does not guarantee that the next part will, too. And the part has been destroyed in the process. The other method – CT testing – is expensive, takes time and does not always yield accurate results when a part has complex geometric structures within it.

Sigma Labs has developed a way to analyze the structure of a part and any variations in its creation when compared to specifications, while the part is being manufactured using additive technology. This methodology identifies the thermal signatures [In-Process Quality Metrics™ (IPQMs®)] of printed metal material (the melt pool) while the part is being manufactured. This methodology maps any flaws in real time. Specific IPQM® thermal signatures can also be used to help optimize part design.

Additionally, this Sigma Labs-developed methodology, as a non-destructive technology that can be used on every part at the time of manufacture, yields comparable results to CT testing. In the case of parts with complex geometric structures, Sigma’s IPQM® technology is actually better.

This paper outlines how the combination of the identification and mapping of thermal signatures using Sigma’s methodology and CT testing furthers the understanding of flaw detection. This combination also reduces risk in parts that are not CT-inspected. The two processes together provide a more complete picture of flaws in the part and what conditions during the process lead to them. The paper also introduces a framework for using CT results to establish confidence in Sigma’s methodology as a complementary quality standard.

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