Quantitative surface inspection methods for metal castings

Voelker, Michelle
Major Professor
Frank E. Peters
Committee Member
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Industrial and Manufacturing Systems Engineering

Inspecting castings to verify the quality of a part is critical for foundries to maintain a high level of customer confidence. Current methods employ qualitative methods, and the manufacturer must correctly interpret the inspection criteria set by the customer in order to meet the design specifications. The interpretation of what is acceptable often differs from the customer to manufacturer and even from inspector to inspector. In this thesis, the visual inspection of cast metal are explored in depth, and improvements to current methods are proposed.

First, the risk of Type I and II errors from the inspection process were evaluated based off of varying states of environmental and human factors in the inspection process; however, it was discovered high variation among inspectors still exists due to the subjectivity of the standards. This signals a need for a more quantitative standard to evaluate the surface of a casting. In response a digital standard is proposed, which specifies three parameters to allow the customer to communicate their exact needs in regards to surface finish to the manufacturer. These parameters are calculated based off of a part’s true geometry post shrinkage in absence of surface roughness and abnormalities, or underlying geometry. Since the underlying geometry differs from the part’s intended geometry, methods will be explored to estimate the underlying geometry from a point cloud of the part’s surface. The proposed methods will be compared to identify which approach best estimates the ideal underlying geometry. Once an ideal method is identified, it will be used as a standard method to calculate the underlying geometry in order to create consistency among inspectors at both the customer and manufacturer.

The work completed in this thesis will raise awareness of the risk associated with current visual inspection methods for cast metal surfaces. The new, digital standard will reduce the variation in this inspection process allowing greater confidence in the parts leaving the manufacturer. Additionally, the standard will allow the customer to improve communication with the manufacturer in order to achieve the quality of surface required for their specific needs.