Variogram Roughness Method for Casting Surface Characterization

Casting surface specifications are set based on aesthetics, functionality, or a combination of both. To classify casting surfaces, visual inspections are performed by an operator who compares the casting surface to pictures or comparator plates (e.g., metal, plastic) that represent a certain roughness level. This inspection process is highly subjective, and disagreements arise on the acceptance of a casting between the casting producer and buyer. To minimize these disagreements and use developments in 3D scanning, this study aims to develop a digital surface characterization method. The method developed and implemented in this study utilizes underlying geometry estimation, abnormality detection, and a new roughness characterization formula based on a variogram to determine a surface roughness value. Tests were done to compare the new roughness characterization formula with existing quantification methods (i.e., Sa, Sq) and to compare the results of the method with human operators. The tests indicated that the variogram roughness was able to differentiate between the roughness levels of the current surface roughness standards GAR-C9 and SCRATA. In addition, the results are repeatable as well as reproducible and agree with operator judgment based on a ranking comparison between the operator and the digital method. Overall, the digital surface roughness method has the potential to improve the communication between casting suppliers and designers and make the surface roughness classification more reliable and repeatable.