A comparative study on the effect of grid printing methods and camera hardware in automatic strain measurement through CGA

Abstract

Strain analysis is an important step in sheet metal forming operations to identify the potential locations of failure. Circle grid analysis is a widely used method to evaluate the strains in sheet metal forming, where deformed circles on a formed component are measured to evaluate the strains at different locations. In this paper, two different USB cameras are used to capture the images of the deformed grids. The images are processed using the in-house software developed in MATLAB for strain measurement. The effect of image acquisition hardware and grid printing methods on strain measurement accuracy has been analyzed. For this, the sheets are printed with circular grids by screen printing, laser engraving, and electrochemical etching. The sheets are then deformed in incremental forming to produce different levels of strain in the formed components. The deformed grids on the formed components are captured using proposed USB cameras with appropriate attachments and processed by in-house strain measurement software. The strain measured using proposed hardware and software is also compared with the commercial strain measurement system. The mean absolute percentage error in strain measurement with the proposed USB cameras was found to be 0.671 and 0.761. The statistical results show that there is no evidence to support the hypothesis that the two hardware perform differently on average. Hence, the proposed hardware and software can be used in industry and research laboratories for strain analysis in sheet metal forming operations.