Double-sided incremental forming (DSIF) has been extensively researched due to its high flexibility, good formability, and low cost when performed in small batches, and it enables the production of personalized sheet parts. However, the influences of process parameters on the geometric accuracy, thickness distribution, and forming quality are not well understood. In this paper, a multipass DSIF method is proposed. Based on the law of sines, the distance between the closest surface of the hemispherical forming tool and the supporting hemispherical tool is given, and a series of experiments are conducted. The influences of process parameters such as the toolpath strategy, incremental depth, and squeeze factor on the quality metrics in multipass DSIF, such as the geometric error, thickness distribution, and forming quality are investigated and compared to those formed by DSIF, accumulative double-sided incremental forming, and mixed double-sided incremental forming. The results show that multipass DSIF can effectively improve the geometric accuracy, thickness distribution, and surface quality. The thinning of the material increases slightly with the squeeze factor of the first D-pass decreases, and the different incremental depths have little effect on the thickness distribution. The multipass DSIF method provides some significant engineering advancements for improving geometric accuracy and forming quality.
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