<p>This study combines experiments and multiscale simulations to elucidate the formation mechanisms of sinuous chips during low-speed orthogonal cutting of commercial pure aluminum. The investigation focused on how cutting speed influences multiscale deformation behavior and chip formation. Results showed that increasing the cutting speed from 30 to 180&#xa0;mm·min⁻¹ effectively suppressed plastic instability and enhanced process stability. Specifically, the chip morphology transformed from sinuous flow to continuous laminar flow. Concurrently, key indicators of instability decreased: the cutting force fluctuation and chip compression ratio were both reduced by over 40%, and the average surface effective strain decreased by 26%. The developed modeling framework successfully reproduced the complete chip evolution process, from buckling initiation and self-contact folding to final separation. The simulated strain distribution and folding morphology matched metallographic experimental results well, validating the model’s predictive capability in establishing the link between microstructure and macroscopic plastic response. The mechanism for sinuous chip formation was found to be periodic buckling triggered by microstructural inhomogeneities. Soft grains acted as localized strain concentration points, initiating the initial buckling. Conversely, hard grains and grain boundaries modulated the buckling and folding geometry through constraint and stress redistribution, ultimately leading to the characteristic alternating mushroom-shaped stacking morphology.</p>