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A flexible die forming process is proposed to form aluminum micro channels with channel widths not larger than 1 mm. Three micro channel dies and two different polyurethanes (40A and 90A) were used to form micro channels on the annealed and as-received aluminum foils (50 and 75 μm). For understanding the influences of size effects, polyurethane hardness and channel width on forming micro channels, a series of experiments were conducted. Through using different annealing conditions, different grain sizes were obtained such that different T/D, the ratio of thickness and average grain size, could be obtained. T/D ratio is used as a parameter to model the size effects in the two models proposed in this paper. These two models can predict the depths of the micro channels formed by the proposed process, so they can be used by industry as a design tool for product design, process design and development, annealing process, etc.

The size effects including the downscaled thickness and grain size presented in the micro‐drawing process were investigated by both the experimental approaches and the finite element analysis. In the present study, experiments were conducted first to establish the stress‐strain relations and r‐values for 304‐O stainless steel sheets with various thicknesses and different grain sizes. The experiment results reveal that the flow stress and r‐value become smaller for downscaled thicknesses and larger grain sizes. The testing results also indicate that the anisotropic properties are dominated by the grain size as the sheet thickness is smaller than 0.2 mm. The micro‐drawing process for producing a vibration motor casing, which bears a circular cylindrical shape, was also examined in the present study. The finite element simulations were performed to evaluate the formability of the multi‐operation drawing process with the initial die design. The forming characteristics were identified and an optimum forming process was then developed. The actual micro‐drawing process based on the finite element analysis was also implemented, and the good agreement between the drawn cups and the finite element simulation results confirms the process design developed in the present study. In addition, the effect of grain size on the micro‐drawing was examined as well in the present study. The finite element analysis reveals that as the sheet thickness is smaller than 0.2 mm, the minimum thickness in the drawn cups was dominated by the r‐value rather than the yield stress.