Abstract
The occurrence of size effects in microforming process may result in nonhomogeneous material characteristics. Heat assisted microforming is an effective approach to reduce the influence of size effects. To improve the heating rate, resistance heating method is introduced to the microforming process. To investigate the size effect of heat on material deformation for thin foils in microforming, uniaxial tensile tests were performed for the foils with different grain sizes at different temperatures by tensile testing system incorporating with resistance heating method. The results show that the reduction of the stress at elevated temperatures compared to room temperature is higher for the foils with larger grain size than that for the foils with smaller grain size. The fracture strain decreases with increasing temperature when the temperature is below 300 °C, and then increases as the temperature increases when the temperature is above 300 °C. In addition, the work hardening behavior of the material is independent of the grain size. As temperature increases, the work hardening increases.
Highlights
Microforming has been received much attention in the recent decades due to the wide use of microparts in electronics and biomedical devices
Due to the decrease in the strength of the material after annealing process, the flow stress decreases with increasing grain size at the same tensile temperature [6]
For the foils with different grain sizes, the fracture strain shows the same tendency of decreasing with increasing temperature when the temperature is below 300 °C, and increasing with increasing temperature when the temperature is above 300 °C
Summary
Microforming has been received much attention in the recent decades due to the wide use of microparts in electronics and biomedical devices. The occurrence of size effect [1] in microforming may result in nonhomogeneous material flow and the scattering of the process parameters. To improve the heating rate, resistance-heating-assisted microforming systems were developed by the authors [3, 4]. These systems have the advantages on improving material formability and reducing forming load with small amount of energy. By using these systems, different kinds of microforming processes, such as micro deep drawing and micro bending were conducted at elevated temperatures. The design of resistance-heatingassisted microforming process is still with difficulty since the size effect of heat on material deformation for metal foils in microforming is not clarified clearly yet
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