Scale effect on springback behavior of pure titanium foils in microbending at elevated temperature

• Springback angle decreases with decreasing foil thickness at elevated temperature.
• Influence of surface area on flow stress dominates in the decrease of springback.
• New theoretical model considering surface is proposed to predict springback angle.
• Reduction of springback angle can be predicted accurately by the proposed model.

The occurrence of size effects in microforming process influences the accuracy of the products significantly. To investigate the scale effect and the mechanism of springback behavior of thin pure titanium (Ti) foils bent at elevated temperatures, scaled microbending processes assisted by resistance heating are performed for the foils with different thickness of 0.02, 0.05, and 0.1 mm. It is found that the springback angle increases with decreasing foil thickness at room temperature. However, after bending at elevated temperatures, the springback angle is found to decrease with decreasing foil thickness. Due to the lower flow stress of surface, the influence of surface area is thought to be the dominating factor that results in the less springback of thinner foils at elevated temperatures. To confirm this and to predict the springback angles at elevated temperatures, a new theoretical model of surface area increasing with increasing temperature is proposed. The springback angles are calculated by theoretical analysis using conventional plastic theory and the proposed model. As temperature increases, the large reduction of springback angles compared to 298 K can be captured by using the proposed model successfully. The validity of the proposed model is confirmed.