Study On The Micro Tube Hydroforming With Axial Feeding

Currently,the demand for miniature of micro tubular components are gradually rising with the application of electronics,telecommunications and medical technology in modern products.Micro Tube Hydroforming received increasing attentions due to it's potential capability to massively produce micro tubular components.As the sizes of the micro components go down to the scale of grain size,the size effects become the major issues,which results in the poor formability of the micro tube.The axial feeding,which is widely used in conventional Tube Hydroforming process to feed the material to forming zone,is introduced to the micro tube hydroforming process to improve the formability of micro tube in this research.First,the friction characteristics of micro tube hydroforming zone were studied.A friction test device designed for micro tube hydroforming was designed and fabricated.The coefficient of the friction in the process of hydroforming of SS304 micro tubes with external diameter 2mm and 1mm were measured.The results showed that the friction coefficient increased significantly with the reduction of the tube diameter.The main cause of the increase in the friction coefficient in micro tube hydroforming is that the amount of the lubricant pockets decreases as the diameter of the micro tube decreases,causing the reduction of lubricant amounts stored in the lubricant pocket.Then,the numerical and experimental analysis of axial feeding process in the free bulging of SS304 micro tubes were carried out to study the effect of the axial feeding on the cracking pressure of the micro tubes.Both the simulation and experimental results showed that:1)the axial feeding process can significantly raise the level of the crack pressure of the micro tubes,2)the data of the cracking pressure have a certain scatterness,which indicates strong size effects.Finally,the numerical and experimental investigation of effects of the axial feeding on the hydroforming of micro bulging shape and micro T shape were done.The results showed that the micro bulging shapes can be hydroformed under different axial feeding,while the forming of micro T shape was not successful due to the limited material flowing into the branch.