Forming mechanism of leaf-like integral outside finned tubes via sequential knurling and cutting-bending method

Sequential knurling and cutting-bending method is proposed to manufacture leaf-like integral outside finned tubes (LIOFT). The numerical analysis method was used to explore the material fracture and plastic forming processes. Single-factor experiments were used to establish quantitative relationships between process parameters and forming quality to guide the design of experimental parameters. The results of the numerical analysis revealed that the teeth of the knurled tube were cut by the tool’s main cutting edge and then slide-bent along the rake face and minor cutting edge during the forming process. The knurling direction significantly affects the fin height and shift, a reasonable knurling direction increases the fin height by 40.1% while reducing the fin shift by 94.0%. Increasing the friction coefficient and tool feeding speed slightly increases the fin height but reduces the fin strength and finning ratio. The combination of experimental parameters was optimized based on the numerical analysis results, and a LIOFT with a maximum fin height of 3.46 mm was manufactured accordingly.