Influence of Punch Radius and Angle on the Outward Curling Process of Tubes

Using the theory of updated Lagrangian formulation, this study adopted the elasto-plastic finite-element method and extended the increment determination method, the

r_min method, to include the element’s yielding, nodal contact with or separation from the tool, maximum strain and limit of rotation increment. The computer code for a finite-element method is established using the modified Coulomb’s friction law. Conical punches with different radii and angles are used in the forming simulation of hard copper and brass tube ends. The effects of various elements including the half-apex angle of punch (α) and its radius (R), the ratio of the thickness of the tube wall to the mean diameter of tube, mechanical properties, and lubrication on the tube’s outward curling, are investigated. Simulation findings indicate that when the bending radius at the punch inlet (ρ) satisfies the condition of ρ≤ρ _c , curling is present at the tube end. On the other hand, if ρ≥ρ _c , the tube end experiences flaring. The variable ρ _c is called the critical bending radius. The value of ρ _c increases as the value of α increases. Furthermore, the findings also show that ρ _c is neither correlated with tube material nor lubrication.