The effects of process parameters on forming limit of rectangular tube in rotary draw bending process

In the manuscript, the forming limit for cross-section distortion is defined according to the employing area and aviation standard. First, the definition and determination method of forming limits is proposed. And then, the effects of process parameters on forming limit are investigated based the 3D FE simulation model. Finally, the 3D forming limit diagrams for cross-section distortion are obtained under different process parameters. KEYWORD: Forming limit; determination method; Forming limit diagram 4th International Conference on Mechanical Materials and Manufacturing Engineering (MMME 2016) © 2016. The authors Published by Atlantis Press 423 sions 24.86*12.2*1mm(b*h*t) as an example, a three dimensional finite elements model of this process, as shown in Fig.2, is built under the ABAQUS/explicit environment based on the solution of several key techniques, such as model creation, contact boundary condition treating, material properties definition, meshing technology, and it is validated to be credible [9]. Fig.1Determination method of forming limit Fig.2 3D FE simulation model 2.2 The effects of material parameters on forming limit 2.2. 1 The effects of elastic modulus. The elastic modulus E is set in the range 40~200GPa respectively, and the curves of minimum bending radius vs elastic modulus are shown in Fig.3. It can be seen that the minimum bending radius increases from 30 to 40mm with elastic modulus increasing from 40 to 200MPa. The elastic modulus is the parameter to measure the ability to resist the elastic deform, while the plastic deform is the main deform. Larger elastic modulus will need larger force imposed by dies, inducing larger elastic springback. Therefore, the effects of elastic modulus on forming limit is not significant. 2.2.2 The effects of strengthen factor. The hardening exponent is set in 100~300MPa, and the curves of minimum bending radius vs strengthen factor are shown in Fig.4. It can be found that the minimum bending radius increases sharply with the strengthen factor from 100 to 300MPa. The minimum bending radius with strengthen factor 300 MPa is twice as the corresponding value with strengthen 100 MPa. The bigger strengthen factor induces bigger yield stress, and the forming energy will be larger subsequently. The force exerted by dies need be larger, and the resistance to cross-section distortion of rectangular tube will be weaker. Therefore, the cross-section distortion is larger, and the tolerant deformation interval is narrow. 2.2. 3 The effects of hardening exponent. The strengthen factor is set in the 006-0.35, and the curves of minimum bending radius vs hardening exponent are shown in Fig.5. The curves of minimum bending radius vs hardening exponent show that the minimum bending radius decreases from 50 to 30 mm with the hardening exponent from 0.05 to 0.35. In the forming process, the work hardening effect will be more significant with bigger hardening exponent, and the the forming zone will transferred to the zone which is more difficult to deform. From macro view, the deformation of rectangular tube will be steady and uniform. Therefore, the rectangular tube with larger hardening exponent can be bent to smaller radius, and the forming limited interval is extended. Fig.3 Curve of Rminvs. E