Incremental hole flanging (IHF) is a relatively new sheet metal forming process to produce intricate shapes without using dedicated punches and dies. The present work focuses on understanding the mechanics of the multi-stage IHF process through experimental studies and the finite element approach. The IHF experiments were performed on deep drawing quality steel sheets with a pre-cut hole diameter of 45 mm, 50 mm, 60 mm, and 70 mm. The cylindrical flanges were formed in four stages with an initial wall angle of 60° to a final angle 90° with an angle increment of 10° in each stage. The maximum and minimum hole expansion ratio was found to be 2.06 and 1.17 respectively. The fracture was observed in a blank of 45 mm pre-cut hole diameter in the third stage at 40 mm depth. The fracture forming limit diagram (FFLD) was determined from incrementally formed varying wall angle conical and pyramidal frustums. Consequently, six different ductile damage models incorporating Hill48 anisotropy plastic theory were successfully calibrated. The Ayyada model showed good agreement with experimental FFLD as compared to all other models. The fracture limit determined experimentally and using the Ayyada model was implemented in the finite element simulation of the IHF process to predict the formability in terms of in-plane strain distribution, forming forces, and thickness distribution. The predicted results matched accurately with the experimental data within a 6% error for all investigated conditions. Noticeably, the strain path in IHF had three deformation modes viz. plane strain, bi-axial stretching, and uni-axial tension, which was comprehended using texture analyses. Finally, irrespective of the initial pre-cut hole diameter, the surface roughness was found to decrease with the number of stages of the IHF process.

增量孔翻边（IHF）是一种相对较新的钣金成形工艺，无需使用专用的冲头和模具即可产生复杂的形状。本工作着重于通过实验研究和有限元方法来理解多级IHF工艺的力学。IHF实验是在具有45 mm，50 mm，60 mm和70 mm预切孔直径的深冲优质钢板上进行的。圆柱形法兰分四个阶段形成，初始壁角为60°，最终壁角为90°，每个阶段的角度增量为10°。发现最大和最小扩孔率分别为2.06和1.17。在第三阶段在深度为40 mm的预切孔直径为45 mm的毛坯中观察到断裂。裂缝形成极限图（FFLD）是由逐渐形成的变化的壁角圆锥形和锥形截头圆锥体确定的。因此，成功地校准了六个采用Hill48各向异性塑性理论的延性损伤模型。与所有其他模型相比，Ayyada模型与实验FFLD表现出良好的一致性。在IHF过程的有限元模拟中，通过实验确定并使用Ayyada模型确定了断裂极限，以根据面内应变分布，成形力和厚度分布预测可成形性。对于所有调查条件，预测结果与实验数据准确匹配，误差在6％以内。值得注意的是，IHF中的应变路径具有三种变形模式。平面应变，双轴拉伸和单轴张力，使用纹理分析可以理解。最后，无论初始切割孔的直径如何，都发现表面粗糙度随着IHF工艺的阶段数而降低。