Study on a New Method for Forming Integral Curved-Hole Structures by Combining Drilling and Plastic Deformation

Structures with curved-holes are of great value for industrial application, but how to realize the formation of integral curved hole is still a huge challenge. In the current study, a novel methodology, called Bulk Forming of Curved Hole (BFCH), was proposed to obtain integral structures with curved holes by combining traditional drilling and plastic forming processes. An analytic formula of cross-section distortion in BFCH was derived based on the upper bound method. The formula shows the influence of three factors, including the bending angle theta, billet thickness-to-hole diameter ratio h/d, and material properties index null (k) related to material strength, on the wall collapse of the curved hole formed. Moreover, three types of curved holes were designed to verify the concept, and the results of experiments and finite element simulation using Al6061 specimens proved that the method is feasible to form integral structures with inside curved-holes. The oval-shaped distortion of the hole cross-sections is the main defect, which increases with the bending angle theta, as well as the value of h/d and null (k). In addition, proper initial temperature difference inside the billet can decrease the distortion of the formed holes.

Automated summary

Structures with curved holes are highly valuable in industrial applications, but achieving the formation of integral curved holes remains a significant challenge. In this study, a novel methodology called Bulk Forming of Curved Hole (BFCH) was proposed to obtain integral structures with curved holes by combining traditional drilling and plastic forming processes. An analytical formula for cross-section distortion in BFCH was derived, taking into account the bending angle, billet thickness-to-hole diameter ratio, and material properties index. Experimental and simulation results confirmed the feasibility of the BFCH method, although oval-shaped distortion in the hole cross-sections was observed as the main defect. Appropriate initial temperature differences inside the billet can mitigate this distortion.