Seamless Die Repair Machining Using Pyramid Spherical Coordinates

Local repair of deformed or worn dies typically involves welding and re-machining using the original numerical control (NC) data. However, this conventional approach often results in repair-machining-mismatch (RMM) marks at the interface between re-machined and unrepaired areas. Even sub-millimeter RMMs can cause visible surface defects on products, requiring additional finishing to fix these imperfections. We propose an RMM-preventive method for die repair machining based on mesh merging with pyramid spherical coordinates (PSC). The original surface is directly reconstructed from NC data to create the source mesh, and the source and target boundaries are specified using coordinate-measuring-machine data from the deformed die. Applying PSC establishes a one-to-one correspondence between boundaries, ensuring the geometric features of the original surface are maintained. Revised NC data are then generated, allowing the re-machined section to join seamlessly with the deformed die surface. Experimental validation on a 500 × 500 mm die with intentional deformation demonstrated that the proposed method reduced boundary RMMs by over 94%, with residual deviations of less than 0.03 mm. These results demonstrate that the approach offers a practical and effective solution for RMM-free die repair machining, eliminating the need for a nominal CAD model, and can also be extended to other types of dies and industrial parts.