Allowance Optimization and Error Compensation in Hybrid Additive and Subtractive Manufacturing of Complex Parts

Abstract

Hybrid Additive and Subtractive Manufacturing (HASM) combines directed energy deposition (DED) and milling processes to achieve near-net shaping and high-precision manufacturing. However, it is crucial to assess the machining allowance of DED blanks for efficient subtractive machining, and the precision of the final HASM is determined by the subtractive milling process. This paper proposes a novel approach to effectively connect the additive and subtractive processes with an integration of On-Machine Measurement (OMM) for machining allowance optimization and error compensation, enabling high-precision HASM. The study considers the characteristics of HASM by utilizing DED scanning paths to construct the inspection paths. An adaptive machining allowance optimization method based on middle surfaces is developed to balance registration requirements in different areas and enhance optimization efficiency. Additionally, an improved method utilizing the offset mirror surface is introduced to compensate for both undercut and overcut milling errors. The proposed allowance optimization and error compensation methods are individually validated through simple cases and further applied to a complex impeller blade case. The results demonstrate that the proposed methods for high-precision HASM enable minimal DED envelope measurement, efficient allowance optimization, and precise error compensation for complex freeform parts.

Keywords: hybrid additive and subtractive manufacturing, allowance optimization, error compensation, impeller blades, on-machine measurement