I. New Demands in Manufacturing
With the surging demand for complex and high-performance parts in high-end equipment, traditional single manufacturing methods are facing bottlenecks in terms of precision, efficiency, and design freedom. Additive-subtractive hybrid manufacturing, on the one hand, possesses the significant advantages of additive technologies (such as laser cladding) in forming complex structures, material utilization, and design freedom. On the other hand, it deeply integrates subtractive technologies (such as five-axis machining) known for their precision control and surface quality, solving core issues such as surface quality, dimensional accuracy, and internal defects in the manufacturing of high-quality core components. By synergistically applying both technologies in the same process, additive-subtractive hybrid manufacturing achieves a complementary effect of "form by additive, precision by subtractive", effectively overcoming the limitations of single technologies. This technology provides an efficient and high-quality integrated solution for the manufacturing of complex and high-performance parts in fields such as aerospace and precision molds, demonstrating huge application potential and broad prospects.

II. Principles and Technologies of Additive-Subtractive Hybrid Manufacturing
The forming principle of additive-subtractive hybrid manufacturing is based on the "discrete-pile-control" theory. By using the three-dimensional model generated by computer-aided design, the model is sliced layer by layer and numerical control codes are generated to achieve precise processing of three-dimensional solid parts. This integrated processing method reduces errors caused by multi-platform processing, improving manufacturing accuracy and efficiency. A typical hybrid processing system usually includes a CNC machining center, an additive manufacturing module, a feeding system, a software control system, and auxiliary facilities.
Various integration methods such as direct energy deposition (DED) and ultrasonic additive manufacturing (UAM) are adopted to enhance processing performance and simplify the process flow. Among them, direct energy deposition technology generates a molten pool through a laser and deposits the required shape, often regarded as a welding-based process. Ultrasonic additive manufacturing combines ultrasonic welding with CNC machining, featuring advantages such as no spatter and oxidation. Additionally, powder bed fusion technology lays powder materials layer by layer on a substrate and processes them with a laser or electron beam, precisely controlling the oxygen content during the process. The OXY-GC-168 oxygen analyzer from Shanghai Gaochuan Company is used to ensure the process flow and manufacture complex mold structures.
In additive-subtractive processing technology, improving production efficiency requires optimizing hardware integration and control system design to achieve flexible switching and feedback control between additive and subtractive processes. The control system needs to precisely control both processing methods and flexibly switch between them during processing. At the same time, real-time feedback on dimensional changes caused by additive processing forms a closed-loop control system to ensure processing accuracy.

III. Trends and Applications of Additive-Subtractive Hybrid Manufacturing
Additive-subtractive hybrid manufacturing shows significant advantages in the production of complex shapes, multiple varieties, and small batches of parts, driving the transformation of manufacturing to the next generation. This technology combines the dual advantages of additive manufacturing and traditional subtractive processing, enabling the production of high-precision and high-quality complex-shaped parts, shortening the manufacturing cycle, saving materials, and reducing costs. It is particularly suitable for the production of small batches of complex-shaped parts. However, due to its nascent stage and multidisciplinary nature, future development requires collaborative efforts across various disciplines.
Additive-subtractive hybrid manufacturing technology holds significant importance in high-value and high-precision military and aerospace fields and is one of the future directions for China's manufacturing industry. By breaking through traditional manufacturing methods, this technology offers new possibilities for these fields and has attracted increasing attention from researchers. With technological development, it will become an important force for China's manufacturing industry to transform from large to strong.