In the mid-1990s, high-speed milling technology began to be integrated into mold manufacturing, especially in the context of hard machining. This marked a significant technological shift in the industry. High-speed hard milling allows for the complete processing of molds under a single clamping setup, significantly reducing processing time, improving surface quality and accuracy, and streamlining the production process. As a result, it helps shorten the overall mold manufacturing cycle and lowers production costs. One of the key advantages of high-speed hard milling is that it often eliminates the need for electrode making, EDM (Electrical Discharge Machining), and polishing. By the late 1990s, this technique had already replaced EDM in many applications, except for narrow slots, deep grooves, and very small internal corners. In recent years, with the development of fine milling cutters—some as small as 0.03mm to 0.1mm—and the application of micro-milling processes, even these challenging areas can now be machined effectively using small-diameter end mills. This has further reduced the reliance on EDM. According to a study conducted by the Fraunhofer Institute of Production Technology in Germany in 2004, the share of high-speed hard milling in tooling and mold manufacturing was expected to increase by 20% over the next few years, while EDM would decline by 12%. This trend highlights the growing popularity of high-speed hard milling in the mold industry, establishing it as a key process in modern mold production. Despite its benefits, the successful implementation of high-speed hard milling requires certain conditions. Companies must have skilled personnel who understand the technology, along with appropriate high-speed machining equipment, suitable tool holders, and tools designed for hard milling. The selection of cutting parameters, cooling methods, and NC programming all play critical roles in determining efficiency, quality, and cost. Some manufacturers still lack practical experience in high-speed hard milling. For example, some companies may invest in five-axis machines without the necessary expertise or training. Collaboration with machine tool manufacturers, tool suppliers, and research institutions is essential. Conducting process tests is also crucial for optimizing production. A case in point is a Chinese toy factory’s injection mold processed on a German Hermle C800V vertical machining center. Using nine different types of end mills and ball end mills, the company achieved a processing time of 125 minutes. However, after milling, EDM was still required for the cavity bottom. Through a Sino-German research project, testing at the Darmstadt Institute of Technology showed that the number of tools could be reduced from 9 to 6, saving 30% in auxiliary time and reducing processing time by 26%. High-speed machining centers must meet strict requirements: high spindle speed, power, rigidity, dynamic performance, and damping. Current models typically operate between 40,000 to 42,000 rpm, which is sufficient for small-diameter cutters (2–12 mm). However, for smaller tools (0.2–1 mm), higher speeds are needed. For instance, a 1 mm cutter needs 51,000 rpm for a cutting speed of 160 m/min, while a 0.2 mm cutter requires up to 250,000 rpm. Most current machines cannot reach these speeds, limiting the effectiveness of ultra-fine cutting. Future developments will likely focus on even faster machines. Mold manufacturing also demands advanced tooling. Solid carbide end mills with fine-grain or ultra-fine-grain structures, coated with TiAlN or TiAlCN, offer excellent wear resistance. These tools can achieve cutting speeds of 200–350 m/min in hard milling, with feed rates of 0.1–0.2 mm per tooth. Proper tool holders, such as HSK shrink-fit systems, are essential to minimize runout errors and improve stability during high-speed operations. Cooling during high-speed hard milling is generally avoided due to thermal shock risks. Instead, dry machining or cold compressed air is used to remove chips and reduce tool wear. Compressed air at 6 bar or colder can extend tool life by 20–30%, especially for high-hardness materials. Special vortex tubes can generate cold air as low as -30°C, enhancing both chip removal and tool durability. To maximize the benefits of high-speed hard milling, several principles should be followed: keep the tool overhang as short as possible, use climb milling for better tool life and surface finish, minimize tool runout, avoid wet machining, choose optimal cutting parameters, and eliminate unnecessary intermediate steps like semi-finishing. These practices ensure efficient, high-quality mold production.

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