**1 Introduction**
Molds are complex and non-standardized products that require a series of intricate processes, including creative design, CNC programming, production preparation, machining, assembly, and trial runs. These steps make the manufacturing cycle long, especially when it comes to machining, which is time-consuming. As a result, mold manufacturers have always faced challenges in improving production efficiency, shortening development cycles, enhancing the level of mold manufacturing, and reducing costs.
Whether it's a stamping die or a forging die, the materials used for the cavity are typically high-strength and wear-resistant, such as various alloy tool steels and stainless steels. After heat treatment, these materials often reach hardness levels above 50HRC, making them difficult to machine using conventional methods.
For many years, Electrical Discharge Machining (EDM) has been the primary method for processing such hard materials. However, EDM has two major drawbacks: low productivity and difficulty in maintaining consistent quality.
The emergence of high-speed cutting technology has introduced a new approach to mold manufacturing. Compared to EDM, high-speed machining offers higher productivity, better surface quality, and the ability to process hard and complex parts. Since the 1990s, many foreign mold industries have started using high-speed cutting for finishing mold cavities.
According to recent data, over 85% of molds in industrialized countries now use high-speed cutting processes. This technique has become the mainstream in international mold manufacturing. China also began researching and applying high-speed cutting technology in the 1990s. The key technologies involved in high-speed cutting include tool technology and machine tool technology. This article focuses on the related technologies of high-speed milling tools used for hardened molds.
**2 Advantages of High-Speed Milling Hardened Molds**
High-speed milling is one of the most commonly used techniques in high-speed machining. Replacing EDM with high-speed milling offers several advantages.
(1) **Superior Processing Quality**
Traditional EDM can damage the physical and mechanical properties of the workpiece surface due to high-temperature discharge. This often leads to micro-cracks and makes it hard to guarantee the final quality. In contrast, high-speed milling operates at speeds about ten times faster than conventional milling, allowing chips to be removed before significant deformation occurs. This results in minimal residual stress and excellent surface quality. After high-speed milling, the surface finish can even reach grinding levels, eliminating the need for additional polishing.
(2) **Higher Production Efficiency**
EDM relies on "micro-cutting" through discharge, which is very slow. Additionally, after EDM, hand-grinding is often required, making the process inefficient. High-speed milling, on the other hand, is significantly faster. It allows roughing and finishing to be done in a single setup, known as "one-pass machining." Furthermore, no electrodes are needed, and the process is easier to automate, greatly speeding up mold development.
(3) **Ability to Machine Complex and Hard Parts**
High-speed milling reduces cutting forces and simplifies the machining process. It can cut hardened steel with hardness over 60HRC without coolants, known as "hard machining" and "dry machining." It’s also ideal for thin-walled and complex structures, like fine ribs and walls less than 1mm thick. However, for deep and narrow cavities, high-speed milling may not be optimal, and combining it with EDM can yield better economic results.
**3 Cutting Tool Technology for High-Speed Milling Hardened Dies**
Tool technology is crucial in high-speed milling, involving material selection, geometry parameters, tool damage detection, and connection systems.
3.1 **Material and Geometry Selection**
High-speed cutting tools must have low chemical affinity, good thermal stability, impact resistance, and wear resistance. Common materials include PCBN, ceramics, and coated carbides. Each material is suitable for different hardness ranges. For example, PCBN is best for materials harder than 55–65HRC, while ceramics are better for softer materials (≤50HRC).
Geometry parameters, such as rake and relief angles, also play a significant role in tool life and performance. Proper selection ensures better cutting efficiency and longer tool life.
3.2 **Tool Damage and Detection**
Tool damage, such as wear, chipping, and fracture, can reduce tool life and increase costs. Detection methods include manual checks, off-line analysis, and real-time monitoring. Early detection helps prevent failures and improves productivity.
3.3 **Tool-Machine Connection Technology**
High-speed cutting requires rigid and balanced connections between the tool and machine. Traditional tool holders are inadequate, so new types like HSK, KM, and BIG-PLUS have been developed. These provide better accuracy, rigidity, and balance, essential for high-speed operations.
3.4 **Tool Safety**
High-speed milling demands strict safety measures. Centrifugal forces at high speeds can cause tool deformation or breakage, leading to serious consequences. Safety standards, such as DIN 6589-1, specify testing and inspection procedures to ensure safe operation.
**4 Conclusion**
By analyzing tool materials, geometry, damage detection, connection technology, and safety requirements, this article highlights the critical factors in high-speed milling for hardened molds. Addressing these issues will not only solve current challenges but also promote the widespread adoption of high-speed cutting technology in mold manufacturing.
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