To stay competitive in today’s global economy, mold manufacturers must continue to produce high-quality products in extremely short time cycles. To achieve this goal, advanced manufacturing process technologies and cutting tool materials must be developed to keep mold shops in a competitive position. Hard milling, as one of these advanced manufacturing technologies, has been continuously developing.
In the past few years, mold manufacturers failed to truly adopt hard milling due to the limitations of machine tools and cutting tools at the time. However, today, most modern machining centers equipped with high-rigidity, high-speed spindle systems and advanced processors are handy for cutting hard materials. At the same time, advanced CAM software packages have specific machining cycles for hard milling and tool path functions designed to optimize tool life.
Selection of Hard Milling Cutting Tools
Mold shops typically use three types of milling tools: solid carbide end mills, indexable carbide inserts, and the more recent development of indexable ceramic inserts. Each of these tools has its own advantages and disadvantages in different machining applications.
Solid carbide end mills are usually precision ground and coated, which is quite expensive. When the tool becomes dull, it must be reground and recoated. However, the cutting performance of a reconditioned end mill is often not as good as that of a new tool.
The second type of hard milling tool is equipped with indexable carbide inserts. In most cases, the carbide grade and insert geometry parameters of this type of insert are not designed for hard milling operations, so they do not provide optimal tool life and productivity when machining hardened materials.
The third type of hard milling tool uses indexable ceramic inserts, especially whisker-reinforced ceramic inserts. Using a tooling system equipped with indexable ceramic inserts can provide many benefits, including faster machining cycles and fewer machining operations per workpiece. However, using this tooling system requires both programmers and operators to rethink the machining process and pay attention to details that may not be considered when using other tools.
Using a complete range of hard milling tools with whisker-reinforced ceramic inserts (including indexable inserts for milling surfaces, cavities and contours), mold and die shops can rough hardened blanks into a part and finish it in a single setup. Ceramic-inlaid milling cutters (from large face mills to small-diameter end mills with indexable ceramic inserts) enable safe high-speed milling. When using ceramic-inlaid milling cutters designed for hard milling at high speeds, it is important to ensure that the inserts are clamped securely.
High-speed milling cutters are developed based on the safety and reproducibility of ceramic inserts at milling speeds. The melting point of the whisker-reinforced ceramics currently used is over 2000°C, which means that ceramic inserts can be machined at cutting speeds far above the failure point of carbide inserts. In fact, whisker-reinforced ceramic inserts can operate normally at temperatures above the melting point of carbide inserts. Coolant is not recommended for hard milling with ceramic inserts, but air cooling is recommended, especially in cavity milling, to avoid secondary cutting of chips. Reducing the use of coolant and waste liquid disposal costs is also an additional benefit of using ceramic inserts in hard milling.
Reduce Machining Costs with Ceramic Inserts
Hard milling with ceramic inserts can help mold shops reduce production costs in a variety of ways. First, it can replace multiple processes with one process. When using ceramic inserts for hard milling, the steel can be hardened first, and then the workpiece can be milled in the hardened state, thus replacing the three processes of machining, quenching, and remachining in the past. By reducing the time to set up and move the workpiece at different stages of processing, the processing cycle can be shortened and the operation path can be improved. In addition, rough milling hardened workpieces with ceramic inserts can avoid expensive and time-consuming EDM (electric discharge machine) processing, without the need to make one or more electrodes.
