\nTypical hardened mold steels fall into the 48-65 HRC hardness range, but Rockwell numbers are only half of the equation in terms of real-world machinability. D2 tool steel, for example, hardens to about 60-62 HRC, but machines more like 62-65 HRC material due to its 11-13% chromium content. So, when machining multi-constituent alloys, it\u2019s best to apply the recommended machining parameters for hard materials set forth by your cutting tool supplier.<\/p>\n
2. Maintain Constant Chip Load\u00a0<\/strong> 3. Minimize Tool Run Out<\/strong> 4. Reduce Finishing Stock<\/strong> 5. Beat the Heat<\/strong> 6. Apply the Right Tool<\/strong> While high-speed hard milling is a great alternative to lengthy rough milling processes, careful consideration of your entire machining system is critical to successful application. Understanding these 6 factors is a good place to start, but you should also consult with your cutting tool supplier to gain the best possible results.<\/p>\n
\nMaintaining a constant chip load on a tool\u2019s cutting edge is important, otherwise it will wear out prematurely, chip or break. Certain situations, such as machining 3D contours into a mold, make chip load management especially challenging. There are, however, steps you can take to simplify the process, including manually reducing your rpm\/feed rate via override controls, or backing the rpm and feed rate down using the combined efforts of your machine\u2019s CAM program and CNC.<\/p>\n
\nOn average, tool run-out greater than 0.0004″ can cut your tool life in half. Therefore, it\u2019s important to do everything you can to minimize it, especially when working with smaller tools. One way to reduce runout is by using high-precision holders such as shrink-fit, hydraulic, and milling chucks in your operations.<\/p>\n
\nBe sure to remove as much part stock as you can during the roughing process. If you\u2019re working with cutters that are larger than 1\/8″ in diameter, it\u2019s best to leave about 1 percent of the cutter diameter for finishing. Smaller tools, however, determining a sufficient amount of stock for finishing may be a case of \u201cfeel,\u201d or trial and error.<\/p>\n
\nExtreme heat has a significant impact on tool life, especially when processing materials harder than 48 HRC. When working with these materials, it\u2019s better to use an air blast or oil\/air mist instead of coolant to avoid thermal shock.<\/p>\n
\nWhen processing molds with tight tolerances, you want to make sure you have the right cutting tool for the job. Because milling hard materials generates a significant amount of heat, it\u2019s best to use tools with a high thermal-barrier and abrasive resistant coatings such as AlTiN. CBN tools are great for premier finishing applications, while inserted end mills prove highly effective in roughing and some finishing operations.<\/p>\n
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