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Software 16 MoldMaking Technology —— MAY 2017 By Karl Guthrie Images courtesy of CGS North America Inc. S tep-up rough cutting is a new roughing strategy designed to maximize metal removal rates by using the side flutes of an end mill to rough out steel. It uses large axial depths of cut and small radial depths of cut, as opposed to the small depths of cut and high feed rates of traditional high-speed roughing strategies. The tool path created by this new roughing strategy con- stantly engages the length of the cutting flutes and steps down to the maximum recommended depth of cut. The key to this roughing strategy is ensuring that the tool is not overloaded. This can be costly with this type of tool path, since the tools are engaged in large depths of cut, causing a tool to break more quickly. Although many CAD/CAM software companies use large depths of cut, step-up rough cutting is different, because it uses a smaller step-up amount to get closer to the net shape. Formula for Reducing Roughing Cycle Times To take advantage of step-up roughing to achieve the highest possible metal removal rates, you need to consider the cutting tool, machine and CAD/CAM software. They work together to reduce roughing cycle times. Using aggressive machining strat- egies with improved cutting tool designs and coatings makes higher feed rates possible on high-speed machines, which helps achieve higher metal removal rates in many different types of materials. This new roughing strategy is particularly successful in hardened steels. To extend tool life and make more accurate cuts throughout the roughing cycle, apply a layer of coating to the cutter flutes. Cutting tool coatings are designed to keep the shape of the cutting edge longer, which minimizes friction and keeps the Stepping Up to the Challenge A new roughing strategy helps maximize metal removal rates and reduce roughing cycle times. This screenshot shows the first Z-level pass for step-up rough cutting. It starts from the outside of the work material and works its way in. temperatures more constant. Common coatings include tita- nium carbo-nitride (TiCN), diamond, chromium nitride (CrN), titanium aluminum nitride (TiAlN or AlTiN) and titanium carbo-nitride (TiCN). Cutting tool designs also impact metal removal rates, so it is important to stay on top of the constantly evolving tool designs that each require specific strategies. This is where the right CAD/CAM software comes into play to ease the use of new machining strategies like step-up roughing. Use a surface-based CAD/CAM to maintain an even ste- pover and maximum tool engagement throughout the whole tool path. By having the ability to limit the tool's engagement, a much safer and more consistent tool path will result. This allows you to move faster and more freely through open areas and to keep the tool path controlled in slotted areas and corners. When machining parts that force the tool into tight cor- ners or slotted areas, the software will recognize this and then apply a fillet arc, or trochoidal movement, to ensure