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Cutting Tools tips for Successful Hard milling of Complex molds By Charles Colonair Today's moldmakers are seeking reduced leadtimes while producing highly accurate molds. When mold and die applications demand hard milling of materials up to 66 HRC, using the right end mills, cutting parameters and machining methods is critical for success. Hard milling is challenging due to several factors, including the requirement of machining hardened steels with defined cutting edges. Milling these materials requires high-speed machining centers that are set up for hard milling, along with CAD/CAM that has been programmed accordingly. Using the latest solid carbide end mills along with proper toolholding, workholding, feeds, speeds and cooling, mold manufacturers can reliably and economically produce complex molds. Complicated contours can be accurately machined, and time-consuming grinding or polishing rework may be omitted entirely, or at least partially. Choose end mills that meet the following requirements: solid carbide substrate with a high hot hardness and toughness; coating and cutting geometry matched to the material hardness; and tool concentricity not exceeding 5 microns nical data recommendations for specific applications. When hard milling, dry machining is preferable in order to avoid thermal cracks in the cutting tool. For example, when using multi-flute end mills, cold air provides an effective cooling of the tool's cutting edges, resulting in efficient chip material removal. Cooled air reduces temperatures in the cutting area, which in turn permits higher cutting speeds and up to 30 percent longer tool life. This type of cooling enables modern TiALN coatings to achieve their full potential, avoiding damage to the cutting edge from thermal shock. In addition, the cold-air nozzle helps to remove the tiny chips produced in copy milling, including from deep recesses or cavities in the mold. Proper clamping of the tool and workpiece are also important for successful hard milling—including high rigidity and good vibration damping of the machine tool and the workholding devices and high concentricity of the toolholder for high surface finish quality and consistent tool life. Hard milling with solid carbide end mills is an established and reliable way to manufacture molds with hardness of up to 66 HRC. Secondary and grinding operations can be omitted for increased productivity and enormous cost savings. Hard milling application example Operation Roughing Pre-fnishing Pre-fnishing Pre-fnishing Finishing Tool Type Ball nose D10 Ball nose D6 Ball nose D4 Ball nose D3 Ball nose D2 EDP-NR. 1976A.010 1976A.006 2806A.005 2806A.003 2806A.002 Speed (SFM) 260 260 260 260 260 fpt (inch) 0.003 0.002 0.002 0.001 0.001 (meeting this requirement will extend tool life and promote excellent surface finish quality). Determining the optimal cutting parameters and methods will yield the best results for hard milling of molds. Select a speed and feedrate that is recommended for the type of workpiece and material hardness, as well as the engagement conditions of the tool. Consult your end mills partner for tech- 76 MoldMaking Technology July 2013 Machine: Hermle C40 Material: CPM 3V (PM-steel), 61 HRC Control: Heidenhain Coolant: Cold Air DOC (inch) 0.020 0.006 0.004 0.002 0.001 WOC (inch) 0.010 0.008 0.004 0.002 0.001 Tool life (min) 20 45 50 60 150 Result: Forging die completely fnished on a 5-axis machining center with excellent form and position tolerances. Time savings: soft machining, EDM and polishing were omitted. ContriButor Charles Colonair is Milling Project Manager at Emuge Corp. For more inFormation: Emuge Corp. / emuge.com / (505) 595-3600 Images by Emuge Corp. This forging die application example was done with just one hard milling operation during the material hardened stage using Emuge hard-cut end mills, eliminating multiple steps such as soft machining, pre-fnishing, fnishing and polishing. Hard milling provides the ability to optimize the process chain, and the successful set-up of the forging die example can easily be transferred to many other applications.