Striving for Consistency (continued) a bore has uneven stock distribution. “Our process is robust when faced with in-process variations such as core shift,” Stead said. Because the centerline in a cast bore can shift depending on the bore’s accuracy, Jim Porter, application engineering supervisor for toolmaker Allied Machine & Engineering Corp., Dover, Ohio, said it is usually more cost effective to drill from solid with an included angle drill. “If the hole isn’t precisely located where you want that centerline to be, the tool is going to want to follow the hole’s existing centerline,” he said. “Our preference is to drill from solid.” Porter added that the downside of drilling from solid is that a ductile iron workpiece cast without cored holes costs more because it contains more material. However, more operations are required to straighten cored holes. “It’s a catch22 situation,” he said. The included angle varies for tools that are appropriate for drilling ductile iron. Traditional twist drills have a 118° included angle, for Allied Machine’s T-A spade drills it’s 132°, and the company’s GEN3SYS replaceable-tip drills have a 140° included angle. “It’s more product dependent than anything,” Porter said. The geometry is also important for the cutting edge when drilling ductile iron. A more neutral geometry is more appropriate for the relatively abrasive material, according to Bob Jennings, product manager for Ingersoll Cutting Tools, Rockford, Ill. “[It should be] more toward the negative side than the positive side but almost neutral,” he said, adding that a hone or other edge prep is required. To prevent a drill’s corners from breaking when machining the abrasive ductile material, Guhring introduced the RT 100 R Ratio solid-carbide drill with a patented full radius point grind. Starting-point speed and feed recommendations for drilling ductile cast iron. Feed: ipr or mm/rev. Nominal hole diameter Hardness HB 140 to 190 Speed 1⁄16" fpm m/min. 1.5mm 851 1152 261 352 0.001 --0.025 --⁄" 3mm 18 Ductile cast irons Ferritic ASTM A536: grades 60-40-181 and 65-45-122 SAE J434c: grades D40181 and D45122 Ferritic-pearlitic ASTM A536: grade 80-55-06 SAE J434c: grade D5506 Condition Annealed ¼" 6mm 0.006 0.15 ½" ¾" 1" 12mm 18mm 25mm 0.010 0.25 0.013 0.33 0.016 0.40 1½" 35mm 0.021 0.055 2" 50mm 0.025 0.065 Tool material grade AISI or C ISO M-10, M-7, M-1 S-2, S-3 0.003 0.075 190 to 225 As cast 70 21 0.001 0.025 0.003 0.075 0.006 0.15 0.010 0.25 0.013 0.33 0.016 0.40 0.021 0.055 0.025 0.065 M-10, M-7, M-1 S-2, S-3 " " 225 to 260 240 to 300 As cast 50 15 45 14 0.001 0.025 0.001 0.025 0.002 0.050 0.002 0.050 0.004 0.102 0.004 0.102 0.007 0.18 0.007 0.18 0.010 0.25 0.008 0.20 0.012 0.30 0.010 0.25 0.015 0.40 0.013 0.33 0.017 0.45 0.015 0.40 T-15, M-42* S-9, S-11* T-15, M-42* S-9, S-11* Pearlitic-martensitic ASTM A536: grade 100-70-03 SAE J434c: grade D7003 Martensitic ASTM A536: grade 120-90-02 SAE J434c: grade DQ&T Normalized and tempered 270 to 330 Quenched and tempered 30 9 ----- 0.001 0.025 0.002 0.050 0.004 0.102 0.005 0.13 0.006 0.15 0.007 0.18 0.008 0.20 T-15, M-42* S-9, S-11 " " 330 to 400 120 to 200 Quenched and tempered Annealed 20 6 35 11 ----0.001 0.025 0.001 0.025 0.002 0.050 0.002 0.050 0.005 0.13 0.004 0.102 0.007 0.18 0.005 0.13 0.010 0.25 0.006 0.15 0.012 0.30 0.007 0.18 0.015 0.40 0.009 0.20 0.018 0.45 T-15, M-42* S-9, S-11* T-15, M-42* S-9, S-11* Austenitic (Ni-resist) ASTM A439: types D-2, D-2C, D-3A, D-5 ASTM A571: type D-2M Austenitic (Ni-resist ductile) ASTM A439: types D-2B, D-3, D-4, D-5B 140 to 275 Annealed 25 8 0.001 0.025 0.002 0.050 0.005 0.13 0.007 0.18 0.010 0.25 0.012 0.30 0.015 0.40 0.018 0.45 T-15, M-42* S-9, S-11* * Reference Source: “Ductile Iron Data for Design Engineers”
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