High-Speed Cutting of Hardened (60HRC) Die Mold Kunio Naito, Kazutaka Ogo, Yasuhisa Takada, Kazuki Watanabe, Kenji Wada 40HRC60HRC 60HRC CBN Hardened die mold steels have been conventionally As a result of the endurance test, the life of the ball made by electric discharge machining. Cutting these end mill was found to be shorter at the cutting plane hardened steels would have large effects, allowing due to its chipping. The damaged cutting edge was speeder delivery and lower production cost of die then analyzed by EPMA, which revealed that the steels molds. In this study, therefore, a ball end mill has been of the workpiece adhered to the cutting edge. developed and conditions for cutting hardened steels For the prevention of the failure, the cutting zone have been investigated. was lubricated with the mist oil which gave a little First, the change in cutting condition and the thermal shock to the cutting edge. Spraying the mist damage to cutting edges have been examined by of the high lubricant lengthened the life of the cutting cutting the die mold steels, which have been hardened tool. from 40 HRC to 60 HRC. Under the condition of the high cutting speed, the Next, the tough sintered CBN was selected for a roughness and the change in hardness were smaller cutting tool material, and a ball end mill was produced than those of the discharge-machined surface, thus by the way of trial. This tool produced had removed producing the higher quality finished surface. end on the rotation axis and cutting edges strengthened by chamfering.
NC (TiAl) N (50HRC) 60HRC 60HRC 510 4 min 1 (TiAl) N 40HRC 60HRC2 2 CBNCBN (1310 6 m) (4060%) 3 CBN CBN Experimental conditions. Machine High-speed machining center (5 10 4 min 1 ) Tool CBN, (Ti, Al)N coated carbides φ 10 10 3 m, 2 flutes ball end mill Work materials SKD11 (5560HRC), SKD61 (4050HRC) Cutting method Plane cutting, Inclined-plane (80degrees) cutting Up cut, Down cut Lubrication Dry cutting, Mist lubrication cutting (Emulsion W1, Oil) 0.11.5 10 6 m 3 /min, Air 30 10 3 m 3 /min Spindle speed 0.12.0, 3.54.5 10 4 min 1 Tool feed rate 0.0670.1350.3 10 3 m/tooth Pick feed 0.3 10 3 m Depth of cut 0.3 10 3 m Under line : Normal condition
EPMA 0.1m 2 55HRC60HRC CBN CBN 400m/min CBN110 6 mcbn (TiN) 4050% 2 θ102540 25 CBN 0.1m 2 Relationship between hardness of work and cutting force. Tool wear condition after 0.0015m 2 cutting hardened SKD11 (60HRC) and shape of developed CBN ball end mill.
2 10 4 min 1 3.510 4 min 1 0.13510 3 m/ 30 1200m/min0.023m 2 (50 150m/min) Fig. 5 EPMA FeCr CBN Relation between tool feed rate and cutting area until tool life at plane cutting. Toll wear after cutting 0.1 m 2 at the inclinedplane cutting. Tool fracture at plane cutting.
CBN 50% Mount of the mist-lubricant equipment on the machine. 2 ( ) 110 6 m 3 /min 0.1m 2 0.07m 2 0.110 3 m CBN Cutting area until tool life. Lubrication and cutting fluids Spraying rate (10 6 m 3 /min) Cutting area (10 4 m 2 ) Emulsion (Conc. 50%) 0.2 80 Active oil 0.1 197 0.2 667 0.1 510 Heavy active oil 0.5 972 1.0 1248 2.4 720 Conventional dry cutting 50891 Conventional wet cutting Emulsion ( Conc. 5%) 40 10 3 m 3 /min 12 Mist lubrication cutting
40 ミスト潤滑により寿命延長効果の認められた工 剤中の極圧添加剤のCl Sおよび油脂の主成分で 具の摩耗面をFeとCrについてEPMA分析した結果 あるCについて調べた その結果がFig. 8で 油 を乾式切削と比較してFig. 7に示す 図から ミ 剤の成分はいずれもFeの分布と重畳する形で認め スト潤滑ではCrがほとんど認められない また られ 図中に示したような低融点 低せん断応力 Feは摩耗端部の切りくずが離脱する箇所で認めら の潤滑物質９ を生成していたと考えられる れ 摩耗面全体に分布している乾式切削とは異な 3 4 切削面の粗さ 硬さ 残留応力 っていた このため ミスト潤滑切削におけるFe 工具回転数2 10 min で傾斜面を高速切削した がどのような状態になっているか Fig. 7中の 切削面を放電加工面と比較した結果をTable 3に で囲んだ部分を拡大分析して調べた 分析は 油 示す 放電加工条件は 直径0.25 10 mの黄銅 Fig. 7 1 Fe and Cr adhesion on the wear of rake face after cutting. Fig. 8 豊田中央研究所 R&D レビュー 4 Lubricating elements on the wear face of mist cutting. Vol. 34 No. 4 ( 1999. 12 ) 3
58V3.5A 0.910 3 m/s3510 3 m 28 34 10 6 mrz 14 1810 6 mrz 910 6 mrz1/2 2010 6 m 51010 6 m 2010 6 m 800MPa 600MPa 160HRC CBN 2 3 4 1) JACT NEWS(1997.11.20)29 2) 1997 107 3) 97 (1997)9 4) 6(1998)808 5) 2(1987)227 6) 4(1993)649 7) (1977)34 8) (C)415(1981)390 9) (1966), 47, Quality of finished surface. Properties Cutting E.D.M. Roughness (10 6 mrz) 34 1418 Hardness (mhv) Unchanged Softning 200Hv at 20 10 6 m depth Surface Good Crack Residual stress (MPa) 800 +600