When cutting hardened steel with end mills, the increase in cutting depth and feed per tooth will cause a significant increase in cutting resistance. Therefore, high speed is used at a small depth of cut without increasing the feed per tooth. Milling this efficient method is very effective. However, as the hardness of the workpiece to be machined increases, the heat of cutting increases, causing the cutting edge of the tool to be at a high temperature. Thus, the wear of the tool will be aggravated due to diffusion and oxidation. Therefore, the tool for high-speed milling of hardened steel is very important at high temperatures.
This article describes cutting examples of hardened steel. The hardened steel is cut using a hard alloy end mill coated with a heat-resistant film layer, which has good oxidation resistance and wear resistance at high temperatures. In addition, the CBN end mills, which are eye-catching in the field of high-speed machining, are also used.
Heat-resistant coating end mill processing example
In order to achieve high-speed milling of hardened steel, in addition to the high bonding strength between the coating and the tool, it is also necessary to improve its hardness, heat resistance and oxidation resistance.
The oxidation start temperature of the heat-resistant coating (WX super-coating) that OSG is developing and putting into use has been greatly increased from the past 800 ° C to 1300 ° C. Even at high temperatures achieved by high-speed cutting of hardened steel, the increase in oxidation temperature can effectively prevent coating damage, thereby preventing deterioration of the wear condition of the cemented carbide substrate due to oxidation and diffusion. Moreover, the hardness of this coating is also improved compared to past coatings, which prevents the abrasive wear of the coating itself.
The following describes the super heat-resistant coated end mill series and its processing examples. SKD11 (62HRC) workpiece is machined with WX special ball end mill (WXS-EBD) (machining conditions: tool used: WXS-EBD
R1×4; workpiece material: SKD11 (62HRC); rotation speed: 32000r/min; feed rate: 2800mm/min (0.038mm/tooth); cutting method: machining cavity; cutting depth: αa=0.04mm, Pf=0.05 Mm; cooling method: air cooling; processing machine: vertical machining center (HSK-E32)). It can be seen from the processing results that the WXS-EBD wears more slowly than the previous coating, and the R shape of the ball end mill can be maintained for a long time.
Example of side milling of SKD11 (60HRC) with WX super heat-resistant square head multi-edge end mill (machining conditions: tool: WXS-EMSФ10; workpiece material: SKD11 (62HRC); cutting speed: 150m/min (4800) /min); Feeding speed: 860mm/min (0.03mm/tooth); Cutting method: side cutting, undercutting; cutting depth: αa=10mm, αr=0.5mm; cooling method: air cooling; processing machine: vertical Machining Center (BT40)). Despite the high cutting speed of 150m/min, tool wear is still relatively stable, showing the effect of a heat-resistant coating.
The development of the new coating (WX Super Coating) greatly improves the performance of carbide-hardened end mills for hardened steel.
CBN end mill processing example
Cubic boron nitride (CBN) is second only to diamond in hardness and thermal conductivity, has minimal reaction with ferrous materials, and has superior thermal and chemical stability than diamond. Therefore, it can be used to process iron group metals in which diamond is difficult to process.
CBN is not a natural material, but is synthesized under the same conditions as polycrystalline diamond under high temperature and high pressure conditions. However, the type of binder and CBN concentration used in the synthesis can greatly affect the mechanical and heat resistance characteristics of CBN.
When the CBN tool was first introduced, it was mainly made of processed cast iron, and its use has gradually become popular. Recently, due to the miniaturization of CBN particles and the improvement of binders, especially the improvement of the shape of the tool, it has shown good effects even for the cutting of ordinary carbon steel and hardened steel. The following is an example of machining a CBN end mill for hardened steel.
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