CBN grinding wheel for HSS(high-speed steel) tools with superhard aluminum-containing has high machining efficiency, good surface quality, no burns, and cracks.
Adding Co, V, Al and other alloying elements to HSS can improve the cutting performance of high-speed steel tools and the wear resistance. But it also reduces the grind ability of the material. When grinding, the grinding force increases and the wear of grinding wheel is intensified, and the heat in the grinding zone is sharply increased, causing the surface burn and roughness reduction. In the past, alumina grinding wheels were used for grinding such high-speed tool steels. With the continuous application of superhard high-speed steel and other difficult-to-machine materials in the tool industry, alumina grinding wheels have not met the processing requirements.
With good thermal stability, strong chemical inertness and good wear resistance, CBN grinding wheel are suitable for superhard aluminum-containing HSS. This paper mainly introduces the performance research of aluminum-containing superhard HSS ground by Cubic boron nitride wheel.
2 CBN grinding wheel for HSS features
According to the grinding experiment we have done, the resin bond CBN wheel has good self-sharpness, small grinding force, low grinding temperature, the good surface quality of the workpiece. Metal bond CBN wheel has a high strength bond, good wear resistance, less wear, and good shape retention. Therefore, under normal processing conditions, the resin bond grinding wheel is used for superhard high-speed steel tool. If there are sufficient coolant and machine tool permission, metal bond CBN wheel is used for a superhard high-speed tool by deep cutting slow feed grinding, which can also achieve better results.
2.2 Grain size
When sharpening with resin bond CBN grinding wheel, 120/140# grain size is usually used, which can meet the surface finish requirements of the tool and high grinding ratio and low abrasive ratio. When forming grinding, 200/230# grain size is used. In addition, when it is required to improve the finish, choose fine grain size appropriately.
When the resin bond CBN wheel is used for sharpening, concentration is 75%, and when grinding the tooth shape, concentration is 100%. When the metal bond CBN wheel is used for sharpening tooth, concentration is 100%-120%.
3 Grinding performance analysis of CBN grinding wheel for HSS
When grinding superhard aluminum-containing high-speed steel with Cubic boron nitride grinding wheel, it needs to obtain good processing quality, high production efficiency and reduces the grinding cost, give full play to the grinding performance of Cubic boron nitride grinding wheel. It is more important to choose the grinding parameters. Now the following experiment for analyzing the study.
3.1 Experimental conditions and requirements
3.1.1 Experimental conditions
The experimental machine tool is MM 6416 tool sharpening grinder:
Experimental grinding wheel
1: CBN 1A1/T2 φ 125×10×32×4,150# 100% B,
2: CBN 1A1/T2 φ 125×10×32×4,150# 100% M; The grinding wheel speed is 2800 rpm; the workpiece is superhard aluminum-containing highspeed steel (W6M0.5Cr4v2Al), HRC is 64-66; the workpiece moving speed Vfis 0.8-5m/min; the grinding depth αP is 0.005-0.06mm.
3.1.2 Experimental requirements
The resin bondCubic boron nitride grinding wheel is dressed with a diamond grinding wheel and is sharpened. The metal bond Cubic boron nitride wheel is EDM dressing. It is cooled with oil when pre-grinding for 10mins during the experiment.
3.2 Experimental analysis
In this experiment, analyze and study the experimental conditions that have an effect on the grinding parameters and grinding performance index of Cubic boron nitride wheel-grinding ratio and grinding powder by the mono factor method.
3.2.1 Effect of the workpiece moving speed on grinding performance
Fig.1 shows that the effect of the workpiece moving speed on the grinding power when the CBN wheel grinds the superhard aluminum-containing HSS workpiece. Fig.2 shows that effect of the workpiece moving speed on the grinding ratio. The experiments show that when the grinding depth is constant, as the workpiece moving speed increases, the grinding powder increases, the grinding ratio decreases, but the grinding ratio and grinding power change little.
3.2.2 Effect of grinding depth on grinding performance
Fig.3 shows that effect of the change of grinding depth on the grinding power. Fig.4 shows that effect of the change of grinding depth on the grinding ratio. It can be seen from the figure that when the workpiece moving speed is constant, as the grinding depth increases, the grinding power increases, and the grinding ratio decreases. It can also be seen from Fig.4 that the grinding ratio is greatly reduced.
It can be seen from Fig.1 to Fig.4 that the strength of the bonding agent of metal bond CBN grinding wheel for HSS is higher than that of resin bond Cubic boron nitride grinding wheel. Compared with resin bond Cubic boron nitride grinding wheel, the grinding power is relatively large, and the grinding ratio is relatively high.
At the same time, it can be seen from the experiment that when Cubic boron nitride grinding wheel is used for superhard aluminum-containing high-speed steel tool, the grinding depth of resin bond grinding wheel is 0.01-0.025mm, the grinding depth of metal bond grinding wheel is 0.01-0.03mm. The thicker the abrasive, the larger the grinding depth is. The moving speed of the workpiece is 1-3m/min.
3.3 Selection of coolant for CBN wheel
It has been found through experiments that resin bond CBN grinding wheel for superhard aluminum-containing high-speed steel is used for dry grinding and with the coolant, the grinding ratio is nearly doubled if adding the coolant under the same conditions. This is because the Cubic boron nitride grinding wheel has high hardness, compact structure, small pores, easy blocking. Therefore, should add coolant with large low as much as possible when the Cubic boron nitride grinding wheel is used.
3.4 Grinding comparison experiment between CBN grinding wheel and alumina grinding wheel
When the tool is sharpened, do the comparative cutting experiment of resin bond CBN wheel and alumina grinding wheel. The alumina grinding wheel is applied 120#, the diameter is 125mm, workpiece moving speed is 2.4m/min, grinding depth is 0.02mm. When drying grinding, the grinding wheel easily blocks, burns the workpiece. The grinding ratio of alumina grinding wheel is about 1mm³/mm³. When wet grinding, no burn, the grinding ratio is about 2 mm³/mm³. Compared with resin bond CBN wheel, the grinding ratio of alumina grinding wheel for superhard high-speed steel is only 1/100 of that of resin bond CBN grinding wheel for HSS.
In the forming grinding, the grinding wheel is dressing by EDM. The outer diameter of the superhard high-speed steel is 110mm. The ring tooth is ground on the workpiece with a tooth depth of 1.75mm. When the tooth profile is not processed before grinding, the grinding wheel speed is 40rpm, the workpiece moving speed is 0.1m/min, the radial feed rate is 0.25mm, and oil is used as the coolant. The grinding is normal and no burn during the grinding process.
The CBN grinding wheel for HSS is dressing again during the whole grinding process. After grinding 40 turns of teeth, the total volume of the workpiece ground out is about 25000m³. It has been found from the universal tool microscope that there is no change of tooth profile from the 1st ring tooth and the 40th ring tooth. The tooth profile error is 0.003mm, and the parallel error between the tooth bottom and the axis is 0.008mm. The wear of the alumina grinding wheel is larger, and the wear amount is 0.25mm.
Compared with the traditional alumina grinding wheel, CBN grinding wheel for HSS tools has good grinding performance and long service life. The grinding ratio is 100 times that of alumina grinding wheel. It has high precision for grinding tooth profile, and the surface finish is improved by 1-2 grade, and the grinding efficiency improves by 10%.