At present, driven by the rapid development of the automotive industry, automotive mold companies are facing dual pressures to reduce costs and shorten delivery cycles. In order to improve processing efficiency, a large number of high spindle speed machining centers are widely used in actual production, so the originally used coated carbide end mills can no longer meet the processing requirements. In order to extend the service life of the mold, the surface hardness of the mold is getting higher and higher, and the processing of the high-hardness mold surface has become the focus of everyone's attention. Under this situation, the launch of Sumitomo Electric's BNBP type CBN end mill provides us with an effective solution.

Characteristics of BNBP type end mill

Compared with superhard tools and high-speed steel tools, CBN tools have the characteristics of high hardness and high thermal conductivity, and are very suitable for cutting quenched steel materials. However, the toughness of CBN cutting tools is not good, and the cutting edge of CBN end mills is easy to break during intermittent cutting.

In order to overcome this technical problem, Sumitomo Electric's BNBP end mill adopts a new CBN material used for intermittent cutting of quenched steel, which greatly improves the fracture resistance. In addition, combined with the blade shape of a large negative rake angle, the strength of the blade Significantly enhanced. Although the wedge angle shape of the blade is increased, the sharpness of the blade is reduced, thereby increasing the cutting resistance of the blade during low-speed machining. However, the BNBP type CBN end mill can perform milling like precision grinding under high-speed machining conditions, so it can achieve mold milling that is close to high-efficiency machining conditions for carbide. If the wedge angle continues to increase, the chisel edge of the ball end of the tool will be reduced, thereby enhancing the sharpness near the center edge.

BNBP type improves the shortcomings of previous CBN end mills that are prone to breakage, improves the sharpness of the center edge, and can be used for both rough machining and finishing machining.

Mold processing

Using STAVAX as the material to be cut, the material hardness is 52HRC, BNBP type and super-hard surface coating end mills are used respectively, and the cutting process is carried out according to the mold shape and conditions specified in the design drawings.

The processing conditions are: rough machining, R1.0mm, depth of cut 0.1mm; finishing machining, R0.3mm. By comparing the blade wear after processing, we found that the wear amount of the super-hard surface-coated end mill reached 0.03mm, and the machined surface produced burrs and was damaged. With the BNBP type end mill, the wear amount is only 0.015mm, showing a fixed wear state, and obtaining a stable surface quality without burrs. Therefore, it can be seen that due to the rapid temperature rise and serious wear of super-hard coated end mills during high-speed cutting, the BNBP type end mills can obtain a longer service life.

Taking the workpiece material SKD11 as an example, the surface hardness of this material can reach 60HRC (Figure 2). The R1.0mmBNBP type CBN end mill is used to complete the entire process from rough machining to finishing. Processing conditions: machine tool spindle speed, 30 000r/min; axial depth of cut for roughing 0.1mm; semi-finishing 0.05mm; finishing 0.03mm. After the processing is completed, take a photo of the tool (Figure 3), and enlarge the photo to see that the BNBP type CBN end mill has less wear and can process stably. This is mainly because, under the processing conditions of the spindle speed of 30,000r/min, the outermost diameter processing speed of the R1.0mm ball end mill is 188m/min, and the contact time between the tool tip rotation and the material being cut (processing time) is only 0.5ms. Because of this, the BNBP type CBN end mill with excellent thermal conductivity can complete cutting before the tool tip temperature reaches the maximum temperature.

The processed BNBP milling cutter head has less wear

If the machine tool spindle speed is reduced to 20,000r/min, the cutting temperature will be significantly reduced, thereby reducing thermal wear, but the impact force during intermittent cutting will increase, and the micro-cracks produced by the tool will increase wear. However, the BNBP type CBN end mill using new materials has a high-strength cutter head design, which can effectively prevent the occurrence of chipping. Compared with super-hard coated end mills under the same speed conditions, it has better wear resistance. Therefore, it can be used for high-precision mold processing for a long time.

Conclusion

CBN small diameter ball end mill BNBP type has a unique negative chamfer structure and narrow chisel edge, which not only improves wear resistance, but also improves the sharpness of the cutting edge. Experiments have proven that the BNBP type CBN end mill can not only achieve high-precision mold processing, but also achieve a long service life.