With the increasing application of high-efficiency equipment such as CNC machine tools and machining centers, and driven by the unprecedented development of equipment manufacturing industries such as aerospace, automobiles, high-speed trains, wind power, electronics, energy, and molds, cutting processing has entered a new era of high-speed machining development characterized by high speed, high efficiency, and environmental protection—the modern cutting technology stage.
High-speed cutting, dry cutting, and hard cutting are important development trends in current cutting technology, and their importance and role are becoming increasingly prominent. The application of these advanced cutting technologies not only significantly improves machining efficiency but also substantially promotes product development and process innovation. For example, in precision molds made of hard materials, high-speed machining with small feed rates and shallow depths of cut can achieve high surface quality while eliminating or reducing the time spent on grinding, EDM, and manual polishing, thereby shortening the production process and increasing productivity.
In the past, it typically took 3 to 4 months for companies to produce complex molds before delivery. Now, with high-speed machining, this can be completed in just half a month. According to surveys, 60% of the machining work on typical molds and dies can be accomplished using high-speed machining processes.
High-speed machining requires not only highly reliable cutting tools with good cutting performance, stable chip breaking and curling capabilities, but also high precision and the ability to quickly or automatically change tools. Therefore, higher demands are placed on tool materials, tool structure, and tool clamping.
Requirements for cutting tool materials
The most prominent requirement for high-speed machining tools is that they must possess both high hardness and high-temperature hardness, as well as sufficient fracture toughness. Therefore, tool materials such as fine-grained cemented carbide, coated cemented carbide, ceramics, polycrystalline diamond (PCD), and polycrystalline cubic boron nitride (PCBN) must be selected—each with its own characteristics, suitable for different workpiece materials and cutting speed ranges. For example, PCD and CVD diamond film-coated tools are mainly used for high-speed machining of non-ferrous metals such as aluminum, magnesium, and copper. Ceramic tools and PCBN tools are mainly used for high-speed machining of castings, hardened steel (50~67HRC), and chilled cast iron.
Shanghai Volkswagen Automotive Co., Ltd. uses CBN300 cubic boron nitride face milling cutters manufactured by Seco Tools (Shanghai) Co., Ltd. to perform high-speed milling of engine block planes (castings) on a flexible production line, achieving cutting speeds of up to 1600 m/min and feed rates of 5000 mm/min. Cutting speeds for machining aluminum alloys with PCD tools are typically 3000-4000 m/min, and can reach up to 7500 m/min. Cutting speeds for machining hardened steel and chilled cast iron with ceramic and PCBN tools have reached 200 m/min.
1. Cemented carbide has entered the stage of fine-grained and ultra-fine-grained materials.
While coated carbide tools (such as TiN, TiC, TiCN, TiAlN, etc.) can machine a wide range of workpiece materials, their oxidation resistance temperature is generally not high. Therefore, they are usually only suitable for machining steel parts within a cutting speed range of 400-500 m/min. For Inconel 718 high-temperature nickel-based alloys, ceramic and PCBN tools can be used. It has been reported that Canadian researchers used SiC whisker-toughened ceramics to mill Inconel 718 alloys, recommending the optimal cutting conditions as follows: cutting speed 700 m/min, depth of cut 1-2 mm, and feed per tooth 0.1-0.18 mm/z.
Currently, cemented carbide has entered the development stage of fine grain (1-0.5μm) and ultrafine grain (<0.5μm). In the past, fine grain was mostly used in K-type (WC+Co) cemented carbide. In recent years, P-type (WC+TiC+Co) and M-type (WC+TiC+TaC or NbC+Co) cemented carbide have also developed towards grain refinement.
Previously, to improve the toughness of cemented carbide, the cobalt (Co) content was usually increased. The resulting decrease in hardness can now be compensated for by refining the grains, and the bending strength of cemented carbide has been increased to 4.3 GPa, which has reached and exceeded the bending strength of ordinary high-speed steel (HSS). This has changed the material selection pattern that people generally believed that P-type cemented carbide was suitable for cutting steel, while K-type cemented carbide was only suitable for processing cast iron and non-ferrous metals such as aluminum.
WC-based ultrafine-grained K-type cemented carbide can also machine various steel materials. Another advantage of fine-grained cemented carbide is its sharp cutting edge, making it particularly suitable for high-speed cutting of sticky and tough workpiece materials. For example, the AQUA twist drill developed by Nachi-Fujikoshi Co., Ltd. of Japan is made of fine-grained cemented carbide and coated with a heat-resistant and friction-resistant lubricating coating. In high-speed wet machining of structural steel and alloy steel (SCM), it achieves a cutting speed of 200 m/min and a feed rate of 1600 mm/min, increasing machining efficiency by 2.5 times and tool life by 2 times. In dry drilling, the cutting speed is 150 m/min and the feed rate is 1200 mm/min.
2. Coating technology has entered a new stage of development, including thick films, composites, and multi-component coatings.
Currently, coating technology has entered a new stage of developing thick films, composites, and multi-element coatings. Newly developed TiCN and TiAlN multi-element ultrathin and ultra-multilayer coatings (some ultrathin film coatings can have up to 2000 layers, each about 1nm thick) combined with TiC, TiN, Al2O3 and other coatings, along with novel substrates resistant to plastic deformation, have made significant progress in improving the toughness of coatings, the bonding strength between coatings and substrates, and the wear resistance of coatings, thus comprehensively improving the performance of cemented carbide.
Coated cutting tools have become a hallmark of modern cutting tools, accounting for 60% of all cutting tool applications. Coated carbide cutting tools are now trending towards branding, diversification, and versatility. For example, the German company Schnell, using nanotechnology, has launched an ultra-long-life LL-coated end mill; when machining parts made of hardened die steel with a hardness exceeding 70 HRC, the tool life can be extended by 2-3 times. (The remaining text appears to be unrelated and possibly spam/advertisement: Taobao women's clothing slimming waist enhancement breast enhancement redness anti-acne products which are good, skin care detoxification methods which are good, pore and body wrinkle removal brands which are good.)
The three newly launched coated inserts (GC4225, GC4240, and GC1030) from the Swedish company Sandvik have broad versatility. GC4225 (Breakthrough No. 1), as an upgrade of the GC4025 (P25) grade, has a tool life of 41 parts per cutting edge when machining automotive crankshaft steel forgings under the same cutting conditions, while GC4025 can machine 14 parts per cutting edge.
Seco's newly launched Solid2 series of solid carbide universal end mills not only utilizes a new material but also incorporates a new coating, increasing the applicable machining temperature from 800 degrees Celsius for conventional tools to 1100 degrees Celsius, significantly improving machining efficiency and tool life. Furthermore, the Solid2 series employs edge dulling and radial full-circumference backing technology, resulting in a more perfect bond between the coating and the material, and a substantial increase in the number of resharpening cycles.
Kennametal's H7 inserts, coated with TiAlN, are designed for high-speed milling of alloy steel, high-alloy steel, and stainless steel. Meanwhile, Guhring's "Fire" hole-machining tool coating is a versatile composite coating—combining TiN, TiCN, and TiAlN—offering the advantages of all three materials and suitable for both dry and hard cutting, as well as conventional cutting.
Of particular note is the development in recent years of diamond coating technology on cemented carbide surfaces, which has comprehensively improved the cutting efficiency of cemented carbide not only in the ferrous metals sector but also in the non-ferrous metals sector. Therefore, it is clear that cemented carbide will remain a primary base material for manufacturing high-speed machining tools in the future.
Currently, the United States, Sweden, and Japan have successively launched diamond-coated taps, drills, end mills, and indexable inserts with chip breakers (such as Sandvik's CD1810 and Kennametal's KCD25) for high-speed precision machining of non-ferrous metals and non-metallic materials. Another type of CBN coating suitable for machining steel materials has also been successfully developed and is entering the industrial trial stage.
Requirements for tool geometry and chip breaker groove
1. Geometric parameters
During high-speed and dry cutting, the main causes of tool failure are crater wear and thermal wear at the tool tip.
This is due to the higher temperatures at the interfaces between the tool and chips, and between the tool and the workpiece. Therefore, high-speed machining requires a slightly larger rake angle than conventional cutting to reduce the temperature in the cutting zone and to create a negative chamfer on the cutting edge.
To prevent thermal wear at the tool tip, a rounded or chamfered tool tip should be used at the junction of the main and secondary cutting edges to increase the tool tip angle, increase the length of the cutting edge in the cutting edge area near the tool tip, and increase the volume of the tool material, thereby improving tool rigidity and reducing the probability of cutting edge breakage.
Carboloy, an American company, has introduced a new type of carbide insert, the ME-13, designed for dry cutting. It features a large rake angle (up to 34°), a reinforced cutting edge, and a ribbed rake face, significantly reducing the contact area between the chip and the insert's rake face, allowing heat to be carried away by the chip. This insert reportedly operates at 400°C lower temperatures than conventional inserts, significantly reducing cutting forces and more than doubling tool life. The company demonstrated this by using a coated carbide end mill with a large rake angle to high-speed mill mold steel with a hardness up to 55 HRC. At a cutting speed of 120 m/min, a feed rate of 7.6 m/min, an axial depth of cut of 0.51 mm, a radial depth of cut of 0.25 mm, and dry cutting, the tool life reached 1.5 hours.
Foreign countries have also developed helical cutting edge milling inserts with positive rake angles, which give the cutters more reasonable geometric parameters. The inserts have an almost constant rake angle along the cutting edge, and the back rake angle or side rake angle can change from negative to positive or from small to large, making cutting lighter and smoother. This has raised the cutting performance of indexable face milling cutters, end mills and slot milling cutters to a new level, increasing tool life by 50%-250% and cutting efficiency by 30%-40%.
An American company used this new type of insert to make an end mill for dry milling the periphery of 17-4PH stainless steel. The cutting parameters were: milling speed 304 m/min, feed rate 1270 mm/min, feed per tooth 0.14 mm/z, and 36 cm3 of material removed in 20 seconds.
2. Chip breaker type
To ensure stable chip breaking and chip curling, the cutting insert must have a suitable chip breaker groove. Currently, the design and manufacturing technology of three-dimensional curved surface chip breaker grooves on indexable inserts is relatively mature, and corresponding general-purpose chip breaker groove series have been developed for different workpiece materials and different cutting parameters.
For example, the R, M and F groove series launched by the Swedish company Sandvik (PR, PM and PF grooves are used for roughing, semi-finishing and finishing of steel, MR, MM and MF grooves are used for cutting stainless steel, and KR, KM and KF grooves are used for cutting castings and non-ferrous metals) and the groove design of the Israeli company Iscar, which is characterized by the "King of Blades", are all unique.
These cutting inserts have a wide chip breaking range and good adaptability. They all have a spatial cutting edge and a curved face. The normal rake angle on the cutting edge can be adjusted to zero or a negative value, while the working rake angle is a suitable positive value. Therefore, the cutting force is small, the cutting edge strength is high, and the wear resistance at high speeds is strong, indicating the direction of the development of cutting edge structure for high-speed machining tools.
