Abstract As the final executor of CNC machining, the machining efficiency, machining quality and stability of the machining process are directly related to the tool. Taking XXC.13.001 as an example, a suitable tool will add one step in the roughing process from the original 8 hours...
As the final executor of CNC machining, the tool's machining efficiency, machining quality, and stability of the machining process are directly related to it. Taking XXC.13.001 as an example, a suitable tool shortens one step in the roughing process from the original 8 hours of machining time to 3 hours, which shows the important influence of the tool on CNC machining.
Modern cutting tool materials have evolved from carbon tool steel and high speed steel to cemented carbide, ceramics, PCBN and PCD. The cutting performance of the tool is getting better and better, which directly promotes the great development of CNC machining. High-speed steel cutters have high heat hardness, high wear resistance, strength and toughness. Compared with cemented carbides, the biggest advantage is that they have good machinability and good comprehensive mechanical properties. Due to its good performance, high speed steel is still one of the most widely used tool materials in the world. The cemented carbide tool is made of carbide (hard phase) and metal bonding phase with high hardness and melting point by powder metallurgy method. Its hardness is much higher than that of high speed steel. At 540 °C, the hardness can still reach 82- - 87HRA, the same hardness as high speed steel at room temperature. The hardness and toughness of cemented carbide tools vary with the content of the metal bonding phase. Generally, as the content of the metal phase increases, the hardness decreases and the toughness increases. Since the successful development of ceramic knives, it has been well received by the market due to its good performance. Ceramic tools have the advantages of high hardness, good wear resistance, low friction factor, high temperature resistance and good heat resistance. Ceramic tools have become one of the main tools for high-speed cutting and difficult-to-machine materials processing. However, ceramic tools have low flexural strength and poor impact load resistance. They are prone to chipping when the machined surface is convex or concave or the vibration during processing is large, and it is not suitable for cutting under low speed and impact load. Ceramic knives are less able to withstand thermal shock loads, and coolants cannot be used during the cutting process to achieve dry cutting. CBN tools are second only to diamond in hardness and thermal conductivity, with high hardness and wear resistance, high thermal stability, excellent chemical stability, good thermal conductivity, low friction factor, etc. With all the performance of the perfect tool, but the strength and toughness is poor, the use should avoid excessive impact caused by the tool chipping, so the high angle cutting with negative rake angle is generally used. The expensive price of CBN tools is also an important factor limiting their widespread use.
In the development of tool materials, the generation and application of coating technology has found a mitigation method for the contradiction between the strength, hardness and toughness of the tool, and has become a revolution in the history of cutting tools. The tool coating technology mainly uses physical or chemical vapor deposition to obtain a hard film of several micrometers to ten micrometers thick on the surface of the tool. The tool coating has high hardness and wear resistance, high chemical stability and anti-blocking properties, and low friction factor. Adding a coating on the surface of the tool base can well solve problems such as hardness of the hard alloy such as hard alloy, poor wear resistance, and easy oxidation at high temperatures. When the performance of the coating differs greatly from the performance of the substrate or the bonding with the matrix material is not strong, a multi-layer coating may be used to gradually improve the toughness of the coating, the bonding strength of the coating to the substrate, the wear resistance of the coating, etc. problem. Coating technology greatly enhances tool hardness and toughness, improves tool wear resistance and oxidation resistance, thereby extending tool life and improving tool cutting performance.
The aluminum-magnesium alloy has low hardness and strength, good thermal conductivity, and is a free-cutting material. The cutting line speed can reach a level of about 1200 m/min. The depth of cut and the width of the cut can give larger parameters. In the roughing process, the method of small depth of cut, high speed and fast feed should be used to improve the efficiency, but the depth of cut should not be too shallow, so that the chips do not spontaneously ignite. During the machining process, when the tool is selected, the larger front and rear corners are selected, and the cutting edge of the tool should be sharp and smooth.
Stainless steel materials have high thermal strength, high toughness, strong adhesion, low thermal conductivity, severe work hardening, strong vibration during cutting, and easy damage to the tool. Choosing the right cutting parameters and the cutting fluid with the right concentration and pressure can achieve the ideal cutting effect with the general carbide coated tool.
Titanium alloys and nickel-based superalloys are relatively difficult materials for the company. To achieve efficient processing of difficult-to-machine materials, the key lies in: preferred tool materials: high-performance high-speed steel, new hard alloys, coated tools, ceramic tools, CBN tools and Diamond tool; select the appropriate tool geometry; use appropriate cooling lubrication conditions; use optimized machining parameters.
The thermal conductivity of titanium alloy is low, the cutting temperature can be more than several hundred degrees higher than that of cutting 45# steel; the elastic modulus of titanium alloy is low, the rebound of the machined surface is serious, the flank face is rubbed against the machined surface, and the cutting temperature is increased. The flank surface of the tool is seriously worn; the contact length between the chip and the rake face is short, and the stress on the contact surface is large; the chemical activity of the titanium alloy is large, and the affinity with the cutter is large, and it is easy to react with various elements in the atmosphere. Forming a hard and brittle outer skin, the tool is prone to build-up edges, and the tool is prone to bond wear during the cutting process. Due to the serious rebound of the titanium alloy, the back angle of the tool during cutting is large, and about 10° is selected. To ensure the edge strength, the rake angle of the tool should not be too large, about 5°. When milling titanium alloy, try to use a large helix angle cutter to increase the sharpness of the tool while ensuring the strength of the tool. A large amount of cutting fluid containing no chlorine is used during the cutting process.
High-temperature alloy has a low thermal conductivity, lower than one-third of 45 steel, high cutting temperature; high temperature strength, still reaches the room temperature strength of medium carbon steel at 600-900 °C, cutting force is two of the general steel cutting Three times; there are a large number of dense solid solution in the alloy, the lattice distortion is serious during cutting, and the chill phenomenon is serious; the hard spots containing a large amount of metal carbides, boride, oxides and intermetallics are extremely wearable. . Taking the company's XX.44.003 parts as an example, the material is GH710, the hardness is about 42-44HRC. Because the material contains a lot of hard spots inside, the actual hardness is far more than 44HRC. The cutting process is easy because the cutting temperature is too high, the cooling effect Oxidation and wear occur in place. The tool also easily encounters hard spots during the cutting process and collapses. When turning, the blade should choose a large front and rear angle as much as possible to improve the strength of the blade. When milling, try to use a large spiral angle cutter. When cutting with ceramic tools and CBN tools, it is important to use a tool with a negative rake angle to avoid chipping due to excessive impact loads during the cutting process.
In the actual cutting process, the choice of the tool and the selection of the corresponding cutting parameters should be determined according to the processing conditions. The overall processing cost, processing efficiency, metal removal amount and other factors, the most suitable tool is the best tool.
