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CNC Tool Technology
1 CNC high-speed cutting tool material requirements
The cutting heat and cutting tool wear generated during CNC high-speed cutting are much higher than those at ordinary speed cutting. Therefore, the material used for CNC high-speed cutting is very different from the tool material used for ordinary speed cutting. There are higher requirements, mainly including:
High hardness, high strength and wear resistance;
High toughness, strong impact resistance;
High thermal and chemical stability
· Strong thermal shock resistance.
Many new tool materials have emerged, but it is difficult to find tool materials that meet the above requirements. Therefore, on the substrate of the tool material with better impact toughness, the tooling technology with high thermal hardness and wear-resistant plating is rapidly developed. In addition, it is also possible to sinter high hardness materials such as CBN and diamond on a matrix of hard alloy or ceramic material with good impact toughness to form a CNC high speed machining tool with excellent overall cutting performance.
2 CNC high speed tool material selection
With the increasing application of difficult-to-machine materials such as high-strength steels, high-temperature alloys, titanium alloys, and composite materials in the aerospace field, modern CNC tool materials cannot be limited to high-speed steels and ordinary hard alloys that are currently widely used, and should be based on different The material is machined and the tool material is selected taking account of tool life and machining quality. The following is a selection of CNC tool materials according to the classification of commonly used materials in the domestic aviation manufacturing industry: 
CNC milling of titanium alloys
(2) Ordinary steel: For CNC cutting of ordinary steel, cobalt high-speed steel M42, carbide, and cermet are used as tool materials in domestic aviation manufacturing.
(3) High-strength steels and high-temperature alloys: In the field of aerospace manufacturing, high-strength steels and high-temperature alloys account for an increasing proportion of materials, and the cutters used to process such parts are mainly used for high strength, high toughness, and high wear resistance. The ultrafine grained alloy substrate is processed with a TiAlN coating of a hard alloy material and a cermet material.
(4) Titanium alloy: Titanium alloy has high strength and impact toughness, and its work hardening phenomenon is very serious. In the cutting process, high temperature and severe tool wear occur. The titanium alloy material often uses cobalt high speed steel M42 and Zhuzhou diamond cutting. Tool Co., Ltd. produced KMG405 series of carbide coated tool materials.
(5) Composite materials: Composite materials have been widely used in the aviation field, and their usage is increasing rapidly. The processing of such materials mainly uses PCD-coated cemented carbide and ceramics as tool materials.
3 CNC high-speed cutting tool geometry parameters and cutting parameters
(1) The requirements of CNC high-speed cutting on tool geometry parameters. In addition to the choice of tool materials, the correct selection of tool cutting edge geometry and tool chip breaking methods have a great influence on the efficiency of CNC high-speed cutting, machining surface quality, tool life, and cutting heat generation, which is the NC An important factor in high-speed cutting tool technology. Several parameters of the tool cutting edge can be considered from the following aspects:
• The proper tool clearance angle and reasonable feed rate produce enough chip thickness to remove heat and avoid cutting and hardening.
· The blade rake angle is an important parameter that affects the cutting load of the tool and should be selected reasonably.
• The cutting load is related to the feed amount of each cutting edge of the tool. For multiple inserts, the cutting load acts on each insert; for solid inserts, the cut load acts on each tooth. Therefore, you should choose the feed between a reasonable number.
In general, most of the geometrical angles of CNC high-speed tools have a corresponding relationship with traditional knives. Choosing reasonable tool parameters, in addition to making the cutting tool sharp cutting edge and sufficient strength, an important goal is to be able to form chips of sufficient thickness so that the cutting chips become the heat sink for the cutting process. The higher the cutting speed, the more heat is generated. Therefore, in the CNC high-speed cutting process, the key problem is to find ways to transfer the cutting heat to the cuttings as much as possible, and use the high-speed cutting chips to quickly take the cutting heat. go.
(2) The correct selection of tool material and cutting parameters based on the workpiece material and machining process is an important link to ensure that CNC high-speed cutting can achieve the desired results. At present, CNC high-speed cutting parameters cannot be selected by cutting manuals as in ordinary cutting. CNC high-speed machining does not have a complete process parameter table and CNC high-speed cutting database. For each tool, there is no specific formula to determine the most. Good combination of cutting parameters. In actual production, the best cutting speed and feed rate are determined through tests based on the processed materials, process characteristics, and other factors.
4 CNC high-speed cutting requirements on the body
(1) High connection strength mosaic cutters. In CNC high-speed cutting, a large number of coating, lamination tool technology and mosaic tools are applied. For inlaid cutters, if the blades embedded in the cutter body do not have sufficient connection strength, they will be separated from the cutter body under the action of a large centrifugal force. The cutter with a rotation speed of 10000r/min or more has this danger. Therefore, it is unsafe to press the blade with only one clamping screw at high speed. The embedded tool used for high-speed cutting is not the same as the ordinary tool. The insert should be embedded in the tool body safely, that is, fit tightly into the slot of the tool body, and fasten the blade to the tool body in the direction perpendicular to the centrifugal force with screws. .
(2) The method of connecting the tool and the tool holder. The requirements for the tool holder and tool holder used in CNC high-speed cutting are: high clamping accuracy; large transmission torque; good symmetry of structure; beneficial to the dynamic balance of the tool; small external dimensions, but the overhang of the tool should be increased appropriately. Quantity to expand the processing range. 5 CNC high-speed cutting tool balancing requirements and other requirements In CNC high-speed cutting, dynamic balance should be considered. The dynamic balance affecting CNC high-speed cutting mainly manifests in the imbalance between the tool and the tool holder and the unbalance of the machine tool spindle. The tool dynamic balance accuracy grade specified in ISO15641 high-speed rotary tool safety standard shall be within G40. Therefore, for CNC high-speed cutting tool, all aspects of the tool should be fully considered, such as in the design of the end mill, as far as possible the use of a good overall tool with good symmetry, the handle is straight, the number of teeth is even , The tool material is made of imported materials with better materials. Strict control of the amount of cutting runout, the concentricity of the cutting edge and the tool holder, and the dimensional accuracy of the cutting edge and the tool holder to ensure the dynamic balance of the tool. In the actual application of CNC high-speed cutting tools, in addition to the correct choice of tool materials, cutting parameters and tool dynamic balance, but also consider other issues related to the tool, including: to improve the stiffness of the cutting system; consider the centrifugal force the tool withstands; Add special safety facilities.
Optimization Design and Tool Manufacturing of CNC Tool Process Parameters
1 CNC tool process parameters optimization design
(1) Front and rear corners of the CNC end mill.
Research shows that the tool rake angle is the main factor affecting the machining quality of the part material. Too large or too small will have a great impact on the machining quality and reduce the tool's durability. The choice of the tool relief angle will affect the tool stiffness. Increasing the relief angle will improve the tool life, but it will reduce the blade stiffness. After many years of practice in the processing of aerospace materials, the front and back corners of the tool should be selected differently depending on the material being processed.
(2) Helix angle.
According to the principle of cutting, increasing the helix angle can increase the number of teeth working at the same time, that is, it actually increases the front angle of the work, making the cutting sharp and the work smooth. However, when the helix angle increases to a certain extent, the tooth strength will be damaged, the overall rigidity will be reduced, the vibration in the cutting process will be increased, the wear of the tooth will be exacerbated, and the service life of the tool will be reduced. Taking into account the high-speed cutting characteristics of CNC machining, the helix angle when machining aluminum alloys can be taken as 25° to 30°; when processing high-strength steels and high-temperature steels, the helix angle is 35° to 40° when machining titanium alloys. The helix angle is 30° to 40°. In order to sharpen the cutting edge, the helix angle can be appropriately increased. For example, when machining titanium alloy, the helix angle of the φ25mm solid cemented carbide end mill with the KMG405 tool material can be increased to 45°, and the effect is ideal.
(3) The cross-sectional shape of the cutter teeth.
For processing aluminum alloys with two or three-tooth end mills, four or six teeth are used to machine the steel parts. Behind the teeth is a land edge, and the back surface is a circular arc curve. This kind of structure has good manufacturability, beautiful appearance, small vibration during cutting, stable cutting, smooth chip removal and improved tool life. Although the end mills with a small number of teeth have large chip flutes and good chip dischargeability, they have a small cross section and low rigidity, and are susceptible to bending deformation during cutting, affecting the perpendicularity and surface quality of the machined surface. In order to increase the rigidity of the tool, we have increased the diameter of the tool core on the basis of the avionics cutter. Although the chip flutes are smaller after increasing the diameter of the core, the chips with high-speed rotation during high-speed cutting are thrown off quickly, and there is no problem that the chips cannot be discharged.
(4) blade length.
The shorter the blade length, the better the tool rigidity and cutting performance. When the cross-sectional area is the same, the blade length of the end mill doubles, and its stiffness is only 1/8 of the original stiffness. Tests have shown that when the end mill blade length is doubled, its tool life is only 1/10 of the original life. Therefore, in the design of numerical control tool, it is necessary to design the short edge tool that meets the machining requirements. 
Walter's CNC Tool Measuring Machine
In order to ensure the connection rigidity and connection accuracy of the CNC end mill and the tool system, the precision tolerance of the shank diameter tolerance is improved to h6, which greatly improves the clamping accuracy and safety reliability of the tool; in order to ensure the processing quality and improve the tool life, the CNC The deviation of the diameter of the end milling cutter is increased to 0.05mm, and the tolerance of the tooth arc is increased to ±0.02mm; in order to ensure the balance of the tool itself, the peripheral teeth of the CNC end mill beats, the end teeth jumps, and the end teeth arc jumps are all Increase to 0.01mm.
(6) Tool coating.
The coated tool is coated with a metal compound film on the tool body to obtain a surface hardness that is much higher than that of the substrate and excellent cutting performance. Commonly used tool matrix materials mainly include high-speed steel, hard alloys, and cermets. The coating can be a single coating, a double coating, or a multiple coating, or it can be composed of several coating materials. Xifei Company cooperates with Shaanxi Jinjincheng Surface Engineering Co., Ltd. in the manufacture of CNC cutting tools. CNC cutting tools for non-ferrous metals use TiCN composite coating DJC-1, and various types of steel parts use TiAlN composite coating DJC-2 and diamond nanocomposite coating. Layer DJC-3. Coated tools have good thermal stability and chemical stability at high temperatures. The coating process gives the tool a smooth surface and high wear resistance. The use of a tool coating significantly improves the cutting performance of the tool, bringing considerable economic benefits to the plant.
2 CNC Tool Manufacturing
The manufacture and measurement of CNC tools must be ensured by high quality equipment and testing methods. Xifei’s technical equipment manufacturing plant imported three CNC grinding machines and several CNC tool measuring machines from abroad. Such as five-axis CNC tool grinding machine (HPR), the grinding machine table size is 660mm × 490mm × 320mm, can cut the diameter of φ3 ~ 240mm, length 240mm or less end mill, taper end mill, drill, step drill , three-faced disc cutters and stepped cutters and other tools. The positioning accuracy of this equipment: X, Y, Z: ≤ 0.008mm; Repeated positioning accuracy: X, Y, Z: ≤ 0.004mm, the equipment is easy to operate, has good stability, and the machining tool has high geometric accuracy. In the processing of high-quality tools such as the overall alloy tool has a strong advantage; CNC tool measuring machine equipment accuracy and equipment measurement accuracy are ± 2μ m, is a fully automatic non-contact high-precision tool measuring system, capable of measuring X ≤ 310mm, Tools with Y ≤ 290mm and Z ≤ 500mm. Complete measurement of the tool's rake angle, back angle, helix angle, blade width, tooth arc, taper, etc. In addition, there are high-precision CNC universal internal and external cylindrical grinding machines such as S21 and other CNC machine tools, providing a powerful guarantee for the manufacturing quality and measurement technology of the tool.
Xifei's CNC equipment and tool applications
Xifei Company is a large-scale aviation manufacturing enterprise in China. With the expansion of the scale of production of military and civilian aircraft and subcontracting, Xifei Company has purchased a large number of advanced CNC equipment at home and abroad, and established a CNC machining center, which is owned by the CNC Center and the Majijia Plant. Each branch is equipped with a large number of advanced CNC equipment. Five-axis CNC milling machine V1-20002T produced by China Aerospace Manufacturing Engineering Institute, machine tool stroke 8000mm×2000mm×650mm, spindle speed 20～4000r/min, capable of processing large aluminum steel structural parts; GMB2040M5X produced by Shenyang Machine Tool Plant of China The five-axis CNC milling machine spindle speed up to 18000r/min, processing range of 4000mm × 2000mm × 1000m m, mainly used to process aircraft aluminum alloy long-type parts; from the Italian production of five-axis CNC milling machine JOMACH145, spindle speed 100 ~ 16000r /min, effective stroke 7000mm × 3000mm × 1400mm, mainly used for processing honeycomb parts and ribs between the beams; produced by Japan's five-axis CNC milling machine HPS4B, spindle speed 150 ~ 15000r/min, the effective stroke of the machine tool is 10400mm × 2286mm × 762mm ,Suitable for processing large aluminum alloy plate parts; Three-axis gantry milling SH1600B, spindle speed 60,000r/min, processing range 12000mm×1600mm×800mm, suitable for processing aircraft girder and other parts; five-axis CNC milling machine MODUMIU250G produced by FORESTLINE, worktable Size 6000mm×2000mm, effective stroke 4000mm×3000mm×800mm, suitable for processing aluminum and steel Titanium and other parts. The numerical control tools used by CNC machine tools of the Xi'an Aircraft Numerical Control Center and the MSC General Plant are mostly manufactured by the tool branch of Xi'an Aircraft Technology Equipment Manufacturing Plant. The tool factory has many advanced numerical control equipments such as CNC grinding machine, high-precision grinding machine and numerical control tool measuring machine. It has strong strength and detection means in tool manufacturing, and the manufactured tools can basically meet the needs of CNC machining. But for high-strength steels, high-temperature alloys, titanium alloys, composite materials and other difficult-to-machine materials, it also purchased some advanced CNC tools at home and abroad. The major purchasers are CNC cutters, followed by CNC lathes. The foreign manufacturers mainly purchase the translatable cemented carbide cutting tools and solid carbide cutting tools manufactured by Sandvik, Seco, Walter, Iska, SGS, and Stilavera. China mainly uses cemented carbide tools such as KMG302 and KMG405 produced by Zhuzhou Cemented Carbide Plant. In addition, it also uses rigid materials produced by Jilin Siping Xinggong Cutting Tools Factory, Shaanxi Cemented Carbide Factory, Hanjiang Tool Factory, and Southwestern Tool Factory. CNC and high-speed steel materials for CNC machining.
Conclusion
CNC high-speed cutting tools and related technologies are the basic conditions for CNC high-speed machining. Due to the high-speed machining process and its complex mechanism, there is still a lack of mature and reliable machining simulation technology. Optimization of CNC machining parameters and structure of high-speed machining tools remains It mainly depends on the cutting test. Therefore, in the future, combining the actual conditions of aerospace materials processing, based on existing tool design and manufacturing capabilities, and drawing on domestic and foreign advanced experience, we should pay attention to and strengthen the research and development of CNC tool materials, tool structure, and tool cutting mechanism, and establish The complete process parameters table and CNC high-speed cutting database. At the same time, on-line high-speed CNC tool monitoring systems, CNC high-speed tool dynamic balance, etc., need to be further studied to further improve the level of aerospace industrial numerical control technology.
CNC high-speed cutting technology is an advanced manufacturing technology that has rapidly emerged in the past 20 years. It has been widely used in aviation, aerospace, and automotive fields due to its high efficiency and high quality. With the continuous development of new aerospace materials, hard-to-machine materials such as high-strength steels, high-temperature alloys, titanium alloys, and composite materials are increasing. This has played an important role in promoting and promoting the development of CNC tool technology. In the development of CNC high-speed cutting technology, the key position of tool and cutting tool technology has become increasingly apparent.