The development and application of surface coating technology has played a key role in improving tool performance and advancement in cutting technology. Coated tools have become an important symbol of modern tools. Commonly used tool coating materials are mainly TiC, TiN, Al2O3, TiCN, TiAlN, CBN and the like. As a new coating material, TiAlN has excellent properties such as high hardness, high oxidation temperature, good thermal hardness, strong adhesion, low friction coefficient and low thermal conductivity, especially for high-speed cutting. In Japan and Taiwan, the application of TiAlN coated tools has been quite extensive. The new TiAlN coated milling cutter described in this paper uses ultra-fine particles (about 1 μm in diameter) of tungsten carbide-cobalt carbide substrate, and the surface is coated with a high-hardness TiAlN single-layer coating by special low-temperature physical vapor deposition (PVD) method. The thickness is about 6 μm). The surface of the TiAlN coating forms a high-strength oxide (corundum). The Ti content in the coating is controlled at about 37%, and the Al content is controlled between 10% and 13% to ensure the sharpness of the cutting edge. The main performance comparison between the new TiAlN coating and the TiN coating is shown in Table 1.
Table 1 Comparison of main properties of new TiAlN coating and TiN coating
Coating properties - TiAlN coating - TiN coating
Vickers hardness Hv(kgf/m2)-2720-1930
Oxidation temperature (°C)-840-620
Scratch test critical load adhesion (N)-80.3-60.3
Structural features - thin cylindrical face-centered cubic structure - face-centered cubic structure
Friction performance - friction coefficient with steel 0.30 - and steel friction coefficient 0.41
2. Application of high speed milling technology in mold manufacturing
In recent years, high-speed cutting technology has developed rapidly, such as milling machine speed has reached 30,000 ~ 50000r / min. High-speed milling has a good application prospect in precision and ultra-precision machining such as mold manufacturing. Due to the sharpness and weakness of the transition edges of some molds, the corners are prone to sag. It is difficult to ensure the machining accuracy at the intersection of the molds by ordinary milling. The high-speed milling can cut the sharp corners of the shape and realize the precision mold. High precision and high efficiency machining.
In recent years, foreign mold manufacturers have developed a number of advanced technologies for high-speed machining of molds, such as: 1 shape pre-identification control technology: This technology can realize high-precision machining control function when machining mold free-form surface at high speed to avoid sharp corner parts due to cutting. Impact, mechanical hysteresis, etc. cause path errors. 2SF technology: When machining a free-form surface of a mold with a spherical milling cutter, the cutting point of the workpiece and the tool is constantly changing, so that the cutting speed of the actual cutting point is constantly changing, which affects the surface processing quality. The SF technology can read out the cutting point information of the time change from the NC data in advance, and keep the cutting speed of the cutting point constant by controlling the spindle rotation speed; at the same time, control the feed amount per revolution to keep the feed speed stable. 3 area processing technology: a certain area is preset in the mold processing surface, and the application area processing technology can be used without changing the original
In the case of a machining program, machining that changes the depth of cut and other cutting conditions is realized in or outside the set area. 4 Right-angled adjacent arc inner angle milling technology: It adopts three-sided milling cutter handle embedded triangle blade for machining, which can directly mill the inner angle of the arc into a right angle, and the processing efficiency can be improved by about 20 times than the electric discharge wire cutting. 5 Using the special CNC code G260 command, it is possible to machine the inclined hole on the plane. When machining, the milling cutter rod utilizes the angle required for the universal joint deflection, which eliminates the need to re-clamp the workpiece and use the special fixture during conventional machining. 6 The control system adopts NURBS (Non-uniform Rational B Spline) compensation, which solves the problem that the control system data transmission has a waiting phenomenon, and the machine tool cannot move during the micro feed (1 μm) processing.
The use of high-speed milling technology for direct molding of the mold can reduce electrical processing and related process flow, significantly improve processing efficiency, processing time can be shortened by 1/3 to 1/4. In order to realize high-speed milling of molds, it is especially important to develop and apply advanced high-speed milling tools. TiAlN coated milling cutters are the most commonly used tools for high-speed milling hardened die steel.
3. Wear and damage performance of high-speed milling die steel with TiAlN coated milling cutter
High-speed milling of AlSi H13/JIS SKD61 hardened die steel (52HRC) with VC-MD model six-tooth TiAlN coated hard milling cutter (φ10mm) (milling speed: 628m/min; milling length: 50m; milling depth: axial cutting The depth of 10mm, the radial depth of cut is 0.5mm), the effect of different cooling methods on the tool wear morphology shows that the tool wear is the least when using air-cooled cutting; the tool wear is the second when using dry cutting; The tool wears the most. Since the milling cutter is in an intermittent cutting state, for example, when the coolant is directly sprayed on the cutter during cutting, the temperature change of the cold when the blade is cold is likely to cause thermal cracking, resulting in cracking of the cutting edge and damage of the blade. Therefore, coolant should not be used when milling high-speed die steel, otherwise tool life will be shortened.
The main failure mechanisms of the tool include crater wear, thermal deformation, and cracking. Cutting heat and mechanical vibration are important factors in tool failure. The crater wear usually occurs on the rake face of the blade. When high-speed machining of steel and other hard materials, the chips are fused to the surface of the tool under high temperature, and the particles of the tool material are peeled off to form crater wear. Excessive crater wear can weaken the cutting edge strength, hinder the flow of the chips, increase the temperature and pressure the tool is subjected to, and eventually cause the tool to break. Coating the tool adds an inert hard medium between the tool and the workpiece, significantly reducing crater wear. By properly applying the coating technology, the blade can have both high hardness and high toughness. When coating, the element distribution of the substrate and the coating can be adjusted as needed to make the cutting edge region have a higher cobalt content, thereby combining the impact resistance of the cobalt-containing matrix with the wear resistance of the coating to make the cutting edge have a good cutting edge. Resilience while the rest of the tool remains at a high hardness.
High-speed milling of AlSi H13 die steel (50HRC) with VC-MD model TiAlN coated milling cutter (feed rate: 0.10mm/tooth; axial depth of cut 10mm, radial depth of cut 0.5mm), milling condition and tool breakage The relationship shows that when the cutting speed is V=157m/min, the cutting length can be up to 300m when using dry cutting and air-cooling cutting; when the cutting is cooled by emulsion, the cutting edge will be cracked at 200m. When the cutting speed is V=314m/min, the cutter will be broken at 150m when dry cutting is used; the milling can still be performed normally at 300m when using air-cooled cutting; the cutter will crack at 50m when using emulsion cooling. When the cutting speed is V=471m/min, the tool wears a large wear at 200m in dry cutting; the tool wears at 300m when using air-cooled cutting; the tool cracks at 50m when it is cooled by emulsion. . When the cutting speed is V=628m/min, the tool wears a large amount of wear at 100m during dry cutting, and the cutter breaks and breaks at 120m. When using air-cooled cutting, the tool breaks and breaks at 150m; when using emulsion to cool the cutting The tool quickly wears and breaks.
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