(5) Lower cutting force and cutting temperature: Diamond has a high thermal conductivity, which is 1.5 to 9 times that of cemented carbide and 2 to 6 times that of copper, making the temperature in the cutting zone very quickly. Therefore, using a PCD tool to cut the temperature of a resin bond or a ceramic bond grinding wheel is many times lower than cutting a metal.
3. How to use PCD tool cutting wheel?
Using a PCD tool to cut a grinding wheel with a hardness of HV2000 to 4000 is as easy as cutting a tofu with a knife, which means that a PCD tool is suitable for cutting a grinding wheel.(1) Tool: The mechanical clamping tool shown in Fig. 15-1 and Fig. 15-2 is used to make the outer circle, inner hole and end face of the car by using a PCD insert. Its longitudinal and lateral rake angles are -10° and its relief angle is 10°. All round blades are used to make the cutting in and out smoothly and the grinding wheel does not collapse.
(2) Cutting amount: Through practice, the cutting amount of PCD tool turning grinding wheel is generally νc = 25 ~ 40m/min, ap = 4 ~ 5mm, f = 1 ~ 1.5mm/r.
(3) Dust removal: Dust generated when turning a grinding wheel with a tool is unavoidable. The dust generated when cutting a grinding wheel with a PCD tool is far lower than the conventional knife bowl extrusion. In order to prevent dust from flying, water spray can be used.In the early 1980s, the grinding wheel was started with a PCD tool. Using the above tool and cutting amount, 50 wheels with inner holes less than 150 mm and a thickness of 120 mm were successfully finished. At this time, the wear of the PCD head was less than 0.5 mm, reflecting the high durability of the cutting tool used to cut the grinding wheel.
4. What are the characteristics of dressing wheel with artificial polycrystalline diamond composite blade?
The artificial polycrystalline diamond composite blade (PCD) was made into a tool as shown in Fig. 15-3. It was used to dress the grinding wheel on the grinding machine and showed outstanding characteristics compared with Other dressing tools.
(1) Long wear life of the blade: Due to the high hardness of the PCD blade, the wear resistance is very good. It is used to replace the traditional tooth profile grinding wheel dressing tool and diamond pen to dress the grinding wheel. Under normal circumstances, a machine processing The shop uses a PCD blade to dress the grinding wheel on the grinder. It can be used for more than one year, and the cost of dressing is only 1/10 of the original.
(2) Good quality after dressing: The grinding wheel dressed with this tool is very smooth and has little radial runout. It takes about a minute or so to dress a grinding wheel with it, and its efficiency is more than 5 times that of a tooth-shaped dressing tool.
(3) Save the grinding wheel: When this tool is trimmed, only the high points of the beating and unevenness are trimmed, and there is very little trimming of the low point, which can save the grinding wheel.
(4) How to use: Hold the tool handle with your hand and place the positioning plane of the front end of the handle against the sharpening plate of the grinder. Slightly loosen the fastening screw at the front and rotate the adjustment screw at the rear to turn the blade. After touching the rotating grinding wheel, knife again depending on the situation, and then move the tool left and right (passing knife). After repeated several times, the wheel will be repaired.
5. What are the cutting characteristics of carbide?
The concept of cemented carbide in people's minds is that it is very hard and brittle. It is used as a wear-resistant part for tool materials, molds, etc. The method of machining it can only be used for grinding. Due to the appearance of super-hard tools, carbide can also be used to cut the tool, its characteristics are as follows:
(1) High hardness and brittleness: The hardness of cemented carbide is HRA85 to 92.5 (HRC67 to 81), which is higher than the hardness of hardened steel by HRC20, so cutting is extremely difficult. It has no plasticity, and it is brittle. It is susceptible to chipping due to cutting forces and cutters.
(2) The chips are in powder form: Since the cemented carbide has a large brittleness, the chips are all powdery, and there is no built-up edge at all, and the finished surface roughness is easily achieved.
(3) Higher thermal conductivity and lower cutting temperature: The thermal conductivity of cemented carbide is 17 to 88 W/(m·K), which is on average 15 times higher than that of hardened steel, so the cutting temperature is much lower than that of hardened steel.
(4) The chip is in short contact with the blade surface: When cutting the cemented carbide, the cutting force is concentrated near the edge of the blade and it is easy to cause blade chipping. The main form of tool wear is flank wear.
6. How to turn carbide with PCD tool?
Carbide processing, generally using green silicon carbide, boron carbide grinding wheel and diamond grinding wheel grinding, PCD tools can also be used for cutting.
The tool geometric parameters during cutting are: γo=-5° to 0°, αo=8° to 10°, kr=30° to 45°, k′r=8° to 10°, rε=0.8 to 1.5 mm.
The amount of cutting when cutting cemented carbide with a PCD tool is: νc=25-35 m/min, ap=0.1-0.5 mm, f=0.1-0.15 mm/r. Take large values ​​when cutting YG15 or YG20.
During cutting, in order to prevent chipping due to the brittleness of the cemented carbide, it is necessary to appropriately reduce the feed amount at the cutting-in and cutting-out place, or to pour an angle here first, and to make the cutting edge sharp. During the cutting process, kerosene is optionally used as cutting fluid.
7. What are the advantages of using PCD tools for machining carbides for molds?
(1) Improve the strength characteristics and performance of the die: When PCD cutters are used to cut tungsten carbide (YG15, YG20) carbide die, the machining surface will have a large residual compressive stress, which can improve the strength characteristics and performance of the die. Such as the use of green silicon carbide grinding wheel, the high temperature generated during grinding, the workpiece surface to produce annealed layer, micro-cracks and residual tensile stress, affecting the abrasive performance.
(2) Improve processing efficiency: If PCD cutters produced by U.S. General Corporation are used, the vertical and horizontal rake angles are -5°, the back angle is 5°, and the tungsten carbide hard alloy with turning hardness HV1204 is νc= 28 to 56 m/min, ap=0.5 mm, f=0.25 to 0.35 mm/r, and in the case of emulsions, the metal removal amount is 3.5 to 8 cm3/min, and the cutting efficiency is higher than other processing methods currently used.
(3) High tool durability: Turn YG15 cemented carbide with PCD blades of DA200, DA150, and DA100 manufactured by Japan's Sumitomo Electric Co., Ltd., at νc=15 m/min, ap=0.5 mm, f=0.1 mm/ In the case of r, the blade with a mixture of coarse and fine grains such as DA100 has a durability of 30 minutes and the flank wears only 0.2 mm.
8. What are the examples of cutting cemented carbide with CBN tools?
Cutting cemented carbide (YG15, YG20, YG25) with CBN tool can replace electro-physical machining, diamond tool cutting and diamond grinding wheel grinding.
(1) Boring: The hole is drilled on a cemented carbide bush with an accuracy of IT6 to IT8 and a surface roughness Ra of 1.6 to 0.8 μm. The cutting amount is: νc = 15m/min, ap = 0.2 ~ 0.5mm, f = 0.1 ~ 0.15mm/r. The tool geometric parameters are: γo=-5°, αo=6° to 8°, κr=45°, κ′r=15°, rε=0.5 mm. The efficiency of boring with a CBN tool is about 10 times higher than with a diamond grinding wheel.
(2) Outer circle: Using a CBN tool on a φ40mm, 100mm long carbide punch, cut away the 3.5 mm allowance for only 25 minutes. If grinding with a diamond grinding wheel, it takes 215 minutes.
(3) Intermittent turning: CBN tools can not only continuously turn carbide, but also can carry out intermittent turning. If the YG20 and YG25 carbide sleeves are intermittently turned, νc=30m/min, ap=0.35mm, and f=0.034mm/r. The geometric parameters of the tool are: γo=-6°, αo=8°, κr=45°, and the tool's durability is 6.5 min.
Using PCD and CBN tools to cut particularly high-precision parts is difficult, it is still necessary to use diamond grinding wheel grinding. This is because the radial component force FP at the time of cutting cemented carbide is large, causing the tool to retract. When νc=10m/min, ap=0.5mm, f=0.1mm/r, flank wear 0.05mm, FP is about 400N; VB=0.1mm, FP=700N; VB=0.2mm, FP= 1300 N. Therefore, when cutting cemented carbide with a super-hard tool, it is necessary to select the process conditions with good rigidity of the process system, and only the parts with the machining accuracy of about IT6 and roughness greater than 0.8 μm.
9. How to grind magnet steel?
Magnetic steel is a general name for magnetic alloys and is the most important permanent magnetic material in modern times. It has good magnetic properties and is widely used in the electromechanical industry. Commonly used magnetic steels are Al-Ni-C05 and Al-Ni-C08 two, commonly known as five magnetic steel and eight magnetic steel.
(1) Grinding characteristics of magnetic steel: It has hard and brittle performance, and it is easy to produce phenomena such as chipping, burn and chipping in the grinding process, especially when the grinding wheel runs out of the workpiece. Five types of magnetic steel are slightly better than the eight types of magnetic steel, and the eight types of magnetic steel are very difficult to mill. There are obvious directional and directional thermal conductivities in the eight magnetic steel lattices. The defects produced in the grinding process are closely related to the crystal orientation. When the grinding direction coincides with the direction of the columnar crystal structure, sharp edges of the magnetic steel plane hardly cause collapse, and even if it is there, it is quite small. When the grinding direction is perpendicular to the direction of the columnar crystal structure, the edges of the grinding wheel will collapse, and in severe cases, exfoliation will occur. Therefore, grinding of magnetic steel is not the same as grinding other materials. Care must be taken when grinding.
(2) Grinding of magnetic steel: Atmospheric-hole grinding wheels with green silicon carbide or alumina as the abrasive, particle size of 46 to 60, hardness of soft 2 and medium soft 1 should be used. In addition, it is also possible to use interrupted grinding of slots in silicon carbide grinding wheels (refer to the basics of questions 72 and 73 of this book). During grinding, microfeeds should be used to increase the cooling fluid flush. In order to prevent the workpiece from collapsing while the wheel is moving out, two general steel protective plates can be joined at both ends of the workpiece, as shown in Figure 15-4. During the grinding process, the sharpness of the grinding wheel must be maintained so that when the grinding wheel comes into contact with the workpiece, a “sand†sound is produced. When the grinding wheel makes a "click" sound when it comes in contact with the workpiece, the grinding wheel must be dressed. Otherwise, the grinding wheel becomes blunt, resulting in burns and other defects. When the grinding wheel is larger than the coverage area of ​​the workpiece, the cooling liquid must be flushed to accelerate the heat dissipation, and the workpiece feed amount is reduced to prevent the instantaneous impact of the grinding wheel on the workpiece to improve the surface quality of the workpiece.
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