11. What are the grinding wheel precision dressing technologies in high-speed grinding?
Answer: At present, the more mature grinding wheel dressing technologies are:
(1) ELID online electrolytic dressing technology;
(2) EDM grinding wheel dressing technology;
(3) Cup grinding wheel dressing technology;
(4) Electrolysis-mechanical composite shaping technology
12. What is precision grinding? Try to briefly describe the selection principle of grinding wheel in precision grinding of ordinary grinding wheel.
Answer: Precision grinding refers to selecting a fine-grained grinding wheel on a precision grinding machine, and by finely dressing the grinding wheel, the abrasive grains have micro-edge and contour properties. The grinding marks are extremely fine, the residual height is extremely small, and the effect of the non-spark grinding stage is added, and the surface grinding method with the machining accuracy of 1 to 0.1 mm and the surface roughness Ra of 0.2 to 0.025 mm is obtained.
Selection principle of grinding wheel in precision grinding of ordinary grinding wheel:
(1) The abrasive of the grinding wheel used in precision grinding is based on the principle of being easy to generate and maintain the micro-edge and its contour.
(2) Grinding wheel particle size? Considering geometric factors alone, the finer the grinding wheel particle size, the smaller the surface roughness value of grinding. However, when the abrasive particles are too fine, not only will the grinding wheel be easily blocked by grinding debris, but if the thermal conductivity is not good, it will cause burns and other phenomena on the machined surface, which will increase the surface roughness value. .
(3) Grinding wheel binder? Grinding wheel binders include resins, metals, ceramics, etc., and resins are widely used. For coarse-grained grinding wheels, a vitrified bond can be used. Metal and ceramic binders are an important aspect of research in the field of precision grinding.
13. What are the characteristics of precision grinding with superabrasive grinding wheels? How to choose the grinding amount?
Answer: The main characteristics of superabrasive grinding wheel grinding are:
(1) It can be used to process various high hardness and high brittleness metal and non-metal materials.
(2) Strong grinding ability, good wear resistance, high durability, can maintain grinding performance for a long time, less dressing times, easy to maintain particle size; easy to control processing size and realize processing automation.
(3) The grinding force is small and the grinding temperature is low, so that the internal stress can be reduced, there are no defects such as burns and cracks, and the machined surface quality is good. When diamond grinding wheel grinds cemented carbide, its grinding force is only 1/4 to 1/5 of green silicon carbide.
(4) High grinding efficiency. When machining hard alloys and non-metallic hard and brittle materials, the metal removal rate of diamond grinding wheels is better than that of cubic boron nitride grinding wheels; but when machining heat-resistant steel, titanium alloys, die steel and other materials, cubic boron nitride grinding wheels are much higher on diamond grinding wheel
(5) The processing cost is low. Diamond grinding wheel and cubic boron nitride grinding wheel are more expensive, but they have long service life and high processing efficiency, so the overall cost is low.
Superabrasive grinding wheel grinding dosage selection:
(1) Grinding speed The grinding speed of non-metal bond diamond grinding wheel is generally 12 ~ 30m/s. The grinding speed of the cubic boron nitride grinding wheel can be much higher than that of the diamond grinding wheel, and the optional 45-60m/s is mainly due to the better thermal stability of the cubic boron nitride abrasive.
(2) The grinding depth is generally 0.001 to 0.01 mm, which can be selected according to the grinding method, abrasive particle size, binder and cooling conditions.
(3) The workpiece speed is generally 10-20m/min.
(4) Longitudinal feed speed? Generally 0.45 ~ 1.5m/min.
14. What is ultra-precision grinding? Try to briefly describe its mechanism, characteristics and application.
Answer: Ultra-precision grinding refers to a grinding wheel grinding method with a machining accuracy of less than 0.1mm and a surface roughness of less than Ra0.025mm. , Iron materials, ceramics, glass and other hard and brittle materials processing.
Ultra-precision grinding mechanism:
(1) Abrasive particles can be regarded as an elastic body with elastic support and a large negative rake angle cutting edge. The elastic support is a binding agent. Although the abrasive particles have considerable hardness and their own deformation is very small, they are actually still elastomers.
(2) The cutting depth of the abrasive grain cutting edge gradually increases from zero, and then gradually decreases to zero after reaching the maximum value.
(3) The whole contact process between abrasive grains and the workpiece is followed by elastic zone, plastic zone, cutting zone, plastic zone and elastic zone.
(4) In ultra-precision grinding, micro-cutting action, plastic flow, elastic destruction action and sliding action appear in sequence according to the change of cutting conditions. When the blade is sharp and has a certain grinding depth, the micro-cutting effect is strong; if the blade is not sharp enough, or the grinding depth is too shallow, plastic flow, elastic damage and sliding will occur.
Features of Ultra Precision Grinding:
(1) Ultra-precision grinding is a systematic project.
(2) Superabrasive grinding wheel is the main tool for ultra-precision grinding.
(3) Ultra-precision grinding is a kind of ultra-micro cutting process.
Applications of ultra-precision grinding:
(1) Grinding of metal materials such as steel and its alloys, especially hardened steel that has been treated by quenching.
(2) Hard and brittle materials that can be used for grinding non-metals? For example, ceramics, glass, quartz, semiconductor materials, stone materials, etc.
(3) At present, there are mainly cylindrical grinders, surface grinders, internal grinders, coordinate grinders and other ultra-precision grinders, which are used for ultra-precision grinding of outer circles, planes, holes and hole systems.
(4) Ultra-precision grinding and ultra-precision free abrasive processing complement each other.
15. Briefly describe the principle and characteristics of ELID mirror grinding.
Answer: The principle of ELID mirror grinding: During the grinding process, electrolytic grinding fluid is poured between the grinding wheel and the tool electrode and a DC pulse current is applied, so that the metal bond of the grinding wheel as the anode has an anode dissolution effect and is gradually removed, so that the The abrasive grains that are not affected by electrolysis protrude from the surface of the grinding wheel. With the progress of the electrolysis process, a layer of oxide film with insulating properties is gradually formed on the surface of the grinding wheel, preventing the continuation of the electrolysis process. When the abrasive grains of the grinding wheel are worn, the passive film After being scraped off by the workpiece, the electrolysis process continues, and the cycle starts again, and the grinding wheel is continuously dressed by the action of on-line electrolysis to obtain a constant protruding height of the abrasive grains.
Features of ELID Grinding:
(1) The grinding process has good stability;
(2) This dressing method prevents the diamond grinding wheel from being worn out too quickly and improves the utilization rate of precious abrasives;
(3) ELID dressing method makes the grinding process have good controllability;
(4) Using the ELID grinding method, it is easy to achieve mirror grinding, and can greatly reduce the residual cracks of the superhard material to be ground parts.
16. What is creep feed grinding? Try the boiling heat transfer theory to explain the phenomenon that the normal slow grinding temperature is very low but it is easy to burn suddenly.
Answer: Creep Feed Grinding has many names in China in the past, such as strong grinding, heavy load grinding, creep grinding, milling, etc. The current exact name should be Creep Feed Deep Cutting Grinding Grinding, usually referred to as slow grinding. The distinctive feature of this process is the low feed rate, which is about 10-3 to 10-2 times that of ordinary grinding. For example, the workpiece speed can be as low as 0.2mm/s during surface grinding, so it is called “slow” grinding. But on the other hand, the primary depth of cut is large, about 100 to 1000 times that of ordinary grinding. For example, the limit depth of cut in flat grinding can reach 20 to 30 mm.
According to the theory of boiling heat transfer in the field of thermal engineering, it is a scientific explanation for the normal slow grinding temperature is very low but it is often prone to sudden burns. During slow grinding, the heating conditions of the surface of the workpiece in the arc zone and the surface of the heated nickel wire immersed in the pool are essentially the same, and the grinding fluid in the arc zone also has a critical heat flux density qlim that can cause film boiling. Grinding refers to grinding heat flux q <> 120~130℃.
That is to say, no matter how large the cutting depth is during slow grinding, whether it is 1mm, 10mm, 20mm or 30mm, as long as the normal slow grinding conditions are met, the surface temperature of the workpiece in the arc area will not exceed 120 ~ 130 ℃, which is also the reason that the slow grinding process is different. Advantages over ordinary grinding. However, this outstanding technological advantage of slow grinding is actually easily lost due to the runaway heat flux density. The grinding heat flow density q is not only related to many factors such as material properties and cutting amount, but also depends on the sharpness of the grinding wheel surface. As long as the condition q ≥ qlim is met, the surface of the workpiece in the arc area will be burnt suddenly due to the grinding fluid entering the film-forming boiling state. .
17. How to carry out continuous dressing in creep feed grinding? What are the advantages of continuous dressing?
Answer: The so-called continuous dressing refers to the method of reshaping and sharpening the grinding wheel while grinding. With the continuous dressing method, the diamond dressing rollers are always in contact with the grinding wheel. In order to realize the dynamic process of continuous dressing grinding wheel and continuous compensation in the grinding process, a special continuous dressing grinding machine must be used. The dynamic process of continuous dressing is shown in Figure 2. The initial grinding wheel diameter is ds1, the workpiece diameter is dw1, and the diameter of the diamond dressing roller is dr. During grinding, if the workpiece radius decreases at the speed of vfr, due to continuous dressing, The grinding wheel should cut into the grinding workpiece at the speed of v2 = vfr + vfrd, and the dressing roller should cut into the dressing grinding wheel at the speed of v1 = 2vfrd + vfr, so that the position of the dressing roller and the grinding wheel has changed. Therefore, grinding machines for continuous dressing of grinding wheels must be able to make relevant adjustments to these geometrical parameters.
The advantages of continuous trimming are many, such as:
1) The grinding time, which is just equal to the dressing time, is subtracted, which improves the grinding efficiency;
2) The longest grinding length no longer depends on the wear of the grinding wheel, but on the available grinding length of the grinding machine;
3) The specific grinding energy is reduced, the grinding force and grinding heat are reduced, and the grinding process is stable.
18. What is belt grinding? Briefly describe the composition and characteristics of the abrasive belt.
Answer: Abrasive belt grinding is a process method for grinding the moving abrasive belt in contact with the workpiece in a corresponding contact manner according to the shape of the workpiece.
The abrasive belt is mainly composed of three parts: matrix, binder and abrasive. The matrix is the support for abrasive grains and can be made of paper, cotton and chemical fibers. Commonly used binders include animal glue, synthetic resin and a combination of the two. Commonly used binders include animal glue, synthetic resin and a combination of the two. Animal glue has low heat resistance, low bonding strength, and is not resistant to erosion by cutting fluid, so it can only be used for dry grinding; synthetic resin binder has high bonding strength and high wear resistance, suitable for manufacturing high-speed Heavy duty belts. The abrasives for making abrasive belts are standard corundum, white and chromium-containing corundum, single crystal corundum, aluminum oxide, zirconium dioxide, green and black silicon carbide, etc.
19. What are the classification methods of abrasive belt grinding? What problems are prone to occur in belt grinding?
Answer: According to the grinding method, abrasive belt grinding can be divided into closed abrasive belt grinding and open abrasive belt grinding. Abrasive belt grinding can be divided into contact wheel type, support plate type, free contact type and free floating contact type according to the contact form between the abrasive belt and the workpiece.
Problems that are prone to occur in abrasive belt grinding: clogging, sticking, and blunting. In addition, the abrasive belt often appears frequent fractures, wear marks and other phenomena during use.
20. What is ultrasonic vibration grinding? Briefly describe the mechanism and characteristics of ultrasonic vibration grinding.
Answer: Ultrasonic grinding is a process method that uses the forced vibration of the grinding wheel (or workpiece) in the grinding process.
The mechanism of ultrasonic vibration grinding: when the magnetizing power source of the ultrasonic generator is started, a certain ultrasonic frequency current and a DC current for magnetization are supplied to the nickel magnetostrictive transducer, and an alternating ultrasonic frequency magnetic field and magnetic field are generated in the transducer coil. The constant polarized magnetic field enables the transducer to generate longitudinal mechanical vibration energy of the same frequency, which is transmitted to the horn at the same time, and the amplitude is amplified to a predetermined value to push the resonant cutter bar for vibration cutting. The transducer, horn, and cutter rod are all in resonance with the ultrasonic frequency output by the generator, forming a resonance system, and the fixed point should be on the displacement node.
Features: Ultrasonic grinding can keep the abrasive grains sharp and prevent chip blocking. Generally, the cutting force is reduced by 30% to 60% compared with ordinary grinding, the cutting temperature is reduced, and the processing efficiency is increased by 1 to 4 times. In addition, ultrasonic vibration grinding also has the advantages of compact structure, low cost, and easy popularization and application.
Post time: Jul-30-2022