Ceramic tool materials are an important area for future development and will be one of the most important tool materials in the 21st century. At present, there are nearly 40 varieties of ceramic tool materials with Al 2 O 3 based, Si 3 N 4 based and ceramic coated knives in the international market. The promotion and application are increasingly widespread, and there are only more than 20 varieties in China. The total output is less than 1% for the machining of difficult-to-machine materials, large castings and steel parts that cannot be processed with cemented carbide. Therefore, the research and development and application of ceramic tools are still quite different from those in foreign countries. This article mainly introduces the author's research on the basic theory of ceramic tool cutting under the support of the National Natural Science Foundation of China, and successfully developed a variety of new ceramic tool materials, and promoted its new progress and achievements in the international advanced ranks.
1 New progress in ceramic tool research
- The establishment of ceramic cutter damage theory
- Ceramic cutter damage type and damage form
- The main form of tool damage during intermittent cutting of ceramic tools is damage. There are two types of damage in the early and late stages of the tool. Early damage is the damage that occurs when the number of general impacts is about 10 3 times after the start of cutting or short cutting. At this time, the front and rear flank surfaces have not produced significant wear, generally VB <0.1 mm. This type of breakage occurs most often when ceramic tools cut high-hardness materials or interrupted cutting. The main reason is that the stress caused by mechanical shock exceeds the allowable strength of the tool material, causing brittle fracture.
- The late damage of the ceramic tool is the damage caused by the impact, mechanical fatigue and thermal fatigue of the tool material after a certain time of processing. Both the early and late forms of damage are characterized by brittle fracture. The brittle fracture of ceramic knives mainly includes chipping, spalling, breaking and cracking, and ceramic cutters have less plastic damage.
- Damage rule and damage life of ceramic cutters
- The damage of ceramic cutters is a typical random phenomenon, which must be studied by probability theory and mathematical statistics. Large-scale experiments show that the damage law of ceramic tools is subject to Weibull distribution during intermittent turning, while the end milling is subject to lognormal distribution (or approximately Weibull distribution). When the brittle ceramic tool is cut intermittently, it is easy to break early. Therefore, it is impossible to determine the relationship between wear life and cutting conditions of ceramic cutters during intermittent cutting according to the traditional Taylor formula. The relationship between damage life and cutting conditions should be determined according to the damage distribution law of the tool. The mean value of Weibull or lognormal parameters is estimated by mathematical statistics based on experimental data to assess the damage life of ceramic tools. The relationship between the damage life and the cutting conditions can be obtained by testing under different cutting conditions.
- Establishment of Damage Criterion for Fracture Mechanics Random Characteristics of Ceramic Tools
- The main reason for the late damage of the ceramic tool is the crack or crack-like instability existing inside the impact cycle load. Due to the randomness of cracks and other defects in the ceramic tool and the complexity of the cutting process, the damage has random characteristics. Therefore, it is more practical to establish the late damage criterion of ceramic tools based on fracture mechanics and probability statistics. According to the fracture mechanics of the fracture mechanics and the crack growth rate, as well as the bending strength of the ceramic tool material and the random distribution characteristics of the crack, the theoretical damage probability of the ceramic tool under different damage life can be established.
- The main form of tool damage during intermittent cutting of ceramic tools is damage. There are two types of damage in the early and late stages of the tool. Early damage is the damage that occurs when the number of general impacts is about 10 3 times after the start of cutting or short cutting. At this time, the front and rear flank surfaces have not produced significant wear, generally VB <0.1 mm. This type of breakage occurs most often when ceramic tools cut high-hardness materials or interrupted cutting. The main reason is that the stress caused by mechanical shock exceeds the allowable strength of the tool material, causing brittle fracture.
- Wear characteristics and wear mechanism of ceramic tools
- The wear characteristics and wear mechanism of SiC whisker toughened alumina ceramic tools were studied in depth. Studies have shown that the orientation of SiC W has a significant effect on the wear resistance of ceramic tools. The plane wear resistance of the SiC W parallel hot pressing axis is better than that of the plane perpendicular to the hot pressing axis. SiC W is oxidized during wear and accelerates wear. The plane in the direction of the parallel hot pressing axis is less affected by oxidation, but the fracture toughness of the plane in the direction of the vertical hot pressing is larger than the plane in the direction of the parallel hot pressing axis. The friction surface is mainly caused by the plastic deformation of the crystal grains, the mechanical friction furrow, and the surface defects caused by the oxidative detachment of SiC W , causing the brittle fracture of the matrix grains to cause wear. The test analysis shows that the Al 2 O 3 matrix has a crystal orientation during hot pressing, and the dense surface of the Al 2 O 3 crystal has a tendency to face the hot pressing surface of the test piece, so the performance is lower than the surface perpendicular thereto.
- The results show that K IC 3â„4 ·H 1â„2 (H is the hardness of the ceramic tool) and the cutting temperature can be used to evaluate the wear resistance of the knives and knives of the ceramic tool, that is, at the same temperature, the smaller the value, the resistance The higher the grinding performance.
- Establish a new method for reliability evaluation of ceramic tools
- The reliability of ceramic tools is a key issue in practical applications. The reliability of the tool has both a certain number of characteristics and a random nature. Reliability is often used as an indicator of tool reliability. The so-called tool reliability refers to the probability that the tool will complete the determined cutting work within the time specified under the specified conditions, that is, the probability that the tool will not be damaged, and is usually expressed by R(t). The main cause of tool damage is wear and tear and the two interact.
- A large number of test results show that for a certain ceramic tool material, the wear life coefficient of variation C S (the ratio of the variance of the sample tool wear life to its mean value) is almost constant. Therefore, C S can be used to evaluate its wear reliability.
- For a certain ceramic tool material, the shape parameter m of the flexural strength Weibull distribution can be used to evaluate the damage reliability under the actual cutting conditions of the ceramic tool. For whisker toughened ceramic tools, K IC , s b and H can be used to evaluate the damage reliability. However, since the interface bonding strength and the microstructure of the material have a more direct and direct relationship, the interface bonding strength is used as an index to evaluate the reliability of the ceramic tool damage, and the reliability of the tool damage and the quality control of the tool material can be predicted. According to the toughening mechanism of whisker toughened ceramic tool materials, the interface bonding strength formula can be derived.
2 Establish a new research system for ceramic tools and accelerate the development of new ceramic tools
- Establish a new research system for ceramic knives and embark on the international advanced
- The most prominent problem with ceramic knives is the excellent cutting performance, that is, the high resistance to wear and breakage, and the high reliability. It is closely related to the composition of the material, the manufacturing process, the microstructure and its physical and mechanical properties. We have studied the effects of the microstructure and mechanical properties of ceramic tool materials on their cutting performance and cutting reliability, which is confirmed. Therefore, it is possible to establish a new ceramic tool research system (see Fig. 1) that integrates ceramic tool cutting and tool material development with the goal of high cutting reliability, and optimizes the design of ceramic tool materials according to cutting reliability.
Figure 1 New system for ceramic tool research - Accelerate the development of advanced ceramic tools
- Based on the above ideas, based on cutting reliability for more than 10 years, we have developed 6 new series of ceramic tool materials with 12 grades. In the early 1980s, LT-55 and SG-4 (LT series) ceramic tool materials were successfully developed. In the late 1980s, SiC whisker (SiC w ) toughened alumina-based ceramic tool materials (JX series) were successfully researched. The w content, according to the principle of thermal expansion mismatch, analyzes the best matching of SiC w , which should be ensured that the load is effectively transmitted to the whiskers through the interface, and the interface is prior to the brittle fracture of the matrix.
- In the mid-1990s, titanium boride TiB 2 reinforced alumina-based ceramic tool materials (LP series) were successfully added. On the condition that the radial residual stress produces a crack that does not penetrate, it is found that the volume fraction of TiB 2 in the Al 2 O 3 /TiB 2 material is 44.5% (limit amount). On this basis, the synergistic effect of whisker toughening and particle reinforcement mechanism is further studied. According to the theory of energy dissipation, the theoretical model of whisker bridging, extraction and crack deflection toughening and the theoretical model of particle crack deflection and microcrack zone are established. Based on this, the addition of SiC w in Al 2 O 3 /TiB 2 and the addition of SiC p particles in Al 2 O 3 /SiC w respectively constitute a new three-phase ceramic tool material. With the deepening of the research on toughening and strengthening mechanism, we have studied the purpose of adding special powder to form very fine cracks to toughen ceramic tool materials, and some rare earth elements can clean the surface and improve the interface bonding strength in multiphase ceramics. The mechanism of activation sintering and particle strengthening to improve the mechanical properties of multiphase ceramic tool materials has successfully developed LD series ceramic tool materials with some special powders and rare earths.
- The thermal conductivity and tensile strength of ceramic tool materials are low. If the composition distribution of ceramic tool materials is designed according to thermal conductivity and stress distribution, the surface layer has the maximum thermal conductivity, which is beneficial to the rapid transfer of cutting heat, and the surface layer has The minimum coefficient of thermal expansion is such that the compressive stress is formed during the hot pressing of the material to counteract the tensile stress of the cutting process, that is, the composition of the material to form a gradient distribution. Based on this concept, a new graded functional ceramic tool material (FG series) has recently been developed, which has been proven to be superior in cutting performance to non-gradient-distributed ceramic tools.
- The biggest weakness of ceramic tools is that the bending strength is still low. If the composite blade form is adopted, the high-hardness Al 2 O 3 -based multiphase ceramic material is selected as the wear-resistant phase, and the cemented carbide with high strength and high elastic modulus is used as the base material, and the ceramic/hard is made by hot pressing. Alloy composite inserts (FH1-1 and FH1-2). Among them, FH1-1 is single-sided ceramic, FH1-2 is double-sided ceramic, and the middle is hard alloy. The equivalent bending strength of the two is 20% higher than that of similar ceramic blades, and the fracture toughness is increased by 8.5% on average. The production trial results show that the tool life is increased by 20% to 30%, and the resistance to breakage is increased. The performance and use of the new ceramic tools we have developed so far are shown in Table 1. These tool materials not only fill the domestic gap, but also JX-2, LP-2, LD-1, FG and FH have not been reported abroad.
Table 1 Physical and mechanical properties of new ceramic tool materials Brand density
(g/cm 3 )hardness
(HRA)Bending strength
(MPa)Fracture toughness
(Mpa·m 1â„2 )use SG-4 6.65 94.7~95.3 850 4.94 Processing all kinds of steel and cast iron, especially suitable for processing hardened steel (HRC60～65) JX-1 3.63 94 to 95 700～800 8.5 Suitable for processing high temperature nickel based alloys JX-2 3.73 93~94 650～750 8.0~8.5 Most suitable for processing pure nickel and high nickel alloys LP-1 4.08 94 to 95 800～900 5.2 Suitable for processing all kinds of steel and cast iron LP-2 3.94 94 to 95 700～800 7~8 Suitable for processing nickel-based superalloys LD-1 4.95 93~94 >750 5.8~6.6 Suitable for interrupted cutting of various steel and cast iron LD-2 6.51 93.5~94.5 700～860 5.8~6.5 Suitable for interrupted cutting of various steel and cast iron FG-1 4.46 94 to 95 700～800 9.0 Suitable for processing ultra high strength steel and high hardness cast iron FG-2 6.08 94.7~95.3 700～800 8.4 Particularly suitable for processing hardened steel FH1-1 complex 94 to 95 800~1000 5.3~5.8 Processing hardened steel FH1-2 blade 94 to 95 800~1000 5.3~5.8 Suitable for interrupted cutting of steel and cast iron (including hardened steel) - Strive to do a good job of transforming results and achieve practical benefits
- Applied basic research must not stop at the publication of the paper, and should strive to be transformed into new technologies and products. After completing the fund-funded projects, we also won the support of the National Natural Science Foundation of China, relevant departments and factories in Shandong Province, batch trial production and testing, and sent to the factory to use the test and verification, continue to improve and improve, while expanding the impact and strive for users. Six varieties of 12 ceramic tools are available in the product range. Among them, JX-2 processing a rocket's electroformed pure nickel parts has a long tool life and is praised by the workers as a "sword". The SG series SG-4 and FG series FG-2 and FH1 series ceramic tools are the best ceramic tools for machining hardened steel (HRC60～65) in China.
- Based on the above ideas, based on cutting reliability for more than 10 years, we have developed 6 new series of ceramic tool materials with 12 grades. In the early 1980s, LT-55 and SG-4 (LT series) ceramic tool materials were successfully developed. In the late 1980s, SiC whisker (SiC w ) toughened alumina-based ceramic tool materials (JX series) were successfully researched. The w content, according to the principle of thermal expansion mismatch, analyzes the best matching of SiC w , which should be ensured that the load is effectively transmitted to the whiskers through the interface, and the interface is prior to the brittle fracture of the matrix.
This 800W Grow Light is a great replacement for hps grow light with full spectrum, can more effectively promote the growth and development of plants. The lights are with dimming function, allowing growers to adjust light intensity according to the plant's growth cycle. And it's with RJ port, can be connected by smart controller, and controlled by it. If with controller, we can adjust lighting intensity, stimulate sunrise and sunset, and also control temperature and humidity to make the plant better adapted to different environments. The controller is sold separately. Welcome to contact us for more details.
Hydroponic Lights,Hid Grow Lights,Hps Grow Lights,Greenhouse Lights, Grow Light 800W 1200w
GuangDong One World High-tech Co., Ltd. , https://www.mkdlights.com