Ceramic cutting tools have the characteristics of high hardness, good wear resistance, strong chemical stability, anti-adhesion and high temperature mechanical properties. In the past 30 years, the research progress of ceramic cutting tools has accelerated, and the strength, toughness and impact resistance of ceramic cutting tools have been greatly improved. Therefore, processing of high-temperature alloys has received more and more attention.
(1) Types of ceramic tools
Ceramic tool materials mainly include alumina (Al2O3), silicon nitride (Si3N4) and Sialon series. Other ceramic materials, such as zirconia and titanium boride ceramics, are also used as tool materials.
Alumina-based ceramic knives: Mainly used in the late 1950s, the material is made of pure Al2O3 ceramics or Al2O3 and a small amount of glass oxides TiO2, Cr2O3, MgO, etc. are added. The addition of oxides is mainly to avoid excessive grain growth;
Silicon nitride-based ceramic tools: The main ceramic tools in the late 1970s and early 1980s, among which Si3N4-TiC-Co composite ceramics have the best performance;
Sialon ceramic tool: Sialon tool is a single-phase ceramic tool successfully developed by LucasAyMon Company in the United Kingdom. It uses Si3N4 as the hard phase, Al2O3 as the wear-resistant phase, and adds a small amount of sintering aid Y2O3, which is sintered by hot pressing. . Used extensively from the late 1980s to the 1990s.
(2) Ceramic knives are divided into three types according to their manufacturing methods;
Cold pressing method, this method has high productivity, low cost, low blade price, and low strength and toughness;
The hot pressing method has high product strength and toughness, but has low productivity and high cost, and the internal crystal grains of the material are directional;
The hot isostatic pressing method has high productivity and good quality, but the equipment is expensive and the cost is high.
(3) Performance of ceramic cutting tools
Has good high temperature performance. The hot-pressed alumina composite ceramic with a hardness of HRC95 at normal temperature has HRA87 at 760°C, HRA85 (equivalent to HRC67) at 900°C, and HRA80 at 1200°C. at such high temperatures. Ceramic tools still have cutting performance. The flexural strength of ceramic blades changes very little below 1100°C. The bending strength of cemented carbide at room temperature is 2-3 times that of ceramic tools, but at a high temperature of 1000°C, it is only 1.5 times that of ceramics;
Good chemical stability and strong anti-adhesion ability. The chemical inertness of ceramics is better than that of tungsten carbide, titanium carbide and diamond. Even in the molten state, it will not react with high-temperature alloys. Therefore, diffusion wear is small during cutting. Chemical inertness makes the affinity between the ceramic tool and the material being processed small, making it less likely to bond, reducing the bonding wear of the tool. Another manifestation of chemical inertness is that ceramics have strong oxidation resistance, and the corresponding oxidation wear is small.
Low coefficient of friction. The friction coefficient is low, which reduces the cutting force and is less likely to produce built-up edges, improving the surface quality of the machine.
Good abrasion resistance. Due to the high hardness of ceramic cutting tools themselves, coupled with good high-temperature performance and chemical stability, the wear resistance of ceramics is much higher than that of cemented carbide.
Ceramic knives have its unique advantages, but they also have their shortcomings. In order to take advantage of their strengths and avoid weaknesses, you should pay attention to the following two issues when using them.
The main disadvantages of ceramic cutting tools are low bending strength, poor toughness, and easy chipping. In order to avoid edge chipping, the first thing to do is to reduce the vibration of the machine tool tool system as much as possible. Secondly, the geometric angle of the tool must be correctly selected, especially the selection of the rake angle is the key to using ceramic tools. Generally, the rake angle is 0° or a negative number. In addition, the tool tip angle and tool tip arc radius should be increased. Before using ceramic tools in production, there should be a trial period to select reasonable tool geometry parameters and cutting amounts. Ceramic tools are sharpened with a diamond grinding wheel. After sharpening, it is best to grind them with boron carbide powder to make the cutting edge have a small arc. No chips are allowed on the cutting edge. Tiny chips are often the main cause of chipping. When using ceramic tools for cutting, a relatively high cutting speed should be selected, not only to improve productivity, but also to facilitate cutting.
(4) Examples of selection of ceramic cutting tools
Geometric parameters of Si3N4-based ceramic tools and alumina-based ceramic tools when turning Inconel718: rake angle -5°, relief angle 6°, edge inclination angle 15°, tool nose arc radius 0.8mm, feed rate: 0.19mm/r, Cutting depth: 0.5mm, cutting speed up to 500m/min, water-based cooling, cooling speed: 4L/min. The relationship between Si3N4-based ceramic tools and Al2O3-based ceramic tools when turning Inconel718 is very similar, but the wear amount of alumina-based ceramic tools is larger than that of Si3N4-based ceramic tools. This shows that Si3N4-based ceramic tools are more suitable for processing Inconel718.
SiC (20%) whisker toughened ceramic tool (CC760) indexable insert SNGN120712T01020 is used when turning Inconel718 (GH4169) workpiece. The main deflection angle is 45°, the rake angle is -6°, the edge inclination angle is 0°, and the tool tip arc radius is 1.2mm. The cutting depth is 1.5mm, the cutting speed can reach 530m/min, and the feed rate is 0.05-0.22mm/r. When processing nickel-based superalloys with whisker-toughened ceramic tools, reasonable cutting parameters should be selected based on their hardness. Whisker toughened ceramic tools can bore holes with a diameter of 87-800mm on nickel-based superalloys at a cutting speed of 100-200m/min and a feed rate of 0.5-0.7mm/r, which is faster than ordinary carbide tools Cutting speeds are 5 times faster, while feed rates are 2 times faster.
The physical and mechanical properties of the SiC whisker-toughened Al2O3 ceramic tool JX-1 (Al2O3-SiCw) developed in my country have reached the advanced level of similar foreign products. A large number of experiments and research have shown that the JX-1 type SiC whisker-toughened Al2O3 ceramic The tool is one of the ideal tool materials for high-speed cutting (cutting speed >180m/min) for processing nickel-based high-temperature alloys.
Diamond tools and cubic boron nitride tools are both superhard tool materials. Since diamond has a strong chemical affinity with iron, nickel, etc., as the temperature increases, diamond (carbon) diffuses into iron, dissolves in iron, and forms cementite. Therefore, diamond is not suitable for processing iron-based and nickel-based high-temperature alloys. . Only cubic boron nitride tools are introduced here. In addition, since high-temperature alloys tend to have affinity with coating materials, coated blades are generally not suitable for processing high-temperature alloys.
Cubic boron nitride (CBN) is a superhard material that was developed rapidly in the 1970s to meet the needs of processing difficult-to-machine materials and precision processing. CBN’s hardness is close to diamond, while its thermal stability and chemical inertness are better than other tool materials. CBN tools have achieved significant technical and economic results in processing high-temperature alloys. The proportion of CNB in tool materials is increasing year by year, and its application scope is also expanding.
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 2001 with a registered capital of 16.8 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
==========================================
www.antonmetal.com
ANTON METAL｜ Your specialty metals manufacturer
Email: dominic@antonmetal.com
Phone: +8613132148618(wechat/whatsapp)
Post time: Sep-02-2023
