Performance and application of the hottest silicon

Performance and application of silicon nitride ceramic tools

silicon nitride (Si3N4) ceramic tools have high wear resistance and red hardness, which can carry out high-speed cutting, reduce the number of tool changes and reduce the dimensional error caused by tool wear. The application in CNC machine tools and machining centers has more obvious advantages, which can greatly improve production efficiency and product quality

2. Cutting performance of silicon nitride ceramic tools

(1) high hardness? The room temperature hardness of silicon nitride ceramic blade has exceeded that of the best cemented carbide blade, reaching 92.5 ~ 94hra, which greatly improves its cutting ability and wear resistance. It can process all kinds of hardened steel and hardened cast iron with hardness up to 65hrc, which can save the power consumed by annealing. Its excellent wear resistance not only extends the cutting life of the tool, but also reduces the number of tool changes in machining, so as to ensure the small taper and high precision when cutting the workpiece, especially when it is used for high-precision continuous machining of CNC machine tools, it can reduce the tool setting error and the unpredictable error caused by wear, and simplify the tool error compensation

(2) high intensity? At present, the bending strength of silicon nitride ceramic blade has reached 750 ~ 1000MPa, which exceeds that of high-speed steel and is equivalent to that of ordinary cemented carbide

(3) good high temperature oxidation resistance? Silicon nitride ceramic blade has particularly good heat resistance and high-temperature oxidation resistance. Even when cutting at 1200 ~ 1450 ℃, it can still maintain a certain hardness and strength for long-time cutting. Therefore, it is allowed to use a cutting speed much higher than that of cemented carbide tools to achieve high-speed cutting. Its cutting speed is 3 ~ 10 times higher than that of cemented carbide tools, so it can greatly improve the production efficiency. Experiments show that Si3N4 ceramics has the best heat resistance among many ceramic materials

(4) good fracture toughness? Fracture toughness is one of the important indexes to evaluate the damage resistance of ceramic blades, which is related to the composition, structure, process and other factors of materials. As a joint venture between CVC investment company and royal DSM of the Netherlands, the fracture toughness of Si3N4 series ceramic blades is better than that of other series ceramic blades (up to 6 ~ 7mpam1/2), which is close to cemented carbide blades of some brands. Therefore, it has good impact resistance, especially in milling, planing, boring and other intermittent cutting, which can show its advantages

(5) strong thermal shock resistance? Thermal shock resistance of ceramic materials is an important index to evaluate their damage resistance when they are subjected to sharp temperature changes. Si3N4 series ceramic blades have high strength, low coefficient of thermal expansion, thermal shock resistance index △ t as high as 600 ~ 800 ℃, which is obviously superior to other series of ceramic blades (300 ~ 400 ℃), so they show unique superior performance in the blank processing of high-strength intermittent parts

3. Practical application of silicon nitride ceramic tools? Although the research level of ceramic cutting tools in China is no worse than that in foreign countries, the practical application development is slow. According to relevant information, at present, the proportion of domestic ceramic cutting tools in the total use of cutting tools is no more than 1%. Silicon nitride ceramic cutting tool is a new type of cutting tool that has been widely used in production in recent years. Therefore, there is a lack of mature experience in terms of geometric parameters, cutting parameters and application technology of cutting tools. The practical application of ceramic cutting tools is a systematic project that needs to integrate all aspects of technology. It is by no means a problem that can be solved as long as you buy ceramic cutting tools and replace them. In addition, the physicochemical properties and cutting performance of ceramic tools are quite different from those of ordinary tools. Therefore, the following aspects must be considered in application

3.1 requirements for machine tools? Ceramic tool materials are sensitive to impact and vibration loads, which is the biggest weakness of ceramic tool materials in impact and vibration resistance. Machine tool? Workpiece? The weak rigidity of the cutting tool process system is the main reason for the reduction of the service life of ceramic cutting tools or the edge collapse. In addition to the rigidity factors of the workpiece and the tool itself, the smaller the rigidity of the machine tool, the greater the vibration and the lower the service life of the tool. In particular, when analyzing the rigidity of machine tools, we must comprehensively consider the machine tools? Workpiece? The rigidity of the tool process system, rather than considering the rigidity of the machine tool in isolation, must also consider the rigidity of the workpiece, fixture, center and tool

the insufficient rigidity of any link will greatly reduce the cutting performance and efficiency of ceramic tools. Practice has proved that machine tools suitable for machining ceramic tools must have good rigidity, sufficient power and high revolutions.? By analyzing the current situation of domestic machine tools, it can be seen that these three aspects of medium-sized machine tools basically meet the requirements in precision and semi precision machining. For the processing of hard to machine materials such as hardened steel or hard nickel cast iron, due to the low cutting speed, even if the ceramic tool is used for processing, its power is sufficient, but it is often not easy to meet these three aspects in the rough machining of ordinary steel or cast iron. The other heavy-duty machine tool in Arkansas has good rigidity and sufficient speed and power. As long as it is used properly, the success rate of using ceramic tools is often high in the processing of 37% of the global products consumed by heavy-duty workpieces

3.2 requirements for machined parts

(1) although ceramic cutting tools can carry out rough cutting processing for most castings and forgings without annealing, the serious sand inclusion and sand holes on the rough of hard castings will cause many unnecessary cutting and increase the consumption of ceramic cutting tools. If the blank can be properly treated before cutting, such as cleaning and correcting the defective part with a hand grinding wheel before cutting, a better machining effect will be obtained

(2) any rough edge of a high-speed rotating high-hardness blank may damage the ceramic tool, but cutting from a rounded blank can be stable for a long time. Therefore, for those rough embryos with high hardness and irregular shape, attention should be paid to chamfering first and then cutting with ceramic tools. The chamfering of the blank cut-in can prevent the ceramic tool from bearing excessive impact load when it just contacts the workpiece. The chamfering of the blank cut-out is mainly to avoid the damage of a circle of material edges left when the ceramic tool cuts away from the part

(3) the condition of the machine tool and the processed parts should be matched to avoid the phenomenon of "small horse pulling the cart"

3.3 selection of reasonable geometric parameters of silicon nitride ceramic tools? Although silicon nitride ceramic tool is a kind of cutting tool with excellent cutting performance, if its geometric parameters cannot be reasonably selected in use, it still cannot play its role well. The so-called reasonable geometric parameters of the tool refer to the geometric parameters of the tool that can ensure that the rough machining or semi finishing tool has a higher productivity and tool life, and the finishing tool can ensure that the workpiece that meets the predetermined dimensional accuracy and surface quality can be processed, and also has a higher tool life.? When choosing the reasonable geometric parameters of ceramic cutting tools, we must consider not only the general rules of cutting tools, but also some special rules of ceramic cutting tools. Silicon nitride ceramic cutting tool is a kind of hard and brittle cutting tool. How to ensure its stability and reliability and prevent blade collapse is still the main basis for selecting reasonable geometric parameters of silicon nitride ceramic cutting tool; The structure of silicon nitride ceramic tool is mainly machine clamp indexable tool, so we must consider the selection of reasonable geometric parameters in combination with its structural characteristics

3.4 reasonable selection of cutting parameters? Reasonable selection of cutting parameters is one of the basic problems to give full play to the cutting performance of ceramic tools. Cutting parameters directly affect machining productivity, machining cost, machining quality and tool life. Because ceramic cutting tools have the advantages of high hardness, good wear resistance, high heat resistance, high brittleness and low strength, these characteristics must be fully considered to select the appropriate cutting parameters in order to improve productivity and ensure processing quality

(1) selection of cutting depth AP? When machining with ceramic tools, in order to shorten the processing time, a larger cutting depth should be selected as far as possible, so that most of the allowance can be cut off after one cutting. Because the cutting depth is limited by the machine power and the rigidity of the process system, the maximum allowable cutting depth is 2 ~ 6mm when roughing steel and cast iron, usually ap>1.5mm; Take AP during finish machining