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Case | difficult to process materials, but requires high surface finish, how to solve?

The landing gear is an appendage for the aircraft that is used for takeoff and landing or on the ground and is used for ground movement. The aircraft bears a great impact during takeoff and landing. Therefore, the relevant parts of the landing gear are specially treated difficult materials and are poorly processed. Its materials are usually stainless steel deposition hardening stainless steel, alloy steel (40Cr), titanium alloy and so on, and the processed state is also tempered and even quenching, the component hardness reaches the hrc50-60 degree. With this difficult processing materials, high performance requirements for tool wear, what is more important in the processing of parts at the same time can have a good surface finish, which requires the blades must have sharp blade tip, but in sharp blade edge and wear resistance in this is contradictory, the requirement for cutting tool design is a huge challenge.

Application of super hard knife

  • 1. Artificial polycrystalline diamond knife and its application:Natural diamond is the hardest material in nature. It is converted into diamond by high temperature and high pressure caused by the changes of earth and crust. Synthetic diamond is made according to the same principle. The polycrystalline diamond composite is composed of polycrystalline diamond and hard alloy matrix. Hard alloy matrix is to make the hardest diamond and the softer carbon steel cutter body has a moderate transition layer, so as to cut the pressure transfer and welding. Although the diamond is of the highest hardness of the material in nature, can be used for processing high hardness of cemented carbide, ceramics, glass and other materials, but because of its chemical affinity and steel material have, thus is widely used in the processing of various non-ferrous metals and non-metallic materials.
  • 2. Cubic boron nitride knife and its application:The hardness and wear resistance of cubic boron nitride is second only to diamond. It is a polycrystalline material made of the same high temperature and high pressure technology of synthetic diamond. Its heat resistance and good chemical stability, during 1300 ~ 1500 ℃ can still normal cutting, and most of the metal, iron series doesn't chemistry material. Therefore, high speed cutting of high hardness of steel materials and heat-resistant alloy, the adhesion of the knife and diffusion wear small; It has good thermal conductivity, bending strength and fracture toughness between ceramic and cemented carbide. Due to a series of advantages of cubic boron nitride materials, so that it can carry out rough machining of hardened steel, chilled cast iron and semi-finishing, as well as high-speed cutting difficult-to-machine materials such as high temperature alloy, thermal spraying materials. The cubic boron nitride also can be in line with the hard alloy to meet the blade, and its bending strength can reach 1.47Gpa and can be used again and again. The cubic boron nitride knife is one of the best tools to realize the mill.
  • 3. Compound nitride ceramic knife and its application:The composite nitride ceramics is the most rich silicon in nature, and its main properties are: high hardness, good wear resistance and hardness of 93-94hra. Good heat resistance, oxidation resistance, can reach 1200 ~ 1300 ℃. The chemical reaction of silicon nitride and carbon and metal elements is small and the friction factor is low. It is proved that the cutting of steel, copper and aluminum is not sticky, and it is not easy to produce debris tumor, thus improving the machining quality of the parts. The biggest characteristic of silicon nitride ceramics is that it can be used for high speed turning, which is more obvious in the materials such as casting gray cast iron, nodular cast iron and malleable iron. The nitride ceramic knife is suitable for fine car, semi-fine car, fine milling or semi-finishing milling. It can be used for hard working materials such as aluminum alloy and high manganese steel.

With the development of knife material, the surface coating cemented carbide has been widely used. Carbide hardness and abrasion resistance is good, but the toughness is bad, can pass on the carbide cutter coated with a layer or multilayer wear good TiN, TiCN, TiAlN and Al3O2, such as the thickness of the coating is 2 ~ 18 microns, the formation of a surface coating cemented carbide, make its surface has high hardness and high wear resistance, and has strong matrix, can improve the dao of life and processing efficiency.

Above all kinds of super hard knife, each has its special characteristic. Along with the machinery, electronics, chemical industry, the rapid development of aerospace industry and the progress of science and technology, these new superhard knife will be more and more widely used in various fields of production in our country, and will bring greater economic benefits.

The problem of the precision of slender rod type tool

Slender rod - shaped tools (like drills, reamer, etc.) are widely used in machining. Because the cutting tool of cutting tool determines the shape and precision of cutting part, it is not only the key process to guarantee the performance of the tool, but also the key process to guarantee the quality of the processed parts. The improvement of the precision of slender rod type tool has always been a difficult point in tool manufacturing, because the effective part of the cutter is too long and the cutting edge of the cutter is too far away from the clamping part. By its edge are too far away from clamping part and chuck has certain gripping accuracy (generally in 0.002 0.005 mm), so before starting grinding, cutting tool edge of radial circular runout could have reached 0.005 mm - 0.01 mm (or even more). Due to grinding tool especially heavy grinding process when grinding groove, grinding force is bigger, increase the elastic deformation of cutting tool and machining process will produce a lot of problems, such as cutting tool trough asymmetry, cylindrical cutter size, blade parameters, the shape error is not in conformity with the requirements, serious when even cause tool was broken. In order to solve these problems, the problem of cutting tool precision is analyzed in order to meet the requirements of high precision and high efficiency in manufacturing.

1. Influence of machine tool on tool accuracy

The precision of the machine tool can affect the precision of the tool. The precision of the machine tool is the key to determine the precision of the tool, and the long, slender rod type cutter is no exception. Australia ANCA company produced A total of five axis CNC tool grinder, namely, X, Y, Z three axes and two axis A, C, and there is A can be used for special workpieces of loading and unloading of P axis). The precision of the shaft is very high, X, Y, Z three axis positioning accuracy can reach 0.001 mm, A, C two axis position precision can reach 0.001 °. The two shafts of the machine are vertically arranged, and different grinding wheels can be chosen for different parts of the cutting tool, and different sand wheel shafts can be selected. When it is necessary to change the grinding wheel shaft, it can be automatically replaced by the program control, and the repeatability of the two axes is very high, which can fully meet the precision requirements of the processing of long and slender rod type knives.

The detection data affects the tool accuracy. The machine is equipped with the detection device (a probe with two shapes), and the measured data is directly related to the precision of the tool. Since the degree of tightness of contact between probe and workpiece is controlled by manual, the measured data contains human error. The machining parameters of grinding wheel can be compensated and modified by detecting data and tool parameter compensation program to meet the precision requirements of the machining tool.

2. Influence of grinding wheel on tool accuracy

Tool of all parameters are determined by the relative motion of the grinding wheel and the cutting tool, as a result, the Angle of the grinding wheel, grinding wheel diameter directly participate in cutting, grinding spindle of flange length, the wear of grinding wheel and grinding wheel grain size influence the precision of the cutting tool.

3. Influence of cooling system on tool accuracy

The cooling effect of coolant on grinding area directly affects the precision of cutter. Select the cooling liquid with excellent performance and proper cooling pressure is favorable for the cooling fluid to enter the grinding zone, remove the cutting heat and chip in time, and effectively reduce the surface roughness of the cutter.

Properties of tungsten metal

As the tungsten element of important strategic materials, with its excellent properties, it is widely used in various industries of modern social economy, and we have a preliminary understanding of the nature of metal tungsten.

1. The physical properties of tungsten Tungsten belongs to the periodic table 6 cycles Ⅵ B group. The appearance of the tungsten powder for dark gray, the main physical properties is tungsten melting point, boiling point is the highest of all metals, respectively, and 5973 + 3683 + 20 k, 20 k density only in the metal and Re (rhenium), Pt (platinum), Os (osmium), the density of them at room temperature were 20.53, 21.37, and 22.5 right to m - 3. Vapor pressure is low on all metals, which is one of the main reasons for making tungsten an important strategic element.

2. Mechanical properties of tungsten The solubility of interstitial impurity carbon, nitrogen, oxygen and hydrogen in tungsten is very small, and the corresponding compounds are often precipitated out in the grain boundary, so its physical properties and mechanical properties are seriously affected.

3. Chemical properties of tungsten The chemical properties of compact tungsten are stable, and the chemical analysis electron spectroscopy (ESCA), such as Anna varens, has studied the oxidation of dense tungsten in dry air, wet air and water.

(1) in the dry air and different temperature insulation 1 h, the thickness of oxide film is different, 23 ℃ cases oxidation film thickness to 1 nm, oxidation film thickness under 100 ℃ condition for 1 nm, oxidation film thickness under 200 ℃ condition 1.6 nm, 400 ℃ ~ 500 ℃ > 10 cases oxide film thickness. This shows that in the dry air temperature is below 200 ℃, the density of tungsten is basically no oxidation. The thickness of the oxide film is 2.0nm and >10nm respectively. In dry air or wet air, the oxide film is WO3. In water and under the greenhouse for a week, the oxide film thickness is > 10nm. The components of the oxide film are WO3, WO2 and hydrated oxide. The tight tungsten can withstand almost all the acid and alkali corrosion at normal temperature, and the high temperature and oxidant can react with certain acid base.

Of course, the above information may have a slight error in different experimental conditions, but only for reference.