1. Purification method of raw materials
Because WBN, HBN, pyrophyllite, graphite, magnesium, iron and other impurities remain in CBN powder; In addition, it and the binder powder contain adsorbed oxygen, water vapor, etc., which is unfavorable to sintering. Therefore, the purification method of raw materials is one of the important links to ensure the performance of synthetic polycrystals. During the development, we used the following methods to purify the CBN micropowder and binding material: first, treat the CBN emblem powder with NaOH at about 300C to remove pyrophyllite and HBN; Then boil perchloric acid to remove graphite; Finally, use HCl to boil on the electric heating plate to remove the metal, and wash it to neutral with distilled water. Co, Ni, Al, etc. used for bonding are treated by hydrogen reduction. Then the CBN and the binder are mixed evenly according to a certain proportion and added into the graphite mold, and sent into a vacuum furnace with a pressure less than 1E2, heated at 800~1000 ° C for 1h to remove the dirt, adsorbed oxygen and water vapor on its surface, so that the CBN grain surface is very clean.
In terms of the selection and addition of bonding materials, the types of bonding agents currently used in CBN polycrystals can be summarized into three categories:
(1) Metal binders, such as Ti, Co, Ni. Cu, Cr, W and other metals or alloys, are easy to soften at high temperatures, affecting tool life;
(2) Ceramic bond, such as Al2O3, is resistant to high temperature, but has poor impact toughness, and the tool is easy to collapse and damage;
(3) Cermet bond, such as solid solution formed by carbides, nitrides, borides and Co, Ni, etc., solves the shortcomings of the above two types of bond. The total amount of binder shall be sufficient but not excessive. The experimental results show that the wear resistance and bending strength of polycrystal are closely related to the average free path (thickness of bonding phase layer), when the average free path is 0.8~1.2 μ M, the polycrystalline wear ratio is the highest, and the amount of binder is 10%~15% (mass ratio).
2. Cubic boron nitride (CBN) tool embryo can be divided into two categories
One is to put the mixture of CBN and bonding agent and cemented carbide matrix into a molybdenum cup separated by the salt carbon tube shielding layer
The other is to directly sinter the polycrystalline CBN cutter body without alloy substrate: adopt the six-sided top press, and use the side-heating assembly heating. Assemble the mixed CBN micro-powder, hold it for a certain time under a certain pressure and stability, and then slowly drop it to room temperature and then slowly unload it to normal pressure. The polycrystalline CBN knife embryo is made
3. Geometric parameters of cubic boron nitride (CBN) tool
The service life of cubic boron nitride (CBN) tool is closely related to its geometric parameters. Proper front and rear angles can improve the impact resistance of the tool. Chip removal capacity and heat dissipation capacity. The size of the rake angle directly affects the stress condition of the cutting edge and the internal stress state of the blade. In order to avoid excessive tensile stress caused by mechanical impact on the tool tip, the negative front angle (- 5 °~- 10 °) is generally adopted. At the same time, in order to reduce the wear of the rear angle, the main and auxiliary rear angles are 6 °, the radius of the tool tip is 0.4 – 1.2 mm, and the chamfer is ground smooth.
4. Inspection of cubic boron nitride (CBN) tools
In addition to testing the hardness index, bending strength, tensile strength and other physical properties, it is more necessary to use a high-power electron microscope to check the surface and edge treatment accuracy of each blade. Next is the dimension inspection, the dimension accuracy, M value, geometric tolerance, roughness of the tool, and then packaging and warehousing.
Post time: Feb-23-2023