Manufacturing technology and application of the ho

CVD diamond film tool manufacturing technology and its application

chemical vapor deposition (CVD) diamond as a new superhard tool material, has opened up a new way for the application of diamond tools. There are mainly two types of CVD diamond tools: CVD diamond film coated tools and CVD diamond thick film welding tools. At present, CVD diamond thick film tools are widely used

I. CVD diamond film coated tools

CVD diamond film coated tools refer to tools that deposit diamonds on some matrix (usually K-type cemented carbide) blades at a certain temperature by CVD method, and the thickness of diamond film is about 10 ~ 30 m

cvd diamond film coated tools are only suitable for rough machining, semi precision machining and complex shape tools because the diamond thickness is thin, it is difficult to grind, and the quality of the front and rear cutting surfaces and cutting edges are poor. Rough machining has a large cutting. When the adhesion between diamond and matrix is not enough to resist the destruction of cutting force, the diamond film will fall off. The surface roughness of the workpiece processed by this tool is generally greater than Ra0.2 M

although the application of CVD film coated cutting tools in China is still in its infancy, with the improvement of CVD diamond growth technology, the size of CVD diamond group particles has been reduced from 40 ~ 50 m to more than a dozen or even several nanometers, resulting in the emergence of nano diamond. For example, Dr. Gruen D.M of Argonne nat. lab in the United States has grown a nano diamond film with good quality, mirror surface (the distance between the highest peak and the lowest peak of the surface is 15nm) and arbitrary thickness, and the adhesion of its coating is sufficient. It is believed that it will promote the application of coated cutting tools

II. CVD diamond thick film welding tool

cvd diamond thick film welding tool is to weld the cut CVD diamond thick film to the substrate (usually K-type cemented carbide) at first to form a composite sheet, then polish the composite sheet, weld it to the tool body twice, and grind the blade to the required shape and edge

manufacturing process: preparation of high-quality CVD diamond film → laser cutting → one-time welding into composite sheet → polishing of composite sheet → secondary welding to the tool body → grinding → inspection. The following describes several key processes, such as cutting, welding, polishing and grinding

1. Laser cutting

CVD diamond film has high hardness, non-conductive (there are conductive CVD diamonds, but their resistivity is very high), and strong wear resistance. Conventional machining and wire cutting methods are not suitable for cutting CVD diamond thick film. The efficient processing method is laser cutting

2. One time welding

one time welding refers to welding CVD diamond thick film to some substrates under vacuum to form composite sheets. The weldability between diamond and general metal is very poor. At present, the welding process of diamond thick film tools mainly adopts the method of surface metallization. The solder is a silver copper alloy containing titanium. The role of titanium is to react with the surface of diamond film during welding heating, produce tic intermediate layer, and metalize the surface of diamond film, so as to improve the welding strength

the matrix for welding is usually K-type cemented carbide. Under the condition of high vacuum, using the process of diffusion welding and brazing, with Ag Cu Ti alloy as the intermediate layer, the diamond thick film is welded on the cemented carbide substrate, and the welding strength meets the requirements of machining

3. Composite polishing

the purpose of polishing is to polish the upper surface of the blade (i.e. the rake face) into a mirror, which is generally required to be less than ra0.1 M. After polishing the front face of the tool, the friction and adhesion with chips can be reduced, and the service life of the tool can be prolonged; At the same time, it can also improve the flatness and sharpness of the blade and improve the accuracy of cutting. A special polishing machine is used for polishing composite sheets

4. Secondary welding

secondary welding refers to welding the composite to the tool body. Most of the equipment used are high-frequency induction welding equipment, and the solder used is silver copper solder and flux. The welding temperature is between 650 ℃ and 700 ℃, which is our strong "manufacturing" ability. The temperature shall not be too high, and all welding surfaces shall be kept clean during welding. The reasonable selection of brazing flux is conducive to improving the welding strength and the welding performance of the composite substrate and the tool body material. Generally speaking, the strength of secondary welding is 180 ~ 200MPa, which can meet the requirements of diamond tool cutting

in addition, in order to improve the appearance of the tool, you can use an oilstone strip to grind away the excess silver and copper, remove the surface oxide layer by sand blasting, and prevent the oxidation and rust of the tool body by Ni plating on the surface or soaking in passivation solution

grinding CVD diamond has high hardness and wear resistance, which is extremely difficult. At present, the grinding method similar to PCD tool is widely used

5. Equipment: special tool grinders are used. The equipment manufacturers include British Coborn company, Taiwan Karmam company, Swiss EWAG company and Beijing Dean company. Its main functions include: straight edge grinding and circular arc grinding. Circular arc grinding also includes the formation of conical and cylindrical flanks and the combination of conical and cylindrical flanks. In order to realize these functions, the main movements of the machine tool are required to include: the rotation movement of the machine tool spindle (grinding wheel); Reciprocating linear motion of spindle; The rotation movement of the tool holder, together with the microscope or projector, accurately align the rotation center to obtain different tool tip arc radii, etc

6. Grinding wheel: the grinding wheel used for grinding is resin bonded diamond grinding wheel, and the grinding process is divided into rough grinding, semi fine grinding and fine grinding. The grain size of grinding wheel ranges from 250 ~ 325 to W10 ~ 07. In order to improve the quality of the cutting edge, sometimes grinding, polishing and other processes are needed, and the particle size used is finer, even 1 ~ 3 m. In order to obtain high-quality cutting edge, sand embedded cast iron disc is usually used for grinding

7. Grinding: in the process of grinding, coolant needs to be added, and attention should be paid to the dressing of the grinding wheel. Usually, correct dressing of the grinding wheel with a suitable oilstone bar can improve the grinding efficiency and quality. Since the impact resistance of CVD diamond is not as good as that of PC, which is not only in line with the market, the cutting edge of some special tools should be blunt after grinding, generally 0.02 ~ 0.03mm

8. The inspection of the quality of the cutting edge of the tool is usually observed with a tool microscope with a magnification of 40 ~ 80 times. The sawtooth degree of the cutting edge of ordinary tools is ≤ 0.02mm. For tools with higher accuracy, after grinding and polishing, the sawtooth degree of the cutting edge is ≤ 0.005mm. In addition, machining different workpiece materials also has different requirements for the quality of the cutting edge. Grinding CVD diamond tools should start from the actual application and blindly pursue high-quality cutting edge, which not only reduces the production efficiency, but also increases the production cost

III. cutting experiment of CVD diamond film tool for machining composite materials

1 Processing metal matrix SiC particle reinforced composites (sicp/ly12)

CVD thick film diamond welding tools for continuous cutting of sicp/ly will not harm people's health. 12 composites (hv>3000, SiCp accounting for 30% by weight, particle size 28 m). The tool wear curve is shown in Figure 1

v=75m/min, f=0.1mm/r, ap=0.3mm

Fig. 1 vb-t curve (dry cutting) of sicp/ly12 composites processed by different material cutters

geometric parameters of cutters:

· ys8:g0=0, a0=12, kr=90, re=1.0mm, ls=0

· pcbn:g0=0, a0=12, kr=90, re=0.1mm, ls=0

· pcd:gg 0=-4, a0=9, re=5.0mm

· CVD thick film: g0=3, a0=13, kr=75, re=0.6mm

it can be seen from Figure 1 that the VB value of the flank wear of TFD (CVD diamond thick film) tool is about 0.05mm and that of PCD tool is about 0.16mm when machining for 38min. The wear resistance of thick film tool is significantly higher than that of PCD tool. The reason is that the diamond thick film is a polycrystalline material composed of pure diamond grains, while PCD diamond is a polycrystalline material sintered with metal co and Ni as adhesives. Metal co reduces the wear resistance of PCD tools. The wear of PCBN tools is much faster than that of PCD and CVD thick film tools, while fine grain cemented carbide ys8 tools are not competent at all. In production, CVD thick film or PCD tools should be preferred

2. Processing resin based glass fiber reinforced composites (GFRP)

Figure 2 shows the wear resistance curve of PCBN, CVD diamond film and thick film processing GFRP

v=80m/min, f=0.1mm/r, ap=0.3mm

Figure 2 vb-t curve (dry cutting) of GFRP composites processed by different material cutters

geometric parameters of cutters:

· pcbn:g0=0, a0=8, kr=45, re=0.5mm, ls=0

· CVD film: g0=-10, a0=8, re=4.0mm

· CVD thick film: g0=-8, a0=8, CVD thick film kr=45, re=0.5mm, ls=0

it can be seen from Figure 2 that the wear resistance of CVD thick film tools is the best, followed by CVD thin film tools, PCBN tools take the second place. The main component of GFRP is SiO2 (85hra), which has high friction and dry cutting. Therefore, the high temperature during processing can lead to rapid wear of the cutting edge and flank of the tool. GFRP material is less difficult to process than sicp/ly12, and the tool life is longer. The three kinds of tools used in the experiment can be used in production

in a word, whether CVD diamond film coated tools or CVD diamond thick film welding tools, if they can make full use of their excellent performance, take their advantages and avoid their disadvantages, their application prospects are very good. At the same time, on the one hand, we should continue to improve the growth technology of CVD diamond film to make its performance better; On the other hand, the manufacturing technology of CVD diamond tools should be improved to make them more widely used in various fields

Beijing Tiandi Oriental Diamond Technology Co., Ltd. Liu Zhiping, Han Yisong

Yu Qixun, Beijing University of technology, Quan Yanming (end)