1. Application of brazing technology in the application of diamond tools
The high hardness and excellent physical and mechanical properties of diamond make diamond tools an indispensable tool for the machining of various hard materials. The adhesion of carcass metal base to diamond (carcass encasing ability) is one of the main factors that affect the service life and performance of diamond tools.
Due to the high interfacial energy between diamond and common metals and alloys, the diamond particles can not be infiltrated by the general low-melting alloy, and the adhesion is very poor. In the traditional manufacturing technology, the diamond particles only rely on the carcass after the cold shrinkage. The generated mechanical clamping force is embedded in the carcass metal base without forming a strong chemical bond or metallurgical bond, which results in the diamond particles being easily separated from the carcass metal base in the work, which greatly reduces the life and performance level of the diamond tool. The use of diamonds in most of the impregnated tools is low, and a large amount of expensive diamond is lost in the waste during work. Lin Zengdong and others took the lead in the use of diamond surface metallization technology to give the diamond surface many new features, such as excellent thermal conductivity and thermal stability, improve its original physical and chemical properties, improve its infiltration of metal or alloy solution.
The problem of diamond surface metallization in the 1970s has attracted the attention of the diamond tool manufacturing community at home and abroad. Many people have devoted themselves to the study of the surface metallization of diamond during the sintering process by adding or pre-adhering strong carbide metal powders to the carcass material. (This diamond did not react with the coating before it was heated. The reaction, which can only be a diamond coating, is expected to achieve chemical bonding of the diamond during sintering. Although the literature has demonstrated that some metals such as tungsten (not oxidized) can form WC layers on the diamond surface at lower temperatures (around 800°C), the process used to achieve pre-metallization of the diamond surface requires vacuum. Under conditions, heating above 600°C for 1 hour will give the desired bonding force. According to the sintering conditions of the current commonly used impregnated diamond cutting tools, heating in a non-vacuum or low vacuum at a temperature not exceeding 900° C. for about 5 minutes is not likely to generate a metallized layer on the diamond surface. Because whether the active metal atom (Ti, V, Cr, etc.) is enriched on the diamond surface or the interface reaction reaches the metallurgical bonding between the binder and diamond, it is an atomic diffusion process. According to the temperature used for the hot press and in such a short time, the process is extremely inadequate. Under solid-phase sintering conditions (sometimes with a small amount of low-strength, low-melting metal or alloy liquid phase), the carcass' chemical bonding or metallurgical bonding to diamond is very weak or not formed at all.
The pre-metallization of the diamond surface is not the ultimate goal, but merely one of the measures that are expected to achieve chemical-metallurgical bonding with the carcass metal. After the plated diamond is sintered into saw (drill) teeth, the exposed diamond on the fractured section loses the coating, and the surface of the pit that has fallen off the diamond is very smooth. This phenomenon seems to indicate that the diamond and the carcass are still Failed to achieve the level of chemical inclusion. Therefore, even if the surface pre-metallization of diamond is realized, the conventional solid phase powder metallurgy sintering method cannot achieve a firm bond between the diamond and the carcass material.
In the late 1980s, people began to explore brazing techniques for the production of diamond tools. Some transitional elements (such as Ti, Cr, W, etc.) are plated on the diamond surface, and a carbide reacts with the carbides on the surface. Through the action of this layer of carbide, the diamond, binder, and matrix can be brazed to achieve a solid chemical-metallurgical bond to achieve true diamond surface metallization. This is the principle of diamond brazing. From the published patents and articles, it can be seen that the technology can make the maximum cutting edge of diamond reach 2/3 of the particle size, and the tool life can be increased by more than 3 times, while the value under normal is less than 1/3, allowing the edge value to be available. Blade operation is achieved when the blade reaches a stable blade value. Therefore, the use of brazing technology is expected to achieve a strong bond between the carcass metal (brazing) and the parent material, diamond and steel substrates.
2. Research status of brazed diamond tools
At present, the production of diamond (or cubic boron nitride) tools by brazing has become a hot technology, but it is limited to single-layer tools. The foreign brazing technology research began in the late 1980s, but due to the complexity of the work, it still remains in the experimental stage, and its application is also limited to single-layer tools; domestic high-temperature brazing technology research started late, and developed countries In contrast, the breadth and depth of research are far from enough. Therefore, the current progress is very slow, but as China's accession to the WTO, the pace of research will inevitably accelerate.
(1) Research status of foreign high temperature brazing diamond tools
AK Chattopadhyay et al. (2008) coated a brazing alloy (72% Ni, 14.4% Cr, 3.5% Fe, 3.5% Si, 3.35% B, 0.5% O2) on a tool steel substrate by flame spraying (oxygen-acetylene welding torch). The diamond (non-coating) cloth is arranged on the solder layer, and then the diamond and steel substrate are bonded by induction brazing at 1080° C. under argon for 30 seconds. The Cr in the solder alloy is a strong carbide element that is enriched on the diamond surface during brazing to achieve surface metallization of the diamond.
The method described by Wiand et al. in U.S. patent is: solder (Ni-Cr) metal powder and organic binder are made into brazing paint, the coated diamond is adhered to the tool steel substrate, then brazing paint is applied, and then heated A moderate temperature and hold for a certain period of time to eliminate volatiles. It is heated to about 1100°C in a vacuum furnace (vacuum 1.333×10-2Pa) or dry hydrogen furnace, and kept at temperature for 1 hour. The surface metallization of the diamond is completed while brazing.
Some patents also use Ni-Cr alloy brazing material to achieve brazing. The brazing material also includes Fe, B elements or Si, Mo and the like. For example, in the reference [14], brazing was performed in a vacuum furnace using a Ni-Cr alloy solder containing Si or Si and Ti, and the brazing temperature was 1126 to 1176°C; the literature [15] adopted a Cu-based alloy containing W and Fe. , Cr, B, Si and other brazing brazed diamond grinding wheels; literature [16] using Ag-Mn-Zr silver brazing brazing tools, in lieu of electroplating tools.
Germany's A Trenker et al. used nickel-based active and nickel-based brazing materials respectively to achieve the bond between the diamond and the matrix during the brazing process. From the comparison with the electroplating tool, it can be seen that the high-temperature brazing diamond tool has much better performance than the electroplated diamond tool. The brazing tool (using active brazing material and PDA989, PDA665 diamond) is the plating tool (Ni More than 3.5 times of base brazing material and PDA665 diamond), life is more than three times that of electroplating tool; due to brazing tools have larger space for chip, diamond abrasive grain has larger free cutting surface and more space between abrasive grains Because the chips can be easily removed, the brazed diamond tools have good grinding performance.
(2) Research status of domestic high temperature soldering diamond tools
The Fourth Military Medical University and Xi'an Jiaotong University, based on the research of brazed diamonds at home and abroad, adopt the method of high-temperature brazing in a vacuum furnace (vacuum 0.2 Pa), NiCr13P9 alloy as brazing filler metal, and a small amount of Cr powder. Brazing was performed under conditions of high temperature (950° C.) pressure (4.9 MPa) to achieve a firm bond between the diamond and the steel substrate. The brazing material is evenly distributed on the surface of the grinding wheel. The diamond has been brazed firmly and the surface of the grinding wheel feels very sharp and rough. The brazing material is distributed evenly between the diamond grains, and the diamond edge height is high. Its durability is significantly higher than that of electroplated grinding wheels, and only a small amount of diamond falls off after work.
Xiao Bing et al. of Nanjing University of Aeronautics and Astronautics made use of high-frequency induction brazing method, using Ag-Cu alloy and Cr powder together as interlayer material, induction brazing in air for 35 seconds, brazing temperature of 780°C, realizing diamond and Solid bonding between steel substrates. Yao Zhengjun and others used the method of induction brazing in an Ar gas protection furnace, using Ni-Cr alloy powder as a brazing material, vacuum induction brazing for 30 seconds, and a brazing temperature of 1050°C to achieve a firm connection between the diamond and the steel substrate. Using scanning electron microscopy and X-ray energy dispersive spectroscopy combined with X-ray diffraction analysis, it was found that during the brazing process, the Cr-rich interface forms a Cr-rich layer and reacts with the C element on the diamond surface to form Cr3C2 and Cr7C3. This is to realize the alloy layer. Diamond has a major factor of higher bonding strength. Grinding experiments were performed with large depth of cut, slow feed, and heavy load. From the surface morphology after grinding, no diamond was removed and the diamond wear was normal wear, indicating that diamond has higher holding strength. For efficient grinding.
KNIK. Inc. of Taiwan introduced a single-layer uniform diamond high-temperature brazing bead, which can reduce the amount of diamond by 50% and increase the cutting speed by 2 times without reducing its lifetime.
The author's research group at home and abroad on the basis of the use of Ni82CrBSi alloy sheet solder, diamond evenly arranged on the brazing sheet, brazing in a low vacuum hot-pressing sintering furnace, a preliminary study of brazing diamond tools , and explore how brazing technology can be used in pregnant tools. From the optimization of the arrangement of diamonds in the carcass, the static structure parameters such as diamond grain size and concentration, and the dynamic parameters such as the number of effective diamonds and the diamond pitch, an orderly arrangement of the single layer diamonds in the transverse plane is achieved, and then the stacking method is adopted. Vertically arranged in a staggered manner, the diamond in the working layer has continuous working capability. In order to test the carcass' ability of inserting diamonds, a table-mounted diamond drill was specially made to carry out 5 edged experiments and the maximum average cutting edge value was measured. Through the testing of the diamond cutting edge height of the brazing single-layer tool (45/50 mesh diamonds), it was found that the maximum cutting edge value can reach more than 70%. It can be seen that the brazing technology can greatly increase the bonding strength between diamond and carcass. improve. The results of a reinforced concrete drilling simulation experiment on a diamond drill (φ63mm) show that the drill bit can continue to work even when the drilling tooth is worn by nearly 2mm. Theoretically, two layers of diamonds have already participated in the work, which seems to indicate that it can be achieved. "Pregnant inlay", the specific application process is still under further study.
3. Brazing technology problems in the application of diamond tools
There are many difficulties that need to be solved when brazing diamonds: 1 It is required that the brazing material has good wettability and bonding strength between diamond and carcass; 2 The selection of brazing materials and brazing technology must ensure the stability of diamond to reduce or avoid Adsorption of diamond by the brazing material; 3 Because the thermal expansion coefficient of diamond and metal matrix differ greatly, the welding residual stress is also greater, reducing the strength of the joint; 4 The melting point of the brazing material is higher than the working temperature of the diamond tool, so you should look for A metal (alloy) material with a lower melting point and close to the diamond expansion coefficient is used as a solder material, and then some active elements are added in order to improve the infiltration and affinity of the diamond, so that both the bonding of the diamond and the mechanical properties of the carcass can be achieved. the goal of. In addition, key technologies such as the realization of diamond surface metallization, the matching and selection of surface metal and solder, and the selection of flux and gas medium need to be further matured and optimized.
The use efficiency and longevity of the diamond tools are not only dependent on the firmness of the diamond abrasive grains being inlaid, but also related to the wear resistance of the carcass. The strength of the carcass itself, the distribution of diamond in the carcass, and the concentration of diamond all have an effect on the wear resistance of the carcass. Therefore, how to make the carcass reach an ideal state is a noteworthy issue in future work.
4. Conclusion
Brazing technology can achieve chemical and metallurgical bonding between diamond, binder (brazing alloy material) and metal matrix, and has high bonding strength. Because of the high bonding strength at the interface, only a very thin bond agent thickness is required to firmly hold the abrasive particles. The exposed height can reach 70% to 80%, which can make the use of abrasives more fully and greatly improve the tool life. And processing efficiency. Compared with the traditional technology, the allowable maximum blade cutting value of the diamond tool can be increased by more than 50%. Under the condition that the power consumption of the tool is not increased or decreased, the diamond consumption of the workpiece material per unit volume is reduced by more than half. Compared with plating tools, it also shows unparalleled advantages. In short, brazing technology has very good prospects for development in the process of diamond tool manufacturing, and this technology should be industrialized as soon as possible.
