A brazing material for PCBN cutting tools and its preparation method and application

Abstract

This invention provides a brazing filler metal for PCBN cutting tools, its preparation method, and its application, relating to the field of brazing technology. Specifically, it comprises the following components: copper, tin, titanium, wear-resistant particles, and a binder; wherein the wear-resistant particles include at least one selected from diamond, cubic boron nitride, alumina, and silicon nitride. This invention avoids excessive stress concentration through the synergistic effect of copper, tin, titanium, and wear-resistant particles; by adjusting the particle size of the wear-resistant particles, a long weld seam is divided into several smaller weld seams, thereby significantly reducing residual welding stress and substantially reducing the proportion of cracks generated after PCBN composite welding. Simultaneously, the wear-resistant particles in the weld seam provide wear resistance, improving the wear resistance of the weld seam and ensuring that the cutting tool does not fail during service due to impact from cutting chips on the weld seam.

Description

Technical Field

[0001] The invention relates to the technical field of brazing, and in particular to a brazing filler metal for a PCBN tool, a preparation method thereof and an application thereof. Background Art

[0002] Polycrystalline cubic boron nitride (PCBN) is a new type of raw material synthesized by artificial methods, and its hardness is second only to natural diamond. Its preparation process is mainly divided into two types: one is the primary polymerization method, that is, directly using hexagonal boron nitride (HBN) to polymerize into a high-density sintered body; the other is the secondary polymerization method, that is, first synthesizing high-density cubic boron nitride (CBN) through hexagonal boron nitride (HBN), and then further sintering it into polycrystalline cubic boron nitride at high temperature and high pressure. The main use of polycrystalline cubic boron nitride is tool material, that is, it is used to prepare "superhard tools", and it has been widely used in the market.

[0003] Welded superhard cutting tools are the most commonly used type of superhard cutting tools, with many advantages such as high cutting speed, high durability, processing accuracy and good surface quality; its welding usually includes the following steps: the operator first applies paste brazing material (solder paste) to the part to be welded on the cemented carbide substrate, then assembles the tool head and the cemented carbide substrate coated with solder paste together, and then puts them into the furnace for brazing. The brazing material used in this process is generally prepared by mechanical mixing of single powder and adding a binder, and has the advantages of low cost and easy availability.

[0004] Copper-tin-titanium brazing filler metal is cheap and is one of the most commonly used active brazing fillers in the preparation process of welded PCBN tools. However, its welding temperature requirement is high, reaching about 900°C. When welding PCBN tools, excessively high welding temperature will increase the linear expansion difference between the carbide substrate and PCBN, causing welding cracks in the PCBN, resulting in a short service life or even scrapping of the blade.

[0005] The patent "A method for reducing residual stress in heterogeneous brazed joints" (CN202210780917.2) provides a method for reducing stress by extending insulation, but the extended time reduces work efficiency and increases welding costs.

[0006] In addition, during the cutting process of welded PCBN tools, the weld will also be impacted by cutting chips, causing the weld to become shallower, resulting in uneven force on the PCBN tool head, and in severe cases, the tool tip may fail.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The first object of the present invention is to provide a brazing material for PCBN cutting tools, so as to solve the problems of weld cracks caused by excessively high brazing temperature of conventional copper-tin-titanium brazing materials and the negative effects of cutting chips on the weld and the cutting head. In order to achieve the above-mentioned object of the present invention, the following technical scheme is adopted:

[0009] A brazing material for PCBN cutting tools comprises the following components: copper, tin, titanium, wear-resistant particles and an adhesive; wherein the wear-resistant particles comprise at least one of diamond, cubic boron nitride, aluminum oxide and silicon nitride.

[0010] Preferably, the solder includes, by mass, 60-80 parts of copper, 10-30 parts of tin, 5-20 parts of titanium, 0.5-5 parts of wear-resistant particles, 0.1-3 parts of adhesive and a solvent.

[0011] More preferably, the solder includes 65-75 parts of copper, 15-25 parts of tin, 5-15 parts of titanium, 0.5-3 parts of wear-resistant particles, 0.1-2 parts of adhesive and 5-30 parts of solvent.

[0012] Preferably, the particle size of the wear-resistant particles is larger than the particle size of the copper, the tin and the titanium.

[0013] Preferably, the particle size of the wear-resistant particles is -200 mesh to +400 mesh.

[0014] Preferably, the particle size of the copper, the tin and the titanium is ≤ -400 mesh.

[0015] Preferably, the adhesive includes at least one of propylene glycol, ethyl carbitol, glycerol, ethylene glycol, diethylene glycol monomethyl ether and diethylene glycol monobutyl ether.

[0016] Preferably, the solvent includes at least one of deionized water or alcohol.

[0017] The second object of the present invention is to provide a method for preparing the solder for PCBN cutting tools, which is simple and suitable for mass production; specifically, it comprises the following steps: fully mixing copper, tin, titanium, wear-resistant particles, adhesive and solvent to obtain a paste solder.

[0018] The third object of the present invention is to provide an application of the brazing filler metal for PCBN cutting tools; superhard cutting tools prepared using the brazing filler metal, or brazing processes including the brazing filler metal, etc., all fall within the scope of the present invention.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the wear-resistant high-melting particles dispersed in the weld cut off the stress line to avoid excessive stress concentration; by dividing the longer weld into several small welds, the welding residual stress is greatly reduced, and the proportion of cracks generated after PCBN composite welding can be greatly reduced. Second, the present invention optimizes the composition and particle size of the solder without changing the existing brazing process. When it is put into production, it only needs to replace the solder and extrude it before the workpiece can be directly welded. Third, the wear-resistant particles in the weld can play a wear-resistant role, improve the wear resistance of the weld, and ensure that the blade will not fail due to the impact of cutting chips on the weld during service. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A set of physical pictures of the cutter head falling off are provided;

[0022] Figure 2 A schematic diagram of the force principle of the weld pit is provided;

[0023] Figure 3 Provides a comparison chart of weld structures. Figure 3 (a) corresponds to copper-tin-titanium solder paste, Figure 3 (b) a solder corresponding to the present invention;

[0024] Figure 4 A microscopic electron microscope image of the weld of a comparative example of the present invention is provided. DETAILED DESCRIPTION

[0025] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0026] The most commonly used brazing material in the preparation process of welded PCBN tools is copper-tin-titanium solder paste, which needs to be brazed at around 900°C. However, since the cemented carbide substrate, brazing metal and tool head do not belong to the same alloy phase, the metal expansion volume is different at high temperature; and the high temperature of around 900°C required by the copper-tin-titanium brazing material further causes the difference in linear expansion between the cemented carbide substrate and PCBN to increase, eventually leading to cracks in the PCBN. The cracks generated after welding will continue to spread as the tool is used, eventually causing the tool head to fall off (such as Figure 1 If the cutter head falls off, it may scratch the workpiece being processed, and in serious cases, the workpiece being processed may be scrapped.

[0027] In addition, PCBN tools will inevitably produce cutting chips during cutting. The weld is impacted by the cutting chips to form pits. During the working process of the tool, as the weld is continuously washed by the cutting chips, the pits of the weld will gradually increase, resulting in uneven force on the tool head and a sharp drop in welding. Figure 2 As shown in the figure, a schematic diagram of the principle of this process is given; F is the force direction of the tool during operation. When the weld is washed into a pit, the tool head at the weld has no welding force, resulting in the tip of the tool falling off.

[0028] In order to solve the hidden danger of the tool head falling off due to cracks or cutting chips, the technical solution of the present invention is specially proposed; the present invention is carried out through the following specific implementation methods: a brazing filler metal for PCBN tools includes the following components: copper, tin, titanium, wear-resistant particles and adhesive; wherein the wear-resistant particles include at least one of diamond, cubic boron nitride (CBN), aluminum oxide (Al2O3) and silicon nitride (Si3N4).

[0029] The present invention adds wear-resistant particles to copper, tin and titanium for synergy; copper is the main element, and a small amount of active element titanium can react chemically with PCBN to form a metallurgical bond during the brazing process, while a small amount of tin can effectively reduce the melting point of the brazing alloy and reduce the thermal expansion damage caused during the brazing process.

[0030] After welding, conventional solder paste forms a complete weld between the two base materials. Figure 3 (a) shows that, due to the large difference in linear expansion coefficient of the parent materials on both sides of the weld, there will be large welding residual stress; specifically: the matrix and the solder are made of different metal raw materials, and have different thermal expansion properties. During the brazing process, whether it is the process of heating welding or cooling, different raw materials will inevitably have different volume expansion or contraction, forming residual stress and eventually causing weld cracking; and when the solder of the present invention is used, after brazing, the wear-resistant particles with larger particle size are evenly distributed in the weld (such as Figure 3(b) shows a long weld that is divided into several small welds by wear-resistant particles, which cuts the stress line and avoids the generation of tiny cracks caused by stress concentration.

[0031] As a preferred embodiment, in the selection of the wear-resistant particles, the present invention does not limit the specific types or crystal forms of the diamond, cubic boron nitride, aluminum oxide and silicon nitride. For example, the aluminum oxide may be α-aluminum oxide or γ-aluminum oxide, and the silicon nitride may be any one of reaction bonded silicon nitride (RBSN), hot pressed silicon nitride (HPSN) or sintered silicon nitride (SSN).

[0032] As a preferred embodiment, the solder includes the following components by mass: copper includes but is not limited to 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80 parts, tin includes but is not limited to 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 parts, titanium includes but is not limited to 5, 8, 10, 12, 14, 16, 18, 20 parts, wear-resistant particles include but are not limited to 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts, adhesive includes but is not limited to 0.1, 0.5, 1, 1.5, 2, 2.5, 3 parts and solvent 5, 10, 15, 20, 25, 30 parts. It should be noted that the weight parts of the components used in the present invention are not limited to the point values ​​given above, and any real value within the numerical range formed by the above point values ​​can be used.

[0033] As a preferred embodiment, the particle size of the wear-resistant particles is larger than the particle size of the copper, the tin and the titanium. As a more preferred embodiment, the particle size of the wear-resistant particles is -200 mesh to +400 mesh, and the particle sizes of the copper, the tin and the titanium are independently ≤-400 mesh. It can be understood that the particle size of the wear-resistant particles is less than 200 mesh and greater than 400 mesh, or 400 mesh is coarse and 200 mesh is fine, which means that the wear-resistant particles can pass through a 200 mesh sieve but cannot pass through a 400 mesh sieve. Similarly, the particle sizes of the copper, the tin and the titanium are independently less than 400 mesh, that is, 400 mesh is fine, which means that the copper, the tin and the titanium can pass through a 400 mesh sieve. It should be noted that only the particle size ranges of the copper, the tin and the titanium are given above. Those skilled in the art can select the particle sizes of the copper, the tin and the titanium respectively, and the particle sizes of the three are not necessarily the same.

[0034] As an optional embodiment, the particle size of the wear-resistant particles includes but is not limited to -210 mesh, -220 mesh, -240 mesh, -260 mesh, -280 mesh, -300 mesh, -320 mesh, -340 mesh, -360 mesh, -380 mesh, and -390 mesh; the particle sizes of the copper, tin, and titanium include but are not limited to -410 mesh, -420 mesh, -450 mesh, -500 mesh, -550 mesh, -600 mesh, -650 mesh, -700 mesh, -750 mesh, -780 mesh, and -790 mesh, respectively.

[0035] As a preferred embodiment, the method for using the brazing material of the present invention comprises the following steps: firstly coating the brazing material on a cemented carbide substrate, then placing a tool head on the coating area, squeezing the substrate and / or the tool head until it cannot be squeezed, then performing high temperature brazing, and obtaining a cemented carbide tool. As a more preferred embodiment, when the number of tool heads is greater than 1, repeat the coating and placement operations until all the tool heads are squeezed. As a more preferred embodiment, the squeezing can be performed by an operator or by a machine. The present invention does not specifically limit the force of squeezing, and those skilled in the art can perform appropriate on-site operations according to the specific type of cemented carbide tool.

[0036] As a more preferred embodiment, the temperature of the high temperature solder is 850°C to 950°C, and the time of the high temperature solder is 8min to 15min.

[0037] Example 1

[0038] Weigh the raw metal powders by mass: 70 parts of copper powder (-400 mesh), 20 parts of tin powder (-400 mesh), 10 parts of titanium powder (-400 mesh), 1 part of diamond particles (-325 mesh to +400 mesh), 0.5 parts of propylene glycol, and 10 parts of deionized water. Stir and mix the raw materials until they are uniform, and use them as the solder paste to be used.

[0039] The object to be brazed uses a PCBN tool with a blade of VNGA160408 type (the cemented carbide substrate is YG8, and the PCBN is 2μm CBN particles with a content of 90%); first apply the solder paste to be used on the cemented carbide substrate, then put the tool head into the position after applying the solder paste, squeeze the substrate and the tool head hard until they can no longer be squeezed, and then transfer the tool to a vacuum furnace for brazing, the brazing temperature is 910℃, and the brazing time is 10min.

[0040] Example 2

[0041] The raw materials were weighed by mass: 100 parts of commercially available copper-tin-titanium alloy solder powder (-400 mesh), 1 part of diamond particles (-325 mesh to +400 mesh), 0.5 parts of propylene glycol, and 10 parts of deionized water. The raw materials were fully stirred and mixed until uniform to prepare the solder paste. The specific implementation of soldering was exactly the same as in Example 1.

[0042] Example 3

[0043] It is basically the same as Example 1, except that the particle size of copper powder, tin powder and titanium powder is -600 mesh.

[0044] Example 4

[0045] It is basically the same as Example 3, except that cubic boron nitride is used to replace diamond.

[0046] Example 5

[0047] It is basically the same as Example 3, except that alumina is used to replace diamond.

[0048] Example 6

[0049] It is basically the same as Example 3, except that silicon nitride is used to replace diamond.

[0050] Comparative Example

[0051] It is basically the same as Example 3, except that no diamond is added.

[0052] No cracks were found in the PCBN tool heads obtained in the above embodiments, and no obvious impact pits were found in the welds during the use of the tool. Figure 4 As shown, cracks generated after welding can be clearly observed; after a period of use, pits are formed by the impact of cutting chips.

[0053] Test example

[0054] The PCBN tools prepared in each embodiment and comparative example were subsequently processed and then subjected to turning tests (10 blades per group, turning HT250 brake disc, turning diameter 210 mm to 330 mm, cutting depth 0.3 mm, cutting speed 550 m / min, feed speed 0.25 mm / r), and the results are shown in Table 1 below.

[0055] Average lifespan / piece Causes of tool failure Example 1 45 Normal wear of the blade tip and poor roughness Example 2 46 Normal wear of the blade tip and poor roughness Example 3 45 Normal wear of the blade tip and poor roughness Example 4 45 Normal wear of the blade tip and poor roughness Example 5 46 Normal wear of the blade tip and poor roughness Example 6 45 Normal wear of the blade tip and poor roughness Comparative Example 31 The tip of the knife is broken or falling off

[0056] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A brazing material for PCBN cutting tools, characterized in that: The invention comprises the following components by mass: 60-80 parts of copper, 10-30 parts of tin, 5-20 parts of titanium, 0.5-5 parts of wear-resistant particles, and 0.1-3 parts of adhesive; wherein the wear-resistant particles include at least one of diamond, cubic boron nitride, aluminum oxide, and silicon nitride; The wear-resistant particles have a particle size greater than that of the copper, the tin, and the titanium.

2. The brazing filler metal for PCBN cutting tools according to claim 1, characterized in that: Calculated by mass, the solder includes 65-75 parts of copper, 15-25 parts of tin, 5-15 parts of titanium, 0.5-3 parts of wear-resistant particles, 0.1-2 parts of adhesive and 5-30 parts of solvent.

3. The brazing filler metal for PCBN cutting tools according to claim 1, characterized in that: The particle size of the wear-resistant particles is -200 mesh to +400 mesh.

4. The brazing filler metal for PCBN cutting tools according to claim 1, characterized in that: The particle size of the copper, the tin and the titanium is ≤-400 mesh.

5. The brazing filler metal for PCBN cutting tools according to claim 1, characterized in that: The adhesive includes at least one of propylene glycol, ethyl carbitol, glycerol, ethylene glycol, diethylene glycol monomethyl ether and diethylene glycol monobutyl ether.

6. The brazing filler metal for PCBN cutting tools according to claim 2, characterized in that: The solvent includes at least one of deionized water or alcohol.

7. The method for preparing the brazing filler metal for PCBN cutting tools according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: fully mixing copper, tin, titanium, wear-resistant particles, adhesive and solvent to obtain paste solder.

8. Use of the brazing material for PCBN cutting tools according to any one of claims 1 to 6 in the field of brazing.

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