vacuum welding superhard tool products

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Superhard tool mainly refers to the tool made of diamond or CBN. At present, there are four kinds of materials used: single crystal diamond, PCD polycrystalline diamond, integral CBN and PCBN composite sheet.

The vacuum welding of superhard tool means that the brazing between the base and the head of superhard tool is completed by heating in the vacuum state. Like flame brazing and high frequency induction brazing, the ultimate purpose of vacuum welding is to make the molten solder flow to all parts of the weld uniformly under the action of capillary straw, so as to achieve the best welding effect. Therefore, it is necessary to select the appropriate solder, carry out the appropriate pre welding treatment and adopt the correct welding process for the superhard tool products suitable for vacuum welding so as to make full use of the advantages of vacuum welding and ensure the performance of superhard tool products.

1. Superhard tool products suitable for vacuum welding
Due to the need to place the tool products in the vacuum environment for heating, the whole furnace will reach the welding temperature, so the size of the tool products to be vacuum welded cannot be too large, it must be able to put into the furnace. At the same time, the tool material must bear the temperature change of the welding process without changing its own performance. The tool manufacturers all pursue high production efficiency, so it can be seen that the vacuum welding process is especially suitable for the large-scale production of the small size and the whole heating super hard tool series, not suitable for the large size or only can accept the local heating super hard tool product welding processing.

The common raw materials of superhard cutting tools are:
① Single crystal diamond;
② PCD polycrystalline diamond;
③ Overall CBN;
④ PCBN composite. They have their own requirements for solder selection:
(1) ④ all of them contain a layer of hard alloy liner, which can be welded with conventional brazing filler metals (i.e. silver welding and copper welding which are widely used at present);
(2) ① ③ it belongs to non-metallic material, which needs active solder to be welded to the cutter body;(3) ① ② all have the characteristics of diamond, and graphitization will occur at high temperature, so the temperature of vacuum welding needs to be controlled at about 700 ℃;
(4) The CBN tool made by ③ ④ has a very high temperature when it is used to process hardened steel. In order to prevent the welding surface from loosening, high temperature solder is needed.
In view of the characteristics of superhard tool materials, for vacuum welding, at least two kinds of solders need to be selected to meet all the requirements, that is, one kind of low-temperature active solder is used for the welding of single crystal diamond and PCD tool; the other kind of high-temperature active solder is used for the welding of the whole CBN and PCBN tool. Although the first kind of low-temperature active solder can weld all super hard tools, it is recommended to use high-temperature solder for CBN tools, so that the stability of CBN tool products at high temperature will be greatly increased.

3 preparations before welding
The strength of brazing is determined by many factors. In order to obtain a good brazing weld, it is necessary to control some details that may affect the welding quality. Compared with conventional welding, vacuum welding has more strict requirements on preparation work.
Only when every detail is guaranteed, the best welding effect can be obtained. The lack or insufficient guarantee of one item will reduce the stability of welding greatly.

4 vacuum welding process
Once the preparation is completed, put the cutter products into the vacuum furnace, and the subsequent production is completely controlled by the heating process. The setting of heating process curve for vacuum welding is mainly restricted by furnace size, temperature field distribution, solid-phase line, liquid-phase line, furnace loading, weld size, etc.

Using vacuum welding technology can effectively eliminate the influence of air on superhard tools, and the appearance of tools is good. The heating temperature in the furnace is uniform, the product deformation is small, and the tool is not easy to crack. Under the condition of stable technology, the products of each furnace have the same quality, especially suitable for the mass production of small size super hard cutting tools.

Learn More: PCD PCBN Vacuum Brazing Furnace