Vacuum brazing cutting tool

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The vacuum brazing of cutting tool is discussed

Characteristics of vacuum brazing

1.1 prevent oxidation and decarburization of the cutting tool body
Vacuum brazing can be used in the brazing (heating) chamber and cooling chamber of the furnace in a full vacuum environment, which completely prevents the oxidation and decarburization of the matrix and welding materials during brazing and cooling. At the same time, the complete vacuum state can also make the molten copper solder wetting the joint surface well without the use of flux, which can avoid the production of fine cavities in the weld and improve the welding strength.

1.2. Better economy
The weight of cutting tool is relatively small, which is very suitable for brazing in vacuum furnace. The vacuum brazing and quenching of cutting tool can be done with intermittent furnace, which can braze a large number of pieces at a low cost. Therefore, vacuum brazing is the most efficient and economical for mass production. It also has good adaptability to the occasional small batch production, especially when the vacuum brazing of cutting tool is combined with the heat treatment and quenching of cutting tool, it can achieve the most economical effect.

1.3 the brazing quality is stable and reliable
The temperature control and operation of cutting tool brazing equipment are monitored digitally by computer. The brazing quality and stability are fully guaranteed by the advanced equipment. However, the quality of traditional brazing depends too much on the technical level and proficiency of operators. In addition, due to the high degree of automation of vacuum brazing and quenching furnace, the labor intensity of operators is greatly reduced and the working environment is greatly improved.

Operation procedure

2.1 cleaning
When cutting tool is machined, the surface will be stained with oil, or the surface will be corroded because of storage after machining. In order to ensure the welding is firm, the surface must be cleaned before brazing, especially the brazing surface. General oil stains can be cleaned with aviation gasoline and acetone; When there is rust, can only use mechanical rust or pickling method to rust. If the pickling cleaning, must immediately clean the pickling surface with clean water and drying treatment. The cemented carbide head and solder also need to be cleaned, solder surface such as oxidation, also want to be pickling treatment, so as not to affect the melting temperature of solder and solder fluidity.

2.2 assembly and clamping
The brazed parts into the furnace are generally designed to be assembled by pressing fit, flaring or other methods without fixture. However, since there must be weld gap between the cutting tool body and the carbide head, special fixture must be designed to keep the cutting tool upright and stable. During assembly, put the cleaned brazing material into the joint hole of the cutting tool body, and then put the cemented carbide into the hole. The assembled assembly parts are fixed into the furnace with a jig. For cutting tool furnace brazing fixture design should be considered: strong, stable, not easy to capsize due to small vibration; Select repeatedly heated and not easy to produce deformation of the material made; Try to limit the weight to reduce the invalid furnace load; A P force shall be applied to the cemented carbide to enable the carbide to reach the predetermined position when the solder melts.

2.3 brazing
The cutting tool assembly installed in the fixture is sent into the brazing chamber of the furnace and heated. When the temperature of the cutting tool assembly exceeds the solder melting point, the solder wetting and diffusing flows under the bottom of the hole and the cemented carbide of the cutting tool body and enters the joint under capillary action. In the weld gap between cutting tool body and cemented carbide. In the forming union, the filler metal forms a solid melt with the surface of unmelted steel and cemented carbide.

2.4 cooling and quenching
After the cutting tool is brazed, it is moved into the cooling chamber of the furnace to cool down, until the cutting tool cools to the appropriate temperature, then the quenching treatment can be carried out directly.

Solder and weld gap
3.1 selection of brazing solder for cutting tool brazing solder shall be considered as follows:
(1) with good wettability, at brazing temperature, it is easy to fill the gap of brazing joint, that is, the filler can be suitable for both steel and cemented carbide materials, so as to form a good brazing joint;

(2) to meet the mechanical properties of the cutting tool, that is, the shear strength of the formed joint weld should be 180MPa, with a certain degree of toughness and meet the requirements of higher working temperature;

(3) to meet the brazing process and brazing property, and to have an appropriate melting point, the brazing temperature is required to be lower than 930e, in order to avoid the cutting tool body at a high temperature, so that the steel structure grain grows up, affecting the cutting tool body toughness.

(4) cost factor. The price difference of brazing material is very big, the cost of copper solder is lower, and the cost of silver solder is higher, it is the same volume copper solder price generally 40~50 times. Considering the above four aspects comprehensively, if there is no special requirement, brazing solder in cutting tool furnace should be selected as much as possible. The main advantages of brazing alloy are low cost and high welding strength. However, the disadvantages are: the temperature of brazing spot is high, generally above 900e, and the weld stress is large.

The advantages of silver solder are: good technical performance, low melting point, good wettability, ability to fill gaps, good strength and plasticity. Its disadvantages are: high price, low operating temperature of brazed joint.

At present, the better cutting tool brazing solder has cu-mn-ni solder and so on.

The size of brazing weld gap is a key factor affecting the density and strength of brazing weld. Too small gap hinders the inflow of brazing solder and too large gap damages the capillary action of brazing weld and makes brazing solder unable to fill the gap. Brazing of cutting tool, it is steel and carbide brazing of dissimilar materials, considering the linear expansion coefficient of carbide smaller than steel, so the brazing seam clearance should be smaller than when steel on steel welding, when using HL105, HL106 copper solder, cutting tool brazing gap generally 0.105 ~ 0.15 mm, in addition to ensure uniform weld gap around carbide, can design the carbide bottom into a cone shape, to take advantage of cutting tool body and carbide two cone self-centering effect.

Conclusion
In summary, due to its high production efficiency and stable quality of the brazing joint, the vacuum brazing and quenching of the cutting tool can be heated, brazed and cooled completely in the vacuum environment to avoid oxidation and decarbonization of the cutting tool. Therefore, the vacuum brazing and quenching process of cutting tool will be more and more widely used.

Learn More : Diamond Vacuum Brazing Furnace