Solution: Who knows what equipment and tools are needed to weld cemented carbide on cutters and milling cutters? Kneel down, you know, explain.

Commonly used welding methods and equipment for cemented carbide are as follows:

Brazing is a traditional and widely used cemented carbide welding method, and its process is mature and reliable. According to the different heating methods, it can be divided into the following processes:

1) flame brazing

Flame brazing is a method of welding with the flame of combustible gas (acetylene, propane, etc.). ) mixed with oxygen or compressed air as a heat source. The flame brazing equipment is simple, flexible and easy to operate, and can be heated and welded simultaneously with multiple flames according to the shape of the workpiece. Filamentous or flaky copper-based and silver-based solders are mostly used, among which HL 105 manganese brass solder is the most widely used; The brazing flux is usually dehydrated borax. Flame brazing is mainly suitable for small batch production of small and medium-sized cemented carbide tools, molds and measuring tools. For large cemented carbide tools, this method is generally not used because the temperature and speed of flame heating are difficult to control, and there will be a large temperature gradient and cracks when heating.

2) Resistance brazing

Resistance brazing can generally be divided into direct heating method and indirect heating method. The direct heating method is to put electrodes on both sides of the joint, so that the current can be heated through the contact resistance on the surface of the brazing seam, thus completing the welding process; The indirect heating method is to place the electrode on the steel substrate at one side of the joint, and use the resistance (or heating element) of the substrate at one side of the brazing seam to heat the current to realize brazing. Indirect heating method can avoid the contact between electrode and cemented carbide, prevent the cemented carbide from overheating and burning, and avoid its hardness reduction and cracking. Copper-based or silver-based solders can be used, such as H68, HL 105, etc. Among them, HL 105 solder has high shear strength, and YT5 tool welding can reach 28.5GPa and YG8 tool welding can reach 29.7GPa. Usually, the brazing agent is dehydrated borax 7.

Heating voltage is an important parameter of resistance brazing, so it is necessary to choose a suitable value to ensure a reasonable heating rate. Secondly, it is necessary to ensure good contact between the electrode and the workpiece. During the heating process, the slag should be discharged in time to prevent the formation of brazing seam inclusions and pores and reduce the strength. When using borax flux, it must be dehydrated first, otherwise, due to the existence of crystal water, the crystal water will evaporate during the welding process, and a large amount of gas will be generated in the welding area, which will not only affect the normal slag discharge, but also easily produce blowholes 7 in the weld.

Resistance brazing is simple and convenient to operate, with higher efficiency than flame brazing and less surface oxidation of the workpiece, but it is easy to cause local overheating and burning loss of the workpiece when heating. In addition, it is inconvenient to operate workpieces with complex shapes, multi-edge tools and workpieces with small sizes.

3) induction brazing

The advantages of induction heating brazing are high heating speed, short liquefaction process of solder, and can be carried out in various atmospheres (air, shielding gas and vacuum), which can reduce overheating and oxidation of cemented carbide and improve welding quality. The disadvantage of this method is that the equipment is complex and the one-time investment is large, and the other is the surface effect of induced current. When brazing thick workpieces, the heating temperature is uneven, the brazing quality is difficult to guarantee, and the efficiency is low. Therefore, it is generally only suitable for small-sized weldments 2 with simple brazing structure (preferably shaft-shaped slender type).

The process parameters of induction brazing generally include brazing gap, heating speed, cooling speed, shape and size of induction coil, way of adding flux, etc. These factors must have a suitable combination range, and the fluctuation of these factors will have a negative impact on weld quality, especially in cemented carbide.

The gap value of brazing seam is an important parameter to ensure brazing quality. It is generally believed that the smaller the brazing seam, the greater the welding stress, and vice versa. When the gap between brazing seams is too small, "extrusion" and "incomplete brazing" will occur, which will reduce the joint strength and increase the welding stress; However, if the gap is too large, the capillary action will be weakened, which will also lead to "incomplete brazing" and reduce the strength of the joint. Therefore, moderate brazing gap plays a great role in reducing welding stress and improving welding fastness.

The heating and cooling rates have great influence on the welding quality of the drill bit. If the heating speed is too fast, greater stress will be generated in the alloy; Too slow heating and long high temperature residence time will make the wetting and diffusion of liquid solder more perfect, but it will cause oxidation and burning loss of the alloy. Generally, the heating should not exceed100℃/s. If the cooling rate is too fast, great shrinkage stress will be generated in the alloy. Too slow cooling rate can reduce welding stress, but it is not good for quenching of steel materials, so 60℃/s is generally suitable for 8.

Induction coil is an important part of induction heating equipment, which transfers the energy of AC power supply to the weldment to realize heating. Therefore, whether the structure of induction coil is reasonable has a great influence on brazing quality and productivity. The principle of correct design and selection of induction coil is that the induction coil should have a shape suitable for the weldment, and the useless gap between the induction coil itself and the weldment should be reduced as much as possible, preferably not more than 2 ~ 3 mm, in order to improve the heating efficiency. In order to heat the weldment stably and evenly and prevent local overheating at the sharp corner of the weldment, the parameters such as the number of turns of the induction coil and the alternating frequency of the induction current should be reasonably selected.

4) Brazing in the furnace

The method of heating and brazing the assembled workpiece in the heating furnace heated by resistance wire is called furnace brazing, which is characterized by the whole heating of the workpiece, uniform heating and small deformation of the workpiece. Disadvantages are slow heating speed and low efficiency. But for mass production, multiple joints and weldments can be brazed in one furnace at the same time, which can make up for the problem of low heating efficiency. The heating atmosphere for brazing in the furnace is as follows:

A) air furnace

Because the workpiece is easy to be oxidized when the weldment is heated in air, and the heating rate is slow, which is not conducive to the removal of oxide film by brazing flux, its application is limited to some extent, and it has been gradually replaced by protective atmosphere furnace and vacuum furnace brazing.

B) protective atmosphere furnace

According to the different protective atmosphere, it can be divided into nine types: reducing gas furnace brazing and inert gas furnace brazing. Generally, H2 or CO is used as reducing gas, which can not only avoid the oxidation of the workpiece during heating, but also reduce the oxide film on the surface of the workpiece, which is helpful for the wetting of solder. Inert gases generally include argon, N2, helium, etc. The requirement for gas purity is higher, generally above 99.99%. The gas must go through dehydration (silica gel, concentrated sulfuric acid) and deoxidation (sponge titanium) devices before entering the furnace. Workpieces should usually be placed in containers, heated and brazed in flowing gas. It is safer to use inert gas than reducing gas. Heating temperature, holding time and cooling rate are the main process parameters. When the heating temperature is higher than 900℃, the hardness of cemented carbide will decrease obviously. If the holding time is too long, the hardness of cemented carbide will also decrease. After welding, it should be cooled slowly to prevent cracking.

C) vacuum furnace

Vacuum brazing is based on the evaporation of metal and its oxide during vacuum heating, which destroys the oxide film on its surface, thus achieving the effect of film removal. Under vacuum conditions, some metals can evaporate significantly below the melting point, and some metal oxides can volatilize. The evaporation of metal, especially the evaporation of metal oxide, can effectively destroy the surface oxide film, making flux-free welding possible under vacuum conditions. For YW cemented carbide with TiC as hard phase, it is a better method to use Ag-Cu-Zn alloy as filler metal and braze it in vacuum furnace, because the volatilization of Zn can enhance the diffusion ability of Cu in the welding process, thus improving the weld strength 13.

The advantage of vacuum brazing is that it can prevent the welded metal, cemented carbide and brazing filler metal from reacting with gas media such as oxygen, hydrogen and nitrogen, and the temperature gradient can be greatly reduced due to the slow heating and cooling of brazing components in vacuum furnace, which is beneficial to reducing brazing stress and obtaining high-quality brazing quality. When welding large workpieces and cemented carbides with complex shapes, vacuum brazing technology is especially beneficial. Because the evaporation of metals and their oxides is 14 with the decrease of ambient air pressure and the increase of temperature, the vacuum degree, heating temperature and holding time in vacuum brazing furnace are the main factors affecting the brazing quality, and it is very important to choose these parameters correctly.

The choice of heating temperature should refer to the actual melting point of the solder used, and heating in air is generally higher than the melting point 10 ~ 30℃. In vacuum brazing, due to the lag effect of heat transfer and in order to improve the fluidity of solder, the heating temperature is slightly higher than in air,14; For weldments of the same size, the holding time in vacuum brazing should be longer than that in air furnace. If the time is too short, it will be too late to form enough metallurgical bonding between the solder and the parent material to be welded, and it may also cause "virtual welding" due to uneven heating. On the other hand, if the holding time is too long, the solder may be seriously burned and evaporated, resulting in the decrease of weld strength 14.

The choice of vacuum degree is related to the material of the welding part, the composition and properties of the solder used, and also to the brazing temperature. Generally, it should be above 10-3Mpa, so as to obtain a good stripping effect. The temperature at which zinc and silver in solder obviously evaporate in vacuum is low. In order to avoid the evaporation of these elements in the solder, the vacuum pumping can be stopped when the melting temperature of the solder is close. In addition, the required vacuum degree in the furnace can be deduced from the heating temperature of weldments and solders of certain materials.

5) laser brazing

As a new type of welding heat source, laser has the characteristics of fast heating speed, narrow heat affected zone, small post-welding deformation and residual stress, and has unique advantages in reducing the embrittlement of joint fusion zone. This makes it possible to apply it to the welding of cemented carbide. According to the relevant literature, the brazing of cemented carbide can be carried out by laser "deep penetration welding" and "thermal conduction welding", and pure Cu and Ag-Cu alloy can be used as brazing filler metals. Relevant process parameters mainly include laser power, welding speed, focus position, filling layer thickness and so on. 15- 17. Because the melting points of cemented carbide and brazing filler metal are quite different, the process parameters should be strictly controlled during welding, so that the brazing filler metal can fully melt and soak the cemented carbide in an instant, and the cemented carbide matrix can be heated to a higher temperature without melting, so that it can be better wetted by liquid brazing filler metal to form an ideal brazing joint 16.

In the process of laser deep penetration welding, the laser power density is very high. In the area directly affected by laser, cemented carbide can reach a very high temperature instantly, and it has a fierce "affinity" effect with Cu in the solder, which is easy to cause evaporation and excessive burning loss of the solder, leading to serious surface depression. Therefore, it is necessary to reduce the burning loss of solder by properly adjusting the process parameters. In addition, because the content of Co in cemented carbide is generally very low, it is easy to escape at the high temperature of laser deep penetration welding, so that WC exists in a loose state. At this time, cemented carbide will not be able to maintain its original compact sintered structure and properties, thus inevitably producing some cracks, pores and other defects in the joint.

In the process of "thermal conduction welding", the laser beam directly acts on the solder, and the surface coating is needed to improve the laser absorption rate of the solder. In addition, in order to make the solder absorb laser energy as much as possible in an instant and melt, a small diameter spot 15 should be used. During welding, most of the energy of the laser beam is absorbed by the brazing filler metal, and the absorbed energy is quickly conducted downward in a very short time, so that it is completely melted and infiltrated into the cemented carbide. In this way, it is easy to obtain a complete brazed joint 15 without depression.

In the process of laser brazing, due to the extremely short thermal process, generally only the Co in cemented carbide dissolves and diffuses to the liquid solder for a short distance, while the Cu in the solder basically does not diffuse to the cemented carbide, so the metallurgical bonding between them is not sufficient, which will directly reduce the shear strength of the joint. Because the physical and chemical properties of Ni are similar to those of Co in cemented carbide, it is well compatible with cemented carbide and infinitely miscible with Cu. Therefore, in order to improve the metallurgical bonding between solder and cemented carbide and improve the joint quality, the method of electroplating Ni on the brazing surface of cemented carbide in advance can be used to improve it.