Specification for high-frequency brazing

High frequency brazing operation specifications

1. Welding equipment and materials

1.1 High frequency brazing equipment Induction brazing is a welding method that provides a heat source through induction heating, and transmits electrical energy to the workpiece through induction or working coils instead of directly energizing the workpiece. It selectively heats the surface of the parts to be welded to the brazing temperature. The equipment used in the welding process consists of high-frequency induction heating equipment, high-frequency induction brazing mechanical devices, water cooling systems, and control systems.

The commonly used hard alloys for 1.2 hard alloy blades include YT5, YT15, YT30, YG3X, YG11C, YN, etc. The physical properties have a significant impact on the weldability due to their linear expansion coefficient. The linear expansion coefficient is (4.2-7) x 10-6/℃, and the thermal conductivity coefficient of hard alloy is 0.08-0.21 cal/cm · s · degrees, which are important reasons for welding stress.

1.3 The commonly used tool bodies for hard alloy cutting tools include materials such as 45 #, 55 #, and 40Cr, with a linear expansion coefficient range of 12.0 to 14.0 × 10-6/℃.

1.4 Brazing Materials: The selected brazing materials for hard alloy brazing have good wettability and high weld strength. At the same time, the brazing materials have good high-temperature plasticity and diverse shapes. The brazing material needs to be wiped clean with alcohol or other substances before use.

1.5 Selection of brazing materials The principle of selecting brazing materials is to wet the base material and form a good brazing joint, meet the requirements of the workpiece, meet the brazing method and brazing performance requirements, and have low cost.

1.5.1 Try to choose the type of brazing material with the same main composition as the base material, so that both will have good wettability;

The liquidus of the brazing material should be 40-50 ℃ lower than the solidus of the base material;

The melting zone of the brazing material, i.e. the temperature difference between the solid phase line and the liquid phase line composed of the brazing material, should be minimized as much as possible, otherwise it will cause process difficulties. A large temperature difference should also cause melting and precipitation.

The main components of the brazing material should be as close as possible to the main components of the base metal in the position of the periodic table, so as to cause less electrochemical corrosion and better corrosion resistance of the joint.

During brazing, if there is no flux coordination, it is easy to form brittle compounds at the joint of the brazing seam. So it is necessary to cooperate with brazing flux during brazing. The high-frequency induction brazing process for hard alloy cutting tools uses a brazing flux with chemical composition of dehydrated borax (50%), boric acid (35%), and dehydrated potassium fluoride (15%).

1.6.1 The brazing flux should be able to dissolve or damage the oxide film on the surface of the brazing component and brazing material well;

1.6.2 The melting point of the brazing flux and the melting temperature below the activation temperature should be slightly lower than (about 10-30 ℃) the melting temperature of the brazing material;

1.6.3 At brazing temperature, it should have low viscosity, good fluidity, and be able to effectively wet the brazing metal and reduce the interfacial tension of the liquid brazing material;

1.6.4 Solder flux and its products after removing oxides have a low density, which is conducive to floating on the surface and forming a thin layer to cover the solder and brazing metal, effectively isolating air and also easy to remove, so as not to become slag in the front;

1.6.5 The corrosiveness of brazing flux and its residue to the brazing metal and joint should be small, and the toxicity of its volatile substances should be low.

2. Key welding process technologies

2.1 Preparation before welding

2.1.1 Check for oil stains and other foreign objects on the hard alloy blade and keep it away from the operating site. Clean with gasoline, alcohol, or acetone; Inspect the blades piece by piece without any visible cracks, chipping or other defects.

2.1.2 For the blade body, in addition to checking whether the shape and size of the groove are similar to the blade, burrs at the groove must be thoroughly cleaned. 2.2 Welding

2.2.1 Application of brazing materials and fluxes The brazing flux on the brazing material should be evenly applied, and the solder should fill the weld seam.

2.2.2 The relative position between the tool and the sensor. The unreasonable relative position between the tool and the sensor often leads to local overheating, which can cause the blade and edge to crack. Therefore, it is necessary to control the relative position between the tool and the sensor. The relative position dimensions between the cutting tool and the sensor are 3-5mm.

2.2.3 The shape of the sensor should be based on the shape of the tool, so that the induced current flows parallel to the welding plane as much as possible. The number of tools in the sensor should be controlled to 1-2.

2.2.4 When heating high-frequency brazing, the brazing temperature and heating speed are the main process parameters that affect the quality of brazing welding. Excessive brazing temperature and heating speed cause significant internal stress inside the tool, which can easily lead to cracks and collapse after welding. The low brazing temperature affects the strength of the brazed weld, and the slow heating speed causes adverse phenomena such as grain growth and coarsening of the base material. The brazing temperature, as the main process parameter during brazing, should generally be 30-50 ℃ higher than the melting temperature of the brazing metal oxygen material. For example, the liquidus of HL105 brazing material is 909 ℃, and the brazing temperature is suitable between 939 ℃ and 959 ℃. At this time, the fluidity and permeability of the brazing material are good. If the heating is too high, it is easy to cause zinc evaporation and manganese oxidation in the brazing material, leading to problems such as slag inclusion and decreased joint strength; If it is too low, it will affect the spreading of the brazing material.

2.2.5 Operation: ① Place the pre welded component into the sensor and continuously press the switch to slowly heat it up; ② When heating to a certain temperature causes the brazing material to seep out like beads of sweat, a copper heating rod should be used to move the hard alloy back and forth along the groove 3-5 times to eliminate the slag in the weld seam. If the slag is not eliminated, it will form slag inclusions, which will affect the welding quality. The advantage of using a copper rod for operation is that it does not stick to flux, solder, and alloy, and it is not easy to sense, which can be used in various brazing heating processes After slag removal, use a lever to place the blade upright, paying attention to the blade and groove.

2.3 Post weld insulation is an important process in hard alloy brazing, and the quality of insulation directly affects the quality of the weld. For hard alloy cutting tools (YT type) with a greater tendency to crack, it is prohibited to contact the newly welded cutting tools with water or damp cold ground, and it is also not allowed to cool them with strong winds. Generally, slow cooling should be carried out in quartz sand, asbestos powder, or aluminum silicate fiber boxes. The cutting tools should be densely stacked in the insulation box, relying on a large amount of heat from the workpiece to maintain insulation and slow cooling. If conditions permit, the method of simultaneous insulation, slow cooling, and low-temperature tempering can be used. The welded cutting tools are immediately sent to the insulation box and kept at 250 ℃ to 300 ℃ for 5-6 hours before being cooled in the furnace.

2.4 Remove excess flux near the weld seam. Boil the cooled workpiece in boiling water for 30-45 minutes after welding, and then perform sandblasting treatment to completely remove excess flux and oxide skin and other dirt at the weld seam. If conditions permit, the workpiece can also be placed in the pickling tank for pickling. After pickling, it must be cleaned successively by a cold water tank and a hot water tank. The pickling time should not be too long, generally ranging from 1 to 4 minutes depending on the specific situation. Prolonged pickling may cause corrosion of the weld seam.

2.5 Quality inspection after brazing without cracks. For workpieces that have been found to have defects, they can be re heated and brazed, but the number of re welds should also be minimized to avoid affecting the quality of hard alloys due to repeated heating. For workpieces that have undergone crack inspection and have been welded, the cracked hard alloy should be removed and re brazed after analyzing the cause.