Differences between vacuum brazing and gas shielded brazing

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The common points of vacuum brazing and gas shielded brazing are as follows:
All the solders are made of metal materials with lower melting point than base metal. The solder (base metal) and solder are heated to a temperature higher than the melting point of base metal, but lower than the melting point of base metal. The liquid solder is used to wet base metal, fill the gap between joints, and diffuse with base metal to connect the solders.

Differences between vacuum brazing and gas shielded brazing:
The principle of vacuum brazing and gas-shielded brazing is basically the same, but there are great differences in details and specific requirements. From the quality point of view, vacuum brazing is much higher than gas-shielded brazing, mainly in terms of strength and cleanliness, but in terms of production efficiency, vacuum brazing is lower than gas-shielded brazing, and its cost is lower. Compared with gas shielded brazing, the difference is as follows:
1. The difference of brazing furnace structure;
2. Material differences;
3. The difference of parts precision requirement;
4. The difference of brazing technology;
5. Differences in product quality;
6. Differences in production efficiency and cost.

1. The difference of brazing furnace structure
Vacuum brazing: A closed furnace body is used. When brazing, the gas in the furnace needs to be pumped out so that it reaches the approximate vacuum state (3.5*10 Pa) and then brazed at elevated temperature. The purpose of vacuum brazing is to prevent the reaction between the workpiece and oxygen and other active gases in the air during the brazing process, and the exhaust gas in the furnace under high vacuum. The residual welding strength will be high with very little welding strength.
Gas shielded brazing: Continuous brazing method is adopted. In the brazing process, nitrogen-filled gas is mainly used to braze. The main purpose of nitrogen filling is to protect the oxidation of the weld, but because the furnace body is lying open, the protective layer of nitrogen can not reach uniformity, so the welding strength will be low.

2. Material differences
Vacuum Brazing Aluminum Material: Vacuum brazing material uses 4104 double composite material, of which 4104 solder contains 1.5% magnesium. Its main purpose is to break through AL2O3 on the surface of workpiece during high temperature brazing process, so that silicon in the material can flow with each other and achieve welding effect. Usually, the surface of aluminium alloy is protected by a thin layer of AL2O3. The melting point of AL2O3 is about 1200 degrees, so magnesium is needed to break it down.
Gas shielded brazing: Vacuum brazing material uses 4343 double composite material. There is no magnesium content in 4343 solder, mainly through flux to break down AL2O3 on the surface of aluminium alloy.

3. The difference of parts precision requirement
The precision requirement of vacuum brazing parts: the precision requirement of the parts is relatively high, which is less than 0.05 mm, otherwise brazing will be virtual welding, which will eventually lead to product leakage;
Gas shielded brazing: The precision of parts is not high, the gap is less than 0.2 mm, and the flux can be filled.

4. The difference of brazing technology
Vacuum brazing process:
At first, the gas in the furnace is evacuated (mainly the oxygen and other active gases in the furnace are removed to prevent Al from reacting again in the brazing process to produce AL2O3, which affects the welding quality) and then the heating welding is carried out. No flux is needed during the welding, because the magnesium element in the vacuum brazing material can break the AL2O3 on the surface of the material, and vacuum brazing is carried out. There is heat preservation process, this process can basically keep the temperature of all products in the furnace consistent, thus improving the brazing strength of products. Vacuum brazing furnace needs about 4 hours, because each product needs to be vacuum brazing, and cooling process before it is out of the furnace.
Gas shielded brazing: No vacuum is needed, the workpiece is directly protected by nitrogen gas. Before brazing, the workpiece needs to be coated with flux. During brazing, the AL3O 2 on the surface of the material is broken. The CAB is continuous track brazing with a speed of 350 mm/min (equivalent to 1.5 hours in a vacuum brazing furnace). There is no heat preservation process and no vacuum pumping. And cooling process.

5. Differences in product quality
Vacuum brazing:
The brazing strength of the products is relatively high, generally reaching more than 60KG (small gap between parts, high vacuum, high magnesium content in furnace seam); cleanliness is relatively high (no flux is needed, cleanliness can reach less than 5mg); the appearance of the products is relatively bright and metallic luster (less exhaust gas content in furnace, no gas oxidation reaction, even solder) This is the case.
Gas shielded brazing:
The brazing strength of products can only meet the requirements of general customers. The general strength is about 30KG. The cleanliness is difficult to guarantee because of the need for flux. The appearance of products is rather dim.

6. Differences in production efficiency and cost
Vacuum brazing:
The production cost of the product is relatively high: because each furnace needs vacuum pumping and heating process, the production efficiency is low; the product can not be reworked after failure, can only be scrapped, so the quality cost is also high;
Gas shielded brazing:
The production cost of the product is relatively low: because it can be produced continuously without vacuum and heating process, and the production efficiency is high; the product can also be reworked after failure, so the quality cost is low.

The cost of products mainly includes brazing manufacturing cost and product qualification rate.
1. Differential cost of brazing for each product;
2. The qualified rate of vacuum brazing is 95%, the qualified rate of gas-shielded welding is 99%, and the difference of manufacturing cost is 4%, which is reflected in the difference of product price by 3%.

Learn more :Vacuum Brazing Furnace Type