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Vacuum Brazing of Auto Parts
Dongfeng Motor Corporation’s new models EQ140, EQ145, EQ153 and Cummins engine return water, oil, steam and other pipe joints, degassing plugs and pump cover joints must have certain strength and high tightness. The original high-frequency brazing process. The brazing filler metal is brass and the flux is borax. In the high temperature brazing process, the brazing filler metal and flux interact with oxygen in the air to produce strong splashes, and the brazing seam produces a large number of shrinkage holes, pores, and poor forming. The outer surface of the part is stuck with rough solder, solder slag and other dirt. It is difficult to clean before galvanizing, and the sealing performance is poor, which affects the quality and service life of the product.
To this end, the heat treatment teaching and research room adopts the vacuum brazing process, and the solder is red copper without flux. Vacuum brazing is a mass production method of metallurgically combining various parts into composite parts in a vacuum furnace. The brazing filler metal of vacuum brazing wets the surface of the base metal to be welded. And form a solid solution intercrystalline bond, which is firm and reliable, and has good sealing performance.
In order to speed up the nationalization of Dongqi imported technology and improve the quality, the heat treatment teaching and research department has undertaken the vacuum brazing test task of pipe joints and degassing plugs for EQ1141G. It has been accepted by Dongqi Technology Office, Technology Center and other units and has been used in production. Various pipe joints and components of automobiles are vacuum brazed and the brazing seam is smooth, clean, beautiful, and has good sealing performance. Therefore, the vacuum brazing process is worthy of promotion and application.
Raw material preparation
A3 steel joints, pipe joints, degassing plugs, pump covers and other parts, high-frequency brazing straight pipe joint assemblies. T2 copper wire φ1.5mm; He copper wire φ1.5mm. EXS – 83 type normal temperature micro-bubble metal cleaning agent.
After the joints, pipe joints, degassing plugs, pump covers and other parts are cleaned of surface dirt, they are dried in a 45kw box-type resistance furnace. Put the T2 copper wire ring on the joint, and press it into the groove of the pipe joint or the degassing plug interface respectively to form a straight pipe joint assembly or a degassing plug assembly. The schematic diagram of the assembly of the straight pipe joint and the schematic diagram of the assembly after brazing are shown in the figure.
Put the assembled copper brazing filler metal into the vacuum brazing furnace. When the vacuum degree in the furnace reaches 1×10-2 Torr and the furnace temperature rises to 1093-1149 °C, keep it for 1 minute. Move to the front chamber of the vacuum furnace. At this time, the vacuum degree of the front chamber is still maintained at 1×10-2 Torr. After cooling, the furnace is air-cooled.
The picture on the left is the straight pipe joint assembly, the degassing plug assembly, and the brazing parts of the end pipe joint assembly. The picture on the right shows the brazing parts of the pump cover. After the joints of the above assemblies are vacuum brazed, the brazing seam is smooth, clean and beautiful, and the whole part has no oxide scale.
The vacuum brazing temperature is high, and the matrix (base metal) has low hardness and good plasticity due to the tendency of grain coarsening.
The high-frequency brazing process has a fast heating rate and a fast cooling rate. Because the cold technology matrix is fibrous, the metallographic structure has little time to change, so the hardness is high.
The microstructure of the vacuum fiber seam transition zone is α+ε solid solution, and the central zone is α solid solution, and they all have the characteristics of solid solution strengthening, while the high frequency brazing zone microstructure α + β, β phase distribution is not uniform, plus the central Zn in the brazing process. Burning, evaporation and strong spatter during welding make the hardness low.
Advantages of vacuum brazing
(1) Parts such as pipe joints and degassing plugs for EQ1141G are vacuum welded, and the brazing seam is smooth, clean and beautiful, and the whole part has no oxide scale. It can be directly electroplated without cleaning, and the electroplating effect is better. The brazing seam has high tensile strength and good sealing performance. Instead of high frequency brazing.
(2) The vacuum brazing process is simple, easy to master, stable in quality, high in automation and good in working conditions for workers.
(3) Vacuum brazed straight pipe joints, end-type pipe joints, degassing plugs and other parts have improved the quality of Dongqi’s three cars and one machine, and have promotion and application value in Dongqi.
Equipment selection: The RHVB series vacuum brazing furnace produced by SIMUWU is a high-quality product for the vacuum brazing process of tools and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum brazing process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.