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Vacuum brazing of cold plate radiator for automobile automatic driving system

Cold plate radiator technical requirements:

As a cutting-edge technology in the field of automobile industry, the cold plate radiator of automobile automatic driving system is gradually moving from technology research and development to market application, and has broad market prospects. The product is manufactured by vacuum brazing process, which has the characteristics of small size deformation and clean inner cavity. At the same time, in order to avoid the risk of product leakage, higher requirements are put forward for welding quality. It is required to carry out ultrasonic testing on the welding surface, and the welding rate within the width range of 3mm along the circumference of the flow channel is required to reach 100%; the welding rate of the rest of the flow channel is required to reach more than 85%; the blasting strength is required to be more than 3MPa.

Product structure: The material of the base and faucet of this product is 6063, and the cover plate, inner fin, and solder sheet are double-coated composite materials 4104/6063/4104. The welding surface is divided into three parts: between the cover plate and the base, between the inner fin and the cover plate and the base, and between the faucet and the base.

Cold plate radiator vacuum brazing process:

Between the cover plate and the base, the base is a forging. Due to the many local hollows at the bottom, the strength is insufficient, and local collapse is prone to occur during welding; the fins are densely corrugated and have high strength. If the wave height is higher than the depth of the runner groove, even in the It is also difficult for the wave height to be reduced to the ideal fit size by the fixture in the hot state. Therefore, it is easy to cause the gap between the cover plate and the base to be too large, and high-quality welding cannot be formed. Thereby the technical requirement of 100% welding rate within the width range of 3mm along the circumference of the flow channel cannot be reached.

Between the inner fin and the cover plate and the base: the matching between the height of the inner fin and the depth of the runner groove is the key. If the inner fin is higher than the runner groove, it will affect the welding between the cover plate and the base. If there are too many grooves below the runner, and if it exceeds the brazing clearance requirement, high-quality welding cannot be formed between itself and the cover plate. The inner fins are double cladding materials with a thickness of 0.2mm, and the corrugation is dense, which is easy to produce welding defects with adhesion and erosion. The window of welding parameters is narrow. Between the nozzle and the base: the nozzle and the base are welded by brazing filler metal, and the brazing filler metal belongs to double-sided welding. It is required to form a precise small clearance fit between the parts, and the nozzle and the brazing sheet are pressed into the nozzle hole under the condition of no lubrication. The processing and assembly of parts are more difficult.

Vacuum brazing parameters:

Four stages of 450C, 565C, 605C, and 595C are used to raise and lower the temperature, and the test effect is good. Rapid temperature rise in the vacuum brazing section and shortening the holding time are effective methods to avoid the adhesion and corrosion of the inner fins. Control the vacuum brazing holding time of the product in the middle of the fixture when the temperature of the workpiece reaches the liquidus of the solder for two minutes, and the temperature difference of the whole product does not exceed 3C, and the vacuum degree of the brazing section is less than 1×10^-3Pa, so as to ensure the reliability of product welding quality and consistency.

Qualified requirements for vacuum brazing:

1) For products with high welding rate and high blasting strength requirements, the vacuum brazing gap is the key to ensure that the products meet the requirements. The gap must be controlled within 0.02mm. The design of products, processes, and tooling must be controlled around this key point. Insufficient structural strength of the product will cause changes in the vacuum brazing gap. When this problem occurs, it can be solved by adding a process boss to the product or adding a support to the fixture.

2) The welding quality of the inner fins has a decisive effect on the burst strength of cold plate products.

3) Vacuum brazing jigs for cold plate products can be designed with a stacked product structure to improve production efficiency as much as possible. The structural design keeps the product in a balanced force, and it is the control point to maintain an appropriate pressure on the product during the process of thermal expansion of the product and dimensional change after the solder is melted.

4) Vacuum brazing parameters should ensure that the solder is fully melted, and the product temperature difference should not be too large. At the same time, avoid fin adhesion and corrosion.

SIMUWU vacuum brazing equipment recommendation:

Uniform zone size (mm) (WHL)	900×900×1800mm
Ultimate vacuum（cold furnace condition）	1×10-4pa
Pressure rising rate（empty cold furnace condition）	≤0.67pa／h (empty cold furnace condition)
Maximum design temperature	750℃
Temperature uniformity(vacuum, empty furnace condition, 650℃)	±3℃(9 points)
Furnace chamber material	Inner wall SS 304 , outer wall carbon steel
Vacuum system	Germany Leybold