As a special connection technology, the success or failure of vacuum brazing depends on precise control of every detail. It is recommended to establish a complete 'Process Traceability File' to record the vacuum curve, temperature log, and quality inspection report for each production. For new product development, DOE experimental design should be carried out to systematically study the interactive effects of temperature, time, and pressure. Only by organically combining scientific theory with practical experience can the technology be fully utilized to manufacture high-quality joints that meet the requirements of working conditions such as aircraft engine blades and nuclear reactor heat exchangers.

Detailed explanation of the entire process of using a vacuum brazing furnace.

1、 Core process flow

Vacuum brazing is an advanced process that achieves metal connection by melting brazing materials at high temperatures in an oxygen free environment. Its standard operating procedure includes the following key steps:

Fixture design → workpiece pretreatment → furnace positioning → vacuum displacement → temperature rise and insulation → cooling and pressure relief → furnace inspection

2、 Deep analysis of each stage

1. Preliminary preparation and process planning

Material compatibility assessment:

Base material combination: Priority should be given to selecting the same type of metal or materials with a thermal expansion coefficient difference of less than 5% (such as titanium alloy/stainless steel requiring special treatment);

Solder selection: Select pure copper (melting point 1083 ℃), nickel based alloys (such as BNi-2, melting point 960-1040 ℃) or precious metal series (gold germanium eutectic alloy) according to the service temperature;

Gap control: The ideal fit gap is 0.05~0.2mm. If it is too large, it will cause capillary action failure, while if it is too small, it will hinder the flow of solder.

Customization of fixtures and jigs:

Using graphite/ceramic materials to make flexible support frames, with reserved space for thermal expansion compensation;

When stacking multiple layers, set up air ducts to ensure uniform vacuum infiltration;

Simulate and optimize key load-bearing areas to prevent misalignment caused by gravity deformation.

2. Assembly and furnace operation

Solder pre setting technique:

The foil shaped brazing material is cut slightly larger than the size of the weld seam, with rounded edges to reduce stress concentration;

The thickness of the paste like flux application should be controlled at 0.10.3mm, and the coverage area should exceed the edge of the joint by 23mm;

The complex structure adopts the segmented filling method, with each segment length ≤ 50mm to prevent collapse.

Load density optimization:

The total projected area of a single furnace shall not exceed 70% of the effective heating zone;

The interval between irregular parts should be ≥ 15mm to ensure smooth airflow channels;

Heavy parts are placed on the lower load-bearing platform with a center of gravity offset of less than 10%.

3. Execution of temperature control curve

Example of typical TC4 titanium alloy brazing process parameters:

Room temperature → [Heating rate 10 ℃/min] → 650 ℃ (preheating for 30 minutes) → [Heating rate reduced to 5 ℃/min] → 920 ℃ (insulation for 20 minutes) → Slowly cool down with furnace to below 150 ℃ and remove from the furnace

Key control points:

>The heating rate after 600 ℃ shall not exceed 8 ℃/s to prevent thermal shock cracking;

Activate the vibration device to promote slag discharge when reaching the liquidus temperature;

The main control Thermocouple deviation in the dual thermocouple temperature measurement system exceeds ± 3 ℃, triggering an alarm.

4. Post processing and inspection

Initial appearance inspection: visually inspect the weld seam for residual height ≤ 0.5mm, with no continuous porosity or incomplete fusion defects;

Non destructive testing: X-ray photography shall be carried out in accordance with ASME Section V, with a sensitivity level of not less than 2T;

Mechanical testing: Shear testing refers to the GB/T 11363 standard, and the qualified indicators are shown in the following table:

3、 Key points of safety protection

Electrical interlocking: It is prohibited to start the heating program when the furnace door is not fully closed;

Explosion proof design: The hydrogen pipeline is equipped with flame arresters and emergency shut-off valves;

Emergency response: equipped with dry powder fire extinguishers and CO ₂ fire extinguishing systems, and posted escape route maps;

Personal protection: Operators should wear aluminum foil insulated clothing and gas masks, and are prohibited from wearing synthetic fiber jewelry.

4、 Advanced Technology Expansion

Pulse pressure brazing: By adding pulsating pressure (0.1~0.3MPa) on top of traditional processes, the gap filling rate can be increased to 98%;

Laser assisted positioning: Real time monitoring of the melting state of the solder material using an infrared thermometer, with an accuracy of ± 2 ℃;

Digital twin application: Predicting temperature field distribution through simulation software to eliminate hot spot hazards in advance.