Induction brazing of double tube pressure plate

Induction brazing of double tube pressure plate

  Abstract: This article proposes a high-frequency induction brazing method for the double-tube pressure plate in the automotive air-conditioning parts. In addition, the process flow and operation method are proposed to improve the existing production process and solve the problem that the aluminum double-tube press plate is difficult to perform induction brazing. 

Key words: high frequency induction brazing, double tube pressing plate, aluminum high frequency induction brazing process

1. Overview of high frequency induction brazing of single tube clamp

1.1 Overview of high frequency induction brazing

 High-frequency induction brazing: The welding seam is heated to the melting temperature of the alloy solder by heating, but the metal being welded at this time still has not reached the melting temperature, and the low melting point alloy bonds the two metals together through strong surface tension After cooling, a solid weld is formed. The parts of the same or different materials can be welded together, the material saving effect is remarkable, and various needs can be met. Suitable for welding various magnetic materials such as steel, copper, aluminum, nickel, and special alloys. High-frequency local welding has high strength, no deformation, and comprehensive mechanical properties are better than other welding.

       Shoulder brazing is one of many brazing methods. It does not use heat radiation to heat the metal, but uses the principle of electromagnetic induction to make the metal itself generate heat. This heating method has high energy utilization rate and rapid heating, and only uses electric energy, and has the characteristics of low energy consumption, low pollution, and low harm.

1.2 Overview of double tube clamp

  The double-tube pressure plate is a very common important functional accessory in the automotive air-conditioning pipeline.

Figure 1 Double tube pressure plate

2. Material welding performance analysis

  Compared with other alloys, aluminum alloy is more difficult to braze, the main reasons are:

(1) It is easy to form an extremely dense oxide film on the surface. The nature of this oxide film is very stable, covering the surface of the workpiece will hinder the wetting of the solder on the surface of the workpiece, thereby affecting the quality of brazing. The melting point of the oxide film on the surface of aluminum alloy is very high, and at the brazing temperature of 500~600℃, the thickness of the oxide film will sharply increase to about 20~40 times that at room temperature, which seriously hinders the wetting and wetting of the brazing filler metal and the base material. Combine. This is also the main reason why it is difficult to repair aluminum alloy after brazing once;

(2) When brazing aluminum alloy, since the melting point of the brazing filler metal is not much different from that of the aluminum alloy, the brazing temperature must be strictly controlled, otherwise it will easily cause the workpiece to burn out.

It should be pointed out that the brazing performance of the material cannot be changed, but we can improve the welding quality by improving the brazing process.

3. Description of process status

  At present, the main method to solve the welding of automobile air-conditioning pipes is through artificial flame welding, but artificial flame welding has disadvantages such as high temperature, glare, noise, smoke, and high-intensity work.

Figure 2 Tunnel brazing furnace	Figure 3 Artificial flame brazing

4. System architecture description

  The system consists of seven parts: chiller, induction power supply, extension, output unit, positioning tooling, auxiliary parts, and cleaning after welding.

Figure 4 System architecture description

  The basic working unit includes a chiller (mainly used for circulating cooling for the output unit and the main extension of the induction heating power supply), and the induction heating power supply, extension and output unit are a mature subsystem. When large-scale mass production is carried out, positioning tooling must be used, otherwise it will not be able to meet the production requirements. Therefore, as long as there is a chiller, an induction power supply system, and a positioning tool, the production work can be carried out. For higher requirements, a complete set of high-frequency induction brazing solutions can be realized with the help of auxiliary equipment, such as infrared thermometers, post-welding cleaning devices, such as ultrasonic cleaning machines.

Figure 5 Equivalent physical diagram of the system framework

5. Process flow
 
  Welding power source selection-sensor selection-solder flux selection-tooling positioning design-accessory selection-welding parameter determination-cleaning after welding

5.1 Selection of welding power source

  According to the pipe diameter and the size of the pressure plate in the double-tube pressure plate in the picture, we choose the dedicated all-digital L-DIH-40 model as the welding power source.
 

Figure 6 All-digital L-DIH-40 welding power source

5.2 Sensor selection

  The bottom of the pressure plate is a flat solid aluminum joint, and the area is larger than that of the aluminum tube, and the wall thickness of the aluminum tube is relatively thin. In the case of absorbing the same energy, the joint generates less heat than the aluminum tube. When designing the inductor, consider the uniform heating of the joint and the aluminum tube, that is, reach the brazing temperature at the same time. At the same time, it is necessary to consider the way the workpiece is put in and taken out during the production process. Combining these two factors, an oval-shaped sensor with two sensors inside and one outside was designed.

Figure 7 Welding output terminal

5.3 Selection of solder additives

  The aluminum double-tube press plate is determined by our company's process department to use flux-cored welding wire or self-brazing wire.

Figure 8 Solder additives

5.4 Tooling positioning design

  Induction heating welding is to place the welding part of the workpiece in an induction magnetic field for heating. The strength of the magnetic field in each part of the magnetic field is different, and there is a high requirement for the positioning repeatability of the workpiece. Therefore, it is necessary to design the corresponding tooling according to the specifications of each workpiece and the welding process at the same time. Our company can provide induction brazing tooling design services.

Figure 9 Tooling fixture

5.5 Auxiliary selection

  In high frequency induction welding, the induction heating power supply needs to be cooled, and an industrial chiller of corresponding specifications is required. When the customer uses the infrared mode and performs temperature monitoring in real time, a digital infrared thermometer needs to be installed. Our company's infrared temperature measurement When the instrument and the power supply work together, the temperature control accuracy can reach up to plus or minus 1℃. Our company can provide water chillers, high-frequency brazing customized infrared thermometers.
 

Figure 10 Industrial chiller	Figure 11 Digital infrared thermometer

5.6 Determination of welding parameters

  After our long-term high-frequency brazing research and a lot of customer experience, we choose the automatic heating mode in this model. The heating current of the automatic heating mode is divided into five sections. In this process, the characteristics of aluminum metal increase with the temperature. High resistance increases, and the Joule effect causes the heating rate to increase during the heating process. This is inconsistent with the welding process summarized by our research. Therefore, we use the method of gradual decrease in current to heat the welding part. In this way, the temperature of the welding part can be increased under the premise of uniform heating, and the workpiece can be prevented from overburning in the high temperature section. Finally, in order to ensure the integrity of the welding process, we set a small current for heat preservation afterwards to ensure that it reaches the penetration standard and has no porosity. And other technological standards.

Figure 12 Heating parameter setting	Figure 13 Display of operating parameters

5.7 Cleaning after welding

 After the soldering is completed, the surface of the solder accumulation area needs to have auxiliary residues, which need to be cleaned. The current environmentally friendly way is to use ultrasonic cleaning. Our company can provide ultrasonic cleaning machine after high frequency welding.

Figure 14 Fully automatic ultrasonic cleaning machine	Figure 15 Industrial single tank ultrasonic cleaning machine

6. Operation steps

  Surface preparation: remove the oxide film and oil stains on the surface of the workpiece

  Positioning of the workpiece: the workpiece is positioned, supported, and fixed to ensure that the relative position of the workpiece and the sensor is unchanged during mass production, and the brazing filler metal is made into a ring and added to the part to be welded.

  Heating process: set the parameters-press the start button-start work, the equipment will accurately weld the workpiece according to the previously set parameters, and automatically stop heating after the welding is completed.

  Post-brazing treatment: directly put the workpiece in the water or clean it with other chemicals

7. Energy consumption comparison

(1) The welding process is equipped to reduce the dependence on manual technology. Ordinary operators can replace the certified flame welders, which reduces the burden of safety and annual certification of the company.

(2) The advantages of induction brazing are not obvious when there are small workpieces and fewer pipelines. However, in the induction brazing welding process, the equipment is automatically welded without manual operation, and the welding time can be used to operate another equipment, so that one person can operate two welding machines at the same time. This can further improve product quality.

(3) According to the data in the above figure, an induction brazing equipment can save 10.6-9600=100,000 yuan per year

8. Summary

  This article describes the seven aspects of high-frequency induction brazing technology, material welding performance analysis, process status description, process flow, operation method, and energy consumption comparison of double-tube press plates in automobile air-conditioning pipelines. It is difficult to conduct aluminum metal The problem of induction brazing proposes a solution based on all-digital induction heating technology, covering all links before, during and after welding. And given detailed and effective data to prove that high-frequency induction brazing is superior to flame brazing in terms of environmental protection, energy consumption, and welding material consumption.