The application of infrared welding technology in fully automatic string welding machines

The fully automatic string welding machine is applied in the production of solar modules, which involves welding solar cells into a string of cells. Due to the direct impact of the welding quality of battery cells on the performance of components, the selection of welding methods is particularly important.

There are two welding methods for solar cells: contact welding and non-contact welding.

Contact welding, also known as soldering iron welding, utilizes the heat of the soldering iron tip for welding. This method is relatively traditional and has many drawbacks, such as poor temperature uniformity, frequent cleaning of the soldering iron head, and longer welding cycles;

Non contact welding mainly includes hot air welding, electromagnetic induction welding, and infrared welding, among which infrared welding technology is most widely used due to its unique advantages. This article mainly discusses infrared welding technology and its specific application in string welding equipment.

Special heating tube for string welding machine

1. Infrared welding technology

1.1 Infrared heater

It is composed of a quartz bubble shell and tungsten wire. Insert the tungsten wire into the inflatable quartz tube, and the tungsten wire generates heat and heats the gas in the quartz tube under the action of AC voltage, generating infrared radiation. When the infrared radiation is absorbed by the object, the object is heated. There is a reflective layer on the back of the lamp tube, which can concentrate light on one side and reduce energy waste. The filament is within a uniform range and is not easily sagging due to the support of tungsten wire.

1.2 Advantages and disadvantages of infrared welding

Advantages: High heating efficiency, low heat loss, low equipment maintenance cost, direct heating of objects without heating the surrounding air, and the optimal wavelength suitable for heating objects;

Disadvantages: Infrared radiation belongs to radiation technology and comes with a weakness in radiation technology - the risk of overheating; The temperature difference between solder joints caused by differences in thermal characteristics.

The application of infrared welding technology in string welding machine equipment

2.1 Infrared radiation module

The series welding machine equipment adopts a half face gold-plated infrared radiation module, which is welded using near-infrared radiation method. In addition, an infrared thermometer is installed as a supporting device. Through the sensing of the infrared temperature sensor, the temperature can be feedback in real time, making it easier for the system to control the temperature and maintain a relatively stable value.

The infrared radiation module mainly consists of half gold-plated reflective film infrared lamp tubes, heat dissipation fans, fixtures for installing the module, insulating porcelain parts, reflective covers, etc. The infrared lamp tube adopts a half face gold-plated coating, which can concentrate infrared heat and reflect it in the same direction, achieving a reflection efficiency of up to 95%. The module adopts 5 evenly spaced heating tubes (with a single heating tube power of 1.5 kW and a maximum module power of 7.5 kW), and uses a unified reflector cover. The heat source can effectively cover the entire battery area and has good temperature uniformity. (As shown in Figure 1)

Figure 1 Distribution of Radiation from Infrared Lamp

The equipment adopts two sets of identical infrared welding modules, with preheating and welding heating areas set up respectively. The preheating temperature is controlled between 120-160 ℃, and the welding temperature is controlled between 230-260 ℃. When the battery cells are transferred to the infrared welding area, the infrared lamp tube will emit a certain wavelength of infrared radiation in the direction perpendicular to the welding strip of the battery cells, rapidly increasing the temperature of the welding strip and the silver grid line of the battery cells. After heating up, welding will be applied simultaneously on both sides of the battery cells.

2.2 Principle of infrared welding temperature control

The principle of infrared welding temperature control: After the infrared temperature sensor collects the temperature, it feeds back to the infrared thermometer. The infrared thermometer outputs the temperature parameters to the input end of the PLC temperature control module. The PLC temperature control module adjusts the output current of 4-20 mA based on the difference between the measured temperature and the set temperature. By adjusting the power of the bidirectional thyristor, the output power of the infrared heating is controlled. The output power of an infrared heating tube is directly proportional to the heating temperature. (As shown in Figure 2)

Figure 2 Schematic diagram of infrared welding temperature control principle

The use of infrared welding can basically ensure uniform temperature distribution in the area, effectively solving the problem of virtual soldering of battery cells. The welding process is completed in one go, and the equipment efficiency has also been improved.

3 Conclusion

Due to the physical characteristics of thinness, brittleness, and susceptibility to cracking of solar cells, the difficulty of using automatic welding technology is relatively high. Infrared welding has the advantages of being clean, pollution-free, efficient, energy-saving, and easy to maintain, and is currently the most mature and stable welding method. This method not only ensures welding quality, but also greatly improves production efficiency. The welding appearance is more aesthetically pleasing compared to spot welding, which greatly reduces the problems of virtual welding and hidden cracks in the welding of solar cells. I believe that the application prospects of infrared welding technology will be even broader!