Laser sensor welding application

Laser welding technology is a high-tech. Due to its unique characteristics, it is especially suitable for use in sensor sealing welding. At present, many foreign manufacturers of sensors use laser welding to produce sensors, but there are not many manufacturers using this technology in China. China's sensor manufacturers should use domestic laser welding machines to produce and process sensors as soon as possible to increase product competitiveness and open up the international market.

First, the sensor

According to the national standard GB7665-87, the sensor is defined as a device device that can be sensed and converted into an available output signal according to a certain law. As a testing tool, the sensor requires the detection of physical or chemical information of the research object. The working process requires stable, reliable and high precision. Therefore, the sensor has the following requirements:

(1) Strong ability to adapt to harsh environments

The sensor generally has a wide working environment, from extremely cold to hot areas, many work in open air environment, can resist sand and dust, and should also resist moisture, high resistance to salt corrosion and acid corrosion, and anti-pollution gas interference. The ability to adapt to high temperature, extreme cold, strong vibration, shock and normal working under other conditions, but also strong anti-noise ability, high signal to noise ratio.

(2) Moderate price, suitable for mass production

It is required to have good sensor consistency, suitable for automated mass production, and has high requirements for processing equipment, so as to eliminate inconsistencies and mistakes caused by manual operations.

(3) High stability and reliability

The sensor is a high-precision testing instrument that has strict requirements in military, aerospace and aerospace applications. Products must be rigorously tested before they can be applied. Therefore, sensor production is a specific application and embodiment of high technology. Whether a sensor has a high technical added value is reflected in whether the technology content and the technology of the processing technology are high. Some sensors require metal packaging due to the condition of their application environment. Generally, welding seals, such as pressure sensors, force sensors, Hall sensors, photoelectric sensors, temperature sensors, etc., have sensitive components and integrated circuits inside, which are filled with inert gas. Or vacuuming is isolated from the outside world. It has pressure and air tightness requirements. It also has welding strength requirements and air leakage rate requirements. It requires high welding quality, and requires small deformation during welding. It cannot damage internal components and microcircuits. . At present, the sensor is sealed with resistance welding, tungsten argon arc welding, plasma arc welding, electron beam welding and laser welding.

Second, laser welding

1. Principle of laser welding

Laser is the abbreviation of stimulated emission light amplification of radiation. Due to its unique high brightness, high directivity, high monochromaticity and high coherence, it has been widely used in industrial processing since its birth, becoming a future manufacturing system. Common processing methods. Laser welding is a laser beam with high radiation intensity. After the laser beam is focused by the optical system, the power density of the laser focus is 104~107W/cm2. The processed workpiece is placed near the laser focus for heating and melting, and the melting phenomenon can be generated. And the degree of strength generated depends mainly on the time, power density and peak power of the surface of the laser-acting material. By controlling the above parameters, various laser welding processes can be performed using a laser.

2. General characteristics of laser welding

Laser welding is a thermal processing process that uses a laser beam as a heat source. It has many advantages over electron beam plasma beams and general machining:

The laser beam has a small laser spot and a high power density, and can weld some high melting point and high strength alloy materials.
Laser welding is non-contact machining with no tool loss and tool changeover. The laser beam energy is adjustable, the moving speed is adjustable, and it can be processed in a variety of ways.
Laser welding is highly automated and can be controlled by a computer. It has a fast welding speed and high efficiency, making it easy to weld in any complex shape.
The laser welding heat affected zone is small, the material deformation is small, and no subsequent processing is required.
The laser can weld the workpiece in the vacuum vessel and the workpiece in a position inside the complex structure through the glass.
The laser beam is easy to guide and focus to achieve various directions.
Compared with electron beam processing, laser welding does not require a strict vacuum equipment system and is easy to operate.
Laser welding has high production efficiency, stable and reliable processing quality, and good economic and social benefits.

3. Process characteristics of laser welding in sensor production.

The laser is used to seal the sensor metal casing is currently the most advanced processing method, mainly based on laser welding has the following characteristics:

(1) High aspect ratio. The weld is deep and narrow, and the weld is bright and beautiful.

(2) Minimum heat input. Due to the high power density, the melting process is extremely fast, the input workpiece heat is very low, the welding speed is fast, the thermal deformation is small, and the heat affected zone is small.

(3) High density. During the formation of the weld, the molten pool is continuously stirred and the gas is easily released, resulting in the formation of a non-porous penetration weld. The high cooling rate after welding is easy to make the weld microstructure fine, and the weld strength, toughness and comprehensive performance are high.

(4) Strong welds. High-temperature heat source and sufficient absorption of non-metallic components produce purification, reduce impurity content, change inclusion size and its distribution in the molten pool, no electrode or filler wire is needed in the welding process, and the melting zone is less polluted, making the weld The strength and toughness are at least equivalent to or even exceed the parent metal.

(5) Precise control. Because the focusing spot is small, the weld can be positioned with high precision, the beam can be easily transmitted and controlled, the torch and the nozzle need not be replaced frequently, the auxiliary assist time is significantly reduced, the production efficiency is high, the light has no inertia, and the emergency stop can be stopped at high speed. And start again. Complex components can be welded with self-controlled beam movement technology.

(6) Non-contact, atmospheric welding process. Since the energy comes from the laser, the workpiece has no physical contact, so no force is applied to the workpiece. Magnetic and air have no effect on the laser.

(7) Since the average heat input is low, the machining accuracy is high, the rework cost can be reduced, and the laser welding operation cost is low, thereby reducing the workpiece cost.

(8) It is easy to automate and effectively control beam intensity and fine positioning.

Third, laser welding and existing welding methods

At present, the methods used for sensor sealing welding include: electric resistance welding, argon arc welding, electric beam welding, plasma welding, and the like.

1. Resistance welding: It is used to weld thin metal parts, and the welded workpiece is clamped between the two electrodes through a large current to melt the surface of the electrode contact, that is, the welding is performed by the resistance of the workpiece. The workpiece is easily deformed, the resistance welding is welded on both sides of the joint, and the laser welding is performed only from one side. The electrodes used for electric resistance welding are frequently maintained to remove oxides and metal adhered from the workpiece. Laser welding of thin metal lap joints is not In contact with the workpiece, the beam can also enter the area where conventional welding is difficult to weld, and the welding speed is fast.

2. Argon arc welding: non-consumable electrodes and shielding gas are used to weld thin workpieces, but the welding speed is slow, and the heat input is much larger than laser welding, which is prone to deformation.

3. Plasma arc welding: similar to argon arc, but its torch will produce a compression arc to increase the arc temperature and energy density. It is faster than argon arc welding and has a deeper penetration, but it is inferior to laser welding.

4. Electron beam welding: It relies on a beam of accelerated high-energy density electrons to strike the workpiece, generating huge heat in the small surface of the workpiece, forming a "small hole" effect, thereby implementing deep-fusion welding. The main disadvantage of electron beam welding is that it requires a high vacuum environment to prevent electron scattering. The equipment is complicated. The size and shape of the weldment are limited by the vacuum chamber. The assembly quality of Korean parts is strict. Non-vacuum electron beam welding can also be implemented, but due to electronics. Scattering and focusing are not good enough to affect the effect. Electron beam welding also has magnetic offset and X-ray problems. Because of the electron charging, it is affected by the magnetic field deflection. Therefore, the electron beam welding workpiece is required to be demagnetized before welding. X-rays are particularly strong under high pressure and require protection from the operator. Laser welding eliminates the need for a vacuum chamber and demagnetization of the workpiece before welding. It can be carried out in the atmosphere without X-ray protection, so it can be operated in-line or in a magnetic material.

Fourth, the application prospect of laser welding in sensor production

Laser welding technology is a high-tech. Due to its unique characteristics, it is especially suitable for use in sensor sealing welding. At present, many foreign manufacturers of sensors use laser welding to produce sensors, but there are not many manufacturers using this technology in China. It is mainly used by some manufacturers and some scientific research institutions that produce military sensor products, and many of them use foreign laser welding machines. At present, domestic laser welding machines are not far from the foreign products in terms of performance, and can fully meet the technical requirements of domestic production of sensors, but the price is 1/3-1/5 of similar foreign products. In order to improve the overall level of domestic sensors and develop the national laser industry, China's sensor manufacturers should use domestic laser welding machines to produce and process sensors as soon as possible to increase product competitiveness and open up the international market.