What are the advantages and disadvantages of laser welding?

What are the advantages and disadvantages of laser welding?

Compared with other welding technologies, the main advantages of laser welding are:

1. Fast speed, large depth and small deformation.

2. Welding is possible at room temperature or under special conditions, and welding equipment is simple. For example, when a laser passes through an electromagnetic field, the beam is not deflected and the laser can be welded in a vacuum, air, and certain gas environments, and can be welded through glass or materials that are transparent to the beam.

3. It can weld refractory materials such as titanium, quartz, etc., and other materials can be welded with good effect.

4. After the laser is focused, the aspect ratio can reach 5:1 and the maximum can reach 10:1 when the power density is high and welding high power devices.

5. Micro welding is possible. After the laser beam is focused, a small spot can be obtained and precise positioning, which is applicable to group welding of fine and small workpieces in mass automatic production. (Minimum spot can reach 0.1mm)

6. It can weld hard-to-reach areas and realize non-contact long-distance welding with great flexibility. In particular, in recent years, the adoption of optical fiber transmission technology in YAG laser processing technology, and the popularization of optical fiber continuous laser, laser welding technology has become more widespread and applied, which is more convenient for automation integration.

7. The laser beam is easy to implement beam splitting according to time and space, and can perform multi-beam simultaneous processing and multi-station processing, providing more precise welding conditions.

However, laser welding also has some limitations:

1. Welded parts require high-precision assembly, and the position of the beam on the workpiece is not significantly shifted. This is because the spot size after laser focusing is small and the weld seam filled with metal material is narrow. If the workpiece assembly accuracy or beam positioning accuracy does not meet the requirements, it is prone to welding defects.

2. The cost of lasers and related systems is high, and the one-time investment is large.

laser welding heat conduction

Laser welding is a method of irradiating a high-intensity laser beam on a metal surface and melting and welding the metal through the interaction between the laser and the metal. Metal dissolution is just one of the physical phenomena during the interaction of the laser with the metal. Sometimes the light energy is not primarily converted to metal melting, but in other forms such as vaporization, plasma formation, etc. However, to achieve good fusion welding, metal melting must be the dominant form of energy conversion. This requires understanding the various physical phenomena that arise from the interaction between the laser and the metal and the relationship between these physical phenomena and the laser parameters so that most of the laser energy can be converted into metal melting energy by controlling the laser. parameters, the purpose of achieving welding efficiency.

Process parameters of laser welding

1. Power density

Power density is one of the most important parameters in laser processing. Higher power densities can cause the surface layer to heat up to boiling in the microsecond time range, resulting in large amounts of vaporization. Therefore, the high power density is advantageous for material removal processes such as punching, cutting and engraving. For low power densities, it takes a few milliseconds for the surface temperature to reach the boiling point. The bottom layer reaches the melting point before the surface vaporizes, making it easy to form a good fusion weld. Therefore, power densities in conduction laser welding are in the range of 104 to 106 W/cm2.

2. Laser Pulse Waveform

Laser pulse shape is an important issue in laser welding, especially in sheet metal welding. When a high-intensity laser beam strikes a material surface, 60-98% of the laser energy is reflected off the metal surface and lost, the reflectance dependent on the surface temperature. During the action of the laser pulse, the reflectance of the metal varies greatly.

3. Laser Pulse Width

The pulse width is one of the important parameters of pulsed laser welding, and is not only the material removal and material melting and other important parameters, but also a key parameter that determines the cost and volume of the processing equipment.

4. Effect of Defocus Amount on Weld Quality

Laser welding usually requires some fuss because the power density in the center of the spot at the laser focus is too high and easy to evaporate into the hole. The power density distribution is relatively uniform across the plane away from the laser focus.

There are two defocusing methods: positive defocusing and negative defocusing. The focal plane above the workpiece is positive defocus, otherwise negative defocus. According to geometrical optial theory, when the defocus is positive, the power density of those planes is about the same, but the shape of the resulting molten pool is actually different. If the defocus is negative, a greater depth of penetration can be obtained, which is related to the formation process of the molten pool. Experiments have shown that when the laser is heated for 50-200us, the material begins to melt, forming a liquid metal and vaporizing to form a market pressure vapor, spewing out at a very high speed, emitting a dazzling white light. At the same time, the high concentration of steam moves the liquid metal to the edge of the molten pool, forming a depression in the center of the molten pool. When the defocus is negative, the light energy can be transmitted deep into the material because the material's internal power density is higher than the surface and it is more prone to forming stronger melting and vaporization. Therefore, in practical applications, negative defocusing should be used when the penetration depth must be large, and positive defocusing should be used when welding thin materials.

Laser welding process method

1. Welding between sheets. It includes butt welding, end welding, center penetration welding, center penetration welding and other 4 process methods.

2. Welding of wire and wire. Including wire-to-wire butt welding, cross welding, parallel lap welding, T-welding and 4 other process methods.

3. Welding of wire and block parts. The connection between the metal wire and the block element can be successfully realized by laser welding, and the size of the block element can be arbitrary. During welding, attention must be paid to the geometric dimensions of the filament element.

4. Welding of different metals. Welding different types of metals covers a range of weldability and weldability parameters. Laser welding between different materials is only possible with certain material combinations.

Laser brazing

Although laser fusion welding is not suitable for the connection of some components, soft soldering and brazing can be performed using laser welding as a heat source, and there are also advantages of laser fusion welding. There are several methods of using soldering, among which laser soldering is mainly used in the welding of printed circuit boards, especially in the assembly technology of chip components. Compared with other methods, laser soldering has the following advantages:

1. Due to local heating, parts are prone to thermal damage, and the heat-affected area is small, so soldering can be performed near thermal parts.

2. It uses non-contact heating to melt the bandwidth without auxiliary tools, so it can be processed after mounting the double-sided components on a double-sided printed circuit board.

3. Good stability in repetitive work. The flux has less contamination on the welding tool, easy to control the laser irradiation time and power, and the laser soldering yield is high.

4. The laser beam is easy to achieve light splitting and can be split in time and space by optical elements such as half mirrors, mirrors, prisms, scanning mirrors, etc., which can realize multi-point simultaneous symmetric welding.

5. Laser brazing mainly uses a 1.06um wavelength laser as a heat source and transmits it through an optical fiber, allowing flexible processing of parts that are difficult to weld with conventional methods.

6. Good focus, easy to realize the automation of multi-station devices.

Laser deep penetration welding

1. Metallurgical processes and process theory

The metallurgical physical process of laser deep penetration welding is very similar to that of electron beam welding. In other words, the energy conversion mechanism is completed through the "pinhole" structure. When illuminated by a beam of sufficiently high power density, the material evaporates to form tiny pores.

This tiny hole filled with vapor is like a black body that absorbs almost all the energy of the incident light, and the hole's equilibrium temperature is about 25,000 degrees. Heat is transferred from the outer walls of the high-temperature cavity, melting the metal surrounding the cavity. The small hole is filled with hot steam generated by the continuous evaporation of the wall material under the irradiation of the light beam, and the four walls of the small hole surround the molten metal, and the liquid metal surrounds the solid material. The liquid flow outside the pore wall and the surface tension of the wall layer are dynamically balanced with the vapor pressure continuously generated in the pore cavity. The light beam continuously enters the eyelet, the material outside the eyelet continues to flow, and as the light beam travels, the eyelet always maintains a steady flow. That is, the molten metal surrounding the hole and the hole wall advances according to the progress speed of the leading beam, and the molten metal fills the void left by the hole removal and solidifies to form a weld.

2. Influencing factors

Factors affecting laser deep penetration welding include laser power, laser beam diameter, material absorption rate, welding speed, shielding gas, lens focal length, focal position, laser beam position, and laser power at the start and end points of the weld. , progressive drop control.

3. Features and advantages of laser deep penetration welding

Features:?

(1) High aspect ratio. The weld deepens and narrows as the molten metal forms around a cylindrical hot vapor chamber and expands towards the workpiece.?

(2) Minimum heat input. Because the source cavity temperature is very high, the melting process proceeds very quickly, the heat input to the workpiece is very low, and the heat deformation and heat affected area are small.?

(3) high density. A non-porous penetration weld is formed because the tiny holes filled with hot steam aid in agitation of the weld pool and leakage of gases. High cooling rate after welding is easy to create weld microstructure.?

(4) Strengthen the welding.?

(5) Accurate control.?

(6) Non-contact, atmospheric welding process.

Advantages:?

(1) The focused laser beam has a much higher power density than conventional methods, so the welding speed is fast, the heat-affected zone and deformation are small, and the following difficult-to-weld materials can also be welded.