Butt welding, lap welding, filler wire welding-the scope of welding terms is as broad and varied as the technology itself. Laser welding and laser brazing are two standardized seam processes in the thermal seam method.
The advantages of lasers
Compared with the traditional arc welding process, laser beam seams have many advantages: selective energy application in a small area: reduced thermal stress and reduced heat affected zone, extremely low distortion. Narrow seams and smooth surfaces: reduce or even eliminate reprocessing. High strength combined with low welding volume: Welded workpieces can withstand bending or hydroforming. Easy to integrate: Can be combined with other production operations, such as alignment or bending. only one side of the seam needs to be approached. High process speed reduces processing time. Especially suitable for automation technology. Good program control: machine control and sensor system detect process parameters and guarantee quality. The laser beam can produce solder joints without touching the surface of the workpiece or applying force to the workpiece.
Welding and brazing metals
Surface is melted during heat transfer welding
The laser beam can be used to connect workpieces or create deep welds on metal surfaces. It can also be combined with traditional welding methods or used for brazing.
1.Heat conduction welding
In thermal conduction welding, a laser beam melts mating parts along a common joint, and the molten material flows together and solidifies, creating a smooth, circular weld that does not require any additional grinding or finishing.
Deep penetration welding produces a hole filled with steam, or a small hole effect
Thermal conduction welding depths range from just a few tenths of a millimeter to one millimeter. The metal's thermal conductivity limits the maximum welding depth, and the width of the welding point is always greater than its depth.
Laser welding cross section observed under a microscope
If the heat cannot be dissipated quickly, the processing temperature will rise above the vaporization temperature, metal vapors will form, the welding depth will increase sharply, and the process will become deep penetration welding.
2.Deep welding
Submerged welding requires a very high power density of approximately 1 MW / cm2. The laser beam generates vapor while melting the metal. The vapor exerts pressure on the molten metal and partially replaces it. At the same time, the material continues to melt, creating a deep, narrow, vapor-filled hole, the small hole effect. The laser beam moves along the weld, and the small hole moves with it. The molten metal circulates the small hole and solidifies in its trajectory, resulting in a deep, narrow internal structure with uniform welding. The welding depth may be ten times greater than the welding width 25mm or more.
Deep welding is characterized by high efficiency and fast welding speed, small heat affected zone, and distortion can be controlled to a minimum. It is often used in applications that require deep welding or multilayer materials that require simultaneous welding.
3. Active gas and protective gas
Active gas and shielding gas assist the laser beam during welding. Active gas is used for CO2 laser welding to prevent plasma clouds from forming on the surface of the workpiece to block the laser beam. Shielding gas is used to protect the welding surface from the ambient air. The flow of shielding gas to the workpiece is non-turbulent (laminar flow).
4.Filling material
Filling materials are usually added to the points to be joined in silk or powder. Its role:
1. Fill gaps that are too wide or irregular and reduce the amount of work required for seam preparation.
2. The filler is added to the molten metal in a specific form of the composition to change the welding suitability, strength, durability and corrosion resistance of the material.
5. Composite welding technology
Composite welding technology refers to the combination of laser welding and other welding methods. Compatible processes are MIG (inert gas shielded welding) or MAG (active gas shielded welding), TIG (tungsten inert gas welding) or plasma welding. Hybrid welding technology is faster and less deformed than MIG welding alone.
6.Laser brazing
In laser brazing, matching parts are connected together through a filler material or solder. The melting temperature of the solder is lower than the melting temperature of the base metal. only the solder is melted during the brazing process, and the matching parts are only heated. The solder melts and flows into the gap between the parts and combines with the surface of the workpiece (diffusion bonding). The strength of the brazed joint is the same as that of the solder material. The surface of the joint is smooth and clean without finishing. It is often used for automotive body processing, such as trunk lids or roofs. Laser welding with filler wire, active gas and shielding gas
sensor
The sensor is used to detect and adjust certain parameters, including the working distance, the position of the laser beam in the seam gap, the adjustment angle of the optical lens, and the amount of filler material to ensure the welding quality during part processing, and detect inferior parts.
Weld seam tracking
When the laser beam is used to weld the butt joints in the material, track the seam gap trajectory and correctly position the laser beam to ensure that the laser beam remains at the same position in the seam gap.
2. Keep monitoring the entire process. The sensor system can be combined to achieve a more comprehensive monitoring of the welding process. Including "Before Welding", "In Welding" and "After Welding" sensors. The pre-weld sensor locates the weld seam and positions the laser beam before the weld. During welding, the sensor uses a camera or a diode to detect the welding process during welding. The camera-based system analyzes the keyhole and the welding pool. The system using a diode can detect the intensity of processing light, thermal radiation, or reflected laser light. After welding, the sensor checks the completed solder joint to determine whether the solder joint meets the quality requirements. The sensor relies on a programmed limit value to distinguish the pros and cons of the part.
Laser welding machine The design of a laser welding machine depends on many factors, such as workpiece shape, welding geometry, welding type, production volume, degree of production automation, and process and materials.
1. Manual welding of small workpieces usually uses manual workstations to perform welding tasks, such as welding jewelry or repair tools.
2. Application Sometimes, the laser beam only needs to be welded along a single moving axis. For example, use a seam welding machine or a pipe welding system for pipe welding or seam welding.
3.Systems and robots
Laser beams typically connect three-dimensional parts characterized by three-dimensional welding geometries. A five-axis coordinate-based laser unit and a set of movable optical accessories are used.
4. The scanning galvanometer or remote welding scanning galvanometer guides the laser beam at a long distance from the workpiece. In other welding methods, the optical lens guides the laser beam at a short distance from the workpiece. The scanning galvanometer relies on one or two movable mirrors to quickly position the laser beam, so that the time required to reset the beam between the welds is close to zero, thereby increasing productivity, suitable for producing a large number of short welds, and can be optimized Welding sequence to ensure minimal heat input and distortion.
5. Remote welding system There are two ways to realize remote welding system. The first is a remote welding system. The workpiece is placed in the working area under the scanning optics and then welded. When welding a large number of parts in a short time, the parts are continuously transported by the machine under an optical galvanometer. This process is called flying welding. The second is a robot that carries a scanning optical galvanometer to perform a large amount of movement. At the same time, the scanning optical galvanometer ensures precise positioning of the laser beam when it moves back and forth along the workpiece. The machine controls the synchronized movement of the robot and the scanning optical lens. It measures the precise spatial position within a few millimeters of the robot, and the control system compares the measured position with the program path. If a deviation is detected, compensation control is performed by scanning the optical galvanometer.
Laser welding will become easier Laser welding processes have developed a wide range of application possibilities. High quality, minimal reprocessing, and low cost benefits have become strong arguments for vigorously promoting laser welding processes. In the future, the laser welding process will become as mature as laser cutting.