Butt welding, lap welding, filler welding - the scope of welding terminology is as varied as the technology itself. Laser welding and laser brazing are two standardized seaming processes in hot seaming methods.
Laser advantage
Compared to conventional arc welding processes, laser beam joints have many advantages: selective energy applications in small areas: reduced thermal stress and reduced heat affected zone, extremely low distortion. Narrow seams and smooth surface: reduce or even eliminate rework. High strength combined with low weld volume: The welded workpiece can be subjected to 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 close. High process speeds reduce processing time. Especially suitable for automation technology. Good program control: machine control and sensor systems 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 metal
In heat conduction welding, the surface is melted
The laser beam can be used to join workpieces on the metal surface or to create deep welds. It can also be combined with conventional welding methods or used as brazing.
1 heat conduction welding
In heat conduction welding, the laser beam melts the matching parts along a common joint, and the molten material flows together and solidifies, creating a smooth, round weld that does not require any additional grinding or finishing.
Deep fusion welding produces a vapor-filled hole, or a small hole effect
The heat transfer welding depth ranges from only a few tenths of a millimeter to one millimeter. The thermal conductivity of a metal limits the maximum weld depth, and the width of the weld is always greater than its depth.
Laser welding cross section observed under the microscope
If the heat cannot be dissipated quickly, the processing temperature will rise above the vaporization temperature, metal vapor will form, the welding depth will increase sharply, and the process will become deep-weld.
2 deep welding
Deep fusion welding requires an extremely high power density of approximately 1 MW/cm 2 . The laser beam melts the metal while creating a vapor that applies pressure on the molten metal and partially replaces it, while the material continues to melt, creating a deep, narrow, vapor-filled pore, the pinhole effect. The laser beam advances along the weld seam, and the small hole moves accordingly. The molten metal circulates into the small hole and solidifies in its trajectory, resulting in a deep and narrow internal structure uniform welding, and the welding depth may be ten times larger than the welding width. 25mm or deeper.
Deep-fusion welding is characterized by high efficiency and fast welding speed, small heat-affected zone, and minimal distortion control, often used in applications that require deep-fusion welding or where multiple layers of material require simultaneous soldering.
3 active gas and protective gas
The active gas and the shielding gas assist the laser beam during the welding process. Active gases are used for CO 2 laser welding to prevent the formation of a plasma cloud on the surface of the workpiece that blocks the laser beam. The shielding gas is used to protect the welding surface from the ambient air, and the flow of the shielding gas to the workpiece is non-turbulent (laminar flow).
4 filling materials
The filler material is usually added as silk or powder to the point to be joined. Its role:
1. Fill in gaps that are too wide or irregular to reduce the amount of work required to prepare the seams.
2. The filler is added to the molten metal in a specific form of the composition to change the weldability, 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) welding, TIG (Tungsten Inert Gas Welding) or plasma welding. Composite welding technology is faster and less deformed than MIG alone.
6 laser brazing
In laser brazing, matching parts are joined together by a filler or solder. The melting temperature of the solder is lower than the melting temperature of the base material, and only the solder is melted during the soldering process, and the matching parts are only heated. The solder melts into the gap between the parts and bonds to the surface of the workpiece (diffusion bonding).
The brazed joint has the same strength as the solder material, and the seam surface is smooth and clean without the need for finishing. It is often used in automotive body machining, such as the trunk lid or the roof.
Laser welding of active gas and shielding gas using filler wire
sensor
The sensor is used to detect and adjust certain parameters, including the working distance, the position of the laser beam at the seam gap, the angle of the optical lens adjustment, and the amount of filler material to ensure the quality of the weld during the machining of the part and to detect inferior parts.
1 weld tracking
When the laser beam is used to weld the butt joint in the material, the seam gap trajectory is tracked and the laser beam is properly positioned to ensure that the laser beam remains in the same position in the seam gap.
2 keep monitoring the whole process
Sensor systems can be combined to achieve more comprehensive monitoring of the welding process. Including "before welding", "in welding", "after welding" sensors.
The pre-weld sensor tracks the weld and locates the laser beam before the weld. The welding sensor uses a camera or diode to detect the welding process in the welding, the camera-based system analyzes the keyhole and the welding pool, and the diode system can detect the intensity of the processed light, thermal radiation or reflected laser. After soldering, the sensor checks the finished solder joint to determine if the solder joint meets the quality requirements.
Sensors rely on programmed limits to distinguish the pros and cons of parts.
Laser welding machine
The design of a laser welder depends on many factors such as the shape of the workpiece, the geometry of the weld, the type of weld, the amount of production, the degree of automation of the production, and the process and materials.
1 manual welding
Small workpieces typically use manual workstations to perform welding work, such as welding jewelry or repair tools.
2 applications
Sometimes the laser beam only needs to be welded along a single moving axis. For example, seam welding or seam welding is used for pipe welding or seam welding.
3 systems and robots
The laser beam is typically connected to a three-dimensional part characterized by a three-dimensional welded geometry. A five-axis coordinate-based laser unit and a set of movable optical accessories are used.
4 scanning galvanometer or remote welding
The scanning galvanometer directs the laser beam at a great distance from the workpiece, while in other welding methods, the optical lens directs the laser beam at a very close 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, which increases productivity and is suitable for producing a large number of short welds and can be optimized The welding sequence ensures minimal heat input and distortion.
5 remote welding system
There are two ways to implement a remote welding system. The first is a remote welding system. The workpiece is placed in the working area under the scanning optical galvanometer 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, a process called flight welding.
The second is that the robot carrying the scanning optical galvanometer performs a large amount of movement, and at the same time, the scanning optical galvanometer ensures precise positioning of the laser beam as it moves back and forth along the workpiece. The machine controls the overlapping movement of the synchronous robot and the scanning optical lens, which measures the precise spatial position of the robot within a few millimeters, and the control system compares the measured position with the program path. If a deviation is detected, the compensation is controlled by scanning the optical galvanometer.
Laser welding will become easier
The laser welding process has developed a wide range of application possibilities. High quality, minimal rework, and low cost benefits have become powerful arguments for the promotion of laser welding processes. Future laser welding processes will become as mature as imaging laser cutting.
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