1. Laser welding process characteristics
According to the mechanism of solder pool formation, there are two basic modes of laser welding: thermal soldering and deep soldering. The former uses a lower laser power density (105-106 W/cm2). After the workpiece absorbs the laser, it only reaches the surface melting. The heat transfer is then transferred to the interior of the workpiece to form a molten pool. This welding mode has a shallow depth and a small depth. The latter has a high density of lasers (106-107W/cm2). The workpiece absorbs laser light and then melts rapidly and even vaporizes. The molten metal forms a small hole laser beam under the action of vapor pressure, which can directly illuminate the bottom of the hole, so that the small hole continues to extend until The vapor pressure in the orifice is balanced with the surface tension and gravity of the liquid metal. When the laser beam moves in the welding direction, the molten metal in front of the small hole flows around the small hole to the rear, and forms a weld after solidification (Fig. 1). This welding mode has a large penetration depth and a large aspect ratio. In the field of mechanical manufacturing, in addition to those thin parts, deep penetration welding should generally be used.
Since the focused laser beam spot is small (0.1 to 0.3 mm) and the power density is high, several orders of magnitude higher than arc welding (5×102 to 104 W/cm 2 ), laser welding has significant advantages unmatched by conventional welding methods: The heating range is small, the weld and heat affected zone are narrow, the joint performance is excellent, the residual stress and the welding deformation are small, and high-precision welding can be realized; the high melting point, high thermal conductivity, heat sensitive material and non-metal can be welded; the welding speed is fast High productivity; highly flexible and easy to automate.
There are many similarities between laser welding and electron beam welding, but it does not require a vacuum chamber and does not generate X-rays, which is more suitable for popularization in production. Laser welding has actually achieved the position of electron beam welding 20 years ago and has become the mainstream of high energy beam welding technology development.
2. Laser welding equipment
Laser welding equipment is mainly composed of a laser, a light guiding system, a welding machine and a control system.
1. Lasers used in laser welding mainly include CO2 gas lasers and YAG solid-state lasers. The advantages and disadvantages of the two are compared as shown in Table 1.
2. Light guiding and focusing system The light guiding focusing system consists of a circular polarizer, a beam expander, a mirror or an optical fiber, a focusing mirror, etc., which realizes the function of changing the polarization state, direction, transmission beam and focusing of the beam. The condition of these optical components has an extremely important influence on the quality of laser welding. Under the action of high-power laser, the optical components, especially the lens performance, will deteriorate and the transmittance will decrease; the thermal lens effect will be produced (the lens is heated and the focal length is shortened); the surface contamination will also increase the transmission loss. Therefore, the quality, maintenance and working condition monitoring of optical components is essential to ensure the quality of the weld.
3. The role of the laser welding machine is to achieve the relative movement between the beam and the workpiece, complete the laser welding, the welding machine and the general welding machine. The latter often uses a numerical control system with a two-dimensional, three-dimensional welding machine or an articulated laser welding robot.
3. New technologies for improving and developing laser welding The following technologies can help expand the application range of laser welding and improve the automatic control level of laser welding.
l. Filler welding laser welding Laser welding generally does not fill the welding wire, but the welding assembly clearance requirements are very high, sometimes difficult to ensure in actual production, limiting its application range. The use of wire laser welding can greatly reduce the requirements for assembly clearance. For example, an aluminum alloy plate with a thickness of 2 mm, if no filler wire is used, the plate gap must be zero to obtain a good shape. For example, a wire of φ1.6 mm is used as the filler metal, and the weld can be ensured even if the gap is increased to 1.0 mm. Good shape.
In addition, the filler wire can also be adjusted for chemical composition or for thick plate multi-layer welding.
2. The method of rotating the laser beam to rotate the laser beam for welding can also greatly reduce the requirements for weldment assembly and beam alignment. For example, when a 2 mm thick high-strength alloy steel plate is butted, the gap for the seam is allowed to increase from 0.14 mm to 0.25 mm; and for a 4 mm thick plate, it is increased from 0.23 mm to 0.30 mm. The alignment of the beam center with the center of the weld increases the tolerance from 0.25 mm to 0.5 mm.
The sensors used in the system and their functions are briefly described as follows:
(l) Plasma monitoring sensor
1) Plasma optical sensor (PS): Its function is to collect the characteristic light-ultraviolet optical signal of the plasma.
2) Plasma charge sensor (PCS); using a nozzle as a probe to detect a potential difference formed between a nozzle and a workpiece due to uneven diffusion of plasma charged particles (positive ions, electrons).
(2) System function
1) Identify how the laser welding process is. Stable deep fusion welding process, with plasma, PS, PCS signals are very strong;
Stable thermal welding process, no plasma generated, PS, PCS signal is almost equal to zero;
In the unstable welding process, the plasma is intermittently generated and disappeared, and accordingly, the PS and PCS signals rise and fall intermittently.
2) Diagnose whether the laser power transmitted to the weld zone is normal. When other parameters are constant, the strength of the PS and PCS signals corresponds to the amount of power incident on the pad. Therefore, by monitoring the PS and PCS signals, it is possible to know whether the light guiding system is normal or not, and whether the power of the welding zone has fluctuated.
3) The nozzle height is automatically tracked. The PCS signal decreases as the nozzle-to-work distance increases. The use of this law for closed-loop control ensures that the nozzle-working distance is constant and automatic tracking in the height direction is achieved.
4) Focus position automatic optimization and closed loop control. In the deep fusion welding range, when the beam focus position fluctuates, the plasma light signal received by the PS also changes, and the PS signal is minimized at the best focus position (the deepest hole of the pair). According to the found rule, the focus position automatic optimization and closed-loop control can be realized, so that the focus position fluctuation is less than 0.2 mm, and the penetration depth fluctuation is less than 0.05 mm.
Explosion Proof Peristaltic Pump
Electric Explosion Proof Peristaltic Pump.Can be installed large flow pump head with maximum flowrate of 12000ml/min (single channel). A sharp explosion peristaltic pump can be mounted high flow pump head. Speed can be adjusted manually adjust the speed planetary CVT. Used in various environments, in particular, the requirement to use explosion-proof environments. Explosion-proof pumps are also used to move gasoline, diesel fuel, oil, ground water, potable water, salt water, wastewater, sewage, sludge, slurry and ash slurry, gas and air, powders, and rendering wastes, a variety of liquids, liquids with solids, etc.
Explosion Proof Peristaltic Pump,Peristaltic Pump Explosion-Proof,Explosion-Proof Peristaltic Pump,Explosion Proof Peristaltic Pumps
Baoding Chuangrui Precision Pump Co., Ltd. , https://www.crperistalticpump.com