In the manufacturing process of the innerliner of the traditional washing machine, the inner tube riveting technologyhas been widely used. At present, most of the manufacturing technology of theinner tube of fully automatic washing machines on the market adopts the"fastening" technology, but there will be gaps or unevenness in thejoint of the inner tube, which causes the strength of the tub to be low andunnecessary wear and tear on the clothes.
In order to further improve the reliabilityand refinement of the inner tube, washing machine manufacturers apply laserwelding technology to the new products of uniform power washing machines,avoiding the gap and unevenness of the inner tube, and comprehensivelyimproving the reliability of the product while taking care of the clothes.
Advantages of laser welding
1) From the perspective of processanalysis, the welded seam of the inner cylinder created by the seamless laserwelding technology has a uniform structure, fewer pores and fewer defects. Thestrength is nearly 4 times that of the inner cylinder using rivetingtechnology, and the smoothness of the interface is increased by nearly 15times. The smooth seam of the inner cylinder is designed to better protect thefabric of the clothing, which is an experience that is difficult to achievewith riveting technology. In addition, due to the increased strength of theinner tube, the maximum rotation speed of the uniform power washing machineduring the dehydration process is also increased by 25% compared with theordinary fully automatic washing machine. The dehydration efficiency is greatlyimproved, and it consumes less power and time, and it is also satisfying theconsumer's demand for quality life under the current consumption upgrade trend;
From the perspective of productionefficiency, the laser seamless welding technology can make the inner cylinderwelding spot small, narrow welding seam, neat and beautiful, without processingafter welding, and the production efficiency can be increased by 3 to 5 times.
Therefore, laser welding technology iswidely used in the washing machine industry due to its high energy, highprecision, and high adaptability. It is not only a technical guarantee for thedevelopment of new washing machines, but also an indispensable technical meansto improve quality and reduce costs.
Difficulties in laser welding
At present, the inner tank of high-endwashing machines on the market is mostly made of stainless steel, and itsthickness is mostly between 0.8mm-1.2mm. When the washing machine is workingnormally, the running speed can reach 1400R/min. Therefore, the inner liner ofthe washing machine has extremely harsh requirements for the weld. For example,the weld is smooth and flat (tested by scratching with stockings), themechanical strength is high enough (the weld strength cannot be less than thestrength of the base material), the weld cannot be oxidized and discolored andis corrosion resistant (after welding, it must pass the 2400h salt spray test).
The high welding requirements for the innertank of the washing machine determine that the welding process is extremelydifficult. The main difficulties in welding are:
1) High welding seam forming requirements:single-sided welding and double-sided forming, the welding seam and the back ofthe welding seam are required to be continuous and smooth, without any nodes,burrs, or welding slag, otherwise the smoothness requirements will not be met;
2) The appearance of the weld is extremelydemanding, and the front and back sides of the weld and the edge of the weldmust not be oxidized, otherwise the corrosion resistance will be reduced andthe salt spray test will fail.
To meet such stringent weldingrequirements, in addition to the extremely high requirements for laser weldingstability, the welding process level is also extremely high.
Laser welding solutions
1) The laser adopts the modulation mode,and the power is set to rise and fall slowly;
Aiming at the problem of nodes at the startand end positions of the weld, the laser modulation mode is adopted, and thepower ramp function is set in the welding equipment control software. The powerramp-up length is set at the start point and the power ramp-down length is setat the light-off point. The node problem at the welding seam of the light-offpoint has been greatly improved, but the light-off point is concave, and thelight-off point can be placed 2mm outside the sample. With the above scheme, theproblem of uneven welding seam and nodes can be solved well.
2) Explore the appropriatewelding defocus amount;
During the weldingprocess, the amount of defocus has a greater influence on the weld shape of thesample. If the defocus is too large, the laser energy loss will be large, andthe weld will be discontinuous and uneven; if the defocus is too small, thelaser energy will be concentrated, which will increase the number of burrs onthe back of the weld (especially for thin plate welding). Therefore, in thewelding of this sample, under the premise of ensuring the penetration of thematerial, properly adjusting the defocus amount can make the front welding seamcontinuous and uniform, and there is no burr on the back welding seam. The backburr not only affects the smoothness of the inner tank, but also affects thesalt spray test effect of the sample.
3) To ensure the appearance ofthe weld, "protective gas" is the key;
In order to ensure the smoothappearance of the weld, and the produced samples can pass the subsequent 2400hsalt spray test, the "shielding gas" during the welding process isvery important. The protection effect is good, not only can make the front andback sides of the weld be smooth and translucent, but also can avoid the oxidationof the weld during the welding process and pass the corrosion test smoothly. Inthe welding process, in order to avoid welding slag adhering to the surface ofthe material, a dust removal device can be installed in the welding direction.In addition, the usual single-pipe side blowing cannot effectively ensure thatthe front welding seam is not oxidized at all. Therefore, the front shieldinggas should be changed to the pipe side blowing to ensure that the front weldingseam is not oxidized. The back of the weld should also be slotted and shieldedgas, so as to ensure the welding quality of the back weld.