1. Special equipment
To reduce the size of the point of focus caused by beam size changes before concentrating, manufacturers of domestic and foreign laser cutting systems have provided special devices to the choice of users:
(1) parallel light tube. This is a commonly used method, that is to say a light tube parallel to the CO2 laser output end for the beam expansion treatment. In the cutting work range, the size of the beam is almost consistent before focusing.
(2) Add an independent lower axis of the mobile lens to the cutting head, which is two independent parts of the Z axis of the control nozzle at the surface distance of the material (affraction). When the machine tool table moves or the optical axis moves, the beam also moves from the proximal end of the distal axis, so that the diameter of the stain remains coherent throughout the area of Treatment after focusing the beam.
(3) Check water pressure from the focus mirror (generally a focusing system reflecting metals). If the size of the beam before concentrating becomes smaller and the diameter of the point of focus becomes larger, the water pressure is automatically controlled to modify the focus curvature and make the diameter of the stain smaller.
(4) Add an optical compensation path system to the X and Y directions to the cutting path of the flight optical path. In other words, when the optical path of the distant ending end is increased, the optical compensation path is shortened;
2. Cutting and perforation technology
Any thermal cutting technique, except in a few cases, can start with the edge of the board, generally requires a small hole in the board. Earlier, on the compound machine of flashing laser, a hole was first struck with a punch, then the cut was started from the small hole with a laser. There are two basic methods for perforation for laser cutting machines without stamping peripherals:
(1) Form of breath: (blastrelling), after continuous laser irradiation, a pit is formed in the center, then the melted material is quickly removed from the coaxial of the oxygen flow to the laser beam to form a hole. Generally, the size of the hole is linked to the thickness of the plate. Not used on parts with higher requirements (such as oil screen seal pipes.), Can only be used on waste. In addition, like the oxygen pressure used for perforation is the same as during the cut, splashes are relatively large.
(2) Impact on pulses: (pulsation) Use a cutting -edge power laser to melt or spray a small amount of material. Smaller than that of oxygen pressure during the cut. Each pulse laser produces only small ejection particles, gradually deepening, so that the perforation time of the thick plate takes several seconds. Once the perforation is finished, immediately replace the auxiliary gas with oxygen for cutting. In this way, the diameter of the perforation is smaller and its quality of perforation is better than that of the perforations of the dynamicing. The laser used for this purpose must not only have higher output power;
In addition, the perforation of pulses requires a more reliable gas circuit control system to switch the gas type switching, gas pressure and the steel time control. In the case of pulse perforation, in order to obtain high quality cuts, the technology for transitioning the perforation of the pulse when the part is stationary to a constant continuous cut of the part of the part must be paid attention . Theoretically, the cutting conditions of the acceleration section can generally be modified: such as focal distance, nozzle position, gas pressure, etc., but in fact, the possibility of modifying the above conditions above is not high due to the short period of time.
3. Hijack design technology and air flow control
When the laser cutting steel, the oxygen and the focused laser beam are slaughtered through the nozzle to the cut material, forming a bundle of air flow. The basic requirement for air flow is that the air flow entering the incision must be important and that the speed must be high, so that sufficient oxidation can be done at the same time as the material D ‘incision is at the same time exothermic; out of the melted material. Consequently, in addition to the quality of the light beam and its control directly affecting the cutting quality, the design of the nozzle and the control of the air flow (such as the pressure of the nozzle, the position of the part in the air flow, etc.) are also very important factors. The laser cut nozzle adopts a simple structure, that is to say a conical hole with a small round hole at the end. Generally designed using experimental methods and error.
Since the nozzle is generally made of copper, it is small and is a vulnerable part and must be replaced frequently, no calculation and analysis of fluid mechanics are carried out. During use, gas with some PN pressure (PG gauge pressure) is introduced on the side of the nozzle, which is called the pressure of the nozzle, which is sprayed from the outlet of the nozzle and reaches the surface of the room through a certain distance. The pressure is called the PC cutting pressure, and finally the gas expands at atmospheric pressure. Research work shows that as PN increases, the air flow rate increases and the PC continues to increase.
You can calculate the following formula: V = 8.2D2 (PG + 1)
Variat V-GAS L / MIN
D-Nonux Diametr MM
PG-NOUNUX pressure bar (gauge pressure)
There are different pressure thresholds for different gases. This threshold is linked to two factors: the PN, PA ratio and the degree of freedom of gas molecules (n): for example, n = 5 oxygen and air, therefore its PN threshold = 1bar × (1, 2) 3.5 = 1.89bar. When the pressure of the nozzle is higher PN / PA = (1 + 1 / n) 1 + N / 2 (PN; 4bar), the normal oblique shock seal of the air flow becomes a positive shock wave, The cutting pressure pc decreases, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, the PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC, PC , PC, PC, PC, PC, PC, PC, PC, PC decreases, the speed of air flow decreases and vortex flow is formed on the surface of the room, which weakens the effect of the air flow to eliminate melted materials and affects the cutting speed. Therefore, a nozzle with a conical hole with a small round hole at the end is used, and the nozzle pressure of the oxygen is generally below 3 bar.
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