The cutting head of the laser cutting machine is used in a very harsh environment, so in order to protect the internal optical path and core components, especially the expensive components such as collimator and focusing lens, the cutting head is installed with upper and lower protective lenses.
The dust and spatter produced on the surface of the workpiece in the cutting process will cause serious damage to the focus lens if it enters the cutting head, and the lower protective lens can block these dust and spatter.
The cleanliness of the protective lens directly affects the processing performance and quality of the laser cutting machine.
If the lens is dirty, not only the cutting effect and efficiency will be affected, but also the internal parts of the cutting head and the laser output head will be burned.
Therefore, first of all, protective mirrors with good material, high light transmittance and low coefficient of thermal expansion should be used.
When the lens is dirty during processing, it needs to be cleaned or replaced.
Fig. 1 Laser cutting head
There are special process requirements for the processing of protective lenses.
There are different processing requirements from the selection of base materials, processing accuracy, surface defects, coating, stability, mechanical properties (specific gravity, brittleness, tensile strength, compressive strength, hardness).
There are different processing requirements in the process of material preparation, waste folding, sand hanging, grinding, coring and coating.
Only after strict quality inspection can the finished products be put on the market.
In order to reduce the cost of inferior protective mirror, ordinary substrate materials are selected, and the coating process is not guaranteed.
The properties such as poor light transmittance, heat resistance, easy to break, and unable to bear the penetration of laser, result in the lens burst and broken.
The powder particles of the lens will pollute the whole cutting head, resulting in the damage of core high-value components including focusing lens and sensor.
The maintenance cost will be as high as 2% of the price of the new cutting head 0-50%, and delay the terminal production and processing, resulting in greater economic losses.
Therefore, we hope that the majority of customers learn from the manufacturer’s regular channels to buy laser accessories, to avoid losses!
2. Adverse effects of poor quality protective lenses
2.1 Thermal lens effect causes the focus shift of cutting head
The poor quality of the protective lens will increase the laser absorptivity.
After continuous irradiation for a long time, the temperature will rise and produce thermal deformation, which will cause the thermal lens effect and lead to the focus drift of the cutting head.
The higher the power and the processing of high reflection materials, the faster the thermal expansion of the optical element, the more obvious the thermal lens.
1) When cutting stainless steel, the focus drift of thermal lens effect will cause inconsistent cutting section effect, it would produce more and more slag, and even cannot cut.
2) When cutting carbon steel, the thermal lens effect will cause more and more slag at the bottom, and even cannot cut.
Fig. 2 Thermal lens effect
2.2 Protective lens burning point / burn-through
The lower protective lens with poor quality has poor ability to block dust and spatter in the process of processing, which is easy to cause fire point;
For the 10000 watt ultra-high power processing head, the protective lens needs to be carefully selected, and the protection lens with poor quality will directly cause burn-through of the lens under the action of 10000 watt laser in some serious situations.
Fig. 3 Protective lens burning point / burn-through
2.3 Burning point of the focusing lens
If the burn-through of the protective mirror is not found in time, the continuous light out processing will produce particulate dust, which will pollute the installation components, sealing ring and the lower surface of the focusing mirror, and cause the burning point on the surface of the focusing lens.
It is necessary to deeply clean and replaces the whole set of installation components and the focusing lens module.
Fig. 4 Burning point of focusing lens
2.4 Burnout of the laser output head
Once the protective lens is burned out, the collimator and focusing lens module in the cutting head are easily burned out under the action of ultra-high power.
In the most serious case, when the internal optical elements of the cutting head are damaged, the optical path will be abnormal, and the return light will cause the abnormal heating of the window piece of the laser fiber output head, and eventually burn the QBH or LOE crystal.
So, the whole laser output head needs to be replaced.
Fig. 5 Burnout of the laser output head
The use of inferior protective lens not only affects the service life of the cutting head and causes all kinds of accidents, but also affects the processing progress and quality of the factory, thus increasing the processing cost and reducing the efficiency of the factory.
Here, we advise the majority of users: the purchase of protective glasses must buy through regular channels, regular manufacturers to avoid losing too much and gaining too less, which is not worth it!
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