The MOPA laser can be used for laser marking processes with different colour gradation from gray to deep black, without damaging the material surface. The result can be equal to the annealing marking on steel, the high quality marking effect is formed clearly, which is easy to read, especially on the natural anodized aluminium.
Material suitable for laser processing of AAO:
Anodic alumina
Natural anodic alumina
Anodic alumina in all colours
Display for laser marking samples of AAO
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The advantages of laser marking, engraving and processing of AAO products
Not only AAO can be engraved (by removing the electroplated coating), but also it can be processed to form a black mark. In particular, marks in all different colour levels from gray to dark black can be printed on the natural AAO.
Analysis on the application of the AAO blackening on the back cover of mobile phones
The 21st century is the era of electrical information, in which mobile phone is becoming more and more inseparable in our daily lives, and also are playing an increasing important role in the mobile terminal market. Which implies that mobile phones will have much broader market share in the future. As the constantly changing consumption concept, consumers have put forward increasing requirements for mobile phone manufacturing industry which make many smart phone brands have strict criteria on the Logo process of the body shell, where the Logos on the power supply adapters, headphones, and mobile power banks are all marked with laser marking machines to achieve the best results.
Material evolution for cell phone bodies
In the early stage, most of the mobile phone bodies were made of plastic material, commonly polycarbonate, including the LG-G series, Nokia (Lumia) and Samsung S5 models, all of which has mainstream plastic shells, hence contributing to shortcomings such as poor texture, poor heat dissipation, cheap appearance, and loose combinations etc. Ceramic materials have become the rising star in the mobile phone backplane in recent years. In September 2017, Xiaomi released MIX2. According to the market research conducted by professionals, ceramic materials are gradually becoming a competitive weapon for high-end consumer electronics differentiation. It is estimated that by 2018, the market share for smart phone ceramic backplane will reach 11.6 billion Chinese Yuan. Manufacturing difficulties such as high cost has not resulted in widely populated the market yet. At present, most models on the market enjoy all-aluminium bodies, usually aluminium alloys which is commonly utilized for back covers of mobile phone after anodizing surface treatment, often known as anodized aluminium oxide.
Introduction of the AAO blackening
There are black fonts on the back cover of the phone with the manufacturer's LOGO and the serial number which looks similar to the ones printed by ink-jet marking machine at first glance. But in fact neither are ink codes, nor silk prints, they are processed by the laser marking machine, commonly known as blackened anodizing alumina. The traditional method is to mark the silk screen on the surface of the work piece, while the screen printing ink is heavy, not delicate enough, difficult to follow colour, hence the printing effect is not ideal, furthermore, the ink composition adopted to screen printing contains certain chemically heavy metal element. Nowadays manufactures apply new low-carbon and environmentally friendly technology which is the laser marking technology. It can help improve the anti-counterfeiting capability, but also increases the added value, by making the product look more excellent with much more brand sense.
AAO refers to the fact that aluminium and aluminium alloys are coated with a dense layer of aluminium oxide to prevent further oxidation, which has the same chemical properties of Aluminium oxide. Anodizing can significantly improve the corrosion resistance function of aluminium alloys, increasing the surface hardness and wear resistance of aluminium alloys, and enjoying good decorative properties after proper colouring.
The theory of the AAO blackening is to further oxidize the anodized aluminium oxide layer with a film thickness of 5-20μm and changes the texture of the surface material in a short period of time by focusing the laser beam with high energy density laser. The principle of the aluminium blackening is based on the nanometer effect, because the laser treatment has made the oxide particle size at the nanometer level, the material's light absorption performance increases, hence the visible light irradiated to the material is absorbed, with very less reflected visible lights left, so that it appears to be black in our naked eye observation, so called the AAO blackening .As for the thickness of the oxide layer and the surface treatment process of the AAO, generally speaking, with a thickness range of 5um to 20um, the film thickness directly determines the effect and efficiency of blackening, often, it is very easy to blacken when the film thickness is between 10um and 20um, if the film thickness is less than 8um, then the oxide film is too thin, which is easy to break and contributes to the phenomenon of white spots, in view of this, laser parameters are needed for compensation. Additionally, the surface treatment process of the AAO will directly affect the blackening effect. since sandblasting and surface drawing are common processes, the thickness of sandblasting will have different effects on the marking effect, which means the finer the sandblasting particles are, the better the blackening effect enjoys . It is recommended that the film thickness of the anode aluminium to be 10-15μm, so that the overall blackness effect is better.
The applications of laser marking of black trademark, model, and text on the surface of the AAO has been widely and early used by electronic manufacturers such as Apple, Huawei, ZTE, OPPO, VIVO, and others for electronic products shells. For these applications, MOPA fiber lasers are currently utilized for processing. Because the MOPA laser has a wide range of pulse width and pulse frequency adjustment, the black marking on the surface of the work piece can be realized by adopting the narrow pulse width and high frequency parameters. Also various effects of gray levels can be achieved through different combinations of parameters.
With the current development and the market requirements, the previous silk screen printing process was gradually replaced by the laser marking. Laser marking, as a modern precise processing method, compared with the traditional processing methods such as printing, mechanical engraving, and electric discharge processing, has unparalleled advantages. Due to the advantages of maintenance-free, high flexibility and high reliability, Laser marking machine is especially suitable for areas with high requirements for precision, depth and smoothness. The personal electronic products represented by mobile phones have changed and facilitated people's lives, with the developing orientation of functionalization, intelligence, and smart appearance. As the technological progress of the microelectronics industry and people's pursuit of personalized mobile phones, precise laser marking processing technology will play an increasingly important role in mobile phone manufacturing. (Source: Laser Fabrication Network)
