Laser Industrial Talking

For those general output lasers, due to manufacturing process or environment pollution, almost all lenses absorb a larger part of a specific laser wavelength, and thus shorten the life of a lens. The damage to laser lens will affect the use or even shut down the machine.

The increase of absorption for wavelength will cause uneven heating, and refractive index changing with temperature; when laser wave length penetrates or reflex through high absorption lens, the uneven distribution of laser power will increase the temperature of lens center and lower the edge temperature. This phenomenon is called lens effect.

Laser welding emerges with the development of science and technology in recent years. What is laser welding? And what are the advantages and disadvantages of laser welding? First, what is laser welding? The world's first laser beam is produced in 1960 by the use of flashbulb stimulating ruby crystalline grain. Limited by the thermal capacity of the grain, the pulsed beams is short and the frequency is very low. Although the instantaneous pulse peak can reach up to 106W, it still belongs to low energy output.

Laser technology adopts the beams of light generated by the reflection of laser from polariscope and congregates the beams in focusing device to generate beams with enormous energy. Once the focus is approaching, the workpiece will be melt or vapored in some milliseconds. This opens up a new welding application domain for high power CO2 and high power YAG laser. The key of laser welding equipment is high power laser, including solid laser and gas laser. Solid laser is the so called Nd:YAG laser. Nd is a rare earth elements and YAG represents Yttrium Aluminum Garnet, with similar crystal structure as ruby. The wavelength of Nd:YAG laser is 1.06μm. It can produce beam transmitted by fiber, so it can simplify beam delivery system, which is suitable in flexible manufacturing systems and remote working as well as high welding precision workpieces. Nd:YAG laser of 3-4 KW output is commonly used in automobile industry. Gas laser is the so-called CO2 laser. Its working medium is molecule gases which can generate iraser of 10.6μm in average. It can work continuously and output very high power; the standard laser power is between 2-5 KW. The Major Traits of Laser Welding Are as Following: 1. The welding is fast and deep with little deformation. 2. It can work in room temperature and disparity conditions with simple equipment and device. For example, the laser beam will not offset; laser welding can be really carried out in vacuum, air or any gas environment, or even through glass or any transparent material. 3. It can weld refractory materials as titanium and quartz and anisotropic materials with good effects. 4. When welding, depth-to-width ratio can reach to 5:1 and the highest can reach up to 10:1. 5. It can applied in microwelding. Slight flare can be generated by focused laser beams which can positioning precisely and be applied in mass automatic production of micro and small workpieces' installation and welding. 6. It is flexible in welding areas that is difficult to access. Especially in recent years, the adoption of optical fiber transmission in YAG laser processing technology has greatly promoted the popularization and application of laser welding technology. 7. Beam split is easy to be realized by time and space and multiple beam can be processed all at once, providing conditions for more precise welding.

However, There Are Some Limits of Laser Welding: 1. It requires high assembly accuracy for weldment and it should has no obvious deviation of beam on workpieces. It is because that the flare is too small and the welding line is too narrow. If the assembly accuracy and beam position cannot meet the requirements, it is easy to make weld defect. 2. The cost and initial investment on laser and the relevant systems are high.

Technological Parameter of Laser Welding (1) Power density Power density is one of the key parameters in laser processing. When the power density is relatively high, the surface would be heated to boiling point in microseconds, thus generate mass vaporization. As a result, high power density is good for material removal processing such as punching, cutting and carving. When the power density is relatively low, it would take some microseconds to meet the boiling point, the bottom can reach the melting point before vaporization occurs, thus a good melt welding is successfully formed. So the power density ranges from 104~106W/cm2 in conductive laser welding. (2) Laser pulse shape Laser pulse shape is an important question in laser welding, especially for foil welding. When high strength laser beam reaches the material surface, 60~98% of the laser energy will be lost by reflection and the reflectivity is changeable by the temperature of the material surface. The reflectivity of mental can vary greatly in a laser pulse period. (3) Laser pulse width Laser pulse width is an important parameter to distinguish material removal and material melting; it is also a key parameter to decide the cost and volume of processing equipment. (4) Influence of defocusing amount on weld quality There are two ways of defocus: positive defocus and negative defocus. It is positive defocus when focal plane is above the workpieces, vise versa. According to geometry optical theory, when positive and negative defocusing plane equals to welding palne, the power densities are almost the same in the corresponding panels, but the actual laser pools have different forms. It can achieve larger depth of fusion when it is negative defocus.

laser welding machine

Application Field of Laser Welding Laser welding has wide application in manufacturing industry, powder metallurgy field, automobile industry, electronics and some other fields.

Volkswagen AG has adopted laser welding in car roof of brands like AudiA6, GolfA4 and Passat. BMW and GM have used laser welding in top of the car frame while Mercedes-Benz has applied laser welding in drive disk assembly.

Except for laser welding, other laser technologies have be applied as well. Companies like Volkswagen GM, Benz and Nissan have used laser to cut covering parts while FIAT and Toyota have adopted laser for coating engine exhaust valve; Volkswagen has used laser for surface hardening on engine camshaft. Domestic vehicle models like Passat, Polo, Touran, Audi, Dongfeng Peugeot and Focus have adopted laser welding technology. Independent automobile brands like Brilliance, Chery and Geely have adopted laser welding as well.

Laser cutting is a non-contact processing method featured high energy and good controllability of density. Focused laser beam can generate high-energy density flare, which has a lot of characteristics in cutting. There are four ways of cutting to cope with different situations.

1. Fusion Cutting In laser fusion cutting, the melt material is sprayed out by airflow after the workpiece is melt partly. Material transfer occurs only in liquid condition so this process is called laser fusion cutting. Laser beam and highly pure inert gas together make the melt material leave the kerf; the gas itself doesn't take part in cutting. Laser fusion cutting can achieve higher speed than vaporization cutting. Energy needed for vaporization is usually more than energy for material fusion. In laser fusion cutting, laser beam is partly absorbed. Maximum cutting speed increases along with the increase of laser power and the speed reduces in inverse proportion when the thickness and material melting temperature grow. Under a fixed laser power, the limiting factors are air pressure in kerf and thermal conductivity of material. Laser fusion cutting can make non-oxidation kerf on iron and titanium metals. The laser power density for fusion but not vaporization is 104W/cm2 ~ 105W/cm2 for steel.

2. Vaporization Cutting In the process of vaporization cutting, the material surface reaches to boiling point so fast that it avoids fusion by heat conduction. Some material disappears in the form of vapor and the other is sprayed out by airflow from kerf. It needs extremely high laser power in this situation. In order to prevent material vapor condensation on kerf, the thickness of material should not exceed the diameter of laser beam too much. This kind of processing is only suited for iron-base alloy field. It can not be applied in wood as well as some of the ceramic material, because their vapors will unlikely become condensation in unmelt condition. In addition, they usually have thicker kerfs. In laser vaporization cutting, the optimal beam focusing depends on material thickness and beam quality. Laser power and heat of vaporization have a certain effect on the optimal focusing position. In a certain plate thickness, maximum cutting speed  is in inverse proportion to vaporization temperature of material. The required laser power density should more than 108W/cm2, depending on material, cutting depth and beam focusing position. In a certain plate thickness, and if the laser power is sufficient, maximum cutting speed is limited by gas velocity.

3. Controlled Fracture Cutting Controlled fracture cutting is an ultra fast and controllable cutting on fragile material. The main process is: Laser beam heat heats part of fragile material, causing huge heat gradient and big mechanical deformation in the heat affected area, thus leading to crack. As long as keep a balanced heat gradient, crack can be formed in any needed direction.

4. Oxidation Fusion Cutting (Laser Flame Cutting) Inert gases are usually adopted in fusion cutting, if replaced by oxygen or other active gases, the material will be lighted by laser beam and chemical reaction will occur to generate another heat source, making material keep heating, this is so-called oxidation fusion cutting. As to constructional steel of the same thickness, this methods can achieve higher cutting speed than fusion cutting. But the quality of kerf is not as good as fusion cutting. Actually, it can make wider kerf, obvious roughness, increased heat area and worse edge quality. And it has danger of burning sharp corners in the processing of precision model by laser flame cutting. Pulse pattern can be used to restrict the heat effect, since laser power decides the cutting speed. Under a fixed laser power, the limiting factors are oxygen supply and thermal conductivity of material.

Laser an acronym for (Light Amplification by the Stimulated Emission of Radiation) is a technology that makes use of the coherent beam of light  in stimulating molecular or electronic transmissions to the lower energy  levels resulting in the emission of the photons. This is the core principle behind the working of the laser drilling machines.

The Laser Drilling

Laser drilling is an automated process that can be used to make drills of alloys and composites that cannot be drilled by the use of the conventional methods. Laser drilling provides the only solution for the toughest and the hardest drilling challenges.

The use of laser drilling machine enables nearly all the solid materials ranging from metals to diamonds can be drilled by the use of a suitable laser. Time minute holes that are impossible to create with the use of mechanical processes cab be facilitated by the use of a laser. The drilling is done contact-free with the use of the extreme small optical systems that make drilling be possible at locations where the use of other methods could fail.

The laser beam melts and evaporates the material. This leads to an increase in the material volume in the drill hole leading to the creation of high vapor pressure. The high vapor pressure drives the melt out of the drill hole. In laser drilling, all the laser light is reflected from the rear mirror with 30-50% of the light passing through the front mirror. The laser light continues through the shutter assembly to the angled mirror and down through the focusing length up to the work piece. The laser beam in the laser hole drilling process is coherent with a high energy content. When focused on a surface, the laser light creates the heat that is used for the hole drilling.

Types of Laser Drilling  Processes

1. The Single-pulse drilling and percussion drilling

This method is used in the penetration of the drill holes which have a small material thickness, creating a few micrometers of depth. Percussion drilling makes use of the desired drilling depth with the thicker materials by the means of a couple of laser pulses with a low pulse energy and short pulse duration. This results in the creation of holes that are deeper, more precise and with the smaller diameter as compared to the single pulse drilling.

2. Trepanning

Trepanning is a combination of the drilling and cutting process that is used in obtaining larger diameter. The starting hole is created by the use of percussion drilling with the use of several laser pulses. The laser beam the travels over the material in increasing large circular tracks over a certain work piece enlarging the initial hole with the melted material displacing downward from the drill hole.

3. Helical Drilling

Helical drilling is used in the creation of large and deep drill holes of high quality. Using this process, no initial hole is created bit the drilling is done with the use of many large pulses in a circular track into the work piece. Here, the material is displaced upwards and the focus is controlled so that it always remains at the bottom of the hole. When the material has been penetrated, the laser is used to widen the bottom of the drilling and to smoothen the edges.

The benefits of using laser drilling include;

– The processing of high alloy metals without difficulty – Low cost tools that do not wear – Facilitation of the angled drilling of holes even at the most difficult access areas. – There is an economic setup time – It is a non-contact process as there is no tooling wear or breakage with minimal material distortion – Produces high accuracy and consistent results – There is the ability to produce small diameter holes with high aspect ratio – Ease of programming and the adaptability to automation – Increases the production rates with flexible and faster setup times and less tooling