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Separating process by laser includes cutting, drilling, material removing and marking by removal (carve or grave). I will present both individually as follows:
Cutting is one of the most important applications for industrial lasers. There are three types of cutting by laser: Sublimation cutting, fusion cutting and flame cutting. These three types used frequently in laser cutting methods
Laser sublimation cutting:
It's idea is to use the laser to vaporize the material with a little melting . In the kerf (a cut made by saw), the material vapor creates high pressure that derives out the molten material from the top and bottom. In order to avoid oxidation of the cut edge we use either argon or nitrogen as cutting gas.
There is a need for more energy to vaporize the metals and melt it. That's why sublimation cutting need laser with great energy and slower than other cutting processes. So, it's produce high quality cutting.
Laser fusion cutting:
In fusion cutting you can cut metals or any other materials able to be melt .such as, ceramic. We can use Nitrogen and/or argon as the cutting gas . The gas is pumped on the kerf at respectively high . nitrogen and Argon are inert (inactive) gases.
In other words they do not interact with the molten metal. They move the molten metal out to the bottom. Simultaneously, they protect the cut edge from the air.
fusion cutting has a great feature that is cut edges are oxide and do not require more treatment. However, the laser must provide all of the power needed for cutting process. For this reason, cutting speeds will be increase as in flame cutting.
Laser fusion cutting requires lower power than laser sublimation cutting as the material is only melted and then blown out of the cut with an inert gas.
Laser flame cutting:
Flame cutting is a standard process mostly used for cutting steel. In this process; oxygen is used as the cutting gas. The oxygen is blown into the workpiece at high pressure so, the heated metal interacts with the oxygen. The chemical reaction releases large amounts of energy up to five times the laser energy and help the laser beam. Flame cutting process makes it possible to increase the speeds of cutting process.
The quality of a laser-cut component can be assessed according to the following criteria, e.g.:
â€¢ Roughness (DIN 4768)
â€¢ Quality of cut edge (DIN 2310: drag-line depth; melting; unevenness; drag-line over travel)
â€¢ Cut width
â€¢ Reaction layers
â€¢ Structural transformations
â€¢ Heat input
â€¢ Cutting speed
In laser drilling, a high power short laser pulse push energy into the workpiece at high speed, causing the material to be melted and vaporize. Evaporation caused the volume of material in the drilling hole to increase suddenly, and create high pressure. Vapor pressure of molten material emitted from the hole.
Single-shot and Percussion Drilling:
In this drilling process a high energetic single laser beam is used to produce the hole. This process allows a large number of holes that will be done in a very short period of time. Moreover, the hole is produced using very short period of time and low energy laser pulses. This technique produces a deeper and more accurate than holes drilling and one-shot , and can also be a smaller diameter hole.
Trepanning uses very high and more than one laser pulses processes to create the hole. In this process, a experimental hole is first done using percussion drilling. Then the laser beam/pulse expand the experimental hole .Most of the molten material is emitted away from the hole.
helical drilling does not involve the making of a expremental hole like trepanning. Firstly, the laser begins moving in circles over the material as the pulses are delivered. The focus always at the base of the hole. When the laser has gone through the material, it can expand the base of the hole increasingly and make the edges soft. So with Helical drilling it possible to create very large and deep holes.
1.1.3- material removal:
Removing process consider one of types of cutting by laser .we use this Process in order to remove impurities from raw materials . removing materials depend on two important factors ; laser used type and material type .we will show them as follow :
1- co2 laser commonly used for laser cutting especialy for large-area removal of varnishes, coatings and impurities, e.g. in rubber vulcanizing (hardening) moulds
2- Pulsed solid-state lasers are also used industrially to remove material from natural stone, e.g. for cleaning limestone monuments
3- Nd:YAG laser has the highest peak power for pulsed operation
4- Nd: Glass laser more economical but has lower thermal conductivity. Used for low pulse repetition rates so it is Ideal for drilling.
5- Nd: Ruby laser is low energy efficiency & power, Limited to pulsed laser operation
-So as we showed above that every laser type is Suitable for a particular material according to it's characteristics .
This process mean that laser used for welding and soldering metals together so we will focuse in this section on welding and soldering process and show the efficiency of laser in this process as follows :
Process of laser welding is one of fast processes that joins two materials together . There are two main welding processes: heat conduction welding and deep penetration welding.
Heat conduction welding:
In this welding process as we know, the laser beam melts the mating parts of any two toined materials. The molten materials overlap together and go hard .Heat conduction welding has many uses so it used to join thin-wall parts as example . as a wellknown example we use in our daily life are corner welds on the visible surfaces of house . there are many Other applications in electronics. The laser produces a smooth seam that does not require any extra finishing. So, we use solid-state lasers in this applications . In this process also, energy is combined into the workpiece only through heat conduction. For this reason, The maximum weld depth is limited by heat conductivity of the material . The width of the weld is always greater than its depth. If the heat is not able to be wasted quickly enough, temperature emitted from the process goes up over the temperature of evaporation. The vapor of the metal make the welding depth increases fastly . for this reason, the process turns into deep penetration welding.
Deep penetration welding:
Unlike heat conduction process ,Deep penetration welding needs extremely high power . In this process, the laser beam do two process melts the metal and produces vapor.
The wasted vapor makes pressure on the molten material and partially displaces it. The material, on the other hand, will be melt. It will cause deep, narrow, vapor-filled hole, which is surrounded by molten material. As the laser beam advances along the weld joint, the hole moves with it through the workpiece. The molten material flows around the hole and harden in its trail. This creat a deep, narrow weld . The weld depth may be greater than the weld width. The laser beam is reflected many times on the walls of the hole. The molten material take in the beam completely, and the efficiency of the welding process rises. when CO2 laser is used for welding,then the vapor in the hole also take in laser light and is ionized. This done in the formation of plasma. As a result,ther are some features for deep penetration welding such as great efficiency and fast welding speeds. Thanks to the high speed, the heat-affected area is small and malformation is minimal . This process is used in applications that need deeper welds or where several layers of material have to be welded together.
In soldering process , the mating parts are joined by a solder. The melting tempe of the solder is lower than the temp of the other material. There for, only the solder is melted.
The mating parts are just heated. during melting process, the solder go into the gap between the parts on the surface of the workpiece . Soldering needs access to only one side of the produced slug.
The soldered slug is as strong as the solder material . solder seams are often used in the car industry for making body parts such as car roofs.
There are Other applications in mixed constructions. Materials made of dissimilar materials that cannot be welded or .one example of this process is Joining aluminum and steel . Soldering consider the best alternative for this work.
1.3 surface treatments:
Surface treatment includes hardening , remelting , Cladding and Alloying. We will illustrate them as follow :
laser Hardening or coating materials gives them surfaces with high resistance against wear, corrosion and high temperatures .
It is worth mentioning that the process of hardening depends on the type and strength of laser as mentioned in material removal .
Ofcourse it's a process related to hardening process becoase to do hardening we must remelt pre-placed or pre-deposited layer
Laser cladding is a process which known as deposition welding ; in which we deposite a layer of special powder on the material , and the two materials are fused by metallic bonding through the action of a laser beam.
The process of laser beam alloying is similar to laser beam cladding but the aim here is to get the two materials to mix forming a third material with the desired properties . Carbides, nitrides, borides are added to improve wear and corrosion properties.
1.4 laser marking:
We will show now laser marking and related things . in beggining there are some things that afficts laser marking as Beam sources , Beam guiding and shaping , Different marking methods ,Advantages and disadvantages of laser marking ,System technology and Applications
Beam sources :
There are several differences between laser used in cutting and laser used for marking as we mentioned previously there are types of laser that used for cutting and welding ,e.g ; CO2 laser , and showed its characteristics . usualy laser used for cutting is high power but the one used for marking is less power
It's rule to choose the type of laser in a certian process and it depends on laser power .
Beam guiding and shaping :
For the generation of characters and shapes, the vector method and various marking techniques are used.the vector process or beam deflectiv (has the greater market significance), in which the laser radiation is guided via two movable mirrors .The mirror axes are arranged perpendicular to each other so that one mirror can turn
the beam in the direction of the X axis and the other mirror is turned in the direction of the Y axis.
after the beam has been skewed(turned) by the mirrors, it is concentrated onto the workpiece, which lies under the equipment of deflection process, through a flat lens. The laser then marks the required image line by line into the material
Note that the beam deflection is controlled by a computer with optimized marking software
- With the mask technology, a stencil of the desired mark is projected onto the workpiece. The picture of the mask on the object is made using a lens. An extremely short impulse of light energy is directed on the workpiece. Therefore, employed in the mask marking are often the pulsed lasers such as pulsed CO2 laser, and pulsed Nd:YAG laser.
Different marking methods:
As we mentioned above that The main parameters which have to be taken into account in order to determine which marking laser to choose for a particular application are (besides the characteristics of the material to be marked), the laser power required, the pulse frequency and the marking speed (line energy).
we will show briefly the most important methods of marking by laser .
If marking involves visible material removal we use this method . in which a groove is made in the material by the focused beam. The material is evaporated and melted and flung (move) out of the groove by the dynamic effects of the process.
If only the colour of the metal is changed by the effects of heat and oxygen without any material actually being removed, the process is called marking by annealing.
3- removal of layers:
was initially developed for backlit illuminated function buttons where the laser burns off an opaque layer from a transparent basic material
Advantages and disadvantages of laser marking:
Laser marking has many other very different advantages. The most important of these are:
(1) permanent process , high quality marks;
(2) high efficiency and low cost;
(3) good accessibility, even to irregular surface;
(4) no special working environmental needed;
(5) easy to automate ( computer-controlled )
(6) a narrow damage zone ;
(7) high reproducibility and high speed and pollution free ;
On the other hand , laser marking has disadvantage as :
marking tool is relatively high costs
(2) the laser is not able to produce multicolour markings except in special materials such as Titanium.
Marking System technology:
Integration of laser marking to a production line can be done in many different ways. We will mention some of those systems (ways) ;
1- The easiest way of manipulating the parts is by manually loading them onto an XY or rotary table. These systems are designed so that the parts are put on a jig or fixture which does the positioning of the parts into the marking area and also provides an enclosure to guarantee laser safety class 1
2- a conveyor system is used when it is impossible to manually load or handle the parts.
- However, in all cases, it is essential to take into account the local regulations or laws which are applicable for laser marking.
Laser marking is used for more industrial applications. Some of these applications are :
in car manufacturing , from marking dashboards and function buttons to brake disks and gear wheels .
in production , marking for identifying components (e.g ; compenent data , serial number ,logo)
marking ( Radio front panels , Telephone front panel , Smartcard , IC (integrated circuit) , keyboard )
there are more applications on laser marking so we refered some of them .
1.5 primary shaping :
Stereo lithography :
"Stereo lithography machines convert three-dimensional CAD () data of physical objects into vertical stacks of slices. A low-power laser beam is then carefully traced across a vat of photocurable liquid polymer, producing a single layer of solidified resin - the first slice of the object under construction. The initial layer is then lowered incrementally by the height of the next slice, whereupon the layer is recoated with resin and another is traced on top of it. This procedure is repeated until the entire part is fabricated." Dr.-Ing. C. Emmelmann
"In the SLS (Selective sintering) process, a modulated laser beam follows the shape of a slice of a CAD (Computer-aided design) generated object ; it traces the object across a bin of special heat-fusable powders, heating the particles so they fuse or sinter together. After the initial layer is formed, powder is reapplied, and the laser processes the next layer." Dr.-Ing. C. Emmelmann
There are many military applications for laser as we will show next:
There are many countermeasure systems use laser as a military applications we will show them below BRIEFLY
- IR countermeasure systems
- High power boost-phase intercept laser systems use a complex system of lasers
- The Mobile Tactical High-Energy Laser (MTHEL) is another defensive laser system under development
But these systems have many problems:
- destroying ICBMs (intercontinental ballistic missiles) at most moment, it will affect badly on the environment
- The nuclear-pumped X-ray laser. This was essentially an orbiting atomic bomb, when the bomb exploded
Highly-energetic gamma-ray photons will spread in the air .
It's another militray application for laser, This is a low-power laser indecator used to indicate a target for a accuracy-guided munition, typically launched from an aircraft
The guided munition set its flight path to home in to the laser light reflected by the target, it enables a great precision in sight . The beam of the laser target designator is set to a pulse rate that matches that set on the guided munition to ensure munitions strike their designated targets and do not follow other laser beams which may be in use in the area.
The laser has firearms applications has been used as a tool to enhance the targeting of any weapon systems
One of this opplications is visible- laser placed on a handgun to be parallel to the target .
Most laser types used in sight are :
- red laser diode
- infrared diode
2.3.2 Eye-targeted lasers: