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This article contains comprehensive information on laser cutting and laser drilling. Read on to learn more about:
What is laser cutting and laser drilling?
Theory and working principle
cutting methods
Laser drilling techniques
And much more…
Laser cutting is a material cutting method that uses an intensely focused, coherent stream of light to cut metals, paper, wood, and acrylics. It is a subtractive process that removes material during the cutting process by vaporization, melting, chemical ablation, or controlled crack propagation. Computer numerical control (CNC) controlled laser optics can drill holes as small as 5 microns (µ). The process does not produce residual stresses in the materials, which allows brittle and brittle materials to be cut.Laser drilling uses several methods, including single shot, percussion, trephination, and twist. Percussive and single-shot laser drilling produces holes at a higher rate than the other processes. Trepanning and twist drilling produce more accurate and higher quality holes.
Laser cutting is a non-contact process in which the cut is completed without making contact with the cut material. It can shape brittle high-strength materials such as diamond tools and refractory ceramics. The first production laser cutting was introduced in 1965 and was used to drill holes in diamond dies. It was later used to cut high-strength alloys and metals such as titanium for aerospace applications. Its range of applications covers the cutting of polymers, semiconductors, gems and metal alloys.
Laser stands for "light amplification by stimulated emission of radiation". Aside from laser cutting applications, they are used for bonding, heat treating, inspection, and free-form fabrication. Laser cutting differs from other laser machining processes in that it requires higher power densities but shorter interaction times.
Lasers are generated by a high intensity light source inside a reflective laser cavity, which contains a laser rod that generates the radiation. The light source stimulates the atoms in the laser bar as they absorb wavelengths of light from the light source. Light is made up of small packets of photons that hit the atoms of the durable media and energizes them. The energized atoms of the photon emit two more photons with the same wavelength, direction, and phase, which is called stimulated emission. The new photons stimulate other energized atoms producing more photons, causing a cascade of excitations.
The photons move perpendicular to the parallel mirrors located at the ends of the laser bar but remain inside the laser bar. A mirror is transmissive, allowing partial light to escape from the cavity. This escaping stream of coherent monochromatic light is the laser beam used to cut the material. Another set of mirrors or fiber optics directs the light into a lens that focuses the light onto the material.
The three main types of lasers used for cutting are CO2 lasers, Nd-YAG (Neodymium, Yttrium, Aluminum, and Garnet) lasers, and fiber optic lasers. They differ in the materials used to generate the laser beam.
Fiber optic lasers are the newest and most popular types of lasers because they can generate different wavelengths for more precise cutting. They use a silica glass fiber optic cable to guide the light. The laser beam produced by fiber optic lasers is more precise because it is straighter and smaller.
Fiber lasers vary in their combination of laser sources, including ytterbium-doped, thulium-doped, and erbium-doped. The choice of mixture depends on the application in which they are going to be used and their wavelengths. For example, erbium generates light in the range of 1528nm to 1620nm. Ytterbium produces light with wavelengths of 1030nm, 1064nm and 1080nm.
The two modes of fiber optic lasers are single and multi, with the core diameter of single-mode lasers between 8 µ and 9 µ, while multi-mode lasers have core diameters of 50 µ to 100 µ. Of the two modes, single-mode lasers are more efficient and produce a better quality light beam.
Fiber optic lasers are classified as solid state since their energy source is silica glass mixed with rare earth elements. This is contrary to CO2 lasers which use gas to create their power. An additional difference between the two forms of energy is their wavelengths: fiber optic lasers produce wavelengths from 780nm to 2,200nm, while CO2 lasers have wavelengths from 9,600nm to 10,600nm.
This type has a gas discharge laser medium filled with 10-20% carbon dioxide, 10-20% nitrogen, trace amounts of hydrogen and xenon, and helium for balance. Instead of light, laser pumping is done by discharging an electrical current. As the electrical discharge passes through the laser medium, the nitrogen molecules are excited, bringing it to a higher energy level. Contrary to what was described above, these excited nitrogen molecules do not lose their energy by photon emission. Rather, it transfers its energy vibrationally to the CO2 molecules. This process continues until most of the CO2 molecules are in a metastable state. The CO2 molecules then emit infrared light at 10.6 µm or 9.6 µm, which brings them down to lower energy levels. Resonant mirrors are designed to reflect photons emitted at those wavelengths. A mirror is a partially reflective mirror that allows the release of the infrared beam that is used to cut the material. After releasing infrared light, the CO2 molecules return to the ground state, transferring the remaining energy to the doped helium atoms. The cold helium atoms then heat up and are cooled by the laser's cooling system. The efficiency of a CO2 laser is around 30%, which is higher than other lasers.
Crystal lasers (ruby, Nd and Nd-YAG)
Unlike the CO2 laser, this type is a solid-state laser that uses a synthetic crystal as the laser medium. The most popular is the YAG crystal (Y3Al5O12) doped with 1% ionized neodymium (Nd3+). Nd ions replace Y ions in the crystal structure of this crystal. The length of the rod is approximately 4 inches (10 cm) with a diameter of 2.4 to 3.5 inches (6 to 9 cm). The YAG rod ends are polished and coated with highly reflective materials that act as a resonator system.
Laser pumping is achieved by krypton flashlamps or laser diodes. This laser pumping excites the Nd ions to higher energy levels. After a while, the excited Nd ions go into a lower, more stable state, emitting no photons. This process continues until the medium is filled with excited Nd ions. From their metastable state, Nd ions release infrared light with a wavelength of 1064 nm.
It is known that as light travels through an optical fiber, it stays inside with minimal energy loss. This makes the optical fiber more stable than other types that require precision alignment.
Auxiliary gases
Laser cutting uses auxiliary gases, such as compressed air, nitrogen, or argon, injected into the nozzle to supplement the cutting process. Auxiliary gases help initiate the cut through an exothermic reaction, a chemical that releases energy through the use of light or heat. The use of auxiliary gases aids in more effective heat transfer than the beam alone can create. When cutting metals, assist gases help remove molten metal.
The previous chapter discussed the different types of lasers based on how the laser beam is formed using different types of pumps and laser media. Next up will be laser cutting methods – how small pieces of materials are removed to produce a cut. There are four main methods of laser cutting: sublimation, fusion, reaction, and thermal stress fracture.
Sublimation or Vaporization
Sublimation is a type of phase change from a solid state to a gaseous state, with no intermediate liquid phase. This is the same process in which dry ice turns to vapor without becoming a liquid. The material rapidly absorbs energy where there is no chance for fusion to occur. The same principle applies to laser cutting, where a large amount of energy is imparted to the material in a relatively short time causing a direct phase change of the material from solid state to gaseous state, with as little melting as possible.
The cut begins by creating an initial keyhole or slot. In the cut, there is more absorption capacity, which makes the material vaporize more quickly. This flash vaporization creates a high-pressure material vapor that further erodes the groove walls while forcing material out of the cut. This deepens and enlarges the hole or cut made.
This process is suitable for cutting plastics, textiles, wood, paper, and foam, requiring only small amounts of energy to vaporize.
melting
Compared to sublimation, fusion requires less energy to achieve. The energy required is about one tenth of sublimation laser cuts. In this process, the laser beam heats the material, causing it to melt. As the material melts, a gas jet from the nozzle coaxial with the laser beam expels the material from the cut. Auxiliary gases used are inert or non-reactive (eg, helium, argon, and nitrogen), which only aid cutting by mechanical means.
Due to its low power requirement, it is used to cut non-oxidizing or active metals, such as stainless steel, titanium, and aluminum alloys.
Reactive laser cutting
In this process, a reactive gas is used to generate more heat by reacting with the material. The process begins by melting the material with a laser beam. As the material melts, a stream of oxygen gas exits the coaxial nozzle and reacts with the molten metal. The reaction between metal and oxygen is an exothermic process, which means that heat is released. This heat helps melt the material, which is about 60% of the total energy needed to cut the material. The molten metal oxides are pushed out by the pressure of the oxygen jet.
In addition to the lower energy required by the laser beam, cutting speeds with reactive gases are faster than laser cutting with inert gases. However, since this process is based on a chemical reaction, molten metal oxide that is not expelled by the oxygen jet forms along the edge of the cut. This produces lower quality cuts than using inert gases.
This process is used to cut thick carbon steels, titanium steels, and other easily oxidizable metals.
This process consists of introducing a small cut to depths of approximately one third of the thickness of the material using a laser. The laser is then used to induce localized stresses. This is achieved by heating a small spot which creates compressive forces around it. After the laser beam passes, the area cools slightly, creating thermal stresses. In some designs, coolants are used to aid in the generation of thermal stress. When these induced stresses reach failure levels, a crack propagates causing separation.
CO2 lasers are widely used for this application, as infrared light with a wavelength of 10.6 µm is ideal for cutting most non-metals. However, not all materials can be cut with one type of laser, as different materials absorb light at different wavelengths. Thermal stress fractures are widely used to cut brittle materials such as ceramics and glass.
Another newer method that uses the principles of thermal stress fracture is Stealth Dicing. This is a laser cutting technology originally developed by Hamamatsu Photonics that is used to cut semiconductor wafers and parts of microelectromechanical systems, or MEMS. In this type of cut, the initial cut is created at an internal point within the material. Stealth dicing is a dry dicing process where the cut produced is clean and contains no molten deposits.
stealth dice
This is a laser cutting technology originally developed by Hamamatsu Photonics that is used to cut semiconductor wafers and parts of microelectromechanical systems, or MEMS. In this type of cut, the initial cut is created at an internal point within the material. Stealth dicing is a dry dicing process where the cut produced is clean and contains no molten deposits.
There are different ways to create a hole using a laser. These are classified based on the movement of the laser beam relative to the work piece. Each technique has its advantages and disadvantages.
In this type of laser drilling, a single high-energy laser pulse is used to create a hole. This single beam laser focuses on a single location until the material is melted layer by layer. The melting process is done efficiently and in a short amount of time, making this process desirable for producing multiple holes quickly.
In percussion drilling, the diameter of the laser beam is the same as the diameter of the hole. To compare with single shot drilling, successive low energy pulses are used to remove material rather than using a single laser pulse. These repetitive pulses eventually penetrate the material, which takes anywhere from 4 to 20 pulses depending on the depth of the material and the properties of the laser beam. This process also completes quickly, making it effective for working with thick materials and producing multiple holes in a short period of time.
In laser trephine drilling, the spot size of the laser beam is significantly smaller than the hole size. When an initial hole is made, the laser beam passes through the hole, expanding the size of the drilled hole to the desired diameter. This is done to drill large holes more efficiently than percussion and single shot drilling. Climbing is slower but can produce holes with better metallurgy and geometry.
Similar to auger drilling, this type uses a moving laser beam to drill into a material. However, it does not require a starter hole. In this method, the laser beam rotates relative to the work piece. The rotation of the laser beam is similar to that of a conventional drill. Rotation is achieved by a rotating pigeon prism or other optical systems rotated by a high-speed motor. The quality of the hole produced is comparable to holes made by trepan drilling.
In the early days, the method of using a laser cutter was to manipulate the workpiece by hand. It was positioned, the cut was made, the laser was removed and the next cut was made. At that time, CNC programming and other technological advances did not exist. Modern laser cutting has eliminated the need for manual positioning of the workpiece and uses computer controlled equipment to make the proper cuts quickly and efficiently.
The main types of gantry laser cutting machines are made of aluminum, have a long horizontal bed, and a gantry placed above the bed. They can be programmed with multiple cuts that are made with a single pass of the laser, which can be fiber optic or CO2 laser. Gantry machines use CNC-controlled programming to produce efficient, accurate cuts quickly and easily. Unlike manual handling machines with footprints of 8 to 16 feet (2.4 to 4.9 m), gantry machines have a footprint of 4 to 8 feet. (1.2m to 2.4m).
Moving Material Setup
In this configuration, the laser cutter is stationary while the material surface is moving. Since no laser movement is required, the optical system is simpler than other configurations. However, this is slower than other methods and is generally limited to cutting flat materials.
Flying optics system
This setting is the opposite of the moving material setting. The flying optics system involves a stationary material and a moving laser cutter. Since the laser is constantly moving, the length of the laser beam must also be constantly adjusted due to the divergence of the laser beam. Higher divergence results in poorer cut quality. To mitigate this, recollimation optics and adaptive mirror control are used. This setting is the fastest of the three as the movement of the mirrors is easier to control.
hybrid system
In the hybrid system, the material moves on one axis while the optics move on the other axis. This configuration combines the advantages and disadvantages of the previous two configurations. An advantage of this flying optics system is that hybrid systems provide a more constant beam path, which reduces energy losses.
Laser marking is the process of creating laser marks by cutting the surface of the work piece to a shallow depth or inducing chemical changes by burning, melting, ablation, polymerization, etc. Just like laser cutting and laser drilling, laser marking can be a non-contact process. Tool wear problems and unwanted work hardening on the workpiece surface are eliminated. In addition, laser marking does not use inks, an advantage over traditional printing. The different types of laser marking processes are summarized below.
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Surface removal:
This process involves removing specific regions of the previously applied coating layer on the workpiece surface. The workpiece has a different contrast than the coating, making the removed regions significantly visible. Materials for this type of laser marking are special films and coated metals.
Recorded:
This is laser marking where the surface is cut to the desired depth. Cutting is usually done using the laser vaporization process. The main advantage of this method is that it can be performed at high speeds.
Thermal bonding:
This is accomplished by fusing additional pigmented materials, such as glass powders or ground metal oxides, onto the surface of the workpiece. The heat applied by the laser fuses the materials.
Annealing:
This process involves heating specific regions using a laser. The heat applied by the laser causes the metal to oxidize producing different colors such as black, yellow, red and green.
Carbonization:
In this process, the plastic bonds between the polymers are broken, releasing hydrogen and oxygen and producing a darker color. This process is carried out on plastics and organic materials.
Sparkling:
This is usually done on plastics where the color pigments and carbon are destroyed and vaporized, resulting in foaming. The foaming process is done on dark colored materials that need to have lighter colored markings.
staining:
This process induces chemical reactions on the surface of the workpiece where the reaction products have different colors.
Laser drilling is widely used in the aerospace, automotive, electronics, and tool industries. Below are the main advantages of using lasers for drilling.
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As mentioned above, since the laser drilling process does not involve cutting tools, there is no issue of tool wear or damage. In conventional drilling, bits can become dull, making the cut slower and producing more heat. This can distort the material and change its mechanical properties due to heating.
Since the laser beams can be focused, this allows precise drilling of small holes that conventional drilling cannot achieve. Hole depth can be controlled even for microscale holes. Furthermore, the process is digitally controlled by CNC methods. All parameters can be controlled automatically, producing consistent and repeatable results.
Secondary processes such as deburring are required in the manufacture of precision parts to remove surface irregularities, metal spurs, raised edges, slag and slag. Even the most precise manufacturing techniques, such as laser cutting technology, tend to develop dross or thermal burrs. However, compared to conventional cutting, laser cut parts still have superior edge quality. This effectively reduces the cost of secondary processes, particularly deburring, which can account for up to 30% of operating costs.
This means that very deep holes with small diameters can be drilled without problems. When drilling these holes with conventional drill bits, the tool heats up, wobbles and breaks due to torsional stress. The use of a laser does not create frictional drag and is only limited by the laser generator and optical systems used.
Lasers can cut and drill different materials that are difficult for conventional machining. Lasers can cut high-strength metals like titanium and super alloy steels. Aside from these high-strength metals, laser cutting is used to cut crystals, ceramics, and even diamonds due to its ability to make counter fractures.
waves.
Since the tool does not need to be positioned against the workpiece, drilling speeds depend only on the optics setup and the movement of the cutting head. Furthermore, the complexity of the profile to be cut has a minimal effect on the incremental cost of running the machine.
Since most of the molten material is expelled by the assist gas, there are no residual stresses along the perforated edges. This results in a clean and mechanically stable cut.
Despite these advantages, current laser drilling technology cannot completely replace conventional methods. Below are the main reasons.
Laser cutting machines can fetch prices twice as high as plasma and water jet cutters. The rate of return on the investment may not be sufficient to produce any economic advantage.
Operating a laser cutting machine requires a specialist with good technical training due to the variety of operating parameters involved. Also, for CO2 and crystal lasers, an expert is needed to return them to operating condition once they become misaligned.
High-precision movements are required in laser cutting, especially in applications on the order of microns. Two factors can affect the movement of the laser beam. One is the accuracy of the control system and controllers. The control system must be able to process and send precise signals to the high-resolution controller to accurately position the laser beam. The other factor is the dimensional accuracy of laser cut parts. Linear guides, lead screws, and other parts of the drive system must be precisely mated. This can be achieved by deburring laser cut parts.
The depth of cut depends on many parameters, but the most important is the power. For the same power rating, plasma cutters can cut deeper than lasers. Common industrial laser systems over 1kW can cut carbon steel up to 13mm thick.
The terms plasma and laser cutting are sometimes used interchangeably, as they are both cutting processes. However, regardless of their basic similarities, they are different in the way they are applied and in their principles. Both methods were developed in the mid-20th century and have been refined and modernized to meet the needs of today's manufacturing techniques.
Laser cutting is a process that cuts materials by amplifying laser light. It has exceptional precision due to being controlled by a CNC controller. Laser cutting involves focusing a laser light using optics. As the light gets smaller and hotter, it melts and cuts a workpiece while a computer directs the process. The work piece is burned during the melting process and an assist gas or vaporization expels the waste material.
Plasma cutting is a method of cutting electrically conductive materials that uses oxygen or nitrogen gas and a hot plasma jet to melt the surface of a workpiece, regardless of how tough or tough it may be. The unique feature of plasma cutting is the limitation of the materials it can cut, which are electrically conductive and include aluminum, stainless steel, steel, brass, and copper. Cutting plasma is a conductive ionized gas that is extremely hot during the cutting process. Although all plasma cutting tools are the same, the type of tool is determined by its temperature.
All plasma cutting tools burn at very high temperatures in excess of 40,000 degrees Fahrenheit (22,200°C). When the process is combined with CNC machining, it produces parts that require no further finishing or machining. Unlike laser cutters, plasma cutters discharge radiation, requiring the use of protective clothing and eyewear for workers.
Main differences between laser cutting and plasma cutting
The main difference between the two processes is the fuel used to power the cutting process with plasma cutting using a plasma gas, while laser cutting involves a beam of light. Also, there is some danger associated with plasma cutting due to the radiation it emits. Both processes are efficient and precise cutting methods that diverge according to how they complete the process.
Laser cutting is a non-traditional machining method that uses an intensely focused stream of coherent light called a laser to cut material. On the other hand, laser drilling is another type of laser machining process that produces a hole through the workpiece achieved by different techniques.
A laser beam is generated by using a high-intensity light source or electrical discharge device to excite atoms or molecules within a lensing medium. This lensing medium produces cascading excitations, which result in the production of photons. The photons then resonate and are partially released. The released photons are converted into the laser cutting beam.
The lens media used for laser cutting are CO2, crystals, and fiber optics.
There are four main methods of producing a cut or hole. These are sublimation, melting, reaction, and thermal stress fracture. Each of these methods has its application.
Laser drilling can be done by single shot, percussion, trephination and twist drilling. Single-shot and percussive laser drilling produce holes at a higher rate than the other two processes. Trepanning and twist drilling, on the other hand, produce more precise and higher quality holes.
Laser cutting machines can be classified based on the movement of the laser relative to the work piece. These are moving material, flying optics and hybrid systems.