Laser Cutting Of Thick Steel Plate - Swinburne University Of Technology
Click to go back Harris and Brandt Materials Forum (2001) 25, 88-115 Laser Cutting of Thick Steel Plate J. Harris and IVI. Brandt Cooperative Research Centre for Intelligent Manufacturing Systems and Technologies Industrial Laser Applications Laboratory IRIS, Swinburne University of Technology PO Box 218 Hawthorn, Melbourne VIC 3122 Australia ABs-rRACT Of the many machining processes used in manufacturing to cut metals and non-metals, laser cutting offers unique advantages in terms of cut quality, speed, absence of tool wear and minimal or no clamping of parts. In industry, the lasers used for cutting are CO 2 (carbon dioxide) and Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) lasers each with their own characteristic output properties such as wavelength, power) mode of operation and beam quality. These properties, together with the optical and thermophysical properties of workpiece material and workpiece handling system, control and determine the cutting performance of any material. Presented in this paper are laser, materials and system properties, and parameters influencing the cutting of metals in particular. The operation of the CO 2 and Nd:YAG lasers and their dominant features is also discussed. The cutting mechanism is described in terms of the energy balance within the workpiece. This is then used to show the difficulties with cutting thick ( 10mm) steel plate with a laser, leading into a number of novel laser methods explored for the cutting of thick plates. Finally, recent work supported by the CRC for Intelligent Manufacturing Systems and Technologies (CRCIMST) on laser cutting with a "spinning laser beam" is presented and its potential for cutting thick steel plate discussed. Institute of Materials Engineering Australasia, Ltd (2001) 88
Harris and Brandt through almost any material by erosion. The kerf is rather large ('"'"' 1 mm) and the cutting speeds are modest compared to the thermal cutting methods. 1. INTRODUCTION Many methods are available to cut materials and metals in particular. Among these are the high energy processes of laser, electron beam, plasma, water jet and oxy-fuel. Oxyfuel or flame cutting, is still largely used for cutting very thick workpieces of metals, typically 100 mm to 500 mm thick (Rickfalt 1995). The edges of the cut are oxidised and the kerf produced is large. The heating fuel is usually propane, natural gas, a hydrocarbon mixture or acetylene, and is delivered through a concentric nozzle with the oxygen nozzle, so that the oxygen jet is surrounded by the fuel gas. The use of the laser as a tool for materials processing began as early as 1963 and is still developing. The first experiments in laser cutting with a gas assist nozzle were made in May 1967 (Hilton 1997) at the Welding Institute in Cambridge, UK, using a 300W CO 2 laser and oxygen assist gas. A 2.5 mm thick plate was cut with remarkable accuracy. The idea of using the laser as a cutting tool for metals belongs to Peter Houldcroft who was then the deputy scientific director at The Welding Institute. He thought of it when confronted with cutting trials using a plasma torch for body panel trimming at the British Motor Company in 1965. The plasma cutting was not accurate enough and produced burning of the edges. The development of plasma tools began in 1941 in the US aircraft industry for welding applications. This process uses an electric arc between an electrode and the metal, and a gas shielding around the arc, blown through the electrode. An innovation by scientists at Union Carbide's welding laboratory in the early 1950s reduced the gas nozzle opening. The result was that the electric arc and the gas were constricted to a small volume in space and the gas velocity increased dramatically, together with the arc temperature and voltage. A cutting tool was thus obtained and a new technology developed that has been continuously improved over the years. Plasma jets can cut through thick materials, but not as thick as those cut with the oxygen flame. They possess very high temperatures and thus can be used to cut materials with very high melting points that cannot be cut with other techniques. With the first industrial laser cutting system supplied in 1970, the progress of the new technology has been fast. In the last three years some 18,000 lasers for metal sheet cutting have been installed world-wide and this number is increasing yearly by some 6000 units (Belfore 2001). The value of these laser cutting systems in 2001 is estimated at about US 1.0 billion. This high level of adoption of lasers for cutting is associated with a number of advantages the technology offers compared with the competitive cutting technologies described above (Steen 1998). These include: Unlike the two cutting technologies mentioned above, abrasive water jet cutting does not melt the material. The operating principle is the acceleration of abrasive particles by mixing them in a stream of water. Passing through a nozzle, a highly focused jet of water is obtained that can cut 89 The non-contact nature of the machining process requiring light or no clamping of the workpiece. This absence of cutting forces also allows precise cutting of light or flimsy materials. The absence of cutting tool wear and tool chatter as a result of no contact.
Harris and Brandt Machining operations are not governed by workpiece hardness, with lasers able to cut many hard materials. Minimal noise pollution as the laser cutting process is quieter than the competitive processes of water jet and plasma. The narrow kerf width, typically 0.1 to 1.0 mm, requires little or no radial compensation for beam diameter. Furthermore, the possibility of nesting of components in production allows minimal wastage of raw material. The clean nature of the cut allows, in most cases, no subsequent cut face processing. Molten or oxidised material is removed by assist gas during the cutting process or falls away during the separation of the part at the completion of the cut. Given that the laser cutting mechanism is fast and the area heated is small, there is a minimal heat affected zone and consequently minimal heat distortion. Given the long time that commercial laser cutting technology has been available to industry and the significant advancements achieved in that time, laser cutting is now considered a mature technology. Consequently, cutting technology and knowledge of the cutting mechanism for thin and medium thickness «10mm) steels have remained basically unchanged during the last ten years and are considered well understood. There is, however, significant demand by industry to increase cut thickness and the quality of cut at those thicknesses. This paper discusses issues associated with the laser cutting of thick ( 1Omm) steel plate and methods currently being examined to cut it. Presented in Section 2 are general aspects of laser cutting and in Section 3 a brief description is given of the laser systems used for cutting. Section 4 summarises the chemistry of laser cutting and Sections 5 and 6 address the issues of, and novel laser technologies for the cutting of thick plate. 2. GENERAL ASPECTS OF LASER CUTTING The disadvantages of laser cutting compared to other cutting technologies are: The process of laser cutting may be considered as a sequence of the following mechanisms: The process effectiveness reduces as the workpiece thickness increases. Commercially, workpiece thicknesses greater than about 15 mm are generally not cut with a laser. Laser cutting produces a tapered kerf shape. This is a result of the divergence of the laser beam and is more pronounced in thicker materials. The taper can be reduced by positioning the focus below the surface of the \vorkpiece. absorption of laser radiation by material; heating and melting of the material, and removal of the molten material by the coaxial assist gas jet. If the assist gas is oxygen the exothetmic chemical interaction with the molten metal will accelerate the cutting process. The key features of laser cutting are illustrated in Figure 1. In laser cutting, the workpiece is placed on a CNC table and moved at a predetermined speed and path designed on a CAD system and converted to machine code instructions. The laser beam The heat affected zone can be a problem in some applications because of the changed microstructure. 90
Harris and Brandt is typically focused to a diameter of 0.1 to 0.3 mm on the workpiece surface (or just below it) with a lens or a lens system held in a specially designed nozzle. The most popular focal length range is 100mm to 150mm giving a good balance between spot size and depth of field. Incident laser power densities are of the order of 106 W/cm2. Once the laser beam has penetrated through the material, an erosion front is established in the cutting direction. The erosion front is covered by a layer of molten material which is continually removed by the assist gas at the lo\ver surface of the cut and created by the absorption of energy from the laser beam (Schuocker 1993). The assist gas, gas pressure, nozzle shape and position above workpiece are all critical process parameters and affect strongly the removal of material from the kerf (Powell 1993). Nozzle diameters vary from 0.8 mm to 3 mm depending on the material being cut and the nozzle position above the workpiece, which influences gas pressure in the kerf. This position is carefully chosen because of the strong variation of the melt removal rate with the complex pressure patterns produced in the kerf due to the supersonic speed of the assist gas (Fieret 1987; Na 1989). means of producing movement of workpiece relative to cutting nozzle, generally CNC controlled. (a) Cutting direction .-- Assist gas Cutting nozzle Narrow kerf (b) 3. LASER SYSTEMS USED FOR COMMERCIAL CUTTING A typical laser system used for cutting consists of: the laser beam source along with its utilities and control unit, a beam guidance arrangement from the laser beam source to the focusing optics, the focusing optics with cutting nozzle and process gas supply system, the workpiece and its support plus fume extractors for vapors, and Figure 1. Illustrated in (a) is laser cutting arrangement and key cutting features and in (b) CO 2 Jaser cutting a component (courtesy Rofin Sinar) , 91
Harris and Brandt Table 1. Principal characteristics of C02 and Nd: Y AG cutting lasers. Active Medium Wavelength CO2 molecule 10.6 Jlm Laser power Beam delivery and focussing Electrical efficiency 4kW (pulsed or CW) Mirrors and lenses 10-15% 2 kW (pulsed or CW) Mirrors optical fibres and lenses 1.06Jlm Ndion 4% (lamp pumped) 10% (diode pumped) energy to the CO2 molecule and enabling it to remain in the upper laser leveL The helium cools the gas mixture through collisions and transfer of stored energy from the CO2 molecule. The CO2 laser produces output at a wavelength of 10.6 flm (invisible part of the spectrum) at power levels from tenths of a watt to forty five kilowatts (Convergent) at an electrical efficiency of about 10%. For conventional cutting applications lasers with powers up to 4kW are used. Higher power lasers normally have inferior beam quality which adversely affects the cutting process. The lasers used for cutting include CW CO2 lasers, pulsed Nd:YAG lasers and more recently CW Nd: YAG lasers. Typical characteristics of these two lasers are shown in Table 1. The CO2 laser is by far the most widely used laser for cutting because of its high power, beam quality and reliability. Typically, for cutting applications the CO2 lasers range in power up to 4.0kW. For the cutting of relatively small, detailed and delicate parts a pulsed Nd:YAG laser is normally used (van Dijk 1993). At power levels up to 500W this type of laser yields very low thermal input into the material and produces kerf widths of 0.1 mm to 0.2 mm compared to the 0.2 mm to 1.0 mm kerf widths produced with a CO2 laser. Some typical cutting parameters for the two types of lasers are illustrated in Figures 2 and 3. The output power and beam quality of a CO2 laser are primarily determined by the method of gas flow. The flow method determines how quickly the carbon dioxide can be removed from the optical cavity so that new ground state carbon dioxide can be introduced for excitation and stimulation. The CO 2 lasers used for cutting can be classified as axial flow and no flow devices. In slow flo\v axial lasers the gas moves slowly in the direction of the laser beam through a glass tube (typically 10 to 14 mm in diameter) which is surrounded by another, co-axial water or oil-cooled tube. The length of the laser tube is typically 1 m and it produces about 50 to 70 W of laser power. The advantages of this type of design include very good beam quality for focusing, high peak power when pulsed and 3.1 The C02 Laser The CO2 laser is a gas laser, whose active medium is a mixture of about 5% carbon dioxide, 10% nitrogen and the balance helium. There are several different designs of CO 2 lasers depending on the method of exciting and cooling the gas mixture in the resonant cavity, however, the principle of the lasing action is the same for all CO2 lasers (Laos 1983). The active laser species is the carbon dioxide molecule. The nitrogen acts as a catalyst, transferring 92
Harris and Brandt (a) (b) 14 -------------------------- 13 12 7 -·-700W -·-1200W -e-1700W 11 9 :" ':' . '-: ': -:. '":' - 3" 7 "0 Q) g. Q) Q) 6 Ol 0. rJJ 0 5 E:;) E \.,\ 5 8 -'-1700W -.-1200W 6 \ \ \, '" 3 " c: :;) () 4 . -- - :'-. . 2 () ; . '-.: 3 2 O L- -L o o o 2 3 4 5 6 7 8 9 10 11 12 1314 1516 2 3 4 5 6 Miterialthickness (nm) Material thickness (mm) Figure 2. Representative cutting speed as a function of material thickness for C02 laser cutting of (a) mild steel with oxygen and (b) stainless steel with nitrogen assist gas. (a) (b) 3.0 , . - - - - - - - - - - - - - - - - - - - - - - - - - - -. 7 A - . - 500 W pulsed 6 \\ .- 1000 W pulsed 2.5 . 5 "2 '2 : .s 1 4 '"0 Q) Q) Q) Q.) 3 tJi c t.) 1.6 a. 0) E::J 2.0 "E ""0 0. rJJ - . - 500 W, pulsed, 0.6 mm fibre -1.- 1000 W, pulsed, 0.6 mm fibre -a- 500 W, pulsed, 0.4 rom fibre 2 -:"'" 1- ".--- 0) c . 1E () ': . 0.5 0.0 o -- -- o 1 234 1.0 0 5 234567 B 9 Material thickness (mm) Material thickness (mm) Figure 3. Representative cutting speed as a function of material thickness for Nd:YAG laser cutting of (a) mild steel with oxygen and (b) stainless steel with nitrogen assist gas and optical fibres. 93
Harris and Brandt the tube it is cooled with a heat exchanger. Laser tube length is considerably reduced compared to slow flow tubes resulting in a more compact device. The advantages of fast axial flow lasers include, in addition to the compact size, high output power and an output which can be electronically pulsed. The main disadvantage is that the Roots or centrifugal compressor needed to circulate the gas is complex and costly to maintain. reduced system complexity and maintenance costs. The main disadvantage is the laser size and the maximum output power. Lasers employing this approach are large because of the necessarily long laser tubes. The maximum power generated is about 2kW from some 20 laser tubes placed in series. This number of laser tubes can present a challenge in keeping the optics aligned. In no-flow or diffusion cooled lasers the gas mix in the optical cavity is cooled by conduction to the walls of the optical cavity. Shown in Figure 5 is a schematic of a diffusion cooled laser. The design involves two flat copper plates placed close together that act as both the RF electrodes and a heat sink. Since the gas transport system is not required the unit size is very compact. These devices are now available in the power range from 1 kW to 3.5 kW with very good beam quality for cutting applications. CroQl1d potenllil Guhdd Figure 4. lllustrated is a schematic of a RF excited fast axial·flow C02 laser (courtesy Rofin Sinar). 3.2 The Nd: YAG Laser The Nd:YAG laser is a solid state laser, usually in the shape of a rod, operating at 1.06 J!ffi (Koechner 1988). The active species are neodymium ions present in small concentrations in the YAG crystal. Both continuous wave and pulsed laser outputs can be obtained at an overall efficiency in the 3 to 5% range. The laser is used in industry because of its efficiency, output power and reliability compared to other solid state lasers. The crystal is grown using the Czocbralski crystal growing technique (Dawes 1995) which involves slowly raising a seed Nd:YAG crystal from the molten crystal constituents to extract a Nd:YAG boule. A single boule typically yields several laser rods. The concentration of Nd ions in the boule is carefully controlled and is not greater than about 1.10/0. Increasing the Nd doping further in Rear mIrror Figure 5. The basic design of a diffusion cooled C02 laser (courtesy Rofin Sinar). In fast axial flow lasers (see Figure 4), as the name suggests, high powers are achieved by transporting the gas very quickly through the laser tube using Roots or a centrifugal compressor thus reducing the time it spends in the heated volume. The gas travels at close to the speed of sound, and before it is recirculated through 94
Harris and Brandt placed close together at the axis. The inside surface of the cavity is normally coated with gold in order to maximise the coupling of lamp light into the rod. Some laser manufacturers also manufacture ceramic cavities which produce more uniform pumping of the rod but at the expense of lower efficiency (some 5% lower) compared to that of the gold-coated cavities. order to increase the laser po\ver produces unacceptable strain in the crystal and leads to a dramatic reduction in laser power. For continuous operation, krypton arc lamps are most widely used while for pulsed operation high pressure xenon and krypton flashlamps are used. Lamp lifetime dominates the service requirement of modern Nd:YAG lasers. For arc lamps the lifetime ranges between 400 and 1000 hours while for pulsed lasers it is about 20 to 30 million pulses depending on operating conditions. Figure 6. Schematic of a Nd:YAG laser (courtesy Rofin Sinar). Laser rods are typically 6 mm in diameter and 100 mm in length with the largest commercial size rods being 10 mm in diameter and 200 mm in length. As a consequence of the crystal's small size Nd:YAG lasers tend to be much more compact than CO2 lasers. Illustrated in Figure 6 are the main components of a single-rod Nd:YAG laser. Laser action is achieved by optically exciting the crystal by lamps placed in close proximity to it. The lamps have an emission spectrum which overlaps the absorption bands of the Nd: YAG crystal at 700 nm and 800 nm. In order to couple the maximum amount of lamp light into the rod and extract the maximum laser power from it, the rod and the lamp are enclosed in specially designed and manufactured cavities. The two most common pump cavity configurations are elliptical and close coupled. In the case of elliptical crosssections the rod and the lamp are placed along the nvo foci, and in the case of closecoupled cavities the rod and the lamp are Figure 7. Rofin Sinar 2.5 kW Nd:YAG laser with four pump chambers. As only a fraction of the emitted spectrum is absorbed by the laser crystal the rest of the emitted light is dissipated as heat in the cavity and has to be removed for efficient laser operation. This is usually achieved by flowing deionised water around the rod and lamp in a closed loop cooling system. The loop is coupled to a heat exchanger for efficient heat removal. 95
Harris and Brandt To increase the laser power above 500 to 600 W typically obtained from a single rod, requires an increase in the laser volume. However, increasing the rod volume has fundamental limitations. Heat generated within the rod causes large thermal gradients which lead to variations in the refractive index, lowering beam quality, as well as large mechanical stresses, which can cause rod fracture. To obtain higher laser powers involves using multiple laser rods (see Figure 7). The rods are ananged in senes and located either within the resonator or some are placed outside the resonator to act as amplifiers. These configurations are discussed and described in more detail by Emmelmann (1995). There are now several systems on the market all giving in excess of 2 kW of laser power with the highest power commercial device producing 6 k W from 8 cavities (Trumpf). Figure 8. 1999). This technology is the high power laser diode and its main advantage lies in having a very narrow spectral output compared with that of the lamp. The diode output is matched to the absorption bands of the Nd: YAG laser rod thus increasing considerably the efficiency of the laser system. Diode-pumped Nd:YAG lasers have much better beam quality because of lower induced thermal stresses, are more compact, require smaller chillers and have much longer lifetimes compared to that of the lamp pumped systems. Rofin-Sinar and Trumpf are now offering commercial 6 kW diode-pumped Nd: YAG lasers with guaranteed 15,000 h diode operation. 3.3 Bealn DelivelY and Focusing To guide a CO2 laser beam to the workpiece, mirrors with precise mechanical guides are used to direct the beam along lightweight, rigid, protective tubes to the optical components near the work surface. Different mirror arrangements are used for 2D and 3D motion. To focus a CO2 laser beam both reflective and transmissive optics are used. Focusing minors tend to be made from copper as it is highly reflective at the laser wavelength and can withstand high energy densities without damage. Copper mirrors are usually cooled with water to minimize thermal distortion. Transmission lenses can be made from gallium arsenide, potassium chloride or zinc selenide. Today, the most common material is zinc selenide. Typically, reflective optics are used with powers in excess of 4kW in order to minimise losses and imaging problems associated with the thermal distortion of the zinc selenide lenses. 2D CO 2 laser cutting system manufactured by Laser Lab. While lamps have been an integral part of the Nd:YAG laser technology to date and will remain so for the foreseeable future because of their relatively low cost, another technology is now emerging for high power laser applications both as a pumping source for Nd:YAG lasers and as a laser source in its own right (Bachmann 1998; Emmelmann In the case of Nd: YAG lasers, mirrors and lenses made from borosilicate crown glass, designated BK7, are used to guide the beam. This material is relatively cheap and has 96
Harris and Brandt while giving good positioning accuracy and repeatability. excellent thetmal and optical properties. The components are coated to minimize reflection losses. The Nd:YAG laser beam, in addition to being able to be directed by mirrors, can also be directed to the workpiece through an optical fibre (diameters typically 0.3 - 1 mm). The laser may be easily switched between optic fibres to share one laser between several share between workstations or to workstations concurrently. Fibres for Nd:YAG transmission are typically of step index design, meaning a high refractive index core surrounded by a cladding of low refractive index materiaL The change of refractive index ensures total internal (and highly efficient) reflection. The optic fiber allows flexible and indeed remote operation by robots with losses of 8% with no end coatings and as little as 2% occurring in the fibres with quartz windows (Rofin 2000). Fibres as long as 100 m can be used effectively (Ishide 1990). Fibres are surrounded by a metallic sheath to provide mechanical protection and typically contain continuity detection in the case of accidental bum through, whereupon the laser is automatically turned off. Figure 9. 3D C02 laser cutting system. An example of a 2D system is shown in Figure 8 where a 2 axis hybrid system using a CO2 laser and flying optics can achieve and speeds exceeding 5Om/min accelerations exceeding Ims·2 with an accuracy of 0.01 mm. This approach offers great flexibility in processing large sheets and allows complex shapes with The main intricate detail to be cut. drawback of these systems is the changing focal spot position as it traverses the working area. Even though this change is slight it is sufficient to affect the spot diameter on the workpiece and hence process efficiency. 3.4 Motion Systems The focused laser beam is positioned on the workpiece either by moving the optics and so the beam itself (flying optics, optical fibres, or galvo optics) or by movement of the workpiece or a combination of both. One-dimensional systems process only in one direction and are typic ally used in the manufacture of pipe, strip or section. Minor process adjustments occur through additional linear positioning axis. Twodimensional systems are used for the processing of flat surfaces. By moving the beam and beam guiding components less inertia needs to be overcome than by moving the workpiece. This allows high speeds and high acceleration to be achieved Three-dimensional systems use 5 or 6 axis gantries or robot systems. For gantry systems, positioning is performed using three linear axes (i.e. X,Y,Z); beam guidance can be by flexible arm or optical fibre. Often the optics are moved in 2 axes 97
Harris and Brandt vapour or the material vapour pressure itself shears and ejects molten materiaL This technique generates narrow kerfs and high quality surfaces for thin sections. with the third performed by movement of the workpiece. The laser optics are also equipped with two rotational axes to ensure the working surface is perpendicular to the beam path. Figure 9 shows a 3D cutting system with a 5 axis CNC hybrid system using a CO 2 laser with mirror beam guidance. Such systems can achieve speeds exceeding 15m/min and accelerations exceeding Ims·2 with an accuracy of O.Ol mm. Figure 10. Robotic Nd:YAG laser cutting at Volvo (courtesy Rofin Sinar). Fusion cutting where the incident laser beam melts the workpiece and highpressure inert gas blows the molten material out of the kerf. This method gives increased cutting rate over sublimation cutting but includes the formation of striations on the cut surface and the adherence of dross to the lower cut edge. The use of inert gas (typically at pressures between 1 and 2 MPa) allows the generation of non-oxidized cut surfaces. Reactive fusion cutting where a reactive gas such as oxygen is used in conjunction with the laser heating of material. The resultant exothennic reaction aids the cutting process and high cutting rates can be achieved. Robot systems are more effective for the processing of 3D components· (e.g. in the automotive industry) and are now becoming increasingly common because of the ease of manipulating the processing head. Robot solutions are typically less accurate than gantry systems but are considerably cheaper to implement. Figure 10 shows a robot cutting system using a 6 axis robot and Nd:YAG laser coupled to the robot using optical fibre. Figure 11. Laser cut edge produced in mild steel in the presence of oxygen assist gas. Note the oxide layer. 4. THE LASER CUTTING MECHANISM The three dominant ways to cut materials commercially are (Steen 1998): 4.1 Reactive Fusion Cutting ofMild Steel Reactive fusion cutting is normally used when cutting mild steel. The interaction between molten iron and oxygen produces Sublimation cutting where the focussed laser beam evaporates the material and the co-axial assist gas removes the 98
Harris and Brandt series of steps shown in Figure 12 (Powell 1993). The cutting mechanism involves the following steps: an additional source of heat due to the exothennic nature of their interaction. The exothermic reaction typically provides 40% (Ivarson 1991) of the overall heat input to the cut. This is done by the conversion of approximately 50% of Fe removed to FeO and small amounts ofFe203. (i) The laser beam and co-axial oxygen move to the edge of the steel sheet and the area of beam illumination on the plate increases and temperature rises to a point where initially ignition and subsequently melting will occur. The exothennic reaction between oxygen and iron is represented by: Fe 02-- (ii) The melt front once established moves away from the center of the illuminated area until reaching the outer regions of illuminated area. FeO MI -257.58 kJ/mol (at2000K) (iii) Having left the energetic area at the site of illumination, the melt front cools and extinguishes. 2Fe 3/2 O2 -- Fe203 AH -826.72 kJ/mo! (at 2000K) (iv) The laser then initiates ignition and melting in the next area and the process repeats itself. The process involves melting the material in the upper section of the workpiece by the focused beam from the laser. This molten material transfers its heat to lower areas which in tum also melt. All the molten material is free to react with oxygen present as the assist gas creating further heat by the exotheffi1ic reactions shown above. Molten material is removed through the bottom of the cut by the shear with the assist gas. As there is continuous interaction between the energy provided by the focused beam and the workpiece during cutting, a dynamic steady state condition is established. The parameters that influence the cutting process include laser power (continuous or pulsed), focus position, surface condition of material, assist gas pressure and cutting speed. The interaction between each of these variables is not completely understood and the influence of lesser factors (eg beam mode, material temperature (Powel1 1993), nozzle clearance (O'Niell 1992») has also been shown to be significant. An example of a reactive fusion cut surface is shown in Figure 11. butrJing extinction reinitiation
of the laser systems used for cutting. Section 4 summarises the chemistry of laser cutting and Sections 5 and 6 address the issues of, and novel laser technologies for the cutting of thick plate. 2. GENERAL ASPECTS OF LASER CUTTING The process of laser cutting may be considered as a sequence of the following mechanisms:
PANASONIC LASER MARKING SYSTEMS. 03 LP-100 CO 2 Laser Marker LP-200 CO Laser Marker LP-F FAYb Laser Marker LP-D Diode Laser Marker LP-300 CO Laser Marker LP-V FAYb Laser Marker 1996 1999 2001 2003 2004 LP-400 Laser Marker LP-G FAYb Laser Marker LP-Z FAYb Laser Marker
Epilog Laser The Leading Worldwide Provider of Laser Marking Technology Since 1988, Epilog Laser has been the leading provider of laser technology. From industrial fiber laser marking solutions to consumer CO2 laser models, Epilog Laser is known for the highest-quality laser etching and marking.
2.3 Laser cutting parameters . Laser cutting is a complex process governed by a multitude of factors with difficult to predict interaction. The parameters of laser cutting process can be classified as system parameters, the workpiece parameters and process parameters as illustrated in Figure 2. Figure 2. Laser cutting parameters
Laser treatment parameters for the Laser RAP sites included an average laser spot size of 4.1mm (range: 4-8mm). The average laser fluence used was 5.22J/cm2 (range 1.5-8.3J/cm2). At the Laser‐Only treated sites, a single laser pass was administered using a laser spot size of 4mm at an average laser fluence of 3.9J/cm2(range: 3.-4.6J/cm2).
Keywords Laser cutting ·Quasi-CW ·Millisecond pulses ·Thermal modeling ·Process efficiency 1 Introduction Laser cutting of metals has been exploited in manufactur-ing since shortly after demonstration of the first laser in 1960 [1-4]. This process currently accounts for a large pro-portion of industrial laser applications, together with laser
Co 2 LaseR CuttinG Cost estiMation: MatheMatiCaL ModeL and appLiCation 173 C f C i C m C lab C lg (2) where C i (EUR/h) is the investment cost of buying a CO 2 laser cutting machine, C m (EUR/h) is the maintenance cost, C lab (EUR/h) is the labour cost and C lg (EUR/h) is the laser gas (mixture of CO 2, H e and N 2) cost.The Invest-ment cost of CO 2 laser cutting machine consider .
Laser workers are responsible for complying with all aspects of this laser safety program: 1. Attend laser safety training ; 2. Develop laser safety protocols for the laser systems for which they are responsible ; 3. Comply with all laser safety controls recommended by the LSO. IV. LASER OPERATIONS
UNITED STATES DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration NATIONAL MARINE FISHERIES SERVICE Northwest Region 7600 Sand Point Way N.E., Bldg. 1 Seattle, WA 98115 Refer to NMFS Nos.: FS: 2008/03505 BLM: 2008/03506 BIA: 2008/03507 June 27, 2008 Calvin Joyner Edward W. Shepard Acting Regional Forester, Region 6 Director, Oregon/Washington USDA Forest Service USDI Bureau .
