HMk@+hJ!iJH% #J$I&Y}B}y53~" The economic aspects of laser usage in manufacturing that form important criteria in the choice of a suitable laser system for thick-section metal cutting include: high processing speeds, high processing depths, high cut edge quality, and high wall-pug efficiency of the laser system. Furthermore, fiber laser beam wavelength offers more flexible beam handling through use of narrow optical fibers. Optimization of the cutting process parameters for enhancement of the cut edge quality in thick-section metal cutting at high cutting speeds using the ytterbium fiber laser has shown that the maximum applicable cutting speed is influenced by the melt removal process. 2 0 obj The variation of melt flow velocity and melt film thickness along the cut depth is shown in Figure 3. Additionally, laser beam combination techniques are also used for power scaling of the ytterbium fiber laser by bundling multiple single-mode fiber laser elements to provide up to 10 kW multi-mode power output. 4 0 obj What adding KW power does do in fiber is increase the Cutting Thickness capacity as the chart below demonstrates. here What we see in the above chart is only a small advantage moving from 2KW to 3KW and even less of a difference adding the additional 1KW of a 4KW system. Absorption increases with increase in temperature of the material due to an increase in the phonon population causing more phononelectron energy exchanges and more tendencies for the electrons to interact with the material structure with the resultant fall in reflectivity [15]. The evaluation of the performance of the high brightness ytterbium fiber laser system in thick-section metal cutting is based on the maximum achievable cutting speeds, maximum cutting depths possible, and cut edge quality attainable. The confinement of pump light rays within the fiber core region subject to some losses through absorption or scattering maintains the pump light intensity propagating in the fiber over a fiber length of several meters. The dross attachment on the cut edge and surface roughness is also reduced with increase in assist gas pressure as shown in Figure 10. support team who will be happy to help. The melting efficiency of a given laser increases with increase in the absorptivity since a larger proportion of the incident laser radiation is absorbed by the material and utilized in melting of the kerf volume during cutting. Typically, the cutting speed giving the best cut edge quality is lower than the maximum achievable speed for cutting through a given material at the given laser power level. Open Access is an initiative that aims to make scientific research freely available to all. However, the minimum focused spot size is also directly proportional to the focal length (see Equation (2)) such that use of longer focal length optics for focusing of the laser beam results in a larger focused spot size with reduced power intensity. ( [24] developed an analytical approximation of the heat conduction losses during laser cutting of metals and provided an expression that can be used to estimate the temperature change in the substrate metal during laser cutting; the temperature change in the substrate metal is inversely proportional to the Peclet number which is directly proportional to the cutting speed. For many years we as manufacturers, distributors and OEMs of laser cutting systems were taught that Power (KW) IS Capacity& Speed. Consequently, the solid-state ytterbium fiber laser has introduced solid-state laser sources to the material processing applications such as thick-section metal cutting and welding that had previously been considered impractical for the traditional solid-state Nd: YAG laser due to its limited beam quality at high output power [3, 4, 9, 10, 11, 12]. %%EOF There is a reduction in the occurrence of the irregular deep grooves on the cut edge with a reduction of assist gas pressure and increase in cutting speed to optimum levels. The core region of highest refractive index is surrounded by two cladding regions of progressively decreasing refractive index which serve to confine the pump light within the core region. Technically speaking Fiber lasers have a different emission wavelength of around 1.07 m, compared to traditional CO2 lasers that emit the beam at 10.6 m. to go back to the article page.Or contact our 0000040160 00000 n The high power intensity enables melting of the workpiece at the laser-material interaction zone at a high processing speed [16]. stream The characteristic gas velocity, Ug, inside the cut kerf is estimated using the Bernoulli equation as presented in Equation 9. Therefore, in a pure laser fusion cutting process typical for thick-section metal cutting where the kerf volume is melted but negligibly vaporized and the conduction power losses from the cutting zone are significant, the power balance at the cutting front is given in Equation 4 [15]. In the oxygen-assisted laser cutting, a smaller nozzle size enhances achievement of a good cut quality with a finer uniform striation pattern on the cut edge by limiting the extent of the sideways burning oxidation reaction. endstream endobj 1527 0 obj<> endobj 1528 0 obj<> endobj 1529 0 obj<>/ColorSpace<>/Font<>/ProcSet[/PDF/Text/ImageC/ImageI]/ExtGState<>>> endobj 1530 0 obj[/ICCBased 1537 0 R] endobj 1531 0 obj[/Indexed 1530 0 R 0 1538 0 R] endobj 1532 0 obj<> endobj 1533 0 obj<>stream After the initiation of cutting, the cutting process progresses by the laser beam absorption on the steeply sloped cut front by the two absorption mechanisms, namely Fresnel absorption and plasma absorption and re-radiation (15). In the relation given in Equation (1), is the wavelength of the laser beam and M2is the beam quality factor (i.e., times diffraction limit factor) which tells how much larger the BPP of the laser beam under consideration is compared to the lowest value of /for the basic Gaussian TEM00 mode (diffraction limit) [3, 15]. Due to the reduction in the proportion of the absorbed laser beam that is lost through conduction to the substrate metal with higher cutting speeds, the potential increase in cutting speed when using the high-power ytterbium fiber laser increases the melting efficiency because the conduction energy losses from the cutting front decrease with increase in cutting speed. The cutting speed difference between the fiber laser and the CO2 laser reduces with increase in metal workpiece thickness to the thick-section domain. [32] reported that for the cut edge quality in 610- mm stainless steel, the location of the boundary layer separation point moves closer to the bottom cut edge with increase in cutting speed. Laser cutting and welding of metals require absorption of high power intensities to enhance cutting and welding at high processing speeds. Therefore, the power contribution to the cutting process by the oxidation reaction (i.e., reaction power) is estimated from either the oxygen flow into the interaction zone or the molten iron flow into the interaction zone [27]. Fiber Lasers - Why the Kilowatt is not the King, Southern Fabricating Machinery Sales, Inc. 0000007219 00000 n When the angle of incidence is zero (i.e., vertical incidence), the parallel polarized laser beam (RP) and the perpendicularly polarized laser beam (Rs) are absorbed equally. However, the plasma buildup is not very significant in cutting due to the assist gas which blows it away; therefore, plasma absorption mechanism is very limited in laser cutting. The striations observed on the stainless steel cut edges during fiber laser cutting with an inert assist gas are associated with the melt flow mechanisms. During reactive fusion cutting, the incident laser beam melts the workpiece and also ignites and carries on the exothermic reaction between the molten metal and the active gas jet. The development in the output power of solid-state fiber laser source has resulted in the increasing interest in the use of the high brightness fiber laser in macro laser material processing applications, especially cutting and welding of metal [1]. Therefore, it is sufficient to assume that molten metal oxide is removed through the bottom of the cut kerf without vaporization. Metallic materials like stainless steel and aluminium are often laser cut using an inert assist gas jet (usually nitrogen) to give clean unoxidized cut edges which do not require any cleaning operation after cutting. The maximum cutting speeds and maximum workpiece thickness that can be cut using the ytterbium fiber laser have been shown to be largely governed by a number of cutting process parameters that affect the melt removal process and influence the resultant cut edge quality. Conduction limited welding occurs when the power density is not sufficient to cause evaporation of part of the melt at the given welding speed. The absorptivity (coupling coefficient), A, of the workpiece to the incident laser beam can be estimated by considering that the absorbed laser power is utilized to account for both the melting of the kerf volume and the inevitable conduction power losses. By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers. A longer depth of focus is essential for good cut edge quality like in thick-section metal cutting. Or contact our The nozzle stand-off distance distance between the nozzle and the workpiece top surface influences the gas flow dynamics at the entrance of the cut kerf and consequently affects the gas flow patterns at the cutting front. The cut kerf is the opening that is created during through-thickness penetration of a workpiece; therefore, the cut kerf width, w, shown in Figure 2 is the separation distance between the two cut surfaces of the cut kerf which represents the amount of material removed during the laser cutting process.The laser power absorbed at the cutting front is utilized in melting the kerf volume at the rate of cutting and part of the absorbed laser power is lost from the cutting zone through heat conduction to the substrate metal. This provides a dramatically higher power density, making metal cutting easier. Andy is able to share this experience to assist you in your machining and fabrication equipment and application needs. Effect of assist gas pressure on the location of boundary layer separation point and kerf width in inert gas-assisted laser cutting, Variation of surface roughness with assist gas pressure for the fiber laser cut edges in 10-mm stainless steel and 4-mm aluminum, Effect of oxygen assist gas pressure on the kerf width and striations. Click HERE to read more articles aboutLaser CuttingClick HERE See our available Laser Systems. 0000003358 00000 n 0000040608 00000 n Maximum cutting speed at a given laser power level and efficient melt removal for prevention of the undesired dross adherence on the cut edge can be achieved through optimization of the cutting process parameters. They observed that the cut edge quality in 610-mm stainless steel improved with increase in cutting speeds, higher nitrogen assist gas pressures, and wider cut kerfs. endobj Fiber Lasers were simply different than their cousin, the CO2 laser resonator. The effects of cutting speed and focal point position on the surface roughness of the fiber laser cut edges are more significant when a short focal length of the focusing optics is used than when longer focal length optics is used. The ytterbium ion-doped core region is surrounded by an inner cladding of lower refractive index than the core and the inner cladding is in turn surrounded by an outer cladding of still lower refractive index forming a step index fiber (see Figure 1a). The cut kerf width is usually a fraction of a millimeter and the molten metal has a high viscosity such that the melt flow can be assumed to cover the entire cut kerf. The gas flow patterns at the cutting front have a strong effect on the resulting cut edge quality especially during high pressure inert gas-assisted laser cutting [40, 41, 42]. Its here that the arguments for, or against, more power become reality. The melt flow velocity increases with increasing assist gas pressure so that the melt film thickness decreases and the boundary layer separation point moves closer to the kerf bottom with increase in assist gas pressure. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the worlds most-cited researchers. In reactive fusion cutting of thick-section metal, the proportion of the kerf volume that is vaporized is considered to be negligible due to the high conduction losses which scale up with increase in workpiece thickness. where Uis the maximum melt flow velocity; is the gas viscosity; is the melt kinematic viscosity ; gis the gas density; Ugis the characteristic gas velocity inside the cut kerf; tis the workpiece thickness ; wis the kerf width; tmeltis the melt film thickness; Vis the cutting speed; dis the workpiece thickness; P is assist gas pressure. The presence of the oxide layer on the cut edge is the downside of this process as the oxide layer on the cut edge influences the final quality of the part; this oxide layer may require to be removed in a cleaning operation prior to further processing of the part in welding and painting operations. 0000002490 00000 n The melt film in the cutting front is generated by the melting action of the absorbed laser beam power and the oxidation reaction power (in the case of oxygen or compressed air assist gas). The absorption of the laser beam within the keyhole is through both Fresnel absorption (i.e., absorption directly by the material) and plasma absorption (i.e., inverse bremsstrahlung effect) by the free electrons in the metallic plasma. If you have a problem obtaining your download, click Therefore, the improved cooling mechanism in the ytterbium fiber laser has enabled the solid-state laser to achieve near diffraction limited beam quality at high output power [3]. Consequently, for the same incident laser power, cutting speeds of the reactive fusion cutting using an active (oxygen or compressed air) assist gas are usually higher compared to the inert gas-assisted cutting process. The location of the boundary layer separation point moves toward the bottom cut edge with increase in the nozzle diameter because of the enhanced melt removal process facilitated by the increased amount of assist gas provided by the large-size nozzle. The beam parameter product (BPP) defined by the relationship in Equation (1) is an important parameter for the comparison of the beam quality of laser beams of different wavelengths from different laser sources. The performance of the high-power ytterbium fiber laser in materials processing applications is enhanced by its high beam quality at high output power, which results in high brightness. There is a minimum melt film thickness necessary for transmission of the absorbed energy from the melt surface to the melt front. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too. There was existence of adherent dross on cut edges obtained at the slow cutting speeds and at the cutting speeds close to the maximum achievable cutting speed for a given laser power level. where: dZis the depth of focus, fis the focal length of the focusing optics, Dis the raw beam diameter on the focusing optics, and BPPis the beam parameter product of the incident laser beam. Therefore, the ease with which a metallic material can be cut depends on the absorptivity of the material to the incident laser beam, and the melting temperature of the material or oxide formed when a reactive assist gas is used [15]. Wandera et al. However, the absorption coefficient of the parallel polarized light (RP) increases with increase in angle of incidence and is highest at the Brewster angle while the absorption coefficient of the perpendicularly polarized light (Rs) decreases with increase in angle of incidence [25, 27, 28]. who will be happy to help. Cutting process parameters that can be altered for the improvement of the cutting process and the resulting cut edge quality include: used laser power, cutting speed, type and pressure of assist gas, nozzle diameter and nozzle stand-off distance, focal point position relative to the workpiece, and focal length of focusing optics. In reactive fusion cutting using an active assist gas jet, there is a significant variation in kerf width with cutting speed because the exothermic reaction is very erratic at slow cutting speeds, resulting in increased sideways burning and widening of the kerf width (see Figure 8). startxref Plasma absorption occurs through absorption of the laser beam by the free electrons in the plasma (i.e., hot metal vapor) leading to plasma re-radiation [15]. The laser beam quality is the critical parameter that influences the focusability of the laser beam; Equation (2) gives the relationship between the BPP of the laser beam and the minimum focused spot size, dffor focusing optics of focal length, f, and a raw beam diameter on the focusing optics, D. [3, 15]. The maximum processing speeds, maximum processing depths, and resulting cut edge quality are governed by a number of parameters related to the laser system, workpiece specification, and the cutting process. The speed of penetration of a metal workpiece during laser cutting depends on the absorbed incident laser power intensity. Dross adherence and presence of the boundary layer separation on the laser cut edges which affect the surface roughness characteristic of a laser cut edge are critical quality aspects that need to be considered in thick-section metal laser cutting. Gaining his knowledge through years dedicated to Tool & Die Making, Machining and Metal Fabrication with hands-on applications at companies such as: Kamashian Engineering, US Navy/DOD, Boeing, Charmilles, AGIE and Calypso Waterjet Systems. Fiber laser cutting machines are designed for metal fabrication. %&'()*456789:CDEFGHIJSTUVWXYZcdefghijstuvwxyz In laser cutting of metal, the cut kerf is created by continuously shearing and acceleration of the molten metal out of the cutting front by action of the drag force of the high pressure assist gas jet acting coaxially with the laser beam. The cut kerf width depends on the focused spot size, laser power absorbed, and the applied cutting speed. [23] developed a theoretical model to estimate the power requirement for melting the kerf volume and the inevitable conduction power losses. Cut kerf generated and the volume of material removed. The efficiency of melt removal from the cut kerf during laser cutting of a metal workpiece plays a very important role on the cutting performance and the resulting cut edge quality. Andy has extensive experience in Machining as well as Metal Fabricating. Fresnel absorption occurs during direct interaction of the beam and the material in which the photons of the incident laser beam radiation are absorbed by the free electrons in the metal structure. About ScienceDirectShopping cartContact and supportTerms and conditionsPrivacy policy. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. They operated much more efficiently, lost far less power from mirrors and lenses then their CO2 counterparts thus put more cutting power to the torch. [32] reported an increase in fiber laser cutting speeds of up to 1.5 times higher than the CO2 laser cutting speeds. BDX$dxX>B] X"+:AC9BBBDB=l^1J $AqH0C@E$XV . The maximum processing speeds, maximum processing depths, and resulting cut edge quality are governed by a number of parameters related to the laser system, workpiece specification, and the cutting process [15]. 0000007165 00000 n At Southern Fabricating Machinery Sales, Inc.we know Lasers and whether your in the market for a new or used system, fiber or CO2 we have the knowledge and systems available to help you make the right choice for your Needs AND Budget. 1547 0 obj<>stream 0000004354 00000 n The ridges observed on the cut edge in laser oxygen-assisted cutting of 15-mm mild steel using the fiber laser is typical of the mechanism of the sideways burning, as originally explained by Arata et al. A minimum melt film thickness should be maintained at the cutting front to enhance efficient energy coupling to the unmelted metal in the line of traverse of the laser beam for continued cutting. Olsen [19, 20], in his description of the mechanisms of the cutting front formation, identified the melt surface, melt film, and melt frontas the three zones that comprise the cutting front. 0000004097 00000 n The tendency of boundary layer separation and dross adherence on cut edges during thick-section metal cutting using an inert assist gas is influenced by the efficiency of melt removal from the cut kerf. Our team is growing all the time, so were always on the lookout for smart people who want to help us reshape the world of scientific publishing. Downstream from the boundary layer separation point, there is a back-flow of the melt adjacent to the kerf wall and the boundary layer flow transitions from a laminar flow into a turbulent flow in which the melt particles move in random paths. The availability of high-power diode lasers as pumping sources for fiber lasers and improvements in fiber laser design have enabled power scaling of ytterbium (Yb3+)-doped fiber lasers to output powers beyond 1 kW in cwoperation with near diffraction-limited beam quality [8, 13]. ( On the cutting of a 10-mm stainless steel workpiece using the fiber laser, the tendency for dross attachment on the lower cut edge is more significant with focal point positions located on the upper half section of the workpiece thickness (see Figure 12). Contact our London head office or media team here.