Parametric influence on cut quality attributes and generation of processing maps for laser cutting
23 Mar 1999-Journal of Laser Applications (Laser Institute of America)-Vol. 11, Iss: 2, pp 54-63
TL;DR: In this article, the authors established a methodology to develop such "processing maps" and illustrate their utility by using laser cutting of mild steel and commercially pure titanium as case studies, which can be used to optimize the process on the basis of operational costs.
Abstract: Laser cutting is an attractive alternative to conventional cutting methods due to its many inherent advantages. However, notwithstanding its promise for processing diverse categories of materials, the understanding of the subject is incomplete. Although numerous processes are known to significantly influence cutting quality, comprehensive data of practical utility—such as identification of processing regimes to achieve optimum cut surface attributes—remain yet to be generated. The present article establishes a methodology to develop such “processing maps” and illustrates their utility by using laser cutting of mild steel and commercially pure titanium as case studies. The processing maps can be constructed based on any chosen cut quality criteria and can be used to optimize the process on the basis of operational costs. Results reveal that, for achieving good quality cuts, such processing regimes constitute only a narrow region within the wide operating window for mere cuttability and vary substantially with material-assist gas combination. Typically, the operating window for inert gas-assisted cutting is narrower than that for oxygen-assisted cutting involving an exothermic oxidation reaction, which contributes significantly to the overall energy input to the cutting front. The influence of the two major process parameters, laser power and cutting speed, on cut quality attributes such as surface roughness, kerf width, heat affected zone, and cut surface morphology is also discussed in detail. The experimental results have also been compared with theoretical predictions of a scaling law for laser cutting.
TL;DR: In this paper, Nd:YAG laser drilling of 4 and 8mm thick sections of IN718 and Ti-6Al-4V materials has been investigated and relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated.
Abstract: Laser drilling is increasingly becoming the method of choice for precision drilling of a variety of components, particularly in the aircraft industry. Notwithstanding the current level of acceptance of laser drilling in the aerospace industry, a number of defects such as spatter, recast and taper are associated with laser drilled holes and elimination of these defects is the subject of intense research. The present paper deals with Nd:YAG laser drilling of 4 and 8 mm thick sections of IN718 and Ti–6Al–4V materials. The influence of type of material and its thickness, as well as parametric impact of key process variables like pulse frequency and pulse energy, have been determined. In the course of this study, relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated. In addition, all metallurgical characteristics of interest, viz extent and nature of spatter, recast and heat-affected zone, have been evaluated. Effort has also been made to obtain some insights into the evolution of a through-thickness hole during laser percussion drilling of thick sections by careful experimentation involving monitoring the progression of the drilled hole with increasing number of laser pulses. Issues pertaining to variation of taper with depth of hole, change in crater depth with progressive drilling and specific energy consumption are also discussed.
TL;DR: In this paper, a typical cutting regime for pulsed Nd:YAG laser cutting of 1mm thick Hastelloy-X sheet has been constructed and explained in terms of extent of spot overlap.
Abstract: Although CO2 lasers have been widely employed for commercial sheet metal cutting operations, increased recognition of the processing benefits afforded by pulsed Nd:YAG lasers has recently fuelled interest in the latter. Pulsed Nd:YAG laser cutting differs from conventional continuous wave laser cutting as it involves overlapping of a series of individual spots generated by each pulse. In this paper, a typical cutting regime for pulsed Nd:YAG laser cutting of 1 mm thick Hastelloy-X sheet has been constructed and explained in terms of extent of spot overlap. The characteristics of single holes drilled employing the same process parameters as those employed for cutting were investigated and correlated with the obtained processing regime. Additionally, the influence of key process parameters like pulse duration on the shift in the constructed processing regime was investigated. Cut quality attributes like kerf width, cut edge kerf profile and surface roughness were also studied and their dependence on process parameters has been discussed.
TL;DR: In this paper, the shape memory effect (SME) and high biocompatibility of 1 mm thick NiTi shape memory alloys for medical applications (SMA-implants) has been investigated.
Abstract: Shape memory alloys (SMAs), in particular Nitinol (NiTi), are of increasing interest in research and industry due to their outstanding properties, e.g. the shape memory effect (SME) and high biocompatibility. Obviously, it is necessary to machine these elements from NiTi sheet materials using suitable processing methods that provide high precision and retain the shape memory effect. Pulsed Nd:YAG laser cutting of 1 mm thick NiTi shape memory alloys for medical applications (SMA-implants) has been investigated. Due to the local energy input only small heat-affected zones (HAZ) occur and the shape memory properties remain. The influence of key parameters like pulse energy, pulse width, and spot overlap on the cut geometry, roughness and HAZ is shown.
TL;DR: In this paper, the effect of the cutting parameters on the cut quality was investigated, by monitoring the variation in hardness, oxide layer width and microstructural changes within the heat affected zone (HAZ).
Abstract: There are many non-linear interaction factors responsible for the performance of the laser cutting process. Identification of the dominant factors that significantly affect the cut quality is important. The present research aims to evaluate the CW ND:YAG laser cutting parameters (the gas pressure, laser power, and scanning speed) for 1.2 mm thick ultra-low carbon steel sheets. The effect of the cutting parameters on the cut quality was then investigated, by monitoring the variation in hardness, oxide layer width and microstructural changes within the heat affected zone (HAZ). Results revealed that good quality cuts can be produced in ultra low carbon steel thin sheets, at a window of laser scanning speed of 1100–1500 mm/min and at a minimum heat input of 337 W under an assisting O2 gas pressure of 5 bar. Higher laser power resulted in either strengthening or softening in the HAZ surrounding the cut kerfs. The oxide layer width is not affected by the energy density input, but is affected by the O2 gas pressure due to exothermal reaction.
TL;DR: In this article, specific point energy (SPE) is applied to laser cutting of various thicknesses of mild steel with a 2kW fiber laser. But it was found that the SPE concept is not applicable for laser cutting within the range of parameters investigated here.
Abstract: Specific point energy (SPE) is a concept that has been successfully used in laser welding where SPE and power density determine penetration depth. This type of analysis allows the welding characteristics of different laser systems to be directly compared. This paper investigates if the SPE concept can usefully be applied to laser cutting. In order to provide data for the analysis laser cutting of various thicknesses of mild steel with a 2kW fibre laser was carried out over a wide range of parameter combinations. It was found that the SPE concept is applicable to laser cutting within the range of parameters investigated here.
Cites methods from "Parametric influence on cut quality..."
...This approach is used for all laser material processing techniques[5-7], including laser cutting[8-12]....
TL;DR: In this article, the authors investigated the cutting capability of COIL and Nd:YAG laser and found that the cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed.
Abstract: The most widely used high power industrial lasers are the Nd:YAG and CO2 lasers. The chemical oxygen iodine laser (COIL), whose wavelength (1.315 μm) is between that of the Nd:YAG (1.06 μm) and CO2 (10.6 μm) lasers, is another high power laser for industrial applications. The cutting capability of these lasers is investigated in this paper. The cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed. The absorptivity is an unknown parameter for which experimental data at high temperatures are currently unavailable. Theoretical values of the absorptivities of various metals are obtained using the Hagen‐Ruben relationship. It is found that the absorptivity of a metal is linearly proportional to the square root of its resistivity and also inversely proportional to the square root of the wavelength. The absorptivities of the COIL and Nd:YAG lasers are 2.84 and 3.16 times larger than that of the CO2 laser, respectively. Based on these theoretical values of the absorptivity, the cut depths for several metals are analyzed at various laser powers and cutting speeds for these lasers. For identical cutting parameters, the cut depths for stainless steel and titanium are deeper than those of most other metals. Due to the wavelength dependence of the absorptivity, the cut depths for COIL and Nd:YAG lasers are expected to be 2.84 and 3.16 times deeper than that for the CO2 laser.
TL;DR: In this paper, the authors investigated the cyclic nature of a cyclic cutting event when a CO2 laser in conjunction with an oxygen jet is used to cut mild steel and showed that the self-limiting nature of the oxidation of the steel in the cut zone can explain the nature of cut edge striation produced by cyclic oxidation reaction.
Abstract: Over the past two decades CO2 laser cutting has grown from an obscure laboratory technique into an important branch of manufacturing engineering. The most commonly cut materials are steels and a great deal of industrial and scientific research has been carried out on the laser-material interactions that generate a cut. This paper concentrates on the phenomena which give rise to a cyclic cutting event when a CO2 laser in conjunction with an oxygen jet is used to cut mild steel. The nature of the cut edge striation produced by the cyclic oxidation reaction is explained thoroughly and a possible oxidation cycle is postulated. It is demonstrated that the key to understanding the cyclic nature of the cutting event is the self-limiting nature of the oxidation of the steel in the cut zone.
TL;DR: In this article, the effects of gas composition on high power CO 2 laser cutting of mild steel is carried out from the experimental point of view, with particular reference to small variations in gas composition.
Abstract: The importance of the exothermic reaction to CO 2 laser cutting was found by many previous researchers and this reaction was also investigated widely over the years. However, a systematic investigation about the effects of gas composition on high power CO 2 laser cutting has not yet been performed. Therefore, an attempt to systematically examine the effects of gas composition on the CO 2 laser cutting of mild steel is carried out from the experimental point of view. There are many non-linear interacting factors responsible for laser cutting process performance. In general, it is impractical to investigate all of the factors at one time. The identification of the dominant factors for which variation could lead to large effects on the cut quality is important. In this research, the gas-composition variation and the gas pressure were selected as the dominant factors. Their effects on the cut quality are investigated, with particular reference to small variations in gas composition. The gas mixtures used in this study are composed of oxygen, argon, nitrogen, helium. From the experimental results, it has been found that a high purity of oxygen is required for the high-performance CO 2 laser cutting of mild steel. Only a tiny oxygen impurity (1.25%) will reduce the maximum cutting speed by 50%. For 3 mm thick mild steel CO 2 laser cutting, a good cut was not found in the present study using low pressure—up to 6 bar—inert gas (nitrogen, argon, helium) cutting.
19 Mar 1984
TL;DR: In this article, a simulation of the model of laser cutting of relatively thick workpieces yields a more detailed understanding of the laser cutting process and agrees well with experimental investigations, and a computer simulation of that model is presented.
Abstract: During laser cutting of relatively thick workpieces the erosion takes place at a nearly vertical plane at the momentary end of the cut. That plane is covered by a thin molten layer, that is heated by absorbed laser radiation and by reaction. The removal of material from that layer is carried out by evaporation and by ejection of molten material due to the friction between the melt and the reactive gas flow. A computer simulation of that model yields a more detailed understanding of laser cutting and agrees well with experimental investigations.
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19 Mar 1984