Kerf Geometry Research Articles

Laser cutting of CFRP by Quasi-Continuous Wave (QCW) fibre laser: Effect of process parameters and analysis of the HAZ index

In the present work, laser cutting of Carbon Fibre Reinforced Plastics (CFRP) is investigated by means of a Quasi Continuous Wave (QCW) fibre laser. The adoption of high pulse power (up to 4.5 kW) and short pulse duration (0.05 ms) may reduce the HAZ formation and allows high cutting speed. For the aforementioned reasons, the improvement of the laser cutting parameters is industrially relevant, especially on materials that are difficult to cut with the standard modes. To assess the influence of the process parameters on kerf geometry and Heat Affected Zone, experimental tests were carried out fixing the average power at 450W and changing the pulse power, the pulse duration, and the overlapping factor. The tests were performed adopting a full factorial design 33 according to the DoE methodology. ANalysis Of VAriance was used to determine which and how the process parameters affect the kerf geometry and HAZ extension. Results show that the laser allows cutting 1.3 mm-thick CFRP sheets with cutting speed up to 2700 mm/min. Also, by an appropriate selection of the process parameters, it is possible to obtain narrow kerfs (smaller than 200 μm) and a limited HAZ (about 0.5 mm). Besides, the correlation between the inner and the outer HAZ was found: the HAZ measured on the bottom surface can be usefully adopted as a damage index to understand the overall thermal damage since it can be correlated to section HAZ. The latter is the reference damage parameter according to UNI EN ISO 12584 standard.

Multi-objective Optimization of Kerf-taper and Surface-roughness Quality Characteristics for Cutting-operation On Coir and Carbon Fibre Reinforced Epoxy Hybrid Polymeric Composites During CO2-Pulsed Laser-cutting Using RSM

Current research focuses on optimizing various quality characteristics for kerf geometry generated through laser cutting of Coir fibre/carbon fibre/epoxy resin hybrid composite adjacent to straight cut profile employing pulsed CO2 laser system. The Kerf taper (KT) and the Surface roughness (SR) are the main quality parameters discussed. Dependent on significant process parameters, namely gas pressure, cutting speed, pulse frequency and pulse width predictive models were developed. In accordance with Taguchi's L9 orthogonal array (OA), the cutting trials are designed. Process-parametric optimization was performed using Response Surface Methodology (RSM). Furthermore, experiments were performed to obtain experimental data for the analysis of cut quality features. The impact of the input variables on the response characteristics is also explored. The morphological characterizations have been performed to analysis the effect of machining-variables and cut-quality for the top and bottom kerf widths with various laser cutting variables in the pulse laser-cutting of Coir-fibre/carbon-fibre/epoxy-resin hybrid composite. For SR and KT, the developed second order surface response model was found very successful. The optimal levels of cutting variables for KT are established at Gas pressure-6 N/mm2, pulse width-2.04 ms, cutting speed-8.01 mm/s, pulse frequency-15 Hz, for sample A1, Gas pressure-5.47 N/mm2, pulse width-2.5 ms, cutting speed-8.81 mm/s, pulse frequency-8.43 Hz, for sample A2, Gas pressure-3.85 N/mm2, pulse width-1.5 ms, cutting speed-9.06 mm/s, pulse frequency-5 Hz, for sample A3 additionally for SR Gas pressure-2 N/mm2, pulse width-1.5 ms, cutting speed-7 mm/s, pulse frequency-5 Hz, for sample A1, Gaspressure-2.36 N/mm2, pulse width-1.5 ms, cutting speed-7 mm/s, pulse frequency-15 Hz, for sample A2, Gaspressure-6 N/mm2, pulse width-1.5 ms, cutting speed-11 mm/s, pulse frequency-8.73 Hz, for sample A3. Regression results and linear and square impact of laser cutting variables have been revealed to be important to validate the model.

Factorial Analysis of Fiber Laser Fusion Cutting of AISI 304 Stainless Steel: Evaluation of Effects on Process Performance, Kerf Geometry and Cut Edge Roughness.

Factorial Design-of-Experiment analyses were applied for conventional and beam oscillation fiber laser cutting of 10 mm thick AISI 304 stainless steel. Considered factors in case of the conventional process with a static beam involve both laser and cutting gas parameters, in particular the laser power, the focal plane position, the cutting gas pressure, the nozzle stand-off distance as well as the nozzle diameter. The conducted trials were evaluated with respect to the achievable cutting speed, the cut kerf geometry and the cut edge roughness. Noticeable correlations between cut edge roughness and cut kerf geometry stimulated the development of a corresponding Computational Fluid Dynamics (CFD) model of the cutting gas flow through the kerf. A specific approach of data synchronization revealed that the experimentally determined roughness values do well correlate with numerically computed values of the backward directed component of the gas-induced shear stress and that the cut kerf geometry as internal process-inherent boundary condition influences relevant cutting characteristics more than controllable external cutting gas parameters. Finally, effects of circular beam oscillation were investigated by an additional factorial analysis considering the laser power, the focal plane position, the oscillation frequency and the oscillation amplitude as factors. The results demonstrate the potential of beam oscillation techniques for quality improvements in laser cutting.

Prediction of laser drilled hole geometries from linear cutting operation by way of artificial neural networks

This paper deals on artificial intelligence (AI) application for the estimation of kerf geometry and hole diameters for laser micro-cutting and laser micro-drilling operations. To this aim laser cutting and laser drilling operation were performed on NIMONIC 263 superalloy sheet, 0.38 mm in nominal thickness, by way of a 100 W fibre laser in modulated wave regime. Linear cuts and holes (by trepanning) were performed fixing the average power at 80 W and changing the pulse duration, the cutting speed, the focus depth and the laser path (the latter only for the drilling operations). Kerf width and the holed diameter, at the upper and downsides, were measured by digital microscopy. Different artificial neural networks (ANNs) were developed and tested to predict the kerf widths and the diameters (at the upper and downside). Two ANNs were addressed to the linear cutting process modelling; also, two further ANNs were developed for micro-drilling on the base of the linear cutting process features. The networks were trained with a subset of data containing the process conditions and the kerf/hole geometry. The ANN test was performed with the remaining data. The results show that ANNs can model the cut and hole geometry as a function of the process parameters. Moreover, the ANN trained with kerf geometry is more efficient. Therefore, a functional correlation between the kerf geometries achievable in the linear cutting process and micro-drilling was assessed.

Experimental investigation on laser cutting of PMMA sheets: Effects of process factors on kerf characteristics

This paper reports an experimental investigation on continuous CO2 laser cutting of polymethylmethacrylate (PMMA) sheet. The influence of four process factors (laser power, cutting speed, assisting gas pressure and sheet thickness) on five process responses (kerf deviation, top heat affected zone, bottom heat affected zone, maximum surface roughness and rough area) has been investigated. The experimental plan was established based on Taguchi L18 mixed design. The kerf geometry and heat affected zones have been measured using polarising light microscopy technique, while the surface roughness was evaluated using 3D laser scanning confocal microscope. Regression models have been derived to correlate different process responses with different process factors. The cut surface could be classified into three zones: rough zone, moderate zone and soft zone. The rough area is increased by increasing gas pressure and laser power and by decreasing the sheet thickness and cutting speed. Increased kerf deviation has been observed at high cutting speed, laser power and gas pressure. High laser power and low cutting speed produced worst surface roughness and wide heat affected zone. Therefore, it is recommended to use low laser power and high cutting speed to minimize the heat affected zone and the surface roughness. However, increasing the cutting speed may result in high kerf deviation.

A study on the interaction of jet with constituent layers of multilayered structure in through kerfing with abrasive waterjets

Abstract Abrasive waterjet technology is favored over solid cutting tools for cutting of multi-layered structures in view of its non-contact nature and its ability to cut a wide range of materials. However, the stochastic nature of abrasive water jet (AWJ) interacting with a multi-layered structure (MLS) produces a non-uniform kerf geometry. This non-uniformity depends on the characteristics of jet i.e. jet energy, the duration of interaction of jet with the material, and the nature of material exposed to the jet during cutting. This paper attempts to cover a study that systematically analyses the geometry of kerf generated in MLS and a stack of multiple materials with each material having different mechanical properties. It also covers a study to analyse the role of interfacial adhesive layer on kerf profile variation, and the preferential orientation of multi-layered structure and stacked materials, with its top layer, having an appropriate mechanical resistance (MR), in order to arrive at a strategy to present the structure or a stack of materials to AWJs for producing near uniform kerf profile. Hence, AWJ cutting experiments were carried out over a single- and double- layered structures (SLSs, DLSs) with two different materials such as aluminum (Al), mild steel (MS), which showed a completely different kerf geometry when these materials are stacked in different ways. Stacking of these materials in different ways produced kerf of different geometry not only in the materials but also at their interface. This systematic study enabled to suggest the correct presentation of MLS and also a stack of multiple materials with a suitable material in top layer, to AWJ, for producing near uniform kerf in them. Further, this study also suggested several hypotheses like the importance of relative MR of adjoining layers, critical jet traverse rate, pseudo focusing nozzle, and the choice of layer placement in producing near uniform kerf on MLS and a stack of materials, so as to minimize the efforts in post machining of AWJ cut surfaces. Finally, the relevance of the proposed hypotheses was validated by analyzing the kerf formed over MS-rubber-MS and rubber-MS-rubber configured three-layered structure.

An Experimental Analysis of Cutting Quality in Plasma Arc Machining

Plasma arc cutting (PAC) is an unconventional process widely used in manufacturing of heavy plate products. This work reports on the research results of machining quality of the workpiece in the plasma arc cutting on the low carbon low alloy steel. An experimental investigation of the characteristics of machining accuracy and surface integrity was carried out for basic machining parameters (cutting speed, arc current, arc voltage, plasma gas pressure, stand-off distance and nozzle diameter). The kerf geometry was determined with three accuracy parameters (top kerf width, bottom kerf width and kerf taper angle). The parameters of deviation present due to plasma curvature were defined by drag and pitch of drag line. The surface roughness was determined with two main roughness parameters through scanning the surface topography (roughness average and maximum height of the profile). The surface properties were determined over microstructure in heat affected zone (HAZ). The results show an acceptable machining quality of the PAC, so that this process is an excellent choice for fast and efficient material removal. However, the plasma arc cutting is not suitable for the final machining because of the metallurgical variations in the HAZ.

Preheating assisted wire EDM of semi-conductive CFRPs: Principle and anisotropy

Introducing small-sized functional features such as anti-drag and anti-icing micro structures on Carbon Fibre Reinforced Plastics (CFRPs) is challenging but a still unmet demand. Existing contact CFRP machining solutions may bring unavoidable tool wear and surface defects. Non-contact approaches may introduce significant thermal damage (laser), inconsistent features (waterjet), and limited achievable micro structure shapes and sizes (die sinking Electrical Discharge Machining). Wire Electrical Discharge Machining (WEDM) has the potential to overcome the mentioned limitations. Both theoretical thermal calculation and experimental demonstration in our work, however, showed that conventional WEDM was not working well. Here we propose and implement a Preheating Assisted Wire EDM (PAWEDM) to cut CFRPs. Machining anisotropy in terms of kerf geometry and morphology at the cut entries, ends, and edges was studied carefully. Discussions on the anisotropy principle, the influence of carbon fibre and epoxy resin, and the minimum achievable feature were also provided. PAWEDM is an entirely new CFRP cutting method and effective to enhance CFRP performances by creating micro functional and structural features on CFRP products.

Experimental Investigation of Industrial Laser Cutting: The Effect of the Material Selection and the Process Parameters on the Kerf Quality

Laser beam cutting is a non-contact, production-flexible and highly productive technique that allows accurate profiling of a wide range of sheet materials. To these and further benefits, laser machining is increasingly being adopted by industry. This paper investigates the effect of material type, workpiece thickness, cutting speed and assistant gas pressure on cut quality for industrial-relevant applications using a CO2 laser. AlMg3 aluminum alloy, St37-2 low-carbon steel and AISI 304 stainless steel were selected to represent the most established materials in many industrial fields and gain insight into different processes (i.e., inert-assisted fusion cutting and oxygen cutting) and absorption behaviors with respect to CO2 laser wavelength. The aim was to enhance the understanding of the mechanisms through which laser cutting parameters and workpiece parameters interact in order to identify general criteria and well-optimized process parameters which guarantee the kerf quality. The quality of laser cut was analyzed in its basic terms: kerf geometry, surface roughness and cut edge quality. The experiments were performed by using a systematic experimental design approach based on Design of Experiments, and the results were validated via Analysis of Variance. Quality assessment was presented and discussed. The visual inspection of cut sections confirms good overall quality and limited presence of laser cut imperfections. The experimental investigation demonstrates that the different materials can be successfully processed within a wide range of the tested values. In addition, optimum cutting conditions which satisfy the straight requirement of the quality standard adopted are identified for each material. This study involves an analysis of both phenomenological and practical issues.

Comparison of abrasive water jet technologies in terms of performance and kerf geometry accuracy for cutting ceramics

Hard machining of brittle materials such as ceramics is a process-oriented challenge. For the machining of such materials, abrasive water jet cutting is an appropriate alternative to the commonly used diamond grinding and laser cutting processes. In abrasive water jet machining the injection technology is currently used almost exclusively. Due to the realisation of the suspension jet technology a higher cutting performance can be achieved. In this article, the known injection technology and the suspension technology are compared. To do so, the influences on the quality were examined for trimming technical ceramics. The investigation illustrates that suspension technology trims with a higher accuracy than injection technology in matters of kerf geometry but with a lower material removal rate.

Comparison of abrasive water jet technologies in terms of performance and kerf geometry accuracy for cutting ceramics

Comparison of abrasive water jet technologies in terms of performance and kerf geometry accuracy for cutting ceramics

An investigation of abrasive waterjet machining of cubic boron nitride (CBN) with a softer abrasive material

For an effective machining of high-performance materials, high-strength cutting materials, e.g. cubic boron nitride (CBN), with high resistance to any kind of wear are used. However, these materials must also be able to be machined in order to produce geometric elements such as chip breakers or chip grooves. According to the current state of the art, grinding and laser beam technology are used for this purpose. In this paper, an attempt was made to use the erosive removal mechanism of abrasive water jet technology to cut a harder material with a softer abrasive. Within the framework of a full factorial test plan, the removal rate, the macroscopic kerf geometry on CBN were investigated by means of abrasive water jet machining. It could be proven that it is possible to remove a harder material with a softer abrasive by means of abrasive water jet technology.

Evaluation of Kerf as a Crack Arrestor in a Plate under Tension Loading using FEA

Crack arrestor means to prolong the life cycle of the crack. There are many methods has been studied to arrest crack but the use of a kerf as a crack arrestor has not been widely studied. Initial study has stated that the value of SIF at the crack tip can be reduced with the presence of the kerf in the same body, but detail dimension of the kerf that will produce best arresting effect is unknown. The finite element analysis was used to model the finite plate which contains different kerf geometries and a crack to obtain crack’s tip stress intensity factor. Four types of kerf’s configuration have been considered which are; single central kerf, double central kerf, single edge kerf and double edge kerf. Each type used different kerf’s geometries selection that is predicted will produce higher kerf-crack interaction. The results of SIF were calculated as a percentage reduction when compared to SIF of a single edge crack without any kerf. Results show double edge kerf type is the most suitable for crack arrestor. Maximum percentage SIF reduction of 34.27% can be achieved when the crack is the shortest and separation to width ratio equal to 0.1. If the longer crack is detected on a structure, highest percentage SIF reduction can be achieved by fabricating maximum kerf length with separation to width ratio in the range of 0.15 and 0.25.

Surface quality and kerf width prediction in abrasive water jet machining of metal-composite stacks

Machinability of stacked Titanium (Ti6Al4V) and CFRP was evaluated using Abrasive Water Jet (AWJ) machining process. The experimental study was conducted using three pressure levels – 200, 275 and 350 MPa. Traverse speed was varied between 1 and 10 mm/s for two stacking configurations (Ti/CFRP, and CFRP/Ti). The erosion characteristics, kerf width and surface roughness was studied as a function of process parameters. Surface roughness and kerf width variation was high at low jet power conditions, as described by lumped parameters (E˙/u and E˙/hu). The minimum average roughness Ra for Ti and CFRP was less than 3.5 μm and 4.5 μm respectively for both the stacking sequence. The kerf width increased significantly, especially when Ti6Al4V is at top in which case low-energy, turbulent jet diverges at the exit from Ti6Al4V. Mathematical regression models were developed to predict kerf width. An energy based, semi-analytical model was proposed to predict the kerf geometry with R2=92.26%.

Study of surface topography in Abrasive Water Jet machining of carbon foam and morphological characterization using Discrete Wavelet Transform

Carbon foam (CFOAM) is a light weight alternative to composite tooling and other applications in aerospace industry. Secondary machining of CFOAM is challenging due to machining induced damage to its thin walled structure and also the production of carcinogenic dust during the conventional machining processes. In this study, machinability of CFOAM was investigated using Abrasive Water Jet (AWJ). Three pressure levels – 200, 275, 350 MPa and jet traverse speed between 2 and 100 mm/s was used to machine 50 mm thick carbon foam. The kerf surface topology and morphology was inspected using non-contact profilometry, optical and scanning electron microscopy. A lumped process parameter – power-to-speed ratio (E˙/u) was effectively used to describe the kerf characteristics in terms of kerf geometry and kerf wall roughness. A novel method using Discrete Wavelet Analysis was proposed to study the surface topology and establish correlation with E˙/u. The most common material removal mechanisms were found to be erosion, cell shape distortion, cell and pore engulfment, ligament fractures, debris entrapment with cell wall cracking. Overall, surface topology and morphology was characterized with a strong correlation with the process parameters which assisted in determining optimal window for AWJ process parameters.

Abrasive water jet machining of Titanium (Ti6Al4V)–CFRP stacks – A semi-analytical modeling approach in the prediction of kerf geometry

The use of stacked metal-fiber material system is limited by machining challenges due to micro and macro level distinction in material phases. This study explores the machinability of stacked Ti6Al4V and CFRP material system using Abrasive Waterjet technology (AWJ). AWJ controlled depth experiments were conducted for stacked Titanium and monolithic CFRP. A strong linear relationship was identified between jet power-to-speed ratio and penetration depth for CFRP and Titanium individually, which was further used to predict the penetration depth in stacked Ti-CFRP configuration. Issues such as kerf rounding at the interface, delamination in CFRP were addressed and optimal process conditions were identified. A simplified model to predict the penetration depth was proposed which was proven to be more effective than multivariate regression model.

Modelling of Abrasive Water Jet Cutting with Controlled Depth for Near-Net-Shape Fabrication

Near-net-shape fabrication of difficult to machine materials is a promising application for the abrasive water jet technology. An effective implementation can be achieved by controlling the kerf depth and cutting off defined material fragments. A model for controlled cutting is introduced to make the machining process design more effective for different materials. An empirical model was combined with the process’ physical behavior, allowing the prediction of the kerf geometry using a minimum number of predictors and thus initial trials. The model tested with metal matrix composites, reveals the capability of transferring knowledge to new materials using few initial trials.

Simultaneous optimization of kerf taper and heat affected zone in Nd-YAG laser cutting of Al 6061-T6 sheet using hybrid approach of grey relational analysis and fuzzy logic

In this paper, laser cutting of Aluminum alloy (Al 6061-T6) thin sheet has been carried out using pulsed Nd-YAG laser to investigate the dimensional accuracy of the kerf geometry and zone of the metallurgical changes in the sheetmetal. These responses are quantified in terms of kerf taper and heat affected zone for the study. The taper in the kerf and heat affected zone are the functions of four laser cutting parameters namely: lamp current, pulse width, pulse frequency and cutting speed and different settings of these laser cutting parameters are utilized to analyze the responses. In order to analyze the experimental results, a systematic design of experiments namely Box Behnken design (BBD) has been employed to conduct the experiments. Further, the experimental results have been optimized using hybrid approach of grey relational analysis and fuzzy logic. The analysis of variance (ANOVA) has been carried out to determine the significance of laser cutting parameters for the process where pulse frequency is found as the most leading parameter in the study. The application of hybrid approach is capable to reduce the kerf taper and HAZ of laser cut kerf by 2.52% and 42.32%, respectively.

Study of correlation between edge roughness and gas flow characteristics in laser beam fusion cutting

Fiber laser fusion cutting trials on AISI 304 stainless steel sheets of 10 mm thickness were performed with the aim to gain further insights into the striation formation process on cut edges. The study is based on a factorial Design-of-Experiment (DoE) approach with consideration of laser power, focal plane position, gas pressure, nozzle stand-off and nozzle diameter as control factors. Analyzed responses include the achievable cutting speed, the cut kerf geometry and the cut edge roughness. In addition, numerical simulations of the cutting gas flow were carried out for adapted kerf geometries and gas parameters. The evaluation of these results reveals strong correlations between experimental roughness values and the numerically computed rear-directed shear stress component within the transition zone between cutting front and cut edge surface. This finding supports the hypothesis that the particular characteristics of the boundary layer zone of the cutting gas flow affects the structure and roughness of cut edges.

Surface integrity of water jet guided laser machining of CFRP

Carbon fiber reinforced plastics (CFRP) is now applied widely in various industries because of its excellent properties. Although conventional processing methods, such as milling and abrasive water jet, are the dominating techniques used, laser cutting of CFRP is still attractive owing to the wear-free, contactless and flexible processing. However, the anisotropic material properties of CFRP, the issues related to the heat affected zone (HAZ) and delamination during laser processing, are major obstacles in its application. In order to reduce the heat damage caused by laser, a compound machining method, water jet guided laser technique, was adopted to cut CFRP in this paper. In addition, we make a comparative investigation for conventional laser beam machining and water jet guided laser machining with an identical material. The difference of kerf geometry, HAZ, surface morphology and efficiency was discussed within this research. The experiments showed that the HAZ of water jet guided laser is smaller than conventional laser beam machining, but much less efficient. Water jet guided laser technique is a potential processing method for CFRP if the efficiency is improved.