Laser Cut Edges Research Articles

Trim-cut technique for analysis of melt flow dynamics in industrial laser cutting machine

Several studies in laser cutting literature have demonstrated that quality aspects of the laser cut edge, such as dross attachment, surface roughness and striation pattern, are highly influenced by the melt flow dynamics. Therefore, in order to visualise the laser cutting process, the trim-cut technique was conceived several decades ago and has been continuously improved by different authors. This tool provides great opportunities to enhance the understanding of the process, such as the origin of quality deterioration, and might help to identify solutions for process improvement. Nevertheless, investigations on laser flame cutting of mild steel are scarce. Within this paper, the design aspects of a setup for high-speed process observation are discussed in detail. The influence of trim-cut parameters on the quality of an obtained cut edge of 15 mm mild steel is investigated. Since the combination of the replacement edge distance and trim-cut width considerably influences the quality of a cutting edge, the similarity of a trim-cut edge with a normal cut edge is examined. A replacement edge distance of 500 µm and a trim-cut width of 50 % are defined as the most suitable set of trim-cut parameters for further high-speed observation of mild steel cutting. The melt flow dynamics of the laser flame cutting process using a commercial 4 kW industrial fiber laser cutting machine are visualised by means of a high-speed imaging system with a frame rate of up to 15 000 fps which allows estimating the velocity of the melt flow inside the cutting front as 5 m/s.

Machine Vision System for Evaluating Performance Measure of Laser Beam on Leather

The manual inspection of leather is sluggish and labor-intensive tasks, they can become precarious in the entire production process. In the present study an attempt has been made to investigate the Heat Affected Zone (HAZ) of leather during the laser cutting process due to the thermal effect caused by a laser at the cut contour edges. To inspect this, a machine vision system is used to capture images of the laser cut edges and then process it using MATLAB to acquire the required information for assessing the quality of leather. The leather can be categorized as good, average or poor quality based on the acquired information for the respective application. As a result, the degree of burn of the leather was determined.

Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing

The study presented investigates the fatigue strength of the (α+β) Ti-6Al-4V-ELI titanium alloy processed by laser cutting with and without mechanical post-processing. The surface quality and possible notch effects as a consequence of non-optimized intermediate cutting parameters are characterized and evaluated. The microstructural changes in the heat-affected zone (HAZ) are documented in detail and compared to samples with a mechanically post-processed (barrel grinding, mechanical polishing) surface condition. The obtained results show a significant increase (≈50%) in fatigue strength due to mechanical post-processing correlating with decreased surface roughness and minimized notch effects when compared to the surface quality of the non-optimized laser cutting. The martensitic α’-phase is detected in the HAZ with the formation of distinctive zones compared to the initial equiaxial α+β microstructure. The HAZ could be removed up to 50% by means of barrel grinding and up to 100% through mechanical polishing. A fracture analysis revealed that the fatigue cracks always initiate on the laser-cut edges in the as-cut surface condition, which could be assigned to an irregular macro and micro-notch relief. However, the typical characteristics of the non-optimized laser cutting process (melting drops and significant higher surface roughness) lead to early fatigue failure. The fatigue cracks solely started from the micro-notches of the surface relief and not from the dross. As a consequence, the fatigue properties are dominated by these notches, which lead to significant scatter, as well as decreased fatigue strength compared to the surface conditions with mechanical finishing and better surface quality. With optimized laser-cutting conditions, HAZ will be minimized, and surface roughness strongly decreased, which will lead to significantly improved fatigue strength.

Effect of process parameters on machinability characteristics of CO2 laser process used for cutting SS-304 Stainless steels

Abstract This project defines there occurs a change in mathematical values of surface roughness (Ra, μm) and Kerf width (Kw, mm), while conducting experimentation of CO2 laser cutting on SS-304 Stainless steel using Nitrogen as assistance gas. The laser kerf width and cut edges quality was influenced by the process parameters like cutting speed (V), Assist gas pressure (p) laser power (P). The experiment was constructed and followed on the base of L27 orthogonal array. A predictive model is generated by using multiple regression analysis through ANOVA and implemented to find relative influence of process parameters on Kw and Ra.

Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules are used that differ slightly in thickness as well as on the basis of the electrode materials: silver nanowires or carbon-based inks. Each type of module is subjected to two different mechanical modes of deformation, bending and torsion, of several thousand cycles per module using a purpose-built robotic device. Analysis of the distribution of stress in the devices performed by finite-element modeling predicts the locations of failure. Failure upon bending originates at the laser-cut edges of the modules from shear at the clamp/module interface leading to crazing of the plastic barrier encapsulant foils. This crazing leads to eventual delamination due first to decohesion of the active layer at the edge of the modules and later to deadhesion between the PEDOT:PSS (electrode) and P3HT:PCBM (semiconductor) layers. The torsion mode imposes greater stresses than the bending mode and thus leads to failure at fewer strain cycles. Failure during torsion occurs through crack propagation initiated at stress concentrations on the edges of the module that were imposed by their rectangular geometry and ultimately leads to bifurcation of the entire module. Rather than the differences in electrode materials, the differences in survivability between the two types of modules are attributed mostly to the thickness of the substrate materials used, with the thinner substrate used in the carbon-based modules (~160µm) failing at fewer strain cycles than the substrate used in the silver-nanowire-based modules (~190µm). Taken together, the results suggest ways in which the lifetimes of devices can be extended by the layouts of modules and choices of materials.

Life Assessment and Crack Growth Properties of Laser Cut Dual-Phase Steel

The effect of laser cut-edges has been studied as a method for producing an optimum fatigue life performance of advanced high-strength steel. During this study, DP600 high-strength steel laser cut-edges have been fatigue tested under S-N and E-N fatigue loading regimes. The cut-edge surface characteristic properties and internal metallurgical alterations have been observed to directly influence fatigue life of the steel. This paper has investigated the crack initiation and growth properties of the initial crack to mode two. It is shown that alterations in the surface properties can be harnessed so that beneficial properties can be produced to retard crack initiation. It was determined that the laser power and cutting speed can be used independently to produce the appropriate balance between microstructure and optimum surface properties. Optimal fatigue lives were attained by minimizing the laser cut-edge surface damage, maintaining the formation of wide area striations and by forming a uniform layer of martensitic material close to the cut-edge. These results suggest that laser cutting can be used to enhance the fatigue life to failure of fracture-sensitive steel grades.

Laser cut hole matrices in novel armour plate steel for appliqué battlefield vehicle protection

During this research, experimental rolled homogeneous armour steel was cast, annealed and laser cut to form an applique plate. This Martensitic–Bainitic microstructure steel grade was used to test a novel means of engineering lightweight armour. It was determined that a laser cutting speed of 1200 mm/min produced optimum hole formations with limited distortion. The array of holes acts as a double-edged solution, in that they provide weight saving of 45%, providing a protective advantage and increasing the surface area. Data collected were used to generate laser cut-edge hole projections in order to identify the optimum cutting speed, edge condition, cost and deformation performance. These parameters resulted in the generation of a surface, with less stress raising features. This can result in a distribution of stress across the wider surface. Provided that appropriate process parameters are used to generate laser cut edges, then the hardness properties of the surface can be controlled. This is due to compressive residual stresses produced in the near edge region as a result of metallurgical transformations. This way the traverse cutting speed parameter can be adjusted to alter critical surface characteristics and microstructural properties in close proximity to the cut-edge. A relationship was identified between the width of the laser HAZ and the hardness of the cut edge. It is the thickness of the HAZ that is affected by the laser process parameters which can be manipulated with adjusting the traverse cutting speed.

Finite Element Analysis of Laser Cut Edge Beam Section for High Stress Intensity Structural Assessment

This research has analyzed the stability of laser cut-edges in the location of high stress intensity of a structural beam. The cut-edge characteristic properties formed during laser-cutting processing have been over prolonged periods determined to have beneficial effects on fatigue life. During this study two high strength steel grades S355MC and DP600 have been examined. Optimal fatigue lives were attained by minimizing the laser cut-edge surface damage, maintaining the formation of shallow striations and by controlling the near edge microstructural deformations during the cutting process. This was validated using a bespoke component in which was tested under four-point loading in which there is a area of stress concentration forming a localized plastic zone. The importance of this region is critical due to the fact that it is the area that influences the fatigue life of the structure. Predicting the lives to crack initiation was determined through FE analysis which is based on the use of E–N cut-edge fatigue data.

Optimising laser cut-edge durability for steel structures in high stress applications

The integrity of steel beam components in high intense stress applications have been observed to be influenced by the condition of the cut edge properties. The cut-edge characteristic properties formed during laser-cutting processing have been over prolonged periods determined to have beneficial effects on fatigue life. During this study two high strength steel grades S355MC and DP600 have been examined. This is important in the case of high strength steels, these were shown to display an increased sensitivity to fatigue cracks initiating from cut-edge regions. It was determined that by controlling the interrelationship between power and traverse cutting speed during the laser cutting process can result in optimised fatigue lives being achieved. Optimal fatigue lives were attained by minimising the laser cut-edge surface damage, maintaining the formation of shallow striations and by controlling the near edge microstructural deformations during each cutting process. This was validated using a bespoke automotive component in which was tested under four-point loading.

Laser cutting of triangular geometry into 2024 aluminum alloy: Influence of triangle size on thermal stress field

Laser cutting of a triangular geometry into aluminum 2024 alloy is carried out. Thermal stress field in the cutting section is predicted using the finite element code ABAQUS. Surface temperature predictions are validated through the thermocouple data. Morphological changes in the cut section are examined incorporating optical and electron scanning microscopes. The effects of the size of the triangular geometry on thermal stress field are also examined. It is found that surface temperature predictions agree well with thermocouple data. von Mises stress remains high in the region close to the corners of the triangular geometry, which is more pronounced for the small size triangle. This behavior is associated with the occurrence of the high cooling rates in this region. Laser cut edges are free from large scale sideways burning and large size burr attachments. However, some locally scattered dross attachments are observed at the kerf exit.

Effect of Cut Quality on Hybrid Laser Arc Welding of Thick Section Steels

From an industrial point of view, in a laser cutting-welding production chain, it is of great importance to know the influence of the attainable laser cut quality on the subsequent hybrid laser arc welding process. Many studies have been carried out in the literature to obtain lower surface roughness values on the laser cut edge. However, in practice, the cost and reliability of the cutting process is crucial and it does not always comply with obtaining the highest surface quality. In this study, a number of experiments on 25mm steel plates were carried out to evaluate the influence of cut surface quality on the final quality of the subsequent hybrid laser welded joints. The different cut surfaces were obtained by different industrial cutting methods including laser cutting, abrasive water cutting, plasma cutting, and milling. It was found that the mentioned cutting methods could be used as preparation processes for the subsequent hybrid laser arc welding. However, cut quality could determine the choice of process parameters of the following hybrid laser arc welding.

On the use of Areal Roughness Parameters to Assess Surface Quality in Laser Cutting of Stainless Steel with CO2 and Fiber Sources

Laser cutting provides various advantages such as high flexibility in terms of process parameters and cut material type, as well as the possibility to obtain complex geometry in different dimensions with high precision. From industrial point of view, the two more competitive laser cutting technologies are based on the use of CO2 and active fiber sources, which produce samples visually different, with non-uniform surface and different depth of the striations. The quality assessment between the two laser systems within the industry is commonly based on standard ISO 9013; that covers several aspects of quality, the most used are the surface roughness and edge perpendicularity; however 2D profilometers adopted for measures are not able to analyze the complex 3D surface topography of the cutting edge. As a result, despite the fact that the differences are visually appreciated, measured 2D roughness values of different CO2 and fiber laser cutting conditions are very similar. Recently, a greater diffusion of 3D surface profilometry devices is present. These devices allow areal surface roughness parameters to be defined, which are potentially suitable to better quantify the laser cut quality. This work points out the use of a focus-variation microscopy to acquire 3D surfaces and evaluate analytically the surface quality of laser cut edges using areal surface roughness parameters. In particular, the purpose is to define a simple and repeatable method to identify the type of cutting process analyzed through the reconstruction of surface characteristics and quality of the cut-edge. As a case study, two stainless steel samples with the same geometry obtained with different laser sources, CO2 and active, fiber is presented. For comparison purposes the cutting conditions were fixed to represent the state of the art of respective laser cutting technologies, which actually show distinct cutting edge characteristics.

Effect of laser microcutting on thermo-mechanical properties of NiTiCu shape memory alloy

The machining of shape memory alloys (SMAs), such as NiTi based alloys, is a very interesting and relevant topic for several industrial applications in the biomedical, sensor and actuator fields. Laser technology is one of the most suitable methods for the manufacturing of products in the aforementioned fields, mainly when small and precise features have to be included. Due to the thermal nature of this process, study of its effect on the functional properties of these materials is needed. Except for binary NiTi, few results on the laser machining of NiTi based alloys are available in the literature. In this work, thin sheets of Ni40Ti50Cu10 (at.%) were processed by a fibre laser and the effect of process speed on the material properties was analysed. Scanning electronic microscopy was adopted for observation of the laser cut edges’ morphology. Chemical composition of the processed material was evaluated by energy dispersion spectroscopy and nanohardness measurements were used to estimate the heat affected zone. SMA functional properties were studied on both base and laser machined material. These characteristics are affected by laser machining for the presence of melted material; this effect can be minimised by increasing the laser process speed.

Laser cutting of triangular blanks from thick aluminum foam plate: Thermal stress analysis and morphology

Laser cutting of triangle blank from aluminum foam is carried out. Thermal stress field in the cutting section is predicted using ABAQUS finite element code in line with the experimental conditions. Laser cutting experiments are carried out prior to the model study to determine the optimum cutting parameters for the quality cuts. Temperature predictions are compared with thermocouple data obtained from the experiment. Morphological and metallurgical changes in the cut section are examined using optical and scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction. It is found that von Mises attains high values along the circumference of the cut edges at the onset of cooling cycle initiation. Laser cut edges are free from defects and asperities; however, locally distributed few dross attachments take place at the kerf exit.

Understanding the Effects of Mechanical and Laser Cut-Edges to Prevent Formability Ruptures During Automotive Manufacturing

The cut-edge condition has an important influence on the formability capacity of high-strength steel (HSS) automotive structures. XF350 and DP600 under examination were observed to display a decreased level of formability in the surface regions because mechanical punched edge hole-flanging capacity is dependent on ductility and the surface quality of the cut-edge produced. Formability was observed to be highly dependent not purely based on the properties of the steel but also the cut-edge properties. Hole expansion capacity (HEC)-forming experiments were performed on flat circular plates with mechanical and laser-cut holes to investigate the fracture and forming limits of HSS. The HEC properties of the cut-edges were determined using mechanical and laser-cutting processes using various cutting process parameters in which certain edge types displayed decreases in edge ductility. It was found that, by altering the processing parameters during the cutting process, the edge quality can be improved, and this has a positive effect on the formability capacity of steel components.

Quality aspects in remote laser cutting

The new single-mode fibre lasers have made it possible to work with long working distances and high power densities in new ways. This enables a process called remote laser cutting, which is still quite new a process in the field of laser cutting but is now already proven to be a successful process for cutting various materials and forms. Process parameters of remote laser cutting differ from those of traditional laser cutting because of differences in basic process principles. Process parameters and performance also vary significantly between different materials and equipment. Parameters have to be optimized for each system in order to achieve the best cut quality. This study focuses on defining the possible quality of the remote laser-cut edge and its comparison to that of conventional CO2 laser cutting with equivalent materials. In this study, various metals were cut with the remote laser cutting process. The quality of the cut kerfs was measured by kerf surface roughness and perpendicularity, kerf width, 90° inner corner cut edge sharpness and burr height. When applicable, the comparison was carried out according to the quality standard for thermal cutting.

FemCerv – Single Pass Device for Targeted Endo-Cervical – In-Office Sampling

Demonstrate use of the FemCerv Endocervical Sampler (FemCerv) prototype as a single-pass 360 degree alternative to the multi- pass Kevorkian device. Evaluate adequacy of sample size for pathological evaluation and tissue type specificity. Design Feasitility Study. Extirpated Uterus in Operating Room under institutional IRB approval. Undergoing hysterectomy for benign disease. The FemCerv single use device (Femasys Inc.) is placed transvaginally into the cervical canal utilizing its self-dilating tapered tip is advanced to the placement marker for targeted sampling of the endocervix. The device collection chamber which measures 2.0 cm is opened only within the endo-cervical canal. With the chamber open, it is rotated clockwise 360 degrees and then counter-clockwise to its original position. During the rotation process the laser cut edges gather tissue into the chamber. It is then closed while in the endo-cervix avoiding ecto-cervical sample contamination during device removal. Sample submitted was 1cm in aggregate dimension and upon histopathological evaluation found to contain only endo-cervical tissue. A single pass endo-cervical sampling device that provides an adequate site specific specimen for pathologic evaluation should reduce false positive findings and in turn decrease the number of unnecessary LEEP and Cone-Biospy procedures. With its ease of use and anticipated decreased patient discomfort, health care providers might be less reluctant to sample the endo-cervix and thus with increased use may improve the early detection of high grade lesions. The device's encouraging initial results warrants a more robust extirpated study leading to an in-office evaluation used to assess its applicability in clinical practice.

The effect of laser cutting parameters on the formability of complex phase steel

An experimental advanced high-strength steel grade CP700 was cut using a matrix of laser process parameters in order to generate an understanding of the influence that traverse cutting speed, power and assist gas pressure have on cut-edge formation. The formation of laser cut-edges has been assessed and related to the heat-affected zone microstructure, kerf perpendicularity, surface roughness and waviness properties. It is these characteristics that are significant towards influencing the hole expansion capacity formability properties of laser cut-edges, which were determined to show significant improvements in the formability when using optimum laser cut-edges. Understanding the effect of laser cutting process parameters on the factors influencing striation formation and microstructural deformations was critical towards being able to produce an optimum level of formability.

Efficient Fabrication of Carbon Nanotube Micro Tip Arrays by Tailoring Cross-Stacked Carbon Nanotube Sheets

Carbon nanotube (CNT) micro tip arrays with hairpin structures on patterned silicon wafers were efficiently fabricated by tailoring the cross-stacked CNT sheet with laser. A blade-like structure was formed at the laser-cut edges of the CNT sheet. CNT field emitters, pulled out from the end of the hairpin by an adhesive tape, can provide 150 μA intrinsic emission currents with low beam noise. The nice field emission is ascribed to the Joule-heating-induced desorption of the emitter surface by the hairpin structure, the high temperature annealing effect, and the surface morphology. The CNT emitters with hairpin structures will greatly promote the applications of CNTs in vacuum electronic devices and hold the promises to be used as the hot tips for thermochemical nanolithography. More CNT-based structures and devices can be fabricated on a large scale by this versatile method.

Laser cutting of Kevlar laminates and thermal stress formed at cutting sections

Laser cutting of Kevlar laminates is carried out and thermal stress field developed in the cutting region is predicted using the finite element code. Temperature predictions are validated through the thermocouple data. The morphological changes in the cutting section are examined by incorporating optical and scanning electron microscopes. It is found that temperature predictions agree well with the thermocouple data. High values of von Mises stress are observed at the cutting edges and at the mid-thickness of the Kevlar laminate due to thermal compression formed in this region. The laser cut edges are free from whiskers; however, striation formation and some small sideways burning is observed at the kerf edges.