Laser cutting of sharp edge: Thermal stress analysis

Laser cutting of sharp edge and thermal stress development in the cutting section is examined. The finite element method is used to predict temperature and stress fields while the X-ray diffraction (XRD) technique is used to measure the residual stress around the cut edges. A mild steel sheet with 5 mm thickness is used in the simulations and the experiment. The morphological and metallurgical changes around the edges are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature remains high at the sharp edge when the laser beam is located in this region. This, in turn, lowers the cooling rate and reduces von Mises stress in this region. The magnitude of the residual stress is about 90 MPa at the sharp corner while the maximum von Mises stress is in the order of 280 MPa, which occurs away from sharp corner. In addition, the residual stress predicted agrees with the experimental data.     

Laser cutting of steel and thermal stress development

In laser cutting of sheet metals, thermal stresses are developed in the region of the cutting section. Depending on the cutting conditions and substrate material properties, the thermal stress levels can attain high values. In the present study, thermal stress developed in the region of the laser cut edges is modeled and temperature as well as stress fields are predicted. Temperature predictions are validated through the experimental results. It was found that the temporal variation of the maximum temperature along y-axis follows the laser heating source. However, temporal variation of von-Mises stress deviates slightly from the temporal variation of temperature along the cutting direction. Increase in scanning speed enhances the von-Mises stress levels due to the attainment of high temperature gradients in the substrate material.     

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.     

Laser cutting of thick sheet metals: Residual stress analysis

Laser cutting of tailored blanks from a thick mild steel sheet is considered. Temperature and stress field in the cutting sections are modeled using the finite element method. The residual stress developed in the cutting section is determined using the X-ray diffraction (XRD) technique and is compared with the predictions. The structural and morphological changes in the cut section are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature and von Mises stress increase sharply in the cutting section, particularly in the direction normal to the cutting direction. The residual stress remains high in the region close to the cutting section.     

Cemented carbide cutting tool: Laser processing and thermal stress analysis

Laser treatment of cemented carbide tool surface consisting of W, C, TiC, TaC is examined and thermal stress developed due to temperature gradients in the laser treated region is predicted numerically. Temperature rise in the substrate material is computed numerically using the Fourier heating model. Experiment is carried out to treat the tool surfaces using a CO₂ laser while SEM, XRD and EDS are carried out for morphological and structural characterization of the treated surface. Laser parameters were selected include the laser output power, duty cycle, assisting gas pressure, scanning speed, and nominal focus setting of the focusing lens. It is found that temperature gradient attains significantly high values below the surface particularly for titanium and tantalum carbides, which in turn, results in high thermal stress generation in this region. SEM examination of laser treated surface and its cross section reveals that crack initiation below the surface occurs and crack extends over the depth of the laser treated region.     

Laser cutting of rectangular geometry into aluminum alloy: Effect of cut sizes on thermal stress field

Laser cutting of a rectangular geometry into aluminum alloy 2024 is carried out. Temperature and stress fields are predicted in the cutting section using the ABAQUS finite element code in line with the experimental conditions. Effect of the size of the rectangular geometry on the thermal stress fields is examined in the cutting section. Temperature predictions are validated through the thermocouple data. To identify the morphological changes in the cutting section, an experiment is carried out and the resulting cutting sections are examined under optical and scanning electron microscopes. It is found that temperature and stress fields are affected by the size of the rectangular cut geometry. Temperature and von Mises stress attains higher values for small size rectangular geometry as compared to its counterpart corresponding to the large size geometry. Laser cut sections are free from large size asperities including sideways burning and out-off flatness at the cut edges. Locally scattered some small dross attachments are observed at the kerf exit.     

Laser cutting of rectangular geometry into alumina tiles

Laser cutting of rectangular geometry into the 5 mm thick alumina tiles is carried out. Temperature and stress fields, which are developed during the cutting process, are simulated in line with the experimental conditions. The morphological changes in the cutting sections are examined using optical and electron scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction technique. The predictions of surface temperature and the residual stress are validated through the experimental data. It is found that von Mises stress attains high values in the region of the mid-thickness of the workpiece. The laser cut sections are free from major cracks and large scale sideways burning. The predictions of surface temperature and residual stress agree well with their counterparts obtained from the experiment.     

Laser cutting speeds for ceramic tile: a theoretical–empirical comparison

This paper presents a comparison of theoretically-predicted optimum cutting speeds for decorative ceramic tile with experimentally-derived data. Four well-established theoretical analyses are considered and applied to the laser cutting of ceramic tile, i.e. Rosenthal's moving point heat-source model and the heat balance approaches of Powell, Steen and Chryssolouris. The theoretical results are subsequently compared and contrasted with actual cutting data taken from an existing laser machining database. Empirical models developed by the author are described which have been successfully used to predict cutting speeds for various thicknesses of ceramic tile.     

A study of laser cutting engineering ceramics

A mechanical chopper Q-switched CO₂ pulse laser with high peak power, short pulse duration, high pulse repetition rate and moderate average power is developed. Using this laser, a multi-pass cutting process with high cutting speed is proposed for cutting hard and brittle materials such as engineering ceramics. Crack-free and fine cut is obtained in cutting Si₃N₄ ceramics. Moreover, the formation and elimination of the cracks are qualitatively analyzed in the paper.     

Laser control melting of alumina surfaces and thermal stress analysis

Laser gas assisted melting of alumina surface is carried out and temperature as well as stress fields developed in the irradiated region are predicted using the finite element method (FEM). An experiment is conducted resembling the simulation conditions. Optical and scanning electron microscope (SEM) are used to examine the morphological and the metallurgical changes in the laser treated region. The X-ray diffraction (XRD) technique is used to determine the residual stress developed in the irradiated region. It is found that the residual stress predicted agreed with the measurement result. High heating and cooling rates result in high von Mises stress levels in the surface region.     

Wedge cutting of mild steel by CO2 laser and cut-quality assessment in relation to normal cutting

In some applications, laser cutting of wedge surfaces cannot be avoided in sheet metal processing and the quality of the end product defines the applicability of the laser-cutting process in such situations. In the present study, CO₂ laser cutting of the wedge surfaces as well as normal surfaces (normal to laser beam axis) is considered and the end product quality is assessed using the international standards for thermal cutting. The cut surfaces are examined by the optical microscopy and geometric features of the cut edges such as out of flatness and dross height are measured from the micrographs. A neural network is introduced to classify the striation patterns of the cut surfaces. It is found that the dross height and out of flatness are influenced significantly by the laser output power, particularly for wedge-cutting situation. Moreover, the cut quality improves at certain value of the laser power intensity.     

Laser welding of low carbon steel and thermal stress analysis

Laser welding of mild steel sheets is carried out under nitrogen assisting gas ambient. Temperature and stress fields are computed in the welding region through the finite element method. The residual stress developed in the welding region is measured using the XRD technique and the results are compared with the predictions. Optical microscopy and the SEM are used for the metallurgical examination of the welding sites. It is found that von Mises stress attains high values in the cooling cycle after the solidification of the molten regions. The residual stress predicted agreed well with the XRD results.     

Laser surface treatment of Inconel 718 alloy: Thermal stress analysis

Laser heating of Inconel 718 alloy is considered and the resulting temperature and stress fields are predicted using the finite element method (FEM). An experiment is carried out to treat the alloy surface by a laser beam at high pressure nitrogen environment. The metallurgical and morphological changes in the irradiated region are examined using the Scanning Electron Microscope (SEM), optical microscope, and X-ray Diffraction (XRD). It is found that the surface hardness of the alloy improves after the laser heating process, which is due to the microstructural changes and γ-phase nitride formation in the surface region. The maximum value of the residual stress predicted in the irradiated region is close to the yielding limit of the alloy.     

Laser bending of AISI 304 steel sheets: Thermal stress analysis

Laser induced bending of steel sheet is carried out and thermal stress developed in the heated region is examined. Temperature and stress fields are predicted using the finite element model. The microstructural changes in the melted region are investigated through scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The residual stress developed at the surface vicinity of the laser treated region is measured using the X-ray diffraction technique, which is then compared with its counterpart predicted from the simulations. It is found that the residual stress at the surface vicinity is compressive and the prediction of the residual stress agrees well with that obtained from the X-ray diffraction technique. In addition, surface temperature predictions are in good agreement with the thermocouple data. The laser treated region is free from major cracks and large cavities.     

Laser cutting of polymeric materials: An experimental investigation

The CO₂ laser cutting of three polymeric materials namely polypropylene (PP), polycarbonate (PC) and polymethyl methacrylate (PMMA) is investigated with the aim of evaluating the effect of the main input laser cutting parameters (laser power, cutting speed and compressed air pressure) on laser cutting quality of the different polymers and developing model equations relating input process parameters with the output. The output quality characteristics examined were heat affected zone (HAZ), surface roughness and dimensional accuracy. Twelve sets of tests were carried out for each of the polymer based on the central composite design. Predictive models have been developed by response surface methodology (RSM). First-order response models for HAZ and surface roughness were presented and their adequacy was tested by analysis of variance (ANOVA). It was found that the response is well modeled by a linear function of the input parameters. Response surface contours of HAZ and surface roughness were generated. Mathematical model equations have been presented that estimate HAZ and surface roughness for various input laser cutting parameters. Dimensional accuracies of laser cutting on polymers were examined by dimensional deviation of the actual value from the nominal value. From the analysis, it has been observed that PMMA has less HAZ, followed by PC and PP. For surface roughness, PMMA has better cut edge surface quality than PP and PC. The response models developed can be used for practical purposes by the manufacturing industry. However, all three polymeric materials showed similar diameter errors tendency in spite of different material properties.     

Picosecond laser cutting and drilling of thin flex glass

We investigate the feasibility of cutting and drilling thin flex glass (TFG) substrates using a picosecond laser operating at wavelengths of 1030 nm, 515 nm and 343 nm. 50 μm and 100 μm thick AF32^®Eco Thin Glass (Schott AG) sheets are used. The laser processing parameters such as the wavelength, pulse energy, pulse repetition frequency, scan speed and the number of laser passes which are necessary to perform through a cut or to drill a borehole in the TFG substrate are studied in detail. Our results show that the highest effective cutting speeds (220 mm/s for a 50 μm thick TFG substrate and 74 mm/s for a 100 μm thick TFG substrate) are obtained with the 1030 nm wavelength, whereas the 343 nm wavelength provides the best quality cuts. The 515 nm wavelength, meanwhile, can be used to provide relatively good laser cut quality with heat affected zones (HAZ) of <25 μm for 50 μm TFG and <40 μm for 100 μm TFG with cutting speeds of 100 mm/s and 28.5 mm/s, respectively. The 343 nm and 515 nm wavelengths can also be used for drilling micro-holes (with inlet diameters of ⩽75 µm) in the 100 μm TFG substrate with speeds of up to 2 holes per second (using 343 nm) and 8 holes per second (using 515 nm). Optical microscope and SEM images of the cuts and micro-holes are presented.     

Thermal and efficiency analysis of the CO2 laser cutting process

In CO₂ laser gas-assisted cutting process, modeling of the interaction mechanism is important. Consequently, the present study treats the complete problem of the interaction of the melting surface with the boundary layer and describes the behavior of the melting layer. In the analysis, gas–liquid interface parameters are developed and relationships between the parameters influencing the cutting action are identified theoretically. To achieve this, effects of momentum and gas–liquid interface shear stress, due to the assisting gas jet, are considered. The approximate magnitude of the heat absorbed is estimated and melting layer thickness is predicted. An experiment is carried out and the theoretical predictions are compared with the experimental findings. First and second law efficiencies of the cutting process are predicted, which may, then, be used to improve the process. It is found that the assisting jet velocity increases the first and second law efficiencies of the CO₂ laser cutting process.     

Laser micro-processing of cardiovascular stent with fiber laser cutting system

A metallic cardiovascular stent cutting system based on fiber laser was designed in this study. In order to achieve the cutting of stent, the main modules and the key technologies were analyzed and achieved. Then with the cutting system, the kerf width size was studied for different cutting parameters including laser output power, pulse length, repeat frequency, cutting speed and assisting gas pressure. Finally, a high quality of cutting of 316L stainless steel cardiovascular stent was achieved.     

Structure and properties of the bronze laser alloyed with titanium

The paper describes the microstructure and properties (microhardness and wear resistance) of the bronze laser alloyed with titanium. The laser alloying was done using a pulsed Nd:YAG laser with a generated beam energy of 25-35 J. A very fine microstructure was formed under such rapid solidification conditions like laser treatment. The high chemical homogeneity and fine structure of the melted zone were attributed to high cooling rates due to the short interaction time with Nd:YAG pulsed laser radiation and relatively small volume of the melted material. The structure obtained in the surface layer after laser alloying permits to get a high level of hardness and an improved wear resistance.     

降低热不稳定性的激光二极管泵浦固体激光器

通过谐振腔腔结构理论研究了在端面泵浦固体激光器中,等效热反射镜曲率半径变化时,振荡光半径的变化速率理论和实验都表明,通过调整谐振腔的参量,使得该变化速率接近零,可以有效地抑制热效应导致的激光功率不稳定性。