Kerf Edge Research Articles

Artificial intelligence based experimental investigation of underwater fiber laser transmission process during micro-channelling operation on PMMA

Industries that engage in laser-based material processing are increasingly turning to fiber lasers as one of the most effective laser systems available. Using a pulsed fiber laser system, an experimental investigation of underwater laser micro-channelling on hard to machine thick PMMA has been conducted in this research work. Submerged laser transmission cutting which is also known as underwater laser induced backside machining helps to generate clean kerf edge without presence of mushy region, which is very common during laser machining of thick PMMA with wavelength of near infrared region. Submerged conditions are used here for laser transmission micromachining in order to reduce adverse thermal effects and microcracking or charring inside the material. Pulse frequency, working power, and cutting speed have been selected as the input parameters. As machining responses, the depth of the micro-channel, the width of the kerf, and the width of the heat affected zone (HAZ) have been considered. To find the ideal parametric condition for simultaneously achieving numerous goals, Response Surface Methodology (RSM) and AI-based Teaching Learning-Based Optimisation (TLBO) have been used. The TLBO technique determined that the optimal laser machining settings are a power setting of 13.98 %, a pulse frequency of 50 kHz, and a cutting speed of 0.20 mm/sec. These parameters result in a minimum HAZ width of 4.1874 µm, a minimum kerf width of 22.3698 µm, and a maximum depth of cut of 37.1478 µm. Underwater laser processing reduces heat affected zone and redeposition surrounding micro-channels, creating a cleaner, finer structure.

Experimental evaluation of cut quality and temperature field in fiber laser cutting of AZ31B magnesium alloy using response surface methodology

Fiber laser cutting of AZ31B magnesium alloy was studied to assess the effect of laser cutting process parameters on the resultant cutting temperature near the cut kerf and the resultant cut quality. To systematically analyze the effect of parameters on the temperature variation and cutting edge surface roughness during the cutting process of the AZ31B magnesium alloy, the Response Surface Methodology (RSM) was utilized to fit a quadratic polynomial model through the experiments. The influence of three main factors including speed of cutting, power of laser and nozzle distance on the major responses of temperature near the cut kerf, average surface roughness of the cutting edge and the cut kerf quality was then evaluated.Changes in the cutting speed had no serious impact on the quality of the cut kerf.Laser power levels from 800 to 1000 W were suitable for laser cutting of magnesium alloy sheets. The results showed thatvariations in the nozzle distance and laser emitted power had a remarkable effect on the temperature variation around the cut kerf width. Changing the nozzle distance and thereby creating different laser beam diameter had a more significant influence on the temperature variation rate (about 15 %), in comparison to the laser power. The nozzle distance had a huge effect on the cutting edge surface roughness due to the significant variation of laser beam energy density and beam diameter and hence, the cut kerf dimensional changes.The optimal cutting condition was obtained at the minimum roughness according to the investigated parameters levels, which included the cutting speed of 6 m/min, the power level of 1000 W and the nozzle distance of 0.8 mm. The SEM images from the top surface of the cut kerf implied the existence of oxidation in the magnesium alloy kerf edges.

High speed pulsed laser cutting of anode material for a Li-ion battery in burst mode

The bursts of picosecond laser pulses have nanosecond-level short interval delay. These bursts contain a variable number of sub-pulses, which are used for laser cutting of copper current collector and graphite anode material for Li-ion battery anode. The influences of 2–10 sub-pulses on kerf edges were studied and were compared with that of a single pulse. The shapes of anode edge cut under different conditions, obtained using scanning electron microscopy (SEM), revealed that using burst mode would yield a smaller heat-affected zone (HAZ) of the copper current collector and smaller delamination width of graphite anode material. The capability of laser cutting of anode was characterized with maximum single-time cutting speed. Results showed that the cutting efficiency was raised evidently with the increase in the number of pulses in a burst, and the maximum cutting speeds for the copper current collector and graphite anode material could reach 3,800 mm/s and 500 mm/s respectively.

Micromorphology of metallic surfaces for hydrophobicity by waterjet-guided laser processing

Waterjet-guided laser processing is a novel machining technique for metallic materials. To investigate and analyse the effects of processing parameters on surface topography change, micro-texturing evolution, and hydrophobicity, micromorphology machining experiments were conducted on stainless steel using self-developed waterjet-guided laser processing equipment. Nd:DPSS laser system with repetition frequency of 20–120 kHz and maximum power of 50W is used in the equipment. A scanning electron microscope (SEM) is used to measure surface topography. Energy-dispersive spectrometer (EDS) is used to evaluate the material composition of processing zone and no processing zone. The effects of grid spacing and laser power coupled into the jet are examined and processing conditions for hydrophobicity are provided. There was oxidation and no crack on the kerf edge. The surface contact angle dramatically increases from 92.94 to 138.41° with the decreasing of the grid size. It has been shown that waterjet-guided laser processing yields textures with a hydrophobic surface and is suit for micro-texture micro-machining.

Experimental study on water jet guided laser micro-machining of mono-crystalline silicon

Water jet guided laser micro-machining is a novel micro-machining technique for hard brittle materials. To investigate and evaluate the effects of water jet guided laser micro-machining on the surface topography changes, highest aspect ratio evolution, and kerf edge variations, water jet guided laser micro-machining experiment was undertaken using Nd: DPSS laser system with the repetition frequency of 20–120 kHz and max. power of 25 W. Surface topography measurements of the untreated and treated specimens were carried out with scanning electron microscope (SEM). The material composition of kerf edge and other area was achieved using energy dispersive spectrometer (EDS). The relationship between water jet guided laser micro-machining parameters, surface topography changes, highest aspect ratio evolution, and kerf edge variations are presented and discussed. The experimental results show that there was no oxidation and cracks on the kerf edge and other surface, aspect ratio of kerf is up to 12.7, so the kerf is very steep, local edge breakage is rarely founded at 350x magnification, cutting speed can up to 1 mm/s. The results showed that performance of the water jet guided laser micro-machining technology is excellent for mono-crystalline silicon cutting.

Femtosecond laser single step, full depth cutting of thick silicon sheets with low surface roughness

Separation of silicon wafers is an integral part of semiconductor device manufacture. The widely used mechanical separation methods produce large kerf widths and micro-cracks. Existing laser separation, singulation and dicing methods can reduce cutting kerf widths, but usually involve multiple steps. Although single step laser through cutting by ablation has been reported before, surface roughness is usually poor. This paper presents a method for single step, full-depth cutting of silicon wafer sheets of 200 µm in thickness with an 800 nm wavelength femtosecond-pulse laser focused using a microscope objective lens under ambient condition. By introducing parallel scan lines, through cut is realized with an excellent sidewall full area roughness of 191 nm Ra, which is much better than that of reported previously in laser through-cutting of thick silicon sheets of similar thickness. It is found that by increasing the number of overscan, pulse energy, or number of parallel scan lines, the sidewall surface roughness reduces and the kerf edge straightness at the bottom surface is improved. The effects of p- and s-polarization on cutting quality are compared. Sidewall quality can be improved by appropriate selection of beam polarization and cutting speed. The mechanisms involved are discussed.

An improved real-time temperature control for pulsed laser cutting of non-oriented electrical steel

An improved method based on fuzzy gain scheduling (FGS) control is developed in this study to tune the PID parameters and precisely control the working temperature in situ during laser cutting of non-oriented electrical steel sheets. Experiments on laser cutting of thin electrical steel sheets are performed to compare the cutting quality of kerf features using an open loop controller with a constant power, a conventional PID controller, and the proposed FGS controller. An unstable and inconsistent cutting quality of kerf with a larger heat affected zone (HAZ) and dross attachment is observed under open loop control due to a significant variation of working temperature and kerf width along the cutting path. The FGS controller shows better cutting performance and tracking response than the conventional PID controller by reducing the settling time as well as enhancing the control stability in the steady period. A better quality of finer and uniform kerf width with parallel kerf edges of a smaller HAZ and dross attachment are thus produced by the improved FGS control through real-time tuning of control parameters. Finally, the average kerf width is well correlated with the set-point temperature in FGS control by a linear equation.

Analysis of kerf quality on ultrafast laser cutting of anode material for lithium-ion battery

The service performance of lithium-ion battery is greatly affected by the cutting quality of sandwich structure electrode materials. Based on the ultrafast laser cutting experimental system, the ultrafast laser cutting processing parameters of anode material were studied, the processing ability of ultrafast laser on anode material was preliminary showed by the maximum single-scan velocity. The depth, heat affected zone (HAZ) and delamination width of anode kerf were characterized by 3D digital microscope and scanning electron microscope (SEM). It is revealed that kerf depth is a piecewise function of laser power and the ultrafast laser cutting process of anode is dominated by the copper foil. Raman analysis of anode active material shows that the ordered graphite structure is partially damaged in the color-changed zone near kerf edge, providing insight into characterization of HAZ. Kerf characteristics indicate that HAZ and delamination were resulted from heat accumulation, while analysis of anode plasma spectra shows potential impacts of plasma thermal radiation on the defects of anode. When anode material was completely penetrated with single-scan laser exposure, the HAZ size and delamination width of anode material increase with laser power and pulse width. Delamination of anode was completely eliminated by multi-scan ultrafast laser cutting at low laser power and high scanning speed.

Laser machining of different diameter holes in alumina ceramic: Thermal stress analysis

ABSTRACTLaser machining of different diameter holes into alumina tiles is carried out. Temperature and stress fields are predicted by using the finite element code. Surface temperature and residual stress predictions are validated through the thermocouple data and X-ray diffraction measurements. Morphological changes in the cutting section are examined by incorporating optical and scanning electron microscopes. It is found that the predictions of surface temperature and the residual stress formed at the cut section agree well with the experimental findings. In general, cut sections are free from large asperities; however, local dross attachments at the kerf edge and crack network formation at the kerf surface are observed.

Laser cutting of 2024 aluminium alloy and cutting quality assessment

Laser gas-assisted cutting of aluminium alloy is carried out and nitrogen at high pressure is used in the cutting section to prevent oxidation reactions during the cutting process. Morphological changes in the cutting section are examined using optical and scanning electron microscopes and kerf width size is examined at the front and back surfaces of the cutting section using the moving microscope. The lamp parameter analysis is introduced to determine the kerf width size for different laser cutting speeds, and the predictions are compared with the experimental data. It is found that predictions of the kerf width size agree well with the experimental data. The laser cutting section is free from large size asperities, such as large size cracks. Some small dross attachments are observed at the back surface of the cutting section. The dross attachments are local and do not extend along the kerf edges.

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 hole cutting into Ti-6Al-4V alloy and thermal stress analysis

Laser hole cutting into Ti-6Al-4V alloy is carried out. Temperature and stress fields during the cutting process are predicted using the finite element code. Temporal variation of surface temperature in the region close to the kerf edge is monitored by a thermocouple and compared with the predictions. The residual stress formed in the cutting region is obtained from the XRD technique and compared with the predictions. The morphological changes around the kerf surfaces are examined incorporating optical and scanning electron microscopes. It is found that von Mises stress attains slightly higher values at the top circumference as compared to that corresponding to the bottom circumference of the hole cut. The prediction of temperature variation agrees well with the thermocouple data. The residual stress predicted also agrees with the results of the XRD technique.

Experimental Investigation on Fiber Laser Cutting of Ti6Al4V Thin Sheet

The high strength to weight ratio and good corrosion resistance of titanium alloys, have led to an increasing use of these materials, particularly in the aerospace industry. The laser cutting technique may be a promising tool in machining titanium alloy parts like those with subsequent welding requirement: in this case, surface quality of the kerf edges is of great importance. The low thermal conductivity and the high chemical activity of titanium alloys lead, in fact, to alterations of the surface properties of the machined zone. This paper presents the results of titanium alloy laser cutting using a 2 kW fiber laser. The cutting process was performed in continuous wave mode and using Argon as shear gas. Laser cuts were realized on titanium alloy Ti6Al4V sheets 1mm thick. Image analysis and microscopy, were carried out to examine the cutting edge quality features including thickness of the recast layer and heat-affected zone.

An Experimental Study on the Kerf Characteristics of Silicon Cut with Micro Abrasive Air Jet

Micro abrasive air jet (MAAJ) cutting technology is being increasingly used in the precision machining of hard and brittle materials, due to its distinct advantages of negligible heat effect zone and small cutting force. In this paper, an experimental study on the kerf characteristics, especially for the effect of cutting parameters on the top edge definition, is presented. It shows that the top kerf edge is straight but not sharp. The top edge definition of the kerf improves with a decrease in the air pressure, while the effect of abrasive flow rate and nozzle traverse speed are hardly discernible. The optimum jet incidence angle for highest top edge definition of the kerf is 60°. The results of this paper may be useful for the cutting parameters optimization in the precision three-dimensional micro-structural machining.

Experimental study of an oxygen plasma cutting torch: II. Arc–material interaction, energy transfer and anode attachment

A study of arc–material interaction and energy transfer in the case of plasma cutting is presented. A fast CCD camera moving with the torch is used to estimate the anodic arc root location inside the kerf. Temperature measurements on the cut-front surface and on the kerf edges are performed by infrared pyrometry. Temperature fields inside the workpiece obtained with inserted thermocouples are compared with the theoretical results of an analytical model to estimate heat conduction losses QHCL (W) dissipated in the plate. For various sets of operating parameters (voltage, inlet oxygen pressure and cutting speed), a complete energy balance of the process is performed with the calculation of the device efficiency on the basis of the various power terms implicated in the cutting tool: the power lost above the workpiece, heat conduction losses, the power involved in melting steel, the energy released by chemical oxidation reactions, the power available for cutting and losses under the plate in the extinguishing plasma.

CO 2 laser cutting of a carbon/carbon multi-lamelled plain-weave structure

Laser cutting of composite structure consisting of 64 layers of plain-weave carbon/carbon fibers with 0° orientation is carried out. The influence of laser power on the kerf size is examined experimentally as well as analytically. The scale law analysis is introduced to predict the kerf width. The striation formation on the kerf edges is examined using a scanning electron microscopy (SEM). It is found that kerf width size increases with increasing laser power intensity. The orientation of the carbon fiber axis relative to the axis of workpiece movement during cutting has significant effect on the kerf size. Use of nitrogen as assisting gas suppresses the oxidation reactions taking place in the cutting section. This, in turn, minimizes the side ways burning and edge irregularities in the cutting section.

Cutting performance of a chemical oxygen-iodine laser on aerospace and industrial materials

A chemical oxygen-iodine laser (COIL) was used for cutting aluminum, titanium, inconel and copper plates. The laser was operated with a stable resonator having an intracavity aperture to produce a circular COIL beam with very few transverse modes. The multimode focal spot diameter was calculated and measured to be approximately 0.24 mm. The new aluminum cut was of good kerf edge quality. These COIL cutting data are compared with an existing theoretical laser cutting model. Using thermophysical data for aluminum, titanium, inconel and copper, this theory agrees very well with the data. To test the versatility of the model, the effects of different assumptions are examined; different assumptions produced very little effect on model predictions at high cutting speeds and a small difference at very slow cutting speeds. Overall, the theoretical model provides good agreement with experiments for a wide variety of metals.

SEM Studies on Laser Trimmed Resistors

This paper reports the studies conducted using scanning electron microscope (SEM) as a tool for optimizing laser trim parameters leading to reliable trimming. The samples drawn from the regular production lots use DUPONT 1400 BIROX series resistor pastes with compatible conductor and dielectric compositions printed on Alsimag 614 substrates. Samples of the typical size of 5 mm × 5 mm prepared by laser cutting were observed in the secondary electron mode of SEM. Teradyne model W311 Q-switched YAG laser was used in trimming the resistors. A substrate surface removal of 3–5 microns which is necessary for the good quality' cut was confirmed in the cross-sectionally observed samples. Also uniform and well fused kerf edges which are another important aspect of reliable trimming were checked. This dielectric protection of kerf edges ensures the non-exposure of disturbed resistor material. Microcracks were found to be present at the end of the cuts but they seemed to have insignificant effect on the thermal stability of the trimmed resistors; the storage at 150°C for 1000 hrs. has brought about the drift (ΔR/R × 100) of less than 0.2% in case of L cut and less than 0.35% in case of double plunge cut. Further efforts are being made to find out the depth of these microcracks using energy dispersive scan.