Experimental study on optimization of CO2 laser welding parameters for polypropylene-clay nanocomposite welds

In this paper, polypropylene-clay nanocomposite sheets of 2 mm thickness with 0 wt%, 3 wt% and 5 wt% nanoclay are butt welded using a CO₂ laser to determine the effect of clay content and laser process parameters on weld tensile strength. For this purpose, Taguchi parametric design and optimization method was used to design experiments and develop a model to predict weld tensile strength as a function of clay content and laser process parameters such as laser power, welding speed and focal position. The adequacy of the model was checked using analysis of variance and by conducting extra confirmation tests. Using Taguchi optimization approach, the optimum levels of parameters were determined. The results indicated that an increase in clay content and welding speed decreased the weld strength, whereas increasing laser power increased weld strength. Furthermore, increase in focal position showed an increasing and then a decreasing effect on weld strength.     

Prediction of depth of cut for single-pass laser micro-milling process using semi-analytical, ANN and GP approaches

The present study is aimed to investigate micro-milling performance of thermoplastics with different parameters, namely laser beam absorptivity, latent heat of vaporization, laser power and cutting speed. The 25-W CO₂ (CW) laser engraving machine is used for the investigation. In total 50 different combinations of laser power and cutting speed with four categories of thermoplastics, namely poly-methyl-methacrylate, poly-propylene, acrylonitrile butadiene styrene and nylon 6, are used in this study. Experimental results suggest that laser beam absorptivity, cutting power and cutting speed are the major influencing parameters on depth of cut. Theoretical model for the prediction of depth of cut in terms of material properties, cutting power and cutting speed has been proposed. Two correction parameters have been introduced in this analysis using non-linear regression method to improve the theoretical model. Comparison has been made between prediction capabilities of theoretical model, model based on multi-gene genetic programming and artificial neural network. The comparison clearly indicates that all the three models provide accurate prediction of depth of cut. The details of experimentation, model development, testing and the performance comparison are presented in this paper.     

Parametric studies on the CO2 laser cutting of Kevlar-49 composite

In the present study, the cutting performance of a CO₂ laser on Kevlar-49 composite materials has been studied. The Taguchi technique is employed to identify the effect of laser control parameters, i.e., laser power, cutting speed, material thickness, assistance gas pressure, and laser mode, on the quality of cut parameters, namely, kerf width, dross height, and slope of the cut. From the analysis of variance (ANOVA) and signal-to-noise (S/N) ratio response tables, the significant parameters and the optimal combination levels of cutting parameters are determined. The obtained results are interpreted and modeled to closely understand the behavior and quality of CO₂ laser cutting. Kevlar-49 composites are found to be cut satisfactorily by the CO₂ laser at the optimum process parameter ranges. The results showed that laser power is the most significant parameter affecting the quality of cut parameters. The optimal combination of cutting parameters minimized the kerf width, dross height, and slope of cut to 0.103 mm, 0.101 mm, and 2.06°, respectively. The error between experimental results with optimum settings and the predicted values for the kerf width, dross height, and slope of cut lie within 2.9%, 7.92%, and 6.3%, respectively.     

Experimental investigation on CO2 laser-assisted micro-slot milling characteristics of borosilicate glass

Demands for micro-machining on glass have been increasing in various industries due to the unique properties of glass, such as transparency or biocompatibility. However, micro-channel fabrication on glass with high precision has been challenging due to its brittle characteristics. This research presents the CO₂ laser-assisted micro-milling process and investigates the machining characteristics experimentally. Micro-channels without cracks were fabricated using micro-end mill and CO₂ laser irradiation as an assisting heat source. Compared to the process without laser heating in the same matching conditions, the average surface roughness was reduced by 96%, and cutting force was reduced by 28% and 66% for the feed and thrust direction, respectively. Continuous and sheared chips were observed with laser heating, indicating the process is in ductile-regime machining. Through the investigation of machining parameters, it was found that micro-channels with low average surface roughness can be achieved at the proper laser power when the workpiece is heated up to the strain point at tool position, at low feed rate, and at high axial depth of cut, as long as the tool withstands the cutting forces. Consequently, it can be concluded that it is possible to increase the material removal rate in micro-milling of borosilicate glass with high quality by using the CO₂ laser, which was found to be an effective and suitable heating method.     

A comparative study on the processing parameters during fibre and CO2 laser surface treatments of silicon nitride engineering ceramic

This paper demonstrates a comparative study of a relatively novel fibre laser and a conventional CO₂ laser to surface-process silicon nitride (Si₃N₄) engineering ceramic. The objective of the research is to investigate the threshold of the novel fibre laser and compare it to the conventionally used CO₂ laser to process Si₃N₄ engineering ceramic and to produce a laser surface treatment free from major surface cracking without using any of the pre- or post heating techniques as this would increase the cost of the process and add more expense to the product when considering a bigger view point. The results showed that the fibre laser surface processing of the Si₃N₄ engineering ceramic differed to that of the CO₂ laser as the Gaussian beam modes, the beam quality factors, wavelength and the beam delivery systems were different between the two lasers. This consequently had a different effect on the surface of the Si₃N₄ engineering ceramic. The CO₂ laser wavelength when surface treating the Si₃N₄ engineering ceramic was being absorbed more than that of the fibre laser as higher power density and same traverse speed was used to reach the threshold for the Si₃N₄ engineering ceramic.     

Gap-free lap welding of zinc-coated steel using pulsed CO2 laser

CO₂ laser welding of zinc-coated steel sheets in the lap configuration has been a major research effort for the automotive industry for many years. The introduction of a gap between the sheets is one way of solving the zinc gas explosion problem. However, this requires sophisticated clamping devices and spacer materials. A homogeneous gap is therefore difficult to realise in high volume production. This paper describes a simple but useful approach for CO₂ laser welding of zinc-coated steel sheets in the lap configuration. By using a gated pulse mode, a seam welding process is developed that allows zinc-coated materials to be welded in a gap-free, overlap configuration. Laser seam welds in the lap configuration were produced in 0.7 mm-thick steel sheet with 7 μm zinc coating on both sides. A number of pulsed CO₂ laser welding parameters, including peak power, duty cycle, travel speed, pulse repetition rate, and pulse energy, were identified. Furthermore, the effects of pulsed CO₂ laser welding parameters on weldability were also investigated. The study shows that through the proper selection of welding parameters, it is possible to produce visually sound welds where porosity is still unavoidably formed. It was observed that decreasing the welding speed could reduce the porosity within the visually sound welds.     

千瓦级轴流CO2激光器设计参数的研究

本文通过较新的快速轴流CO₂激光器理论及理论模型,讨论了各主要物理参数对出光特性的影响,并提出了较佳的设计参数。     

尼龙6/硅灰石混合粉末选区激光烧结成型精度研究

收缩是尼龙材料选区激光烧结成型的常见问题,不均匀的收缩将导致翘曲变形。影响成型精度的因素很多,包括材料本身的特性,烧结工艺参数等。本文通过添加硅灰石来提高尼龙材料的成型精度,用翘曲高度法分析了制件翘曲高度随硅灰石用量和烧结工艺参数,如激光功率、预热温度变化的规律。     

Crack separation mechanism in CO2 laser machining of thick polycrystalline cubic boron nitride tool blanks

An improved method for cutting thick polycrystalline cubic boron nitride (PCBN) tool blanks is explored because current methods of pulsed Nd:YAG laser cutting and wire electrical discharge machining (EDM) are constrained by low speed and low precision. We present a CO₂ laser/waterjet (LWJ) process to cut 4.8-mm-thick PCBN tool inserts by a crack separation mechanism. In LWJ, the PCBN blank is locally heated using a high-power continuous wave CO₂ laser to cause phase transition from cubic to hexagonal followed by water quenching to generate thermal stresses and form boron oxide leading to increased brittleness, subsequent cracking, and material separation. A 2³ fractional design of experiment (DOE) approach was employed to determine the factors of laser power, cutting speed, and waterjet pressure on the responses of phase transformation depth, taper, and surface roughness. A numerical heat flow model, based on Green’s function, was used to calculate the temperature distributions along the depth. Surface profilometer, scanning electron microscopy, and Raman spectroscopy were utilized to analyze the phase transformation and crack zones. Results from LWJ compared with pulsed Nd:YAG laser and laser microjet? methods indicate LWJ cuts 30 times faster; this was attributed to a nonconventional material removal (crack separation) mechanism. When LWJ was compared against nitrogen-assisted CO₂ laser cutting, improved cut quality (less taper and smaller heat-affected zone) was observed due to a greater control on phase transformation and crack propagation. DOE analysis revealed laser power and waterjet pressure, and the interactions among them are more significant factors than others.     

Development and research of a laser photo-acoustic SF<Subscript>6</Subscript> gas analyzer

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.     

Theoretical and experimental investigation of pulsed laser grooving process

A theoretical model has been developed for simulating the laser grooving process. It takes into account the interaction among subsequent pulses, the required time for the melting temperature to be reached and the subsequent removal of a finite volume of material during each laser pulse. The model predicts the maximum groove depth that can be achieved for a specified set of process parameters, such as laser power, pulsing frequency, and scanning velocity. The theoretical predictions have been experimentally tested with a medium-power laser beam.     

Effect of external constraint on the characteristics and behavior of the plasma plume during high-power CO2 laser welding

Laser-induced plasma has been one of the hotspots of high-power CO₂ laser welding for many years. A novel method was proposed to suppress the plasma plume through external constraints, which resulted in more stable welding process and slightly increased penetration depth. Based on high-speed camera and image processing technology, it was demonstrated that the expansion of plasma plume both in height and width was suppressed by a pair of water-cooled copper blocks laid near laser incident point along the direction of seam. Besides its intensity and size, the dynamical behavior of plasma plume under spatial constraint was observed and analyzed by the characteristic parameters. The constraint mechanism and influence of the spacing between the two copper blocks was discussed. Results showed that external constraint was effective to suppress plasma plume, stabilize welding process, and to increase weld penetration for high-power CO₂ laser welding.     

Tribological properties of plasma sprayed and laser remelted 75/25 Cr3C2/NiCr coatings

A CO₂ laser was used to fuse based Ni–Cr Cr₃C₂ coatings for the purpose of homogenizing their microstructures and eliminating their porosity. Tests of layer control and wear resistance were carried out on the samples treated with the laser. The results have shown that laser remelting improves the microstructure of the coatings, increases the coating microhardness, and improves coating–substrate adherence. The dry sliding wear behaviour was characterized by the existence of two periods. During the first period the square of the wear volume is proportional to the sliding distance. During the second, the wear volume is proportional to the sliding distance.     

CO2 Laser Processing On Ceramic Substrates Of Light Emitting Diode Assisted By Compressed Gas

The use of ceramic substrates in high power LEDs is becoming increasingly common. However, the brittleness of ceramics makes them difficult to process and susceptible to cracking. This study used a CO₂ laser with auxiliary gas to drill and cut Al₂O₃ and AlN ceramic substrates. The authors investigated the influences of parameters such as auxiliary gas pressure, laser power, repetition rate, and working speed on processing quality, in terms of pattern size, surface roughness, hole taper angle, and fracturing. The experiment results show that Al₂O₃ low-cost processing can be achieved with low laser power and high auxiliary gas pressure. In contrast, AlN has a high melting point and high thermal conductivity, for which lower auxiliary gas pressure is required to ensure high-quality processing.     

The effects of low-frequency workpiece vibration on low-power CO2 laser cutting of PMMA: an experimental investigation

The effect of workpiece vibration on low-power CO₂ laser cutting of polymethyl methacrylate (PMMA) has been investigated. 6-mm-thick PMMA sheets have been cut using a 70-W continuous wave CO₂ laser moving at speeds in the range of 0.1–2.0?m/min. The workpiece was vibrated in a direction parallel to the laser cut at frequencies of 0, 12, 18 and 24?Hz. The use of workpiece vibration was shown to enhance the cutting process. At 12?Hz, the cutting speed was increased to 0.4?m/min compared to 0.2?m/min for the 0-Hz sample. However, the extent of the HAZ increased when workpiece vibration was used.     

Effects of single-pass laser heat treatment on erosion behavior of cast irons

A single-pass laser heat treatment was performed on the surfaces of pearlitic gray and ductile cast irons using a 5 kW continuous wave CO₂ gas laser. Surface-hardened layers affect solid particle impingement erosion in that, for given abrasive flow conditions, the erosion rate of laser-treated gray iron was five times greater than that of untreated gray iron while the erosion rate of laser-treated ductile iron was 25 times greater than that of untreated ductile iron. The erosion mechanisms of gray iron included micromachining and ploughing in the untreated condition and intergranular cracking in the laser-treated condition. In contrast, ductile iron was eroded by severe plastic deformation and tearing in the untreated condition and by the fatigue mechanism in the laser-treated condition.     

In-process monitoring of the cutting front of CO2 laser cutting with off-axis optical fibre

A new method is presented in this study to test a way that can effectively provide detailed information on the surface morphology during CO₂ laser cutting by directly measuring the emitted light from the cutting front. The system consists of a copper tube, glass fibre, polymer fibre and photodiode sensor. In this study, the laser power was modulated from 50 Hz to 300 Hz to disturb the natural burning cycle during gas assisted CO₂ laser cutting. The optical fibre was set at 75° to the cutting direction. The wave frequency of the detected signal was very close to the striation frequency of the cut surface, which shows that the sensing system designed and developed in this research can effectively in-process monitor the CO₂ laser cutting process.     

Influences of laser welding parameters on the geometric profile of NI-base superalloy Rene 80 weld-bead

In the present study, autogenous laser butt joint welding parameters of Ni-base super alloy Rene 80 has been investigated by using a continuous wave 2.2?kW CO₂ laser. The experiments were performed based on the response surface methodology as a statistical design of experiment approach in order to investigate the effect of parameters on the response variations, achieving the mathematical equations and predicting the new results. Laser power (1,000?C2,200?W), welding speed (120?C360?cm/min), laser beam focal point position (?0.5?C0.5?mm) and inert gas pressure (0.2?C1?bar) were considered as the input process variables while welding surface width (W1), welding pool area (A), width of the weld-bead at the middle depth (W2), undercut welding and drop of welding were considered as the five process responses. Analyzed by statistical techniques, the results show that the welding bead profile is influenced by the laser heat input and input laser process parameters. Welding speed is known as the most important parameter with the reverse effect on process outputs. Inert gas pressure is the next significant parameter, and higher gas pressure causes welding geometry defects. Laser power has a direct influence on all investigated responses.     

Drilling of micro-holes on copper using electrochemical micromachining

Electrochemical micromachining (EMM) is one of the best micromachining techniques for machining electrically conducting, tough, and difficult-to-machine materials with suitable machining parameter combinations. For the micro-fabrication of components like nozzle plate for ink jet printer head and delicate 3D electronic circuit board components, EMM is predominantly used. In this paper, the effect of process parameters such as such as electrolyte concentration, machining voltage, frequency, and duty cycle on the material removal rate (MRR) and overcut were studied using copper workpiece. According to Taguchi’s quality design concepts, an L₁₈ orthogonal array is used. ANOVA is also performed to determine the most significant parameter that influences the EMM process. The optimum process parameters for lower overcut and higher MRR are found out and confirmation tests were carried out to validate the prediction. The confirmation test results show 19 and 20.78?% improvements of overcut and MRR, respectively, with respect to the initial parametric setting.     

尼龙6/铜复合粉末选区激光烧结制件翘曲研究

通过大量的对尼龙6/铜复合尼龙粉末烧结试验,研究不同工艺参数,如激光功率、铺粉厚度以及扫描速度对制件翘曲程度的影响,并采用翘曲高度法来表征翘曲程度。根据试验数据绘出了尼龙制件翘曲程度随各工艺参数的变化曲线,总结出了制件翘曲程度随各工艺参数变化的趋势。