Surface roughness analysis and improvement of PMMA-based microfluidic chip chambers by CO2 laser cutting

For the microfluidic chip, the surface roughness of the chamber sidewall is an important parameter in estimating its quality. In this work, the chambers of the polymethyl methacrylate (PMMA)-based microfluidic chip were fabricated by CO₂ laser cutting, and then the surface roughness of the sections cut using different laser parameters and ambient temperature was studied by a non-contact 3D surface profiler. Our observation shows that the surface roughness results primarily from the residues on the laser-cut edge, which are produced by the bubbles bursting. To reduce the surface roughness of the cut section, a new approach is proposed, that is preheating the PMMA sheet to a suitable ambient temperature during laser processing. The results indicate that at a preheat temperature of 70-90 °C, the surface roughness resulting from the cut would be reduced. In our experiment, the best result was that the arithmetical mean roughness is R_a = 100.86 nm when the PMMA sheet was heated to 85 °C.     

Nanosurface Mechanical Properties of Polymers Based on Continuous Stiffness Indentation

A systematic experimental study of the large strain surface mechanical properties of a number of polymers {polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polystyrene (PS), polycarbonate (PC), polypropylene (PP), and ultra-high molecular weight polyethylene (UHMWPE)} at the nanometer scale is described. The polymeric surfaces were indented and the data were analyzed using a contact compliance method in conjunction with a nano-indenter system. The indentation experiments were performed using a Berkovich Tip indenter with a continuous contact compliance indentation mode. The indentations were performed using a constant loading rate (300 μN/sec) to a maximum penetration depth of 5 μm. The experimental results showed a considerable strain-rate hardening effect for the polymers and a peculiarly harder response of these surfaces at the near-to-surface (submicron) layers. PMMA was the hardest polymer of the selection, whereas UHMWPE and PP were observed to be the softest polymers. The paper includes practical consideration of a creeping effect and appropriateness of tip calibration using harder surfaces for nanoindentation experimentation of polymers.     

An investigation of pulsed laser cutting of titanium alloy sheet

Subsequent welding requirement calls for high-quality laser cut surfaces in the laser cutting of bladed ring parts for aeroengines. This paper presents pulsed laser cutting of titanium alloy sheet and investigates the influences of laser cutting parameters on laser cut quality factors including heat-affected zone (HAZ), surface morphology and corrosion resistance. The thickness of HAZ lasers is studied in detail as a function of laser cutting parameters. For different assist gases the surface morphology and corrosion resistance show great differences. In comparison with air- and nitrogen-assisted laser cutting, argon-assisted laser cutting comes with unaffected surface quality and is suitable for laser cutting with subsequent welding requirement.     

Use of the grey relational analysis to determine optimum laser cutting parameters with multi-performance characteristics

This paper presents an effective approach for the optimization of laser cutting process of St-37 steel with multiple performance characteristics based on the grey relational analysis. Sixteen experimental runs based on the Taguchi method of orthogonal arrays were performed to determine the best factor level condition. The response table and response graph for each level of the machining parameters were obtained from the grey relational grade. In this study, the laser cutting parameters such as laser power and cutting speed are optimized with consideration of multiple-performance characteristics, such as workpiece surface roughness, top kerf width and width of heat affected zone (HAZ). By analyzing the grey relational grade, it is observed that the laser power has more effect on responses rather than cutting speed. It is clearly shown that the above performance characteristics in laser cutting process can be improved effectively through this approach.     

Multi-objective optimization of laser cutting for flash memory modules with special shapes using grey relational analysis

This paper presents a novel effective method for optimizing laser cutting of specially shaped electronic printed circuit board (PCB) carrier substrates of advanced integrated circuit (IC) back-end packages that have multiple performance characteristics identified using grey relational analysis (GRA). Laser cutting parameters, including laser beam parameters (average laser power and Q-switch frequency), focusing parameters (laser beam focusing spot size), and machine parameters (laser cutting speed), were optimized based on multiple performance characteristics. Some characteristics of the specially shaped flash memory module for IC packages, such as smart disk (SD) cards are verified. The characteristics of interest are the average surface roughness on a PCB substrate cross-section, and the maximum width of the heat-affected zone (HAZ). Eight experiments were conducted using GRA to optimize the settings for laser beam cutting parameters to generate various quality characteristics. Analysis of the grey relational grade indicates that parameter significance and the optimal parameter combination for the laser cutting process are identified. The analytical results from two confirmation experiments using the optimal parameters confirm that laser cutting technology can be effectively applied to cut substrates into special shapes.     

Modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile

Thin sheets of aluminium alloys are widely used in aerospace and automotive industries for specific applications. Nd:YAG laser beam cutting is one of the most promising sheetmetal cutting process for cutting sheets for any profile. Al-alloy sheets are difficult to cut by laser beam because of its highly reflective nature. This paper presents modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile. In the present study, four input process parameters such as oxygen pressure, pulse width, pulse frequency, and cutting speed and two output parameters such as average kerf taper (T_a) and average surface roughness (R_a) are considered. The hybrid approach comprising of Taguchi methodology (TM) and response surface methodology (RSM) is used for modelling whereas multi-objective optimization is performed using hybrid approach of TM and grey relational analysis (GRA) coupled with entropy measurement methodology. The entropy measurement methodology is employed for the calculation of weight corresponding to each quality characteristic. The results indicate that the hybrid approaches applied for modelling and optimization of the LBC process are reasonable.     

The effect of moisture content in fibre laser cutting of pine wood

This paper reports a statistical analysis of the multiple-pass laser cutting of wet and dry pine wood with a Ytterbium fibre laser. As multiple factors affect the laser wood cutting process, finding the optimal combination of process parameters is necessary to achieve good quality and high process efficiency. Design of experiments (DOE) and statistical modelling were used in this study to investigate the significant process parameters and their interactions. A high brightness, 1 kW IPG single mode, continuous wave Ytterbium doped fibre laser was employed to cut wet and dry pine wood samples. The parameters investigated are laser power, traverse speed, focal plane position (f.p.p.), gas pressure, number of passes, direction of cut (normal or parallel to wood's tracheids) and the moisture content. The experimental results were compared against process responses defining the efficiency (i.e. kerf depth and energy consumption) and quality of the cut section (i.e. kerf width, heat affected zone—HAZ, edge surface roughness and perpendicularity). It has been found that the laser cutting process was mainly affected by the moisture content and the cut direction with respect to the wood's tracheids, followed by traverse speed, laser power and the number of passes. The effect of moisture content on energy consumption in the laser cutting process of both wet and dry wood is analysed. The wood cutting results with fibre laser are compared with those from a CO₂ laser.     

Simultaneous optimization of multiple quality characteristics in laser cutting of titanium alloy sheet

Titanium and its alloys have high demand in different industries due to their superior properties. The conventional cutting methods face difficulties for cutting these alloys due to their poor thermal conductivity, low elastic modulus and high chemical affinity at elevated temperatures. Laser cutting may be used for quality cuts by proper control of different process parameters. The aim of present research is to simultaneously optimize kerf taper and surface roughness in the laser cutting of Titanium alloy sheet (grade 5). The developed regression models for kerf taper and surface roughness have been taken as objective functions for the genetic algorithm based multi-objective optimization. The paper presents optimal solutions and improvements in different quality characteristics thereof. The significant control factors have been found with further discussion of their effect on two important quality characteristics kerf taper and surface roughness.     

Effect of CO2 laser cutting process parameters on edge quality and operating cost of AISI316L

Laser cutting is a popular manufacturing process utilized to cut various types of materials economically. The width of laser cut or kerf, quality of the cut edges and the operating cost are affected by laser power, cutting speed, assist gas pressure, nozzle diameter and focus point position as well as the work-piece material. In this paper CO₂ laser cutting of stainless steel of medical grade AISI316L has been investigated. Design of experiment (DOE) was implemented by applying Box–Behnken design to develop the experiment lay-out. The aim of this work is to relate the cutting edge quality parameters namely: upper kerf, lower kerf, the ratio between them, cut section roughness and operating cost to the process parameters mentioned above. Then, an overall optimization routine was applied to find out the optimal cutting setting that would enhance the quality or minimize the operating cost. Mathematical models were developed to determine the relationship between the process parameters and the edge quality features. Also, process parameters effects on the quality features have been defined. Finally, the optimal laser cutting conditions have been found at which the highest quality or minimum cost can be achieved.     

Prediction of weld strength and seam width for laser transmission welding of thermoplastic using response surface methodology

In the present work, a study is made to investigate the effects of process parameters, namely, laser power, welding speed, size of the laser beam and clamp pressure, on the lap-shear strength and weld-seam width for laser transmission welding of acrylic (polymethyl methacrylate), using a diode laser system. Response surface methodology (RSM) is employed to develop mathematical relationships between the welding process parameters and the output variables of the weld joint to determine the welding input parameters that lead to the desired weld quality. In addition, using response surface plots, the interaction effects of process parameters on the responses are analyzed and discussed. The statistical software Design-Expert v7 is used to establish the design matrix and to obtain the regression equations. The developed mathematical models are tested by analysis-of-variance (ANOVA) method to check their adequacy. Finally, a comparison is made between measured and calculated results, which are in good agreement. This indicates that the developed models can predict the responses adequately within the limits of welding parameters being used.     

Prediction of laser cutting heat affected zone by extreme learning machine

Heat affected zone (HAZ) of the laser cutting process may be developed based on combination of different factors. In this investigation the HAZ forecasting, based on the different laser cutting parameters, was analyzed. The main goal was to predict the HAZ according to three inputs. The purpose of this research was to develop and apply the Extreme Learning Machine (ELM) to predict the HAZ. The ELM results were compared with genetic programming (GP) and artificial neural network (ANN). The reliability of the computational models were accessed based on simulation results and by using several statistical indicators. Based upon simulation results, it was demonstrated that ELM can be utilized effectively in applications of HAZ forecasting.     

High-aspect-ratio microdrilling in polymeric materials with intense KrF laser radiation

UV laser microdrilling of high-aspect-ratio holes has been studied by using an intense beam with a low numerical aperture (KrF laser). The UV laser ablation produces a minimum of thermal or mechanical damage on the target. Under some particular experimental conditions (many high-fluence pulses), it is shown that long deep holes are obtained with reproducible aspect ratio (up to K/d길) in a variety of materials. Experiments with polymers (PMMA, PC, PET, PI, PS, PEEK) show that the more absorbing the polymer is, the better the resolution. However highly absorbing materials exhibit a low ablation rate. These promising results on laser microdrilling can be extended to new applications, for example, when the beam/target relative movement is computer driven. For instance this approach can be applied to cutting micro-objects with complicated shape or to machining fragile or brittle materials.     

Optimized laser cutting on light guide plates using grey relational analysis

This paper present the optimum conditions for direct CO₂ laser cutting of 6-mm-thick polymethylmethacrylate (PMMA) for backlit module applications. The influence of the major processing parameters on the optical transmittance ratio and surface roughness of cut samples material have been discussed. In order to assess the effects of several operational parameters on multiple-performance characteristics, we applied the grey relational analysis method. In this paper, we studied the effects of several laser direct cut parameters, such as assisted gas-flow rate, pulse repetition frequency, cutting speed, and focus position to achieve optimum characteristics for two product characteristics, optical transmittance ratio and work-piece surface roughness. The study involved nine experiments based on an orthogonal array, and results indicate the optimal process parameters as 20 NL/min for assisted-gas flow rate, 5 kHz for pulse repetition frequency, 2 mm/s for cutting speed, and 0 mm for laser focusing position. Additionally, by analyzing the grey relational grade, we found that the assisted-gas flow rate has more influence than any other single parameter.     

The effects of power rippling on CO2 laser cutting

A power rippling method was proposed in this study to improve the cut edge quality by disturbing the natural frequency of the periodic striations in high power C0₂ laser cutting. A pilot study was also designed and set up to examine the power responsibility of the laser system, which is externally controlled by a modulated analogue signal from a signal generator. Several aspects were examined in this study. The effects of different power rippling frequencies on the cut surface roughness is the first such aspect, and the different power modulation depth on cut surface roughness is another. The power rippling shape is the third important parameter examined in this study. It was found that the amplitude and frequency of the striation pattern on the cut surface were significantly affected by the characteristics of the rippling power. Cutting quality can be significantly improved by rippling the laser power.     

Multiple-objective optimization in precision laser cutting of different thermoplastics

Thermoplastics are increasingly being used in biomedical, automotive and electronics industries due to their excellent physical and chemical properties. Due to the localized and non-contact process, use of lasers for cutting could result in precise cut with small heat-affected zone (HAZ). Precision laser cutting involving various materials is important in high-volume manufacturing processes to minimize operational cost, error reduction and improve product quality. This study uses grey relational analysis to determine a single optimized set of cutting parameters for three different thermoplastics. The set of the optimized processing parameters is determined based on the highest relational grade and was found at low laser power (200 W), high cutting speed (0.4 m/min) and low compressed air pressure (2.5 bar). The result matches with the objective set in the present study. Analysis of variance (ANOVA) is then carried out to ascertain the relative influence of process parameters on the cutting characteristics. It was found that the laser power has dominant effect on HAZ for all thermoplastics.     

The use of grey relational analysis to determine laser cutting parameters for QFN packages with multiple performance characteristics

This paper reports an application of the grey relational analysis (GRA) to directly optimize laser cutting of a quad flat non-lead (QFN) strip using six performance characteristics. The most important performance characteristics include the cutting depth, the width of heat affected zone (HAZ), and the width of cutting line for both epoxy and Cu+epoxy materials along the cutting path. During the GRA, higher grades are obtained from any of the deeper (more complete) cutting depth, reduced widths of the HAZ and reduced widths of the cutting line. From nine experiments based on the orthogonal array of L9(3⁴), a current of 29 A, a frequency of 2 kHz, and a cutting speed of 2 mm/s were found to be the best parameters for laser cutting of a QFN strip with a thickness of 0.9 mm. Moreover, the analysis of variance (ANOVA) is also employed to determine the contribution of each control parameter on the cutting quality characteristics. The three largest measured contributions on the cutting quality in decreasing order are the frequency, the current, and the cutting speed. Compared with the Taguchi optimization method, the GRA approach is significantly simpler because it directly assigns appropriate weighting factors to the required qualities. Finally, confirmation experiments are performed to ensure the robustness of the GRA predicted optimal configuration for laser cutting a QFN strip.     

Investigating the CO2 laser cutting parameters of MDF wood composite material

Laser cutting of medium density fibreboard (MDF) is a complicated process and the selection of the process parameters combinations is essential to get the highest quality cut section. This paper presents a means for selecting the process parameters for laser cutting of MDF based on the design of experiments (DOE) approach. A CO₂ laser was used to cut three thicknesses, 4, 6 and 9 mm, of MDF panels. The process factors investigated are: laser power, cutting speed, air pressure and focal point position. In this work, cutting quality was evaluated by measuring the upper kerf width, the lower kerf width, the ratio between the upper kerf width to the lower kerf width, the cut section roughness and the operating cost. The effect of each factor on the quality measures was determined. The optimal cutting combinations were presented in favours of high quality process output and in favours of low cutting cost.     

Influences of various cutting parameters on the surface roughness during turnings stainless steel

This paper presents an investigation of the process factors affecting the surface roughness in ultra-precision diamond turning with ultrasonic vibration. Stainless steel was turned by diamond tools with ultrasonic vibration applied in the feed direction with an auto-resonant control system. Surface roughness was measured and compared along with the change of the cutting parameters. The relation curves between the cutting parameters and surface roughness were achieved by comparing the experimental results with different cutting speeds, feed rates, cutting depths. Experimental results indicate that cutting parameters have an obvious effect on the surface roughness. The conclusions are draw in given conditions, the smaller amplitude of the vibration, the worse the surface quality and the higher vibrating frequency, the better surface quality, and the deeper the cutting depth and the more the feed rate, the worse the surface quality. Among these parameters, the feed rate was the most important factor on surface quality.     

Estimation of the most influential factors on the laser cutting process heat affected zone (HAZ) by adaptive neuro-fuzzy technique

Heat affected zone (HAZ) of the laser cutting process may be developed on the basis on combination of different factors. In this investigation was analyzed the HAZ forecasting based on the different laser cutting parameters. The main aim in this article was to analyze the influence of three inputs on the HAZ of the laser cutting process. The method of ANFIS (adaptive neuro fuzzy inference system) was applied to the data in order to select the most influential factors for HAZ forecasting. Three inputs are considered: laser power, cutting speed and gas pressure. According the results the cutting speed has the highest influence on the HAZ forecasting (RMSE: 0.0553). Gas pressure has the smallest influence on the HAZ forecasting (RMSE: 0.0801). The results can be used in order to simplify HAZ prediction and analyzing.