Laser cutting of thick ceramic tile

This paper details developments in the CO₂ laser cutting of thick ceramic tiles, that is thicknesses of 8.5 mm and 9.2 mm. These tiles were cut at a combination of different cutting speeds to determine the necessary cutting parameters for various tile geometries. Different cutting modes were used in conjunction with different cutting speeds to investigate cut quality after laser processing. The work also looked into the effects on cutting through using various shield gases. Multipass cutting and underwater cutting were performed to examine their effects on thermal load during processing.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

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.     

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.     

Optical fiber cleaved at an angle by CO2 laser ablation: Application to micromachining

Laser ablation can be achieved by delivering short power pulse with durations much smaller than the heat diffusion time. In this investigation, we are collimating and magnifying a beam from a CO₂ laser with a Keplerian telescopic system. Then we study the quality of the cut performed by scanning the beam at a fast speed over an optical fiber just after focusing a well collimated CO₂ beam at λ=10.6 μm. It is found that the best results for cutting optical fibers depend upon both the time required in raising matter temperature to the vaporization point and the scanning speed of the CO₂ laser beam. Some aspects of the laser beam collimation before focusing is reviewed briefly and results for optical fibers being cleaved at low and fast speed under various conditions are also shown and discussed.     

Study into penetration speed during CO2 laser cutting of stainless steel

Laser cutting quality depends upon the proper selection of laser and workpiece parameters. Laser cut quality drops considerably when the size of the surface plasma increases. This plasma affects the speed of penetration, which in turn affects the cut quality. The present study examines the measurement of the penetration speed during CO₂ laser cutting of stainless steel workpieces. To achieve this, three different methods were employed, namely, optical, thermocouple and wire methods. Oxygen and an argon-oxygen gas mixture were used as assisting gases. Penetration speed was also predicted, using a one-dimensional heat transfer model. It was concluded that the cut quality improves when penetration speed is at a maximum.     

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.     

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.     

Frequency Stabilization of Waveguide CO2 Laser by a Digital Technique

In this work we present a simple technique for laser frequency stabilization, based on Digital signal processing. The technique is used to stabilize a waveguide CO₂ laser of wide tunability by using three kinds of reference signals: the CO₂ laser ouptut power, an infrared absorption optoacoustic signal and the output power of a Far-Infrared optically pumped molecular laser.     

CO2 laser cutting of MDF: 1. Determination of process parameter settings

This paper details an investigation into the laser processing of medium-density fibreboard (MDF). Part 1 reports on the determination of process parameter settings for the effective cutting of MDF by CO₂ laser, using an established experimental methodology developed to study the interrelationship between and effects of varying laser set-up parameters. Results are presented for both continuous wave (CW) and pulse mode (PM) cutting, and the associated cut quality effects have been commented on.     

Cutting glass substrates with dual-laser beams

In order to improve the cutting quality, a dual-laser-beam method was proposed to cut glass substrates in the current study, where a focused CO₂-laser beam was used to scribe a straight line on the substrate, and a defocused CO₂-laser beam was used to irradiate on the scribing line to generate a tensile stress and separate the substrate. The finite-element-method (FEM) software ANSYS was applied to calculate the temperature distribution and the resulting thermal stress filed. Through experimental study, it concluded that the glass substrate can be separated along an expected path with dual-laser beams and the cutting quality can be improved comparing with the cutting using a defocused laser beam alone. The relation between the cutting speed and the defocused laser power was also investigated in cutting glass with this method.     

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.     

Comparison of Cut Path Deviation Between CO2 and Diode Lasers in Float-Glass Cutting

Laser cutting of glass using the controlled fracture technique leads to cut path deviation at the leading and trailing edges of the float glass sheet. In this technique, thermal stresses are used to induce the crack, and the material is separated along the cutting path by extending the crack. We show that the cut path deviation is partly due to high magnitudes of thermal stresses generated near the sheet edges. The absorption of intense radiation from the CO₂ and diode laser beams in the glass causes local temperature increases and consequently generates different thermal fields and stress distributions due to surface and volumetric heat absorption. In this paper, we report the effect of the CO₂ and diode laser wavelength interaction with the float glass and its effect on the magnitudes of thermal stresses generated near the edges of the glass sheet. We simulate the distribution of the thermal stress and temperature using finite-element analysis software Abaqus and validate it against the experimental data. We show that the CO₂ laser produces a lower surface quality and a larger cut path deviation at the leading and trailing edges of the glass sheet as compared to the diode laser.     

A numerical simulation of machining glass by dual CO2-laser beams

In the flat panel display (FPD) industry, lasers may be used to cut glass plates. In order to reduce the possibility of fracture in the process of cutting glass by lasers, the thermal stress has to be less than the critical rupture strength. In this paper, a dual-laser-beam method is proposed, where an off-focus CO₂-laser beam was used to preheat the glass sample to reduce the thermal gradients and a focused CO₂-laser beam was used to machine the glass. The distribution of the thermal stress and the temperature was simulated by using finite element analysis software, Ansys. The thermal stress was studied both when the glass sample was machined by a single CO₂-laser beam and by dual CO₂-laser beams. It was concluded that the thermal stress can be reduced by means of the dual-laser-beam method.     

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.     

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 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.     

Cutting copper sheets using CO2 lasers

In this work various problems concerning cutting copper sheets using CO₂ laser are reported. First, all copper thermophysical properties, that regulate the process dynamics, and then the weight of each parameter has been evaluated numerically, even though only approximately. The surface absorption value of copper at room temperature and near the melting point and the order of laser power that is necessary to cause a gradual raise of the workpiece temperature from room to melting have been estimated. Then, the order of the cutting speed at which a sheet of a known thickness can be cut has been calculated. The analysis of all these problems, and the process dynamics and state of the art seem to confirm the validity of the current thesis on the impossibility of cutting copper by CO₂ laser. In the second part of the work the experimental data relating to the first ever tests on 0.2–4.0 mm thick copper sheet cutting by 2 kW CO₂ laser are reported. These first interesting results have been obtained thanks to the possibility of making overlapped layers of cupric oxide CuO, mixed with a small quantity of cuprous oxide Cu₂O grown under laser beam irradiation (CuO and Cu₂O, together, allow the laser cutting to be carried out). This has been confirmed by the analyses of the cutting edges with a computerized X-ray diffractometer. We have also seen that the per cent absorption of laser radiation at 10.6 micron does not increase in the presence of just cuprous oxide while, when the experimental conditions allow it, the growth of cupric oxide increases the absorption value to around 52–58 per cent, giving rise to the loop process with three variable quantities (temperature-oxide-absorption) that has been the winning clue of cutting process. The behaviour of the critical cutting speedV, the cutting widthsb and the productV·b versus the thickness for 2 kW CO₂ laser using a 4″ ZnSe and 3.5″ KCl focusing lens have been tested. Moreover, the influence of different gases and flows on the cutting process have been experimented. The work-speed turned out to be significant and various micrographic sections, performed on the workpieces have shown that the laser cutting quality is quite good. A first analysis of the results has shown that laser cutting is not comparable to the one of steel, so much so that the mathematical formalism developed for steels has proved to be unsuitable for copper. This paper was done under research contract with Italian Governmental Agency ISMEZR-INTERVENTO STRAORDINARIO NEL MEZZOGIORNO, which is supporter and financing organization within the project P.S. 35-105 IND. The first, the second and the third paper on this topic has been published on:-Review LA MECCANICA ITALIANA, n. 190, 1985, 45–47, ITALY (all rights reserved)-Review LASERS & APPLICATIONS, n. 3, Vol. 5, 1986, 59–64, High Tech. Publications Inc., Torrance, CA-USA (all rights reserved)-Proceedings of ECOOSA'86-European Conference on Optics, Optical Systems and Applications, Sept. 30–Oct. 3, 1986, Florence, ITALY (all rights reserved)     

Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

Generation of third harmonic of CO₂ laser radiation has been obtained in a type-II, ϑ=57° cut 9 mm thick AgGaSe₂ crystal for the first time by sum-frequency-mixing of the fundamental with its second harmonic, the latter being obtained using another type-I, ϑ=55° cut 11 mm thick AgGaSe₂ crystal. The energy conversion efficiencies obtained for second harmonic and third harmonic generations are 6.3% and 2.4% respectively with the input fundamental pump power density of 5.9 MW/cm² only. The wavelength of the fundamental CO₂ laser radiation used for the generation of harmonics is 10.6 μm, P(20) line. A compact TEA CO₂ laser source has been built in the laboratory.     

High-power multibeam CO2 laser for industrial applications

Multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes, all sharing a common plane parallel resonator. This paper describes construction and operation of a CW multibeam CO₂ laser consisting 20 discharge tubes and cooled length of 1500 mm, delivering 1 kW power. A high-frequency pulser is used for producing preionization in all discharge sections for initiating the main DC discharge simultaneously in all discharge tubes. Plane parallel resonator consists of a plane ZnSe mirror of 90 mm diameter having 60% reflectivity and a gold-coated copper mirror of same diameter. This laser operates in waveguide regime and laser power is not critically sensitive to mirror misalignment.