Improving the appearance of all textile products from clothing to home textile using laser technology

Denim trousers, commonly known as “blue jeans”, have maintained their popularity for many years. For the purpose of supporting customers’ purchasing behaviour and to address their aesthetic taste, companies have been trying in recent years to develop various techniques to improve the visual aspects of denim fabrics. These techniques mainly include printing on fabrics, embroidery and washing the final product. Especially, fraying certain areas of the fabric by sanding and stone washing to create designs is a popular technique. However, due to certain inconveniences caused by these procedures and in response to growing demands, research is underway to obtain a similar appearance by creating better quality and more advantageous manufacturing conditions.

As is known, the laser is a source of energy which can be directed on desired objects and whose power and intensity can be easily controlled. Use of the laser enables us to cut a great variety of material from metal to fabric. Starting off from this point, we thought it would be possible to transfer certain designs onto the surface of textile material by changing the dye molecules in the fabric and creating alterations in its colour quality values by directing the laser to the material at reduced intensity.

This study mainly deals with a machine specially designed for making use of laser beams to transfer pictures, figures as well as graphics of desired variety, size and intensity on all kinds of surfaces in textile manufacturing such as knitted—woven fabrics, leather, etc. at desired precision and without damaging the texture of the material.

In the designed system, computer-controlled laser beams are used to change the colour of the dye material on the textile surface by directing the laser beams at a desired wavelength and intensity onto various textile surfaces selected for application. For this purpose, a laser beam source that can reach the initial level of power and that can be controlled by means of a computer interface; reflecting mirrors that can direct this beam at two axes; a galvanometer which comprised of an optical aperture; and a computer program that can transfer images obtained in standard formats to the galvanometer control card were used.

Developing new designs by using the computer and transferring the designs that are obtained on textile surfaces will not only increase and facilitate the production in a more practical manner, but also help you to create identical designs. This means serial manufacturing of the products at a standard quality and increasing their added values. Moreover, creating textile designs using laser will also contribute to the value of the product as far as the consumer is concerned because it will not cause any wearing off and deformation in the texture of the fabric unlike the sanding and stoning processes.

Another advantage of this system is that it gives a richer look to the product by causing the textile surfaces to get wrinkled and become three-dimensional by deformation as well as enabling you to create pictures and patterns on leather and synthetic fabrics by means of heat.

As for the results of the study, the first step was to prepare 40 pairs of denim trousers, half of which were prepared manually and the other half by using laser beam. Time studies were made at every step of the production. So as to determine the abrasion degrees of the trousers in design applications, tensile strength as well as tensile extension tests were conducted for all the trousers.     

Droplet printing through bubble contact in the laser forward transfer of liquids

The deposition process of the laser-induced forward transfer of liquids at high laser fluences is analyzed through time-resolved imaging. It has been found that, at these conditions, sessile droplets are deposited due to the contact of a generated cavitation bubble with the receptor substrate, in contrast to the jet contact mechanism observed at low and moderate laser fluences. The bubble contact results in droplets with a larger diameter, a smaller contact angle and a lower uniformity than those of the jet mechanism. Therefore, in order to attain a high degree of resolution this mechanism should be prevented.     

Study of liquid deposition during laser printing of liquids

Laser-induced forward transfer (LIFT) is a direct-writing technique which can be used to successfully print various complex and sensitive materials with a high degree of spatial resolution. However, the optimization of its performances requires a deep understanding of the LIFT dynamics. Such understanding should allow correlating the phenomena underlying the liquid transfer process with the morphology of the obtained deposits. To this end, in this work it is presented a study related to two aspects: first, the correlation of the morphological characteristics of the transferred droplets with the variation of the film thickness combined with laser fluence; and second, a correlation of the dependences observed with the dynamics of the transfer process. The work is focused on the understanding of the observed dependences for which the information provided by time-resolved analysis on liquid transfer dynamics has proved to be crucial.     

CO2 laser beam modulating for surface texturing machining

Laser texturing is a novel technique that may be used to texture a cold roller in the process of manufacturing high quality steel sheets. With the aim of improving the quality of the textured roller by using a CO₂ laser, a new laser beam modulating device is proposed. An optical beam expander with a fast rotating chopper system is designed. The laser pulse is split into two parts by the chopper blades; one is the preheating pulse that is reflected onto optical loop mirrors; the other is the directly transmitted pulse that creates the craters at the preheated spots. The preheating beam focus spot size and position can be adjusted. The focusing characteristics and optical parameter compensation for the flying optics are investigated. The heat transfer and melt process of laser texturing are numerically simulated. The effects of the double pulses on the texturing are analyzed. The effect of preheating the sample ahead of the laser texturing pulse is examined. The surface profile and bump hardness show improvements by using this approach.     

Removal of the indigo color by laser beam–denim interaction

Our experiments show that the laser fading process removes efficiently indigo-dye from denim support. We use the beams from Nd : YAG laser (1064 nm and its second harmonic 532 nm) and CO₂ (10.6 μm) lasers. Different laser pulse parameters were used in order to obtain laser power density and fluency to start the ablation process. The purpose of this work is to determine the change of denim diffuse reflectivity spectra after laser irradiation with different wavelength and different power density. The change of diffuse reflectivity coefficient was up to 17% at 450 nm wavelength (from 8% reflectivity for unirradiated denim).     

Fine metal line patterning on hydrophilic non-conductive substrates based on electrohydrodynamic printing and laser sintering

We present a electrohydrodynamic (EHD) fine metal line patterning on a hydrophilic non-conductive substrate for the repair of flat panel displays. There are two crucial problems to solve for fine metal line patterning: 1) The scattering effect caused by the charges accumulated on the printed lines, 2) the unwanted thermal effect around patterned lines during sintering. We found that the scattering can be curbed by optimizing head parameters, and the unwanted thermal effect around patterned lines by directly applying laser sintering to printed lines. We achieved a 3 μm width of metal line patterns with the electrical resistivity of 17.48 μΩ cm.     

Roughness and gradient parameters for characterising shape uniformity of laser beams

We define six parameters, the roughness parameter, the local gradient parameter, the directionless gradient parameter, the integral gradient parameter, the directionless integral gradient parameter and the absolute gradient parameter for characterising the uniformity of a laser beam in its transversal section. For shape-invariant beams the roughness parameter is propagation invariant. The absolute gradient parameter is propagation invariant for symmetric shape invariant beams. As an example, five of the defined parameters are calculated for a dummy irradiance. The values of the roughness parameter and the absolute parameter are calculated and tabulated for symmetric Hermite–Gaussian, Laguerre–Gaussian, spherical Gaussian, flattened Gaussian (at the waist plane) and super Gaussian beams (at the waist plane). The results are discussed.     

Numerical calculation of the use of a concave–convex lens for shaping axisymmetric laser beams

Based on transformation matrices in meridian plane and sagittal plane, a geometrical lens design method is presented with the aim of obtaining an improved spot. A concave–convex convergent lens (CCCL) is employed as a shaping lens to focus a group of oblique laser beams from a CO₂ laser with axially symmetrical fold combination (ASFC) resonator. The cases including interference, noninterference, different wavelength, and misalignment have been analyzed. Through theoretical analysis and numerical calculation, a smaller beam radius in a specific reference plane and a smaller far-field divergence angle can be obtained.     

Laser ablation of multilayers of ink from a paper substrate for tactile printing

This paper reports the effects of laser ablation upon multiple-layered coloured inks which have been printed on an ordinary white paper. The aim of this work is to examine the feasibility of generating a fully tactile three-coloured image by selectively removing ink layers to reveal underlying layers of a different colour. In this paper laser ablation has been carried out upon four layered ink samples consisting of white/cyan/white/black layers. Ablation was carried out using a Q-switched Nd : YAG laser. The results show that it is possible to selectively remove the inks to expose both the top white and the cyan layers, although charring occurs with deeper ablation. An evaporation/decomposition mechanism is proposed to describe process of ink ablation.     

Analysis of beam quality for the laser beams after spectral beam combining

The beam quality of the laser beams after spectral beam combining (SBC) has been analyzed in this paper. Based on the propagation model of the spectral beam combining system, the expression for the output field of an individual beam passing through the spectral beam combining system with lens aberration has been given and the intensity distribution of the combined beam has been studied by the principle of incoherent superposition. Consequently, according to the intensity second-order moments method, the M²-factor of the combined beam has been calculated and the effect of lens aberration on the characteristics of the combined beam has been analyzed quantitatively. It can be shown that the SBC system can improve the beam quality of laser array significantly, and the M²-factor of the combined beam passing through the ideal spectral beam combining system is almost the same as that of an individual beam. For the spectral beam combining system with lens aberration, the spherical aberration has greater effect on the off-axis beam than on the on-axis beam, and the beam quality of combined beam degrades with increase in lens aberration.     

Dual beam method for laser welding of galvanized steel: Experimentation and prospects

Laser welding of zinc-coated steel sheets in lap configuration poses a challenging problem, because of the zinc vapours spoiling the quality of the weld. In continuation to the earlier work, the novel solution of dual laser beam method for lap welding of galvanized steel sheets is discussed here in view of the recently obtained observations and ensuing concerns. In this method the precursor beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The metallurgical analysis of the welds is encouraging showing absence of zinc in the welded area. In the current work on this technique, new experimental results have been obtained verifying the earlier observations. Along with this, the possibility of using a transversely split-up beam for the welding purposes with this approach is discussed and analyzed in this paper. This new technique is expected to be very useful in prospective industrial applications requiring higher welding throughput along with the needed quality.     

Numerical calculations of temperature distribution of double layer metallic surface treated by laser beams

A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials.     

Composition design and laser cladding of Ni-Zr-Al alloy coating on the magnesium surface

The cluster line criterion was used for optimized design of a Ni-Zr-Al alloy used as coating on the AZ91HP magnesium alloy by laser cladding. Results show that the coating mainly consists of an amorphous, two ternary intermetallic phases with Ni₁₀Zr₇ and Ni₂₁Zr₈ type structures resulting in high hardness, good wear resistance and corrosion resistance. The interface between the clad layer and the substrate has good metallurgical bond.     

Numerical approach to laser beam propagation through turbulent atmosphere and evaluation of beam quality factor

In this paper, propagation of a Gaussian laser beam through turbulent atmosphere is evaluated numerically. The beam quality factor for the propagated beam has been estimated for different turbulent conditions that are characterized by parameter C_n. The calculations show that the beam quality can be affected dramatically by atmospheric turbulence and the laser beam size and wavelength have major role in the results. Furthermore, the propagation of laser beam in longer distance results in more spatial perturbation of the beam. The results of these calculations and evaluation of beam quality factor M² can be used for estimating the refractive index structure parameter (or atmosphere turbulent parameter) C_n.     

Real-time detection of focal position of workpiece surface during laser processing using diffractive beam samplers

The real-time fabrication of microgrooves on a curved surface using a laser beam, without preprogramming their shapes into the machining instructions, is a major challenge in laser processing owing to limitations associated with the real-time detection of the focal position. A new approach using a sampled fraction of the beam from a diffractive beam sampler (DBS) is therefore presented in order to overcome this limitation. By considering the sampled fraction of the beam an analysis of the results allows for precise positioning of the specimen for focal-point identification. This allows for the determination of the focus for a broad variety of laser types and laser powers, thereby providing stringent focusing conditions with high numerical apertures. This approach is easy to implement, inexpensive, independent of the roughness or granularity of the workpieces, and more importantly does not require auxiliary lasers and displacement sensors for real-time measurement during the fabrication process.     

Ultraviolet laser microstructuring of silicon and the effect of laser pulse duration on the surface morphology

The study of the laser pulse duration effect on the silicon micro-spikes morphology is presented. The microcones were produced by ultraviolet (248 nm) laser irradiation of doped Si wafers in SF₆ environment. The laser pulse duration was adjusted at 450 fs, 5 ps and 15 ns. We have analyzed the statistical nature of the spikes’ morphological characteristics, such as periodicity and apex angle by exploiting image processing techniques, on SEM images of the irradiated samples. The correlation of the quantitative morphological characteristics with the laser parameters (pulse duration, laser fluence and number of pulses) provides new insight on the physical mechanisms, which are involved on the formation of Si microcones.     

Emergent intensity from a plane-parallel medium exposed to a Gaussian laser beam: A comparison of Rayleigh and isotropic scattering

The focus of this two-dimensional study is the radially varying intensity emergent from a plane-parallel scattering medium exposed to a collimated, Gaussian laser beam directed perpendicular to the upper surface. The method of analysis is the integral transform technique. Specifically, this work uses the generalized reflection and transmission functions from a previous study to construct the emergent intensity with the use of an inverse Hankel transform. Radially varying backscattered and transmitted intensities are calculated for media with isotropic and Rayleigh scattering phase functions and optical thicknesses that range from 0.125 to 8.0. The behavior of the emergent radiation inside and outside the beam is investigated for both narrow and wide beams. A new integration method is implemented to compute the emergent intensity at the beam center. The emergent intensity at the beam center is used to quantify when a one-dimensional model may be used. As expected, for small optical thicknesses and near the beam the phase function has significant influence, while far from the beam multiple scattering reduces the influence of the Rayleigh phase function. Results from this study will be useful in understanding and interpreting more complicated situations, such as those that include polarization.     

Axisymmetric laser welding of ceramics: comparison of experimental and finite element results

In this paper, we compare experimental data for a laser spot weld on a ceramic to the solution from an adaptive finite element model of the system. Our focus is on validating the finite element model, which necessarily includes numerous simplifications. We assume an axisymmetric geometry and flow profile, with a flat free surface. Buoyancy and surface tension drive the liquid motion in the molten ceramic pool beneath the laser, which is calculated using the axisymmetric forms of the continuity, momentum and energy equations. Latent heat, temperature-dependent material properties and radiation effects are all included in the formulation. These equations are solved with standard finite element techniques utilizing mesh relocation with a movement indicator based on solution gradients. Comparision with experimental data indicates that the numerical techniques used successfully predicted the depth and diameter of the actual ceramic weld pool.     

Beam alignment with the axis of a rotation stage for laser fabrication of microcircular structures

An optical technique to align laser beam with the axis of a rotating stage is proposed for laser fabrication of circular microstructures. The laser beam is first aligned parallel to the rotation axis and subsequently adjusted to coincide with the axis. An optical arrangement consisting of two quadrant photodiodes for the x- and y-directions and a specially designed beam splitter is utilized for the alignment. Mathematical modeling of the alignment system is carried out to estimate alignment errors caused by misalignment of mirror surfaces in the beam path. It is shown that parallelness of the laser beam to the rotation axis is a key factor to reduce alignment errors. The proposed method was applied to a microstereolithography system and proved that the laser beam can be aligned within a distance of about 25 μm from the rotation axis.     

高光束质量、高功率稳定性激光器的设计及实验研究

高光束质量、高功率稳定性激光器在激光加工、激光测量等领域具有广泛的用途.为了实现激光器腔内光斑聚焦同时减少色散和体积,人们常常将曲面反射镜用在激光谐振腔中,但光束倾斜入射到曲面反射镜往往会引起像散,从而导致光斑质量恶化,并降低激光器的性能.另一方面,在高功率激光器或超短脉冲激光器中,激光增益介质热透镜焦距的起伏,是导致激光输出功率波动的主要原因之一.针对激光器的像散和功率波动这两个问题,本文提出了一套简单高效的解决方案,在考虑像散补偿和热透镜效应的基础上,基于传播变换圆理论,首次提出一种可实现高光束质量、高功率稳定性激光器谐振腔的设计方法,并对采用该方法所设计出的超短脉冲激光器进行理论与实验研究.研究结果表明,利用该方法设计的激光谐振腔,两端臂像散能够完全被补偿,实验上实现了基模高斯光束输出;当激光晶体热透镜焦距改变时,该方法所设计出的激光谐振腔内各关键位置光斑半径的变化,显著地小于普通谐振腔,在相同外界条件下,其输出激光功率稳定性明显优于普通激光器.