Laser rapid manufacturing of Colmonoy-6 components

This paper introduces a new manufacturing technique for the fabrication of Colmonoy-6 components using laser rapid manufacturing (LRM). LRM is a upcoming rapid manufacturing technology, being developed at various laboratories around the world. It is similar to laser cladding at the process level with different end applications. In general, laser cladding technique is used to deposit material on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high power continuous wave (CW) CO₂ laser system, integrated with a co-axial powder-feeding system and three-axis workstation was used. The effect of processing parameters during multi-layer deposition of Colmonoy-6 has been studied and optimized to fabricate about a dozen bushes. Thus fabricated bushes were finally machined and ground to achieve the desired dimensions and surface finish. These bushes were tested for non-destructive testing (like-ultrasonic testing, Dye-penetrant testing), metallographic examinations, micro-hardness measurement, X-ray diffraction and thermal ageing. Results compared well with those fabricated by deposition of Colmonoy-6 on austenitic stainless steel rods using gas Tungsten arc welding (GTAW). Thus, the new manufacturing technique not only produced quality product, but also minimized machining of hard-faced material and brought significant saving of time and costly Colmonoy-6 material.     

Automated laser fabrication of cemented carbide components

Automated Laser Fabrication (ALFa) is one of the most rapidly growing rapid-manufacturing technologies. It is similar to laser cladding at process level with different end applications. In general, laser cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn-out parts, while ALFa is capable of near net shaping the components by layer-by-layer deposition of the material directly from CAD model. This manufacturing method is very attractive for low volume manufacturing of hard materials, as near net shaping minimizes machining of hard material and subsequently brings significant savings in time and costly material. To date, many researchers have used this technology to fabricate components using various alloy steels, nickel-based alloys and cobalt-based alloys. In the present study, the work is extended to tungsten carbide cobalt (WC–Co) composites. A set of comprehensive experiments was carried out to study the effect of processing parameters during multi-layer fabrication. The process parameters were optimized for the component-level fabrication. Fabricated components were subjected to dye-penetrant testing, three-point flexural testing, hardness measurement, optical and scanning electron microscopy and X-ray diffraction analysis. The test results revealed that the laser-fabricated material was defect free and more ductile in nature. Thus, ALFa technology, not only produced the quality components, but also minimized machining of hard material and brought significant saving of time and costly WC–Co material.     

Research on the processing experiments of laser metal deposition shaping

Laser additive direct deposition of metals is a new rapid manufacturing technology, which combines with computer-aided design (CAD), laser cladding and rapid prototyping. The advanced technology can build fully dense metal components directly from CAD files with neither mould nor tool. Based on the theory of this technology, a promising rapid manufacturing system called “Laser Metal Deposition Shaping (LMDS)” has been constructed and developed successfully by Chinese Academy of Sciences, Shenyang Institute of Automation. Through the LMDS system, comprehensive experiments are carried out with nickel-based superalloy to systematically investigate the influences of the processing parameters on forming characteristics. By adjusting to the optimal processing parameters, fully dense and near-net-shaped metallic parts can be directly obtained through melting coaxially fed powder with a laser. Moreover, the microstructure and mechanical properties of as-formed samples are tested and analyzed synthetically. As a result, significant processing flexibility with the LMDS system over conventional processing capabilities is recognized, with potentially lower production cost, higher quality components, and shorter lead-time.     

The effects of process parameters on spatter deposition in laser percussion drilling

This paper reports on the characterisation and analysis of spatter deposition during laser drilling in Nimonic 263 alloy for various laser processing parameters using a fibre-optic delivered 400 W Nd:YAG laser. The principal findings are a large proportion of the spatter (approx. > 70%) was deposited due to the initial laser pulses (before beam breakthrough) required to drill a through-hole. Short pulse widths, low peak powers and high pulse frequencies generated smaller spatter deposition areas. At high pulse frequencies, the spatter distribution/thickness can be altered as a result of laser-ejected material interaction. Focal plane positions between −0.5 and +1.5 mm produced relatively similar spatter areas of about 14 mm². As a result of the reduction in the material removed per pulse, a longer focal length of 160 mm generated smaller areas of spatter deposition in comparison to a shorter focal length of 120 mm. In addition, a generic relationship between the spatter area and d_entrance/d_exit with increasing total laser energy has been established.     

The influence of temporal pulse train modulation during laser percussion drilling

The temporal pulse train modulation during laser percussion drilling was found to effect significant changes to the material ejection processes. In particular, distinct differences in the material ejection processes have been observed between a temporal pulse train shaping technique termed as sequential pulse delivery pattern control (SPDPC) and the normal delivery pattern (NDP), wherein the parameters of successive laser pulses were constant. Due to the reduced upward material removal fractions in SPDPC drilling, the spatter deposition area was reduced from approximately 6.7 to 2.7 mm². In addition, the melt layer thicknesses at the hole bottom were significantly increased from 11–61 to 18–369 μm. Such changes were identified as being due to the low laser pulse intensities before beam breakthrough associated with the SPDPC method. It was observed that the use of the linearly increasing SPDPC method increased the downward material removal fractions, from 20% to 28% observed in NDP drilling, to 34%–39%. Such an increase in the downward material ejection mechanism in SPDPC drilling was identified as being primarily due to the pointed blind-hole profile generated before the onset of beam breakthrough. The work has shown that modulating the entire pulse train in laser percussion drilling could control the material ejection processes. Furthermore, the fundamental elements of the SPDPC technique are given in terms of the rate of energy deposition and total pulse train energy.     

Morphologies,microstructures, and mechanical properties of samples produced using laser metal deposition with 316 L stainless steel wire

Laser metal deposition (LMD) with a filler has been demonstrated to be an effective method for additive manufacturing because of its high material deposition efficiency, improved surface quality, reduced material wastage, and cleaner process environment without metal dust pollution. In this study, single beads and samples with ten layers were successfully deposited on a 316 L stainless steel surface under optimized conditions using a 4000 W continuous wave fibre laser and an arc welding machine. The results showed that satisfactory layered samples with a large deposition height and smooth side surface could be achieved under appropriate parameters. The uniform structures had fine cellular and network austenite grains with good metallurgical bonding between layers, showing an austenite solidification mode. Precipitated ferrite at the grain boundaries showed a subgrain structure with fine uniform grain size. A higher microhardness (205–226 HV) was detected in the middle of the deposition area, while the tensile strength of the 50 layer sample reached 669 MPa. In addition, ductile fracturing was proven by the emergence of obvious dimples at the fracture surface.     

Experimental approach to the laser machining of PMMA substrates for the fabrication of microfluidic devices

This paper deals with CO₂ laser machining of a suitable amorphous polymer (PMMA) as a flexible technique for the rapid fabrication of miniaturized structures such as microfluidic devices.A model to estimate the main dimensions (depth and width) of the grooves produced by the laser on PMMA is presented, taking into account the influence of the main process parameters (incident power, scanning speed and spot diameter). This theoretical model allows to control the engraving process showing that laser could represent a valid alternative for the production of microchannels. PMMA single-use devices are found to be easier to manufacture with respect to the conventional glass or silicon products.In a second step, IR laser vaporization is adopted for the removal of a single layer of PMMA. This is achieved using multiple overlapping sequences of straight grooves with different scanning directions. The proposed technique showed that the removal depth varied proportionally with the number of layers machined, while surface roughness is influenced by the grooves spacing and the orientation of the scanning direction between successive layers.A method for thermally bonding the PMMA sheets, constituting the 3D structure of the chip, is also presented. The combination of high temperatures and low bonding pressures makes it possible to generate a bulk junction enabling good performances in terms of sealing characteristics.     

Pulsed laser ablation of borocarbide targets probed by time-of-flight mass spectrometry

Excimer laser ablation of superconductive borocarbide material (YNi₂B₂C) in typical conditions for the deposition of superconductive thin films has been investigated using time-of-flight mass spectrometry. The mass spectra show the presence of all the target elemental ionized atoms as well as diatomics. The ablation yield of the metal ions is a strongly increasing function of the laser fluence, while the contrary is true for non-metal ions. The dependence of non-metal light mass diatomic ions on laser fluence indicates the presence of aggregation processes as the laser fluence is increased. Moreover, evidence of aggregation processes involving metallic ions at high laser fluence is also obtained by the mass spectra. An interesting aspect of our results is the observation of an ion spatial distribution characterized by the presence of the lighter species at the plume edges, while the heavier ones are concentrated at the plume center.     

Prediction of clad angle in laser cladding by powder using response surface methodology and scatter search

Currently, laser cladding is an important process that allows the deposition of thick protective coatings on substrates. The article presents an experimental investigation of the influence of processing parameters on clad angle in laser cladding by powder (LCP). The clad angle is determined from the mathematical expression relating to the clad height and clad width. The cladding angle model was developed in terms of laser power, scanning speed, and powder mass flow rate by means of response surface methodology. A first-order equation covering a narrow range of the variables and a second-order equation covering a wide range of the variables are presented. An optimization technique, Scatter Search, is used to determine optimal processing parameters. The adequacy of the predictive model was tested by analysis of variance and found to be adequate.     

Laser printing of nanocomposite solid-state electrolyte membranes for Li micro-batteries

The electrochemical and mechanical properties of nanocomposite solid-state electrolyte membranes deposited using a laser direct-write technique from a suspended solution comprised of an ionic liquid (1,2-dimethyl-3-n-butylimidazolium-bis-trifluoromethanesulfonylimide)-polymer (poly(vinylidene fluoride-co-hexafluoropropylene)) matrix with dispersed nano-particles (TiO₂) are reported and discussed. These laser printed nanocomposite solid-state membranes are shown to exhibit the proper electrochemical behavior for ionic liquids while maintaining the strength and flexibility of the polymer matrix. This combination of physical properties and deposition technique makes these deposited nanocomposite membranes ideally suited for use as an electrolyte/separator in Li micro-batteries. Sample Li micro-batteries using these laser printed nanocomposite membranes have been fabricated and their charge/discharge behavior tested, demonstrating the feasibility of using these nanocomposite membranes in Li micro-battery applications.     

Application of laser ultrasonic technique for non-contact detection of drilling-induced delamination in aeronautical composite components

The detection of drilling-induced delamination in composite components is a vital and challenging task in aviation industry. Numerous key components of aircrafts are made of composite materials, and drilling is often a final operation during assembly. Drilling-induced delamination is a very serious defect that significantly reduces the structural reliability, but it is rather difficult to be detected effectively due to its special location. A novel application of laser ultrasonic technique for the detection of drilling-induced delamination in composites is presented in this paper. A carbon fiber reinforced plastic laminate with drilling holes was made as specimen. A laser ultrasonic system was constructed and experiments were performed to detect the drilling-induced delamination, based on propagation characteristic of ultrasonic waves generated by pulse laser with a wavelength of 1064 nm and pulse duration of 10 ns. A laser interferometer based on two wave mixing is used to measure ultrasonic wave signals, and the morphology features of the delamination are imaged clearly by laser ultrasonic C-scan testing. The results proved that the laser ultrasonic technique is a feasible and effective method for the detection of drilling-induced delamination in composite components.     

Study of the laser-induced forward transfer of liquids for laser bioprinting

Laser-induced forward transfer (LIFT) is a direct-writing technique that allows printing patterns of diverse materials with a high degree of spatial resolution. In conventional LIFT a small fraction of a solid thin film is vaporized by means of a laser pulse focused on the film through its transparent holder, and the resulting material recondenses on the receptor substrate. It has been recently shown that LIFT can also be used to transfer materials from liquid films. This widened its field of application to biosensors manufacturing, where small amounts of biomolecules-containing solutions have to be deposited with high precision on the sensing elements. However, there is still little knowledge on the physical processes and parameters determining the characteristics of the transfers.In this work, different parameters and their effects upon the transferred material were studied. It was found that the deposited material corresponds to liquid droplets which volume depends linearly on the laser pulse energy, and that a minimum threshold energy has to be overcome for transfer to occur. The liquid film thickness was varied and droplets as small as 10 μm in diameter were obtained. Finally, the effects of the variation of the film to substrate distance were also studied and it was found that there exists a wide range of distances where the morphology of the transferred droplets is independent of this parameter, what provides LIFT with a high degree of flexibility.     

Nanosecond laser ablation for pulsed laser deposition of yttria

A thermal model to describe high-power nanosecond pulsed laser ablation of yttria (Y₂O₃) has been developed. This model simulates ablation of material occurring primarily through vaporization and also accounts for attenuation of the incident laser beam in the evolving vapor plume. Theoretical estimates of process features such as time evolution of target temperature distribution, melt depth and ablation rate and their dependence on laser parameters particularly for laser fluences in the range of 6 to 30 J/cm² are investigated. Calculated maximum surface temperatures when compared with the estimated critical temperature for yttria indicate absence of explosive boiling at typical laser fluxes of 10 to 30 J/cm². Material ejection in large fragments associated with explosive boiling of the target needs to be avoided when depositing thin films via the pulsed laser deposition (PLD) technique as it leads to coatings with high residual porosity and poor compaction restricting the protective quality of such corrosion-resistant yttria coatings. Our model calculations facilitate proper selection of laser parameters to be employed for deposition of PLD yttria corrosion-resistive coatings. Such coatings have been found to be highly effective in handling and containment of liquid uranium.     

Experimental fatigue performance of laser-formed components

Much knowledge has been gained with respect to the forming of sheet material by laser technology since its inception during the mid-1980s. However, many press-formed sheet metal components are subjected to cyclic loading conditions during their service life. It is from this standpoint that the work reported in this paper originates. This work deals with some aspects of the structural integrity of laser-formed plate samples that were formed to a radius of curvature of approximately 125 mm. Furthermore, a comparison is drawn between laser-formed and stock plate samples fatigue tested under reverse-bending cyclic conditions. The results indicate that the fatigue life of the laser-formed samples was substantially enhanced when compared to that of the stock plate samples. This observed improvement in fatigue life is attributed to the laser-hardening mechanism, i.e., the phase transformation and rate of cooling of the material from above the A₃ temperature, i.e. approximately 1200 °C. This aspect of improved fatigue life is considered to be beneficial to the motor manufacturing industry that could result in the possible use of thinner gauge material.     

Research of rapid and direct thick coatings deposition by hybrid plasma-laser

In this paper, a new technology of direct and rapid thick coatings fabrication with hybrid plasma-laser deposition manufacturing (PLDM) technology is advanced which is also suitable for functional prototyping and tooling applications. It emphasizes on the influence of laser to the microstructure of coatings and physical properties of surface layers. Unlike the direct rapid plasma deposition manufacturing (PDM), in hybrid plasma-laser deposition manufacturing, the laser beam enters into plasma arc beam and focuses on the molten pool as assisting heat energy. A 280 W pulsed Nd:YAG (yttrium-aluminum garnet) laser machine is used to inspect the effect. The experimental results show that the laser beam could improve the surface state; the elements distribution of coatings deposited by PLDM was even; the physical properties of surface coatings fabricated with PLDM were better than that deposited by PDM.     

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.     

A comparative study of gadolinium gallium garnet growth by femtosecond and nanosecond pulsed laser deposition

The growth of epitaxial Nd:Gd₃Ga₅O₁₂ (GGG) on Y₃Al₅O₁₂ (YAG) by femtosecond pulsed laser deposition is reported. We have used a Ti:sapphire laser at a wavelength of 800 nm and pulse length of 130 fs, operating at a repetition rate of 1 kHz. The film properties have been studied systematically as a function of the deposition parameters of laser fluence, spot-size, oxygen pressure, target-substrate distance and temperature. Scanning electron microscopy, atomic force microscopy and X-ray diffractometry were used to characterise the surface structure and crystallinity of the films. X-ray diffraction analysis shows that epitaxial growth has occurred. A comparison between the ion velocities produced by nanosecond and femtosecond laser ablation of the GGG target material has been investigated by the Langmuir probe technique. The results indicate a large difference in the plasma characteristics between femtosecond and nanosecond ablation, with ion velocities up to eight times faster observed in the femtosecond case.     

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.     

Accuracy control of three-dimensional Nd:YAG laser shaping by ablation

Improving the dimensional accuracy along the optical axis without decreasing the materials removing rate is a key issue in three-dimensional laser shaping. This paper presents a concept for performing three-dimensional laser shaping by directly using machining laser as the photo source of the non-contacting measuring device. Due to the high power measuring photo source and a 1.06 μm bandpass filter, the interference caused by the emission light of ablated surface can be effectively avoided, the delay time is not needed to be inserted between the laser pulse and the measurement. So the measurement will not decrease the material removal rate and productivity. By using this system, the shaping accuracy of 30 μm can be achieved at the removing rate of about 4.0×10⁻² mm³/sec for Si₃N₄ ceramic, both are much better than the results obtained before.     

Supersonic laser spray of aluminium alloy on a ceramic substrate

Applying a ceramic coating onto a metallic substrate to improve its wear resistance or corrosion resistance has attracted the interest of many researchers during decades. However, only few works explore the possibility to apply a metallic layer onto a ceramic material. This work presents a novel technique to coat ceramic materials with metals: the supersonic laser spraying.In this technique a laser beam is focused on the surface of the precursor metal in such a way that the metal is transformed to the liquid state in the beam-metal interaction zone. A supersonic jet expels the molten material and propels it to the surface of the ceramic substrate.In this study, we present the preliminary results obtained using the supersonic laser spray to coat a commercial cordierite ceramic plate with an Al-Cu alloy using a 3.5 kW CO₂ laser and a supersonic jet of Argon.Coatings were characterized by scanning electron microscopy (SEM) and interferometric profilometry.