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The past decade has seen the introduction of high performance short-pulse systems such as fiber and disk lasers with repetition rates in the several hundred-kHz range. These have provided the user with a wide range of interaction parameters to chose from. The availability of high speed optical imaging techniques has also provided the opportunity to explore high-speed laser matter interactions in greater detail. In this paper we demonstrate a single pulse study of a decaying tail in the pulse envelope using “unfilled” and “energy filled” pulses. We demonstrate a Pulsed digital holography (PDH) system used to study the shock wave dynamics, laser induced plasma and energy deposition efficiencies of single and multi-pulse interactions of 200 ns shaped laser pulses, with a temporal resolution of < 10 ns. Finally, we demonstrate novel designer pulses that show improved material response and increased penetration depth at a fraction of the energetic cost of conventional pulses.The past decade has seen the introduction of high performance short-pulse systems such as fiber and disk lasers with repetition rates in the several hundred-kHz range. These have provided the user with a wide range of interaction parameters to chose from. The availability of high speed optical imaging techniques has also provided the opportunity to explore high-speed laser matter interactions in greater detail. In this paper we demonstrate a single pulse study of a decaying tail in the pulse envelope using “unfilled” and “energy filled” pulses. We demonstrate a Pulsed digital holography (PDH) system used to study the shock wave dynamics, laser induced plasma and energy deposition efficiencies of single and multi-pulse interactions of 200 ns shaped laser pulses, with a temporal resolution of < 10 ns. Finally, we demonstrate novel designer pulses that show improved material response and increased penetration depth at a fraction of the energetic cost of conventional pulses.

The capability of manufacturing coatings is of central importance in engineering design. Many components require nowadays the application of additional layers, to enhance mechanical properties and protect against hostile environments. Supersonic Laser Deposition (SLD) is a novel coating method, based upon Cold Spray (CS) principles. In this technique the deposition velocities can be significantly lower than those required for effective bonding in CS applications. The addition of laser heat energy permits a change in the thermodynamic experience of impacting particles, thereby offering a greater opportunity for metallurgical bonding at lower velocities compared to the CS process technology. The work reported in this paper demonstrates the ability of the SLD process to deliver hard facing materials to engineering surfaces. Stellite-6 has been deposited on low carbon steel tubes over a range of process parameters, determining the appropriate target power and traverse speeds for coating deposition. Coating properties and parameters were examined to determine the main properties, micro-structure and processing cost. Their morphology was studied through optical microscopy, SEM and X-Ray Diffraction. The results have shown that SLD is capable of depositing Stellite-6, with enhanced properties compared to laser clad counterparts.

Since the exchange coupling theory was proposed by Kneller and Hawig in 1991 there has been a significant effort within the magnetic materials community to enhance the performance of rare earth magnets by utilising nano-composite meta-materials. Inclusions of magnetically soft iron smaller than approximately 10 nm in diameter are exchange coupled to a surrounding magnetically hard Nd2Fe14B matrix and provide an enhanced saturisation magnetisation without reducing coercivity. For such a fine nanostructure to be produced, close control over the thermal history of the material is needed. A processing route which provides this is laser annealing from an amorphous alloy precursor. In the current work, relationships between laser parameters, thermal histories of laser processed amorphous stoichiometric NdFeB ribbons and the magnetic properties of the resulting nanocrystalline products have been determined with a view to applying the process to thick film nanocomposite magnet production.

The importance of metal coating technologies drives the continuous improvement of metal deposition techniques for application in a wide range of industrial sectors. This work presents the foundations of a new process technology for the deposition of Ti and Ti64 coatings on various substrates using supersonic powder streams and impact site laser heating. Full density metallic deposits are obtained under appropriate impact conditions without the need for transiting the melting point of the deposited material or substrate leading to large energy savings. Details of the experimental approach will be presented along with the general characteristics of the titanium coatings produced using this novel coatings method.

A study on the nanosecond fiber laser interaction with silicon was performed experimentally for the generation of percussion drilled holes. Single pulse ablation experiments were carried out on mono crystalline 650µm thick Si wafers. Changes of the mass removal mechanism were investigated by varying laser fluence up to 68 J/cm2 and pulse duration from 50 ns to 200 ns. Hole width and depth were measured and surface morphology were studied using scanning electron microscopy (SEM) and optical interferometric profilometry (Veeco NT3300). High speed photography was also used to examine laser generated plasma expansion rates. The material removal rate was found to be influenced by the pulse energy, full pulse duration and pulse peak power. Single pulse ablation depth of 4.42 µm was achieved using a 200 ns pulse of 13.3 J/cm2, giving a maximum machining efficiency of 31.86 µm per mJ. Holes drilled with an increased fluence but fixed pulse length were deeper, exhibited low recast, but were less efficient than those produced at a lower fluence. The increased peak power in this case led to high levels of plasma and vapour production. The expansion of which, results in a strong driving recoil force, an increase in the rate and volume of melt ejection, and cleaner hole formation. The experimental findings show that for efficient drilling at a given energy, a longer, lower peak power pulse is more desirable than a high peak power short pulse.A study on the nanosecond fiber laser interaction with silicon was performed experimentally for the generation of percussion drilled holes. Single pulse ablation experiments were carried out on mono crystalline 650µm thick Si wafers. Changes of the mass removal mechanism were investigated by varying laser fluence up to 68 J/cm2 and pulse duration from 50 ns to 200 ns. Hole width and depth were measured and surface morphology were studied using scanning electron microscopy (SEM) and optical interferometric profilometry (Veeco NT3300). High speed photography was also used to examine laser generated plasma expansion rates. The material removal rate was found to be influenced by the pulse energy, full pulse duration and pulse peak power. Single pulse ablation depth of 4.42 µm was achieved using a 200 ns pulse of 13.3 J/cm2, giving a maximum machining efficiency of 31.86 µm per mJ. Holes drilled with an increased fluence but fixed pulse length were deeper, exhibited low recast, but were less efficient than tho...

Laser micro machining is fast gaining popularity as a method of fabricating micro scale structures. Lasers have been utilised for micro structuring of metals, ceramics and glass composites and with advances in material science, new materials are being developed for micro/nano products used in medical, optical, and chemical industries. Due to its favourable strength to weight ratio and extreme resistance to chemical attack, glassy carbon is a new material that offers many unique properties for micro devices.The laser machining of SIGRADUR® G grade glassy carbon was characterised using a 1065 nm wavelength Ytterbium doped pulsed fiber laser. The laser system has a selection of 25 preset waveforms with optimised peak powers for different pulsing frequencies. The optics provide spot diameter of 40 µm at the focus.The effect of fluence, transverse overlap and pulsing frequency (as waveform) on glassy carbon was investigated. Depth of removal and surface roughness were measured as machining quality indicators.The damage threshold fluence was determined to be 0.29 J/cm2 using a pulsing frequency of 250 kHz and a pulse width of 18 ns (waveform 3). Ablation rates of 17 < V < 300 µm3/pulse were observed within a fluence range of 0.98 < F < 2.98 J/cm2. For the same fluence variation, 0.6 µm to 6.8 µm deep trenches were machined. Trench widths varied from 29 µm at lower fluence to 47 µm at the higher fluence.Square pockets, 1 mm wide, were machined to understand the surface machining or milling. The depth of removal using both waveform 3 and 5 showed positive correlation with fluence, with waveform 5 causing more removal than waveform 3 for the same fluence. Machined depths varied from less than 1 µm to nearly 40 µm.For transverse overlap variation using waveform 3, the best surface finish with Rz ≤ 1.1 µm was obtained for fluence 0.792 J/cm2 for transverse overlap of 1 µm, 6 µm, and 9 µm at machined depths of 22.9 µm, 6.6 µm, and 4.6 µm respectively. For fluence of 1.426 J/cm2, the best surface finish with Rz ≤ 1.2 µm was obtained for transverse overlap of 6 µm, and 9 µm at machined depths of 12.46 µm, and 8.6 µm respectively.The experimental data was compiled as machining charts and utilised for fabricating a micro-embossing glassy carbon master toolsets as a capability demonstration.Laser micro machining is fast gaining popularity as a method of fabricating micro scale structures. Lasers have been utilised for micro structuring of metals, ceramics and glass composites and with advances in material science, new materials are being developed for micro/nano products used in medical, optical, and chemical industries. Due to its favourable strength to weight ratio and extreme resistance to chemical attack, glassy carbon is a new material that offers many unique properties for micro devices.The laser machining of SIGRADUR® G grade glassy carbon was characterised using a 1065 nm wavelength Ytterbium doped pulsed fiber laser. The laser system has a selection of 25 preset waveforms with optimised peak powers for different pulsing frequencies. The optics provide spot diameter of 40 µm at the focus.The effect of fluence, transverse overlap and pulsing frequency (as waveform) on glassy carbon was investigated. Depth of removal and surface roughness were measured as machining quality indicators.T...

Metal coating and cladding techniques employ high temperatures to melt the metal particles which can undermine the integrity and stability of the resulting deposit material and substrate. This paper introduces a new process for the deposition of metallic coatings in the solid state using a supersonic particle stream in conjunction with laser energy input, named Laser Assisted Material Spray, LAMS. This alternative approach circumvents, at lower cost, some key problems associated with current conventional high temperature thermal spray and laser-clad processes, as well as the Cold-Spray process. The quality of the bond between deposit and substrate, together with structural integrity of the deposit, rely heavily on the energy supplied to the system, whether it be by propulsion or heat source, as in related thermal spray methods. LAMS allows the precise and controlled addition of laser energy to both the supersonic metal particle stream and substrate interaction site. Preliminary results show that deposition can be achieved without melting the deposit material or generating a heat-affected zone in the substrate. Such a deposit does not form without the supplementary energy input of the laser.Metal coating and cladding techniques employ high temperatures to melt the metal particles which can undermine the integrity and stability of the resulting deposit material and substrate. This paper introduces a new process for the deposition of metallic coatings in the solid state using a supersonic particle stream in conjunction with laser energy input, named Laser Assisted Material Spray, LAMS. This alternative approach circumvents, at lower cost, some key problems associated with current conventional high temperature thermal spray and laser-clad processes, as well as the Cold-Spray process. The quality of the bond between deposit and substrate, together with structural integrity of the deposit, rely heavily on the energy supplied to the system, whether it be by propulsion or heat source, as in related thermal spray methods. LAMS allows the precise and controlled addition of laser energy to both the supersonic metal particle stream and substrate interaction site. Preliminary results show that depositio...

The measurement of high speed laser beam parameters during processing is a topic that has seen growing attention over the last few years as quality assurance places greater demand on the monitoring of the manufacturing process. The targets for any monitoring system is to be non intrusive, low cost, simple to operate, high speed and capable of operation in process.A new ISO compliant system is presented based on the integration of an imaging plate and camera located behind a proprietary mirror sampling device. The general layout of the device is presented along with the thermal and optical performance of the sampling optic.Diagnostic performance of the system is compared with industry standard devices, demonstrating the high quality high speed data which has been generated using this system.The measurement of high speed laser beam parameters during processing is a topic that has seen growing attention over the last few years as quality assurance places greater demand on the monitoring of the manufacturing process. The targets for any monitoring system is to be non intrusive, low cost, simple to operate, high speed and capable of operation in process.A new ISO compliant system is presented based on the integration of an imaging plate and camera located behind a proprietary mirror sampling device. The general layout of the device is presented along with the thermal and optical performance of the sampling optic.Diagnostic performance of the system is compared with industry standard devices, demonstrating the high quality high speed data which has been generated using this system.

Despite substantial experimental effort, the meltflow in kerfs is still poorly understood. The ability to expel the melt effectively is severely limiting process performance and cost, especially in narrow thick sections cutting. Various hypotheses exist in the current literature but conclusive proof is still elusive. In order to further the understanding, coupled gas-dynamics/melt-flow interaction simulations were performed. Phenomena observed in the simulations match microstructural features found in optical micrographs, taken from cross sections coplanar to the workpiece surface. Simulation results and an outlook on the future development of simulation capabilities will be presented.Despite substantial experimental effort, the meltflow in kerfs is still poorly understood. The ability to expel the melt effectively is severely limiting process performance and cost, especially in narrow thick sections cutting. Various hypotheses exist in the current literature but conclusive proof is still elusive. In order to further the understanding, coupled gas-dynamics/melt-flow interaction simulations were performed. Phenomena observed in the simulations match microstructural features found in optical micrographs, taken from cross sections coplanar to the workpiece surface. Simulation results and an outlook on the future development of simulation capabilities will be presented.

Laser beam diagnostic devices have been used extensively in laboratory environments and in process development work ever since the evolution of laser technology began. However, industrial laser users have had to rely on basic instruments and measurement techniques in order to assess the state of their lasers. Recent product introductions have gone a long way in breaking the barrier between the laboratory and the shop floor. Some of these new devices are compact and low cost with simple user friendly interfaces that can be used by the average machine operator.Some enlightened users are now looking to greater levels of beam monitoring to assist in preventive maintenance schedules, as a tool to maintain product quality and even for on-line and in-line beam monitoring applications to provide input to process control.Laser beam diagnostic devices have been used extensively in laboratory environments and in process development work ever since the evolution of laser technology began. However, industrial laser users have had to rely on basic instruments and measurement techniques in order to assess the state of their lasers. Recent product introductions have gone a long way in breaking the barrier between the laboratory and the shop floor. Some of these new devices are compact and low cost with simple user friendly interfaces that can be used by the average machine operator.Some enlightened users are now looking to greater levels of beam monitoring to assist in preventive maintenance schedules, as a tool to maintain product quality and even for on-line and in-line beam monitoring applications to provide input to process control.

Fiber lasers offer a significant increase in performance flexibility from a single technology not yet realized by traditional sources. As fiber lasers provide improved beam quality, new opportunities are emerging for high power, high brightness laser sources. A review of current state-of-the-art for fiber laser technology and specifications of a new high power high brightness industrial fiber laser will be discussed. Of particular interest is the enhanced beam characteristics and delivery options offered by the single fiber high power fiber laser. The availability of low beam parameter product values, 1kW power levels, places Yb fiber lasers in a world leading position within the industrial marketplace.

The interaction phenomena of nanosecond Q-switched diode-pumped solid state (DPSS) laser using 355nm radiation with 0.2mm thick 316L stainless steel foil was investigated at incident laser fluence range of 19 – 82Jcm−2. The characterization study was performed with and without the use of assist gas by utilizing micro supersonic minimum length nozzles (MLN), specifically designed for air at inlet chamber pressure of 8bar. MLN ranged in throat diameters of 200µm, 300µm, and 500µm respectively. Average etch rate per pulse under the influence of three micro supersonic impinging jets, for both oxygen and air showed the average etch rate was reduced when high-speed gas jets were utilized, compared to that without any gas jets, but significant variation was noticed between different jet sizes. Highest etch rate and quality was achieved with the smallest diameter nozzle, suggesting that micro nozzles can produce a viable process route for micro laser cutting.The interaction phenomena of nanosecond Q-switched diode-pumped solid state (DPSS) laser using 355nm radiation with 0.2mm thick 316L stainless steel foil was investigated at incident laser fluence range of 19 – 82Jcm−2. The characterization study was performed with and without the use of assist gas by utilizing micro supersonic minimum length nozzles (MLN), specifically designed for air at inlet chamber pressure of 8bar. MLN ranged in throat diameters of 200µm, 300µm, and 500µm respectively. Average etch rate per pulse under the influence of three micro supersonic impinging jets, for both oxygen and air showed the average etch rate was reduced when high-speed gas jets were utilized, compared to that without any gas jets, but significant variation was noticed between different jet sizes. Highest etch rate and quality was achieved with the smallest diameter nozzle, suggesting that micro nozzles can produce a viable process route for micro laser cutting.

There is a quest in industry to cut faster and deeper, to improve efficiency or open up whole new areas of processing capability. It is clear from an examination of the standard laser cutting process that the laser is more than capable of generating sufficient melt volumes to allow faster or deeper cuts. When such cuts are attempted either they fail or the quality is poor.One of the problems appears to lie with the inadequate axial forces that the coaxial gas jet imparts to the melt volumes within the kerf. Increasing the speed or thickness limits requires better control over the gas jets.This paper examines the effects of fundamental gas jet/material interactions, for both conical and supersonic nozzles using computational fluid dynamics. The work includes a detailed examination of the effect of nozzle offset on the flow through narrow kerfs. Optimum theoretical parameters for assist gas jets are then presented.There is a quest in industry to cut faster and deeper, to improve efficiency or open up whole new areas of processing capability. It is clear from an examination of the standard laser cutting process that the laser is more than capable of generating sufficient melt volumes to allow faster or deeper cuts. When such cuts are attempted either they fail or the quality is poor.One of the problems appears to lie with the inadequate axial forces that the coaxial gas jet imparts to the melt volumes within the kerf. Increasing the speed or thickness limits requires better control over the gas jets.This paper examines the effects of fundamental gas jet/material interactions, for both conical and supersonic nozzles using computational fluid dynamics. The work includes a detailed examination of the effect of nozzle offset on the flow through narrow kerfs. Optimum theoretical parameters for assist gas jets are then presented.

The characterisation of industrial laser beams is soon to become a necessary step as manufacturing industries around the world improve the quality assurance of production processes. Laser beam characterisation is made possible with the development of high-speed on-line laser beam measuring device that is capable of measuring critical beam parameters during processing operations. The dynamic behaviour of freely and guided propagating laser beams is characterised using the device. In addition to the results of system performance and capability, case studies for online process monitoring are given.The characterisation of industrial laser beams is soon to become a necessary step as manufacturing industries around the world improve the quality assurance of production processes. Laser beam characterisation is made possible with the development of high-speed on-line laser beam measuring device that is capable of measuring critical beam parameters during processing operations. The dynamic behaviour of freely and guided propagating laser beams is characterised using the device. In addition to the results of system performance and capability, case studies for online process monitoring are given.

Laser beam diagnosis is usually carried out off-line in order to minimise the disruption to the process being carried out. This paper presents the results of a fractional sampling device for a high power beam diagnosis system capable of measuring in process beam properties such as beam diameter, intensity and beam position. The paper discusses the application of this sampling technique for monitoring beam properties during the laser materials processing operation.Laser beam diagnosis is usually carried out off-line in order to minimise the disruption to the process being carried out. This paper presents the results of a fractional sampling device for a high power beam diagnosis system capable of measuring in process beam properties such as beam diameter, intensity and beam position. The paper discusses the application of this sampling technique for monitoring beam properties during the laser materials processing operation.

Laser beam diagnosis is usually carried out off-line in order to minimise the disruption to the process being carried out. This paper presents the results of a fractional sampling device for a high power beam diagnosis system capable of measuring in process beam properties such as beam diameter, intensity and beam position. The paper discusses the application of this sampling technique for monitoring beam properties during the laser materials processing operation.Laser beam diagnosis is usually carried out off-line in order to minimise the disruption to the process being carried out. This paper presents the results of a fractional sampling device for a high power beam diagnosis system capable of measuring in process beam properties such as beam diameter, intensity and beam position. The paper discusses the application of this sampling technique for monitoring beam properties during the laser materials processing operation.

A second-order method of characteristics (MOC) algorithm was used to determine the flow field and wall contour for supersonic axisymmetric, minimum length micro nozzles with a straight sonic line. Contours for axisymmetric supersonic micro nozzles were predicted with a stagnation pressure of 8 atmospheres. These profiles were then tested using a compressible Computational Fluid Dynamic (CFD) code. The CFD codes were also used to model pressure distribution and shock formation during the laser cutting and drilling mechanisms. Results obtained were compared with experimental analysis.A second-order method of characteristics (MOC) algorithm was used to determine the flow field and wall contour for supersonic axisymmetric, minimum length micro nozzles with a straight sonic line. Contours for axisymmetric supersonic micro nozzles were predicted with a stagnation pressure of 8 atmospheres. These profiles were then tested using a compressible Computational Fluid Dynamic (CFD) code. The CFD codes were also used to model pressure distribution and shock formation during the laser cutting and drilling mechanisms. Results obtained were compared with experimental analysis.

Diode pumped solid state lasers (DPSS) with multiwavelenth capability have become an industrial reality over the last few years. Multi wavelength capability allows DPSS lasers to microdrill and micromachine in industrially relevant materials such as ceramics, metals, and polymers. A systematic series of experiments was performed to investigate the process parameters needed to cut and machine 316L Stainless Steel. Processing was carried out under controlled gas environments using directed gas jets. Results from this study reveal that traditional plasma controlling gases whilst providing efficiency gains have a detrimental affect on the surface morphology of micomachined components. This paper presents the results of this study and makes recommendations for optimum process parameters.Diode pumped solid state lasers (DPSS) with multiwavelenth capability have become an industrial reality over the last few years. Multi wavelength capability allows DPSS lasers to microdrill and micromachine in industrially relevant materials such as ceramics, metals, and polymers. A systematic series of experiments was performed to investigate the process parameters needed to cut and machine 316L Stainless Steel. Processing was carried out under controlled gas environments using directed gas jets. Results from this study reveal that traditional plasma controlling gases whilst providing efficiency gains have a detrimental affect on the surface morphology of micomachined components. This paper presents the results of this study and makes recommendations for optimum process parameters.

Recently there has been an explosion of interest in applications, which require miniaturisation of micro mechanical components. These components are produced in many ways, but the majority relies on some form of etching, lithography or electro-forming. The reliance on these processes severely limits the choice of material and design available to the micro engineer at the concept stage, and adds months to new product lead-time. This paper investigates the design, development and performance characteristics of supersonic micro nozzles, that will enable the downscaling of many macro laser materials processing techniques, including cutting and machining.The initial nozzle design was developed using the method of characteristics. These profiles were then tested using a compressible computational fluid dynamics (CFD) code. The use of CFD code, gives the ability, to adjust the nozzle profile allowing speedy assessment of the suitability of the flow field for the particular process in question. The authors were particularly interested in developing, shock free, supersonic flow with maximum free jet length and maximum mass flow rate of process gas. Final prototype nozzles were manufactured using stereolithography and subsequently tested experimentally using pressure mapping techniques and Shadowgraph imaging. The effect of the position of the nozzle on its performance in the kerf was then examined using CFD to investigate the performance of these nozzles in industrial applications.Recently there has been an explosion of interest in applications, which require miniaturisation of micro mechanical components. These components are produced in many ways, but the majority relies on some form of etching, lithography or electro-forming. The reliance on these processes severely limits the choice of material and design available to the micro engineer at the concept stage, and adds months to new product lead-time. This paper investigates the design, development and performance characteristics of supersonic micro nozzles, that will enable the downscaling of many macro laser materials processing techniques, including cutting and machining.The initial nozzle design was developed using the method of characteristics. These profiles were then tested using a compressible computational fluid dynamics (CFD) code. The use of CFD code, gives the ability, to adjust the nozzle profile allowing speedy assessment of the suitability of the flow field for the particular process in question. The authors were p...

This work investigates the use of laser cladding and laser surface-welding techniques as mechanisms for eliminating steps on the surfaces of metallic laminated objects for tooling applications. Results of machining of the laser-processed surface, carried out to bring the laser-processed laminated objects to design tolerance, are also presented. The work shows the use of the above processes in the production of hemispherical tool primitives. It also presents results of tests to ascertain the resistance of these tools to typical working environments. The tool-making routes investigated are concluded to be viable for further development into an industrial tool-making application.This work investigates the use of laser cladding and laser surface-welding techniques as mechanisms for eliminating steps on the surfaces of metallic laminated objects for tooling applications. Results of machining of the laser-processed surface, carried out to bring the laser-processed laminated objects to design tolerance, are also presented. The work shows the use of the above processes in the production of hemispherical tool primitives. It also presents results of tests to ascertain the resistance of these tools to typical working environments. The tool-making routes investigated are concluded to be viable for further development into an industrial tool-making application.

Direct Tool Production (DTP) by Laminated Object Manufacturing (LOM) technique is being widely investigated to replace conventional tool production techniques. The advantages of LOM techniques lie in their reduction in both manufacturing cost and the lead time. Given this scope for cost reduction, industries are concentrating on the DTP to increase their flexibility and reduce lead times. The major problem with the LOM techniques is the ‘staircase’ effect that occurs due to the discrete height of the laminates. Various techniques are being investigated to remove the steps such as high speed machining, electric-discharge machining (EDM) and slant cutting. This paper presents the results of experimental investigations to remove or overcome the “staircase” effect using slant cutting, laser machining or blown powder cladding techniques.The slant cutting and cladding processes were investigated using CO2 laser. The effect of different cutting gases and cutting gas pressures has been investigated including the use of oxygen, air and nitrogen. A high pressure Laval nozzle was used for air and nitrogen assist gas cutting. On the other hand, the blown powder technique was investigated to fill the steps on laminated parts. An appropriate sized clad track is deposited in the bottom of each step to improve the overall smoothness of the partAn Nd:YAG laser (LUMONICS JK704TR) was used in the laser machining of the laminated steps. The influences of laser parameters and traverse speed were investigated.Direct Tool Production (DTP) by Laminated Object Manufacturing (LOM) technique is being widely investigated to replace conventional tool production techniques. The advantages of LOM techniques lie in their reduction in both manufacturing cost and the lead time. Given this scope for cost reduction, industries are concentrating on the DTP to increase their flexibility and reduce lead times. The major problem with the LOM techniques is the ‘staircase’ effect that occurs due to the discrete height of the laminates. Various techniques are being investigated to remove the steps such as high speed machining, electric-discharge machining (EDM) and slant cutting. This paper presents the results of experimental investigations to remove or overcome the “staircase” effect using slant cutting, laser machining or blown powder cladding techniques.The slant cutting and cladding processes were investigated using CO2 laser. The effect of different cutting gases and cutting gas pressures has been investigated including the ...

Laser welding, cutting and surface treatment have become accepted means of processing materials. The future integration of lasers and machine tools would be supported by the development of a laser machining process. At present laser systems are used to selectively remove material by melting and evaporation followed by ejection with high speed gas jets. Removing material by melting and evaporation leads to very low wall plug efficiency and the process has difficulty competing with conventional mechanical removal methods. If mechanical removal methods are incapable of performing the required task then efficiency is not so important. However, mechanical removal methods are capable of performing the majority of machining processes. When processing high tensile steels and super alloys the situation becomes rather different, here mechanical methods are slow with tool wear becoming a major problem. Adopting a laser solution would seem appropriate but efforts must be made to avoid bulk melting and vaporisation regimes in order to maximise efficiency. This paper examines the new process of laser slot cutting (laser slotting). The laser is used to remove material to a given depth in the form of a narrow slot (blind cut). Slot forming mechanisms and some process variables are discussed. Methods of bulk removal through multi-slot production are also presented.Laser welding, cutting and surface treatment have become accepted means of processing materials. The future integration of lasers and machine tools would be supported by the development of a laser machining process. At present laser systems are used to selectively remove material by melting and evaporation followed by ejection with high speed gas jets. Removing material by melting and evaporation leads to very low wall plug efficiency and the process has difficulty competing with conventional mechanical removal methods. If mechanical removal methods are incapable of performing the required task then efficiency is not so important. However, mechanical removal methods are capable of performing the majority of machining processes. When processing high tensile steels and super alloys the situation becomes rather different, here mechanical methods are slow with tool wear becoming a major problem. Adopting a laser solution would seem appropriate but efforts must be made to avoid bulk melting and vaporisation re...

Previous works by the authors highlighted the detrimental effect that entrainment of atmospheric gases into the laser cutting gas jet can have on the whole cutting process. Early works concentrated on the influence of the entrainment effects when cutting thick section steel. A buffer jet arrangement designed to prevent impurity entrainment was successfully applied when cutting 10,15, and 20mm thick steel. The main action of the buffer jet was to preserve the oxygen concentration within the cut and ensure sufficient exothermic reaction energy was available to maintain melt temperatures. This paper presents more comprehensive results on the subject of gas entrainment. The effects operating within conventional laser cutting operation are examined and the entrainment operating window is given in terms of typical laser cutting conditions. The benefits of using the buffer jet system are presented in terms of quality and performance improvements when cutting 43A steel in the range 3 to 20mm thick.Previous works by the authors highlighted the detrimental effect that entrainment of atmospheric gases into the laser cutting gas jet can have on the whole cutting process. Early works concentrated on the influence of the entrainment effects when cutting thick section steel. A buffer jet arrangement designed to prevent impurity entrainment was successfully applied when cutting 10,15, and 20mm thick steel. The main action of the buffer jet was to preserve the oxygen concentration within the cut and ensure sufficient exothermic reaction energy was available to maintain melt temperatures. This paper presents more comprehensive results on the subject of gas entrainment. The effects operating within conventional laser cutting operation are examined and the entrainment operating window is given in terms of typical laser cutting conditions. The benefits of using the buffer jet system are presented in terms of quality and performance improvements when cutting 43A steel in the range 3 to 20mm thick.

The efficiency and overall quality of a laser cutting operation is highly dependent on the assist gas parameters. The desire to cut thicker material has led to the observation of small process operating windows for thicker sections. The gas jet delivery and subsequent dynamical behaviour have significant effects on the cutting operation as the sample thickness increases. To date, few workers have examined the dynamical behaviour of the gas jet. This paper examines the characteristics of oxygen gas jets during CO2 laser cutting of steel. Particular emphasis is placed on the mass transfer effects that are operating within the kerf. Oxygen concentration levels within a model kerf are measured for various laser cutting set-ups. The results show a substantial reduction in oxygen concentration within the kerf. A system for oxygen concentration maintenance is described and cutting results from this system are compared with conventional techniques for cutting steels in the range 10 to 20mm thick. A theoretical analysis of turbulent mass transfer within a kerf is presented and compared with experiment.The efficiency and overall quality of a laser cutting operation is highly dependent on the assist gas parameters. The desire to cut thicker material has led to the observation of small process operating windows for thicker sections. The gas jet delivery and subsequent dynamical behaviour have significant effects on the cutting operation as the sample thickness increases. To date, few workers have examined the dynamical behaviour of the gas jet. This paper examines the characteristics of oxygen gas jets during CO2 laser cutting of steel. Particular emphasis is placed on the mass transfer effects that are operating within the kerf. Oxygen concentration levels within a model kerf are measured for various laser cutting set-ups. The results show a substantial reduction in oxygen concentration within the kerf. A system for oxygen concentration maintenance is described and cutting results from this system are compared with conventional techniques for cutting steels in the range 10 to 20mm thick. A theoretical an...

Enhanced coupling of a CO2 laser has been observed on Cu and Al surfaces as a result of a surface modification generated by an Excimer laser. This paper presents the results of such experimentsEnhanced coupling of a CO2 laser has been observed on Cu and Al surfaces as a result of a surface modification generated by an Excimer laser. This paper presents the results of such experiments