A thermo-mechanical model for simulating the temperature and stress distribution during laser cladding process

Numerical simulation and experimental analysis of thermal conduction and stress in laser cladding repair of thin-walled parts

Laser cladding has become an important surface modification technique in today’s industry. It is not only applied for coating new products but also for repair and refurbishment as well as in rapid prototyping. A laser clad workstation has been developed. It uses a 4 kW Nd:YAG fibre coupled laser as heat source. A specially developed optical system combines the benefits from a Top-hat energy distribution with a practical working distance. The clad material is supplied to the melt pool by a lateral powder nozzle. A camera based monitoring system for the laser cladding process has been developed. This system determines the main dimensions of the melt pool in real-time. A developed FEM model of the laser cladding process accurately predicts the shape and temperature of the clad layers by including the interaction between the laser beam and the powder jet. The model results are in good correspondence with experimental results. An extensive set of cladding experiments has been performed with variable spot size, laser power, cladding speed and powder mass rate. From the experimental work, a clear correlation between the dilution and the width of the melt pool was found. This correlation was found to be independent of the substrate temperature, enabling real time control of the dilution by adjusting the laser power. A feedback control strategy was developed and implemented based on the melt pool width information from the camera. As a result, the energy input into the substrate and consequently thermal distortion of the products is minimized, while a good metallurgical bonding and minimal dilution are obtained. Due to this minimal dilution, the hardness of the clad layer can be controlled and maintained to be uniform. High temperature gradients and different material properties may cause high residual stresses or even cracks. To investigate this effect, a simple and fast method based on deflection measurements has been developed. The residual stress values obtained by this procedure have been compared with stresses from X-ray measurements. The results show tensile stresses of large magnitude develop in the layer, which increase with the cladding speed.

Impacts of laser cladding residual stress and material properties of functionally graded layers on titanium alloy sheet

The paper discusses the advantages and shortcomings of alternate double single track (ADST) lines with respect to double track lines for high speed lines. ADST lines consists of sequences of double and single track segments optimally selected in order to reduce the construction and maintenance costs of railway lines and to optimize the timetables used to satisfy a given demand. The single tracks are selected to coincide with expensive segments (tunnels and viaducts) and the double tracks are chosen to coincide with flat areas and only where they are necessary. At the same time, departure times are adjusted for trains to cross at the cheap double track segments. This alternative can be used for new lines and also for existing conventional lines where some new tracks are to be constructed to reduce travel time (increase speed). The ADST proposal is illustrated with some examples of both types (new lines and where conventional lines exist), including the Palencia-Santander, the Santiago-Valparaíso-Viña del Mar and the Dublin-Belfast lines, where very important reductions (90 %) are obtained, especially where a railway infrastructure already exist.DOI: http://dx.doi.org/10.4995/CIT2016.2016.3426

The laser cladding process is associated with having a non-uniform material strength within the clad bead and the heat-affected zone. As well, residual stresses can develop, which in turn increase the crack driving force and reduce the strength and fatigue life of the part. In the present work, a finite element model was developed to simulate the temperature history, microhardness values, and induced residual stresses for a coaxial powder injection laser cladding process for P420 stainless steel powder on low/medium carbon steel plates. Residual stress developments for 10 single-track cladded specimens fabricated using different process parameter sets were studied by a simulation model. The model was validated with microhardness measurements and residual stress values. The effect of a heat treatment on the microhardness values and reduction of residual stress were also investigated. In the next research phase, a multi-track cladded specimen model was validated by microhardness measurements and a study was carried out on microhardness variations and residual stresses. A comparison between the simulation and experimental results exhibits the accuracy of the model to capture the laser cladding process phenomena. A well-designed simulation model can be used to determine the process parameters to avoid tensile and compressive residual stresses in the component and achieve the desired strength with more uniformity in the clad.

• 3D finite element modelling of laser cladding process has been developed to predict residual stress at clad, substrate and interface. • Effect of Similar and dissimilar materials on the development of residual stress during laser cladding. • Benchmarking the model with experimental results. • Laser materials interaction of alloy and ceramic materials, and their effect on generation of residual stress. • Use of commercial software for any material system to select appropriate clad materials with minimised residual stress. The formation of residual stresses due to thermo-mechanical effect and microstructural transformation in the Laser Cladding process predominantly affects the final product integrity and service life. A 3D finite element transient thermo-mechanical model has been developed to predict thermal profile and residual stress distribution for repair application of Ti6Al4V alloy using a moving heat source. Then the developed model was applied for the deposition of ceramic materials Al 2 O 3 and TiC on Ti6Al4V alloy substrate. The outcome of this model is to predict temperature distribution, cooling rate, melt pool depth, heat affected zone and residual stress. This study mainly highlights the thermal effect on the residual stresses for similar and dissimilar clad/substrate materials and suggests the suitable cladding material with minimum residual stress.

Enhancement in fatigue property of Ti-6Al-4V alloy remanufactured by combined laser cladding and laser shock peening processes

Evaluation of the mechanical properties of Inconel 718 components built by laser cladding

In order to improve the work efficiency and save resources in the process of laser cladding on the H13 steel surface, based on COMSOL, by combining computer simulation and experiment, a plane continuous heat source model was used to simulate and analyze the temperature and stress field. The optimal power and scanning speed were obtained. It is found in the simulation process that the thermal sampling points stress increases with the increase of laser power and scanning speed. Because of the existence of solid–liquid phase variation in the laser cladding process, there are two peaks in the maximum thermal stress cycle curve of the sample points located in the molten pool, and the starting and ending time of each sample point’s peak value is basically the same. When the sample point is outside the molten pool, because the metal at the corresponding location is not melted, so there is no obvious peak value in the thermal stress cycle curve. With the increase of cladding layer depth corresponding to each sample point, the variation range of the two alternating thermal stress peaks increases first and then decreases, while the duration increases. According to the peak value of alternating thermal stress at the sampling point, the molten pool depth can be predicted. The residual stress analysis of the cladding layer is carried out according to the analysis results of temperature field and stress field. Through the actual cladding experiment, it is found that the depth of molten pool in the simulation results is basically consistent with the experimental results. All simulation results are verified through actual cladding experiments.

In the development of protective alloy layers by laser cladding residual stresses can lead to final cracking of the deposited coating and a certain mechanical deformation of the processed part. These stresses are of thermal nature and result from very high thermal gradients and cooling rates associated to laser heat treatments. A numerical model based on a thermo-mechanical finite element analysis was developed and is presented which allows to obtain the thermal and stress fields in the laser cladding process. The nature of the stress fields (compressive-tensile) is explained and the effect of the geometrical features of the deposited clad, the thickness of the substrate material, the process scan speed and substrate preheating temperature on the resulting stress fields and mechanical distortions is discussed. The study includes some characteristic features arising in the processing of overlapping laser scans for covering extended areas as well as multilayer single laser scans for 3D direct fabrication. Comparison with experimental results obtained on Co-based laser clad coatings show a good qualitative agreement.

Geometry modeling of single track cladding deposited by high power diode laser with rectangular beam spot

Microstructure and performance evolution of Ti-6Al-4 V alloy coating by laser cladding and laser shocking composite remanufacture

The laser cladding process has achieved a wide level of acceptance in recent years from various sectors of industry due to its minimal heat input into the part and its inherent ability to achieve low dilution rates. However, the deposition rates of the laser cladding process are typically lower when compared to competitive cladding technologies. This research paper evaluates Induction Assisted Laser Cladding using Fraunhofer’s new COAXpowerline nozzle system and documents the improvements in clad travel speeds and powder feed rates which can be achieved using Inconel 625 and 60-40 Tungsten Carbide-Nickel base powder.The laser cladding process has achieved a wide level of acceptance in recent years from various sectors of industry due to its minimal heat input into the part and its inherent ability to achieve low dilution rates. However, the deposition rates of the laser cladding process are typically lower when compared to competitive cladding technologies. This research paper evaluates Induction Assisted Laser Cladding using Fraunhofer’s new COAXpowerline nozzle system and documents the improvements in clad travel speeds and powder feed rates which can be achieved using Inconel 625 and 60-40 Tungsten Carbide-Nickel base powder.

To further develop the advantages of face gear drives and improve their anti-sticking performance and wear resistance, a novel method using laser cladding as the primary process is proposed; here, grinding processing is used as the secondary process, i.e., achieving tooth surface strengthening of the orthogonal offset face gear using two types of materials to form a material gradient based on a laser cladding technology. Then, grinding processing is performed using a five-axis grinding machining. First, according to the forming principle of the face gear tooth surface, we establish the coordinate system of the orthogonal offset face gear and the gear cutter coordinate system; we also derive the tooth surface equation of the virtual gear cutter and the tooth surface equation of the orthogonal offset face gear. Second, we research the principles of the laser cladding and establish a laser cladding test bed for the orthogonal offset face gear. Based on the analysis of the design of the cladding layer and the process parameters of the face gear, the selection of the scanning path, the heat accumulation during the laser cladding process, and the accuracy control of the scanning position, we perform a laser cladding experiment on the offset orthogonal face gear. Third, we establish the machining coordinate system of the face gear based on the machine tool structure and conduct a grinding experiment for the face gear after the cladding process. Finally, we analyze the morphology and hardness of the face gear after grinding. A bench test verification of the axle face gear transmission system is completed. The results show that the precision and surface hardness of the tooth surface are significantly improved after grinding. Meanwhile, the accuracy and feasibility of the laser cladding surface of the face gear are verified.

Over the last decade, researchers have demonstrated interest in tribology and prototyping by the laser cladding process. In-situ laser cladding enables the formation of a uniform clad by melting the powder to form desired composition from pure powder components. Since TiC has desirable properties, such as hardness, wear and corrosion resistance, Ti and Graphite (C) are used as a composite material (i.e., TiC) to increase hardness and wear resistance of AISI 1030 carbon steel.In previous papers, the effect of laser parameters on the clad quality was investigated. In this paper two combined parameters (i.e. the effective energy per unit area (Eeff) and the powder deposition density (PDD) were plotted in order to recognize the high quality clad zone. Afterward a range of clad conditions with constant and variable effective energies in high quality clad zone were conducted to study the role of the effective energy on morphology and distribution of TiC particles.Complete metallurgical bonding between substrate and the clad was observed in all samples.SEM analysis has been used to study the TiC particles’ morphology from the bottom to the top of the clad. Presence of in situ TiC particles in Fe (Ti) solid solution has been confirmed by XRD and EDS analysis.Over the last decade, researchers have demonstrated interest in tribology and prototyping by the laser cladding process. In-situ laser cladding enables the formation of a uniform clad by melting the powder to form desired composition from pure powder components. Since TiC has desirable properties, such as hardness, wear and corrosion resistance, Ti and Graphite (C) are used as a composite material (i.e., TiC) to increase hardness and wear resistance of AISI 1030 carbon steel.In previous papers, the effect of laser parameters on the clad quality was investigated. In this paper two combined parameters (i.e. the effective energy per unit area (Eeff) and the powder deposition density (PDD) were plotted in order to recognize the high quality clad zone. Afterward a range of clad conditions with constant and variable effective energies in high quality clad zone were conducted to study the role of the effective energy on morphology and distribution of TiC particles.Complete metallurgical bonding between substrate...