Advancement in additive manufacturing & numerical modelling considerations of direct energy deposition process

The development speed and application range of the additive manufacturing (AM) processes, such as selective laser melting (SLM), laser metal deposition (LMD) or laser-engineering net shaping (LENS), are ever-increasing in modern advanced manufacturing field for rapid manufacturing, tooling repair or surface enhancement of the critical metal components. LMD is based on a kind of directed energy deposition (DED) technology which ejects a strand of metal powders into a moving molten pool caused by energy-intensive laser to finally generate the solid tracks on the workpiece surface. Accurate numerical modelling of LMD process is considered to be a big challenge due to the involvement of multiple phase changes and accompanied mass and heat flows. This paper overviewed the existing advancement of additive manufacturing, especially its sub-category relating to the DED. LMD process is analyzed in detail and subsequently broken down to facilitate the simulation of each physical stage involved in the whole process, including powder transportation and dynamics, micro-mechanical modelling, formation of deposited track and residual stress on the substrate. The proposed modelling considerations and a specific CFD model of powder feeding will assist in accurately simulating the DED process; it is particularly useful in the field of aerospace manufacturing which normally has demanding requirement on its products

Numerical modelling of the gas-powder flow during the laser metal deposition for additive manufacturing

As one of the most popular additive manufacturing (AM) technologies in the aerospace industry, laser metal deposition (LMD) employs moving laser to melt the coaxially ejected metal powders near the laser focal point, forms a molten pool on the substrate and consequently traps the powders and solidifies the tracks to construct the components with complex geometry layer-by-layer. The mechanical properties and functionality-related performance of the deposited components by LMD depend on the factors such as metal powder’s material/shape, supply status of powders and gas, laser-related manufacturing parameters. According to these influencing factors, there are 4 sub-processes to be modelled in sequence to realize holistic LMD modelling: (1)CFD simulation of the gas-powder flow; (2)laser-powders interaction; (3)formation of molten pool due to laser irradiation with mass and heat addition; (4)solidification of molten pool with deposited metal powders and formed solid track. In this paper, gas-powder flow within the internal passages of laser deposition head and then ejecting from the nozzles’ tips were modelled and analyzed to give a well-depicted image of the related key physics during the LMD process. An in-depth study of the gas-powder flow in LMD via numerical simulation could give a better understanding of subsequent formation mechanism of molten pool and deposited tracks, which will eventually offer more controllable and optimized processing parameter sets to improve the functionality-related performance of LMDed parts

散料在锥仓中的静压接触状态与影响因素

Finite element models, which employ the Drucker-Prager yield criterion, have been developed to simulate the static contact statuses between conical silos and granular materials in 3 forms: the near contact, the sliding contact and the sticking contact. Contact conditions are established when 2 separated surfaces touch at normal direction while maintaining tangential relative movement. In general physical meaning, the surfaces in contact status have the following characteristics: 1) No penetration between each other; 2) The normal pressure and the tangent friction force may be transferred during contact; 3) Generally the normal pulling force cannot be transferred when surface separation occurs. Due to the symmetric property of conical structures, simplified two-dimensional contacting simulations are carried out in this paper, nonlinear finite element software ANSYS is used and the contacting surfaces between granular materials and conical silos are defined with rigid-to-flexible surface-to-surface contact pair. The target surfaces of conical silos are modeled with TARGE169 element and the contact surfaces of granular materials are modeled with CONTA171 element. During finite element analysis, conical silos and granular materials are meshed with two-dimensional solid element, PLANE42. The static contact statuses are investigated with conical silos containing different granular materials. The silo geometries vary at a dip angle of 20°, 33.7° and 45°. Sunflower seeds, corn, coal, rounded gravel and wheat are selected as the granular materials. Results show that the mechanical properties of granular materials (including bulk density, elastic modulus, Poisson's ratio, dilation angle, internal friction angle, cohesion) and silo designs (especially dip angle) have significant effects on the contact statuses at the interface between conical silos and granular materials: 1) For various granular material, 3 contact statuses, i.e. the form of near contact, sliding contact and sticking contact, can be found between granular materials and conical silo walls; 2) The contact statuses between conical silos and granular materials do not depend on (or not mainly depend on) any mechanical property of granular materials. The contact statuses are a combined effect of all mechanical properties of granular materials. Those granular materials with very small dilation angle may have the near contact statuses. Those granular materials with higher cohesive force usually present a smaller sticking contact area, and those granular materials with higher elastic modulus and bulk density usually present a larger sticking contact area than those with opposite material properties; 3) With the decreasing of conical silo depth, the near contact area disappears, the sliding contact area decreases and the sticking contact area increases. 4) Under the sliding contact status, the friction energy dissipation is mainly due to the relative motion between contact surfaces. Under the sticking contact status, the friction energy dissipation is mainly due to the elastic deformation because of the contact. The greater the sticking contact area, the more difficultly the silo discharges. The greater the sliding contact area, the more seriously the silo internal surfaces could be damaged. Since larger sticking/sliding contact area inevitably causes unloading difficulties or friction damage, contact statuses between granular materials and conical silos should be optimized in the silos design in order to boost storage efficiency

Modelling of powders dynamics for 3D printing of metal powders deposition

Application of 3D printing technologies for manufacturing metal products, are receiving ever-increasing attentions in advanced manufacturing fields e.g. aerospace, automobile and biomedical engineering. Laser metal deposition (LMD) is one of the promising 3D printing techiques suitable for depositing fully-densed critical metal components of complex geometry layer-by-layer. Based on directed energy deposition, LMD sprays metal powders into a moving molten pool generated by energy-intensive laser and consequently deposits solid tracks on the substrate surface with the movement of laser spot. Accurate numerical modelling of this 3D printing process is really a challenge due to involving in multiple physical-mechanical actions along with the mass and heat flows. This research reviews the existing 3D printing technologies using metal powders and especially focusing on the LMD process. To facilitate the numerical modelling, the 3D printing process for LMD is decomposed into several interlinked physical stages, including (1) powders convey and dynamics, (2) laser- metal powders interaction, (3) formation of molten pool due to laser irradiation with mass and heat addition; (4) solidification of molten pool and formation of solid tracks on the substrate. In this research, gas-powder flow within the internal passages of laser deposition head and powder dynamics after being ejected from the nozzles are modelled and analyzed to give a better understanding of the key physics during the LMD process. An in-depth study of the powder flow and its dynamics in LMD via numerical simulation will definitely facilitate subsequent formation mechanism of molten pool and deposited tracks. The proposed CFD model of powder convey and dynamics will finally assist in accurately simulating the whole LMD process and consequently help enhance the functionality-related performance of LMDed components

A study of performance characteristics of hybrid energy harvesting systems based on photovoltaics and thermoelectrics

The hybrid photovoltaic/thermoelectric generator (PV/TEG) technology is an advanced and efficient technology that combines the power from PV and TEGs to generate sustainable electricity. This hybrid approach optimizes energy output and ensures cleaner power by connecting IoT devices. Comprehensive studies have been conducted in the past to improve the efficiency of TEG modules. Various material parameters of TEG legs, such as the Seebeck coefficient, thermal conductivity, and electrical resistivity, and geometric parameters, including the cross-sectional area, leg size, leg height and the number of leg pairs, influence the TEG characteristic and determine with this the performance of the hybrid system. This work explores the influence of the TEG leg lengths and numbers of TEGs at various weather conditions on the power generation of a hybrid PV/TEG device, using an analytical model verified by experiments. The paper also analyses the performance characteristics of TEGs along with the hybrid PV/TEG system and concludes that the maximum output power from the TEG module in the hybrid PV/TEG model can be achieved by increasing the leg length

A pilot prototype production line for the hot-forming of aluminium alloy sheets with fast contact-cooling and multi-point tooling

This paper reports the study of the process chain for sheet metal forming using multi-point tooling for stamping at elevated temperatures and developing a complete production line integrating heating, intermediate fast-cooling, forming and aging. It aims to deliver a high-efficient and cost-effective sheet-metal forming technology with improved process capability and flexibility for the forming of high-strength sheet metal parts. Multi-point tooling sets are employed to test the flexibility of hot/warm-forming the lightweight high-strength metal sheets with fast tooling reconfigurability. The intermediate cooling with high cooling rates was achieved with a contact cooling system recently developed at the University of Strathclyde. With this pilot line, the aluminium sheets heated to the solution heat treatment (SHT) temperature were subjected to the intermediate cooling prior to forming with multi-point tooling. The cooling step is fast and controllable, with different cooling rates tested. The tests conducted on the pilot line demonstrated significant enhancement of the forming limit and manufacturing flexibility

Development, optimization, and testing of a hybrid solar panel concept with energy harvesting enhancement

Photovoltaics (PV) is one of the important technologies for electricity generation from renewable energies today and has an excellent environmental sustainability. It is a fast-growing market worldwide and also offers opportunities for aviation to intensify the use of renewable sources. Although the efficiency of PV systems has increased to a certain extent in recent years, a predominant part of solar radiation acting on a PV system is still lost to the environment through reflection and convection as well as heat radiation from the heated PV system. In addition, the efficiency of these systems decreases with increasing heating. Possible solutions for energy harvesting of this energy loss through thermoelectric (TE) have been investigated theoretically and in part experimentally in various cases but have not yet been transferred to larger PV systems. At the same time, cooling the PV system through thermogenerators (TEG) allows its efficiency to be increased. This contribution presents first results from investigations into the design and testing of hybrid PV/TEG systems, which aim to increase the efficiency and improve economic manufacturability of such systems. Among others, important design aspects of hybrid PV/TEG systems and integration of IoT elements (Internet of Things) are addressed and the development of an analytical model to optimise hybrid systems is presented

Simulation of thermal behaviours and powder flow for direct laser metal deposition process

Laser engineering net-shaping (LENS), based on directed energy deposition (DED), is one of the popular AM technologies for producing fully dense complex metal structural components directly from laser metal deposition without using dies or tooling and hence greatly reduces the lead-time and production cost. However, many factors, such as powder-related and laser-related manufacturing parameters, will affect the final quality of components produced by LENS process, especially the powder flow distribution and thermal history at the substrate. The powder concentration normally determines the density and strength of deposited components; while the thermal behaviours of melt pool mainly determines the cooling rate, residual stress and consequent cracks in deposited components. Trial and errors method is obviously too expensive to afford for diverse applications of different metal materials and various manufacturing input parameters. Numerical simulation of the LENS process will be an effective means to identify reasonable manufacturing parameter sets for producing high quality crack-free components. In this paper, the laser metal powder deposition process of LENS is reported. The gas-powder flow distribution below the deposition nozzle is obtained via CFD simulation. The thermal behaviours of substrate and as-deposited layer/track during the LENS process are investigated by using FEM analysis. Temperature field distributions caused by the moving laser beam and the resultant melt pool on the substrate, are simulated and compared. The research offers a more accurate and practical thermal behaviour model for LENS process, which could be applied to further investigation of the interactions between laser, melt pool and powder particles; it will be particularly useful for manufacturing key components which has more demanding requirement on the components’ functional performance

Numerical study on nozzle-field cooling of heated aluminium blanks for hot-stamping

Nozzle-field cooling is a popular cooling technology which uses a flexible array of low-pressure gas jets to quickly cool down components in a device working in conventional atmosphere. This cooling process is energy saving, free of toxic gases, and it can reduce workpiece distortion during cooling. In this study, nozzle-field cooling is adopted for a potential, fast cooling process for large metal blanks. Numerical simulations were conducted to investigate the performance of a designed cooling tool with different design parameters. In this paper, simulation results are presented, along with several considerations for the nozzle-field cooling system design

On the modelling of powder flow, material addition and thermal behaviours in LENS process

Application of 3D printing technologies for fabricating various metal products are receiving ever-increasing attention in the advanced manufacturing fields, e.g. aerospace, automobile and biomedical engineering. Laser engineering net shaping (LENS) is one of the promising 3D printing techniques that suitable for depositing fully-densed critical metal components of complex geometry layer-by-layer. Based on directed energy deposition, LENS process sprays metal powders into a moving molten pool generated by an energy-intensive laser and consequently deposits solid tracks on the substrate surface with the movement of the laser spot. Accurate numerical modelling of this additive manufacturing process is really a challenge due to involving in multiple physical-mechanical interactions along with the mass and heat flows. This research first reviews the existing metal powders technologies using and especially focusing on the LENS process. Then, powder dynamics for the metal powders being conveyed by carrier gas within the internal passages of laser deposition head and after being ejected from the nozzles are modelled and analysed to give a better understanding of the key physical stage during the LENS process. Material addition on the deposition layer is modelled by using finite element addition; thermal behaviours of substrate and temperature distribution caused by the moving laser beam during the LENS process are also studied by using FEM analysis. An in-depth study of the powder flow and its dynamics in LENS process via numerical simulation will facilitate subsequent research on mass addition on the deposited layers. An accurate thermal-mechanical model could be applied to further investigate the interactions between laser, molten pool and deposited track and finally predict the residual stress and possible cracks on the deposited layers. This research will be particularly useful for investigating the production of key complex components which are made by LENS process due to difficult-to-machine materials properties and have more demanding requirement on their functional performance