This study examines whether post-deposition aging alone, without solutionizing and quenching, can recover strength in AA6060 builds produced by friction screw extrusion additive manufacturing (FSEAM), a solid-state process that avoids melting-related defects. In FSEAM, the feedstock is preheated inside the printhead by a rotating threaded tool before deposition, which can generate temperatures high enough to dissolve strengthening precipitates. If cooling during deposition is sufficiently rapid, a supersaturated solid solution may be retained, enabling strength recovery by aging only. AA6060, an Al–Mg–Si alloy with a relatively low critical cooling rate, was selected to assess this concept. Builds were fabricated at deposition velocities of 100-500 mm/min. Samples produced above 200 mm/min showed no major defects, and printhead temperatures increased with deposition velocity, exceeding the alloy solvus temperature at velocities above 200 mm/min. After fabrication, samples were aged at 170 °C for 3 h and 20 h, omitting the conventional solutionizing and quenching steps of the full T6 treatment. Aging significantly increased hardness and strength, particularly in the top layers of builds processed above the solvus temperature. Hardness reached 85-88 HV, compared with about 76 HV for the T6 feedstock and 79 HV after a full T6 treatment. The ultimate tensile strength increased to approximately 230 MPa after aging-only, compared with about 211 MPa for the feedstock. These results indicate that solute supersaturation can be retained during FSEAM and exploited by post-deposition aging alone. The findings show that key elements of T6 strengthening can be partially integrated into FSEAM, reducing post-processing requirements.

Friction surface cladding (FSC) is a newly developed solid-state cladding process. The effect of the process parameters on the residual stress is one of the aspects of this new process which has very high potential for research. The present study has been carried out to investigate the effect of three parameters; h0: predefined height from the substrate, Ω: tool rotation velocity and Vf: the clad material supply feed rate on the residual stress. A design of experiments method was used to select the parameter values in a validated process simulation model. The results showed that the effects of the three parameters are interrelated. Both Ω and h0 have a linear effect on the residual stress value and changing the Vf, changes the slope of this linear effect. Vf itself may have linear or nonlinear effect on the residual stress. It is found that for some values of Vf, variation of Ω and h0 does not affect the residual stress. An optimized set of the three parameters is also suggested.

Manufacturing through powder-bed fusion laser-beam (PBF-LB) enables innovative part design strategies, facilitating weight reduction, and capitalizing on the metallurgical conditions developed during the manufacturing of designed alloys. Consequently, Al-based light alloys hold enormous potential for reducing fuel consumption in the transport industry. Fabricating such small features has a significant impact on heat dissipation, thereby affecting microstructure, porosity, and, consequently, mechanical properties. This study proposes the use of near-net shape miniaturized tensile specimens in both horizontal and vertical orientations to characterize Al-Mg-Sc-Zr, commercially known as Scalmalloy®, and AlSi10Mg, two aluminum alloys typically employed in PBF-LB. The size and distribution of both grains and pores were analyzed and compared, with Al-Mg-Sc-Zr exhibiting a more competitive set of properties compared to AlSi10Mg. This difference also influences mechanical properties. Al-Mg-Sc-Zr demonstrated double the Ultimate Tensile Strength (UTS) of AlSi10Mg (450 MPa versus 225 MPa) and higher hardness values (142 HV30 versus 75 HV30), with similar elongation in both alloys (approximately 12–16%), owing to its fine microstructure and low porosity of the near-net shape miniaturized tensile specimens. Neither material exhibited any form of anisotropy. In-situ SEM tensile tests were conducted to monitor damage evolution, allowing continuous observation of crack nucleation and propagation through imperfections typically encountered in PBF-LB. Despite differences in static strength, the fracture surfaces of the samples displayed a ductile behavior in both materials.

Solid-state additive manufacturing may solve critical issues typically arising during fusion-based additive manufacturing of high-strength aluminium alloys. In this work, the recently introduced Friction Screw Extrusion Additive Manufacturing (FSEAM) process was employed to manufacture wall-like rectangular builds of AA6060 T6 deposited with deposition speeds from 300 mm/min to 500 mm/min. All builds were manufactured at a tool rotation rate of 400 rpm with 1 mm layer thickness. The volumetric supply rates were adjusted to maintain constant build width. Solid builds were formed without major defects over the full range of deposition speeds. The process generated sufficient normal force and heat at all deposition speeds which resulted in manufacturing of defect free builds. The resulting average grain size was consistently below 5 micrometer throughout all builds independent of deposition speed or location through the height. Microhardness measurements revealed a decrease in hardness from a feedstock value of 80 HV to around 50 HV in all manufactured builds. Tensile tests in the building direction showed consistent results for all the samples as a result of defect-free parts, demonstrating a tensile strength of approximately 150 MPa, yield strength of 100 MPa, and uniform elongation of 12-15%. The fracture surfaces revealed large amounts of dimples at all deposition speeds in line with the high degree of plastic deformation preceding fracture observed from the tensile tests. The obtained results indicated that FSEAM is a promising process for solid-state additive manufacturing of aluminium alloys.

The Friction Screw Extrusion Additive Manufacturing (FSEAM) process is a newly created process for additive manufacturing of low weight-high strength aluminum and magnesium alloys in the solid state which are unsuited for many fusion-based approaches. The process is based on a rotating threaded tool located within a stationary housing that is equipped with a feeding mechanism. The dimensions and shape of the deposited layers can be controlled through a dedicated printhead design. This work reports the results on the fabrication of rectangular structures composed of AA6060 T6 feedstock. The study mainly focused on the influence of the feed ratio on the quality, the microstructure and mechanical properties of the fabricated builds. The feed ratio, defined as the fraction of volume of material deposited per unit of time relative to the volume of material necessary per unit of time for a given cross sectional shape, was varied between 0.995 and 1.7. Solid builds free from macroscopic defects were fabricated at feed ratios of 1.3 and above. Tensile tests performed on samples from the interior of the structure in the build direction showed values for ultimate tensile strength and homogeneous elongation in excess of 100 MPa and 12.5 %, respectively. At feed ratios close to one, layers were formed with fabrication defects, such as macro voids and insufficiently bonded areas, that caused a significant reduction in the elongation values to typically below 5 %. The average grain size of the deposited layers was 3 - 4 micrometers for all builds. The hardness of the builds was reduced from 80 HV to about 40 HV which was ascribed to the thermo-mechanical processes taking place during transport of the feedstock material by the threaded tool and the subsequent deposition. The appearance of the builds and the occurrence of fabrication defects could be explained using a descriptive model by the way the feedstock material was distributed underneath the printhead during deposition. Lateral plastic deformation occurred both within the current layer being built and in the previously deposited layers. Further exploratory tests of the FSEAM process showed that the deposition speed can be increased to 490 mm/min at a favorable feed ratio of 1.3, corresponding to a build rate of about 400 cm3/hour, while maintaining good deposition without macroscopic defects demonstrating the future potential of the process.

The bond strength is an essential property of cladded products, which are produced by deposition processes such as friction surface cladding (FSC). Friction and severe plastic deformation of the deposited material cause the process to take place at elevated temperatures, and inhomogeneous cooling after the deposition process can lead to the formation of residual stresses that influence the remaining bond strength. A novel simulation method for the evaluation of the residual stress distribution in clad layer and substrate after the cladding of AA6060 onto an AA2024 substrate is proposed in this study. The effect of residual stresses on the bond strength was correlated with data gathered from 3-point bending tests aimed at the determination of the mechanical properties at the clad layer–substrate interface. The results show that on the one side, the occurrence of a higher compressive residual stress magnitude increases the bond strength, but on the other side, this relationship is not always true for average tool temperature, tool rotating speed, normal force, and tool tilt angle. Therefore, it is necessary to investigate the effect of average tool temperature, tool rotating speed, normal force, and tool tilt angle parameters on the residual stress to find the best process window for carrying out the process to have optimal bond strength.

Solid-state additive manufacturing constitutes a worthwhile alternative for many precipitation-based aluminium alloys that cannot be processed through fusion-based approaches due to metallurgical problems. In this work, the newly developed solid-state friction screw extrusion additive manufacturing (FSEAM) approach has been employed to study the processability of AA6060 T6 as a function of the printing velocity. Various wall-like builds were fabricated at printing velocities of 100 mm/min to 250 mm/min by deposition of 50 layers of 1 mm thickness, 14 mm width, and 150 mm length. No major defects were observed in cross section, and the microstructure showed equiaxed grains with an average size of 2–4 μm for all builds. Promising mechanical properties were obtained for all tensile test specimens extracted in the deposition direction of the layers. For specimens extracted in the build direction, only the builds fabricated with sufficiently high normal force to ensure proper bonding between successively deposited layers showed similar results to the deposition direction. The relatively high temperatures obtained during fabrication led to the dissolution of strengthening precipitates for the 150–250 mm/min samples as indicated by serrated yielding effects. Post-manufacturing heat treatment of these samples was successful, partially restoring the feedstock hardness.

Additive manufacturingAdditive manufacturing in the solid state opens up possibilities for many alloys that are not suitable for fusion-based approaches. Following the advances in friction-based joiningJoining processes for high-strengthStrength aluminum and magnesium alloysMagnesium alloys, the Friction Screw ExtrusionScrew extrusion Additive ManufacturingAdditive manufacturing (FSEAM) process has been developed for deposition of thin layers for cladding and additive manufacturingAdditive manufacturing on a variety of substrates. In this work, the first results on the manufacturing of wall-like rectangular builds from AA6060T6AA6060T6 are reported. Multiple layers of about 15 mm width and 1 mm thickness were deposited with print velocities of 100–250 mm/min at constant toolTools rotation speed. Solid walls were formed without major macroscopic defects. Promising mechanical propertiesMechanical properties were measured with a yield strengthStrength of about 80 MPa and a tensile strengthTensile strength increasing from 112 to 144 MPa as function of the print velocity. The material was characterized by a fine microstructureMicrostructure with an average grain size below 10 μm for all builds. At the microscale, strings of unbonded regions have been observed at lower print velocities possibly related to insufficient mixing of the deposited material with the previous layer during manufacturing leading to reduced ductility. The observed results are encouraging, indicating that additive manufacturingAdditive manufacturing of aluminum alloys through FSEAM is feasible after further optimization of the process.

Predicting rolling bearing fatigue life requires knowledge of the three-dimensional (3D) stress fields in the roller and raceway near the lubricated contact. Owing to the increasingly severe operating conditions, the effect of localized features such as surface roughness, subsurface inclusions, and even the crystallographic structure of the material becomes important. Achieving such detail requires (locally) extremely dense gridding in simulations, which in 3D is a major challenge. Multigrid techniques have been demonstrated to be capable of solving such problems. In this study, multigrid techniques are shown to further increase the efficiency of the solution by exploiting local grid refinement while maintaining the simplicity of a uniform discretization. This is achieved by employing increasingly finer grids only locally, where the highest resolution is required. Results are presented for dry contact and elastohydrodynamically lubricated contact cases, circular as well as elliptic, with varying crystallographic structure, and with surface roughness. The results show that the developed algorithm is very well suited for detailed analysis, with also excellent prospects for computational diagnostics involving actual material crystallographic structure from electron backscatter diffraction measurements.

The optical properties of unidirectional (UD) fiber reinforced thermoplastic (FRTP) tapes were characterized to enable a better description of the heating phase in laser-based manufacturing process of FRTP composites. The tapes included PP-GF (glass-fiber) 45% fiber volume content (FVC), PVDF-CF (carbon-fiber) 45% FVC, PVDF-CF 60% FVC and PA12-CF 60% FVC. The transmittance of the tapes was found to be 0.00-0.2% whereas the reflectance was 9.8-11.8% corresponding to a refractive index of 1.91-2.05. The anisotropic reflectance measurements, as obtained through a gonioreflectometry, were used to fit the bidirectional reflectance distribution function (BRDF) for the first time. The obtained BRDF parameters sigma t and sigma f had a range of 0.1-0.18 and 0.006-0.015, respectively, for different tapes. Employing the new BRDF parameters empowers a more accurate prediction and optimization of the process settings of laser-based composite manufacturing. Laser-assisted tape placement/winding (LATP/LATW), anisotropic reflection, unidirectional tape (UD), bidirectional reflection modelling.

A numerical process simulation framework is introduced in this paper to describe and predict the process temperature evolution during the laser-assisted tape winding (LATW) process of a type-IV pressure vessel made of glass-reinforced high-density polyethylene (G/HDPE). A local optical-thermal model is fully coupled with a global thermal model for the simulation of continuous adjacent hoop winding cases. The predicted tape and substrate temperatures are compared with the experimental data to validate the process model’s effectiveness. The inline temperature was measured by an infrared thermographic camera during the continuous winding. The continuous process temperature of the substrate is affected significantly due to the previously wound layers including the pressure vessel, and a gradual increase of the temperature of the roller and the air inside the liner. A considerable temperature increase calculated as 80-120°C takes place for the substrate during winding of two consecutive layers of (G/HDPE) prepreg tape at the liner ends. The influence of pressure vessel size on the tape and substrate temperatures is investigated for different liner radii using the validated process model. The peak substrate temperature is found to increase approximately 45°C by reducing the radius of the pressure vessel from 272 mm to 68 mm while maintaining all other process conditions constant.

Laser-assisted tape winding is an automated process to produce tubular or tube-like continuous fiber-reinforced polymer composites by winding a tape around a mandrel or liner. Placing additional layers on a previously heated substrate and variation in material and process parameters causes a variation in the bonding temperature of fiber-reinforced thermoplastic tapes which need to be understood and described well in order to have a reliable manufacturing process. In order to quantify the variation in this critical bonding temperature, a comprehensive temperature analysis of an adjacent hoop winding process of type-IV pressure vessels is performed. A total of five tanks are manufactured in which three glass/HDPE tapes are placed on an HDPE liner. The tape and substrate temperatures, roller force and tape feeding velocity are measured. The coefficient of variation for each round is characterized for the first time. According to the statistical analysis, the coefficient of variation in substrate temperature is found to be approximately 4.8–8.8% which is larger than the coefficient of variation of the tape temperature which is 2.1–7.8%. The coefficient of variations of the substrate temperatures in the third round decrease as compared with the coefficient of variations in the second round mainly due to the change in gap/overlap behavior of the deposited tapes. Fourier and thermographic analysis evince that the geometrical disturbances such as unroundness and eccentricity have a direct effect on the temperature variation. In addition to the temperature feedback control, a real-time object detection technique with deep learning algorithms can be used to mitigate the unwanted temperature variation and to have a more reliable thermal history.

Laser powder-bed fusion (LPBF) technology is one of the additive manufacturing (AM) processes that uses metal powder to produce parts for various industry sectors such as medical, aerospace, automotive and oil & gas. As an 'additive' based process, the material is selectively melted by a focused laser. By this working principle material is added in a layer-by-layer approach only where is needed. Therefore, this technology enables a high reduction of waste by avoiding chips typically generated in 'subtractive' based processes such as milling and drilling. However, to ensure lower waste consumption the metal powder surrounding the solidified part must be reused in subsequent build jobs. Current knowledge on the effect of powder reuse on LPBF builds is mostly limited to titanium- and nickel- based alloys. The aim of this paper is to study the effect of powder reuse on Al-Mg-Sc-Zr, a high strength aluminium-based alloy, manufactured by LPBF. Here, powder properties such as morphology, composition, particle size distribution are studied of virgin (pristine) and reused Al-Mg-Sc-Zr powder. The mechanical properties of specimens made of virgin powder and after four build cycles are analysed and compared to assess the influence of a mixture of virgin and reused powder material on the consolidated material properties. In general, the powder does not present large differences in composition and morphology, only the reused powder presents coarser particle size distribution (PSD) as previously observed in other alloy compositions. The microstructure of the studied specimens is very similar unlike the porosity. The specimens built with reused powder show a few small micro-sized pores which do not show significant differences in the mechanical properties. In fact, the ultimate tensile strength (TITS) and elongation to break of specimens, respectively built with virgin and reused powder are 565 MPa, 13% and 537 MPa, 11%. Based on the obtained results, it is concluded that it is feasible to reuse Al-Mg-Sc-Zr powder in four subsequent build jobs with proper powder sieving and a rejuvenation step mixing 40% of virgin powder.

This paper presents an effective process optimization methodology for laser assisted tape winding (LATW) of complex part geometries by means of a numerical optical-thermal model. A winding path on the cylindrical and ellipsoidal (dome) part of a pressure vessel is considered with varying tooling curvature. First, the process model output is verified with the literature data based on the laser intensity distribution. Then, the transient laser irradiation and temperature distributions on the tape and substrate are described comprehensively. It is shown that the maximum laser intensity increases approximately by 80% and the process (bonding) temperature changes by 80 °C at the intersection of the cylindrical and dome section of the pressure vessel. In order to keep the transient process temperature constant, a robust optimization scheme is utilized by means of a genetic algorithm. The design variable is determined as the total laser power and temperature constraints are defined. The proposed optimization methodology regulates the temperature within 1.5 °C variation with respect to the desired value. In order to compensate the transient local curvature effects on the process temperature, the total laser power varies approximately between 30% and 175% of the reference (non-optimized) case.

For AM processes—specifically Laser Powder Bed Fusion (L-PBF) processes—powder flowability is essential for the product quality, as these processes are based on a thin layer spreading mechanism. However, the available techniques to measure this flowability do not accurately represent the spreading mechanism. Hence, this paper presents two novel applicator tools specifically designed to test the spreadability of l-PBF powders in thin layer application. The results were checked by running standard tests to analyze the powder morphology, moisture content, chemical composition and flowability using the Hall-flowmeter. For this study, four common l-PBF metal powders were selected: Inconel 718, Ti6Al4V, AlSi10Mg and Scalmalloy. From the as-received state, drying (vacuum and air) and moisturizing treatments were applied to compare four humidity states and investigate the feasibility of pre-treating the powders to remove moisture, which is known to cause problems with flowability, porosity formation and enhanced oxidation. The tests reveal that AlSi10Mg is the most susceptible alloy to moisture and oxygen pick-up, considerably decreasing the spreadability and relative density on the build platform. However, the results also reveal how challenging the direct measurement of moisture levels in metal powders is.

Advanced thermoplastic composites manufacturing using laser assisted tape placement or winding (LATP/LATW) is a challenging task as monitoring and predicting nip point (bonding) temperature are difficult especially on curved surfaces. A comprehensive numerical analysis of the heat flux and temperature distribution near the nip point is carried out in this paper for helical winding of fiber reinforced thermoplastic tapes on a cylindrically shaped mandrel. An optical ray-tracing technique is coupled with a numerical heat transfer model in the process simulation tool. The developed optical-thermal model predictions were compared with experimental data available in literature to validate its effectiveness. The influences of winding/placement angle, mandrel curvature and tape width on the incident angles, the laser absorbed intensity, and the process temperature distribution are studied extensively using the validated model. Winding/placement angle has a considerable effect on the temperature distribution. Increase in winding angle results in a higher temperature for tape due to more reflections coming from the substrate. On the other hand, substrate temperature decreases as the winding angle increases due to a decrease in the laser incident angles based on the local surface curvature. An increase in mandrel curvature results in higher nip point temperatures for substrate and lower one for tape. Different mandrel sizes for 90 ∘ placement path do not have a strong effect on the substrate process temperature as for other winding angles because of less curvature change of the corresponding irradiated area. Tape width causes local temperature variations at the edges of the tape/substrate. In order to obtain the desired process temeprature during LATW or LATP processes, the laser intensity distribution on the tape and substrate surfaces should be regulated.

Ablation of bulk polycrystalline zinc in air is performed with single and multiple picosecond laser pulses at a wavelength of 1030 nm. The relationships between the characteristics of the ablated craters and the processing parameters are analyzed. Morphological changes of the ablated craters are characterized by means of scanning electron microscopy and confocal laser scanning microscopy. Chemical compositions of both the treated and untreated surfaces are quantified with X-ray photoelectron spectroscopy. A comparative analysis on the determination of the ablation threshold using three methods, based on ablated diameter, depth and volume is presented along with associated incubation coefficients. The single pulse ablation threshold value is found to equal 0.21 J/cm2. Using the calculated incubation coefficients, it is found that both the fluence threshold and energy penetration depth show lesser degree of incubation for multiple laser pulses.

A combined approach of laser-induced forward transfer (LIFT) and chemical etching of pure metal films is studied to fabricate complex, free-standing, 3-dimensional gold structures on the few micron scale. A picosecond pulsed laser source with 515 nm central wavelength is used to deposit metal droplets of copper and gold in a sequential fashion. After transfer, chemical etching in ferric chloride completely removes the mechanical Cu support leaving a final free-standing gold structure. Unprecedented feature sizes of smaller than 10 pm are achieved with surface roughness of 0.3 to 0.7 pm. Formation of interfacial mixing volumes between the two metals is not found confirming the viability of the approach.

The friction development between Aluminium AA1050 and Dural AA2024 is studied. Continuous full surface rotational sliding experiments of AA1050 over AA2024 were performed at temperatures between 150 and 350 C and at contact pressures between 2 and 15 MPa. The required torque was measured as function of rotation angle. A model is set up for the evolution of the friction coefficient, which takes into account temperature, normal pressure and sliding distance. Validation of the model is done by implementation in a finite element program and reproduction of observed behaviour. (C) 2017 The Authors. Published by Elsevier Ltd.

Friction surface cladding is a newly developed solid state cladding process to manufacture thin metallic layers on a substrate. In this study the influence of process conditions on the clad layer appearance and the mechanical properties of both the clad layer and the substrate were investigated. Thin layers of commercially pure aluminum (approximately 0.2mm thick and 20mm wide) could be successfully deposited on top of an AA2024-T351 substrate within a range of process conditions. The quality of the deposited layers was shown to be highly dependent on the process temperature. Homogeneous, well bonded and defect free layers could be deposited within a 300–420°C temperature range. At lower process temperatures no continuous layers were deposited, whereas at higher process temperatures mixing of the clad material with the substrate took place. Thermal simulations confirmed the relation between the process conditions and the amount of heat generated. An analytical model was developed to predict the occurrence of mixing. Additional bending and corrosion experiments demonstrated the high bonding quality and proper intrinsic and sacrificial corrosion performance of the manufactured layers.