DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATION

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATIO

The potential of additive manufacturing in the smart factory industrial 4.0: A review

Additive manufacturing (AM) or three-dimensional (3D) printing has introduced a novel production method in design, manufacturing, and distribution to end-users. This technology has provided great freedom in design for creating complex components, highly customizable products, and efficient waste minimization. The last industrial revolution, namely industry 4.0, employs the integration of smart manufacturing systems and developed information technologies. Accordingly, AM plays a principal role in industry 4.0 thanks to numerous benefits, such as time and material saving, rapid prototyping, high efficiency, and decentralized production methods. This review paper is to organize a comprehensive study on AM technology and present the latest achievements and industrial applications. Besides that, this paper investigates the sustainability dimensions of the AM process and the added values in economic, social, and environment sections. Finally, the paper concludes by pointing out the future trend of AM in technology, applications, and materials aspects that have the potential to come up with new ideas for the future of AM explorations

Size effects on geometrical accuracy for additive manufacturing of Ti-6Al-4V ELI parts

A comprehensive investigation of the size and geometry dependency of the dimensional accuracy of direct metal laser sintering (DMLS) for Ti-6Al-4V ELI is presented. For features such as walls, squares, tubes, and rods with different sizes, the percent error significantly increases with decreasing the feature size. The polynomial function a t-b is suggested to describe this size dependency of the dimensional error where a and b are parameters depending on the geometry, material, and DMLS process parameters. This function is used to successfully predict the dimensional error in DMLS of two spinal cages. Therefore, these functions can be used to account for these errors in DMLS by design change or by adjusting DMLS scaling factors. Furthermore, the inconsistency of the DMLS-manufactured dimensions within the feature is shown to be in the same range of the dimensional inconsistency for features located at different positions on the build platform, implying that the location of the feature on the build platform has a negligible effect on the dimensional accuracy. Finally, it is shown that the error in the position accuracy of DMLS-manufactured features is negligible when the size dependency of the dimensional features is considered in the measurements

Coating Techniques for Functional Enhancement of Metal Implants for Bone Replacement: A Review

To facilitate patient healing in injuries and bone fractures, metallic implants have been in use for a long time. As metallic biomaterials have offered desirable mechanical strength higher than the stiffness of human bone, they have maintained their place. However, in many case studies, it has been observed that these metallic biomaterials undergo a series of corrosion reactions in human body fluid. The products of these reactions are released metallic ions, which are toxic in high dosages. On the other hand, as these metallic implants have different material structures and compositions than that of human bone, the process of healing takes a longer time and bone/implant interface forms slower. To resolve this issue, researchers have proposed depositing coatings, such as hydroxyapatite (HA), polycaprolactone (PCL), metallic oxides (e.g., TiO2, Al2O3), etc., on implant substrates in order to enhance bone/implant interaction while covering the substrate from corrosion. Due to many useful HA characteristics, the outcome of various studies has proved that after coating with HA, the implants enjoy enhanced corrosion resistance and less metallic ion release while the bone ingrowth has been increased. As a result, a significant reduction in patient healing time with less loss of mechanical strength of implants has been achieved. Some of the most reliable coating processes for biomaterials, to date, capable of depositing HA on implant substrate are known as sol-gel, high-velocity oxy-fuel-based deposition, plasma spraying, and electrochemical coatings. In this article, all these coating methods are categorized and investigated, and a comparative study of these techniques is presented

Modeling and optimization approaches of laser-based powder-bed fusion process for ti-6al-4v alloy

Laser-based powder-bed fusion (L-PBF) is a widely used additive manufacturing technology that contains several variables (processing parameters), which makes it challenging to correlate them with the desired properties (responses) when optimizing the responses. In this study, the influence of the five most influential L-PBF processing parameters of Ti-6Al-4V alloy—laser power, scanning speed, hatch spacing, layer thickness, and stripe width—on the relative density, microhardness, and various line and surface roughness parameters for the top, upskin, and downskin surfaces are thoroughly investigated. Two design of experiment (DoE) methods, including Taguchi L25 orthogonal arrays and fractional factorial DoE for the response surface method (RSM), are employed to account for the five L-PBF processing parameters at five levels each. The significance and contribution of the individual processing parameters on each response are analyzed using the Taguchi method. Then, the simultaneous contribution of two processing parameters on various responses is presented using RSM quadratic modeling. A multi-objective RSM model is developed to optimize the L-PBF processing parameters considering all the responses with equal weights. Furthermore, an artificial neural network (ANN) model is designed and trained based on the samples used for the Taguchi method and validated based on the samples used for the RSM. The Taguchi, RSM, and ANN models are used to predict the responses of unseen data. The results show that with the same amount of available experimental data, the proposed ANN model can most accurately predict the response of various properties of L-PBF components

On Coating Techniques for Surface Protection: A Review

A wide variety of coating methods and materials are available for different coating applications with a common purpose of protecting a part or structure exposed to mechanical or chemical damage. A benefit of this protective function is to decrease manufacturing cost since fabrication of new parts is not needed. Available coating materials include hard and stiff metallic alloys, ceramics, bio-glasses, polymers, and engineered plastic materials, giving designers a variety freedom of choices for durable protection. To date, numerous processes such as physical/chemical vapor deposition, micro-arc oxidation, sol–gel, thermal spraying, and electrodeposition processes have been introduced and investigated. Although each of these processes provides advantages, there are always drawbacks limiting their application. However, there are many solutions to overcome deficiencies of coating techniques by using the benefits of each process in a multi-method coating. In this article, these coating methods are categorized, and compared. By developing more advanced coating techniques and materials it is possible to enhance the qualities of protection in the future

Process-property-geometry correlations for additively-manufactured Ti–6Al–4V sheets

This study presents results and statistical analysis of more than 300 mechanical tensile testing and their associated microstructure, microhardness, porosity, and elemental analysis for additively-manufactured Ti–6Al–4V sheets. Square sheets of 84 mm with thicknesses ranging from 0.5 mm to 1.6 mm are fabricated using direct metal laser sintering (DMLS) and traditionally-manufactured sheets are used for the benchmark experiments. The effect of thickness, orientation, distance from free edges, and height and their correlation to material microstructure and thermal history as dictated by DMLS process parameters are investigated. First, a method is developed to differentiate the specimen geometry effect on mechanical properties from the effects of material/manufacturing process, allowing specimen geometry-independent study of the thickness effects on DMLS-manufactured sheets. The results show that the tensile strength linearly decreases by decreasing the thickness while there is no statistically significant variation in elongation at break. The tensile strength increases as the orientation angle of the specimens increases to 30°–45° followed by decreasing to the vertically-oriented specimens; the reverse of this behavior is observed for elongation at break. Furthermore, the tensile strength slightly decreases by increasing the height till ~40 mm followed by a more severe decrement at higher heights. Finally, no significant variation of tensile strength is observed by variation of the specimen distance from the free edges. Moreover, the microhardness variations with respect to thickness and height are studied. These observations are correlated to the porosity volume fraction variation and their elongation direction, prior β grain width variation, and their relationships to the thermal history of the sheets during the DMLS process, β nanoparticle volume fraction, martensitic α’ decomposition to α+β and α” orthorhombic structure, and Oxygen content variation

Heat treatment of Ti-6Al-4V alloy manufactured by laser-based powder-bed fusion: Process, microstructures, and mechanical properties correlations

The present study comprehensively a investigates the correlations between the heat treatment process parameters (temperature, time, and cooling rate) with the microstructure and tensile properties of Ti-6Al-4V samples manufactured by laser-based powder-bed fusion (L-PBF) additive manufacturing process. Understanding these correlations results in better engineering of the microstructure to obtain a desirable combination of ductility and strength for different applications. The primary, secondary, and tertiary α\u27 with β particles are seen in the microstructure of the as-built sample. The heat treatment at below β transus temperature (Tβ) shows a similar microstructure to the as-built samples with a considerable increment in elongation. Increasing temperature in the range of α + β region illustrates the formation of α + β lamellar structure (primary, and secondary α) with increasing elongation and decreasing tensile strength. While increasing temperature above Tβ deteriorates the mechanical properties due to increasing the thickness of α lath, increasing the time of annealing leads to increasing and then decreasing elongation. Increasing the cooling rate from furnace cooling to air cooling and finally to water quenching results in increasing yield strength and ultimate tensile strength and decreasing the elongation due to the microstructural features such as α\u27, α, and β. Finally, the fractography of brittle and ductile samples is presented and correlated with the obtained microstructural and mechanical properties

Surface roughness and densification correlation for direct metal laser sintering

The increasing use of metal additive manufacturing (AM) technologies, such as direct metal laser sintering (DMLS), requires an in-depth understanding of how the optimum DMLS process parameters can be determined to achieve the target properties, such as reduced defect densities and/or desired surface characteristics. To this end, it is important to develop simple strategies that assess part quality and are fast and cost-effective. In this study, the in-plane surface roughness of components fabricated with AM is correlated with the DMLS process parameters and fractional density, enabling rapid and accurate indirect determination of the fractional density of AM components through surface roughness measurements. To this end, two sets of DMLS process parameters and a geometrical parameter are utilized to fabricate more than 150 rectangular cubic samples with varying parameters. All the samples are fabricated using Ti-6Al-4 V powder, which is a frequently used metal alloy for DMLS. Second, two line roughness parameters are defined and measured for all the samples, and their correlations with the DMLS and geometrical parameters are reported. Third, the fractional densities of all the samples are measured and their correlations with the DMLS process parameters are demonstrated. Lastly, a thorough analysis of the observed correlations between the line roughness parameters and fractional density are discussed