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In the optimisation of processing parameters for additive manufactured parts using, e.g. selective laser melting (SLM) or electron beam melting, the measurement of the part densities is essential and of high interest. However, there is no common standard. Different institutes and system providers are using their own principles and guidelines. This study investigates the accuracies of the three measurement principles: Archimedes method, microscopic analysis of cross sections and X‐ray scanning.

A total of 15 test samples on five density levels (densities between 90 and 99.5 per cent) were produced using the SLM process. The samples are analysed regarding the accuracy of the measurement principles and their reproducibility taking into account influencing parameters like the buoyancy of a sample in air (Archimedes method) or different magnifications of a cross section.

The Archimedes method shows a very high accuracy (±0.08 per cent for high densities) and repeatability (±<0.1 per cent) on all density levels. In contrast to the Archimedes method, taking a micrograph of a specific cross section allows to influence the resulting density and the coefficient of variation reaches values>4 per cent. However, for low porosities, mean densities are comparable to the results of the Archimedes method even though calculated densities are typically somewhat too high. The advantage of the image guided analysis (2D and 3D) is getting more information about the distribution, size and form of pores in the part.

The findings do not only refer to metallic parts but generally to all parts having a specific porosity. The study is a contribution to the American Society for Testing and Materials initiative F42 “Additive Manufacturing Technology” and especially to the subcommittee “test methods”.

The purpose of this paper is to examine the effect of internal pores on the tensile properties of a Co–Cr–Mo alloy fabricated by selective laser melting (SLM).

The size and volume fraction of pores were controlled through high temperature annealing (HTA) and hot isostatic pressing (HIP).

After HTA, the size and fraction of pores decreased compared with the as-built SLM sample, and no pores were observed after HIP. Tensile tests of the HTA and HIP samples showed nearly similar tensile deformation behavior. From the results, the authors found that the size of the internal pores formed in the SLM process had little effect on the tensile properties. The as-built SLM sample had less elongation than the HTA and HIP samples, which would not the effect of porosity, but rather the effect of the residual stress and the retained ε phase after the SLM process.

Although pores are a main factor that influence the mechanical properties, the effect of pores on the tensile properties of Co–Cr–Mo alloys fabricated by SLM has not been studied. Therefore, in this study, the effect of pores on the tensile properties of a Co–Cr–Mo alloy fabricated by SLM was studied.

A recent study confirmed that the particle size distribution of a metallic powder material has a major influence on the density of a part produced by selective laser melting (SLM). Although it is possible to get high density values with different powder types, the processing parameters have to be adjusted accordingly, affecting the process productivity. However, the particle size distribution does not only affect the density but also the surface quality and the mechanical properties of the parts. The purpose of this paper is to investigate the effect of three different powder granulations on the resulting part density, surface quality and mechanical properties of the materials produced.

The scan surface quality and mechanical properties of three different particle size distributions and two layer thicknesses of 30 and 45 μm were compared. The scan velocities for the different powder types have been adjusted in order to guarantee a part density≥99.5 per cent.

By using an optimised powder material, a low surface roughness can be obtained. A subsequent blasting process can further improve the surface roughness for all powder materials used in this study, although this does not change the ranking of the powders with respect to the resulting surface quality. Furthermore, optimised powder granulations lead generally to improved mechanical properties.

The results of this study indicate that the particle size distribution influences the quality of AM metallic parts, produced by SLM. Therefore, it is recommended that any standardisation initiative like ASTM F42 should develop guidelines for powder materials for AM processes. Furthermore, during production, the granulation changes due to spatters. Appropriate quality systems have to be developed.

The paper clearly shows that the particle size distribution plays an important role regarding density, surface quality and resulting mechanical properties.

Our study explores the effects of immigration on the employment of native middle-skilled workers, focusing on how this effect varies with the specificity of their occupational skill bundles.

Exploiting the 2002 opening of the Swiss labor market to EU workers and using register data on the location and occupation of these workers, our findings provide novel results on the labor market effects of immigration.

We show that the inflow of EU workers led to an increase in the employment of native middle-skilled workers with highly specific occupational skills. This finding could be attributed to immigrant workers reducing existing skill gaps, enhancing the quality of job-worker matches, and alleviating firms' capacity restrictions. This allowed firms to create new jobs, thereby providing increased employment options for middle-skilled workers with highly specialized skills.

Previous literature has predominantly highlighted the disadvantages of specific occupational skills compared to general skills in the context of labor market shocks. However, our findings reveal that workers with specific occupational skills can benefit from an immigration-driven labour market shock. These results suggest that policy conclusions regarding the role of specific occupational skills should be more nuanced.

The body of the literature on the Arburg Plastic Freeforming process is still very limited despite the increasing industrial importance of this technology. This paper aims to contribute to a better understanding of this technology by investigating relations between characteristic process parameters and part features. Particularly, the effects of nominal dimension, drop aspect ratio, build chamber temperature and part position on accuracy are investigated. The density of manufactured parts is also measured to understand its relation with dimensional error.

A benchmark part was designed and manufactured in Polycarbonate on an Arburg Plastic Freeformer 2K-3A. The process was repeated with two levels of drop aspect ratio (1.2125 and 1.2150) and two build chamber temperatures (90°C and 120°C). Each build job included five parts in different positions of the chamber. The dimensional accuracy of benchmarks was measured by using a digital caliper, while Archimede’s principle was used for density measurements. All the acquired results were processed through an analysis of variance to investigate the role of experimental factors.

Results demonstrate that the linear shrinkage occurring at the end of the 3D printing process is the main source of inaccuracy. The higher the building chamber temperature, the most the part accuracy is influenced by the nominal dimension. The drop aspect ratio affects the dimensional error in the XY plane by increasing the overlap of adjacent droplets. On the other hand, this parameter does not influence the accuracy along the Z direction. The position of the parts inside the building chamber exhibited an influence on results, arguably due to the hot airflows.

This research did not allow for a complete understanding of the role of part positioning on part accuracy. Further study is needed to understand the detail of this phenomenon.

The results of this study can aid the users of Arburg Plastic Freeforming technology by uncovering the role of the main process parameters.

This paper expands the body of knowledge on the Arburg Plastic Freeforming process by providing new information on the role of the main process parameters on dimensional accuracy and density. Particularly, the results answer a research question on the role of the drop aspect ratio, demonstrating that its main effect is to vary the droplets overlap, which, in turn, affects the thermal shrinkage.

To fabricate a selective laser melting (SLM)-processed AlSi10Mg part with almost full density and free of any apparent pores, this study aims to investigate the effect of ambient argon pressure and laser scanning speed on the particles splash during the AlSi10Mg powder bed laser melting.

Based on the discrete element method (DEM), a 3D model of random distribution of powder particles was established, and the 3D free surface of SLM forming process was dynamically tracked by the volume of fluid, where a Gaussian laser beam acts as the energy source melting the powder bed. Through the numerical simulation and process experimental research, the effect of the applied laser power and scanning speed on the operating laser melting temperature was studied.

The process stability has a fundamental role in the porosity formation, which is process-dependent. The effect of the processing conditions on the process stability and the resultant forming defects were clarified.

The results shows that the pores were the main defects present in the SLM-processed AlSi10Mg sample, which decreases the densification level of the sample.

The optimal processing parameters (argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm ) applied during laser melting can improve the quality of selective laser melting of AlSi10Mg,

It can provide a technological support for 3D printing.

Based on the analysis of the pore and balling formation mechanisms, the optimal processing parameters have been obtained, which were argon pressure of 1,000 Pa, laser power of 180 W, scan speed of 1,000 mm/s, powder layer thickness of 35 µm and hatch spacing of 50 µm. Then, a near-fully dense sample free of any apparent pores on the cross-sectional microstructure was produced by SLM, wherein the relative density of the as-built samples is larger than 97.5%.

The purpose of this study is, to compare laser-based additive manufacturing and subtractive methods. Laser-based manufacturing is a widely used, noncontact, advanced manufacturing technique, which can be applied to a very wide range of materials, with particular emphasis on metals. In this paper, the governing principles of both laser-based subtractive of metals (LB-SM) and laser-based powder bed fusion (LB-PBF) of metallic materials are discussed and evaluated in terms of performance and capabilities. Using the principles of both laser-based methods, some new potential hybrid additive manufacturing options are discussed.

Production characteristics, such as surface quality, dimensional accuracy, material range, mechanical properties and applications, are reviewed and discussed. The process parameters for both LB-PBF and LB-SM were identified, and different factors that caused defects in both processes are explored. Advantages, disadvantages and limitations are explained and analyzed to shed light on the process selection for both additive and subtractive processes.

The performance of subtractive and additive processes is highly related to the material properties, such as diffusivity, reflectivity, thermal conductivity as well as laser parameters. LB-PBF has more influential factors affecting the quality of produced parts and is a more complex process. Both LB-SM and LB-PBF are flexible manufacturing methods that can be applied to a wide range of materials; however, they both suffer from low energy efficiency and production rate. These may be useful when producing highly innovative parts detailed, hollow products, such as medical implants.

This paper reviews the literature for both LB-PBF and LB-SM; nevertheless, the main contributions of this paper are twofold. To the best of the authors’ knowledge, this paper is one of the first to discuss the effect of the production process (both additive and subtractive) on the quality of the produced components. Also, some options for the hybrid capability of both LB-PBF and LB-SM are suggested to produce complex components with the desired macro- and microscale features.

The pulsed-laser powder bed fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case, stainless steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density.

The response surface method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually.

A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density.

The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties.

This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of the SS316L alloy components.

Laser additive manufacturing is widely utilized to fabricate the Ti6Al4V alloy, but it requires post-processing to improve its performance. This paper aims to propose laser peening (LP) as an effective way to improve the surface characteristics of the Ti6Al4V alloy fabricated by direct laser deposition (DLD).

Surface integrity including surface roughness, porosity, residual stress and microhardness are investigated in detail before and after LP treatment. Microstructure evolution is characterized by the electron backscatter diffraction (EBSD) to analyze crystal phase, grain boundary misorientation and texture.

Multiple overlapping layers of LP treatment result in slight influence on the polished surface of DLD-built samples. Porosity measured by the Archimedes test is found to be greatly decreased after LP treatment. Compressive residual stresses are significantly induced, the magnitude of which is greatly increased by increasing layers of LP treatment. And, local weakening or enhancement of residual stress in depth is observed because of pore and inclusion defects in the DLD-built Ti6Al4V alloy. Favorable hardness property can be obtained after multiple overlapping layers of LP treatment. EBSD analysis shows that LP treatment with multiple layers can introduce a large amount of lower-angle boundaries, indicating that dislocations beneath the top surface could induce a strain-hardened layer. The microtexture of the DLD-built Ti6Al4V alloy cannot be eliminated to decrease the anisotropy of the mechanical property.

The variation of porosity observed after LP inside the DLD-built Ti-Al-4V is attractive but requires more detailed work to analyze the evolution of pore geometry.

Surface treatment of an additive manufactured titanium alloy was carried out to improve its fatigue resistance.

This work is original in proposing LP as an effective post process for the surface treatment of an additive manufactured titanium alloy through analyzing the surface integrity and microstructure evolution.

The purpose of this paper is to investigate the tensile strength, Young’s modulus, dimensional stability and porosity of acrylonitrile butadiene styrene (ABS)–oil palm fiber composite filament for fused deposition modeling (FDM).

A new feedstock material for FDM comprising oil palm fiber and ABS as a matrix was developed by a twin screw extruder. The composite filament contains 0, 3, 5 and 7 Wt.% of oil palm fiber in the ABS matrix. The tensile test is then performed on the fiber composite filament, and the wire diameter is measured. In this study, the Archimedes method was used to determine the density and the porosity of the filament. The outer surface of the wire composite was examined using an optical microscope, and the analysis of variance was used to assess the significance and the relative relevance of the primary factor.

The results showed that increasing the fiber loading from 0.15 to 0.4 MPa enhanced tensile strength by 60%. Then, from 16.1 to 18.3 MPa, the Young’s modulus rose by 22.8%. The density of extruded filament decreased and the percentage of porosity increased when the fiber loading was increased from 3 to 7 Wt.%. The diameter deviation of the extruded filaments varied from −0.21 to 0.04 mm.

This paper highlights a novel natural resource-based feedstock material for FDM. Its mechanical and physical properties were also discovered.