The resulting properties of parts fabricated by powder bed fusion additive manufacturing processes are determined by their porosity, local composition, and microstructure. The objective of this work is to examine the influence of the stochastic powder bed on the process window for dense parts by means of numerical simulation. The investigations demonstrate the unique capability of simulating macroscopic domains in the range of millimeters with a mesoscopic approach, which resolves the powder bed and the hydrodynamics of the melt pool. A simulated process window reveals the influence of the stochastic powder layer. The numerical results are verified with an experimental process window for selective electron beam-melted Ti-6Al-4V. Furthermore, the influence of the powder bulk density is investigated numerically. The simulations predict an increase in porosity and surface roughness for samples produced with lower powder bulk densities. Due to its higher probability for unfavorable powder arrangements, the process stability is also decreased. This shrinks the actual parameter range in a process window for producing dense parts.
Purpose
The purpose of this study is the introduction and validation of a new technique for process monitoring during electron beam melting (EBM).
Design/methodology/approach
In this study, a backscatter electron detector inside the building chamber is used for image acquisition during EBM process. By systematic variation of process parameters, the ability of displaying different topographies, especially pores, is investigated. The results are evaluated in terms of porosity and compared with optical microscopy and X-ray computed tomography.
Findings
The method is capable of detecting major flaws (e.g. pores) and gives information about the quality of the resulting component.
Originality/value
Image acquisition by evaluating backscatter electrons during EBM process is a new approach in process monitoring which avoids disadvantages restricting previously investigated techniques.
An oxide dispersion strengthened (ODS) copper powder containing 5 vol% Al 2 O 3 as finely dispersed particles is processed by selective electron beam melting (SEBM), a powder bed based additive manufacturing technology. Contrary to usual powder characteristics used for SEBM, the particles show a non-spherical morphology and a copper oxide layer on their surface. A preheating strategy as well as melting parameters for successful generation of ODS-Cu samples is developed to achieve processability despite the adverse powder conditions. Specimens are built and their meso-and microscale structures are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM) as well as energy dispersive X-ray analyses (EDX). Temperature depending phase separation effects previously encountered in literature during fabrication of ODS-Cu powders are taken into account. [1] Alumina particles were found to coagulate during the process. Partly the Al 2 O 3 was melted and separated from the Cu which resulted in heavy demixing of the system and subsequent loss of dispersion strengthening effect.
Powder bed-based additive manufacturing has become increasingly important for industrial applications. In the light of this, qualitative considerations such as the geometrical accuracy, the resulting mechanical properties, and the surface quality of additively manufactured parts must be taken into account. Optical measuring techniques such as confocal laser scanning microscopy, fringe projection and focus variation as well as profilometers are evaluated here, to determine the surface quality of powder bed-based manufactured parts. Even though these surface evaluation methods are established commercially, no standardized measuring procedure has yet been established. Within an experimental study the validity and accuracy of surface measurement methods are evaluated below, taking the limitations of each measurement system and the comparability of areal surface textures into account. The examinations are carried out with the powder materials EN-AW2024, Ti-6V-4Al and PA12, which are processed by electron beam melting, and laser beam melting of metals and polymers. Guidance for a consistent and comparable surface evaluation is thereby provided.
Purpose
Selective electron beam melting (SEBM) is a highly versatile powder bed fusion additive manufacturing method. SEBM is characterized by high energy densities which can be applied with nearly inertia free beam deflection at high speeds (<8.000 m/s). This paper aims to determine processing maps for Ti-6Al-4V on an Arcam Q10 machine with LaB6 cathode design.
Design/methodology/approach
Scan line spacings of 100, 50 and 20 µm in a broad parameter range, focusing on high deflection and build speeds are investigated.
Findings
There are broad processing windows for dense parts without surface flaws for all scan line spacings which are defined by the total energy input and the area melting velocity.
Originality/value
The differences and limitations are discussed taking into account the beam properties at high beam energy and velocity as well as evaporation related loss of alloying components.
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