Alexander Walzl

The volumetric energy density (VED) is often used to characterise the process window in laser beam powder bed fusion of metals (PBF-LB/M), commonly referred to as laser powder bed fusion (L-PBF). We assessed its explanatory value using an EOS M280 system on two alloys: stainless steel 304L and the TiB₂-modified Al–Cu aluminium alloy A20X. The porosity was measured by light optical microscopy. Furthermore, the pore morphology was quantified, and the results were compared with the densities measured using the Archimedes principle. For 304L, the VED explained 71% of the in-sample variance of the logarithmic porosity, compared with 93% for the factorial model. Scan speed dominated, and irregular pores consistent with lack of fusion predominated. For A20X, no monotonic correlation between porosity and VED was detected. A series of tests at constant VED (62.5–64.8 J/mm³) led to an increase in porosity from 0.03% to 1.08%, which was associated with the accompanying increase in line energy; a contribution of the largest hatch distances could not be excluded. At equal scan speed, hatch distances up to 140 µm had no detectable effect, and pores ≥ 20 µm were compact (median aspect ratio 1.15), consistent with keyhole or gas porosity.

Compression testing combined with laser ultrasonics enables non-destructive, in situ material characterisation during thermo-mechanical loading, but the shortening and radial expansion of the specimen displace the laser focal points during deformation and therefore require active repositioning of the laser-ultrasonic optics. This work addresses this engineering problem by providing a modular positioning-control system that couples a Gleeble 3800 thermo-mechanical simulator and a laser-ultrasonic measurement unit. The Gleeble provides two analogue shaft-position signals, which are digitised and used as real-time reference signals for stage-position control. The excitation and detection optics are mounted on motorised Zaber linear stages; two stages translate the optics along the compression direction, while a third perpendicular stage adjusts the detection focus to compensate radial specimen expansion and the limited depth of field of the detection optics. The control software was implemented in Rust and computes the stage target positions from the digitised Gleeble voltages output using user-configurable mathematical expressions. It further provides process-data access through an embedded OPC UA server and a browser-based graphical user interface through an integrated HTTP server. A custom ADC-based acquisition chain was introduced because the built-in ADC inputs of the Zaber controllers showed a significant noise level when used for the Gleeble shaft-position signals. Profiling showed that the control-loop runtime was dominated by ADC read/write operations; by reorganising acquisition into a parallel setup, the mean control-loop time was reduced from approximately 130 ms to approximately 27 ms. The resulting system provides an active, configurable, and retrofit-capable link between Gleeble compression testing and laser-ultrasonic measurement. It improves the temporal response available for laser-focus tracking on deforming specimens and provides a foundation for future quantitative validation of tracking error, positioning uncertainty, and LUS signal quality during real compression experiments.

This study examines the deformation behaviour of laser powder bed fusion-produced A20X aluminium alloy and its accurate representation using flow curve models that account for die–specimen friction. Tests across multiple strain rates at room temperature were conducted on a Gleeble 3800; force–displacement data were friction-corrected to derive constitutive flow curves. A mathematical model was developed to capture barrelling and its impact on the stress–strain response, yielding corrected stresses significantly lower than measured values and validating the correction. An equation linking key post-deformation geometric parameters to their mathematical representation correlated well with a calibrated 2D finite element model, which reliably predicted plastic strain and deformation. The model’s friction factors agreed with experimental data, enabling efficient determination of the friction coefficient. Microstructural analysis and micrographs supported the predicted plastic strain distributions. Together, the corrected experiments and validated simulations provide a robust description of A20X’s response and inform performance and application potential.

Metal–polymer hybrid joints are gaining importance as they combine high structural rigidity with a low weight. Additive manufacturing processes such as the laser powder bed fusion process (L-PBF) enable the production of complex metallic lattice structures that allow for form-fitting force transmission between the metal and polymer as mechanical interlock elements. In this work, metal–polymer hybrid compounds with additively manufactured transition zones are systematically investigated and mechanically evaluated. Three different lattice geometries (z4A, z8A, z8V) were fabricated from maraging steel (1.2709) using L-PBF and then hybridised with injection moulding using polypropylene (PP C7069-100NA). Mechanical characterisation was performed by tensile tests according to DIN EN ISO 527, in combination with statistical analyses and an analytical serial three-spring model to determine the homogenised elasticity modulus of the transition zone. The results show significant geometry-related differences in tensile strength, maximum force, and effective stiffness. The A-shaped transition zone geometry (z4A) achieves the highest mechanical performance and up to 82% of the tensile strength of the pure polymer, while the V-shaped transition zone geometry (z8V) has significantly lower load-bearing capacities. Variance analysis shows a dominant geometric influence with effect strength of η² ≈ 0.99. The analytically predicted stiffness values match the experimental results within 5–10%. This work demonstrates a reproducible, simulation-sparse approach to the analysis and design of metal–polymer hybrid connections.