PSI - Issue 77

Roman Hofmann et al. / Procedia Structural Integrity 77 (2026) 237–247

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Roman Hofmann et al. / Structural Integrity Procedia 00 (2026) 000–000

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mal homogeneity regardless of geometric features such as strongly changing dimensions between the layers or tapered ends. As demonstrated in the literature [1], the thermal history is of significant importance to successful production, and consequently to the resulting microstructure and mechanical properties. Therefore, it is necessary to consider the e ff ects of each laser path on the preceding ones[2]. Material properties can be influenced by optimizing existing scan strategies or by developing novel ones [9]. Among the various approaches explored, four strategies were selected for further investigation and subsequent experimental evaluation. 2.2.1. Index Reorder Index Reorder represents the most straightforward approach to path reordering and highlights the potential of purely programmatic modifications. In this strategy, the sequence of scan vectors — stored as an indexed array within the slicer — is rearranged based on their index values. In its simplest form as illustrated in Figure 1, every second vector is exposed in the first pass, while the remaining vectors are completed in a subsequent iteration. This staggered exposure reduces the concentration of energy input within a small region, thus reducing the risk of local overheating. This method was first proposed in 2008 [5] and subsequently investigated in di ff erent papers to reduce residual stresses and warpage [19]. It remains a viable approach at the present time, but still can be further developed. Due to its simplicity, the method is highly transferable to other slicers and machine control systems. Moreover, it provides a flexible framework in which diverse sorting algorithms, including multidimensional reordering schemes, could be implemented by assigning surrogate values to scan vectors. Although this strategy focuses on the index based reordering, the framework inherently allows for line-specific parameter variation, such as applying di ff erent parameter sets in successive iterations (e.g. initial sintering followed by remelting) and thus expands the possibilities for optimization. However, these advanced parameter adaptations are beyond the scope of this method in this paper, as the emphasis here is on demonstrating simplicity and transferability.

1st iteration

2nd iteration

Fig. 1. Illustration of index-based reordering of a conventional linear hatch.

2.2.2. Time Reorder Time Reorder is a physically motivated approach that reorders scan vectors based on their spatio-temporal relation to previously exposed tracks. For each new scan vector, the algorithm identifies the nearest point on the most recently processed line and calculates the time di ff erence between them, the calculation takes into account laser scan velocity and inter-track jump times as illustrated in Figure 2. The exact time di ff erence taking into account the production speeds is highlighted in purple in the illustration. Skywriting delays were not considered in this method, as they are strongly machine-dependent and di ffi cult to quantify. If the temporal di ff erence is below a defined threshold, and if the spatial distance of those points is below a thresh old, the vector is considered thermally “critical” and is postponed to later in the sequence. (Despite a typically constant hatch distance, the distance between two points can be relevant depending on the contour geometry or if several lines may to be skipped at once). As a result, regions at risk of excessive reheating are given additional cooling time before being exposed. Importantly, the strategy does not rely on explicit waiting periods, which would reduce productivity, but instead reshu ffl es the sequence of vectors to maintain build e ffi ciency. 2.2.3. Pilger (Backstep) Pilger Strategy derives its name from the “pilger step” known in rolling processes [7] and is also applied in welding, where it is also referred to as back-step welding[10, 18]. In welding, this technique involves short, oscillating stitch