Melt Pool Shape Evaluation by Single-Track Experiments and Finite-Element Thermal Analysis: Balling and Lack of Fusion Criteria for Generating Process Window of Inconel738LC

Abstract

Defects occur in laser powder bed fusion (L-PBF) such as the keyholing, lack of fusion, and the balling depending on the laser power (P) and the scan speed (V). The figure shows that the occupied regions of each defect are the process window and are essentially important to fabricate a high-quality part. This paper is a study of process window generation using single-track experiments and finite-element method simulation of thermal conduction for Inconel738LC alloy. A series of single-track experiments were conducted varying the range of P and V and the results were classified into keyholing, lack of fusion, balling, and good track. A series of simulations were conducted and validated by comparison with the experiments. To quantitively identify the balling, the isolines from the contour map generated by the results of simulations and the balling criteria of the ratio of melt pool length and the depth (L/D) of 7.69 were determined considering the past theoretical studies. The lack of fusion criteria: the ratio of the overlap depth in fabrication using multi-scan (Dov) and powder layer thickness (t) of 0.1 was obtained. Using the criteria obtained from the experiments and simulation, the process window was generated.

Particle Size Effect on Powder Packing Properties and Molten Pool Dimensions in Laser Powder Bed Fusion Simulation

“…As described above, an average particle diameter slightly larger than the thickness of the powder bed is used in some conventionally used L-PBF systems. For example, a thickness of 30 or 50 µm for the powder bed formation region was set for powders with an average particle diameter of 29 µm in [10,40]. In the present study, the ratio between the average diameter (even up to 40 µm) and the powder bed formation region thickness was smaller compared to our previous studies.…”

“…The particle size distribution of the Ni-based alloy (Hastelloy X) powder used in this study is shown in Figure 1. The average particle diameter of Hastelloy X powder was 28.9 µm [10,40]. To investigate the effect of particle size within a range similar to that of the Hastelloy X powder used in this study, five different particle size distributions based on Gaussian distributions were used.…”

“…Moreover, previous studies have reported that defects produced during the L-PBF fabrication process are strongly correlated with the shape and size of the molten pool [6][7][8][9][10]. Previous studies have reported that different types of defects, such as keyhole pores [11][12][13], lack of fusion [6,7], and balling [14][15][16][17][18][19], can occur depending on the laser conditions, namely laser power and scanning speed.…”

Influence of Recoil Pressure, Mushy Zone Flow Resistance and Reflectivity on Melt Pool Shape in Laser Powder Bed Fusion Simulation

“…A procedure for the single-track experiment has been described in detail in the cited Refs. [24]. A brief summary of the experimental procedure is described here.…”