Laser Powder Bed Fusion of Polymers: Quantitative Research Direction Indices

Abstract

Research on Laser Powder Bed Fusion (L-PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published on the topic of L-PBF of polymer powder feedstocks in the last decade, being cited more than 10,000 times leading to an h-index of 46. This study statistically evaluates the 100 most cited articles to extract reported material, process, and as-built part properties to analyze the research trends. PA12, PEEK, and TPU are the most employed polymer powder feedstocks, while size, flowability, and thermal behavior are the standardly reported material properties. Likewise, process properties such as laser power, scanning speed, hatch spacing, powder layer thickness, volumetric energy density, and areal energy density are extracted and evaluated. In addition, material and process properties of the as-built parts such as tensile test, flexural test, and volumetric porosity contents are analyzed. The incorporation of additives is found to be an effective route to enhance mechanical and functional properties. Carbon-based additives are typically employed in applications where mechanical properties are essential. Carbon fibers, Ca-phosphates, and SiO₂ are the most reported additives in the evaluated SCI-expanded articles for L-PBF of polymer powder feedstocks. A comprehensive data matrix is extracted from the evaluated SCI-index publications, and a principal component analysis (PCA) is performed to explore correlations between reported material, process, and as-built parts.

Keywords: 3D-printing; PA12; PEEK; SLS; additive manufacturing; additives; bibliometry; nano; selective laser sintering.

Figure 1

Bibliometrics on L-PBF of PA12, PA11, PA6, PP, PEEK, TPU, PEK, PS, PE, and PBT powder feedstocks processed by L-PBF over the last decade: (a) cumulative number of publications and corresponding h-index; (b) the cumulative number of citations and average citations per item.

Figure 2

The topic of the five most cited SCI-expanded publications of the statistically evaluated references [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111] and their average citations per year over the last decade.

Figure 3

Reported material properties of polymer powder feedstocks and their reporting frequencies in the L-PBF articles [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111]. The inset classifies the material properties into four general groups, powder size, flowability, thermal behavior, and others, defining the colors of the bars in the main graph.

Figure 4

Reported polymer powder feedstocks processed by L-PBF. Others consist of POM, PU, DF, PA12-PEG blend, PA12-PVA blend, PEKK, PMMA, cellulose acetate, and starch-cellulose studied three times or less in the publications [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111]. The inset shows the share of parent class polymers.

Figure 5

Range of reported polymer powder size characteristics: (a) statistics on the reported powder sizes as mean, D10, D50, and D90 values [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111] (b) D50 values of polymer powders used in L-PBF of Amorphous Standard (A-S) including polymers such as TPU, PS, PMMA; of Semicrystalline Standard (S-S) including polymer as HDPE; Amorphous Engineering (A-E) including polymer as PDLLA; Semi-Crystalline High-performance (S-H) including polymers such as PEEK, PEK, PEKK; Semi-Crystalline Engineering (S-E) including polymers such as PBT, PA6, PA11, PA12, and PA12 powder feedstocks. Outlier points are not shown in plots.

Figure 6

Statistics on flowability and sintering parameters of (a) Hausner Ratio and (b) angle of repose reported for flowability behavior, and (c) sintering window reported for thermal behavior of polymer powder feedstocks.

Figure 7

Bibliometrics of additive material classes and subtypes. The inset shows the overall share of additives within reported powder compositions and the additive classes percentage.

Figure 8

Share of L-PBF machine manufacturers reported for L-PBF of polymer powder feedstocks in the studies [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111].

Figure 9

Reported process properties for L-PBF of polymer powder feedstocks and their reporting frequencies in the articles [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111].

Figure 10

Bibliometrics of the most reported L-PBF process parameters: (a) laser power, (b) scanning speed, (c) powder layer thickness, (d) hatch spacing, calculated (e) volumetric energy density, and (f) areal energy density. The study differentiates between all polymers, PA12, A-S, S-S, S-E, and S-H powder feedstocks [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111]. Outlier points are not shown.

Figure 11

Reported as-built part properties of polymer powder feedstocks processed by L-PBF and their reporting frequencies in the studies [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111]. The inset shows the grouped sum of the reported as-built part properties, defining the colors of the bars in the main diagram.

Figure 12

Statistics of the most reported as-built part properties of all polymers, PA12, A-S, S-S, S-E, and S-H powder feedstocks processed by L-PBF process: (a) ultimate tensile strength, (b) elastic modulus, (c) elongation, (d) flexural strength, (e) flexural modulus, and (f) volumetric porosity. Outlier points are not shown.

Figure 13

Principal component analysis 2D loading plot of various material, process, and as-built part properties.

Figure 14

Scatter plots for (a) powder layer thickness vs. UTS, (b) AED vs. UTS, (c) powder size vs. UTS, and (d) powder size vs. laser power according to Table 1. A 68% confidence ellipse is depicted for each plot.