Introduction

Additive Manufacturing (AM) technologies have revolutionized the production of geometrically complex parts. Among these, Fused Deposition Modeling (FDM) remains popular due to its affordability and versatility, particularly with materials like acrylonitrile butadiene styrene (ABS). Nonetheless, FDM parts often suffer from layer-induced roughness and anisotropy, limiting their functional usability.

Various post-processing techniques have been proposed to enhance surface quality. Chemical methods such as acetone vapor smoothing have demonstrated effective reduction of surface roughness for ABS parts1. Demircali et al. (2024) further showed that cold-vapor acetone smoothing not only improved surface quality but also enhanced tensile strength by nearly 20%, albeit with minor dimensional deviations2. Review studies on vapor polishing underscore its effectiveness but highlight concerns regarding process safety, dimensional stability, and reproducibility3.

Beyond chemical treatments, mechanical strategies such as ironing—a secondary nozzle pass to flatten layers—have been explored to improve surface finish without introducing solvents4. Hybrid techniques including CNC machining after FDM printing also show promise by significantly reducing surface roughness; however, they are often expensive and require additional equipment5. Additive manufacturing reviews have consolidated findings across thermal, chemical, and mechanical treatments, highlighting the need for method-selection frameworks based on desired part functionality6.

Regarding metal coating approaches, sputtering and ion-assisted deposition can deposit thin metallic films onto polymer substrates. For instance, Cr-ion bombardment before copper sputtering enhances coating adhesion on ABS7, and magnetron-sputtered copper films have been shown to improve UV and moisture resistance of ABS surfaces8. Recent studies have also explored hybrid approaches such as integrating Response Surface Methodology (RSM) with machine learning techniques to model and predict surface quality in FDM9.

Taken together, the existing literature suggests a gap in systematic, experimental comparisons of FDM post-processing techniques for ABS parts, particularly integrating chemical, mechanical, and coating methods under consistent conditions. Moreover, standardized guidelines for selecting optimal finishing techniques remain lacking, limiting broader industrial uptake.

Novelty of this work rests in the side-by-side evaluation of three post-processing methods spray painting, acetone dipping, and copper sputtering—applied to ABS FDM parts manufactured under controlled settings. Morphological characterization via SEM, EDX, and image analysis enables quantitative comparison of improvements in surface roughness and hardness.

The objectives of this study are:

  1. 1.

    Produce ABS samples under predefined FDM parameters and apply the three post-processing methods.

  2. 2.

    Quantitatively compare the surface finishing efficacy of each technique.

  3. 3.

    Determine the most effective and scalable method for improving the functional quality of ABS FDM parts.

Setting up the sample

To prepare the ABS specimens, a StratasysuPrint SE Plus FDM system was used. The printer has a build volume of 203 × 152 × 152 mm and a standard nozzle diameter of 0.254 mm. The ABS filament (Stratasys P430 ABSplus, stabilized grade) was used as feedstock. Based on the manufacturer’s guidelines and prior literature, the following parameters were selected: nozzle temperature 300 °C (system setting; material stabilized for this range), layer thickness 0.254 mm, raster angle 45°, and flat orientation in the XY plane.

A total of 15 specimens (50 × 25 × 5 mm) were produced, with 5 samples assigned to each post-processing technique: spray painting, acetone dipping, and sputtering. This allocation ensured consistency and repeatability for comparative analysis. While Design of Experiments (DOE) methods such as Taguchi or RSM are often used to minimize runs, the present study was designed to perform a direct morphological comparison across three finishing techniques under fixed, controlled conditions.

Figures 1 and 2 illustrate the printer setup and the as-printed ABS samples, respectively. The detailed printing parameters used for the fabrication of ABS specimens are summarized in Table 1.

Fig. 1
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The StatasysuPrintSEPlus printing samples.

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Fig. 2
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ABS 3D printed samples—Uncoated.

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Table 1 Printing parameters for ABS specimens fabricated using FDM.
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Surface finishing techniques

Three post-processing techniques were applied to the printed ABS samples: acetone dipping, copper sputtering, and spray painting. Each method corresponds to different categories—chemical, physical, and coating—and has demonstrated effectiveness in previous studies.

Acetone dipping

Acetone vapor smoothing is a widely used chemical treatment for ABS FDM parts, capable of reducing surface roughness by up to 90% in 10 s10. In our study, samples were immersed in acetone for 30 s and air-dried. Although surface smoothing was achieved, some dimensional distortion occurred with prolonged exposure.

Copper sputtering

Metallic coatings via copper plating or sputtering enhance polymer durability and surface properties. Maciąg et al. (2019) demonstrated effective copper plating on ABS following vapor smoothing11, while Afshar (2020) showed that copper-coated ABS retained mechanical strength under extended UV and moisture exposure8. In this study, ABS parts were sputter-coated with copper for 10 min. Coating improved hardness, though coverage was inconsistent due to sputtering’s directional nature.

Spray painting

Spray coating has been used to improve surface thickness and aesthetics in ABS FFF prints. A recent study reported that multiple layers of spray coating significantly increase surface thickness on ABS parts12. Broader reviews confirm that spray and other chemical coatings are effective post-processing methods for enhancing surface functionality13. Here, samples were sanded, primed, and spray-painted with copper-based paint, followed by curing at 50 °C for 24 h. Spray painting resulted in the highest improvement in smoothness and hardness.

A comparative summary of the three surface treatment methods is presented in Table 2. The results clearly demonstrate that spray painting achieved the highest improvement in both surface roughness (70% reduction) and hardness (19% increase), while acetone dipping and sputtering offered moderate improvements but introduced limitations such as dimensional changes or non-uniform coatings. These findings corroborate the SEM/EDX analyses discussed earlier.

Table 2 Comparative results of post-processing techniques on ABS FDM parts.
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Surface morphology

Surface morphology and topography play a crucial role in determining the functional quality of polymeric materials, particularly in applications where adhesion, wettability, or wear resistance are critical. Since FDM components are formed through layer-by-layer deposition, their surface characteristics are often irregular, requiring detailed microscopic analysis.

In this study, Scanning Electron Microscopy (SEM) was employed to evaluate the surface features of ABS parts before and after post-processing. SEM was selected due to its high resolution and ability to reveal microstructural defects, surface irregularities, and coating distribution. Complementary Energy Dispersive X-ray Spectroscopy (EDX) was used to assess the elemental composition of the treated surfaces. These methods have been widely applied for analyzing the effectiveness of chemical and coating-based finishing techniques on FDM polymers14,15.

The SEM micrographs provided insights into the smoothing effect of acetone treatment, the deposition patterns of sputtered copper, and the uniformity of spray-painted coatings. EDX analysis confirmed the expected elemental signatures, such as increased copper content in sputtered and spray-coated samples. Together, these techniques offered both qualitative and quantitative evidence of the effectiveness of the different post-processing strategies.

Comparison of 3D printed ABS samples

To evaluate the effectiveness of the three post-processing techniques, ABS specimens were characterized using SEM imaging, EDX analysis, and surface profilometry. The uncoated samples served as a baseline for comparison against acetone-dipped, copper-sputtered, and spray-painted specimens. Each treatment was applied to five replicate samples to ensure reproducibility.

Uncoated samples

The unprocessed ABS specimens displayed distinct bead structures and inter-bead grooves characteristic of FDM parts. SEM micrographs (100× and 500×) confirmed the presence of parallel deposition lines and surface valleys, which contributed to an average roughness (Ra) of 22.0 μm. Similar findings, have been reported in prior studies, where FDM-produced ABS parts exhibited layer-induced anisotropy and poor surface finish14.

Figure 3(1) and 3(2) shows a micrograph of the same part at 100 x and 500 x magnification. This shows a few more of the surface irregularities of the printed part. This is obtained by the Image Processing & Analysis software package. The irregularities on the surface are amplified by 7% to better visualize the surface.

Fig. 3
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Micrograph of uncoated ABS sample.

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This along with the curve in Fig. 4, which shows the extracted profile, indicate the surface’s average roughnessfalls in the same range as the measurements, the profile extracted as per the dotted line indicated. This profile was selected by identifying the highest and lowest points on the topographic image.

Fig. 4
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Extracted profile of the surface of uncoated ABS sample at 500x.

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SEM/EDX is employed to determine the elemental makeup of the material that makes up the surface coating on the ABS sample. Figure 5; Table 3 show the elemental analysis and break-up of the material that’s on the sample’s surface.

Since the sample hasn’t undergone any surface treatment, the presence of Carbon and Oxygen is expected as it is part of the atmospheric composition and the ABS, being a hydrocarbon is predominantly made up of Carbon. These inferences are as per extant literature.

Table 3 Elemental breakup of uncoated ABS sample.
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Fig. 5
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EDX Elemental analysis of uncoated ABS sample at 500x.

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Acetone dipped sample

Acetone treatment partially dissolved the outer polymer layer, reducing surface irregularities. SEM images revealed that the grooves were less distinct compared to the uncoated samples. Quantitative roughness decreased by ~ 35% (Ra = 14.2 μm), but hardness remained nearly unchanged. This aligns with Demircali et al. (2024), who observed smoother surfaces but reduced dimensional accuracy following acetone vapor treatment2. Figure 6(1) shows the acetone dipped printed part at a magnification of 100x. While the print roads and grooves are not as easily visible when compared to the uncoated sample, they do appear as faint parallel lines on the image. This is line with the AFM images in extant literature15.

Figure 6(2) shows a micrograph of the same part at 500 x magnification. This shows a few more of the surface features of the printed part. The grooves that were identifiable in the uncoated part in Fig. 3 are no longer visible and smoother surface can be seen.

Fig. 6
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Micrograph of an ABS dipped in acetone.

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The curve in Figs. 7 shows the extracted profile, the surface’s average roughness falls in the same range as the measurements. The graph does show that dipping a sample in acetone does smoothen out the surface. However, as described in the earlier chapters, the hardness of the sample is not necessarily improved using this process.

Fig. 7
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Extracted profile of the surface of ABS sample dipped in acetone.

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SEM/EDX is employed to determine the elemental makeup of the material that makes up the surface coating on the ABS sample. Figure 8; Table 4 show the elemental analysis and break-up of the material that’s on the surface of the sample. Since the sample has undergone any surface treatment where the active agent is wiped away and does, in fact evaporate quickly, the presence of Carbon and Oxygen is as expected. However, the trace amounts of Tungsten, is unexpected and can’t be suitably explained.

Fig. 8
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EDX Elemental analysis of an ABS sample dipped in acetone.

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Table 4 Elemental breakup of an ABS sample dipped in acetone.
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Sputtered sample

Sputtering deposited copper clusters on the ABS substrate. SEM analysis showed that peaks of the surface received more coating, while valleys remained uncovered, leading to non-uniform morphology. Average roughness improved by ~ 42% (Ra = 12.8 μm) and hardness increased by 8%. Elemental EDX confirmed significant copper presence (~ 31 wt%). Similar non-uniform coatings have been noted in sputtering literature for polymer substrates10,15. Figure 9(1) shows the printed part with copper deposited on it at a magnification of 100x. While the print roads and grooves are not as easily visible when compared to the uncoated sample, they do appear as pale grooves on the image. This is line with the AFM images in extant literature.

Figure 9(2) shows a micrograph of the same part at 500x magnification. This shows a few more of the surface features of the printed part. The grooves that were easily identifiable in the uncoated part in Fig. 3 are visible at the top of the image. The deposited copper can be seen as clusters on the ABS substrate.

Fig. 9
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Micrograph of ABS sample coated with copper via sputtering.

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Fig. 10
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Extracted profile of the surface of ABS sample sputtered with copper.

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The curve in Fig. 10, shows the extracted profile, indicate the surface’s average roughness falls in the same range as the measurements. The graph and the clumps of copper support the rough and irregular surface observed under AFM and contact measurement.

SEM/EDX is employed to determine the elemental makeup of the material that makes up the surface coating on the ABS sample.

Figure 11; Table 5 show the elemental analysis and break-up of the material that’s on the surface of the sample. Since the sample has undergone physical vapour deposition through sputtering where elemental copper is coated on the substrate, the presence of significant amount of copper, around 31% by weight, is expected. These results do back up the procedure described in literature.

Fig. 11
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EDX Elemental analysis of an ABS sample sputtered with copper.

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Table 5 Elemental breakup of an ABS sample sputtered with copper.
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Spray coated sample

Spray painting produced the most uniform surface modification. SEM and AFM analysis showed that valleys were filled, creating a continuous layer with minimal irregularities. Roughness reduced by ~ 70% (Ra = 6.5 μm), and hardness increased by 19%. EDX confirmed both carbon (substrate) and copper (paint) elements. These results demonstrate spray painting as a practical and scalable solution, consistent with recent reports on spray-coated ABS13. Figure 12(1) shows a 100x magnification of the printed, spray-painted portion. The grooves are visible as they take up more of the polythene putty, polyurethane primer and copper. The entirety of the surface is also covered with the material.

Figure 12(2) shows a micrograph of the same part at 500x magnification. This shows a few more of the printed part’s surface characteristics. The picture displayed near uniform distribution of the coating material on top of the substrate.

Fig. 12
figure 12

Micrograph of a spray-painted ABS sample.

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The curve in Fig. 13, shows the extracted profile, indicate the surface’s average roughness falls in the same range as the measurements. The graph and the sprayed material on the substrate seen in relevant figures support the fact that the newly identified technique does have reduced surface roughness.

Fig. 13
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Extracted profile of the surface of a spray-painted ABS sample.

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Figure 14 shows a micrograph at 5000 times magnification. The sprayed particles of copper can be easily distinguished from the smoothened layer of polyurethane underneath. This image corroborates the procedure which describes the polyurethane primer that has been sanded down smooth before the copper paint is sprayed on top.

SEM/EDX is employed to determine the elemental makeup of the material that makes up the surface coating on the ABS sample. Figure 15; Table 6 shows the elemental analysis and break-up of the material that’s on the surface of the sample.

Fig. 14
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Micrograph of spray-painted ABS sample at 5000 x.

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Fig. 15
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EDX Elemental analysis of a spray-painted ABS sample.

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Since the sample has sprayed with polyethylene putty, then polyurethane primer and a copper-based paint, the presence of significant amount of copper, around 21% by weight, and carbon, around 64% by weight, is expected. These results back up the procedure described in earlier sections.

Table 6 Elemental breakup of a spray-painted ABS sample.
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Comparative analysis

The numerical results are summarized in Table 2, which highlights the improvements in roughness and hardness for each treatment method. Among the three, spray painting provided the highest enhancement, whereas acetone dipping and sputtering offered moderate improvements with noted limitations.

Fig. 16
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Average surface roughness (Ra) of ABS FDM samples under different post-processing treatments.

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Fig. 17
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Hardness (Shore D) of ABS FDM samples under different post-processing treatments.

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The comparative improvements in surface roughness and hardness across the three post-processing methods are illustrated in Figs. 16 and 17. As shown in Fig. 3, uncoated samples exhibited an average surface roughness of ~ 22 μm, while acetone dipping and sputtering reduced Ra values to 14.2 μm and 12.8 μm, respectively. Spray painting achieved the most significant improvement, lowering surface roughness to 6.5 μm (a 70% reduction).

Figure 17 demonstrates the effect of each treatment on hardness. While acetone dipping resulted in negligible improvement, sputtering increased hardness by approximately 8%. The spray-painted samples again showed the greatest enhancement, with hardness increasing by 19% compared to uncoated specimens. These quantitative results corroborate the SEM and EDX observations, establishing spray painting as the most effective and scalable method among those studied.

Conclusion

The present study investigated the effect of three post-processing techniques—acetone dipping, copper sputtering, and spray painting—on the surface morphology of ABS parts fabricated by FDM. The following key conclusions can be drawn:

  • Uncoated samples exhibited poor surface finish (Ra ≈ 22 μm) and hardness (72 Shore D), characteristic of the anisotropic layer-by-layer FDM process.

  • Acetone dipping reduced surface roughness by ~ 35% (Ra = 14.2 μm) but caused dimensional variation and yielded negligible hardness improvement.

  • Copper sputtering decreased roughness by ~ 42% (Ra = 12.8 μm) and increased hardness by 8%, though coatings were non-uniform due to line-of-sight deposition.

  • Spray painting provided the most significant improvements, reducing roughness by ~ 70% and increasing hardness by 19%, producing a smooth and uniform surface.

  • SEM and EDX analyses confirmed the morphological changes and elemental composition, validating the effectiveness of the treatments.

  • Comparative analysis identified spray painting as a low-cost, scalable, and practical method for industrial applications, whereas acetone dipping and sputtering showed process limitations.

  • Acetone treatment, while effective in smoothing, compromises dimensional accuracy and may reduce mechanical strength.

  • Sputtering offers improved hardness but is time-intensive and less viable for large-scale parts.

Future studies should explore hybrid post-processing approaches i.e., parameter optimization with coating and extend testing to functional properties such as wear, adhesion, and fatigue. Future work may benefit from hybrid post-processing approaches, as highlighted by recent studies16, which demonstrate the potential of combining different techniques to overcome the limitations of single-method treatments.