Printing Defects Research Articles

Enhanced detection of surface deformations in LPBF using deep convolutional neural networks and transfer learning from a porosity model

Our previous research papers have shown the potential of deep-learning models for real-time detection and control of porosity defects in 3D printing, specifically in the laser powder bed fusion (LPBF) process. Extending these models to identify other defects like surface deformation poses a challenge due to the scarcity of available data. This study introduces the use of Transfer Learning (TL) to train models on limited data for high accuracy in detecting surface deformations, marking the first attempt to apply a model trained on one defect type to another. Our approach demonstrates the power of transfer learning in adapting a model known for porosity detection in LPBF to identify surface deformations with high accuracy (94%), matching the performance of the best existing models but with significantly less complexity. This results in faster training and evaluation, ideal for real-time systems with limited computing capabilities. We further employed Gradient-weighted Class Activation Mapping (Grad-CAM) to visualize the model’s decision-making, highlighting the areas influencing defect detection. This step is vital for developing a trustworthy model, showcasing the effectiveness of our approach in broadening the model’s applicability while ensuring reliability and efficiency.

Analysis of quality control in clothing production using SQC (Statistical Quality Control) and 5W+1H methods

CV Tujuh Pusaka Tala is a start-up company engaged in the clothing and sports jersey convection industry, as well as marching band musical instruments known by the brands 7MJR Store for clothing and SevenMajor for marching band musical instruments. This study was conducted to analyze the quality control of clothing production at CV. Tujuh Pusaka Tala using the Statistical Quality Control (SQC) method and the 5W and 1H approach to minimize defective products. The SQC methods used include Checksheet, Control Map, Histogram, Pareto Diagram and Cause and Effect Diagram to identify and control variability in the production process. While the 5W and 1H approach is applied to understand the main causes of product defects and find the right solution. The results of the study showed that there were 4 types of defects in the production process at CV. Tujuh Pusaka Tala, namely printing defects, screen printing defects, stitching, and material defects. The main factors causing production defects include humans, materials, machines, methods, and the environment. It can be concluded that the quality control of clothing production at CV. Tujuh Pusaka Tala using the Statistical Quality Control (SQC) method and the 5W and 1H approach to minimize defective products has been implemented well so that it can minimize the existence of defective products.

Challenges on extrusion-based additive manufacturing of thermoplastic polyurethane

Fused filament fabrication (FFF) offers rapid production with user-friendly operation and cost-effectiveness, yet challenges in printing with thermoplastic polyurethane (TPU) persist. This study identifies causes of print defects in FFF-TPUs and their relation to process parameters, by visually analysing samples produced with various TPU materials. Extrusion temperature, printing speeds, filament cooling, overlap, and extrusion flow are subject to evaluation. Common issues include filament entanglements, under-extrusion, stringing, or geometric deviations. Among other approaches, results highlight the importance of slow, constant print speeds and careful optimization of extrusion temperature.

EFFECT OF BUILD POSITION ON SURFACE ROUGHNESS OF SLM PRINTED INCONEL 718

The present work investigates the variation of the surface roughness due to the build position of specimens with respect to the inert gas flow direction and re-coater movement direction. Selective laser melting (SLM) method was used to study this effect using Inconel 718 as workpiece material. A total of 21 samples were placed equidistant from each other on the built plate to observe the effect of gas flow and re-coater movement. The effect of these parameters on the printed samples was analyzed in terms of the profile surface roughness parameter such as Ra and Rz in the build direction. The result showed that samples placed near the gas inlet and the re-coater starting position had larger roughness as compared to the samples placed further from the gas inlet and re-coater end position. The result showed that the profile average roughness parameter values varied from Ra = 5.02 µm to 14.7 µm and profile maximum height surface parameter varied from Rz = 47.61 µm to 118.3 µm for all the printed samples. Surface topography of the samples was also studied which showed common printing defects such as cracks, micropores, local solidified melt pools, and dimples. The study opens an avenue to explore and optimize the placement of the printing sample on the build plate with respect to the inlet gas flow and re-coater movement directions for better surface roughness.

Experimental investigation of material extrusion additive manufacturing of copper with high powder loading rate

Beam-based additive manufacturing has challenges in fabricating pure copper due to high reflectivity. Material extrusion additive manufacturing (MEAM) avoids these issues with low costs, making it suitable to fabricate complex structures in pure copper. In this work, the effects of several printing parameters on the geometry of the samples are studied from single line, thin wall to cube using homemade copper feedstocks with high powder loading rate (65 vol%). The results show that the single line is most affected by layer thickness, while the thin wall has stricter requirements for printing temperature and printing speed. The geometric accuracy of the cube demonstrates large parametric tolerance due to the overlap and support between the lines. Central composite face-centered (CCF) design and central composite design (CCD) are used to analyze and optimize process parameters for densification. The measured porosity at the optimized printing (printing temperature = 177 °C, air gap = −0.05 mm, layer thickness = 0.3 mm) and sintering parameters (sintering temperature = 1045 °C, holding time = 4 h) is in good agreement with the predicted values. Air gap and sintering temperature have the greatest influence on the porosity, and other parameters within a certain range of on-demand adjustments do not have a significant effect. The ultimate tensile strength and elongation of the sintered samples under the optimal parameters are 153.9 ± 6.1 MPa and 31.36 ± 3.24%, respectively. No printing defects are found at the fracture and the elongation is good, showing the effectiveness of the parameter optimization.

Roles of Modeling and Artificial Intelligence in LPBF Metal Print Defect Detection: Critical Review

The integration of LPBF printing technologies in various innovative applications relies on the resilience and reliability of parts and their quality. Reducing or eliminating the factors leading to defects in final parts is crucial to producing satisfactory high-quality parts. Extensive efforts have been made to understand the material properties and printing process parameters of LPBF-printed geometries that trigger defects. Studies of interest include the use of various sensing technologies, numerical modeling, and artificial intelligence (AI) to enable a better understanding of the phenomena under investigation. The primary objectives of this article are to introduce the reader to the most widely read published data on (1) the roles of numerical and analytical models in LPBF defect detection; (2) AI algorithms and models applicable to predict LPBF metal defects and causes; and (3) the integration of modeling, AI, and sensing technology, which is commonly used in material characterization and has been proven efficient and applicable to LPBF metal part defect detection over extended periods.

A two-stage defect detection method for unevenly illuminated self-adhesive printed materials

The process of printing defect detection usually suffers from challenges such as inaccurate defect extraction and localization, caused by uneven illumination and complex textures. Moreover, image difference-based defect detection methods often result in numerous small-scale pseudo defects. To address these challenges, this paper proposes a comprehensive defect detection approach that integrates brightness correction and a two-stage defect detection strategy for self-adhesive printed materials. Concretely, a joint bilateral filter coupled with brightness correction corrects uneven brightness properly, meanwhile smoothing the grid-like texture in complex printed material images. Then, in the first detection stage, an image difference method based on a bright–dark difference template group is designed to effectively locate printing defects despite slight brightness fluctuations. Afterward, a discriminative method based on feature similarity is employed to filter out small-scale pseudo-defects in the second detection stage. The experimental results show that the improved difference method achieves an average precision of 99.1% in defect localization on five different printing pattern samples. Furthermore, the second stage reduces the false detection rate to under 0.5% while maintaining the low missed rate.

The effect of Polyolefin elastomer on the 3D printing properties of Acrylonitrile butadiene styrene, Polyethylene, and Polypropylene

This study investigates the influence of incorporating 30 wt.% polyolefin elastomer (POE) on the physical, mechanical, and microstructural properties of 3D printed three widely used thermoplastic: acrylonitrile butadiene styrene (ABS), low density polyethylene (LDPE), and polypropylene (PP). Three ABS-POE, LDPE-POE, and PP-POE blends were prepared by melt mixing method and printed by direct granule-based material extrusion, and finally the printability, microstructure, thermal, and mechanical properties aiming for potential usage in various applications were investigated. Dynamic Mechanical Thermal Analysis (DMTA) results revealed a notable shift in the glass to rubber phase to a higher temperature range and an increase in the glass transition temperature due to the presence of POE elastomers. Mechanical properties of the 3D printed samples were meticulously examined and compared with prior research. All blend samples containing 30 wt.% POE exhibited significantly enhanced ductility, attributed to aligned polymer chain reactions. ABS-POE samples demonstrated superior mechanical properties compared to PP-POE and LDPE-POE samples, likely attributed to fewer potential failure points, as evidenced by Scanning Electron Microscope (SEM) analysis of fractured cross-sections of 3D-printed samples immersed in liquid nitrogen. Additionally, 3D-printed samples with combined infill orientations (0° and 90°) were generated and subjected to tensile strength testing. Furthermore, samples 3D-printed specimens by honeycomb filling pattern for compression tests were included in the study. Microstructure analyses identified common 3D printing defects responsible for failure modes in the printed samples.

Warpage control in thermoplastic ABS parts produced through material extrusion (MEX)-based fused deposition modeling (FDM)

PurposeAdditive manufacturing (AM) is a layer-by-layer technique that helps to create physical objects from a three-dimensional data set. Fused deposition modeling is a widely used material extrusion (MEX)-based AM technique that melts thermoplastic filaments and selectively deposits them over a build platform. Despite its simplicity and affordability, it suffers from various printing defects, with partial warping being a prevalent issue. Warpage is a physical deformation caused by thermal strain incompatibility that results in the bending of the printed part away from the build platform. This study aims to investigate the warpage characteristics of printed parts based on geometrical parameters and build orientations to reduce the warpage extent.Design/methodology/approachCuboidal samples of thermoplastic acrylonitrile butadiene styrene ranging from 5 to 80 mm were printed using a commercial MEX system. A Taguchi method-based design of experiment trial was performed to optimize the placement and orientation of the part for minimal warpage.FindingsIt was found that a lower value of the “in-plane” aspect ratio and a more prominent part thickness are favorable for minimal warpage. The part should always be placed near the region with the highest temperature (least thermal gradient) to minimize the warpage.Originality/valueA novel dimensionless parameter (Y) is proposed that should be set to a minimum value to achieve minimal warpage. The results of this study can help improve the design and part placement for the MEX technique, thus elevating the print quality.

Critical Review of LPBF Metal Print Defects Detection: Roles of Selective Sensing Technology

Critical Review of LPBF Metal Print Defects Detection: Roles of Selective Sensing Technology

Evaluation of microstructure and mechanical properties of additively manufactured Ti–5V–5Mo-5 Al-3 Cr alloy

Ti–5V–5Mo–5Al–3Cr (Ti-5553) is a near-beta titanium alloy commonly used in aerospace applications. It is currently being explored for additive manufacturing (AM), but the fatigue behavior of this AM alloy needs to be well-understood for adoption. This paper explores the tensile and high-cycle fatigue behavior of laser powder bed (LPBF) manufactured Ti-5553 that has been post-print heat treated with a beta anneal and age (BAA), with a focus on the microstructural evolution and effects of surface roughness and print defects. Fatigue lives of as-LPBF and BAA material are nearly identical and both are far below fatigue lives of conventionally manufactured Ti-5553. As-built samples contain columnar β grains with a [001] texture in the build direction with a negligible fraction of α phase confirmed by electron backscatter diffraction (EBSD). The BAA material contains HCP alpha-phase precipitates: grain boundary α, primary α, and secondary Widmanstätten α. Fatigue samples were printed in the vertical direction and tested with an as-printed and machined surface. Both the as-LPBF and BAA samples exhibit similar fatigue strengths despite their vastly different microstructures. Machined surfaces led to an increase in tensile strength, ductility, and fatigue strength. This work emphasizes the importance of heat treatment and minimization of flaws inherent to AM processing of near-beta Ti-5553.

Pengendalian Kualitas Produk Cacat Jumbo Bag Menggunakan Siklus Pdca (Plan-Do-Check-Act) di PT. XYZ

PT. XYZ, a plastic bag packaging industry, is still facing poor quality problems and a high level of malfunction. The sewing and printing sectors are the biggest contributors to defects in the production of Jumbo Bag. The objective of this research is to identify the causes of dominant defects, provide repair solutions, and reduce product defects, as well as decrease the value of defects per unit of dominating defects. To solve this problem, the researchers used the plan-do-check-action method (PDCA). The PDCA method is used to identify and address defects, while the 5W1H is used for identifying the cause of defects and developing corrective solutions. Using this method, PT. XYZ can reduce product defects and improve the quality of the Jumbo Bag. The result is a reduction in defects per unit of wrong sewing defect from 0.014 DPU to 0.005 DPU, accessory deficiency defects from 0.008 DPU to 0.04 DPU, hole defects of 0.007 DPU to 0.001 DPU, and printing defects from 0.004 DPU to 0.044 DPU. Thus, the company can improve product quality and meet customer expectations.

Effects of different binder systems on the characteristics of metal-based diamond composites fabricated via fused deposition modeling and sintering technology

In material extrusion of metal-based composites, binder system plays a vital role and its performance directly influences the quality of the final product and process efficiency. Despite different binder systems have been produced, most studies only concentrated on single binder system without comparison between different binder systems. In this work, two different binder systems were used to fabricate metal-based diamond composites by fused deposition modeling and sintering technology. Morphology of printed metal-based composites samples were compared. Thermal properties of composites samples with different binder systems were analyzed via TG-DSC test, and debinding was carried out at heating rate of 5 °C/min and 2 °C/min, respectively. Then the brown samples were densified via hot-pressing sintering, and the sintered samples were evaluated by scanning electron microscopy, hardness tester and universal testing machine. During the printing process, the feedstock using TP-based binder system exhibited better printing performance compared with that using the PW-based binder system. The results also revealed that appropriate nozzle temperature should be determined according to the thermal properties of the feedstocks so as to minimize printing defects. The debinded samples with different binder systems can retain structural integrity when the heating rate controlled properly. As for the samples after sintering, it has to be highlighted that the hardness on the top surface of the sintered sample was higher than the hardness on the side because of different deposition characteristics. In addition, the samples using TP-based binder presented a more uniform microstructure and thus obtained better flexural strength and relative density. It can be concluded that the TP-based binder is preferable as it contributes to better performance of the metal-based diamond composites compared with the PW-based binder.

Interlaminar tensile properties of raw and carbon fiber‐wrapped additively manufactured polyetherimide

AbstractHigh‐performance engineering thermoplastics are important emerging materials, particularly when processed using additive manufacturing technologies. One of the most important among these is polyetherimide, also known as PEI or ULTEM. Using the fused filament fabrication (FFF) additive manufacturing (AM) process to form this material is a good option, but it is difficult to control the properties in some cases due to the very high processing temperature compared with most engineering thermoplastics. One way to “even‐out” the properties is to wrap the specimens in continuous glass or carbon fibers embedded in a thermosetting matrix, as this allows strategic placement and orientation of reinforcement. This also complements the natural structure of the FFF‐manufactured materials, helping to minimize the amount of additional weight that needs to be added to a part. To further knowledge in this area, the present study explored and compared the interlaminar tensile strength of FFF‐processed PEI/ULTEM 9085 specimens and compared them with ones wrapped in carbon fibers with a 2‐part resin matrix. Experiments were performed in accordance with the guidelines given in the ASTM D6415 standard and replicated five times. Variations were introduced in thickness of the specimen and raster angle during the manufacturing process to identify the significant impact of the failure. The results show a fall in interlaminar tensile strength with increasing specimen thickness and a very large effect from natural printing defects in the samples. The carbon fiber wrap decreased the ILTS but made the results far more consistent between experimental runs. This study provides a good, replicated dataset on the performance of raw and fiber‐wrapped FFF‐processed ULTEM 9085 and gives insights into the structural behavior of the material that will be useful for use in design decisions and material selection.Highlights Polyetherimide, also known as PEI/ULTEM, is a high‐performance engineering thermoplastic. Explored the interlaminar tensile properties (ILTS) of this material using ASTM D6415. Raster angle, thickness, and use of fiber wrap were experimental parameters. Fiber wrap was found to have little effect on strength but made results more consistent. Results are useful for material selection and design decisions using PEI.

The role of crystallization and annealing on the thermal conductivity of material extrusion additively manufactured parts

Despite the significant research being conducted on the mechanical reliability of additively manufactured parts, comparatively little focus has been paid to the property of thermal conductivity. Additively manufactured thermally conductive parts have the potential to benefit thermal management technologies that are currently a bottleneck of many classes of advanced electronic devices. Creating parts with high thermal conductivities remains a major challenge for the most prevalent form of material extrusion additive manufacturing, fused filament fabrication, which creates parts by extruding multiple layers of molten polymeric extrudate using an automated gantry system. The low thermal conductivity of these parts stems from several types of interfaces and voids inherent to the fused filament fabrication additive process, which create significant internal resistance to the flow of heat through a part. To increase thermal conductivity, many researchers and companies have added thermally conductive particles into the polymeric filaments. Still the achievable properties are largely constrained by the printing defects inherent to the printing process, especially when compared to injection molded parts. In this work, we investigate the role of thermal post-processing to both anneal the printed part and to tune the crystallization state of the polymer. We find that careful thermal post-processing of parts made with commercial filaments can improve thermal conductivity values to 2.5 times the as-printed property values. Further, we detail several correlations between processing conditions and thermal conductivity outcomes that will improve the implementation of fused filament fabrication for addressing thermal management challenges in industry.

FFF print defect characterization through in-situ electrical resistance monitoring

Fused filament fabrication is a popular fabrication technique. Currently there is a need for in-situ monitoring modalities to gather real-time information on prints, both for quality control and closed-loop control. Despite current advancements, effective and affordable in-situ monitoring techniques for non-destructive defect detection of voids and bonding quality are still limited. This work demonstrates in-situ monitoring of fused filament fabrication through electrical resistance measurements as an alternative to thermal and optical methods. A new, easy-to-implement setup is demonstrated which measures the electrical resistance of a conductively doped filament between the nozzle and single or multi-electrodes on the bed. Defects can be located in an unprecedented way with the use of encoded axes in combination with the observed resistance variations throughout the part. A model of the anisotropic electrical conduction is used to interpret the measurements, which matches well with the data. Warping, inter-layer adhesion, under-extrusion and overhang sagging print defects can be observed in the measurements of parts with a complex geometry, which would be difficult to measure otherwise. Altogether in-situ electrical resistance monitoring offers a tool for optimising prints by online studying the influence of the print parameters for quality assessment and it opens up possibilities for closed-loop control.

Experimental and numerical investigation of the squeegee process during stencil printing of thick adhesive sealings

ABSTRACT To reliably compensate fuel cell stack tolerances, sealings with a layer thickness of at least 500 µm are necessary. Additionally, threads positioned at the upper region of the stencil apertures need to be integrated to print closed-loop designs under cycle times of as low as 3 seconds. All these requirements can intensify the occurrence of print defects and diminish the process stability. This paper addresses the issues of incomplete regions and air bubbles emerging during the squeegee process. It was detected that the cleanliness state of the stencil directly impacts the formation of incomplete regions by affecting venting conditions inside the aperture. Moreover, it was identified that bubbles are either transferred from the adhesive roll into the aperture or created due to interactions between the moving adhesive and stencil threads. Further, it was shown that bubbles cannot be completely eliminated using a stencil with threads but their size can remain smaller than 300 µm when printing with a new adhesive roll. Finally, distinct strategies were derived and verified experimentally to successfully print a basic sealing design. By introducing a small local gap between substrate and stencil, the entire sealing aperture was reliably filled without the need of a cleaning step.

Boundary Gaussian Distance Loss Function for Enhancing Character Extraction from High-Resolution Scans of Ancient Metal-Type Printed Books

This paper introduces a novel loss function, the boundary Gaussian distance loss, designed to enhance character segmentation in high-resolution scans of old metal-type printed documents. Despite various printing defects caused by low-quality printing technology in the 14th and 15th centuries, the proposed loss function allows the segmentation network to accurately extract character strokes that can be attributed to the typeface of the movable metal type used for printing. Our method calculates deviation between the boundary of predicted character strokes and the counterpart of the ground-truth strokes. Diverging from traditional Euclidean distance metrics, our approach determines the deviation indirectly utilizing boundary pixel-value difference over a Gaussian-smoothed version of the stroke boundary. This approach helps extract characters with smooth boundaries efficiently. Through experiments, it is confirmed that the proposed method not only smoothens stroke boundaries in character extraction, but also effectively eliminates noise and outliers, significantly improving the clarity and accuracy of the segmentation process.

An easy-to-build, accessible volumetric 3D printer based on a liquid crystal display for rapid resin development

Additive manufacturing has revolutionized the way prototypes and one-off parts are produced, but standard additive manufacturing techniques such as material extrusion or vat photopolymerization still present various issues like high print times and defects due to the layer-by-layer nature of the print process. Computed axial lithography (CAL), a novel volumetric additive manufacturing technique, solves many of the issues associated with traditional 3D printing, like staircasing defects and long printing times. However, state of the art CAL requires complex optical setups, limiting access to a working machine, greatly reducing the pace of new material and technologies being adapted to CAL. The Liquid Crystal Display-based computed axial lithography (LCD-CAL) setup here presented keeps many of the advantages of CAL, but utilizes a single lens and an LCD for its optical setup. By moving to LCDs, the machine cost is greatly reduced, and the extremely simplified optical setup of LCD-CAL makes CAL widely accessible. To highlight the versatility of the developed LCD-CAL, we design and characterize two high-viscosity resins for CAL printing based on highly crosslinked and bio-based acrylates, respectively. This work paves the way for widespread adoption of volumetric 3D printing by making a low cost, high speed CAL printer available.

Enhancing the Performance of the Mesoporous TiO2 Film in Printed Perovskite Photovoltaics through High‐Speed Imaging and Ink Rheology Techniques

AbstractMesoscopic carbon‐based perovskite solar cells (C‐PSCs) have the potential to be manufactured at an industrial scale by utilizing screen‐printing, a simple, affordable, and commercially mature process. As such, many recent publications have focused on enhancing performance through modifying cell architecture and perovskite chemistries. This work examines how ink rheology can be tuned to optimize cell performance through reducing the occurrence of common print defects to create higher quality m‐TiO2 films. Inks with different solvent dilutions and rheological profiles are assessed using high‐speed imaging through the screen‐printing visualization (SPV) technique, to investigate the impact of the viscosity and elasticity on ink separation mechanisms. The resultant film quality and its influence on device performances are then assessed. Ink separation lengths are minimized, and the formation of filaments ceases during printing, leading to improved TiO2 film topography and homogenous infiltration of the perovskite precursor. Consequently, PCE is improved by over 10% of the original efficiency in cells and 224 cm2 active area modules due to enhanced Voc and FF. These results not only provide key insights into tailoring ink rheology, to achieve improved print homogeneity and higher performing cells, but also aid further work on enhancing the performance of other screen‐printed functional films.