Printing Defects Research Articles

Efficient modelling of surface roughness effects in additively manufactured materials

3D printing defects are often used to explain the mismatch between numerical predictions and experimental results of additively manufactured acoustic materials. Although they are often perceived as desirable, as in most cases, they improve the absorptive behaviour of the system, occurring gains are unplanned and uncontrollable. Among different 3D printing inaccuracies, surface roughness provides additional acoustic losses, mostly due to the enlargement of the boundary layer thickness. On the other hand, roughness is responsible for the shift of the operating frequency compared to the numerical predictions. The goal of this research is to provide efficient modelling methods to capture the effects of surface roughness arising from the additive manufacturing process. First, a direct modelling method will be discussed, which can be computationally expensive as it relies on an accurate geometrical representation of surface roughness. Second, an alternative indirect modelling approach will be presented, which mimics the presence of roughness by adjusting specific air parameters in the locations of interest of the smooth geometry to reduce the computational cost. The two strategies will be compared with each other and to the results of an experiment where additional roughness is added to target locations within the design.

Additive manufacturing of sensor prototype based on 3D-extrusion-printed zirconia ceramics

Additive manufacturing of ceramics has attracted large interest due to its unique ability to rapidly prototype, low cost, and increased geometric complexity. Material extrusion technique is often considered for processing and shaping fine and dense ceramic structures because of the high solid loading in ink. In this work, 8 mol.% yttria-stabilized zirconia ink with 70 wt% ceramic loadings was prepared to print zirconia samples in horizontal and vertical directions, following two different filament orientations: 0/90° and ±45°. The study's main objective was to evaluate printing design influences on mechanical properties. This was assessed through flexural testing and digital image correlation analysis. Experimental findings showed that samples printed horizontally with ±45° filament orientation displayed the highest strength. A detailed inspection of fracture surfaces revealed that printing defects were the critical failure location sites formed after sintering and intimately related to printing design issues. After that, a conductive sensor was integrated into the surfaces of 3D-printed specimens by screen-printing silver-based conductive ink to analyze the structural health of zirconia samples. The sensing capabilities of printed conductive patterns were investigated using the four-point bending tests. The results demonstrated that the electrical resistance of the printed silver patterns increased as the applied load on zirconia substrates rose. It indicates that hybrid material extrusion and screen printing techniques are favored ways to manufacture sensors for structural detection of advanced 3D-printed ceramics.

Enhancing additive manufacturing precision: Intelligent inspection and optimization for defect-free continuous carbon fiber-reinforced polymer

Artificial intelligence (AI) has emerged as a pivotal tool in managing extensive datasets, enabling pattern recognition, and deriving solutions, particularly revolutionizing additive manufacturing (AM). This study intends to develop AI deep machine learning image processing techniques for real-time defects detection in additively manufactured continuous carbon fiber-reinforced polymer(cCFRP) specimens. Leveraging YOLOv8- a state-of-the-art, single-stage object detection algorithm, this study focuses on the relationship between printing parameters and defect occurrences, specifically misalignment errors. The research delineates a methodological advancement by correlating detected defects with parameter optimization, leading to significant quality improvements in cCFRP specimens. An impressive 94 % accuracy in detecting misalignments was achieved through fine-tuning the nozzle temperature adjustment, resulting in significant reductions in misalignment errors, while minimal impact is observed from print bed temperature, feed amount, and feed rate/sec on refining the proposed model for identifying optimal parameters.

Experimental and numerical investigation on novel three-dimensional printed bio-inspired hexagonal lattices for energy absorption and stiffness behavior

In the current study, a new type of novel lattice structures with the concept of bio-mimicking three different nature-inspired designs from the honeycomb patterns, the overlapping phenomenon of the scales present on fish dermal layers, and scutes pattern observed from the top skin layers present on crocodile species are developed. These lattice structures are designed within a cubic volume of 30 mm. The design of lattice unit cells is made with two different geometrical sizes of 4 and 6 mm with different overlapping areas of 20, 30, 40, and 50% calculated from each cell area. All the unit cells’ walls are maintained at 0.4 and 0.6 mm only. The specimens are modeled and manufactured through the VAT photopolymerization process, one of the significant additive manufacturing principles for great dimensional accuracy with negligible defects in 3D printing (3DP). The research approach used to develop lightweight bio-inspired structures has been laid out, starting with observing design that served as inspiration. The cured 3D-printed specimens are examined under quasi-static compressive loading carried out on all specimens as per ASTM 1621 standards to measure the crashworthiness response of designed specimens. The energy ingestion capacity of all the specimens is assessed. A good correlation is observed between the experimental and numerical results for better validation. The best design parameters among all 16 specimens are identified for applying energy absorption applications in the automobile and aviation fields in real-time.

Research and Analysis of Modern Printer and Printing Defects

A printer is already crucial office equipment. However, when using any printer, it is normal to see defects in the printed contents. The research integrates the common defects that users will encounter and analyzes some feasible solutions. The paper focuses on the basic procedures of the laser printer and analyzes the common printing defects based on the procedures. After some analysis, the paper finds that most regular defects can result from malfunctioning charging units for the charging process, the laser path and its optical components, or the photosensitive drum. Afterward, the paper addressed some improvements to inhibit the defects, including enhancing craftsmanship to different units. The paper has left the common users some insights on solving the defects and has provided the manufacturers or the researchers with ideas for further improvement.

Enhancement of fatigue properties of selective laser melting fabricated TC4 alloy by multiple shot peening treatments

This study investigated the impact of multiple shot peening (SP) treatments on the surface morphology, microstructure, residual stress and fatigue performance of TC4 alloy manufactured by selective laser melting (SLM). The multiple SP treatments were conducted sequentially using cast steel beads, ceramic beads and glass beads at different peening intensities. In comparison to the conventional single SP process, multiple SP treatments reduced surface roughness and stress concentration coefficient while further increasing the residual compressive stress on the alloy surface. SP significantly enhanced the fatigue life of the alloy by 6.4 to 9.6 times, with a more pronounced improvement observed with multiple SP. Fatigue fracture analysis revealed that the untreated alloy showed multiple fatigue sources which all located on the surface, with surface printing defects acting as potential sites for crack initiation. After SP treatments, all fatigue cracks were initiated beneath the surface. The improved fatigue performance of SLM-formed TC4 alloy could be mainly attributed to the SP-induced surface microstructure refinement and residual compressive stresses. Furthermore, results indicated that, for subsurface crack initiation, the initial cracks primarily stemmed from the fracture of α/α' martensite in the primary β columnar grains.

Design of intelligent inspection system for solder paste printing defects based on improved YOLOX

Aiming at the current SPI (solder paste inspection) system for printing solder paste similar defects detection accuracy is not high, the system intelligence degree is low and so on, design a for the solder paste similar defects and combined with phase modulation profile measurement technique and improve the YOLOX intelligent detection system. The core of the system is the improved YOLOX depth model based on s-mosica and kt-iou algorithms proposed in this paper. The experimental results show that the proposed s-mosica and kt-iou algorithms can effectively improve the detection accuracy of printed solder paste, and when combined with the YOLOX model, the best 90.33% detection accuracy is obtained, which is better than the detection performance of the existing algorithms in the same scenario, and it provides an effective and feasible reference program for the design of the SPI high-precision intelligent detection system.

In-situ qualification and physics-based process design for aerosol jet printing via spatially correlated light scattering measurements

Aerosol jet printing is a contactless, digital, and additive technique broadly used for manufacturing flexible, hybrid, and conformal electronics. However, both intra-batch and batch-to-batch variability have hindered widespread industry adoption and scaling to production volumes. Recently, light scattering measurements have emerged as a tool to measure aerosol volume fraction – a key parameter determining deposition rate – and have proven an effective feedback source for closed-loop control on timescales ranging from tens of minutes to hours. While this is a promising capability to mitigate long-term process drift, it lacks the temporal resolution to validate print quality for complex and precise electronic circuits. Here, real-time process monitoring with <1 s resolution is demonstrated for in-situ qualification of aerosol jet printing. To begin, the correlation between light scattering and aerosol deposition is validated at 500 ms time intervals, allowing deposition rate to be mapped to positional coordinates and providing a new data stream to drive quality control assessments. This allows optical scattering to be connected to electrical properties including line and sheet resistance, resulting in predictions nominally within 10% of measured values for sets of printed devices. Finally, the ability to spatially correlate print defects during fabrication is demonstrated as a foundation for a print repair framework, successfully repairing prints with randomly induced defects to achieve resistance within 5% of a control set.

Corrosion behavior of selective laser melting-manufactured bio-applicable 316L stainless steel in ionized simulated body fluid

Additive manufacturing (AM) is gaining increasing popularity in various fields, including biomedical engineering. Although AM enables fabrication of tailored components with complex geometries, the manufactured parts typically feature several internal issues, such as unpredictable distribution of residual stress and printing defects. However, these issues can be reduced or eliminated by post-processing via thermomechanical treatment. The study investigated the effects of combinations of AM and post-processing by the intensive plastic deformation method of rotary swaging (variable swaging ratios) on microstructures, residual stress, and corrosion behaviors of AISI 316L stainless steel workpieces; the corrosion tests were performed in an ionized simulated body fluid. The results showed that the gradual swaging process favorably refined the grains and homogenized the grain size. The imposed swaging ratio also directly influenced the development of substructure and dislocations density. A high density of dislocations positively affected the corrosion resistance, whereas annihilation of dislocations and formation of subgrains had a negative effect on the corrosion behavior. The first few swaging passes homogenized the distribution of residual stress within the workpiece and acted toward imparting a predominantly compressive stress state, which also favorably influenced the corrosion behavior. Lastly, the presence of the {111}||swaging direction texture fiber (of a high intensity) increased the resistance to pitting corrosion. Overall, the most favorable corrosion behavior was acquired for the AM sample subjected to the swaging ratio of 0.8, exhibiting a strong fiber texture and a high density of dislocations.

Defect monitoring in additive manufacturing through OpenCV-based remote video access

Errors in additive manufacturing are a significant obstacle to its widespread adoption in various application. The developments of 3D printed parts are prone to various types of defects, which are difficult to monitor in real-time through human vision. The use of 3D printers has increased in diverse fields, leading to a significant rise in the need of continuous monitoring during the manufacturing process. Prompt action should be taken to stop or correct errors immediately to prevent a defective part. However, continuous monitoring of 3D printer through human vision is impractical for longer tasks and cannot be accurate. Human inspection is not infallible and could introduce its own errors. Given the multitude of application, continuous defect monitoring is extremely challenging, particularly for longer tasks. Based on these constraints a suitable remote monitoring system through open-source computer vision has been proposed. Incorporating the concept of Internet of things, the video of printing process could be viewed by a user or controller from a remote location enabling to monitor the printing process. With the use of Haar classifier in the program, the printing defects that occur in the 3D printed part could be identified immediately through contours drawn over the defective part. Depending upon the severity of defect indicated, the user could take respective action to control the defect formation. With Industry 4.0 in the implementation stages, this method of video monitoring of defects in 3D printers could be an effective method for widespread use of additive manufacturing systems in industries.

Elimination of gas entrapment in droplet-based 3D printing by induced electric-field

Gas entrapment during droplet deposition may induce pinhole defects in droplet-based 3D printing. However, achieving effective suppression of gas entrapment is challenging given that gas entrapment behavior is the physical essence of droplet impact. Inspired by that charged droplets will be deformed in the electric field, a method of suppressing gas entrapment by weakly charging the droplet was proposed. Here, a numerical model is developed to systematically investigate the gas entrapment behaviors during neutral droplet and charged droplet deposition. Results show that the electric field will be induced before the instant of droplet impact on the substrate, which fundamentally changes the gas entrapment behavior. Moreover, the competition mechanism between Maxwell stress and lubrication pressure during droplet deposition is revealed, and the pressure inside and outside the droplet bottom profile is quantified. Compared with the neutral droplet, the additional electric stresses act against the lubrication pressure, which increases sharply before the droplet touches the substrate. When the charge level reaches a critical value, the electric stresses are slightly stronger than the lubrication pressure at the bottom center, and the decrease rate of electric stresses along the horizontal distance r is higher than that of gas film pressure, leading to a central touchdown with residue concentric circle gas rings. Furthermore, the evolution of phase fraction, velocity field, and pressure field during droplet deposition with different charge level is investigated comprehensively. Based on this, the dimensionless scale of critical charge level to fundamentally eliminate gas entrapment is obtained. This work may provide new insights into various applications involving droplet deposition, such as eliminating pinhole defects in droplet-based additive manufacturing.

Impact of Element Layout and Notching Technique on the Fracture Toughness of FFF-Processed Thermoplastics

This work explores the effects of notching method and element layout on the fracture loading properties of thermoplastic materials processed using fused filament fabrication (FFF). Three common thermoplastic materials were used (acrylonitrile butadiene styrene, polylatide, and polycarbonate). Four different notching methods were used, with printed and machined notches and with and without pre-cracking on ASTM D5045 compact tension specimens (n = 36). It was concluded that the notching method has a statistically significant impact on the sample preparation and that pre-cracking is necessary in all cases. Using this information to prepare specimens, a designed experiment using four different element layout strategies and two different nozzle sizes was completed with a total of 72 tests. The layout pattern was shown to have a very strong effect on the maximum fracture load, with the nozzle size showing a smaller but still statistically significant impact. With the exception of one layout using polycarbonate with likely design-driven printing defects, the results were very consistent through several replications. The results of this study are useful for making design decisions with FFF-processed materials, for better understanding the impact of the process design, and for working toward standardized printing and testing methods for additive manufacturing.

Limiting defect in vat photopolymerization via visual-guided in-situ repair

Vat photopolymerization 3D printing has gained significant attention due to its fast printing speed and high precision. However, the absence of effective quality assurance methods greatly limits its applications. Current vat photopolymerization cannot deal with commonly occurring defects during the printing process, such as random bubbles and resin underfill, making it challenging to consistently produce products that match designed geometry and functions. To address this, we propose an innovative vat photopolymerization solution via visual-guided in-situ repair to effectively eliminate printing defects. By utilizing an enhanced YOLOv5 network and K-means algorithm, real-time detection of bubbles and resin underfill can be achieved using image analysis. The optimal method for defect repair was then automatically generated via the adaptive scraper control and the repair slice edge smoothing generation algorithm, which was immediately received by hardware to adjust the ongoing printing parameters without interrupting the continuous printing process. Experimental results demonstrate that the aforementioned strategy can accurately differentiate typical defects such as bubbles and resin underfill, and precisely carry out in-situ defect repairs. Comparisons between repaired samples and defect-free samples show minimal differences in surface morphology and fracture strength (¡0.6%). The proposed solution is also applicable to various precursors. Clearly, the strategy above offers a universal approach to avoid defects in vat photopolymerization, which effectively enhances printing efficiency, reduces material wastage, and ensures the quality, accuracy, and reliability of printed products.

Effects of dispersant concentration on the properties of hydroxyapatite slurry and scaffold fabricated by digital light processing

For the UV-curable hydroxyapatite (HA) slurry used in digital light processing (DLP), the optimal dispersant concentration is always selected based on the viscosity and stability of the slurry. However, the interaction mechanism between the dispersant and HA particles and its influence on the fabrication process were overlooked. In this study, the dispersion mechanism of BYK111 and its effects on the rheology, stability, and curing behavior of the HA slurry, as well as the linear shrinkage and layer morphology of the HA scaffold, were systematically investigated. The results indicated that changes in viscosity and stability affected the penetration of UV light and the propagation rate of the polymerization reaction. Insufficient dispersion of the slurry (3 wt% BYK111) led to reduced printing precision due to high viscosity, settling, and scattering. Interestingly, the lower viscosity and enhanced stability of HA slurry with 4 wt% BYK111 did not yield both the deepest curing depth and narrowest excess curing width. The high curing accuracy of the HA slurry (4 wt% BYK111) was evidenced by the largest broadening depth. Moreover, the improved slurry performance also helped reduce printing defects and improve surface quality.

Pressure-based process monitoring of direct-ink write material extrusion additive manufacturing

As additive manufacturing (AM) has become a reliable method for creating complex and unique hardware rapidly, the quality assurance of printed parts remains a priority. In situ process monitoring offers an approach for performing quality control while simultaneously minimizing post-production inspection. For extrusion printing processes, direct linkages between extrusion pressure fluctuations and print defects can be established by integrating pressure sensors onto the print head. In this work, the sensitivity of process monitoring is tested using engineered spherical defects. Pressure and force sensors located near an ink reservoir and just before the nozzle are shown to assist in identification of air bubbles, changes in height between the print head and build surface, clogs, and particle aggregates with a detection threshold of 60–70% of the nozzle diameter. Visual evidence of printed bead distortion is quantified using optical image analysis and correlated to pressure measurements. This methodology provides an ability to monitor the quality of AM parts produced by extrusion printing methods and can be accomplished using commonly available pressure-sensing equipment.

Geometric Accuracy and Energy Absorption Characteristics of 3D Printed Continuous Ramie Fiber Reinforced Thin-Walled Composite Structures

The application of continuous natural fibers as reinforcement in composite thin-walled structures offers a feasible approach to achieve light weight and high strength while remaining environmentally friendly. In addition, additive manufacturing technology provides a favorable process foundation for its realization. In this study, the printability and energy absorption properties of 3D printed continuous fiber reinforced thin-walled structures with different configurations were investigated. The results suggested that a low printing speed and a proper layer thickness would mitigate the printing defects within the structures. The printing geometry accuracy of the structures could be further improved by rounding the sharp corners with appropriate radii. This study successfully fabricated structures with various configurations characterized by high geometric accuracy through printing parameters optimization and path smoothing. Moreover, the compressive property and energy absorption characteristics of the structures under quasi-static axial compression were evaluated and compared. It was found that all studied thin-walled structures exhibited progressive folding deformation patterns during compression. In particular, energy absorption process was achieved through the combined damage modes of plastic deformation, fiber pullout and delamination. Furthermore, the comparison results showed that the hexagonal structure exhibited the best energy absorption performance. The study revealed the structure-mechanical property relationship of 3D printed continuous fiber reinforced composite thin-walled structures through the analysis of multiscale failure characteristics and load response, which is valuable for broadening their applications.

Industry-Scale Application of Full-Width Digital Camera Inspection during Effective Printing on Plastic Foil at the Company "Flexograf"

The company printing plastic sheets with eight-color machines has sought help from the Faculty of Computer Science to reduce wastage of raw materials. During the study and research in this matter, it was found that the losses in raw materials are caused by the impossibility of controlling the printing through the current adequate technology that the "Flexograf" company had at its disposal. The printing on the plastic film was supervised with a digital camera with the possibility of control at a dimension of 15 [cm]. On the other hand, the width of the printed plastic film is consistently 130[cm]. Therefore, the digital control camera for control is moved along the x-axis nine times to control the printing width of 130[cm] of the plastic film. After each displacement, the digital camera was stopped for a duration of three seconds. Wherever there was a printing defect in the part that was not monitored by the digital camera and given the printing speed of the machine for a length of 400 meters of plastic sheet per minute, it caused a significant loss of raw material if there were printing defects or lack of color. This problem has been solved by replacing the 15[cm] wide inspection digital camera with a 130[cm] wide full inspection digital camera. The effect of changing the full inspections digital camera achieved the goal and reduced the raw material losses to the minimum very close to zero.

Additively Manufactured Foot Insoles Using Body-Centered Cubic (BCC) and Triply Periodic Minimal Surface (TPMS) Cellular Structures

This study presents the development of insoles using 3D scanning and additive manufacturing; additionally, the feasibility of implementing cellular structures in their design was evaluated. Using finite element models, the displacements and Von Mises stresses in the insoles were obtained considering the exerted pressures of a person during walking. The insoles developed in this work presented a decrease of 91.48% in deformation while the maximum Von Mises stress increased by 32.62%, compared with what other authors reported. The Von Mises stresses and displacements in the insole were calculated when two cellular topologies, triply periodic minimal surfaces (TPMS) and body-centered cubic (BCC), and different relative densities (10.33%, 14.67%, and 20.19%) were implemented. When compared to solid insoles, the Von Mises stresses and displacements for the models with cellular structures increased. The maximum Von Mises stresses and displacements resulted for the insoles with a relative density of 10.33%; for the insole with the BCC cellular structure, the displacement was 2.06 mm, and the Von Mises stress was 22.17 MPa, while for the TPMS structure, these were 2.7 mm and 23.84 MPa, respectively. The designs were additively manufactured, and the printing defects were visually characterized.

Printable-Microencapsulated Ascorbic Acid for Personalized Topical Delivery.

This study presents the successful development of printable-microencapsulated ascorbic acid (AA) for personalized topical delivery using laser printing technology. Rice flour with a 10% AA content was selected as an encapsulation material. Hydrophobic nanosilica was used to create negative electrostatic charges on the microencapsulated surfaces via a high-speed mixture. This process facilitated the microencapsulated AA fabrication using a commercial laser printer and produced a well-patterned design with some minor print defects, such as banding and scattering. The amount of encapsulated AA per area was 0.28 mg/cm2, and the RGB color code was 0,0,0. An emulsion carrier system comprising pentylene glycol (P5G) or diethylene glycol monoethyl ether (DEGEE), Tween 20, oleic acid, and deionized (DI) water at a ratio of 20:30:30:20 was developed to enhance AA transmission into the skin. The Franz diffusion cell technique was used to investigate topical absorption on Strat-M membranes using P5G and DEGEE as enhancers. The steady-state fluxes were 8.40 (±0.64) and 10.04 (±0.58) μg/h/cm2 for P5G and DEGEE, respectively. Cytotoxicity tests conducted on fibroblast cells revealed low cytotoxicity for the encapsulation products and carriers.

The evolution of print defects in inkjet printers at elevated print gap height

Image uniformity is a key requirement for inkjet printers. When the gap between the print-face and media is large, one of the main causes of non-uniformity is the misplacement of droplets due to air-flow instabilities. Here, we characterise the onset of printed image non-uniformity by measuring the optical density variation of images printed with varying numbers of active nozzles. The optical density data are obtained by scanning printed images, which are corrected to remove any scanner-related effects. Several transects across the image are extracted, the peak spatial frequency is computed using Fourier transform analysis, and the results from these different transects are averaged. The amplitude of the main frequency peak in image density variation exhibits the same onset behaviour as seen in numerical simulations of the fluid flow in the printhead-media gap. Using numerical simulation, we extend the range of the study to estimate the operating envelope for the printing system.