Progress in Laser Ultrasonic Testing Applications for Metal 3D Printing

0 Introduction
Metal 3D printing, a core additive manufacturing technology, forms complex structures by layered material deposition, demonstrating significant advantages in aerospace, medical, and other fields. The global market reached $13.5 billion in 2023, yet internal defects such as porosity and lack of fusion remain key factors limiting its large-scale adoption (Figure 1). Consequently, timely detection and investigation of defects arising during the printing stage have become a primary research focus. As a mature non-destructive testing method, ultrasonic testing is gaining increasing attention for metal 3D printing defect identification due to its high speed, precision, and ease of operation. Yu Lili et al. [1] reviewed current domestic and international research progress in architectural 3D printing. They systematically analyzed concrete 3D printing versus traditional construction methods in terms of raw material selection, process details, and quality control. The study also summarized major challenges facing 3D printing technology at this stage and outlined future development prospects. Wang He [2] noted that in metal laser additive manufacturing, the formation of porosity defects is influenced by multiple factors including print parameter selection, powder material properties, and laser energy density. These defects not only compromise the mechanical properties of parts but may also lead to premature failure during actual use. Xu Wanwei [3] discovered that compared to traditional ultrasonic testing methods, laser ultrasonic testing offers higher spatial resolution and stronger sensing capabilities, making it the optimal choice for in-process inspection during metal additive manufacturing. Wang Chaoqun [4] employed machine learning-based acoustic field diagnostics and defect imaging technology, significantly enhancing the accuracy and efficiency of ultrasonic detection. Wu Hongqin's [5] research demonstrates that photonic backscatter technology enables detailed mapping of microstructures and minute defects within metals, offering novel insights for evaluating 3D-printed metal quality. Bai Xue et al.'s [6] work further compares laser ultrasonics and conventional ultrasonics in metal 3D printing inspection, revealing that laser ultrasonics not only exhibits higher sensitivity but also detects fine defects as small as approximately 1μm, showcasing distinct advantages.
 

Consequently, emerging methods such as laser ultrasonic testing and electromagnetic acoustic ultrasonic testing are gaining prominence [7]. In-depth exploration of ultrasonic testing applications in metal 3D printing holds both significant theoretical importance and immense practical value. Related research not only promises to overcome current technical bottlenecks but also lays a solid foundation for the future development of intelligent manufacturing.
1 Overview of Metal 3D Printing Technology
1.1 Process and Principles of Metal 3D Printing
Metal 3D printing employs a layer-by-layer material deposition approach to fabricate metal parts with complex three-dimensional structures. Its operational principle involves computer-guided layered forming: First, a 3D digital model is imported into the printer's control software. Based on the model's geometric features and design requirements, the model is sliced into a series of two-dimensional cross-sections, with each layer's thickness typically controlled between 20μm and 100μm. Next, suitable metal powder is selected as the raw material. A powder spreading system uniformly deposits the powder onto the first layer of the printing substrate. Subsequently, a laser beam or electron beam selectively melts the powder, solidifying it into metallic material. This cycle of powder spreading, melting, and solidification is repeated layer by layer until the complete three-dimensional structure is formed. Finally, the finished metal part is removed from the substrate and undergoes necessary post-processing and surface finishing. Compared to traditional manufacturing methods requiring molds, metal 3D printing completely eliminates the need for molds, significantly shortening production cycles and reducing costs.
This production method encompasses multiple additive manufacturing processes, with typical examples including: Selective Laser Melting (SLM), Electron Beam Melting (EBM), Laser Metal Deposition (LMD), and Fused Filament Fabrication (FFF). Among these, SLM and EBM are most widely applied in metal part manufacturing due to their high precision and superior forming quality.
SLM[8-9] is an additive manufacturing technology utilizing high-energy lasers as a heat source. Its core principle involves selectively melting pre-deposited metal powder layer by layer to build complete parts from the bottom up. Success hinges on precise control of parameters such as laser power, scanning speed, scan spacing, and layer thickness, as these factors directly determine the melt pool shape and the physical properties of the final product, as shown in Figure 2. Experiments by He et al.[10] demonstrated that higher density and superior mechanical properties are achieved when laser power is controlled between 200W and 400W, scanning speed ranges from 700 mm/s to 1500 mm/s, and scanning spacing is maintained between 0.05 mm and 0.1 mm. Consequently, SLM achieves 99.9% density and is widely adopted in aerospace and medical fields for manufacturing high-performance metal components.
 

Similar to EBM and SLM, EBM employs a layer-by-layer powder deposition and melting approach, but utilizes an electron beam as the energy source [8]. This process is particularly suited for metals with high melting points and vapor pressures, such as titanium alloys and nickel-based alloys. The electron beam's concentrated energy and rapid scanning speed, combined with powder layer thicknesses typically controlled between 50μm and 100μm, synergistically reduce forming time significantly. This provides distinct advantages in manufacturing large-scale, complex structural components.
Numerous researchers are deepening their understanding of the relationships among various parameters in metal 3D printing, including laser power, scanning speed, powder layer thickness, and powder material properties. They are also actively exploring novel applications of metal alloy materials, aiming to achieve superior product outcomes through the use of higher-performance alloys. These academic investigations not only enrich the theoretical framework of metal 3D printing but also provide valuable theoretical foundations and operational guidelines for future technological advancements and practical applications. Analysis of existing data indicates that replacing traditional material-removal manufacturing methods with metal 3D printing can reduce material consumption by up to 50% while shortening production cycles by 30% to 50%. These advantages are particularly pronounced in high-end manufacturing sectors such as aerospace and medical applications. However, current processes still exhibit certain defects, such as incomplete fusion, microcracks, and residual stresses [1]. Overcoming these challenges requires multifaceted approaches, including further optimization of process parameters, development of novel alloy materials, and improvements in post-processing techniques. These efforts will continuously enhance the overall performance and reliability of printed components.
1.2 Analysis of Metal 3D Printing Application Fields
Metal 3D printing technology has demonstrated unique advantages and broad prospects across numerous sectors. Its practical impact and latest advancements in core application areas like aerospace, medical, and automotive warrant in-depth examination.
In aerospace, metal 3D printing holds significant strategic importance. Its core value lies in substantially reducing component weight while maintaining or even enhancing structural strength and overall performance. Take aircraft engine fuel nozzles as an example: compared to traditional casting or machining processes, metal 3D-printed fuel nozzles achieve over 30% overall weight reduction while improving temperature resistance by approximately 50% [11], as illustrated in Figure 3. GE has successfully industrialized 3D printing technology in its GE9X and Leap series aeroengines, developing and mass-producing over ten complex structural components including fuel nozzles, heat exchangers, sensor housings, and turbine blades [12]. International manufacturers such as Safran [13] and MTU [14] also utilize additive manufacturing to produce fuel nozzles and combustion chamber casings, significantly boosting production efficiency. Domestically, the Hunan Power Machinery Research Institute of Aero-Engine Corporation of China [15] integrated nearly 100 components of a micro turbofan engine into ten monolithic structures—including an integral disk—via 3D printing, successfully passing engine test verification.
 

In healthcare, metal 3D printing is driving profound transformation amid rising aging populations and personalized medical demands. Through additive manufacturing, physicians can customize implants like joints and dental crowns for individual patients using the same data source, ensuring better anatomical fit. Market projections indicate the 3D-printed medical implant sector will approach $4.5 billion by 2025. Metal 3D printing also delivers higher precision for surgical instruments while substantially shortening supply chain cycles.
In the automotive industry, metal 3D printing is not only used for prototype development of new models but also delivers tangible value to mass production by reducing part counts and enhancing performance. Manufacturers like Porsche and Ferrari have adopted this technology for producing critical components such as shock absorber towers and transmission housings: certain 3D-printed parts can reduce vehicle weight by approximately 20%, while increasing tensile strength and significantly shortening new vehicle launch cycles.
Beyond aerospace, medical, and automotive sectors, industries including oil and gas, renewable energy, and jewelry/art are actively adopting metal 3D printing. Research indicates that 3D-printed components can boost wind turbine efficiency by 5% to 10%, contributing substantial renewable energy gains globally. Market surveys reveal that the global 3D-printed jewelry market approached $5 billion in 2022 and is projected to grow steadily.
2 Fundamental Analysis of Laser Ultrasonic Detection Technology
2.1 Analysis of Laser Ultrasonic Propagation Principles
Currently, non-destructive testing for metal additive manufacturing components has established a technical framework centered on CT 3D scanning, industrial radiography, fluorescent penetrant testing, and ultrasonic NDT. Among these, CT technology can identify micro-defects within the 4μm to 200μm range with high precision, though it is constrained by testing efficiency and component size limitations; Radiography excels at detecting porosity and inclusions within complex structures; fluorescent penetrant testing offers sensitivity and visual clarity for surface-opening defects but is limited to smooth surfaces and cannot probe internal flaws [16-18]. Ultrasonic testing represents an advanced NDT method capable of operating in extreme environments—including high/low temperatures and radiation—while also accommodating complex geometries or hard-to-reach components, thereby holding significant value in industrial inspection. Among these, laser ultrasonic technology stands out: it offers high detection sensitivity and enables rapid on-site inspection without coupling agents. Leveraging optical transmission properties, it can also integrate seamlessly with fiber optic technology for long-distance and online monitoring. Due to these advantages, laser ultrasonics has garnered extensive attention and ongoing research in the NDT of 3D-printed components [19-21].
Laser ultrasonic technology is a non-destructive testing method that integrates the advantages of laser and ultrasonic technologies. Based on the level of laser energy density, it can be categorized into laser ultrasonic NDT based on the thermoelastic mechanism and laser ultrasonic NDT based on the thermal ablation mechanism. This technology utilizes high-energy pulsed lasers to irradiate the material surface, inducing ultrasonic signals within the material through thermoelastic effects or ablation effects [7], as illustrated in Figures 4 and 5. The core principle of laser ultrasonic technology lies in using lasers as excitation sources. The high energy density of laser pulses rapidly heats the material surface, causing localized thermal expansion and generating stress waves—ultrasonic waves. In metallic materials, laser-induced ultrasonic waves primarily include P-waves (longitudinal waves) and S-waves (transverse waves). P-waves propagate faster, while S-waves exhibit stronger contrast during inspection. Under the thermoelastic mechanism, when the incident laser pulse power density is below 10⁶ W/cm², the thermal diffusion depth is extremely shallow. This causes only the micrometer-scale surface layer to instantaneously heat up by tens to hundreds of degrees Celsius, generating transient thermal expansion and inducing thermal stress/strain without surface melting. Under the thermal ablation mechanism, the incident laser pulse power density exceeds 10⁶ W/cm². The solid surface temperature rapidly rises above the melting point. The high-power laser causes micrometer-scale ablation of the surface layer and generates plasma. The expansion of this plasma produces a recoil force perpendicular to the surface, thereby exciting ultrasonic waves. In quality inspection of 3D-printed components, while the thermal ablation mode can generate stronger ultrasonic signals, it causes micrometer-scale ablation damage on the material surface, which contradicts the fundamental requirements of non-destructive testing. In contrast, the thermoelastic mode employs precisely controlled low-power lasers to induce only reversible thermal expansion effects. This approach enables internal defect detection while fully preserving the surface integrity of the component, making it more suitable for online quality monitoring of precision additive manufacturing parts [21,22].
 

Since White [23] first discovered in 1963 that pulsed lasers could excite ultrasonic waves in solids, the academic community achieved substantial progress in the principles, detection techniques, and engineering applications of laser ultrasonics throughout the 1980s. This laid a solid foundation for the application of laser ultrasonics on metal surfaces. In 2004, Shen Zhonghua et al. [24,25] employed finite element simulation methods to systematically investigate the ultrasonic excitation characteristics of plate-like materials under laser thermoelastic effects. They established single-layer and double-layer material models, successfully reproducing the transient temperature field evolution and ultrasonic wave propagation dynamics under laser irradiation. They quantitatively revealed the relationship between key parameters such as laser energy density and pulse width and ultrasonic spectral characteristics, providing a crucial theoretical framework for the engineering application of laser ultrasonic non-destructive testing technology.
Since White's initial discovery of the laser-ultrasonic phenomenon, global research teams have established a tripartite research system encompassing “theoretical modeling—experimental validation—numerical simulation.” Through multidimensional cross-validation, they have continuously refined the theoretical foundations and application models of laser ultrasonic testing technology. However, existing research exhibits notable limitations: findings predominantly focus on surface defect detection, with relatively weak investigation into the identification mechanisms for internal defects in components. Particularly in the field of 3D printing, systematic exploration of the influence patterns of key parameters—such as surface topography features (e.g., roughness Ra value) and internal porosity (typically 0.1%–5%)—on ultrasonic defect signals remains absent.
2.2 Analysis of Laser Ultrasonic Detection Systems
2.2.1 Analysis of Laser Ultrasonic Detection Systems
As shown in Figure 6, modern laser ultrasonic detection systems employ a modular design primarily comprising a laser excitation unit and an optical reception unit. The operational workflow is as follows: A high-energy pulsed laser (typical parameters: wavelength 1064 nm, pulse width 10 ns) irradiates the surface of the material under test, exciting broadband ultrasonic waves (frequency range 0.1 MHz–20 MHz) through the thermoelastic effect. As the acoustic waves propagate within the material, they interact with defects or structural features, inducing modal transitions. A precision laser interferometer (displacement resolution 0.1 nm) captures the resulting surface vibration signals in real time. Through time-frequency analysis techniques, critical quality parameters such as internal stress distributions and lattice defects can be reconstructed.
 

Research worldwide indicates that laser selection is a critical factor determining system performance. Currently, Nd:YAG solid-state lasers are widely adopted. Their fundamental output wavelength of 1064 nm, coupled with high pulse energy and narrow pulse widths (ranging from several to tens of nanoseconds), provides ample energy for ultrasonic excitation. The receiving end typically employs a laser interferometer, which precisely measures the phase changes in light caused by surface vibrations induced by ultrasonic waves through the principle of optical coherence. In 1996, Murray's team [26] first demonstrated that combining an Nd laser array (wavelength 1064 nm, with single-pulse energies of 50–100 mJ) with phased array technology, while synergistically controlling pulse timing (with microsecond-level synchronization accuracy), energy distribution (fluctuations controlled within ±5%), and spatial modulation (dynamic focusing based on acousto-optic deflectors), can enhance the system signal-to-noise ratio by over 40%. This established a technical pathway for optimizing the sensitivity of modern laser ultrasonic equipment. Millon et al. [27] investigated the impact of laser beam parameters on detection performance using steel as the test material. They found that laser spot size and beam quality directly determine the detectable frequency range, recommending laser sources with diameters less than 0.2 mm. Recent studies further indicate that employing hybrid frequency excitation between 2 MHz and 10 MHz holds promise for achieving precise localization and imaging of micro- and nano-scale defects.
Laser ultrasonic testing is commonly employed in scenarios requiring non-contact operation, high/low temperature environments, couplant-free inspection, and rapid scanning. Traditional non-contact ultrasonic testing primarily relies on electromagnetic acoustic transducers, capacitive or electrostatic transducers, and air-coupled ultrasonic transducers. However, these methods all possess inherent limitations. Consequently, researchers worldwide have increasingly turned to optical detection technologies to achieve truly non-destructive testing [28]. Optical ultrasonic detection systems can be categorized into two major approaches: non-interferometric and interferometric. Non-interferometric methods, exemplified by edge-of-blade detection technology, utilize subwavelength detection spots (10–50 μm diameter) interacting with surface ultrasonics. By measuring the optical intensity modulation of reflected light through an edge-of-blade filter (achieving sensitivities down to 10⁻⁶ rad), these techniques quantitatively capture surface acoustic wave amplitudes. Interferometric methods encompass three mainstream technologies: (1) Optical heterodyne interferometry systems, achieving displacement resolution of 0.1 nm by extracting vibration phase through coherent demodulation of reference and signal light; (2) Differential interferometers, based on Mach-Zehnder structures, which eliminate common-mode noise via dual-beam path difference; (3) Velocity interferometers (VISAR), achieving velocity resolution at the 0.1 m/s level through Doppler frequency shift. These technologies collectively form a comprehensive optical solution for modern non-destructive testing [28].
2.2.2 Laser Ultrasonic Testing Data Analysis
In-depth analysis of laser ultrasonic testing data is equally critical. Its core task involves processing and interpreting data collected by testing equipment to extract information about internal structural defects in materials. This analysis process primarily comprises four steps: data preprocessing, signal feature extraction, defect identification, and quantitative defect evaluation.
Prior to analyzing ultrasonic inspection data, data preprocessing must be completed. This step aims to enhance the signal-to-noise ratio and suppress interference from external noise. In practical inspections, instrument and environmental noise are often unavoidable. Therefore, filtering optimization using low-pass, high-pass, or bandpass filters is necessary. Further noise reduction techniques such as envelope analysis, wavelet transform, and Fourier transform can be applied to highlight the effective components within the signal.
Following data preprocessing, the signal feature extraction phase commences. Its objective is to distill key parameters with clear physical significance from the processed acoustic data. Common feature extraction methods include time-domain analysis, frequency-domain analysis, and combined time-frequency domain analysis.
Following the extraction of waveform feature parameters, defect identification and quantitative assessment can be conducted. As ultrasonic testing analysis grows increasingly complex, machine learning and artificial intelligence algorithms are being widely adopted. Research indicates that convolutional neural networks (CNNs) can achieve over 85% accuracy in identifying or locating micro-pore defects in metal 3D-printed parts. To further enhance the stability and reliability of ultrasonic testing, researchers often fuse its data with other non-destructive testing methods for joint analysis. For instance, integrating X-ray computed tomography (CT), scanning electron microscopy (SEM), and ultrasonic inspection results enables the construction of more detailed three-dimensional images of metal interiors, significantly improving detection accuracy.
Through continuous and in-depth optimization and refinement of analytical algorithms and processing workflows, the depth and breadth of material inspection can be substantially expanded. This provides a more accurate and reliable foundation for quality monitoring and performance enhancement.
3 Applications of Laser Ultrasonic Testing Technology in Defect Detection
3.1 Applications of Laser Ultrasonic Testing in Metal Materials
In 2000, leveraging its non-contact nature and exceptional resistance to harsh environments, laser ultrasonic technology rapidly emerged as a research hotspot. Through theoretical modeling and experimental validation, scholars achieved significant breakthroughs in conventional metal inspection.
Laser ultrasonic technology is playing an increasingly critical role in the fields of non-destructive testing, online monitoring, and structural health monitoring of metal materials. By generating broadband ultrasonic signals through laser pulses, this technology enables real-time acquisition of internal microstructural information without damaging components. For high-temperature service components like turbine blades and nuclear power equipment, laser ultrasonic testing operates stably in extreme environments up to 1000°C, accurately identifying minute defects such as cracks, voids, and inclusions. Research by Bai Xue et al. demonstrates that the detection accuracy of this technology has reached the micrometer level, capable of detecting defects smaller than 0.1 mm. In online inspection of aluminum alloys, it can even identify pores as small as 50 μm in diameter [6]. Wei Heming [29] further confirmed that the system maintains stable performance at 1000°C, making it highly valuable for thickness monitoring of hot-rolled steel plates. Leveraging these advantages, laser ultrasonic testing has become an ideal method for quality control and defect identification in critical metal components.
In the field of composite materials, laser ultrasonic testing also demonstrates exceptional applicability. Composite structures widely used in aerospace and other industries feature complex geometries and multiple layers, where the bonding quality between different materials and delamination conditions directly determine overall mechanical properties. Leveraging the strong penetration and high resolution of pulsed waves, laser ultrasonic testing can precisely identify hidden defects such as interfacial delamination and material porosity. Research by Yang Hongjuan et al. [30] indicates that compared to traditional methods, laser ultrasonic testing can enhance the detection sensitivity of composite delamination defects by approximately 30%, significantly improving inspection accuracy.
Beyond metals and composites, research on laser ultrasonic technology applications in novel materials is also on the rise. High-entropy alloys and nano-reinforced composites, valued for their exceptional comprehensive properties, are widely deployed in extreme environments. However, precise detection of internal defects is critical for ensuring their performance reliability. Consequently, optimizing detection parameters—such as laser energy and wavelength—to suit different material characteristics has emerged as a new research focus, enabling laser ultrasonic technology to better accommodate diverse material requirements.
Laser ultrasonic technology also holds great promise for assessing material fatigue life. By analyzing acoustic spectrum changes induced by laser ultrasound, fatigue life and fatigue crack propagation rates can be predicted. Experimental results demonstrate significant correlations between amplitude decay and spectral broadening of laser ultrasonic signals and material fatigue damage severity. Zhao Cang et al. [31] achieved over 85% accuracy in fatigue crack life prediction through real-time laser ultrasonic monitoring of metallic fatigue cracks.
In semiconductor material inspection, laser ultrasonics primarily detects surface microdefects and interfacial state changes. Given the intricate structures and extreme sensitivity to minute defects in semiconductors, traditional methods struggle to meet modern manufacturing's stringent demands. Laser ultrasonics not only rapidly and non-destructively identifies internal defects but also adapts to diverse semiconductor materials by adjusting laser parameters, providing reliable quality assurance for semiconductor industrial production.
In summary, laser ultrasonic detection technology has demonstrated outstanding advantages and broad application prospects across diverse material fields. With the continuous advancement of high-precision instruments and complex analytical algorithms, research into this technology across multiple materials will deepen further, providing stronger support for materials science. Simultaneously, it lays a solid foundation for laser ultrasonics in quality control, non-destructive testing, online monitoring, and structural health monitoring within the 3D printing sector.
3.2 Application of Laser Ultrasonic Testing in Metal 3D Printing Materials
The rapid advancement of 3D printing technology has spurred in-depth research into laser ultrasonic testing. This technology enables both online monitoring of temperature variations during printing and offline detection of internal micro-defects in components, establishing itself as a critical tool for quality control in additive manufacturing [32].
At the application level, Bai Xue et al. [6] employed laser ultrasonics to analyze acoustic wave propagation characteristics in 316L stainless steel, successfully detecting micro-pore defects smaller than 100 μm in diameter. Liu et al. [33] utilized X-ray computed tomography to capture manufacturing defects and investigate their impact on the overall mechanical properties of 3D-printed metal structures. Xu Zhao [34] discovered during research on porosity defects in selective laser melting of 316L stainless steel that laser ultrasonics not only accurately locates pores but also quantitatively assesses their size and shape, with measurement errors controlled within 5%. Zhao Cang et al. [31] demonstrated that real-time laser ultrasonic monitoring enables dynamic adjustment of process parameters during metal additive manufacturing, suppressing internal defect formation and significantly enhancing product quality and reliability. This online monitoring system has been deployed in multiple aerospace manufacturing enterprises, substantially reducing scrap rates while effectively boosting production efficiency.
Laser ultrasonic detection can also monitor temperature fields and melt pool dynamics in real time during 3D printing. By continuously acquiring these critical parameters, the system instantly adjusts print paths and process parameters to optimize forming conditions, significantly improving yield rates. Wang Shuxiang [35] discovered in titanium alloy additive manufacturing research that coupling laser ultrasonic detection with thermal modeling, through precise control of laser power and scanning speed, can increase the relative density of formed parts by approximately 20%. Wu Hongqin [5] further demonstrated that laser ultrasonic technology can dynamically capture the real-time evolution of microstructures during additive manufacturing. It not only detects macroscopic defects but also identifies microscopic metallurgical flaws within materials, providing crucial insights for understanding and proactively controlling quality issues in additive manufacturing. In recent years, extensive research has systematically validated the reliability and effectiveness of laser ultrasonic technology in 3D printing defect detection. The laser ultrasonic line scanning system developed by Chen Shuai's team [36] can accurately identify printed defects as small as 2 mm × 1 mm × 1 mm and enables quantitative analysis of defect width. Yu et al. [37] established a quantitative relationship between Rayleigh wave amplitude and porosity defects by comparing with XCT technology, confirming the system's ability to detect pores as small as 0.8 mm in diameter. Zhang et al. [38] overcame surface roughness limitations by successfully detecting 0.05 mm-level microdefects on the surface of SLM components without post-processing, fully demonstrating the technology's adaptability to complex operating conditions. In summary, laser ultrasonic detection technology has demonstrated outstanding performance in quality control for metal 3D printing. It not only provides robust support for enhancing the quality of additive manufacturing products but also points the way for further development of related equipment and processes. However, the current application of this technology in the 3D printing field exhibits a “domestic-international disparity”: domestic research remains in its infancy, primarily focused on verifying artificially pre-fabricated defects [39-41], with the impact of surface roughness on detection accuracy yet to be effectively resolved. In contrast, the international academic community has established a more systematic research framework and is continuously deepening the exploration of laser ultrasonic applications throughout the entire additive manufacturing quality control process. Notably, enhancing detection sensitivity through optimized surface treatment processes has become a shared focus for breakthroughs among researchers worldwide, with international efforts actively advancing laser ultrasonic non-destructive testing research [42-50]. Researchers have currently identified the limit dimensions for laser ultrasonic defect detection as 0.05 mm in width and 0.1 mm in depth. Therefore, future research should focus on algorithm optimization, signal processing technology enhancement, and integration with other detection techniques to further improve the application depth and detection accuracy of laser ultrasonic testing in metal 3D printing.
4. Development Trends and Challenges in Laser Ultrasonic Detection
Future advancements in laser ultrasonic detection technology can be summarized in the following key areas:
(1) Hardware Enhancement: Continuous development of higher-power, more stable lasers and higher-sensitivity ultrasonic sensors to improve system signal-to-noise ratio at the source and enhance detection of minute defects. Concurrently, miniaturization of optical and mechanical structures will facilitate the implementation of portable, field-deployable laser ultrasonic equipment.
(2) Deep integration of machine learning algorithms—particularly convolutional neural networks—into signal processing chains to enable automatic classification, localization, and severity assessment of defect echoes. This approach significantly compresses inspection cycles while maintaining high detection rates.
(3) Multi-technology integration: Seamlessly combining laser ultrasonics with complementary methods like X-ray digital imaging and computed tomography (CT) overcomes limitations in resolution, penetration depth, or contrast inherent to single techniques. This delivers a comprehensive, panoramic assessment of internal porosity, cracks, and surface defects down to microscopic levels.
(4) Standardization Development and Promotion: Collaboration with international organizations such as ISO and ASTM remains essential to establish unified standards covering equipment performance, inspection procedures, defect criteria, and traceability of results across all stages of the additive manufacturing process chain. This ensures data obtained from different laboratories and production lines is comparable, reliable, and reproducible.
Finally, with the mass adoption of complex-shaped metal components—such as aeroengine blades, lightweight automotive structural parts, and personalized medical implants—laser ultrasonic testing technology will inevitably evolve toward full coverage, full-dimension, and full-thickness inspection of complex curved three-dimensional components. Developing inspection techniques and equipment capable of adapting to curvature variations, material gradients, anisotropy, and surface conditions will become the core focus of the next research phase. The synergistic advancement of these four major trends will significantly enhance the comprehensive performance of laser ultrasonic testing technology, further broaden its application scenarios in the field of metal additive manufacturing, and ultimately achieve greater industrial value on a larger scale and at a deeper level.
Reference: Guangzhou Architecture 2025, Issue 12; Progress in Laser Ultrasonic Testing Applications for Metal 3D Printing; Zhou Jin1, Li Zhanshuo2,3, Zhang Gengbiao2,3;
Refractory metal 3D printing is an advanced additive manufacturing technology targeting high-melting-point, high-hardness metals and alloys such as tungsten, molybdenum, tantalum, and niobium. It effectively overcomes processing challenges in traditional casting and forging methods when producing complex structural components. Its core advantage lies in achieving near-net-shape forming of complex components without molds, offering high material utilization and shortening product development cycles. It meets the demand for high-performance components in extreme environments across aerospace, nuclear, and other industries. Current mainstream processes include powder bed fusion, directed energy deposition, and powder extrusion printing. Among these, powder extrusion printing employs an indirect manufacturing approach of “low-temperature forming + high-temperature sintering,” mitigating defects like deformation and cracking that often occur during direct printing. The technology still faces development challenges such as improving process stability and refining industry standards, and is gradually advancing from laboratory research to practical application scenarios. For more product information, please contact our Sales Manager, Cathie Zheng at +86 13318326187.