Detection of Internal Holes in Additive Manufactured Ti-6Al-4V Part Using Laser Ultrasonic Testing

Exploring Piezoelectric Actuation towards Its Applications in Laser Powder Bed Fusion Additive Manufacturing

Piezoelectric materials, which exhibit a charge distribution across the surfaces in reaction to mechanical strain, find significant utility in actuation and sensing applications. Apart from actuation applications like acoustic devices, motors, and vibration damping, an emerging domain for ultrasonic actuators lies in additive manufacturing processes. Ultrasonic waves applied during solidification aim to modulate grain structure and minimize defects. This research focuses on a fixture designed to facilitate and optimize ultrasonic wave propagation through the build plate in laser powder bed fusion additive manufacturing by utilizing a piezoelectric transducer. Three implementations of piezoelectric transducers were evaluated based on their out-of-plane ultrasonic velocity transmissions. It was determined that a thin plate adhered to the surface of the piezoelectric transducer yielded the most favorable outcomes for implementation, achieving 100% transmission of velocity and energy. Preliminary analysis of melt pool morphology and defects in single-track laser scanning experiments demonstrated the impact of ultrasound on solidification, hinting at a novel approach to enhancing the printability of alloys in laser powder bed fusion additive manufacturing processes. The optimal fixture and the explored transducing efficiency could further guide advanced ultrasound testing to enable in situ defect and texture detection during the additive manufacturing processes.

Single-Point and Surface Quality Assessment Algorithm in Continuous Production with the Use of 3D Laser Doppler Scanning Vibrometry System

In the current economic situation of many companies, the need to reduce production time is a critical element. However, this cannot usually be carried out with a decrease in the quality of the final product. This article presents a possible solution for reducing the time needed for quality management. With the use of modern solutions such as optical measurement systems, quality control can be performed without additional stoppage time. In the case of single-point measurement with the Laser Doppler Vibrometer, the measurement can be performed quickly in a matter of milliseconds for each product. This article presents an example of such quality assurance measurements, with the use of fully non-contact methods, together with a proposed evaluation criterion for quality assessment. The proposed quality assurance algorithm allows the comparison of each of the products' modal responses with the ideal template and stores this information in the cloud, e.g., in the company's supervisory system. This makes the presented 3D Laser Vibrometry System an advanced instrumentation and data acquisition system which is the perfect application in the case of a factory quality management system based on the Industry 4.0 concept.

Ultrasonic testing of thick and thin Inconel 625 alloys manufactured by laser powder bed fusion

Additive manufacturing of alloys enables low-volume production of functional metallic components with complex geometries. Ultrasonic testing can ensure the quality of these components and detect typical defects generated during laser powder bed fusion (LPBF). However, it is difficult to find a single ultrasonic inspection technique that can detect defects in the large variety of geometries generated using LPBF. In this work, phased array ultrasonic testing (PAUT) is suggested to inspect thick LPBF components, while guided waves are explored for thin curved ones. PAUT is used to detect cylindrical lack of fusion defects in thick LPBF rectangular parts. Practical defects are generated by reducing the laser power at prespecified locations in the samples. The defects' shape and density are verified using optical microscopy and X-ray computed tomography. Partially fused defects down to 0.25 mm in diameter are experimentally detected using a 10 MHz PAUT probe with the total focusing method post-processing. The experimental results are compared to defect images predicted by finite element simulations. For thin components with curved geometry, guided waves are used to detect powder-filled cylindrical defects. The waves are generated using piezoelectric transducers, and the spatiotemporal wavefield is measured using a scanning laser Doppler vibrometer. Using root-mean-square imaging of the wavefield, defects down to 1 mm are clearly detected despite the complex internal features in the samples.

Nondestructive measurement of the grain size of laser cladding coatings using a laser ultrasonic method

Due to the processing characteristics of laser cladding, the beads and joints of the laser cladding coatings have different grain sizes. We used the laser ultrasonic (LU) method to measure the distribution of the grain sizes of laser cladding coatings nondestructively. The surface acoustic wave amplitude was influenced by the grain size; hence, the amplitude varied for beads and joints because of their different attenuations. The spatial resolution of LU is higher than that of the traditional ultrasonic testing method, leading to a fringe distribution of the C-scan results in the scanning area. The LU results were verified through metallographic experiments. It was concluded that the LU method can be used to determine the grain sizes of coatings.

A Review of Diagnostics Methodologies for Metal Additive Manufacturing Processes and Products

Additive manufacturing technologies based on metal are evolving into an essential advanced manufacturing tool for constructing prototypes and parts that can lead to complex structures, dissimilar metal-based structures that cannot be constructed using conventional metallurgical techniques. Unlike traditional manufacturing processes, the metal AM processes are unreliable due to variable process parameters and a lack of conventionally acceptable evaluation methods. A thorough understanding of various diagnostic techniques is essential to improve the quality of additively manufactured products and provide reliable feedback on the manufacturing processes for improving the quality of the products. This review summarizes and discusses various ex-situ inspections and in-situ monitoring methods, including electron-based methods, thermal methods, acoustic methods, laser breakdown, and mechanical methods, for metal additive manufacturing.

Non-Contact Inspection of Railhead via Laser-Generated Rayleigh Waves and an Enhanced Matching Pursuit to Assist Detection of Surface and Subsurface Defects

Laser ultrasonic technology can provide a non-contact, reliable and efficient inspection of train rails. However, the laser-generated signals measured at the railhead are usually contaminated with a high level of noise and unwanted wave components that complicate the identification of defect echoes in the signal. This study explores the possibility of combining laser ultrasonic technology (LUT) and an enhanced matching pursuit (MP) to achieve a fully non-contact inspection of the rail track. A completely non-contact laser-based inspection system was used to generate and sense Rayleigh waves to detect artificial surface horizontal, surface edge, subsurface horizontal and subsurface vertical defects created at railheads of different dimensions. MP was enhanced by developing two novel dictionaries, which include a finite element method (FEM) simulation dictionary and an experimental dictionary. The enhanced MP was used to analyze the experimentally obtained laser-generated Rayleigh wave signals. The results show that the enhanced MP is highly effective in detecting defects by suppressing noise, and, further, it could also overcome the deficiency in the low repeatability of the laser-generated signals. The comparative analysis of MP with both the FEM simulation and experimental dictionaries shows that the enhanced MP with the FEM simulation dictionary is highly efficient in both noise removal and defect detection from the experimental signals captured by a laser-generated ultrasonic inspection system. The major novelty contributed by this research work is the enhanced MP method with the developments of, first, an FEM simulation dictionary and, second, an experimental dictionary that is especially suited for Rayleigh wave signals. Third, the enhanced MP dictionaries are created to process the Rayleigh wave signals generated by laser excitation and received using a 3D laser scanner. Fourth, we introduce a pioneer application of such laser-generated Rayleigh waves for inspecting surface and subsurface detects occurring in train rails.

Delamination Detection in Bimetallic Composite Using Laser Ultrasonic Bulk Waves

In this study, a method based on laser ultrasonic bulk waves is used to detect delamination in a bimetallic composite. For this purpose, several artificial delamination defects were created in a copper-aluminum sample using wire-electrode cutting. The research includes numerical simulation and experimental analysis. The propagation process of laser ultrasonic in Cu/Al bimetallic compo-site, the interaction between bulk waves and composite interface, and the effect of delamination defects on the ultrasound field were studied by numerical simulation. Suitable parameters and features were determined by numerical simulation, which provided a basis for the parameter se-lection of experimental research. The reflected shear waves from the composite interface can act as a sensitive feature to detect the delamination in Cu/Al bimetallic composites. The distance between the detection point and the excitation point was set to 2 mm to take into account the detection resolution and efficiency. The experimental results were in good agreement with the simulation results, and the C-scan image can intuitively show the location and size of delamination defects. The detection method based on laser ultrasonic bulk waves can effectively detect the delamination in Cu/Al bimetallic composite, which is suitable for the on-line detection of the rolling composite process.

A review of ultrasonic testing applications in additive manufacturing: Defect evaluation, material characterization, and process control

Ultrasonic testing (UT) techniques are highly capable of detecting defects in engineering components. The present manuscript intends to review the ultrasonic testing techniques applied to additive manufacturing products; either in-situ or offline. While the in-situ applications of ultrasonic testing to additive manufacturing are more favorable, literature holds a few research works on this topic. On the other hand, most of the works reported on ultrasonic testing of additive manufacturing products deal with offline applications. In many of these works, samples with artificial defects are prepared and tested through ultrasonic testing techniques including laser ultrasonics, phased arrays, guided waves and immersion ultrasonic testing. These UT methods and their applications in damage detection of additive manufacturing products are discussed in detail. Moreover, the codes and standards which are currently being developed for ultrasonic testing of additive manufacturing products are introduced. The choice of UT methods in detecting defects and material characterization in additive manufacturing is found to be highly dependent on the manufacturing process and capabilities of UT techniques.

Investigation of Laser Polishing of Four Selective Laser Melting Alloy Samples

Selective laser melting (SLM) is a layer by layer process of melting and solidifying of metal powders. The surface quality of the previous layer directly affects the uniformity of the next layer. If the surface roughness value of the previous layer is large, there is the possibility of not being able to complete the layering process such that the entire process has to be abandoned. At least, it may result in long term durability problem and the inhomogeneity, may even make the processed structure not be able to be predicted. In the present study, the ability of a fiber laser to in-situ polish the rough surfaces of four typical additive-manufactured alloys, namely, Ti6Al4V, AlSi10Mg, 316L and IN718 was demonstrated. The results revealed that the surface roughness of the as-received alloys could be reduced to about 3 μm through the application of the laser-polishing process, and the initial surfaces had roughness values of 8.80–16.64 μm. Meanwhile, for a given energy density, a higher laser power produced a laser-polishing effect that was often more obvious, with the surface roughness decreasing with an increase in the laser power. Further, the polishing strategy will be optimized by simulation in our following study.