Laser metal deposition (LMD) is an additive manufacturing technique that utilizes powder as its material. The powder is transported through the nozzle coaxially, where it converges with the laser beam onto the surface of the substrate. With the assistance of auxiliary gas, the powder melts upon laser irradiation and is deposited layer by layer onto the substrate, forming the desired component. Real-time monitoring of the deposition height plays a crucial role in enhancing the precision of LMD, reducing defects such as edge collapse and surface unevenness. It represents one of the fundamental aspects in achieving high-quality metal additive manufacturing. In this study, a laser metal deposition height prediction method based on a multi-modal neural network was proposed. The network architecture consisted of a convolutional neural network (CNN) and a fully connected network (FCN). The CNN extracted and analyzed the characteristics of the molten pool, generating a feature vector. This feature vector, along with the molten pool temperature, was fused as input into the FCN, ultimately predicting the deposited height. Compared with the predicted results of support vector regression (SVR), multi-modal neural networks can quickly predict the deposited height and track their changing trends. The model achieves a remarkable prediction accuracy of 95% and exhibits robustness in handling outlier values. The proposed network framework holds considerable potential in facilitating real-time control and fine-tuning of the laser metal deposition process.
Refractory metal tungsten (W) has a very high melting point (3420℃) and excellent high temperature mechanical properties, and has great prospects for application in aerospace, nuclear industry and other defense fields. Due to the high melting point and high thermal conductivity of pure tungsten, high power is required to melt it, while tungsten has a high ductile-brittle transition temperature (DBTT) and a low room temperature brittleness. These two aspects make it impossible to avoid porosity or cracking during machining, limiting its further application. So more effective tools are needed. The ultrafast laser can reach high peak power due to its extremely short pulse width. Adjusting the frequency can achieve heat accumulation in the heated region. These two effects make it possible to process materials with high melting points without having to increase the power all the time. The ultra-fast laser excessively high peak power can lead to cold processing of the material for removal, so figuring out the right process parameters is especially important. Femtosecond laser additive manufacturing of pure tungsten has been previously documented and compared with parts made using different pulse widths and CW lasers, showing that fully dense tungsten parts with finer grain size and increased hardness were obtained. By further reducing the pulse width at 200 fs, we achieved printing of pure tungsten at higher densities. Hardness tests demonstrated the superior performance of the printed samples compared to those made by conventional casting, continuous wave laser and 800 fs laser-selective melting, and this study is expected to promote the wide application of narrow pulse width lasers in laser additive manufacturing.
We demonstrate a power combining pulse laser system with 1 kW average power output based on spectrum filtering of four subset pulse amplifiers. The output spectrum with and without spectrum filtering are compared. The result shows that, without spectrum filtering, nonlinear spectrum component from subset amplifier will accumulate along the QBH fiber and leads to serious spectrum broadening as well as stimulated Raman scattering (SRS) effect. By spectrum filtering with a band pass filter (BPF) inside the subset amplifier, nonlinear spectrum component is successfully mitigated and high purity spectrum pulse laser output is also achieved at the output power of 1kW.
We present a coaxial laser metal deposition (LMD) system based on the single mode laser. The influence of input beam diameter on the ring spot properties such as spot shape, filling factor and ring width are investigated through numerical simulation. The result shows that the smaller ring spot and narrower ring width can be obtained by adopting the single mode laser in the coaxial LMD system, compared with the traditional coaxial LMD system based on the multimode laser (Flat-top beam). This also indicates that our system has advantages in the application of high-precision additive manufacturing (AM).
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