## 4 Discussion of the Research Results
In order to ensure high efficiency of filler powder utilization, which is mainly set by value \(d_{\text{t}}\), condition \(B\geq 2r_{0}\) should be fulfilled [37]. The coefficient of concentration \(k\) of the specific heat flow of the microplasma arc without powder feeding was determined via the procedure of ref. [34] using calorimetry in a two-section flow calorimeter. For a microplasma arc in the current range of 20-40 A with an equivalent diameter of the heating spot of 2.5-5.0 mm, the experimental \(k\) values are equal to 3.5-5.5 cm\({}^{-2}\), depending on the degree of its constriction by plasma-forming (\(d_{\text{pl}}\) = 1.0-2.5 mm) and -transporting (\(d_{\text{t}}\) = 2.5-4.5 mm) nozzles of the plasmatron. A comparison of experimental data on the effective diameter of powder feeding (Table 10) and specific heat flow on the product surface shows that, during additive building-up of the layers with powder feeding into the microplasma jet, the relationship between the respective coefficients is in the range of 1.1-1.6. During microplasma powder deposition of the wall with a thickness of 2.5 mm, the filler consumption can be reduced not only due to the reduction in \(d_{\text{t}}\) in the microplasmatron, but also due to the optimization of the microplasma powder's flow concentration by a rational selection of the distance from the transporting nozzle edge to the product. An analysis of powder flow concentration was performed in the mode of monitoring its feeding with the flow rate of 2.0-7.0 g/min, which allowed deposition of a layer of 0.5-0.8 mm height in one pass. It was found that such a flow preserved its concentration, assigned by the diameter of the transporting nozzle channel at the distance of up to 3-5 mm from its edge, and then it expanded significantly. Considering the dependence of the duration of the weld pool metal staying in the molten state on the energy input value [38], the modes of microplasma powder deposition may need optimization of their parameters via the criterion of the weld pool volume (deposited metal weight). At the average deposition current of up to 40 A, the criterion of average input energy 0.8(_I-U_)/_V_ < 130 J/mm promotes a limitation of the weld pool dimensions, deposited metal weight, and duration of the layer deposition. Such an approach \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(D_{\text{T. mm}}\) & \(D_{\text{ef.}}\) **mm** & \(S_{\text{ef.}}\) **mm\({}^{2}\)** & \(r_{0}\) **mm** & \(B\) **mm** & **PUF** \\ \hline
4.5 & 7.0 & 38.5 & 2.5 & 5.0 & 0.72 \\ \hline
3.5 & 5.5 & 23.8 & 2.25 & 4.5 & 0.82 \\ \hline
2.5 & 4.0 & 12.6 & 1.75 & 3.5 & 0.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: The experimental parameters of the effectiveness of powder additive microplasma deposition. helps analyze the modes of multilayer microplasma powder deposition when building-up elements of a complex profile. Thus, the following technological recommendations can be defined: application of a transporting nozzle with channel diameter close to 2.5 mm; stabilization of the microplasmatron-to-product distance at the level of 3 mm (3-5 mm) with the accuracy of \(\pm\)0.5 mm; delivery of filler material to the weld pool through the high-temperature region of the arc; and additive powder microplasma deposition of beads with widths of 2.5 mm. These recommendations can be used for further optimization of structural parameters of industrial microplasmatrons with a high concentration of the dispersed filler feed, the application of which allows achieving minimal possible dimensions of the built-up layers, as well as the maximal precision and roughness of the products in the manufacture of 3D metal products.