For the purpose of contributing to sustainable machining, the aim was to investigate the turning of martensitic stainless steel X20Cr13 under alternative cooling and lubrication techniques. The minimum quantity lubrication technique in combination with the vortex tube cooling, as the determined optimal cooling method using the Taguchi-based entropy weighted grey relational analysis (compared to emulsion and minimum quantity lubrication technique) in previous research when turning martensitic stainless steel X20Cr13, were applied in this research in accordance with the Box–Behnken design. The aim is to investigate, when applying the optimal cooling condition (minimum quantity lubrication + vortex) with the Box–Behnken design, which parameters have a significant influence on reducing the surface roughness parameters Ra and Rz and also on the tool life (T). The cutting speed (v_c = 260, 290 and 320 m/min), feed rate (f = 0.3, 0.35 and 0.4 mm/rev) and depth of cut (a_p = 1, 1.5 and 2 mm) were selected as cutting parameters. An exponential model for Ra, Rz and T was obtained. According to the ANOVA results, it can be seen that only the feed rate had a significant influence on Ra and Rz. For tool life, according to the ANOVA results, it can be seen that all three parameters (cutting speed, feed rate and depth of cut) have significant influence on the tool life (T). Experimental results were compared with the results of the exponential mathematical model and presented in diagrams. A new nozzle was designed for this research to allow micro-droplets from the MQL unit and chilled compressed air from the vortex tube to be connected in one stream (single-channel system) before entering the cutting zone, thus allowing for simultaneous lubrication and cooling. For the used vortex tube system with an air flow of 708 L/min and the inlet air pressure of 0.69 MPa, a temperature drop of −29 °C can be achieved in regard to the inlet air temperature of 21 °C. Therefore, the minimum quantity lubrication technique with vortex tube cooling can be recommended for turning of martensitic stainless steel X20Cr13.

The paper presents the development of a correlation model for initial tensile elastic modulus for flexible polymers as a function of Shore hardness in OO and A scale based on measurement. Measured polymers are in groups of silicone rubber, nitrile butadiene rubber (NBR), thermoplastic polyurethane (TPU) and silicone. The model is composed of piecewise exponential functions with fixed coefficients chosen to minimize the S₂ error norm and absolute value of relative error at the measured data points. Every chosen section of the hardness scale has one exponential function correlating the hardness to tensile elastic modulus with the argument in the form of a polynomial up to the fourth degree. The coefficients for the polynomial arguments were determined by enforcing interpolation conditions in a chosen set of points in the logarithmic scale for the elastic modulus. The correlation model possesses C0 continuity. For each material, five specimens were used for hardness measurements and five for the elastic modulus testing. The correlation model gives a positive value for elastic modulus of 0 for hardness, and a “finite”, “reasonable” value of 100 for hardness and is monotonic. Tensile properties were evaluated using true stress and logarithmic (Hencky) strain, with iterative correction of the changing cross-sectional area to account for large strain. The maximum relative error achieved in the correlation model for the OO scale is 13.4%, while for the A scale it is 7%. The developed model provides a practical and rapid method for estimating the initial tensile elastic modulus from non-destructive hardness measurements and is particularly useful in industrial applications and in the development of material models for dental surgery simulations.

Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between material hardness, water absorption, diffusion behaviour, and dimensional stability remains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using an FDM 3D printer under controlled processing conditions and immersed in physiological solution (0.9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analyzed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results suggest a transition in behaviour between lower- and higher-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorption (up to ~1.80%) and an apparent linear trend between hardness and absorption within the investigated material group (R² = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorption (~1.18–1.42%) and a weaker apparent relationship with hardness (R² = 0.4214). Diffusion coefficients ranged from 1.40 × 10⁻¹³ to 3.40 × 10⁻¹² m² s⁻¹, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings indicate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling may be influenced by different mechanisms. The identified transition from hardness-dependent to behaviour potentially influenced by material structure provides new insight for the design and selection of flexible polymer components in moisture-exposed environments, particularly in biomedical applications.

Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between mate-rial hardness, water absorption, diffusion behaviour, and dimensional stability re-mains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using FDM 3d printer under controlled processing conditions and immersed in physi-ological solution (0,9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analysed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results revealed a clear transition in behaviour between lower- and high-er-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorp-tion (up to ~1.80%) and a strong linear relationship between hardness and absorption (R² = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorp-tion (~1.18–1.42%) and no clear correlation with hardness (R² = 0.4214). Diffusion coef-ficients ranged from 1.06 × 10⁻¹² to 3.40 × 10⁻¹² m²s-1, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings demonstrate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling are governed by different mechanisms. The identified transition from hardness-dependent to structure-controlled behaviour provides new insight for the design and selection of flexible polymer components in moisture-exposed environ-ments, particularly in biomedical applications.

This paper studies the importance and development of additive technology through technical and economic aspects. The technical aspect includes research about the influence of surface inclination and layer thickness on the surface roughness of the produced test samples. Two AM technologies or processes (FDM and SLS) were used, with the use of three different materials (PLA, PETG and PA12) and two subsequent treatments (compressed air and glass bead blasting). Surface roughness parameters (Ra, Rz and Rmax) were measured and analyzed after different manufacturing conditions. Their variability and statistical analysis are presented. From the obtained results, it is evident that with increasing slope (from 0° to 90°) the values ​​increase to a maximum (between 10° and 40°), after which they decrease (from 50° to 90°), while increasing the thickness of the layer causes higher values of roughness parameters. Also, the aim of the paper is to determine the economic profitability of the used procedures, that is, the impact of the manufacturing procedures on the price of the product. Modern and innovative materials and technologies are used in the research. By using innovative technologies, we influence on sustainable development, which speaks of the fact that we need to meet our needs with quality, while taking care that the generations that come after us also have this opportunity.