Additive manufacturing, in particular the powder bed fusion of metals using a laser beam, has a wide range of possible technical applications. Especially for safety-critical applications, a quality assurance of the components is indispensable. However, time-consuming and costly quality assurance measures, such as computer tomography, represent a barrier for further industrial spreading. For this reason, alternative methods for process anomaly detection using process monitoring systems have been developed. However, the defect detection quality of current methods is limited, as single monitoring systems only detect specific process anomalies. Therefore, a new methodology to evaluate the data of multiple monitoring systems is derived using sensor data fusion. Focus was placed on the causes and the appearance of defects in different monitoring systems (photodiodes, on- and off-axis high-speed cameras, and thermography). Based on this, indicators representing characteristics of the process were developed to reduce the data. Finally, deterministic models for the data fusion within a monitoring system and between the monitoring systems were developed. The result was a defect detection of up to 92% of the melt track defects. The methodology was thus able to determine process anomalies and to evaluate the suitability of a specific process monitoring system for the defect detection.

Powder bed fusion of metals using a laser beam (PBF-LB/M) is a process that enables the fabrication of geometrically complex parts. In this process, a laser beam melts a metallic powder locally to build the desired geometry. The melt pool solidifies rapidly, which results in high cooling rates. These rates vary during the process in line with the geometric characteristics of the part, which leads to a non-uniform microstructure along with anisotropic mechanical properties. The unknown part characteristics prevent the process from being used in safety-critical applications. Thermographic in situ process monitoring provides information about the thermal field, enabling predictions of the resulting material properties. This study presents a novel methodology for the thermographic measurement of cooling rates during the PBF-LB/M process using a high-speed thermographic camera. The cooling rates occurring during the manufacturing of 316L tower-like specimens were measured. The cooling rate decreased with increasing build height, due to the heat accumulation in the parts. The microhardness profile of the parts was tested perpendicularly and parallel to the build direction. A significant decrease in hardness values was observed along the build height. The measured cooling rate was correlated to the microhardness profile of the specimens using a Hall–Petch type relationship. The results show a high level of reproducibility of the cooling rates between different specimens in the same build job as well as between subsequent build jobs. The presented methodology allows studying the effects of the geometry on the cooling rates and the resulting mechanical properties of 316L specimens.

Additive manufacturing of metal components offers a high potential for many industrial applications due to the cost-efficient manufacturing of geometrically complex and individualized components, for example, to manufacture connections for steel constructions. Different process classes of metal additive manufacturing exist. The powder bed fusion and the directed energy deposition processes are especially relevant for industrial applications. In comparison, the powder bed fusion processes achieve a higher accuracy but have a lower build rate than directed energy deposition processes. This publication focuses on the combination of powder bed fusion of metals using a laser beam and directed energy deposition using a plasma arc for the fabrication of 316 L stainless steel. The differences in temperature profiles and solidification conditions between the two processes cause variations in the microstructure of the 316 L material. These microstructural differences lead each processed version of 316 L to develop distinct properties. The microstructure and mechanical properties were investigated in detail. All tensile specimens failed away from the interface. The integral tensile properties were in between the values of the individual materials. The microstructure showed five different zones. These were attributed to the different thermal characteristics of the two processes and the effect of the heat input of the directed energy deposition additive manufacturing on the powder bed fusion material, which was fabricated first. The results give insight into the differences in the metallurgical and mechanical properties of 316 L manufactured by these two processes. The results also highlight the importance of characterizing the process and material combination for applying a hybrid additive manufacturing process routine.

Objective: To identify factors related to the conversion of robot-assisted partial nephrectomy (RPN) to robot-assisted radical nephrectomy (RRN) based on data collected by a statewide database in Michigan. Methods: Using the Michigan Urological Surgery Improvement Collaborative-Kidney mass: Identifying and Defining Necessary Evaluation and therapY (MUSIC-KIDNEY) database we identified 574 patients for whom RPN was planned. Patient and tumor characteristics were obtained including body mass index (BMI), Charlson comorbidity index (CCI), RENAL nephrometry score, tumor size, and pathologic staging. Treating centers were subdivided by annualized case volume and academic status. Bivariate and multivariate analyses were performed to assess the impact of these factors on the risk of conversion to RRN from RPN. Results: The conversion rate of RPN to RN was 5.75% (33/574). The difference in RENAL nephrometry score, tumor stage, and size reached statistical significance on bivariate analysis (p<0.001). The tumor stage also reached statistical significance on multivariate analysis [odds ratio (OR); 95%CI (8.97; 3.93-20.48) p<0.001]. The conversion rate was lower among high-volume versus low-volume practices; however, statistical significance was not reached [5.2% (27/520) vs.11% (6/54); p=0.11]. Conclusions: Patient factors such as tumor size and renal nephrometry score are likely related to the conversion of RPN to RRN decisions. The data shows that Michigan urologists appear to appropriately assess intra-operative findings and convert to RRN in cases of more advanced kidney tumors. Lower volume centers appear to trend towards a higher conversion rate. Continued quality improvement tracking analysis may further clarify this relationship.

The integration of lattice structures into parts using powder bed fusion of metals using a laser beam (PBF-LB/M) allows tailoring mechanical properties by adjusting their geometric parameters. A composite material created by filling the voids in the lattice structures with a second, viscoelastic material offers promising dynamic properties. However, understanding the relationship between the lattice geometry and the resulting dynamic mechanical behavior is essential for designing composite materials and applying them to industrial components, such as boring bars. This study investigated the dynamic structural behavior of various strut- and wall-based lattice structures filled with epoxy resin. Lattice structures were integrated into IN718 beams manufactured by PBF-LB/M. Experimental modal analyses were conducted to evaluate the changes in the eigenfrequency, the dynamic compliance, and the damping ratio before and after the filling. Microscopic and cross-sectional analyses supported examinations. The results showed that the unit cell size and the volume fraction significantly influence the infiltration. In addition, the eigenfrequency and the dynamic compliance can be effectively adjusted by changing the volume fraction. In particular, the epoxy resin filling had a large effect on the damping ratio and increased it by a factor of up to 3.6 for the body-centered cubic cell. Among all the studied lattice types, the diamond TPMS structure had the highest eigenfrequency and the lowest dynamic compliance. From the results of the statistical evaluation, recommendations of action for the design of composite lattice structures were derived.