The availability of effective and eco-friendly powertrain systems for electrification of passenger and commercial traffic is a crucial requirement for achieving current climate targets. With increasingly limited energy resources, fuel cell technology is gaining interest as an alternative to conventional electrical drives. Especially for heavy-duty and long-distance vehicles, where the required payload and range would require enormously heavy batteries, fuel-cell-technology offers a promising solution. Critical components of such modern fuel cells are metallic bipolar plates (MBPP) manufactured by high-precision embossing of thin metallic foils. The critical point is that even slightest fluctuations within the manufacturing process can lead to forming defects and result in unacceptable springback of metallic bipolar plates. Combined with the dimensional accuracy required for MBPP, extensive quality assurance and thus relatively low cycle times are inevitable in today´s production of these components. In this context, this paper deals with an approach to actively control the manufacturing process of MBPP based on numerical data sets. For this purpose material characterization of 0.1 mm stainless-steel foil (1.4404) was performed, allowing for comprehensive modelling of the embossing process and the springback behavior. In order to maintain a robust forming process aimed at increasing productivity, a numerical analysis was then conducted under variation of different geometric parameters using AutoForm R10. It was found that variation of selected geometric parameters such as channel width, channel height, draft angle and tool radii can remarkably reduce thinning and springback in MBPP production in compliance with tight tolerance specifications. Furthermore, the investigations show that active control of the lubrication conditions offers an additional possibility for subtle adjustments of the dimensional accuracy of produced components.

The extreme sensitivity of quantum magnetometers enables new applications in material testing such as the identification of single defect events in the bulk of small volume specimen (0.1 mm³). Exposing ferromagnetic materials to strain alters their magnetic response. Due to uncompensated spins, defects arising from the fatigue process interact with magnetic domain walls. Optically pumped zero-field magnetometers (OPM) provide the sensitivity required to measure small variations in the magnetic response and potentially to quantify damage in the material. We provide first results of a novel micro fatigue setup with an integrated OPM to correlate variations of the magnetic response in a multimodal approach. The position of the Villari reversals within the magneto-mechanic hysteresis and the amplitude of magnetic field are potential candidates to estimate fatigue damage within the specimen.

By means of fracture mechanics evaluation concepts, the most accurate possible estimation of the crack growth behaviour of complex and highly loaded structures is to be aimed for a more efficient use of components, a more precise planning of inspection intervals and for the realization of advanced design approaches. Standard fracture mechanics specimen used in materials testing are globally subjected to purely uniaxial loading. In contrast, the technical components usually experience multi-axial stresses due to the external loads and to their complex geometry. The influence of multi-axial far-field loads on the crack propagation rate and the crack closure behaviour is unclear and controversially discussed in literature. In this context, the crack propagation behaviour of uniaxially loaded corner-crack specimens and multiaxially loaded cruciform specimens is systematically studied in this investigation. Here, the multiaxiality condition is characterized by the so-called T-stress and systematically varied within the tests. The results so far show no significant influence of the far-field multiaxiality or the T-stress on the crack propagation behaviour. However, the evaluation of the crack closure behaviour indicates that an engineering approach for thin-walled structures leads to a non-conservative estimation.

Materials with magnetic shape memory (MSM) are promising candidates for application in next generation devices, such as actuators and switching valves. They exhibit elongation and contraction in a magnetic field and allow to achieve fast switching times in the order of milliseconds while maintaining high positioning precision over millions of cycles. Studying and developing applications using these materials creates a need for fast and accurate methods for analyzing their shape and deformations. We present a technology that utilizes capabilities of two interferometric methods - digital holography (DH) and electronic speckle pattern interferometry (ESPI). While digital holography enables high-precision 3D measurement of the object surface, electronic speckle pattern interferometry provides data on high-frequency deformations with nanometer accuracy. Combining both techniques allows to obtain comprehensive information about the morphology and dynamics of samples.

In this study, the effect of die attachment delamination on deformation of power devices during passive heating is investigated. For this purpose, Insulated Gate Bipolar Transistors (IGBT) are silver sintered with defects in their die-attachment on Printed Circuit Board (PCB) substrates. The passive heating process takes place on a hotplate under isothermal loading conditions between $50^{\circ}\m...

Die attachment delamination is one of the most common defects that happen over the life-time of a power electronic module [1]. It is usually the consequence of thermal mechanical stress that occurs during active operation of the device due to CTE (coefficient of thermal expansion) mismatch of its components. Additionally, even during the production cycles, errors can emerge, where the chip is not fully attached to the substrate. This can lead to premature failure of the final product. Aim of this paper is the detection of local delamination spots through pre-existing optical techniques. This novel non-destructive method will allow the isolation of defective devices during production or warn the overall system during operation, if a failure is imminent.

Die Suche nach neuen Verzahnungsmessverfahren führt unweigerlich zu optischen Methoden: Diese Verfahren liefern hochpräzise Daten in kürzester Zeit und das nicht nur punktweise sondern flächig. Bisher scheitern optische Messungen in der Verzahnungsmessung jedoch an steilen Flanken und Mehrfachreflexionen. Wir zeigen am Beispiel eines prototypischen Systems wie diese Aspekte überwunden werden können, um Präzision und Geschwindigkeit in der Verzahnungsmessung zu kombinieren. Dabei wird die digitale Mehrwellenlängenholographie eingesetzt. Basierend auf dieser Technologie erfasst unser Inspektionssystem eine vollständige Zahnflanke in einer einzigen Aufnahme mit Millionen von 3D-Punkten und einer Genauigkeit von unter einem

Hybrid manufacturing processes, high level of automation, short product service life and decreasing vertical range of manufacture in production request for increasing flexibility and speed of quality control.With HoloCut we previously introduced the world's first wireless digital-holographic sensor system prototype for fast and precise measurements inside a machine tool.With the experience gained so far, we now present an improved, even more compact sensor system, for the use on various multi-axis systems such as coordinate measuring machines (CMM), robots and machine tools and show first results with different handling systems.Besides improved mechanical stability, a size and weight reduction resulted from a new design approach: The arrangement of components around a central "core" made it possible to create a very compact design with a diameter of 125 mm, a height of ~180 mm and a weight of ~2 kg.The system features a 12.5 × 12.5 mm² measuring field with a lateral sampling of 4 μm.An NVIDIA Xavier embedded system enables pre-evaluations of the recorded measurement data in order to allow re-recording them, even before the complete data transmission (up to 160 MB with 2 Hz measuring rate) and evaluation.This is especially important for the use in vibration-prone environments such as multi-axis systems.Various handling systems such as a HERMLE C32U machine tool, an undamped LEITZ Reference HP 15.9.7 CMM and a UNIVERSAL ROBOT UR16e are examined with regard to vibrations.In future work, the behavior of the system under higher vibration amplitudes will be characterized.

The electronics industry is creating complex miniaturized devices with steadily higher power density. The increase of maximum operating temperatures affects the thermo-mechanical load and imposes greater requirements on the quality of electronic packages. Fast and reliable methods for inspecting the quality of electronic components can help to improve production quality and to reduce waste and environmental burden. We present a compact optical sensor based on Electronic Speckle Pattern Interferometry (ESPI) that provides a possibility to carry out such control in a fast, precise and non-contact manner and can be integrated directly in a production line. Analysing thermo-mechanical deformations of objects under study, the system is capable of identifying common defects in electronic modules, such as die attachment delamination.

Experiments to describe the crack growth behavior are expensive and complex, while the evaluation depends mainly on the determined crack lengths over the testing period. Digital image correlation (DIC) is well established for crack-length and displacement measurements, but it normally requires sample preparation with speckle paint and interferes with mechanical extensometers. Novel GPU-based DIC system capable of measuring total strain at rates up to 850 Hz and strain-fields overcome these limitations. We present first results of fatigue crack growth experiments with uniaxially und biaxially loaded specimens. The force controlled tests under room-temperature conditions were accompanied by conventional measuring systems comprising a side extensometer, an ACPD-measurement system and the GPU-based DIC system. The results indicate that DIC-measured crack depth correlates well with ACPD crack depth values. Furthermore, the crack-flank displacements derived from DIC-evaluation are in good agreement with 2D-FEM simulations. The GPU-based DIC-System appears as a promising measurement technique for crack growth investigations.

Digital-holographische Messsysteme erlauben eine echte 100-Prozent-Qualitätskontrolle – inline in der Fertigungslinie und sogar direkt in der Werkzeugmaschine. Die hochgenauen und sehr schnellen 3D-Sensoren erfassen dabei makroskopische Topografien mit Genauigkeiten bis in den Sub-Mikrometerbereich.

This article reports a novel GPU-based 2D digital image correlation system (2D-DIC) overcoming two major limitations of this technique: It measures marker-free, i.e. without sample preparation, and the sampling rate meets the recommendations of ASTM E606. The GPU implementation enables zero-normalized cross correlation (ZNCC) calculation rates of up to 25 kHz for 256 × 256 pixel ROIs. This high-speed image processing system is combined with a high-resolution telecentric lens observing a 10 mm field-of-view, coaxial LED illumination, and a camera acquiring 2040 × 256 pixel images with 1.2 kHz. The optics resolve the microstructure of the surface even of polished cylindrical steel specimen. The displacement uncertainty is below 0.5 μm and the reproducibility in zero-strain tests approximately 10-5 (1 σ) of the field-of-view. For strain-controlled testing, a minimum of two displacement subsets per image are evaluated for average strain with a sampling rate of 1.2 kHz. Similar to mechanical extensometers, an analogue 0-10V displacement signal serves as a feedback for standard PID controllers. The average latency is below 2 ms allowing for cycle frequencies up to 10 Hz. For strain-field measurement, the number of ROIs limits the frame rate, e.g., the correlation rate of 25 kHz is sufficient to evaluate 10 images per second with 2500 ROIs each. This frame rate is still sufficient to compare the maximum and minimum strain fields within a cycle in real-time, e.g. for crack detection. The result is a marker-free and non-contact DIC sensor suitable for both strain-controlled fatigue testing and real-time full-field strain evaluation.

With state-of-the-art 3D measurement systems, short-wave structures such as tool marks cannot be resolved directly inside a machine tool chamber. Up to now, measurements had to be performed outside the machine tool. We present an interferometric sensor that carries out such measurements inside the machine tool, which saves time-consuming and expensive setup procedures. Our sensor HoloCut uses digital holography as measurement principle. By the use of multiple wavelengths, we get a large unambiguous axial measurement range of up to 2 mm and achieve micron repeatability, even in the presence of laser speckles. With a lateral resolution of 7 μm across the entire 20 x 20 mm2 field of view, both macro- and microstructures (such as tool marks) are measured with an axial resolution of 1 μm. Consequently, this qualifies HoloCut for in-situ measurements and integration in a machine tool. In this paper, the boundary conditions of integrating interferometers inside a machine tool are evaluated. Occurring vibrations and limited available space are particularly challenging constraints: The optical and mechanical design of HoloCut is introduced along with numerical correction algorithms: A piezo-stage setup is used to induce known displacements. Using these algorithms, measurements even with a closed-loop control of the machine tool head activated are demonstrated on a coin measurement. The use of HoloCut is motivated on the base of the daily operation of a 5-axis machine tool: We present an evaluation of an exemplary ISO 25178 parameter Sq using HoloCut measurements and compare those with reference, yet not inline-capable systems.

Digital multiwavelength holography is a technique for precise 3D height measurements of optically rough surfaces. We demonstrate measurements on a milled surface, using four wavelengths between 514 and 532 nm, and achieve precision in the submicrometer range. Height structures of < 400 nm can be resolved up to an unambiguous height of 370 μm and with a lateral resolution of 7 μm. Acquisition times of < 400 ms, including the time needed for parallel processing of the data, make our sensor a versatile tool for high-throughput 100% inspection in manufacturing environments.

This paper presents a new technology, which allows the reduction of the micro dimensional trench width below the technological limitations of the Deep Reactive Ion Etching (DRIE) process. The high-accuracy and high-throughput femtosecond laser-micro-welding of aluminum was performed for the first time by Micro Electrical Mechanical System (MEMS) fabrication to realize this permanent trench width reduction. Therefore, this technology has been applied for the electrode gap reduction of high precision vibration sensors, based on the capacitive working principle, resulting in a fourfold improvement of the sensitivity without changing the size of the sensor chip itself.

illuminating apparatus for surface inspection of strip products or the like goods continuously produced with at least one lighting device, the at least one light source has a surface area of ​​the to be tested, quickly moving the test specimen (2) with light emitted from its light, and with a detection device (30), the optical information from the illuminated test specimen (2) receives, and a control means (16) having at least a logic circuit, which control means (16) detecting means (30) controls and analyzes of these received signals, wherein the detection means (30) is formed in several stages and the control means (16) depending on the result of an evaluation of the optical information of a first detection stage (10) initiates the execution of the recording of optical information of a second detection stage (11), characterized in that the first detection stage (10) of the detection device (30) as De Tektor (8) is provided with a plurality of detection channels, which is in each case at least one sensor (9) associated with the sensors (9) form at a predeterminable distance from the surface area of ​​the test piece (2) a spatial arrangement in which the sensors detecting (9) scattered light from the surface area, and that the second detection stage (11) is formed as an image processing system (12) with at least one camera (13) and a lens (14).

This contribution reports on the analysis of metal-metal contacts of MEMS switches. A novel high aspect ratio MEMS fabrication sequence in combination with wafer level packaging is applied for fabrication of an RF MEMS switch with lateral motion. It allows for a relatively large actuation electrode area in a small package, and for high actuation force even with an actuation voltage of 5 V. The focus of this contribution is on the contact behavior. It is shown how operation conditions as like as actuation voltage, RF power, and DC bias influence the contact resistance. The power handling capability and its influence on the contacts, and the intermodulation were investigated also.