In the monitoring of mechanical components for lifetime prediction and detection of critical load conditions, especially strain gauges play a major role. They can be integrated into components to measure strain in the components themselves. This places special demands on the sensors used because of higher temperatures in the manufacturing phase of the components like additive manufacturing. This is why the sensors need to be polymer-free and cannot be applied with an adhesive. For this, directly deposited polymer-free sensors have been developed. In this article, the advantages of conventional polymer-foil based strain gauges (batch production) and directly deposited sensors (polymer-free) are combined by depositing the sensors on a metal foil and applying them polymer-free to metal specimens. This enables the batch production of strain gauges for use in harsh environments. Therefore, steel and aluminum foils were used as sensor carrier materials with aluminum oxide insulation layers and Platinum and NiCr sensor layers on the front side. On the back side, a tin layer was applied to enable thermocompressive bonding on the specimens leading to maximum tensile shear strengths of 10.7 MPa. After application, the sensors showed a k-factor of about 3.6 for the platinum sensors and about 2.4 for the NiCr sensors proving the functionality of the sensor concept.

AbstractThis contribution summarizes the current state of research regarding so‐called sensor‐integrating machine elements as an enabler of digitalization in mechanical engineering and——if available—their application in industry. The focus is on the methodical aspects of the development of these machine elements in general as well as specific sensor‐integrating machine elements that are either already in use or currently under development. Developmental aspects include the robust design of initially evaluated concepts for sensor‐integrating machine elements as well as their modularization. Smart materials with sensory functions are included in the analysis as well as the differentiation with regard to add‐on sensors. The aim of the authors interlinked by a special research program funded by the German Research Foundation (DFG) is to facilitate the exchange with other researchers with the help of the comprehensive overview given in this contribution. The contribution concludes with a brief discussion of open challenges, such as the energy supply and data transfer in rotating systems and also data security.

Many industrial production processes use sensors to generate information about the manufacturing process. In this way, monitoring machine tools ensures the proper functionality of the system and detects unexpected behavior due to, for example, material inhomogeneity, incorrect data input, temperature influence or tool wear. In large production machines, such as portal milling machines, the sensor equipment of guide carriages can be an important possibility since they are a standardized component and can be easily integrated into existing machines. Here, conventional polymer foil-based strain gauges show several disadvantages due to reproducibility and reliability of the sensor connection via adhesive. Thus, this article addresses the manufacturing of directly-deposited chromium thin-film strain gauges on a guide carriage with integrated programmable data pre-amplification. Tests with different sensor materials on steel substrates showed that chromium was the most suitable sensor material with a high k-factor. Then, one end face of the carriage was polished before sputtering an Al 2 O 3 insulation layer and a chromium sensor layer that was laser-structured afterward to produce two Wheatstone full-bridges at previously simulated sensor positions. In a tensile test stand, the calibration of the sensors took place in the two spatial directions perpendicular to the guide rail direction. With an additional sensor data fusion for the final interpretation of measured forces, it is shown that this sensor technology is suitable for force measurement at guide carriages.

Precision machining is becoming more and more important with the increasing demands on surface quality for various components. This applies, for example, to mirror components in micro-optics or cooling components in microelectronics. Copper is a frequently used material for this purpose, but its mechanical properties make it difficult to machine. In this study, a process strategy for finishing copper surfaces with batch-manufactured micro-grinding tools in an electrochemically assisted grinding process is demonstrated. The tool heads are manufactured from a polyimide-abrasive-suspension and silicon as a carrier substrate using microsystems technology. The matching shafts are milled from aluminium. The tools are then used on pure copper and oxidised copper surfaces. By using finer abrasives grains (1.6–2.4 µm instead of 4–6 µm) than previously, similar surface roughness values could be achieved ( R a = 0.09 ± 0.02 µm, R z = 1.94 ± 0.73 µm) with the same grinding process. An optimised grinding process that combines the use of rough and fine tools, on the other hand, achieves significantly better surface finishes in just four grinding iterations ( R a = 0.02 ± 0.01 µm, R z = 0.83 ± 0.21 µm). In order to achieve a further increase in surface quality, this optimised grinding process is combined with the anodic oxidation of the copper workpieces. The surface modification is done to increase the machinability of the surface by creating an oxide layer. This is confirmed by the results of scratch tests carried out, which showed less force acting on the tool during machining with the oxide layer than with a pure copper surface. To realise this within the machine tool, an electrochemical cell is shown that can be integrated into the machine so that the oxidation can be carried out immediately before the grinding process. The copper layers produced inside the electrochemical cell in the machine tool show similar characteristics to the samples produced outside. Processing the oxidised samples with the optimised grinding process led to a further reduction of about 17% in the R z values ( R a = 0.03 ± 0.01 µm, R z = 0.69 ± 0.20 µm). The combination of the shown grinding process and the integration of anodic oxidation within the machine tool for the surface modification of copper workpieces seems to be promising to achieve high surface finishes.

The world's electrical energy demand is rising permanently and, at the same time, resources must be used economically and responsibly.An important part of the energy turnaround are wind mills, where conventional machine elements such as gears or rolling bearings find application.These parts have optimization potential in terms of service life and reliability.To advance this potential, sensor integration for intelligent system monitoring combined with a compact electronic solution has to be realized.In contrast to conventional condition monitoring systems (CMS), this article addresses thin-film sensors that will be applied inside the bearing system directly inside or close to the tribological contact enabling maximum information about the system's condition.For this purpose, thin-film strain gauges are directly deposited onto small steel bearing washers of a cylindrical roller thrust bearing system (CRTB) by photolithography and sputtering processes.The layer stack includes an aluminum oxide insulation layer, the sensor layer and an aluminum oxide wear protection coating.The sensor layer consists of an array of three differently aligned meander-shaped constantan strain gauges.Therefore, bearing washers with the sensors are tested on a pin-onplate tribometer under defined load conditions.The influence of normal force as well as velocity on the thin-film sensors could be detected in this study.During the tests, under Hertzian pressure up to 1 GPa and a constant sliding velocity of 8 mm/s, a maximum nominal resistance change ΔR/R 0 of up to -0.13 ‰ was measured.Changing the velocity from 1 mm/s to 8 mm/s resulted in maximum ΔR/R 0 values of -0.17 ‰.This enables the determination of the correlation between sensor signals and tribological stresses.Though Hertzian pressures of 950 MPa were applied, no sensor failure was observed during the experiments proving the functionality of the sensor layer system.

Current limitations of silver sintering are long processing times and high processing temperatures. To overcome these restrictions, different tin contents are added to the sintering paste. Various preheating times and processing times are evaluated at a processing temperature of 235°C. The positive effect of micro scale tin particles on shear strength and porosity at reduced process parameters is demonstrated. The addition of tin particles enables a reduction of both the processing temperature and time while maintaining high shear strengths. At a processing time of 60 s and no preheating time, the addition of 27.5 at% tin to the sintering paste leads to an increase in shear strength of 417 % from 4.6 MPa to 19.2 MPa, compared to the sintering paste without an alloying element. Energy-dispersive X-ray spectroscopy shows the homogeneous distribution of the alloying element in the joint that has been fabricated with the produced sintering paste. The porosity of the sintered layer is reduced by the addition of tin as alloying element which can improve the electrical and thermal properties as well.

In the context of intelligent components in industrial applications in the automotive, energy or construction sector, sensor monitoring is crucial for security issues and to avoid long and costly downtimes. This article discusses component-inherent thin-film sensors for this purpose, which, in contrast to conventional sensor technology, can be applied inseparably onto the component’s surface via sputtering, so that a maximum of information about the component’s condition can be generated, especially regarding deformation. This article examines whether the sensors can continue to generate reliable measurement data even after critical component loads have been applied. This extends their field of use concerning plastic deformation behavior. Therefore, any change in sensor properties is necessary for ongoing elastic strain measurements. These novel fundamentals are established for thin-film constantan strain gauges and platinum temperature sensors on steel substrates. In general, a k-factor decrease and an increase in the temperature coefficient of resistance with increasing plastic deformation could be observed until a sensor failure above 0.5% plastic deformation (constantan) occurred (1.3% for platinum). Knowing these values makes it possible to continue measuring elastic strains after critical load conditions on a machine component in terms of plastic deformation. Additionally, a method of sensor-data fusion for the clear determination of plastic deformation and temperature change is presented.

The sensory equipment of components of large production machines plays a major role for quality monitoring. In portal milling machines, conventional foil-based strain gauges can be applied manually on guide carriages in order to measure the process forces and torques in all directions. Here, an improvement regarding accuracy, positioning and automatability concerning the sensor application is aimed by directly deposited thin-film sensors. Therefore, this article shows and evaluates a method for trimming of sputtered resistive thin-film strain gauges during their vacuum plasma fabrication process. In this way, an adjustment of the output signal of a thin-film chromium Wheatstone full-bridge circuit to 0.02 mV/V is possible, assuring a proper functionality with low apparent strain values of 6 µm/m up to temperature values of 90 °C.

Background Commonly, polymer foil-based strain gauges are used for the incremental hole drilling method to obtain residual stress depth profiles. These polymer foil-based strain gauges are prone to errors due to application by glue. For example zero depth setting is thus often erroneous due to necessary removal of polymer foil and glue. This is resulting in wrong use of the calibration coefficients and depth resolution and thus leading to wrong calculations of the obtained residual stress depth profiles. Additionally common polymer foil-based sensors are limited in their application regarding e.g. exposure to high temperatures. Objective This paper aims at a first step into the qualification of directly deposited thin film strain gauges for use with the incremental hole drilling method. With the directly deposited sensors, uncertainties regarding the determination of calibration coefficients and zero depth setting due to the absence of glue can be reduced to a minimum. Additionally, new areas of interest such as the investigation of thermally sprayed metallic layers can be addressed by the sensors due to their higher temperature resilience and their component inherent minimal thickness. Methods For the first time, different layouts of directly deposited thin film strain gauges for residual stress measurements were manufactured on a stainless steel specimen. Strain measurements during incremental hole drilling using a bespoke hole drilling device were conducted. Residual stress depth profiles were calculated using the Integral method of the ASTM E837 standard. Afterwards, strain measurements with conventional polymer foil-based strain gauges during incremental hole drilling were conducted and residual stress depth profiles were calculated accordingly. Finally the obtained profiles were compared regarding characteristic values. Results The residual stress depth profiles obtained from directly deposited strain gauges generally match the ones obtained from conventional polymer foil based strain gauges. With the novel strain gauges, zero depth setting is simplified due to the absence of glue and polymer foil. With the direct deposition, a wide variety of rosette designs is possible, enabling a more detailed evaluation of the strain field around the drilled hole. Conclusions The comparative analysis of the obtained residual stress depth profiles shows the general feasibility of directly deposited strain gauges for residual stress measurements. Detailed investigations on uncertainty sources are still necessary.

This paper shows the possibility of direct deposition of strain gauge sensors on curved metallic surfaces of arbitrary size. A novel, patented sputtering system from the IMPT guarantees the manufacturing directly onto the surface of any component. By this, the need of the undesirable polymer foil and adhesive vanishes, which are both necessary for conventional sensors. Thin-film metal strain gauges thereby enable new measurement positions in harsh environments due to their minimal total thickness of under 5 µm, for example in industrial applications with special needs, as they exist for drilling bottom hole assemblies. This article discusses the optimization of laser cut stainless steel shadow masks for structuring the sensor layer resulting in low resistance differences of 5.3 % for sputtered sensors. The developed constantan strain gauges show a low temperature coefficient of resistance of 74.8 ppm/°C, stability up to at least 210 °C and a k-factor of 1.98. Half-bridge measurements revealed an apparent strain of 156 µm/m at 200 °C and an error of only 6 µm/m when strain is applied.

Silver sintering is a very important state-of-the-art joining process in the production of high-performance electronic components, as conventional assembly and connection technology is reaching its limits, especially due to the increasing requirements of e-mobility. Silver sintering is particularly suitable for today’s high-performance electronic components such as IGBTs or diodes. However, the silver compound sintering process is not yet widely used. This is due to the very high process pressures, the high process temperatures, long process times and fluctuations in the strength of the joint. This work shows the potential and preliminary results on the optimization of silver compound sintering by using ultrasound in the joining zone and by adding low melting alloy partners to reduce the required sintering temperature. This generates a completely new process which is introduced by the authors as Ultrasonic Transient Liquid Phase Sintering (UTLPS). Without ultrasound, the shear strength of pure silver sintering joints increases as the temperature and process duration increase. When ultrasonic vibration is applied, for selected process parameters, the shear strength could be improved from 6 MPa to 12 MPa with the increasing of ultrasonic power. The addition of low-melting point alloy partners reduces the required sintering temperature. The combination of the addition of the alloying element indium and the application of ultrasonic vibration leads to an increase in shear strength with a maximum value of about 20 MPa.

New sensor and sensor manufacturing technologies are identified as a key factor for a successful digitalisation and are therefore economically important for manufacturers and industry. To address various requirements, a new sputter coating system has been invented at the Institute of Micro Production Technology. It enables the deposition of sensor systems directly onto technical surfaces. Compared to commercially available systems, it has no spatial limitations concerning the maximum coatable component size. Moreover, it enables a simultaneous structuring of deposited layers. Within this paper, characterisation techniques, results and challenges concerning directly deposited thin film strain gauges with the new sputter coating system are presented. Constantan (CuNiMn 54/45/1) and NiCr 80/20 are used as sensor materials. The initial resistance, temperature coefficient of resistance and gauge factor/k-factor of quarter-bridge strain gauges are characterised. The influence of a protective layer on sensor behaviour and layer adhesion is investigated as well. Moreover, the temperature compensation quality of directly deposited half-bridge strain gauges is evaluated, optimised with an external trimming technology and benchmarked against commercial strain gauges. Finally, the suitability for high-temperature strain measurement is investigated. Results show a maximum operation temperature of at least 400 °C, which is above the current state-of-the-art of commercial foil-based metal strain gauges.