The loads acting on a workpiece during machining processes determine the modification of the surface of the final workpiece and, thus, its functional properties. In this work, a method that uses thermocouples to measure the temperature in precision fly-cutting machining with high spatial and temporal resolution is presented. Experiments were conducted for various materials and machining parameters. We compare experimental measurement data with results from modern and advanced machining process simulation and find a good match between experimental and simulation results. Therefore, the simulation is validated by experimental data and can be used to calculate realistic internal loads of machining processes.

Fully screen-printed resistive pressure sensors have attracted rising attention in recent years. The possibility to fabricate them on any substrate as well as their low thickness and overall flexibility allow their application on curved surfaces or for material integrated sensing. However, these applications often apply additional loads other than only pressure to the sensors. A major concern is the cross-sensitivity of the sensors to strain. Thus, this work investigates the influence of the electrode geometry used for screen-printed pressure sensors on the device performance and on the cross-sensitivity to strain. It is shown, that the performance as well as the cross-sensitivity to strain are affected by electrode setup and orientation. The pressure sensitivity increases with the number of interdigital electrodes. The cross-sensitivity to temperature is not affected by the electrode setup.

Deep rolling is a common machining process, which is used to induce residual stress into the surface area of steel workpieces. However, the formation of the residual stress is merely understood. We present a method to measure sub-surface strain in-situ during a deep rolling process. The strain is measured by sensorial inlays, which are integrated into the machined workpiece. The recorded strain data can be used to describe the formation of residual stress in the surface area of the workpiece as well as to verify modelling results of the deep rolling process.

In recent years, it has been shown that the degradation of an O-ring gasket during its lifetime can be correlated with the change in signal of a strain gauge, which has been embedded into the gasket. Yet, the deduction of an easy to understand, direct performance indicator for the gasket has not been addressed. In this work, we present a method that allows the interpretation of the measured signal change and results in the calculation of a simple performance indicator. This is achieved by using a Finite Element Analysis assisted signal evaluation approach. A model of an installed gasket is modified until the simulation predictions match the experimental data. The model is based on the assumption that the degradation of the gaskets performance is mainly driven by stress relaxation phenomena inside the elastomer material. By tuning stress relaxation parameters, the signal change of an embedded strain gauge can be adjusted. The remaining contact pressure of the gasket-to-compression plate-interface can be calculated from simulation and can be used as performance indicator for the gasket as the contact pressure mainly determines the sealing capability of the gasket.

We present a novel approach for the differentiation between temperature and strain influence on resistive strain gauges. Two strain gauges are placed in a nested shape. The strain gauges are made from different materials. Due to the difference in strain sensitivity and thermal coefficient of resistance (TCR) of both materials, we can distinguish between resistance changes caused by temperature and by strain. Both strain gauges are exhibited to the same temperature and strain as they are placed very close to each other. In this work, we implement the concept on silicon substrates. The resistors are made from Platinum and Titanium which have a gauge factor of G.F.(Pt) = 5,933 and G.F.(Ti) = 0,0683 and a TCR of alpha(T),(Pi) = 2.138*10(-3) K-1 and alpha(T),(Ti) = 1.733*10(-3)K(-1), respectively. The strain gauges are separately characterized for strain and temperature sensitivity. The concept is proved by measuring strain under the influence of an unknown temperature change. (C) 2018 The Authors. Published by Elsevier B.V.

Integrating sensors into machine parts is a necessary step for the development of smart or intelligent components. Sensors integrated into materials such as concrete, fiber compounds, or metals are already used to measure strain, temperature, or corrosion. The integration is mostly done during fabrication, where the sensor is recast in the material during processing. However, approaches to integrate sensors into parts fabricated by additive manufacturing are still rarely found. Especially in the case of rapid prototyping, additive techniques are already substituting the machining of parts using classical technologies like cutting, drilling and milling. To characterize such 3-D-printed machine parts the direct integration of sensing elements is the next logical step. This can be done in multi-material printing by using insulating, magnetic, and conductive materials. In the case of single material printing, our idea is to integrate a sensing element during the printing process itself. As proof-of-concept, we present the functionalization of 3-D-printed screws. Strain gauges screen-printed on a 6 µm thick foil are interposed into the 3-D part during microstereolithography printing. We measure the torsional strain in the screw head to calculate the prestressing force in screws made from different plastic materials. We also analyze the defect effect by comparing it to screws without integrated elements.

Online monitoring methods for the production of carbon fiber reinforced polymers (CFRP) enable a fast and reliable manufacturing of CFRP parts for example for automotive and aerospace applications. With our miniaturized flexible dielectric sensor we realized online monitoring without harming the structural integrity of the produced part. We use the method of impedance spectroscopy where the changes of the dielectric parameters during curing are measured. The changes can directly be related to the curing degree. However during the curing strain can appear inside the part which is transferred to the flexible substrate of the sensor. Here we demonstrate that strain can also be measured with the sensor but the changes of the capacitance related to dielectric changes during the curing are several times higher. Therefore we can state that small strain, which can appear, does not influence our impedance measurement during curing.

Commercial pressure sensors are often fabricated using well-established silicon micromachining technologies. The thickness and stiffness of silicon-based sensors make them in most cases unsuitable for the integration into materials and surfaces. We present a flexible pressure sensor fabricated by printing technology. Therefore, an intrinsically pressure sensitive ink is screen printed on interdigital electrodes on a thin and flexible foil substrate. The sensor shows sufficient sensitivity and is applicable in a wide pressure range from 0 to 2 MPa. The sensor can completely be fabricated using a low-cost screen printing process. It is very thin and flexible, making it possible to be applied on curved surfaces or to be integrated into materials in a minimal invasive way.

Smart factories are supposed to provide an overview on the current status of installed production machines. In order to collect data, intelligent machine parts have to be designed. We present a method to monitor the condition of elastomer gaskets, which are crucial parts of many machines. The monitoring is done by a strain gauge, which is integrated into the gasket. This paper describes the overall concept of the monitoring system as well as the challenges by varying temperature and pressure of the sealed fluid on the sensors signal.

Functionalization of machine parts by integrating sensors into the surface or bulk is necessary when we think about smart or intelligent components.So far different sensors measuring strain, temperature or e.g.corrosion have been integrated in various materials like concrete, metals or plastics.The integration is mostly done during fabrication, where the sensor is recast in the material during processing.Approaches to integrate sensors into parts fabricated by additive manufacturing are still rarely found.Especially in the case of rapid prototyping, additive techniques are going to substitute the machining of parts using classical technologies like cutting, drilling and milling.To characterize such 3D printed machine parts the direct integration of sensing elements is the next logical step.This can be done in multi-material printing by using insulating and conductive materials.In case of single material printing, our idea is to integrate a sensing element during the printing process itself.As proofof-concept, we present the functionalization of 3D printed screws.Strain gauges screen-printed on a 6 µm thick foil are interposed into the 3D part during microstereolithography printing.We measure the torsional strain in the screw head and compare the defect effect to screws without integrated elements.

The fabrication of a thin film hyperelastic nitrile butadiene rubber (NBR) substrate, for micro-structured strain gauges, has been developed. These NBR sensors are integrated into silicone and rubber materials for the purpose of monitoring a change in material properties, such as stress-strain behavior. As an example, they were integrated into silicone gaskets. The signal of the embedded sensors was measured while compressing the gaskets. The change of resistance depends on the applied compression force and is directly correlated with the stress-strain properties of the host material. By using a hyperelastic substrate with similar physical properties as the host material, the distortion on the sensor signal, regarding the properties of the host material, can be minimized. Uniaxial tensile tests were performed on test specimens containing the NBR sensors. It was discovered that the integrity of the host material is slightly less influenced by the embedded NBR sensors compared with commonly used polyimide substrates. However, the test also revealed that the sensor size highly influences the stability of the host material.

This paper presents the design, fabrication and characterization of foil-based strain gauges using nanogranular Platinum (ng-Pt) as strain sensing material. The strain gauges are later to be integrated into elastomer gaskets to allow condition monitoring. In this work, Focused Ion Beam Induced Deposition (FIBID) is used for the formation of ng-Pt structures. Using this technology, ng-Pt structures can be deposited in any shape and on almost all surfaces. Due to the very small dimensions of the sensing elements, the overall size of the strain gauges can also be very small and is only limited by the possibilities to handle them. Thus, it is not only possible to integrate the strain gauges into elastomer gaskets causing minimum damage in the host material matrix, but also to measure strain locally on very small areas. Additionally, the formation of a Wheatstone Bridge circuit on the strain gauge is possible without enlarging the strain gauges dimensions dramatically. This enhances the strain sensitivity even further and compensates temperature dependency. A full bridge strain gauge with dimensions below 20 μm is feasible.

To allow for smaller sizes, smoothness and robustness of exposed surface, and for integration in flexible sensor arrays, an innovative piezoresistive pressure sensor design has been developed. In contrast to known concepts, the sensing elements and the conducting tracks are positioned within the pressure reference chamber and, thus, protected against environmental influences such as water or particles. Sensing elements are electrically accessible from the backside by vias, thus enabling a fully flat surface totally free of electrical elements as desired for flow experiments. The sensor comprises a thin silicon sensing membrane and a body made from glass holding the reference chamber and the vias. The structuring of the sensor body is performed by femtosecond laser ablation. Steep ablation edges are realized, leading to small sensor dimensions. The sensing membrane is fabricated using potassium hydroxide (KOH) wet etching. The glass body and the silicon membrane can be connected with different techniques; hitherto, adhesive bonding by an epoxy resin layer was successfully tested. A sensitivity of 10 mV/V/bar and stable operation up to 7 bar absolute pressure could already be demonstrated. The new concept simplifies micromanufacture and allows for flip-chip-assembly in foil-based flexible systems that can be used in liquids and harsh environments.