In these days industry 4.0 resounded throughout the land and means the fourth industrial revolution. The industry has to tackle the task of a flexible and customer-oriented production. Therefor the need of sensor systems for the measurement of temperature and load, the two most important categories in production, is rising. For getting the real specification during the production process the integration of sensor elements in high load regions of machinery is very important. Thus wear resistant thin film sensor systems directly applied onto the surface of plant components are in development. These multilayer systems combine excellent wear resistance with sensory behaviour. The sensor data will lead to a deeper process understanding, to optimization of simulation tools, to reduction of rejects and to an improvement of flexibility in production.
The two most important measurement categories in production are temperature and load. Therefore commercial sensors are applied in machinery as near as possible to the working parts. For a cost efficient production the integration of sensor elements directly on top of the surface in the heavily loaded regions is essential to get the real temperature and load distributions during the production process. Therefore a new multifunctional thin film sensor system is in development. This multilayer system combines thermoresistive sensor structures with piezoresistive ones and exists out of wear resistant carbon based layers [1, 2, 3, 4, 5]. The sensor data will lead to a deeper process understanding, to optimization of simulation tools, to reduction of rejects and to an improvement of flexibility in production.
Thin film sensor systems based on hydrogenated carbon have the advantage to combine two very important
characteristics. They show a piezoresistive behaviour and also a tribological stability caused by a high hardness and wear
resistance. Therefore they can be applied on the surface of machine parts or used for building up universal insertable
sensor systems like sensory washers.
A real challenge is the deposition of a whole sensory layer system on technical components like a spindle, which have
a length of 480 mm and an outer diameter of about 90 mm. The functions of the layer system directly applied in the
contact zone between spindle shaft and tool holder are the measurement of the clamping force of the tool holder, the
imbalance of the used tool and the process forces during machining. For this application a self-contained thin film sensor
system is investigated. Directly in the spindle shaft an insulating alumina layer is deposited in a thickness of about 4 μm
followed by electrode structures out of 200 nm thin chromium coating. On top of this the piezoresistive hydrogenated
carbon layer in a thickness of about 1 μm is deposited, covered by a wear resistant and insulating top coating. Therefore a
silicon and oxygen modified carbon layer in a thickness of about 2 μm is used. The piezoresistive sensor layer and also the
top layer are part of the diamond like carbon layer family [1,2,3,4].
Another very important application is the sensory washer. The thin film sensor system, consisting out of the
piezoresistive sensor layer deposited directly on the washer surface, the electrode structures out of chromium for the local
detection of the load distribution in the washer system and the insulating layer as top layer out of the silicon and oxygen
modified carbon layer, has a thickness in the range of 9 μm. In the latest investigations this layer system is connected with
a RFID-chip for contactless data transmission.
The investigation of a novel sensor system, integrated in the main load region of forming machines, is the challenge.
Therefore it is important that the thin film system is multifunctional. It has an excellent tribological quality in
combination with a piezoresistive behaviour. The layer system is deposited on the polished surface of a steel substrate. It
has such geometries that it can be easily integrated in the drawing cushion of a deep drawing machine. The thin film
sensor system exists out of a piezoresistive hydrogenated carbon layer, deposited in a PACVD process. Onto this layer
arrays of chromium structures are deposited in a PVD process. The structures are protected against wear by an insulating
silicon doped hydrogenated carbon layer. The whole thin film system has a thickness of about 9 μm.
During the forming process the steel plate is in direct touch with the sensor system and moves over it. The position of the
steel and the load distribution is measured in dependence on the forming stadium. The sensor system works as a control
system to ensure that the shape of the product is perfect and without any cracks or creases.
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