JEC COMPOSITES MAGAZINE - Issue #72 - April/May 2012 - 39

Other sensor systems like dielectric sensors for cure monitoring are used for documentation purposes. The uncertainties related to the degree of cure, risks of process breakdowns and production of scraps are some of the challenges that must be tackled.

part prevention. Besides cure cycle recipes developed in the laboratory for use in manufacturing, advanced cure cycles can be run in a controlled way.

The new approach
The analysis of quality-relevant parameters leads to a better understanding of the physical and chemical interactions that take place inside the material. We can only build up this knowledge if these parameters are recorded and analyzed during the whole curing process, in a central control and processing unit. For this purpose, the Masterbox is developed to record, to process and to analyse all information flow within the system (see Fig. 2).

Process transparency through efficient communication systems
The decisions in the Masterbox are only possible through the use of efficient communication systems with the capability to provide information about part quality and properties. There is a difference between the information on relevant process parameters that must be measured directly by sensors and those that cannot be measured directly and must be calculated by numerical simulation. Sensors are an essential part of quality-assured production. Each sensor provides valuable information and leads to a better understanding of the processes inside the autoclave. A disadvantage associated with the harsh environment in the autoclave (pressures up to 10 bar and temperatures up to 250°C) is a long development time for establishing of sensor technologies and taking in the operation. In addition to thermocouples, sensor technologies for temperature measurement include resistance temperature detectors (RTD) to measure local temperatures and movable thermal cameras to collect information about temperature distribution on the part surface. Piezoceramics, ultrasound and dielectric sensors are used for cure monitoring. Pressure transducers are applied in the mould to monitor

the vacuum pressure actually applied inside the vacuum bag. Finally, chargecoupled device (CCD) cameras deliver a live feed inside the autoclave (see Fig. 3). A physical-mathematical based computational fluid dynamic (CFD) simulation of the autoclave process is integrated in the communication system. This virtual autoclave displays polymer reactions, fluidic and thermal processes. It is able to predict the whole process in a numeric model precisely. In parallel to the real autoclave process, the virtual autoclave uses the process predictions to generate different control strategies for optimizing the autoclave cycle (see Fig. 4).

Fig. 4: Virtual autoclave (MET GmbH, Rostock)

Fig. 2: Masterbox – a central control and processing unit

The data analyzed in the Masterbox is taken into consideration for an open loop process control allowing direct control and resulting in the desired part quality, optimized process cycle duration, quality assurance and scrap

Fig. 3: Piezoceramics for cure monitoring

In contrast to conventional sensor systems, virtual sensors are nodes in the physical-mathematical model of the numerical simulation that calculate parameters that may or may not be directly measurable. Three-dimensional temperature and cure degree distribution, chemical shrinkage and warpage are some of these parameters. In case of a failure of conventional sensor systems, the missing data can be compensated by calculated values. This unique technology allows more flexibility and redundancy concerning measured data. Obtained data from the system is recorded into a central database. Thus, it

No72 April - May 2012 /

jec composites magazine 39

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JEC COMPOSITES MAGAZINE - Issue #72 - April/May 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #72 - April/May 2012