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Use of Process Knowledge in Thermoforming of Packaging

The study investigated the production of packaging in thermoforming processes to roll machines. As part of the study, it can be shown that the monitoring of process variables can obtain useful information in the thermoforming process. The focus was on the processing of polypropylene materials, which due to its characteristics and price has a share of about 20% of all packaging. To compare to other thermoforming materials, amorphous PET was included in the study. The paper is divided into two main subjects. First, the influence of the setting parameters of the system at the product features is examined. The control of the system was revised and peripheral systems such as preheating were optimized. The second part shows how to use process variables to monitor operating conditions of the system and predict quality characteristics of the molded parts.

The analysis of influencing factors has been shown that variations of the properties of the molded part in a current production are either caused by the temperature control or sheet properties. For this reason, opportunities are identified related to how to optimize, to monitor, and to control temperature setting.

To identify faults in the temperature control, as an extension to the prior method in addition to the temperature sensor, a method for the identification of the material behavior was developed. This method is based on measuring the deformation force of the pre-stretcher, which was used in some publications to identify the thermoforming or description of the operating point of the thermoforming machine. In this research it was shown that the deformation force and its course is an indication of the ability to process a semi-finished product or can be used to describe a point of operation. This allows the detection of changes in the material properties, which are caused by changes in the heating process, the environmental conditions or the semi-finished product itself. In particular in semi-crystalline polymers such as polypropylene and polyethylene terephthalate the measurement of the plug force, the torque of the motor and the tool clamping force are an alternative to the temperature measured by optical sensors. An advantage of this measure is its insensitivity to optical properties of the material and radiation sources in the environment.

Finally, the laboratory hypotheses and control strategies can be tested. It has been proven that it is possible to identify by monitoring the pre-stretching changes in material properties. In the laboratory, this has been demonstrated in related single-layer films; the hypotheses could also be confirmed for unknown coextruded multilayer composite made from recycled materials.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Andreas Moser

Andreas Moser
Lehrstuhl für Konstruktion und Kunststoffmaschinen
Universität Duisburg-Essen

Information

Free keywords: thermoforming, polymer, polymer processing, packaging, polypropylene, deformation force, plug-assist thermoforming, quality control, temperature control, characteristics of moulded part
Institute / chair: Fakultät für Ingenieurwissenschaften, Abteilung Maschinenbau und Verfahrenstechnik der Universität Duisburg-Essen
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. Johannes Wortberg (Betreuer), Prof. Dr.-Ing. Elmar Moritzer
Publication year: 2013
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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