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MODELLING OF THERMOPLASTIC FILM AND SHEETS FORMING

Objective


This program was combining an experimental program and the development of a process simulator including a new mathematical model.
This mathematical model makes possible to analyze:
- the deformation of the membrane,
- the stress field in the membrane,
- the contact with the mould,
- the evolution of the temperature in the membrane (coupled with the evolution of the temperature of the mould),
- the pneumatic aspects linked to the discharge of the air through the vents.

From the understanding of these fields during the operation, it is possible to deduce the essential result which is the final thickness of the part after forming and cooling. The mathematical model is fully dynamic, what is involved is a true representation of all the transformation stages.
The major results of the experimental program are:
A new method of strain measurements based on an optical method without contact.
The characterization of 3 materials: Polystiren, polypropilen and a 2 layer material PMMA/ABS.
Measurements of the membrane displacements during the forming step and the demonstration of the importance of temperature control during the heating step and of the air vents locations and pressure control during the forming step.

This program has successfully combined the use of simulation and experimental methods to study the dynamics of forming and has demonstrated that significant progress are still to be expected by combing these two approaches.
It is proposed to develop a reliable mathematical tool for the simulation of the plastic thermoforming process to be used in defining optimum operational processing modes.

The corresponding research programme will include the following major tasks:

1. Survey of available data and constitutive laws for hot thermoplastic materials with relative assessment of materials characteristic constants.

2. Specific experimental programmme for thermoforming physics understanding and code assessment. Well instrumented molds, sophisticated measurement and data processing systems will be defined.

3. Development of a production engineer oriented software encapsulated in several CAD environments. This finite element code will take advantage of the experimentation and of the materials constitutive laws researches. It will use a dynamic approach and will be able to handle viscoelastic laws and multi-sheets forming.

4. Selection of thermoplastic sheets and films to study linked to the knowledge of the main industrial thermoforming problems and criticisms.

With the proposed simulation tool a recovery of 10 to 15% of production waste and an increasing in production volume rate varying from 20 to 25% could be expected. Due to the overcoming of traditional trial and error design techniques, the speed of new applications start up will rise by a factor of 3.

The more scientific approach will permit new and more sophisticated applicative sectors to be covered by the thermoforming technology; some structural application in the transporting sector or in the appliances sector could open new very interesting market opportunities.

The proposed work is considered to be pre-competitive since the software development will be based on an open system approach and software tools will require up to 3 years to become commercially available.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CISI Ingénierie SA
Address
3 Rue Le Corbusier Silic 232
94528 Rungis
France

Participants (3)

Centro Sviluppo Settori Impiego Srl
Italy
Address
Viale Lombardia 20
20021 Bollate Milano
Cisi Italia Aid SpA
Italy
Address
Piazza Della Repubblica 32
20124 Milano
VALFRIO SA
Portugal
Address
Estrada Vale Da Rosa,119 Ap41
2901 Setubal