ADAPTIVE PROCESS CONTROL FOR
THERMOPLASTIC INJECTION MOULDING MACHINES: RELATIONSHIP BETWEEN CONTROL MODE,
WEIGHT, DIMENSIONS and IMPACT TOUGHNESS
Ecole des Mines de Douai,
Polymers and Composites Technology Department,
941 rue Charles Bourseul, BP
838, 59508
ABSTRACT
The production stability and the dimensional precision of
thermoplastic injection moulded parts are key issues for the current plastic
industry. However, the classical control modes of injection moulding machines
become limited when facing the more and more demanding specifications, and
require therefore new developments. Three different control modes are assessed
in this paper. Two of them are designed to have a better control of the holding
pressure, through an on-line measurement of the pressure within the cavity, in
order to reduce the weight and dimension scattering during production. The most
elaborate mode uses a linear model to correlate the main parameters of the
process and the quality of the previous manufactured parts, and subsequently to
adjust the processing conditions to the actual state of the system. The
comparison of the different modes for various material/mould/machine configurations
validates the efficiency of the advanced control systems for the weight
stabilisation (different neat and fibre reinforced semi-crystalline
thermoplastics, single and multi-cavity moulds, hot and cold runners, electric
and hydraulic machines). Besides, the control of the weight has globally a
positive influence on the scatter of dimensions and shrinkage without
penalizing too seriously the impact toughness.