Fault Detection in a Thermoplastic Injection Molding Process using Neural Networks Abstract

F ault Detection in a Thermoplastic Injection Molding Process

using Neural Networks

B Ribeiro

CISUC-Centro de Informática e Sistemas da Universidade de Coimbra Department of Engineering Informatics,Coimbra University,PT

fax:+35139701266e-mail:bribeiro@dei.uc.pt

Abstract

Injection molding technology should assure a high level of quality control of the molded parts in an au-tomated way.Inherent complexities of the process make mathematical modeling di¢cult,hindering the control quality demands of conventional meth-ods.Neural networks adaptive data based tech-nology has been successfully applied in industrial applications since these rely on highly nonlinear models and are able to provide enough rich data for modelling the required process relationships.Neu-ral networks are used herein in a…rst step for fault detection in the injection molding process,the next step being the development of a system for auto-matic tuning of machine setups.

Keywords:Fault Detection and Diagnosis,Intel-ligent Control,RBF networks.

1Purpose

The objective of this work is to present the po-tential of neural networks technology in the…eld of process modelling and fault detection via one project in the…eld of the plastics industry[1][2] [3][4].Quality monitoring and optimization of the injection molding process require models which de-scribe the complex relationships between process parameters and product properties[5][6][7].From historical production data it is useful to describe the process behavior when operating normally as well as to incorporate in the model abnormal be-havior due to unexpected processing disturbances and/or incorrected machine setup parameters[8].

The paper describes the approach selected to per-form fault detection corresponding to part quality in the injection molding machine.In section2a short description of the plastics injection molding process will be given;in section3the method for fault detection is described;in section4results are presented and discussed;in section5the new aspect of the work is pointed out;and,…nally in section6 the conclusions and future work are addressed.

2Plastics Injection Molding Injection molding of thermoplastics is a process where the material is heated up to reach a state of‡uidity,being then injected under pressure into a mold cavity where it cools.Cooled in the mold it then reaches a solid state conforming the details of the mold producing a component part which re-produces it[9].

The molding machine has an injection unit to melt and transfer the plastic into the mold.A sec-ond component is a clamping unit that secures the mold against injection pressure.This clamping unit also allows the part removal.

The injection machine molding(see Figure1) converts thus resin pellets into molded parts.Plas-tics pellets are fed through a heated screw and bar-rel.Under high pressure,the lique…ed material moves through a runner system into the mold.The cavity of the mold determines the external shape of the product while the core shapes the interior. When the material enters the cavities,it starts to re-plasticize and return to the solid state acquiring the con…guration of the molded part[10][11].The 1