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Quality-Oriented Analysis of Gas Injection Technology in Injection Molding

This study discusses gas injection technology (GIT) based on a partial filling method, and provides solution approaches as well as interpretation aids for the analysis of this process.

First, the bases known from literature and experimental results will be subject to a phenomenological observation. While presenting the experimental results, the process behavior of flow canal cross-sections of varying sizes will be analyzed. An empirical correlation between pressure, the flow cross-section, and the gas blowing cross-section will be shown. It can be confirmed that the gas volume stream or the temporarily achievable pressure in the inside of the form when injecting the gas correlates with the flow speed and gas blowing cross-section. The gas-blowing cross-sectional area AGas increases from zero with the increasing gas pressure pG1 and reaches a threshold value AGas,Grenz .

In regards to the design of the mold, there are many publications that deal with the constructive optimization of the molds, and which indicate the necessity of matching the front flow path in the mold and the gas injection point. This will be focused upon in this study by presenting a method to determine suitable melt and gas injection points, and will be verified using an example. Here, an essential aspect is the assumption that the GIT user only has very little leeway to change the mold geometry, as is often the case in customer-supplier relationships.

Another chapter in this study shifts its focus to the presentation of methods for optimizing and monitoring GIT processes. The methods are based upon multiple linear regression models, which can be referenced for target value optimization depending upon the data base, or for quality monitoring based on actual process values. The utilization of statistical process models for quality monitoring in injection molding has already been described by various authors in diverse publications. When transferring the methods to GIT, the GIT-specific process variables must be considered, which are shown in a short depiction and are explained. The capacity of characteristics to allow themselves to be predicted using correlating process parameters plays a central role in model-assisted quality assurance. For this reason, the determination of replacement criteria for the group of so-called undefinable characteristics was discussed, meaning for those characteristics that cannot be depicted with a process model or which are unsuitable for model-assisted process monitoring due to their limited or high-cost measurement.

The targeted use of the methods shown in this study – not necessarily in their full scope, but adjusted to the according task – and the consideration of all presented process correlations contribute to the positive solution of the problem of how to control gas injection in the injection molding process.

Lesen Sie die deutsche Zusammenfassung auf
 Hans-Peter Heim

Hans-Peter Heim
Fachbereich 10 Maschinentechnik
Universität Paderborn


Free keywords: Gas-Injection-Technique, GIT, Injection Moulding, Quality Assurance, Statistical Process Control, Mold Design
Institute / chair: Institut für Kunststofftechnik der Universität Universität Paderborn
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. H. Potente (Betreuer), Prof. Dr.-Ing. A. Limper
Publication year: 2001
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) /

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