Precision Injection Moulding of Micro Features using Integrated Process and Product Quality Assurance

The scope of this thesis is the development of a fast quality assurance system in the terms of a methodology than can ensure the stable manufacturing of injection moulded components with micro features, while maintaining a cost efficient production and short cycle times by limiting extensive off line metrology efforts. Multiple aspects of the production were considered for the development of the monitoring system, though the focus was on the extraction of quality indicator indices that could act are product and process quality fingerprints for the monitoring of the overall product quality.

First the state of the art of injection moulding technology and process monitoring systems in the area of conventional and micro injection moulding is introduced in the theoretical part of the thesis to set the base to the objectives and scope of the issues presented. The concept of process and product fingerprints is presented and the mathematical background for the calculation of the proposed fingerprints is outlined, together with the properties of the material used for the investigations.

In correspondence with the traditional product quality assurance procedure, the experimental part of the thesis commences with the introduction of product and process fingerprint concept. Initially with the introduction of fingerprint structures on the runners of the moulded components in the form of product micro features that can be used as an overall quality index of the product.

Thereinafter the integration of the product and process fingerprints from product and process data (transient and single value) is introduced. The setup of an effective quality monitoring method that requires the coupling of a measurand / product quantity or fingerprint to the proper process fingerprint in order to monitor the quality of both products and process is presented. The method is implemented on the manufacturing of micro surface structured test disks in a two cavity mould to access the quality of features and evaluate their suitability as product fingerprints and correlation to the process fingerprints.
The process and product fingerprint integration is further elaborated based on the behaviour of µ­flashes and weld lines formed on the micro channels during the injection moulding of micro channels. The moulded part is comprised of two plates (thickness = 1 mm) containing half-circular micro channels (radius = 300 µm) manufactured in identical mould cavities. The position of the weldlines reveals the sensitivity of the micro features while the formation of µ-flashes provides a measurand of the quality and cycle time as product fingerprint.

To further support the investigation in the concept the design of the demonstration mould tool, sensor placement and validation test are covered. Firstly, the selected geometry is presented; as well as the position of the sensors in the cavity and product fingerprint structures. Then the list of the available process parameters for data collection is presented and the validation experimental plan is outlined. The results from the validation experiment, with the extraction of the process and product fingerprints utilizing the developed process monitoring method are presented.

Finally a special case of process fingerprint based on vibration measurement from external accelerometer sensors is presented and the relationship of product dimensions to the first type of process fingerprints, which are calculated a deviation based indices from a based on a reference is investigated.