In process quality control on micro-injection moulding: the role of sensor location

Abstract

Micro-injection moulding is a high-throughput manufacturing process capable of producing micro-sized or meso parts containing micro-features. Quality inspection of these micro-components is usually costly and time consuming. Different process control strategies based on pressure monitoring are currently used to detect deviations in part quality. Because of the size of parts to replicate, pressure monitoring is generally performed by means of pins or ejectors inside the micro-featured cavity, leading to an indirect measure of the pressure in the mould during the injection cycle. In present study, direct monitoring of process signals during micro-injection was addressed via pressure and temperature sensors placed in two different mould locations: the runner system and the mould micro-featured cavity. Input parameters were varied following Design of Experiments methodology to analyse the variation in monitored signals as a function of replication quality. Injected micro-parts were quality controlled using confocal microscopy to correlate the recorded sensor signals to quality deviations. It has been observed that both runner system and micro-featured cavity pressure signals are linked to the replication quality level of the micro-injected part and show similar performance in terms of part quality differentiation. The process parameter which causes the greatest variations is the temperature set-point of the machine nozzle.