Abstract
Scientific moulding, also known as decoupled injection moulding, is a production methodology used to develop and determine robust moulding processes resilient to fluctuations caused by variation in temperature and viscosity. Scientific moulding relies on the meticulous collection of data from the manufacturing process, especially inputs of time (fill, pack/hold), temperature (melt, barrel, tool), and pressure (injection, hold, etc.). This publication presents a use case where scientific moulding was used to enable the transfer and optimisation of an injection moulding process from an Arburg 221M injection moulding machine to an Arburg 375 V model. The part was an endovascular aneurysm repair dilator device where a polypropylene hub was moulded over a high-density polyethylene dilator insert. Upon transfer, multiple studies were carried out, including material rheology study during injection, gate freeze study, cavity balance of the moulding tool, and pressure loss analysis. A design of experiments was developed and carried out on the process with a variety of effects and responses. The developed process cycle time was compared to that achieved theoretically using mathematical modelling and the original process cycle time. The studies resulted in the identification of optimum parameters for injection speed, holding time, holding pressure, cooling time, and mould temperature. The process was verified by completing a 32-shot study and recording part weights and dimensional measurements to confirm repeatability and consistency of the process. The output from the study was a reduction in cycle time by 12.05 s from the original process. A cycle time of 47.28 s was theoretically calculated for the process, which is within 6.6% of the practical experiment results (44.15 s).
Highlights
Scientific moulding is based on applying the laws of physics to properties of moulded plastic parts
This study focuses on optimizing the injection moulding process
The data shows that at injection speeds above 50 mm/s, the shear rate and viscosity of the material has a negligible effect on the filling of the part
Summary
Scientific moulding is based on applying the laws of physics to properties of moulded plastic parts. It is ‘the science of process development, recording, standardization and repeatability’ [1]. Scientific moulding outlines various tests and studies to accurately examine the machine capability and qualify the mould and part based on these four steps. These studies include rheology/viscosity study, cavity balance, pressure drop study, gate seal study, and cooling time [4,5]
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