A simulation-based robust methodology for operator guidance on injection moulding machine settings

Injection moulding of plastic parts is a long established manufacturing process requiring rich experience both on mould design and on machine settings. It is customary to use process simulation software, which is considered mature enough, in order to validate tooling design and machine settings before these are tested in production. In this work, the baseline is the correct design of the tooling, i.e. the premise is that acceptable part quality can be reached, if the right values in the machine settings are used. It is not sufficient to discover these values, because they are often superseded by the operator when quality problems arise, mainly due to cycle variability. Hence, it is much more useful to determine the influence of the respective factors on part quality as a solid basis for interactive process adjustment. Thus, three main digital experiments are advocated, corresponding to the filling, cooling and packing stages of the injection moulding cycle. The control factors for each experiment are determined by referring to process ‘mechanics’ knowledge. Taguchi cost functions are setup, involving the most important responses related to the product (sink marks and shrinkage), the process (cooling time) and the machine (pressure). Nested experiments are performed for better focus on a particular range of values as necessary or desired. Analysis of variance provides information as to factor inter-dependencies and completeness of modelling. The trends are tabulated to provide interaction guidance to the machine operator.