Today, the tools to produce injection-molded parts are often built from modified CAD data. These modifications include the incorporation of uniform and non-uniform shrink factors, adding of draft angles, parting lines etc. Best practice knowledge is also incorporated to reduce thick versus thin material areas and the possible addition of features to reduce the warping and twisting of the part. Using these basic rules, tools for simple parts can usually be calculated and milled to produce good quality parts with no further modifications needed.
However, simple parts are no longer standard today. The parts are becoming more and more complex in order to reduce mounting times. In addition, the miniaturization, elevated design demands, haptic feeling and the fitting accuracy require small manufacturing tolerances. Standard products are replaced by trendy products which need to be marketed fast. Therefore, a fast and efficient first article inspection and production control is essential for injection-molded products today.
The quality control team has to carry out a first article inspection based on the pre-production series samples and needs to monitor the quality of the product during the entire production process. For the first article inspection, the parts have to be verified quickly and reliably in order to give the green light for the production in time. These tested and complete data sets are also used as basis to validate future product modifications.
To ensure the product quality, the wearing of the mold and possible modifications of the production process have to be measured and visualized as early as possible, at minimum costs.
To measure the shape of a part on a conventional CMM (coordinate measuring machine), the part needs to be fixed and aligned to the measuring table with an individual fixture. In most cases, such a part is measured with just a few hundred measuring points leaving large areas of the part unchecked. Based on this sparse measurement information, the decision regarding the product quality and the "go" or "no go" of the production has to be taken.
If the part does not meet the expectations, the quality team has to identify the area and cause of the problem. Especially for assembly groups, consisting of multiple individual components, it is very difficult to analyse the cause of the problem.
Therefore, a measuring sequence can take several days until exact guidelines of how to correct the mold can be defined.
Today, innovative companies use optical measurement technology to speed up the first article inspection process and to minimize the effort needed to ensure the product quality. Using optical systems, stable parts can be measured efficiently and with high data density (millions of measuring points) without the need to produce and to manage individual fixtures (Fig. 1, 2). Single components can be measured unmounted, or in an assembled configuration, as well as under load in order to define their shape, deformation and behavior in use.