A faster way to the perfect injection molding tool

Volume reduction caused by shrinkage occurs when plastics cool. These shrinkage dimensions must be considered during the development of injection dies in order to meet the increasingly tighter tolerances specified in the CAD model. In many companies up to ten tool adjustments are therefore still customary. Each time the tool has to be reground a large number of work steps are involved, for example dismantling the tool, measurement of the components, interpretation of the results, redesign in the CAD model, reprocessing and adjustment of the tool. In the experience of Marius Häusele, Product Manager of the ZEISS Metrology Application Software Business Unit, several months pass until the perfect tool is fitted into the machine.

Designers become faster and more efficient in tool correction when using ZRE as many time-consuming work steps are no longer necessary, for example defining a large number of contact points for subsequent coordinate measurement of the initial trial components. Without ZRE they would also have to manually enter the measured values in an Excel file and then compare these with the nominal data of the CAD model. After all this, they still have to spend a lot of time ‘tweaking’ the individual deviations into the CAD model.

This process was quite prone to mistakes, especially since only a few error points are generally recorded and corrected. This explains why engineers have to undertake numerous correction loops with a lot of grinding on the way to the optimum result. On the other hand, ZRE simplifies tool correction substantially: as a first step highly precise actual data is captured for the test components. In the ZEISS solution, it is immaterial whether the user generated the scan data with a computer tomograph, an optical sensor or a coordinate measuring machine (CMM).

The point cloud or mesh is then imported to ZRE, as are the CAD models for the tool and the product. A nominal / actual analysis is then performed in defined areas. The software informs the operator how the error points are inverted and transferred to the CAD model for the tool. Finally, a new surface is matched with the corrected points using the Reverse Engineering function and refitted to the original CAD model. This eliminates the need for any time-consuming grading.

Unlike in other solutions, in ZRE the user draws on their experience to decide which error values should be transferred to the tool and marks the corresponding surfaces in the CAD model. Ideally, the test part manufactured with the corrected tool should be immediately within the tolerance range specified. But even if the designer’s expertise is still required, by using ZRE even those developers still without a comprehensive practical knowledge of materials can reach the end point faster. According to Häusele, “The reason is that no-one has to use “gut feel” to come to a decision. The designer now has much more relevant data available for tool correction.”