MoldMaking Technology

AUG 2018

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Page 36 of 83 35 shrinkage and deformation during the molding process and during de-molding. Putting CT Scanning to Work: Measurement Comparisons and Evaluations With so many obstacles to overcome, how can CT scanning be a blessing and not a curse? What does it take to use the tech- nology in a way that actually lets a moldmaker increase accu- racy and speed up the process? For Hachtel, it is many years of experience in the company's own moldmaking facility and a high level of expertise in the injection molding process. As early as 2008, Hachtel pioneered the first 3D-computed tomography method as a way of qualifying plastic components that were manufactured in-house and in combination with simulation methods to optimize mold design. Although it was initially treated with skepticism, expertise in industrial com- puted tomography is now highly valued, particularly when it is combined with the moldmaking activities of injection mold- ers, moldmakers or end users. The company grew from one employee and one CT scanner to what is now eight employees and five CT scanners. Sample components are almost exclusively qualified with CT scanning. "The voxel data models obtained from computed tomography and the CAD models of the component make it possible to make comparisons. Currently, this is our main piece of equipment for making tool optimizations," Hachtel says. CT scanning opens up opportunities to understand the complete process, from design to the end-use part, and it makes everything transparent. "You can also outsource CT scanning and then analyze the part and compare it to the CAD data in-house, keeping the intellectual property in-house, optimizing shrinkage and proving the reproducibility of the processes," Hachtel says. Hachtel also uses VG Studio Max software from Volume Graphics for the most critical measurement comparisons and evaluations. The software offers a corresponding module that makes it possible to compare nominal and actual values. A best-fit function is used to overlay CT and CAD data sets in any position in free space, making it possible to calculate deviations in advance. It is possible to question the alignment according to a drawing (as in the era of tac- tile measurement technol- ogy), and quite often it turns out not to be useful. For first article inspection and quality control, the CT measuring data of the digitized components can be directly compared with the original CAD master data. Moldmakers can use such a full-surface compari- son of the nominal and actual values to determine quickly whether the defined tolerance limits have been maintained or to control which areas of a component have been deformed. The measured data and the CAD model are then imported into the inspection software VG Studio Max. After the align- ment to the CAD coordinate system (reference point-system registration 3-2-1, Best-Fit), the software immediately visual- izes any deviation using a color plot of the entire component surface, which permits quick, easy interpretation. "It is important to compare the measured data with the CAD data and not with the drawing because very often, the draw- ings don't take the whole process, the shrinkage or deformation Computed tomography scanning, or CT scanning, is like having X-ray vision. Join the Discussion! E N G I N E E R B U I L D M A I N T A I N BL OG Conversation. Communication. Community.

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