MoldMaking Technology

AUG 2018

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International Perspective 34 MoldMaking Technology —— AUGUST 2018 By Barbara Schulz CT Scanning Accelerates Adjustments and Corrections on Injection Molds Industrial computed tomography scanning (CT scanning) is a quality-assurance technique that is making its way into mold shops for speedy adjustments and corrections on injection molds, but only if it is used correctly. C omputed tomography scanning, or CT scanning, is like having X-ray vision. One can see into a part and dimensionally measure features and structures without destroying the part while simultaneously taking numerous, accurate measurements. CT scanning quickly provides moldmakers and molders with the ability to overlap actual scan data with that of the original CAD model, or the "perfect part," showing user-defined pass or fail criteria, comparing actual values to nominal values, and displaying in graphics the out-of-tolerance variances in easy-to- see colors. The process can be used to reverse-engineer existing products and create files that, in turn, can generate tool paths for mold, die or fixture tooling. If this technology is such a great thing to have, why don't all moldmakers own a CT scanner to produce the "perfect mold" and ultimately have the mold produce the "perfect part?" The most obvious reason is the high investment cost. Steffen Hachtel from F. & G. Hachtel GmbH & Co. KG, a plastic injec- tion molder based in Aalen, Germany, explains that a CT scanner costs between 300,000 and 600,000 euros, and annual mainte- nance costs amount to 10 to 15 percent of the initial investment. The company currently runs four GE scanners and one Nikon CT scanner. Despite the high cost, the most significant benefit of CT scanning for injection-molded parts can offset the high price tag in the long run. That is, CT scanning easily indicates the amount and location of any shrinkage and warpage that has occurred throughout the part, significantly accelerating tool qualification before production molding, especially for complex parts. However, there is one caveat. Very often, parts are not accurate according to the drawing specs data, Hachtel says. Comparisons of the CT scan data with the original drawing Is CT scanning a blessing or a curse? For Steffen Hachtel, it is certainly a blessing, as it allows for speedy adjustments and corrections on injection molds, but only if it is used correctly. Image courtesy of Susanne Schröder. show that massive deviations can occur, which might lead a moldmaker to believe that the mold is wrong, but that is not necessarily the case. "If the final molded part does not conform to specs, people conclude that the mold was not designed and machined precise- ly, when in reality, the mold is often not to blame. The measure- ment alignment, drawing or data interpretation might be wrong. Additionally, the warpage is often not from the mold design but results from the chosen part geometry. The lesson here is that if CT scanning technology is not used correctly, it can lead to mis- interpretations and wrong conclusions," Hachtel says. Using CT scanning properly, drawing the appropriate con- clusions and reaping all of its benefits requires knowledge of comparing CAD data with CT data and knowledge of

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