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cost. And it combines internal and external measurement. In all these ways, it does what no other system can. HOW CT SCANNING WORKS CT scanning is a powerful tool for mold designers and for produc- tion and quality departments. In medicine, it can be used to find abnormalities in the brain or heart or fractures in a bone. In industrial pro- cess like moldmaking and molding, it is used to find voids and other flaws inside castings and for other kinds of troubleshooting as well. Here's how it works: An item to be evaluated is placed on a rotary table and turned as multiple two-dimen- sional x-ray images are made. The computer joins these images into a detailed three-dimensional image. Traditionally that 3D CT image has been used to identify the presence or absence of specific features or flaws, but not to perform dimensional measurements. CT was essentially a pass/ fail imaging process, and for this reason it was not originally focused on extreme dimensional accuracy. Today, however, enhanced technology allows the capabilities of CT to be combined with the precision of metrology to not just find flaws, but to measure the dimensions, both internal and external, of parts and even assemblies. Sophisticated software combines the functions of CT and CMM (coordinate measuring machine) and lets actual measurements be overlaid with CAD models to see where the two differ, how they differ, and by exactly how much they differ. The enhanced measure- ment capabilities of CT scanning provide the information designers and engineers need to revise processes or remake molds. It allows faster, more accurate evaluation of molded parts and provides more exact information for revising production processes or re-cutting molds. With CT scanning, the total time required to evaluate the shape and size of test parts can be slashed from weeks to hours. As a result, the speedy redesign of processes and molds can be based less on intuition and more on hard data and trace- able dimensions. The number of iterations goes down, along with the drain on resources and the cost of final mold production. Molded parts are available sooner, allowing products to go to market faster. THE PAYOFF FOR MOLDERS FAI of injection molded parts is an ideal application for CT scan- ning. In molding, each iteration of measurement and mold modifi- cation imposes large costs and significant delay, so anything that increases accuracy and speeds up the process is valuable. Second, plastic of almost any sort is an ideal material to image with X-rays. And with suitable hardware and software, it is equally well suited when the plastic includes metal inserts. Enhanced CT scanning is like having x-ray vision, making it ideal for non- destructive testing (NDT). It provides the ability to see into a part, and provides dimensional measurement of features and structures without destroying the part. Where CMM touch probing, microscopes, and optical checks are currently utilized, numerous accurate measure- ments can be taken simultaneously with CT scanning, all in one go. CT scanning quickly provides molders the ability to overlap actual scan data with that of the original CAD model—the "perfect part"—showing user-defined pass/fail criteria, comparing actuals to nominals, and graphically displaying out-of-tolerance variances in easy-to-see colors. The process can be used to reverse-engineer existing products, creating files that can, in turn, generate toolpaths for mold, die, or fixture tooling. QUESTIONS ABOUT QUALITY CONTROL? Visit the Testing and Quality Control Zone. CT scanning is ideal for analyzing very small parts and very small features that would be difficult or impossible to measure using other technologies. In this application—a button for a seat-belt buckle— the best fit of CT data and CAD data are shown in blue and gray, respectively. Measured values outside tolerance are marked in red. @plastechmag 59 Plastics Technology C T S C A N N I N G