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Inspection/Measurement 20 MoldMaking Technology November 2014 Metrology Molds a Better Bottom Line By Jonathan Dove T he moldmaking industry is often at the cutting edge of metalworking technology. Innovations in machine tool design, cutting tools and CNC programming are typically champi- oned by moldmakers in their quest for increasingly precise tools. Highly accurate measurement tools are also becoming necessary for mold design and manufacturing, though the industry has been slower to adopt them. The expanding use of CAD to design products and drive manufacturing processes has solidified the need for metrology to play a larger role in the mold- making process. Historically, product designs were conveyed with a series of lines, circles and other geometric entities. With the advent of CAD, designs morphed into three-dimensional shapes primarily composed of surfaces. A car body is a good example. Years ago, automobiles were very boxy, but as tech- nology advanced, their profiles became sleeker and more aerodynamic. Conventional measuring tech- niques using calipers, micrometers and height gages could handle lines, circles and radii, but struggled with freeform shapes that needed to be compared to the original 3D CAD model. Metrology software is designed to verify freeform shapes with CAD-to-model comparison functionality found in sophis- ticated inspection solutions. Metrology hardware, such as a coordinate measuring machine (CMM), enables such CAD-to- model comparison by measuring a point on a part's surface and relating it to its nominal value. Manual measuring gages are not able to handle such tasks to the level of precision required by the increasingly tighter tolerances across the industry. The need for tighter tolerances on finished parts neces- sitates the move to higher-precision molds. This is due to the simple concept of compounded error. Any part, including a mold, will not be 100-percent perfect. It will include some slight error. Equally true, the material that fills the mold will also contain a slight error. If a machining process is to be performed on the finished mold, that step will introduce error as well. As error is added from each of these sources, it is compounded. If too much of the error is contained within the mold itself, it will have "used up" the allowable tolerance without factoring in error of the material and any machining process. Improved accuracy saves time and drives down costs in the moldmaking process. Innovations in machine tool design, cutting tools and CNC programming lead to increasingly precise molds and fnished goods.