Bringing Model-Based Definition to the Masses

Dave Olson, marketing manager at Verisurf (Anaheim, California) notes that large numbers of shops still tend to rely on 2D drawings and hand tools for their inspection needs. He finds this odd because CAD systems model parts in three dimensions, CAM systems create tool paths in three dimensions and obviously, parts are machined in three dimensions. So why don’t these shops use 3D capability for inspection as well?

Mr. Olson contends that there is no reason for shops to cling to outmoded techniques that leave inspection out of the integrated, 3D digital loop. That’s why Verisurf has partnered with select Mastercam resellers to offer Master3DGage, a hardware/software solution designed to bring manufacturers into the realm of rapid, shop-floor inspection without tedious data entry or documentation. The product combines a six-axis, portable CMM from Hexagon Metrology (Elgin, Illinois) with Verisurf’s 3D, model-based inspection software, which is built on the CAD engine in Mastercam (a product of Tolland, Connecticut-based CNC Software). According to the company, the system enables users to quickly and accurately verify part quality at any stage of the manufacturing process.

The idea is to use the CAD model as a "master data source" to drive the entire manufacturing process, including inspection. Known as model-based definition, this strategy has already gained traction in the aerospace industry, where Boeing and other large OEMs are increasingly foregoing the use of 2D drawings in favor of "intelligent" CAD models. "In some cases, it’s been calculated that creating 2D drawings to manufacture parts downstream can double engineering time," Mr. Olson explains. "Instead of spending all that time to make drawings, it’s faster to apply model-based definition data—which is basically 3D geometric dimensioning and tolerancing (GD&T) information—directly to the CAD model."

The transition to model-based definition wasn’t a matter of choice for suppliers of Boeing and other such companies that abandoned 2D drawings entirely. However, these shops have realized significant improvements in their own operations—improvements that prove the worth of adopting the portable CMMs and 3D inspection software typical of this strategy, Mr. Olson says. Master3DGage provides an affordable way for shops in other industries to realize the same benefits. Even those manufacturers whose customers still employ 2D drawings can take advantage of the system because Verisurf software enables users to embed GD&T and other data into virtually any CAD model.

Parts can be quickly inspected anywhere on the shop floor—including on the machine—and at any point in the manufacturing process with three simple steps. First, the part is aligned by probing points specified by the CAD model. Then, inspection proceeds via manual probing or by following an automated inspection plan. The system automatically pinpoints areas that deviate from the model in real-time. Finally, reports are generated automatically in industry standard formats, including GD&T constraints and color deviation maps.

Real-time display of the deviation between the actual part and the model improves efficiency on all types of inspections, whether in-process, first-article or final. Additionally, using the CAD model as the basis for inspection eliminates discrepancies with 2D drawings that can result when a design is revised in the model and not the corresponding drawing. A related benefit is that Master3DGage makes communication with designers easier when a part is out of tolerance. "When you start inspecting to a 3d model, you can start to feed back statistical 3d information back to the engineer—you now have a closed loop, like a servo," Mr. Olson explains. "Displaying data directly on the CAD model makes it easier for engineers to adjust the model and address issues uncovered during the manufacturing process."

Unlike a traditional CMM or hand gages, the measuring arm incorporated with Master3DGage enables users to access complex profiles and other challenging part features without refixturing. Because the system attains accuracy of 0.0007 inch, only the most demanding applications would require the high precision of a traditional CMM, and no programming is required, Mr. Olson says. Moreover, with the trend toward lean manufacturing and just-in-time (JIT) production, shops are seeing less of the large batch sizes that would make a traditional CMM more practical than a portable model. "In fact, portables are outselling fixed programmables right now," Mr. Olson notes.

"Can anyone in the machine shop industry tell me why you would print a drawing and pick up a hand tool?" he concludes rhetorically. "Inspection is a broken process until you can measure in 3D directly to the CAD model and eliminate errors, eliminate discrepancies between drawings and models and eliminate a lot of wasted steps."