Software boosts shop efficiencies

Manufacturing Engineering, Aug 2003 by Waurzyniak, Patrick

Latest CAM packages aid shops with machining solid models, knowledge-based systems, multiaxis machining

Manufacturing software holds the key to refining shop processes and improving efficiencies. In the past year, CAD/CAM developers continued adding more functionality aimed at machining solid models, high-speed machining, automatic feature recognition, and other advanced capabilities.

Today's CAD/CAM software redefines the way machinists use solid models, and other manufacturing software packages offer improvements in areas including NC toolpath simulation/verification and estimating job costs. Standards efforts like STEP-NC also continue to promise future CAM software that's easier to use with the potential elimination of the G and M codes used in programming parts today on the shop floor.

CAD/CAM interoperability and the STEP standard recently made some headway, as evidenced by the successful STEP-NC demonstration in June at the National Institute of Standards and Technology (NIST, Gaithersburg, MD) Manufacturing Engineering Laboratory, where STEP Tools Inc. (Troy, NY) and Boeing personnel used STEP-NC in cutting a multiaxis part on a Deckel Maho Gildemeister machine tool.

Several advances at the STEP/NIST demonstration included integrating complex surface models into STEP-NC (AP 238) CNC-independent control data, plus the debut of an ST-Machine plug-in for the Mastercam (CNC Software, Tolland, CT) CAM software used for toolpath generation. STEP Tools presented the definition of geometric dimensions and tolerancing in STEP-NC with its ST-Plan software. In addition, STEP Tools demonstrated its new STEP Index Library (STIX), a C++ and COM (Common Object Model) library of functions for creating and modifying applications using STEP-NC (AP-238) machining data. The STIX library is available free by download from the STEP Tools web site at www.steptools.com.

According to STEP Tools, the full-fidelity data was successfully used to machine a demonstration part constructed by Boeing on a multiaxis CNC machine tool, displaying that OEMs can send the definition of a surface model to their suppliers as a part of the STEP-NC file, and that suppliers can evaluate a full-fidelity description of the surface on the CNC machine tool. The resulting benefits include greater production accuracy and greatly reduced data volume, since a surface's functional STEP-NC definition is very small compared to megabytes of G and M codes. "We're now seeing CNC vendors approach us to do STEP-NC prototypes," notes Martin Hardwick, STEP Tools president. "I believe that there are going to be a lot of STEP-NC prototypes at next year's IMTS show."

With the STEP-NC plug-ins available now for both Mastercam and for GibbsCAM software, manufacturers can construct their own prototype translators, says Hardwick, who notes machine tool builders Cincinnati Machine (Cincinnati) and Hurco Companies (Indianapolis) have inquired about developing STEP-NC prototypes. "It's much easier to get started with, because it's like Visual Basic programs, there's a viewer [STEP-NC Explorer] you can use. COM lets you work from Visual Basic, C++, Java, or any programming language-it's really universal.

"The other major technical development was advanced surfacing," Hardwick adds. "We've been working with Boeing Defense, and they have this procedure for packaging up the definitions of surfaces as DLL [dynamic link library] functions. The way you do surfacing today for molds and dies and things is you generate literally reams of these M and G codes, describing in excruciating detail every little tool movement, and if you're making some kind of smooth surface, you can imagine how many tool movements there are in there, and how big those files get. In many cases, you can describe that surface with a system of linear equations that's really only a couple of hundred lines long.

"What we're doing with this Boeing technology is we packaged it up in a function, then within the STEP-NC file, we say 'use that function in Working Step #3 with this tool, and we're going to get this tolerance.' The function gets loaded into the CNC, the CNC does direct interpolation, there's no need to generate all those M and G codes, and because you're doing interpolation on the machine tool and not via something else which really doesn't understand the machine tool, you're getting more accuracy, you're getting better surfaces-and you're getting vastly reduced data volume. It's a huge breakthrough in some ways, not only for the industry but also for STEP-NC, because it's something which is highly tangible. If your competitor can make surfaces better than you, you're not going to like that for very long."

In practical applications, Boeing is considering such capabilities in developments like the Predator, which requires low radar signatures and low optics, Hardwick says. "Today they can't really subcontract that work, because they can't figure out any way to get the description to the machine tool vendor, or the description to the machine shop," Hardwick explains. "They don't know what kind of machine's going to be used at supplier XYZ, and so they could interpolate the surface with those M and G codes, but they might not get the best ones. So by sending this DLL function, this STEP-NC file, which is basically the recipe saying 'mill this pocket, drill this hole, go ahead and make the surface,' they can send that as a STEP-NC data set to the job shop and the job shop can interpolate on the machine and make the part for them."