"Beyond Step," Feature Article, October 2007

beyond step

With a new standard, CNC machines can read CAD and CAM files directly.

by Jean Thilmany, Associate Editor

Modern-day computer numerically controlled machines are no longer modern enough. The 50-year-old G and M codes that drive those machines can't transfer valuable geometric information from CAD and CAM systems, according to a group of experts who are advocating for widespread use of the recently approved STEP-NC standard. With the new standard, CAD and CAM applications have the capability to send product information to CNC machines.

But getting equipment and software suppliers on board with the new standard might take a while, the experts add. Still, if universally adopted, the standard could make subcontracting of machining across many manufacturing industries much easier.

Today's global engineering companies commonly pass CAD files back and forth. There are a number of ways for suppliers to translate their own CAD files into a format that original equipment manufacturers can read. Although the system is not always effective, suppliers and OEMs can almost get by. But engineering organizations can sometimes perceive CNC machines as the weak link that holds back a data stream that flows seamlessly from design to manufacturing, said Xun Xu, an associate professor of mechanical engineering at the University of Auckland in New Zealand.

Now comes STEP-NC, the machine-language standard first published by the International Organization for Standardization in 2003. Ten years in the making, STEP-NC includes tolerance and process planning capabilities that G and M codes can't accommodate, Xu said. He's looking at how STEP-NC can be adapted to all machining environments.

With the standard, a cutting tool is driven by geometric representation of the part to be made, said Martin Hardwick, president of STEP Tools Inc. of Troy, N.Y. His company sells software libraries that help companies write STEP-translation programs. It now sells similar tools for STEP-NC applications.

A machine tool creates a metal part. With the STEP-NC standard, the tool could read geometrical data from both CAD and CAM files.

Just as STEP has standardized the description of product data, allowing it to be passed with translation between varied CAD and CAM systems, STEP-NC is expected to streamline the passing of vital product data as well as geometric information across a global manufacturing chain, Xu said.

With STEP-NC, a machine tool can receive a file with extended product data, know what it means, and proceed to mill the piece without any more instructions. No more programming the machine tool for each job.

"Really, today, the guy on the CAM system generates codes for one specific CNC machine in his plant that he understands well," Hardwick said. "With geometric representation that machining program could be sent anywhere in the world and they could make it on their machine."

In terms of interoperability, the new standard promises to do for CNC tools what STEP and IGES have done for computer-aided design and computer-aided manufacturing, Hardwick said.

The ISO standard STEP, which stands for the "standard for the exchange of product model data," allows all CAD and CAM systems to exchange information, regardless of file format. The U.S. National Institute of Standards and Technology has a standard called initial graphics exchange specification—usually shortened to IGES—which also functions as a translator.

According to Hardwick, machine shops using the STEP-NC standard could reduce setup times by as much as 35 percent by seamlessly reading the 3-D product geometry and manufacturing instructions supplied by their customers. Original equipment manufacturers could reduce the time they spend preparing data for suppliers by 75 percent because they could share the design and manufacturing data straight from their databases.

A STEP-NC converted CAD file can whiz via Internet from a New York OEM to a California machine shop, which can then immediately start milling the part, Hard- wick said.

Adoption Obstacles

Given all these benefits, manufacturers and vendors should be lining up for STEP-NC, right? Not yet. Experts generally agree adoption isn't around the corner. It will happen eventually, although no one can yet say how long it will take.

Hardwick expects adoption of STEP-NC to mirror that of STEP, which users have been slow to accept. STEP for CAD became an ISO standard in 1995. Three years later, the large manufacturers—the early adopters, who saw the business case for STEP—began using the standard.

"In 2001 other enterprises started using it, and in 2003 all the complaints and whining disappeared as people realized what it did," Hardwick said. "There's a tremendous amount of resistance when these standards come out."

But more than users' reluctance holds back full-fledged adoption. CAM vendors will need to add system interfaces that write STEP-NC data while CNC machine makers will have to add interfaces to read data. Without significant customer demand for STEP-NC, vendors are hesitant to make the necessary investment in their systems, said John Callen, vice president of marketing at Gibbs and Associates of Moorpark, Calif., which sells CAM and NC programming software. Callen has partic-ipated in the STEP standards community and was a member of the STEP-NC industry review board for STEP Tools.

Vendors could also start making CNC machine tools that could read STEP-NC files. But the manufacturing world isn't exactly clamoring for those machines, so companies haven't stepped up to produce them.

"The audience that STEP-NC addresses is extremely conservative," Callen said. "Manufacturers say, if it ain't broke don't fix it. If they've got a system that works, they're not interested in jeopardizing that.

"A lot of them have spent years getting their operating procedures to the point they're fairly canned," he added. "Introduce STEP-NC and that throws a significant wrench in the works that they have to modify their system around. Most manufacturers will go, 'I want to do this why?' "

Gibbs and Associates' customers aren't yet asking for systems that can output to the new STEP-NC format, he added. When they do, Gibbs will provide them.

For his part, Hardwick thinks more companies will create their own postprocessors, based on STEP-NC libraries like those his company provides. These types of postprocessors offer a STEP-NC interface between CAM and CNC systems.

So STEP-NC proponents must lead the way by making the business case for the CNC standard. Boeing has taken a point position here, Callen said. Representatives from the aircraft company have been part of STEP-NC deliberations and recent prototype demonstrations.

An aircraft manufacturer has been particularly interested in a CNC-language standard because its CAM systems generate APT CL language, an intermediate file format that—when sent through a postprocessor—automatically generates machine-specific G codes, Callen said.

STEP-NC files could include information that APT CL files can't handle, such as part-model geometry, part dimensions, and tolerances, as well as machine probing commands. The manufacturer would like to work with the new standard on the company's next-generation aircraft.

Still Lost in Translation?

Should STEP-NC follow STEP's customer acceptance model as Hardwick predicts, it will likely face some adoption impediments along the way.

OEMs, well aware of STEP's limitations, don't make widespread STEP use easy, Callen said.

"In our industry, we see a lot of doublespeak when it comes to using STEP," he said.

A number of big players give lip service to STEP, he said. They agree the translation standard can be used to pass information from supplier to OEM. But, in reality, these large manufacturers require that suppliers use the same CAD system the OEM uses to avoid loss of data during translation.

"They're saying one thing and requiring something entirely different," Callen said. "Many say something about STEP in the contract, but suppliers are encouraged to adopt the same CAD system the OEM uses."

So STEP itself still isn't an optimal interoperability format and that'll likely be the case with STEP-NC, said Ken Tashiro, vice president and chief operating officer at Elysium Inc. of Southfield, Mich. The company sells CAD translators that Tashiro said can ease the headache that engineers face when translating STEP or IGES files.

The STEP and IGES translation programs have the same problems as human translators. Sometimes, there just isn't a one-to-one correlation between words or, in the case of CAD systems, pieces of product data, like geometry features or attributes.

And there's another issue as well. IGES and STEP standards have to evolve as fast as today's engineering technologies are evolving. And a slow-moving standards committee can't keep up.

Specialized translators like the ones Elysium makes are specifically written to translate files from one brand of software to another such as, say, UGS to Catia. Engineers who rely only on STEP or IGES as their translation tool of choice rather than on specialized translators can lose data in the translation process, Tashiro said.

Translators like Elysium's have been programmed to understand the characteristics of each of the supported CAD systems, keep on top of them, and make the required adjustments and corrections required for any data conversion, Tashiro said.

Elysium's STEP product is based on STEP tools.

"STEP Tools tells us how to build something, so we conform with STEP, and we add our own spice," Tashiro said. "If we know that some CAD format has something weird, like it calls a cylinder a truncated cone, but every other format calls it a cylinder, we know we should pop it into STEP as a cylinder."

Down the line, Tashiro expects to see specialized STEP-NC readers similar to the enhanced translators his company provides.

For his part, Xu is working to develop portable STEP-NC data that can be adapted to different machining environments. The key to this is to capture the information about machining tasks unambiguously and leave the decision on machining methods until the last moment when a machine tool is chosen.

So why don't software vendors get together and agree upon standard language? That way, a fillet would be a fillet— whatever CAD system it originated in, whatever CNC machine eventually machines the part.

The answer is easy, Tashiro said. For competitive reasons, vendors simply aren't willing to reveal their algorithms. That makes it impossible to transfer both files and codes among unlike systems without the use of a translator, whether STEP, or a spiced-up STEP.

Hardwick is hopeful that when manufacturers see STEP-NC in action, they'll get behind the new stan-dard. Next month in Dallas, STEP Tools will help to demonstrate the new standard for participants from Airbus, Lockheed Martin, Boeing, and Sandvik, among others.

"It'll be a fairly big demonstration to show the CAD/CAM vendors and hardware control vendors that all these people are interested in doing STEP-NC and to get them to move forward," Hardwick said. "But we still need to put forth more effort and get more vendors jumping in."

The road toward STEP-NC has been long and often filled with setbacks. But Callen said he hopes talk of the newly approved standard sparks user interest.

"We're getting there," he said. "We need to keep it in perspective, though. But I don't want to lose sight of the real benefits of STEP-NC and what it's done as far as making people aware of the type of product infor- mation that's required for next-generation manufacturing systems."