Taking the next STEP in CNC programming

By Control Engineering Staff September 28, 2006

The vision is a workflow for part production in which information flows seamlessly and automatically from product design requirements through detailed designs embodied in CAD data, then to a CNC program optimized for the particular machine tool that will make the part. The reality is that the pipeline from design to machine tool is full of blockages requiring tedious and error-prone manual intervention.

The Machine Tool Working Group of the Open Modular Architecture Control Technologies (OMAC) Users Group (part of ISA-The Instrumentation, Systems, and Automation Society) pinpointed the key technology needed to break those blockages and is taking steps to put it in place. The aim is to create an international standard for representing product and process information to CNC machines in an eloquent way: ‘eloquent’ meaning flexible, concise, machine-readable, and robust.

Referred to as STEP AP238, or ‘STEP-NC,’ the required standard has already received Draft International Standard (DIS) status by the International Standards Organization (ISO) as part of the ISO suite of STEP (Standard for the Exchange of Product Data) standards. In a nutshell, STEP-NC is a standard way of sharing part and process information between CAD/CAM systems and CNC machine tools.

The next step in the 3-5 year process of promulgating STEP-NC as a new ISO standard is publication with full International Standard (IS) status. STEP-NC is expected to reach that level in March 2007. In the meantime, the Machine Tool Working Group expects to roll out software to implement AP238 in January 2007.

We already know that the system will work in principle. Boeing completed a demonstration project in October 2005, machining an aerospace component using the prototyped STEP-NC software available at that time. The goal was to determine whether AP238 is practical. Specifically:

Are file sizes reasonable?

Is the processing time reasonable?

Can STEP-NC make a real part?

Table 1: Results of Boeing STEP-NC demonstration project

CATIA CL file size 2077 KB

AP238 Part 21 file size 2305 KB

NC file size 560 KB to 1304 KB

Total processing time ( 1 GHz Intel Pentium ) 20 seconds

Table 1 shows the results Boeing obtained. Clearly, the files are of moderate size. The total processing time for cutting the part was within reason for an aluminum support bracket approximately 300 x 150 mm in size. Completion of a finished part fabricated during the demonstration answered the final question.

Sid Venkatesh, associate technical fellow at Boeing, presented these and other results at the OMAC Machine Tool Meeting held Sept. 11 in conjunction with the International Manufacturing Technology Show (IMTS 2006) in Chicago, IL. He also provided a review of STEP-NC development progress.

Perhaps the biggest hurdle STEP-NC now faces is competition from proprietary methods. Open standards always present a threat to existing proprietary technologies, and vendor companies have little motivation to support the standard. At the same time, no communication protocol can be of any use unless vendors producing the equipment make it available in their products.

Vendor representatives, such as John Callen, vice president of marketing at CAM technology supplier Gibbs and Associates , pointed out that their companies would be willing to develop extensions to their existing products needed to support STEP-NC when customers start requesting it. ‘Though we’ve been closely following STEP-NC from the beginning,’ Callen pointed out, ‘without that customer demand, we can’t make a business case for expending resources to add those features instead of other enhancements that customers are asking for.’

Historically, vendors can only make a business case for incorporating open standards into their products when users—especially those with large market presence—demand it. The debate usually grows from most stakeholders ignoring the proposed standard, through a stage with vendors claiming that their proprietary methods are technically superior, to a crescendo when one or more high-profile customers simply issue an edict that they will not consider any equipment that does not include the open standard at least as an option. At that point, successful vendors develop the required features while those who don’t fall by the wayside.

The really successful vendors, of course, are those who joined in developing the standards along the way. They have a head start when it comes time to implement the technology.

For related reading from Control Engineering , click into: ‘ CNC Programming .’

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— C.G. Masi , Control Engineering senior editor