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A choice subject: systems that match the CNC machine tool can give a better ROI.

For those in the market for CNC controls, decisions can be a tall order.

But in the simplest terms, it comes down to matching the CNC controls to the machine, several control builders told Tooling & Production.

"If you are buying a custom machine, you're going to have a lot of choices because they haven't even started building it," said Paul Webster, CNC product manager for GE Fanuc. "If you are buying a commodity machine off the shelf, your choices are limited at that point."

Karl Rapp, Bosch Rexroth applications manager for machine tools, interjected the cost factor.


"Machine builders typically offer the lowest price for a machine if the customer does not want to change the CNC that is already engineered to run the machine," he explained. "In some cases however, a user may want more flexibility and/or different functionality or has specific process needs, and a different CNC platform may be required."

"Usually what your choices come down to is what the machining requires," Webster said. "The most important thing is getting the control system that matches the machine tool correctly," and gives the better ROI.

Another consideration is employee familiarity with the CNC platform.

"General wisdom is to choose the same CNC supplier again, that the staff may already know, to minimize training or use established connectivity," Rapp said. "But it never hurts to review the latest CNC controllers, as many of them use ISO-based G-code formats and offer PC-based human machine interfaces (HMI) that easily can be configured by the operator as needed."

Jon Cruthers, business development manager for the Motion Control Business Unit at Siemens, said the leading CNC suppliers have levels of controls to suit virtually all applications.

"This means they range from the simple prismatic parts to the most complex aerospace structures or medical implants, where axis interpolation and volumetric error compensation are critical to effective, repeatable machining," he noted.

"The most advanced CNCs now have full conversational programming, as well as cycle simulation software onboard," Cruthers said.

Operator interfaces should be considered, too. Conversational programming, which uses graphical input, is popular in small and medium operations, where machinists may design their own part programs. However, in a production facility run by a robotic system, conversational programming may not be needed.

"For the most part, complex parts are programmed offline and downloaded to the control for execution," said Heidenhain's Chris Weber, national product and sales manager, machine tool division. "It is good, however, to have the option of conversational programming for smaller simpler jobs or to edit the part programs."

Another good thing to consider is sole source, he said.

"A 'system' is much easier to support (for example, Heidenhain makes the control, drives, motors, scales, encoders, probe systems, etc.)," Weber added. "All of the components are designed to work together, and there are onboard diagnostics through the CNC for commissioning and troubleshooting all of the 'pieces of the puzzle.'"

Rapp said CNC systems built around a PC (Microsoft operating system-based computers) can offer advantages. For instance, a complete CNC can be simulated on an office PC.

Weber said simple controls for simple tasks (i.e., 3-axis, drilling holes, making pockets, facing parts, etc.) do not require many bells and whistles.

"However, canned cycles for frequent operations always make the job easier," he explained.

A final consideration is in some respects an intangible one--training and service, Cruthers said, along with something that is key for the large plant.

"That's the CNC's ability to interface with the network topology in the plant and also legacy systems for parametric comparison between machining lines," he said.

Bosch Rexroth,; Heidenhain,; Siemens Energy & Automation,; GE Fanuc,

By Dennis Seeds, Editor-in-Chief
COPYRIGHT 2009 Nelson Publishing
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Title Annotation:CNC controls
Author:Seeds, Dennis
Publication:Tooling & Production
Date:Mar 1, 2009
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