Rapid prototyping on a CNC machine tool

Say the words “rapid prototyping” and most people think of 3D printing. But until recently, most prototyping was performed by skilled machinists who cranked the handles on knee mills and engine lathes to make parts far more quickly than was possible with cam-driven and, subsequently, CNC production machines.

That decades-old paradigm has begun to shift. Machine tool builders, tool suppliers and software developers now deliver technology that makes it possible for CNC operators to set up jobs in minutes rather than hours, and deliver parts in days instead of weeks.

Schunk’s VERO-S workholding system can be loaded into a machine in seconds and offers repeatability within 0.0002″. Image courtesy of Schunk.

Pieces of the Puzzle

Jeff Estes, director of Partners in THINC Technology Centers for Okuma America Corp., Charlotte, N.C., said numerous technologies are needed for machining-related rapid prototyping, including quick-change tooling and workholding, smart software systems and offline tool presetting, as well as a flexible machine tool and CNC.

“You have to look at all the pieces,” he said. “It’s about doing whatever you can to save time.”

Some shops use 5-axis mills or multifunction lathes to achieve that. Estes noted, however, that shops with even basic equipment can take several easy steps to improve throughput. One is cataloging cutting tools into groupings able to perform various types of work. “When you’re making one of this or three of that, you can’t afford tool changeovers,” Estes said. “You want to find the commonalities among all the tools resident in your turrets or carousels, standardizing wherever possible and organizing the work for your machines based on what kind of tools they carry. This helps minimize those that need changing.”

Conversational controls make machine operation more efficient while reducing setup times, both of which are important factors for anyone doing prototype work. Image courtesy of Okuma America.

Estes added that this grouping comes naturally to machinists, who mentally keep track of what tools are in which lathe or machining center and set up jobs accordingly. The key is documenting what’s in everyone’s head, collecting tool types, drawings and dimensions, and then placing all this information into a central location for everyone to see. This documentation is especially important as older generations of machinists retire and new employees take their place.

In some cases, standardizing the tool set means using a cutting tool that is less than optimal. This is a big no-no in a production environment, but it certainly reduces setup time when prototyping. “If it takes you 10 minutes to change a tool and set the offset, who cares if it takes 30 seconds longer to machine the part using the existing tool?” Estes asked. “You’re saving 9½ minutes of changeover during the setup. That’s what people need to think about.”

Push the Button

Workholding is something else to think about. “For job shops and production manufacturers alike, rapid prototyping requires the ability to load a workholding device in the machine without having to probe its position or set a work offset, and have confidence it will be within two-tenths (0.0002″) of where it was the last time you used it,” said Brad Evans, workholding product manager at Schunk Inc., Morrisville, N.C. “You should be able to drop a fixture, vise or rotary table on the machine and hit ‘cycle start.’ “

Many shops without a quick-change capability toe-clamp their indexers or 6″ machinist’s vises on the machine table, leaving them there indefinitely. They know moving them is not worth the hassle. Leaving them in place, however, not only consumes valuable working space, it also reduces flexibility. Then when these shops have to change over, several hours are lost in the process.

Evans suggests modular workholding as an alternative, one where quick-change receivers are bolted to the table, dialed in one time, and then used as datum points for whatever pallets, vises or workholding fixtures are required.

Worried about the cost? Don’t be. Reducing downtime by even a few hours a week brings a quick return on workholding investment—often measured in months—and provides opportunities that didn’t exist previously. “I recently worked with a shop in Wisconsin that implemented our VERO-S system,” Evans said. “His best customer called with a rush order for a part he needed that same day. Normally, this order would have been a problem, but because the shop could change over in a few minutes, they were able to break into an existing setup and run the job in a few hours. By the time the driver left with the new part, the shop was back making chips on the previous job. The customer was happy, the shop received a nice premium for the rush order and did it without disrupting the production schedule.”

Get Modular

Along with toolholding, modularity offers the flexibility shops need if they’re to compete in the rapid-prototyping realm.

“Success with rapid prototyping benefits from modularity,” said Tom Raun, milling product manager at Iscar Metals Inc., Arlington, Texas. “The first thing that comes to mind is the toolholder, where quick-change adapters have long offered big setup-time savings. But there’s also the cutting tool itself to consider. The ability to customize the tool in terms of reach, type of application and type of shank is a huge benefit for rapid prototyping.”