Page 28 - MetalForming June 2019

Fabrication: CNC Punching
mimicking a press-brake cycle. The tool, with its lower-cam design, allows for heights not typically achievable in a punching machine. On a turret press, the operation is not limited by the tool having to travel above or beyond the form as would be the case with a tra- ditional lance and form of 90 deg. or even with a 90-deg. wipe.”
The Trumpf-style tool has achieved a 0.984-in. overall feature height, with the thick-turret ver- sion approaching a 0.600-in. feature height, reports Erler—even higher when upforming.
“Again, if the tool had to travel above and beyond the form, these heights would be impossible to achieve due to lack of clearance,” she says.
Another advantage: the tool allows for a 3-deg. overbend to account for springback.
“If the part requires a tolerance of ±1 deg., a traditional tool won’t suffice,” says Erler. “Sometimes a fabricator can cheat by using multiple hits, but often, meeting that tolerance is just not pos- sible. Plus, due to the tool’s lower-unit cam, it provides a virtually mark-free form—beyond the typical capability of a traditional tool. Traditional tools usually leave marks due to the need to smack material fairly hard to reach and hold a 90-deg. angle.”
This same tool can be used for mul- tiple material gauges without pulling the sheet from the clamps, Erler reports.
Hinges
Several options exist for fabricating hinges directly in a punching machine. “Electrical boxes, computer boxes ...any type of part with a door needs a hinge,” explains Erler. “Not only must a fabricator perform a secondary oper- ation to install the hinge, but must buy the hinge itself. But, by manufacturing the whole box in a punching machine, instead of using that secondary oper- ation to weld or rivet a hinge, the hinge
can be created in the machine.”
Erler offers some options for creat-
ing the hinge.
“A fully enclosed hinge requires two
For applications requiring hinges, CNC punching tools offer effective solutions without the need for secondary operations.
tools: a progressive-hit operation using the first tool that wipes the material with, typically, two or three hits, then the use of a second rollover tool that curls it over,” she says. “To maximize diameter and material thickness for that hinge, Wilson Tool offers the Opti- Bend as the first tool.
“A punching machine also can cre- ate a half-knuckle hinge, aka a one-hit hinge,” Erler continues. “One stroke can form multiple knuckles—a more efficient process than creating a fully enclosed hinge. This provides a good choice for applications requiring larg- er-diameter pins. Again, either method eliminates the need for expensive hard- ware and reduces assembly time, enabling fabrication of complete pan- els in the machine.”
Larger, Higher Embosses Minus Distortion
Given the right
tooling, large, high, dis- tortion-free embosses can be accomplished via a punching machine.
“Distortion presents a limiting factor in any turret application, whether sheet
distortion from an emboss or blank distortion,” Erler explains. “A rolling tool works with the material’s natural inclination to stretch and move. Instead of just forming the entire emboss with one hit, the tool works with a circular motion along the grain of the material, stretching and forming a little bit at a time. That eliminates the distortion because the tool does not try to form all of the material at once. It takes advantage of the material’s natural inclination to stretch with each tool move.”
Large-Diameter Flares
Use a punching machine to create large-diameter flares via, again, rolling tools. These essentially glide along around a shape to create the form, allowing the forming of shapes much larger than the tool-station size, accord- ing to Erler.
“For example, the Wilson Wheel Rolling Flare tool creates a flare—any- where on the sheet—via a horizontal rolling motion without leaving burrs or nibble marks,” she says. “Typically, the fabricator thinks that the largest possible form cannot be larger than the largest station or tool in the machine. Wheel tools get around that limitation to create the radiused form. Also, using a single rolling tool results in a much faster process—with higher feature quality—than nibbling, where an incremental move may be the length of material thickness or less. Program- ming out the nibbling most likely will reveal a prohibitive timeframe—nib- bling eats up a lot of machine time.”
A thread- form tool produces an offset emboss with a hole, enabling a self- tapping screw to sit flush with or below the sheet.
26 MetalForming/June 2019
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