Page 32 - MetalForming August 2011

Perforated Metals
Ferguson press operators prepare a tool set loaded with hundreds of perforating punches, aligned in rows and staggered
to control press tonnage.
dimensions and surface finish. The press drives the punches about 30 percent through the thickness, then the material fractures when stressed to its shear strength. The process creates considerable compression in the bottom of the sheet and tension in the top, so secondary lev- eling plays a critical role in equalizing these stresses and creating a flat part, typically to meet IPA or customer stan- dards for camber and flatness.”
We met up with Colombi at Ferguson’s
plant in New Castle, PA; the company’s
headquarters and 65,000-sq.-ft. main pro-
duction facility are in Providence, RI,
which also houses a fully equipped CNC machine shop and toolroom. “Levelers are not designed for perforated sheet,” says Ferguson plant manager Howard Turner. “Maintaining critical hole and web tolerances adds a whole new dimension to the process. We might have to run material through in dif- ferent directions, using five or six passes in some cases.”
“When you’re talking about punching more than 1000 holes/sq. in., in some cases,” says Colombi, “alignment of the punch, stripper and die plate is critical during perforating. Designing and manufacturing our own tooling inhouse helps to ensure the required level of quality.”
Other critical technology focal points for Ferguson and other IPA member companies include punch coatings, to minimize heat input to the workpiece material during per- forating, and new tool steels such as powdered-metal alloys, which prove particularly useful for those applications requir- ing punching hole diameters exceeding material thickness. Minimal heat input from the perforating process proves particularly beneficial in numerous applications, as cus- tomers consider competitive processes such as plasma and laser drilling.
“Thermal drilling always creates some heat-affected zone on the rim of each hole,” says Ferguson plant manager Howard Turner, “which affects material properties. Perfo- rating, being a purely mechanical process, avoids this con- cern. We’ve seen designers opt initially for laser drilling and then later come to recognize the negative impact from the heat-affected zone created—such as weldability—and switch to perforating. This has occurred in the aerospace and nuclear-industry applications, in particular.”
“The one-to-one ratio of hole diameter to workpiece thickness pretty much holds true when perforating carbon and stainless steels,” continues Turner, “but in aluminum and copper, we can exceed that ratio. For example, we routinely
punch 0.040-in.-dia. holes in 0.080-in. alu- minum-alloy sheet.”
Holes can be round (0.016- to 2.0-in. dia.), as well as oblong, square, hexagonal and conical; hole patterns can be straight or stag- gered. In addition to hole diameter, hole spacing becomes a crit- ical variable—in design and in accurate pro- duction.
“While some appli- cations call for a wire mesh product,” says Colombi, “where more strength is needed in the perforated part, we
can precisely control hole spacing. The web typically should be equal to or larger than the material thickness.”
Heavy Hitters
The 60,000-sq.-ft. Ferguson facility in New Castle spe- cializes in perforating material 20 gauge to 1⁄2 in. thick; its RI sister plant tackles thinner work. “We’re the heavy hitters,” says the plant’s manufacturing operations supervisor Gary Mrosko. “In addition to perforating, we can shear to width and length, and level to hold tight dimensional tolerances on per- forated parts.”
The plant also houses a limited number of metal-fabri- cating machines —a press brake and a three-roll plate roll, for example. “Our Rhode Island facility offers more robust metal- fabricating capabilities,” says Mrosko, “while here we out- source most fabrication work to local shops that specialize in forming, welding etc.”
We toured the New Castle facility to see perforating in action, and learn first-hand about continuous-improve- ment initiatives that most metalformers are familiar with— setup-time reduction and first-part quality, for example. These initiatives were cited by Colombi as focal points for other IPA members as well.
“We’ve reduced setup times by 50 percent during the last few years,” he says, “primarily thanks to better planning and assigning specific tasks to each individual responsible for changing over our lines. We’ve also improved, by 50 percent, our first-time run success, thanks primarily to improved tool alignment and press setup.”
“Everyone in the plant is an internal customer of someone else,” Turner adds. “The tooling person supplies the press operator, the press operator supplies the leveler operator, and so on. We nurture the philosophy that everyone has to satisfy their particular customer.” MF
30 MetalForming/August 2011
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