Fabricating Curved Metal

Because of this and the widespread use of 3-D CAD designs and BIM, the demand to fabricate curved metal continues to increase. But fabricating curved metal requires considerable skill and forethought, and is dependent on a number of variable factors.

CURVING TECHNIQUES FOR METAL WALLS

To create unique designs, metal can be curved with minimal distortion. Qualified fabricators have internal quality control systems and internal tolerances they implement when curving metal. Fabricating curved metal does not affect the strength or structural integrity of the metal. When metal has been curved successfully with no buckling or localized cracking, any strains it experiences under actual service conditions will be much smaller than those associated with the curving operation. Straight metal and curved metal with the same theoretical outside dimensions can be welded together after the bending process. Qualified fabricators can control the amount of deformation or distortion of the curved metal to ensure proper fit/alignment to the straight metal.

Generally, there are two curving techniques for metal walls, both of which are secondary processes for straight panels. “The most common, called crimping, is typically done with 7.2-rib style exposed fastener wall panels,” says George “Ronnie” Jones, director of field services, Innovative Metals Co. Inc. (IMETCO), Norcross, Ga. “Panels are fed through a secondary crimping and curving machine that crimps the panel to allow for curving. The second technique involves a rollforming and curving machine for concealed fastener ribbed wall panels. This process creates a continuous non-crimped curved panel that will match up exactly with straight panels. In our case, we can provide 12- and 16-inch-wide curved Latitude wall panels (in 0.032-inch and 0.04-inch aluminum) in radiuses as tight as 15 feet. This process is available in both three- and four-rib standard profiles, and each panel typically includes a 4- to 6-inch straight end to allow for smooth transitions to straight wall conditions.”

Jones explains a crimping and curving machine consists of a feeding device, a curving and pressing device, and an electric control system. “The curving machine adopts the formed pressing die to press the ‘pit’ on the formed panels and make the panel curved. Changing the distance of the wave mark and adjusting the depth of the pit can form into the panels with different radians. A rollforming and curving machine consists of a series of roller stations and an electronic control system. This machine traps the panel and rollforms it into a continuous curved panel with no noticeable wrinkling or folding.”

Zeke Miller, president of The MillerClapperton, Austell, Ga., says his company uses pyramid rollers to curve it metal panels. “It’s three rolls, two on the bottom, one on the top. You feed the machine the metal in between the top row and the bottom two rolls. You continually roll it back and forth until you get the proper radius. Some people curve their metal with a brake where they just bump their metal with a die. People who don’t have pyramid rollers do it that way. People within the industry can usually tell whether it’s been pyramid rolled or bump rolled.”

AIDING ARCHITECTS’ DESIGNS

Overall, how do these fabrication machines and procedures aid architects’ designs? Jones says being able to seamlessly transition from a curved to straight wall condition provides designers a new level of creativity when working with metal. “Considering this along with all of the new color and finish options available for metal, we should see some cool designs in the future.”

To fully optimize architects designs for curved metal, Miller emphasizes the importance of the submitted architectural drawing. “Architects can’t just draw a curved wall and make the assumption that everybody knows it’s curved. Architects need to note on the drawing that it needs to be a true curve and not segmented. If they do want a true curve, they need to give the radius of the curve and where it stops and where it starts. A true curve is formed from an actual radius. A segmented curve is just a segmented panel that gives the illusion that it’s a curved façade.” Jones explains, “It’s very important to get accurate field measurements for curved wall conditions to ensure a proper fit. Taking the proper steps to call this out early in the design process and verify on the jobsite will help to avoid costly mistakes.”

CURVING LIMITS

Despite producing inspired structures, metal curving does have some limitations that could affect design decisions. Miller explains that there are the limits of the metal material itself. “For metal column covers, there’s very few people that can do them large than 16 feet in height. [Also,] rainscreen panel systems are not good systems to be curved and should not be curved. [This is] because you have to do a process called stretch forming and there’s limitations on the radiuses that can be done in curved metal. Stretch forming is done in a lot of ways. We have return flanges.

We have extrusions that are typically male/female and often supplemental framing behind that. It’s difficult to segment parts and pieces, and put it over a radius wall and stretch forming heats up the metal and radiuses it. You could radius it with machines but often you need very expensive dies for certain samples.”

Jones explains another possible limit to metal curving is, “With the crimping technique, you may be able to achieve tighter radius but the tighter you go, the more crimps/folds will be in the panel. This creates a rigid aesthetic and puts additional stress on the paint system. For the rollforming technique, radiuses as low as 15 feet can be easily reached with no crimps or additional folds to the metal. In both cases, we suggest using aluminum as it is easier to manipulate and impervious to potential rust.”

It’s more expensive to curve a metal wall instead of keeping it flat. “When we curve our metal, you have to have a person on either side of the roll, so your man hours are twice as much,” Miller says. “Then you have to take it to another table to further the fabrication. Crating is more expensive since you are creating a curved shape and not a flat shape—you are creating a lot of air.”