How to ensure your roll forming operation is a good fit
April 10, 2007
When deciding whether to produce roofing panels, you need to determine your ROI, based on if you can use existing equipment or need new equipment, the required panel appearance; possible line configuration; and material handling options.
In recent years the metal building industries have grown substantially. According to the Metal Roofing Alliance, the residential metal roofing market doubled its market share from 3 percent to 6 percent in five years. To take advantage of this growth, more fabricators are increasing the versatility of their manufacturing capabilities by adding to or expanding the metal building products they offer.
Besides the more commonly produced metal studs, fabricators have been adding metal roofing and accessories to their current product lineups. The roofing panels come in many different types, with the more common ones being R, A, AG, corrugated, standing seam, and roof decks (see Figures 1, 2, and 3).
When deciding whether or not to produce these panels either as an expanded line or a new product, you must decide if your return on investment (ROI) makes sense for your business model. The rule of thumb is if you must run at least 500,000 linear feet of sheet metal to justify purchasing a new, complete roll forming line.
If you have an existing roll forming line and are planning to run fewer than 500,000 linear feet of sheet metal, you must calculate the current capacity of your line to see if the new components can be run on it. You might be able to retool your existing line, which can be a big cost savings.
Of course, the type of product you are going to run and its requirements (number of passes, horizontal spacing, roll space, and so on) will dictate whether you can run it on existing equipment. Your tooling vendors should be able to help you with this determination.
If you do not have an existing roll forming line or have insufficient capacity on your current equipment, you will need to purchase a new, complete line. New lines come in many configurations; some are high-speed, in-plant machines while others are less capital-intensive feed-to-stop and portable units for smaller footage requirements. The portable machines usually are entry-level, with capacities limited to the smaller footage requirements of on-site fabrication.
Roof and wall panels are highly visible "appearance" components. Most are fabricated from prepainted coil, so care must be taken to avoid damaging the coil's coating during the roll forming process (see lead image). This is achieved by having enough roll tooling passes and by chromed roll tooling.
In addition, roll forming can contribute to oil canning, which is the waviness in the flat areas of roofing and siding panels. Generally, the period and amplitude of the wave depend on the continuous width of the flat, so that must be monitored closely. The panels need to be straight, especially on the sides of standing seam panels, so that they can be joined. Therefore, flare must be minimized.
R, A, AG, and other panels run on wide roll formers (44- to 48-inch-wide roll space mills) that produce a panel with 36-in.-wide coverage. The most common standing seam panel widths are 12 and 18 in., and there is no center forming. To change widths quickly, you can produce standing seam panels on a duplex-style mill. The panels also can be run on conventional, raft-style roll formers. Portable mills have made big inroads in this market, because contractors can produce panels on-site, oil canning and all, and put them right on the roof.
Panel roll forming lines can be configured in a couple of different ways.
One is a start-stop line. The material starts moving by ramping up to speed and then decelerates and stops when it is time to cut. This type of line typically is inexpensive overall, because you do not have to fly the cutoff die. However, since the line has to stop, total throughput is limited. The line might run at a top speed of 100 feet per minute, but the average line speed for the day might be only 60 FPM.
A continuous roll forming line runs constantly. However, the overall cost usually is higher than on a start-stop line, because you must add a flying cutoff configuration.
With either of these configurations, you can add a precut/shear die or a postcut die (see Figure 4). Most new panel lines have a precut die. Precut dies use a common stationary or flying cutoff set for the maximum width, which provides versatility. Even a common stacker can be applied. You can change part widths (such as from 36-in. to 24-in. coverage) with a simple stock guide adjustment and coil change and no die changeout.
Depending on the panel type, a postcut die might require a die insert changeout or complete die changeover. When running precut products, you need to be careful not to add flare on the ingoing and outgoing ends of the material—a common occurrence on precut lines.
With a postcut die, you will typically get a better overall profile because you eliminate some of the additional flare that can occur during precutting. Also, depending on the panel profile and the roll tooling design, you might be able to use a common cutoff die by simply changing the material strip width. For uncommon shapes, a cutting blade or entire die changeover might be required.
Roll tooling change is an issue because the sets have a lot of rolls. Rafting, double-wide roll formers, two-part roll formers, and machines with combination tool sets can help minimize the machine downtime. However, making the roll forming system more complex to decrease downtime usually increases the overall machine cost.
To further customize your line, you can add different material handling options at the feeding end. There are more options than a typical uncoiler (in a continuous-feed line) or hand-feeding sheets (in a precut line). You can use coil cars, coil upenders, turnstiles, and stacking systems to help decrease changeover time. Quick coil change is important, because the faster you can feed new materials and different colors of coils into the roll forming line, the more panels you can run overall.
The most common choice for the exit end of a panel roll forming mill has been a drop stacker. Another option is a magnetic stacker. While it costs more, it involves less maintenance.
Additional building products that can be roll formed on dedicated machines are soffits, fascia, gutter guards, and drip edges. Most of these lend themselves to being produced on precut or postcut roll forming lines, with the same benefits and limitations as panel manufacturing.
For an in-depth analysis of metal roofing panels for your specific application, it's best to contact a roll forming equipment manufacturer.