The ins and outs of sheet fabrication for architectural metal envelopes
by David Flaherty | 16 June 2024 1:54 pm
The Rainscreen Association in North America (RAiNA) defines rainscreen as an “assembly applied to an exterior wall which consists of, at minimum, an outer layer, an inner layer, and a cavity between them sufficient for the passive removal of liquid water and water vapor.”
Proper design, engineering, code adherence, performance, and installation aside, proper fabrication of said outer layer is key. The outer layer can consist of a wide range of materials—masonry, porcelain, terra-cotta, fiber cement, wood, high-pressure laminate (HPL), and engineered stone—and that range is ever expanding. But just how are metals fabricated?
Metal composite materials
Metal composite materials (MCM) are most frequently represented by aluminum composite material (ACM) but can also include zinc composite material (ZCM), copper composite material, and other exotics. Two metal skins, typically 0.020 painted aluminum, are bonded to a fire-retardant core to form a large, 4-mm (0.15-in.) thick flat sheet of raw material. Though custom sizes are available, and projects are frequently large enough to justify a custom production run, the most common size sheet is 1,574 x 4,978 mm (62 x 196 in.).
Fabrication of ACM can be as simple as using a hand router and a straight edge, even a vertical panel saw, but these are archaic options and not nearly as precise or efficient as computer numerical control- (CNC-) based options. The very best and most consistent option for producing the highest quality MCM results is an industrial router, and there are several good offerings on the market. Table sizes are offered to accommodate single sheets of ACM, and sometimes even multiple sheets at a time for pendulum processing (the router is constantly cutting while one finished sheet is being offloaded and a fresh sheet is reloaded). Software to draw, route, and cut panels will also nest panels to use material most efficiently.
MCM panels for a rainscreen can be produced as face-fastened and potentially only cut to size and installed, but in most cases the material is routed out with a 110-degree V-bit to create bend lines and tight corner conditions, and a cutting bit is used to trim the panel to size. While the MCM is in this stage of fabrication, weep holes, perforations, and even custom designs and cutouts can be added.
Subsequent to the cutting operation, dry joint MCM systems are folded along the bend lines manually, and then a fabricator will mount an aluminum extrusion to the perimeter (and occasionally add a stiffener in the middle, engineering dependent) of each panel.
Single-skin metal cladding
Single-skin metal cladding has also been gaining popularity as a rainscreen panel due to its wide variety of available materials, seemingly endless possibilities for custom shapes and colors, and ease of installation. Often, it represents a good value alternative. Popular materials include painted steel and aluminum, stainless steel, zinc, copper, Corten/A606 weathering steel, and even titanium and other exotics. These materials can be face-fastened or utilize either a male/female interlock or a hidden clip system for a concealed fastener arrangement to attach to the substructural components.
Repeatable, lighter gauged panels (typically not thicker than 22-gauge steel or 0.040 aluminum) can be fabricated through dedicated rollformers, with stations of dies specific to a panel profile. Special width slit coils are used in this process to produce a very consistent panel as efficiently as possible, but outside of the length of the panel, no variation is possible.
Custom profiles can be produced via several different types of machinery, including press brakes and traditional folders. While most commonly found in 3- to 3.6-m (10- to 12-ft) lengths, longer versions are entering the market, offering the ability to fabricate not only single long parts, which are often heavily profiled and even tapered, but also multiple parts that can be formed simultaneously. While heavier folders are available, 13- to 16-gauge mild steel is a typical limit and a press brake is used to fabricate materials beyond the capability of a folder.
Most blanking of material for the folding operations is done by a shear that uses two blades in a guillotine arrangement to cut larger sheets down to usable sizes. However, as complexities and desire for custom panels increase, lasers, turrets, and waterjets can be used to produce high-precision parts in a very efficient manner. Akin to the folding operations, common shears in a sheet metal shop will handle cutting to 13 gauge. While heavier-duty shears are available, the other three types of machinery are better fits for heavier material, especially if it needs anything beyond a straight cut. Lasers, turrets, and waterjets can be used to cut designs, pixelate, perforate, and add countersunk mounting holes; turrets can even additionally louver, dimple, emboss, and tap. It should be noted that, outside of Corten/A606, lasers and waterjets will leave a raw edge on ferrous materials that is prone to rust and thus are not recommended.
All these materials lend themselves well to unique and custom designs and are only limited by material properties and fabrication capabilities. As always, the perceived flatness of a material is increased as material is specified thicker, and flat planes are reduced either by overall panel dimensions or increased profiling. While there is seemingly an infinite selection of materials able to be used in a rainscreen, metal should certainly be considered favorably for its performance, aesthetic, high incoming recycled content, and its ability to be recycled at the end of use.
Ben Kweton is president of Sheet Metal Supply Ltd. Founded in 1991, Sheet Metal Supply Ltd. is a leading fabricator/supplier of metal composite materials (MCM), custom-formed perimeter edge systems, wall facades, flat lock tiles, substructural components, ES-1-rated perimeter systems, architectural zinc, glazed-in panels, standing seam, and more. The company ships internationally and is regarded for its high-quality products and quick turnaround. For more information, visit sheetmetalsupplyltd.com.
Source URL: https://www.metalconstructionnews.com/articles/sheet-fabrication-architectural-metal-envelopes/