Fabricating with a digital foundation
Architectural metal fabricator embraces the 3-D model approach
An architectural metal fabricator takes a building-information modeling (BIM) approach, using enhanced computer modeling to streamline operations.
A shop floor technician at A. Zahner Co. powers up a laptop—a mundane sight, until you consider what he's about to view. He opens a dynamic PDF, zooms in, rotates the image, and uncovers cross sections. He's comparing a part not with a 2-D drawing, but with a copy of the original 3-D computer model.
This PDF comes from a solid model that's part of a building information modeling, or BIM, approach the Kansas City, Mo., fabricator has been practicing for more than a decade. The model does something many in the architectural world yearn for: to get all parties—the architect, engineers, general contractors, fabricators, specialty contractors, and others—on the same page.
A Modeling Advocate
President and CEO Bill Zahner, great-grandson of founder Andrew Zahner, is a passionate modeling advocate, evident by his verbiage on the company Web site: "Over the last decade, the design, engineering, and construction industries have been working to integrate digital technology into the process of construction. Like a growing leak in the dike of ingrained conventions, the integration of digital technology is dissolving the barriers that slow down the building process. Companies that do not embrace this technology will be overwhelmed by the shift that is occurring."
The company has worked on some landmark structures. The CEO is friends with pre-eminent architect Frank Gehry, and Zahner has fabricated the metallic skins and substructures for Gehry's Experience Music Project in Seattle and the dramatic amphitheater in Chicago's Millennium Park, among others. Zahner also had a hand in Apple's flagship store in New York City's trendy Soho neighborhood; San Francisco's de Young Museum; a new facade at the Suzanne Roberts Theatre in Philadelphia (see Figure 1); the new metallic crown above the fanavision at the Kansas City Royals ballpark (see Figure 2, Figure 3, Figure 4); and the NASCAR® Hall of Fame in Charlotte, N.C., to open next year.
In an industry in which disparate companies must collaborate to finish a job on schedule, having one model, one central depository of all engineering and design data, is revolutionary. It's an approach that, according to Bill's brother Robert, senior vice president, is usually embraced—but not always. "We get everything from incredibly enthusiastic support to projects where they don't understand what's going on," he said.
Digitizing the Process
The earlier Zahner gets involved in the process, the smoother the project likely will run. Engineers get involved sometimes years ahead of actual construction. This means that if something can't be fabricated within budget or in a timely fashion (or if something physically can't be fabricated at all), the fabricator, architects, engineers, and others work as a team to develop solutions. Engineers and designers don't simply throw over a drawing to the fabrication company—analogous to engineers throwing a design "over the wall" to manufacturing at an OEM.
In typical situations, the company receives a digital model from the designer and then creates a separate digital model that is an exact overlay of the original. That model is transformed into a parametric surface, which incorporates information needed to drive the fabrication processes.
Zahner's parametric 3-D model has nonuniform rational B-splines, or NURBS, today a near-ubiquitous part of 3-D CAD that uses a mathematical model to generate freeform surfaces. Initially the architectural form is guided by such factors as aesthetic intentions, light reflections, site restraints, and structural rationale. The company's software engineers have developed some proprietary algorithms to generate elements such as skin textures (see Figure 5). The model incorporates seam locations, flashings, interface connections, and the like. Most important, the designer's original model file remains as a master for comparison.
The parametric model is then evaluated for structural stability, including effects of wind loading, gravity loading, member joining, and load transfer throughout the structure. Engineers instruct CAD software to take cross sections from this freeform model to help develop the structural frame members underneath.
Only after thorough analysis comes fabrication, a process greatly streamlined thanks to that digital model, which has information that takes specific fabrication techniques into account. Most processes on the floor use instructions drawn from unfolded DXF files or IGES files. "We avoid shop floor programming when we can," Robert said. "I would love to say we've eliminated it altogether, but there's still some shop floor programming."
The 60,000-square-foot floor includes a 10- by 20-foot waterjet system, purposely large to cut some of the firm's huge panels (see Figure 6). The shop cuts "absolutely everything as far as metals," Robert said, from aluminum and stainless to specialized Muntz metal. Thicknesses are from 24 gauge to 0.75 in. and thicker.
Zahner not only fabricates the exterior skin but also the substructure that supports and defines the skin's complex geometry. This way, the company can be sure the skin fits over the substrate before it leaves the fab shop floor. The substructure usually is made up of aluminum or galvanized material and can vary in depth from a few inches to 5 ft. or more, depending on the project (see Figure 7). It can consist of thin layers of material, a series of webs and flanges, or other methods to hold the exterior skin and make it structurally sound.
"Before, the substrate would have been built by another company out in the field," Robert explained. "Now the substructure is being fabricated here, and because it is, the accuracy we're able to attain is tremendous."
Complementing the BIM approach, Robert said, are elements of lean manufacturing, including continual 5S and the use of kanban bins to ease part flow and avoid flooding the floor with work. This is especially valuable because subassemblies fabricated in-house have grown larger over the years. Zahner's fab shop is a controlled environment; the job site is not. The larger a component can be built and remain cost-effective for transport to the job site, the better.
This makes coordinating part flow all the more challenging, as company managers first discovered when fabricating panels for the Experience Music Project (EMP), a downtown Seattle museum made possible by Microsoft co-founder (and multibillionaire) Paul Allen. Previous to this project, parts just flooded the floor, and tracking was a nightmare. Since the EMP job, though, the company has perfected the use of kanban carts between workcells. Workers fabricate piece parts and load them onto the kanban cart. Once the cart has all the parts necessary, a tag goes on it, which signals another worker to move it to welding and assembly. Engineers design parts with errorproofing in mind; most parts fit together only one way.
BIM Meets DFM
The company's BIM approach brings design for manufacturability (DFM) concepts to the architectural arena. The more problems that are solved upfront, the fewer there are at the job site, at least ideally.
The dreary business climate is a good proving ground for the company's model-based approach, but Robert admitted it hasn't been all smooth sailing. The collaboration traditionally involved in building construction weaves a complex web of relationships and paper trails that could be seen to dilute risk and responsibility. With BIM comes traceability and, ultimately, accountability.
"The traceability actually spooks a lot of people," Robert said, "because there have been some projects where nobody seems to want to own the model. Part of the issue is often not everyone is in the model space, so the general contractor tries to coordinate people on and off the model."
But on balance, Robert said, the BIM approach likely will evolve to become the preferred method of construction. For investors who put up the money that gives jobs to so many—architects, designers, engineers, general contractors, specialty contractors, and metal fabricators like Zahner—traceability and accountability matter.
As CEO Bill Zahner put it on the company's Web site: "Older traditions that often act to slow the process or confine the process need to be revised or eliminated. If performed correctly, the [BIM approach gives] information that is significantly more accurate and robust. Litigious concerns about who is responsible for checking or validation are less and less of an impediment."
In recent months the company, like many fabricators, has had to deal with project cancellations. It's proof that so many variables remain out of the fabricator's control. But over the next several years, managers hope to squeeze further efficiencies out of the processes they can control. The smoother internal operations are, the thinking goes, the less effect external schedule changes will have.
"More projects today are going with the integrated approach," concluded Robert, "so that everything flows smoothly from the solid model to the installation. We've been doing it for 10 years. It's not second nature yet, but we're getting pretty good at it."
During these economically tumultuous times, A. Zahner Co., Kansas City, Mo., hasn't felt nearly as much pain as other companies. At this writing, its order book is full, and a plethora of projects are even lined up for 2010. But the building industry has always been plagued with delays, and the problem has gotten worse since the financial crisis hit.
Delays aren't always about a lack of funding. Last year, for instance, New York City, responding to the tragic crane collapse, halted all construction projects. This left Zahner with finished subassemblies ready for shipment just sitting there for weeks—far from ideal in a lean environment. For this reason the company recently hired a new manager to handle the inventory problem.
Related efforts also involve another first for Zahner: implementing enterprise resource planning (ERP) software to not only manage work orders, bill of materials (BOM), company databases, and other information, but also extend the system's reach to the company's on-site work.
"It's a struggle," said Robert Zahner, senior vice president, "because we're not just manufacturers. The [ERP system] has to go all the way out to assembly in the field. You have piece parts that become an assembly that then gets shipped on-site and installed onto a building. There's a lot of complexity."
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.