Modular Welding by Robots

by Tim Heston, Senior Editor The Fabricator

Visit a typical structural metal fabricator, and you might see a beam line with cutting and drilling automation, perhaps even a robotic plasma system for coping. The farther you walk down the value stream, though, the more manual the operation becomes.

These days, intelligent robotic welding systems can program themselves and even automate the fitting process, attaching plates to beams in a variety of configurations. But get to the final stages, and structural fabrication remains mostly manual. Trusses have weld sequences that account precisely for distortion associated with weld shrinkage; connection designs, bolted or welded, leverage a fab shop’s core strengths; cambered and rolled sections each have their own springback idiosyncrasies. Demands in structural steel are just too various.

Except when they’re not. Walk through the Chandler, Ariz., plant run by Z Modular, and you witness a very different kind of operation. Robots are everywhere. Some form of automation touches nearly every stage of metal fabrication. Welcome to the world of modular steel construction.

About Time

“I’ve been doing [modular construction] for 36 years. The whole idea is to compress timing and bring traditional on-site construction tasks under roof, in a controlled environment.” Said  Ky Ghosh, Z Modular’s vice president of operations.

The company is a subsidiary of Zekelman Industries, which also owns Atlas Tube, the largest independent steel pipe and tube manufacturer in North America and a major supplier of hollow structural sections (HSS).

Ghosh joined Z Modular in 2019, back when it was a much smaller startup operating out of a rented space in Birmingham, Ala. The idea came from the top of the organization—Barry Zekelman himself. After his father’s sudden passing in 1986, Zekelman took over as CEO and grew the organization from $2 million to more than $1.2 billion in 2007. Zekelman Industries’ annual sales today exceed $2.7 billion.

Zekelman sees Z Modular as part of a long-term strategy, promoting a construction method that makes good use of HSS and, most importantly, could help solve the country’s housing shortage. The organization aims to shorten the construction cycle dramatically. Timelines for traditional construction can take two years or more. Z Modular’s goal for constructing a typical apartment complex, from start to finish, is just nine months. “We’re at 12 months now, and we’re getting closer to our goal with each development,” Ghosh said.

In 2019, Z Modular was touting the modular construction concept for a wide variety of developers, from hotels and hospitals to college dormitories.

“Since then, we gradually narrowed our focus,” Ghosh said. “We did this by asking, ‘What are we really good at? What makes sense for us to make a serious investment?’ That’s how we landed on three-story walk-up apartments.”

The narrower approach has helped Z Modular focus its efforts with a powerful message about tackling the nation’s housing shortage. From a fabrication perspective, the focus helped streamline operations and standardize processes.

Unlike other structural fabricators, Z Modular produces a standard product. The final look of the developments might change, but the individual modules at their core do not. The approach to modular construction helps standardize a fabrication’s product mix, opening the door to a host of manufacturing efficiencies.

The Z Block, a precision-cast component, acts as the cornerstone of Z Modular’s chassis design

Making the entire module design possible started with the engineering that went into perhaps the most critical component: the Z Block, a precision-cast component with a tapered section that slides into the HSS inside diameter. They’re placed at the corners of each module chassis (the framing without the decking and drywall). Considering the tolerances and structural integrity requirements, a tube-to-tube weld at these critical connection points just wasn’t practical. From the start, engineers knew a precision casting was the way to go.

The Z Block’s latest iteration has extremely tight tolerances, allowing for a repeatable weld joint at the connection point, with no excessive gap between the tube wall and casting. This innovation, Ghosh said, set the stage for Z Modular’s ambitious production plans—including a deep dive into welding automation.

A Welding Automation Journey

Z Modular launched more than eight years ago as a manual operation out its Birmingham location. Early on, however, company leaders knew that to really scale the operation, they needed to automate.

Because most fabrication and assembly occur under roof, protected from the elements, the schedule becomes much more predictable. But there remained one challenge: the shortage of skilled labor, especially welders. If Z Modular didn’t automate, leaders knew that scaling up would be difficult. Moreover, modular construction offered a level of standardization that, again, opened the door to more automation.

Walk into a conventional heavy or large-workpiece fabrication facility with welding robots, and you’ll likely see some impressively large systems, some with articulating arms traveling on gantries to access all joint locations. Before welding, though, you’ll also see an extensive area for fitting and tacking—a manual process. The automation frees welders from spending their days laying down meters-long welds, but they still spend plenty of time measuring, fitting, and tack-welding assemblies before robots strike an arc.

Z Modular’s approach to welding automation is far more comprehensive. To start, custom racks, each configured to hold a specific type of precut HSS, present the material to robots. These have long grippers that place a range of HSS in a fixture comprising of two parallel, adjustable rails. Material handling and welding robots work together to build the frame, placing and welding the HSS cross members, then the vertical members of the chassis. The corner members of each module mate precisely to Z Blocks.

The automation is even more impressive when you consider just how tight a module’s dimensional tolerances are. The module chassis has a unilateral tolerance so tight, you would never guess you’re in a structural fabrication operation.

“You’re not going to believe this when I tell you, but it’s true,” Ghosh said. “Our tolerance is 0, +0, -1/64 in.—that’s across sections 60 ft. long and 15 ft., 6 in. wide. That’s dead-nuts tight. The tolerances we need for the modules to connect correctly are nominally zero.

“I’ll be honest,” Ghosh continued, “it was slow-going [ramping up the welding robotics]. But we had some very talented control engineers who programmed each step of both the material handling robots and the welding robots. It took time, but within the past four or five years, we’ve perfected the process. We’ve overcome the challenges, and now the process is really dialed in.”

The company’s first automated welding cell opened in Killeen, Texas, a plant where engineers gradually worked through the proof of concept, developing and perfecting programs for each “product family” of modules. The company now operates a second facility in Chandler, Ariz.—where the welding automation initiative ramped up quickly. Control engineers had already perfected the process; moving it elsewhere involved replicating the fixturing and programming, then dialing in the process.

Still, “dialing in” wasn’t simple, especially considering the tight dimensional tolerances control engineers needed to hold for each module chassis. Metal behaves differently depending on the environment. “The environment in Texas is completely different from Arizona,” Ghosh said. “We factor that in when we start every weld.”

He added that the company collects data on expansion, shrinkage, and deflection. And even in this controlled environment, variation outside the tolerance can still happen. “If we’re varying by 3/8 in., we need to stop. That’s major for us. When we stop, we forward that information to the structural engineer in-house. We hold until we get a report from our engineer.”

The process might take several hours or days, depending on the problem. During this time, the chassis is moved to a staging area while the robotic welding cell continues with the next module. Once the review is made, the engineer either tells the operation it can move forward or works with the fabrication team to make the necessary adjustments. The staging area is small enough to handle the occasional issue but not so large as to allow a number of module chassis to accumulate. At this point, Ghosh said, such issues are a rarity.

About Reach

In conventional construction, structural fabricators have little control over design. They might have some sway over certain aspects—the connection design, for instance (whether they’re welded or bolted)—but for the most part, they build based on the drawings given to them.

Z Modular operates very differently. Prefabricated modules are the company’s “products,” and a lot of collaborative engineering goes into designing them. Most welds within each module are in a butt-joint configuration, and engineers designed procedures to accommodate gap tolerances and weld shrinkage.

But all these need to be put in context of robotic welding: How exactly can these gas metal arc welding robots reach the mating HSS? These large modules are assembled in a single cell. Rotating the work on a positioner simply isn’t an option.

“We talked about welding robot reach every day,” Ghosh said. “For instance, is that reach going to be enough for proper welding from the floor joist to the perimeter edge?”

In a sense, the modules were designed both for structural integrity and manufacturability. If a welding robot couldn’t reach a specific joint, changes were made. Module design changes worked in concert with the weld fixture design and the entire joining process, from fitting to final welding.

Each module “product” is tailored for the apartment building Z Modular aims to produce, including the number of stories, the soil conditions at the foundation, and the loads the modules are designed to endure. Taller structures demand thicker-walled HSS.

The thickness ranges from 0.125 to 0.5 in. Perimeter HSS members hold the greatest loads and, hence, have the thickest walls. Floor joints can be 0.25 in. or less.

A New Approach to Construction

After welding is complete, modules are transferred to bays for final assembly, including decking (wood or concrete), fireproofing, mechanical, and even drywall, trades that would traditionally do most of their work on-site. In fact, modules leave the factory more than 90% complete, and this percentage continues to increase. Most of these downstream processes aren’t automated, but the fact that workers finish so much on-site work under roof, in a controlled environment, helps streamline the process tremendously.

“We might have three modules to one apartment,” Ghosh explained. “You’ve got a bedroom, a kitchen and living room module, and another module that handles all the utilities. All those boxes are 100% complete when it comes to electrical, plumbing, and any mechanical work. Once they’re shipped, all that’s left is to make the connections between the boxes.”

The framework Z Modular works under to fabricate and build a structure mirrors that of conventional construction, but with a few key differences. Every project has an owner, general contractor, an engineer of record, a designer, a detailer, a fabricator, and erector—but every one of them is under the Zekelman Industries umbrella. The only significant outsourcing occurs with licensed subcontractors that prepare the building site and create the foundation. The permitting process for all this occurs as normal as well.

“After the site is prepared, Hayes Modular, one of our sister companies, sets all of our boxes,” Ghosh said. “They also do exactly the same thing as anything a contractor would normally do building multilevel, multifamily housing.”

A Testbed for a New World in Construction

Z Modular today has three plants, the original one in Birmingham, one in Texas, and another in Arizona. The Birmingham operation, still largely manual, produces certain parts that feed the automated production at the other two plants.

Today, the company operates as a kind of proof of concept for the construction industry—and it’s vertically integrated. Zekelman Industries owns the properties and rents or leases the units once they’re complete and occupied.

Ghosh added that, at some point, the company will work with outside owners, developers, and investors. The overarching idea is bold: A streamlined construction method could help chip away at the country’s worsening housing shortage.

The concept changes the traditional roles of architects and designers. Modules do have some variety, but architects can’t work from a blank slate. They need to meet the specifications of Z Modular’s process. Call it “Building for manufacturability.”

Barry Zekelman summed up his aspirations in a 2024 interview with Forbes. “Hopefully, I can be that pied piper and everyone will believe in my story and want to be part of it. I’ve done it before, and I want to do it again. I think this is a bigger opportunity than my steel tubing business ever could be.”

Source: The Fabricator