If an industrialized construction firm wants to succeed, it must embrace this design approach.
- Design for Manufacturing and Assembly (DfMA) need not inhibit creativity. Although components and processes are standardized, they can be combined to make a wide range of finished designs.
- A manufacturer’s parameters can be programmed into a piece of 3D design software, so that the architect can focus on design without worrying about production line nuances.
- Team members need to collaborate to perfect the design before it’s manufactured. This eliminates errors and saves time and expense later on.
In another article in this issue (see “A Vision for the IC Future”), Nolan Browne defines Industrialized Construction, or IC, as “the application of advanced manufacturing principles to the art of construction.” A crucial part of this is product design, which needs to consider how a product will be manufactured.
Design for Manufacturing and Assembly, or DfMA, is an essential component of IC. How should it be done? How can it go wrong? And what difference does it make to the finished product?
What is DfMA?
In conventional construction, architects and engineers create designs, and construction teams figure out how to build them. “Say that a builder, general contractor, or framing subcontractor, is provided with the shape of a wall,” says Dennis Michaud, Managing Director of Offsite Solutions at CertainTeed, which is headquartered in Malvern, Pa., and has developed a closed-panel framing system called One Precision Assemblies. “The wall dimensions, as well as the dimensions and locations of any windows and doors, is usually enough to communicate the desired end result.”
With DfMA, by contrast, a lot more detail needs to be communicated. “Where are each of the studs? How are those studs fastened? How many fasteners and where do they go?” asks Michaud. If the building will be assembled from panels and other components, the design must account for how to transport them and assemble them at the jobsite. If it’s a modular project, the design needs to take the boxes’ size into consideration.
“If the designer wants a 20-ft. wide living room, that would need to be built out of two modules because you can’t ship 20-ft. wide boxes over the road,” says John McElroy, former VP of Engineering at Plant Prefab in Rialto, CA who now serves as CertainTeed’s Advanced Construction Manager of Offsite Solutions.
To be manufactured successfully, a design also must stay within the manufacturer’s specified parameters. In an automated factory, for example, that would mean considering the maximum size and weight for pieces that the robots can handle.
“Over time, we’ve developed parameters that all parties are aware of and agree to stay within,” says Hans Porschitz, Chief Operating Officer at Bensonwood, a Walpole, N.H. manufacturer of prefabricated homes. “If someone wants to pencil outside of that, there needs to be a conversation.” That might, for example, mean talking with the factory’s production manager to see if it’s feasible to exceed the robots’ handling capacity for a specific project. In most cases, however, Porschitz says that “the parameters are so broad that designers can stay within them and still provide good designs.”
Despite this standardization, Michaud is keen to point out that DfMA need not lead to boring results. The architect can still envision a unique finished building but needs to take that vision and translate it — using DfMA principles — into a design that can be efficiently manufactured.
Unique but Repeatable
This begs the question of how unique buildings can be efficiently manufactured. Isn’t manufacturing about repeatable designs?
Not necessarily. For instance, Bensonwood’s business is custom homes, so although they are manufacturers using DfMA, they don’t make cookie-cutter products. They’re not a Honda plant making identical Civics. At the same time, however, their homes are assembled from repeatable components. A wall panel in one part of the house might be identical to a wall panel in another part, as well as in the company’s other custom homes.
Of course, if Bensonwood’s priority was maximum efficiency — creating as much high-quality housing as possible, as quickly as possible — it wouldn’t be manufacturing custom single-family homes. As Porschitz puts it, “Our system obviously doesn’t reach the same level of efficiency and cost reduction that it would if we built the exact same home every time.”
The advantage of DfMA is that it increases the efficiency of manufacturing. If a design adequately incorporates manufacturing and assembly factors, then the line won’t be slowed down by things that will need to be adjusted on the fly: manufacturing processes, transportation problems and assembly needs. That’s because everything is defined before production begins.
DfMA also eliminates a lot of human error. As McElroy puts it, “People make mistakes. For example, I’m dyslexic and could misread 2’4” for 24”. Computers and CNC machines don’t know how to make those kinds of mistakes.”
Michaud adds that DfMA processes also reduce material waste. “If you need to cut an 8 ft. piece of plywood or gypsum board down 6 ft., you can plan in advance where to use that 2 ft. piece. On a jobsite, that’s next to impossible and certainly not efficient.”
Defining Details
All our interviewees mentioned the importance of having experts from every stage of manufacture and assembly involved early in the design process.
The building owner might start with a vague vision that they communicate to the designer who creates an initial design. Then, the whole team needs to communicate and provide input. (In experienced teams, like Bensonwood’s, much of that input is already baked into the design parameters in the design software.)
The point of getting the production team involved early in the design is to avoid conflicts that have to be fixed later. Michaud says that the production manager or the head of engineering in a factory — who works with framers, plumbers, electricians, insulators, etc. — will ensure that those details are internally coordinated in the design so that production can proceed without interruption. “A stud won’t need to be moved to accommodate an electrical box, no penetrations will run into structural conflicts, and so on.”
Over time, a company using DfMA can incorporate lessons learned into its design software parameters. From the framing system to the MEP details, the limitations imposed by automation, transportation, craning, and assembly, will be taken into consideration. “The architect doesn’t have to plan for those details from scratch every time,” Porschitz says.
He says that, during the design process, a very detailed ‘digital twin’ 3D model of the building is created. The model can be viewed all at once, or in layers “that show the sheathing, the studs, the penetrations, the fasteners, and so on.” Once the model is complete, it’s “sent both upstream and downstream, to the designers and owners at one end, and to the manufacturing and building teams at the other. This is to verify that the virtual creation maintains design and structural intent and also fits within manufacturing and assembly constraints such as maximum panel size and site access,” Porschitz explains.
During this check, things that are acceptable are marked green. If anything needs to be tweaked, or if there are complete showstoppers, “conversations are had until everything’s green and we know the model can be built,” he says. After that, the digital data from the software is exported as machine-appropriate data to the machines on the shop floor.
What Can Go Wrong?
One potential problem is when the design and manufacturing processes are looked at sequentially, like in conventional construction, “instead of putting all the parties around the table at the beginning,” as Michaud puts it. This can result in time-consuming — and expensive — back and forth as parties need to make adjustments and corrections. Those changes would have been unnecessary if they had been incorporated into the design from the beginning.
Another mistake is to change manufacturing or assembly processes that are already successful. Michaud gives the example of a factory that’s set up to flash windows in a certain way. If it’s set up to successfully execute that detail, then changing it can cause problems with quality control, and can also slow down production.
The building owner or occupant doesn’t care how the building is manufactured. They don’t care about the window flashing processes — they just don’t want the windows to leak. But the factory does care about the process, and the design should not require unnecessary changes in manufacturing.
A third error is doing things in the factory that are better suited to the field. “We experimented with putting wiring inside our wall panels in the factory,” Porschitz says. The result was a lot of short wires that electricians would need to connect on-site, which was very time-consuming.
Instead, the company made the on-site process more efficient, by drilling holes in the factory for the electrician to run wire through on-site. As Michaud puts it, “You want the electrical team using their technical expertise; you don’t want to pay them to drill 1000 holes in the framing. The CNC machine can do that better, faster and cheaper.”
The Finished Product
According to McElroy, “There’s not a lot you can see in a finished building that would tell you whether it was designed for manufacturing and assembly, or not.” An example is a modular home that was ‘stick-built under a roof’ using conventional plans that weren’t DfMA optimized.
To spot DfMA in a finished house, you could compare the as-built house to the plans. Michaud says that although “the quality of stick-built and factory-built housing can be the same, there’s accuracy to design intent when DfMA is followed.”
According to McElroy, a stick-built house will likely have “variances relative to the design, such as a light switch, a plumbing pipe, or even a window, being an inch — or more — away from where it was supposed to go. But you won’t see that in a DfMA house, because everyone does their checks before the data is fed to the machines.”
If you could ‘dissect’ houses and look at their components, it would be easier to spot DfMA-built ones. First, you’d see the unique identifying numbers that are printed onto every piece. Even if two DfMA homes from the same manufacturer look completely unique, there are similarities between their components. For example, McElroy says the panels from the Plant Prefab factory, “whether they’re roof, floor, or wall panels — will have 1-in. diameter holes for straps that are used by the crane for lifting and setting the panels in place on the jobsite.”
In the conventionally stick-built home, you would also find what McElroy calls patch work — where tradespeople fixed their earlier mistakes or “created workarounds because of other trades’ work.” You won’t find that in a DfMA building. The error-proofing is all done in the 3D model on the computer.
“In traditional construction, it’s common to find multiple studs right next to each other,” says Michaud. “One was needed for one purpose, and another was needed six inches over for another purpose — and those two purposes weren’t coordinated.” He notes that it’s a waste of materials to have those extra studs and it also “has an impact on energy performance, because where there’s a stud, there’s no insulation.” That’s another problem that DfMA eliminates.
Zena Ryder writes about construction and robotics for businesses, magazines, and websites. Find her at zenafreelancewriter.com. All images courtesy of Bensonwood.
