Going Green? Design For Disassembly Can Help

Environmentally intelligent design requires attention not just to how products go together but also to how they come apart. Two major office furniture makers, Haworth and Steelcase, learned about the importance of designing for disassembly when they created chairs won an environmental certification from McDonough Braungart Design Chemistry (MBDC), a leading green design consulting firm.

MBDC’s Cradle to Cradle certification scrutinizes every aspect of the design for its environmental impact--from the materials that go into a product to the potential for reclaiming those materials at the end of that product’s life.

And no one should be too surprised that recycled materials play an essential, though not exclusive, role in this kind environmentally intelligent design. Indeed, both Haworth’s Zody chair and Steelcase’s Think chair do start with about fifty percent recycled content.

Another important aspect of recycling, though, involves how much of a product can be reclaimed at the end of its life. On this score, both chairs shine. Roughly 98 percent percent of both chairs’ components lend themselves to recycling at the end of their working lives, according to their creators.This high-degree of recyclability creates all sorts of engineering challenges and drives many of the design decisions.

Chief among them is designing for disassembly (DFDA). Both chairs have to hold up to their share of abuse but still break down into recyclable bits and pieces at the end their working lives. “One of the driving issues is how you separate components,” says Kurt Heidmann, chief engineer for Steelcase. And both Steelcase and Haworth cut down on this separation anxiety by using fewer types of materials but greater amounts of each type.

A related strategy involves not permanently mixing materials that don’t go into the same recycling stream--a tactic that can put green engineering at odds with conventional design-for-assembly wisdom. For example, techniques such overmolding plastics can help consolidate multiple components into one. Or adhesive bonding can slash the component count by doing away with mechanical fasteners. But Heidmann points out that these techniques can mix materials in a way that makes it night unto impossible to get them apart for recycling. “We had to stay away from some of the ways that engineers trust to make things stay together,” he says. Steelcase does still look at techniques that permanently mix materials but only as long as those mixed materials go into the same recycling stream--such as a TPO skin on a PP substrate.

Mark Bonnema, a senior environmental design engineer for Haworth, makes the same point about permanent mixing of materials, noting that engineers shouldn’t just assume that parts consolidation techniques will have a positive net effect from an environmental standpoint. “You might use fewer components but re-use fewer still.”

Haworth and Steelcase also rejected another shibboleth of the design-for-assembly movement; they both employed more mechanical fasteners than they would in have used in the past. “People get schizophrenic about screws,” Heidmann jokes. But screws and their ilk can hold components and subassemblies together both securely and reversibly. Among the mechanical fastening alternatives found on the Think, the chair uses a j-channel to secure its seat upholstery.

Steelcase also molded in an important mechanical fastening feature, showing that parts consolidations doesn’t have to fall completely by the wayside. Heidmann notes that the chair features a molded-in threaded connection that attaches the back to the bottom of the chair. With a thirty degree rotation, the back flips into place. Steelcase adds a couple fasteners to the threaded connection to keep it tight. “But the back passes all our testing without the fasteners,” Heidmann says.

With Zody, Haworth engineers also simplified the way its back attaches to the rest of the chair. “We use just a single bolt,” says Bonnema says.

The end result of these DFDA efforts are that the chairs not only disassemble fully but also quickly. Heidmann says the Think can be disassembled at the end of its life in about five minutes using common handtools. Bonnema makes a similar claim for the Zody.

Both the Think and Zody embody green engineering strategies that go well beyond designing for disassembly. For a more detailed look, check out the feature article in the January issue of Design News.