Has lean peaked as an operational strategy for U.S. manufacturers? Maybe so, suggests Theodore Duclos, president of Freudenberg-NOK Sealing Technologies, a Detroit-based manufacturer of advanced sealing technologies. While admitting that "lean manufacturing is as critical as ever," he notes, "We are reaching the limits of the efficiencies we can expect to achieve because of the capital investments and processes we rely upon."

Explaining his next-gen lean concept at a recent manufacturing leadership conference, Duclos suggested that the long-term future of manufacturing will depend on the development of a sustainable manufacturing model. Sustainable manufacturing, he believes, should be designed "to mimic biological processes to produce products from the materials in the environment."

He cites an example from his own industry: the raw materials used in the manufacture of seals. These materials are readily found in nature, and the capture of carbon dioxide, its conversion to methane and the polymerization of methane at the production site could dramatically reduce waste.

There are many such opportunities within the supply chain to reduce the carbon footprint, Duclos points out. "We need to look more closely at our surroundings for ideas."

This type of sustainable manufacturing is what's known as a closed-loop supply chain, explains Paul Myerson, a professor of supply chain management at Lehigh University and author of Supply Chain and Logistics Management Made Easy (Pearson, 2015). Such a supply chain, he says, "is designed and managed to encompass both forward and reverse flows activities," or what's known as the "four R's of sustainability": reuse, remanufacturing, refurbishing and recycling.

Many manufacturers have adopted an extended product responsibility (EPR) program, Myerson points out, focused on the total life of the product. These companies, he says, "are looking for ways to prevent pollution and reduce resource and energy usage through the product's lifecycle." This gets back, then, to the original premise of lean: the reduction of waste wherever it exists, whether on the shop floor or throughout a company's extended supply chain.