A case study in lean manufacturing: Opening the door to single-piece flow

Total Door Systems has integrated punching and bending directly into its main build line. Work flows through the two fabrication processes in a single-piece part flow, with no work-in-process in between.

A little more than six years ago, Total Door Systems was about to move into a new building in Waterford, Mich. But this wasn’t a typical “plant upgrade” for which you hear company leaders trumpeting the fact that a new building would give them more space to grow the business. The facility uses 40 percent less power than the previous building, is 20 percent smaller, and yet can produce four times the production compared to the old plant.

Walk into the brightly lit facility with polished floors and you can see a commercial door being made, flowing from one process to the next, with no piles of work-in-process in between, no significant racking for inventory. It’s single-piece flow, adapted to the fabrication of commercial integrated door systems destined for hospitals, schools, office buildings, and elsewhere—including some of the entryways to the new Freedom Tower in New York. Its products range from functional fire doors to what could be called artistic creations.

It would be impressive enough if Total Door ran just an assembly operation, which, according to President and CEO Patricia Yulkowski, is par for the course in door manufacturing. Most in the industry purchase components, often from overseas, then assemble them stateside.

Total Door doesn’t outsource much, and when it does outsource—such as for aluminum extrusions, door cores, and injection molded components—it does so locally. It performs most processes in-house, from the punching of stretcher-leveled galvanneal steel (which makes up the door skins) to bending, roll forming, stamping, coating, welding, brazing, final assembly, packaging, and shipping.

It has integrated most of these processes, including punching and bending, which are traditionally batch processes, into a single-piece flow operation. This has decreased lead time to four to six weeks and, for certain quick-ship items, just 10 days. “In [the door] industry, you can end up waiting that long for a lock,” Yulkowski said. “But we’re literally building the whole system.”

Hence the word total in the company name. This unique selling point, besides setting the company apart from its competitors, is really what has made the company’s transformation to single-piece flow so effective.

Engineering the “Total” Door

Yulkowski’s parents, Leon and Christine, had been in the door business since the 1950s, importing and eventually making mortise lever locks, ubiquitous today but at the time a rarity in the U.S. They sold that company to Schlage in 1972 and, two years later, launched Total Door Systems with a strategy that was then (and still is) an unconventional approach to door manufacturing.

Instead of assembling parts from dozens of different manufacturers, Total Door designs and engineers every door component, including the locks, closers, hinges, and exit devices like panic bars (horizontal bars that open fire doors). They look at a door as a system, not as a collection of various parts.

This approach allows Total Door to customize an order to meet exacting customer demands. If a client wants a specific look, for instance, Total Door can engineer that look to suit.

The approach theoretically can help shorten the order-to-delivery cycle, too, because Total Door doesn’t rely on numerous outside manufacturers for parts. If something needs to be changed, Total Door can engineer and make it, either right on the floor or by working with local suppliers.

Door bodies hang from an overhead conveyor on the main build line. The technology eliminated most manual material handling in Total Door’s production system.

Still, back in the old building, the company relied on a supplier network to make those components. In some cases, like with roll forming, local suppliers over the years either closed shop or consolidated. Some preferred or required large orders, which didn’t work with Total Door’s just-in-time approach.

The company also relied on a lot of hard tooling, and the manufacturing was (at least in retrospect) slow and laborious. Parts were pulled from a warehouse and assembled, with a lot of manual lifting to get from one step to the next.

The Road to Better Flow

“I realized the infrastructure we had wasn’t going to ensure the future of the company,” Yulkowski said. “We really had to assess where we were, perform a gap analysis, and figure out what we needed to do to position the company to remain viable.”

“Assess where we were” is the key phrase. When Yulkowski took the helm as CEO in 2009, she and her management team didn’t just set out to make changes for their own sake. Things had been done a certain way for years, and they didn’t want to change such entrenched procedures without careful analysis through a structured problem-solving process.

After measuring and mapping every process—including material handling time and how long parts sat as WIP—managers and staff made a strategic decision: Bring more processes in-house to have more control over quality, quantity, and delivery.

Most significant, they designed a U-shaped production line for single-piece (or “single door”) flow, with a custom overhead conveyor designed specifically to handle a range of door shapes. Clamping mechanisms hang down, and end effectors clamp to workpieces with a toggle mechanism. The conveyor effectively automates the act of moving an unwieldy door from one station to the next. Only for special projects (like architectural embellishments) must workers manually move components.

Though certainly not conventional in door manufacturing, a single-piece flow line isn’t entirely unusual in manufacturing overall, especially for final assembly. What sets Total Door apart is that its manufacturing line isn’t just assembly; it entails nearly every process needed to make a door. No wonder the company refers to it as “the build line,” not an assembly line.

In a conventional arrangement, turret punching and bending might be in a separate department, or at least separated from the main line. The punch would produce a batch of door skins, with all the necessary cutouts. (Previously workers manually sheared sheets, hemmed the edges, and used a plasma torch for secondary operations, which wasn’t particularly efficient or repeatable.) Door skins would travel to the build line where the door bodies would be fabricated. The batch of doors would then get stocked at the point of use on the main line.

The WIP buffer would depend on the takt time of the main line, the punching and forming cycle times, and the setup time. In other words, the WIP buffer would absorb process variability.

Managers and engineers at Total Door looked at all this and came to a realization: Unlike at most custom fabricators, the punch presses at Total Door do not cut a complicated nest of various small parts, which can change the cycle time greatly from one sheet to the next, depending on the parts in the nest. Although each door skin can be a different size with different cutouts for hardware (which is why Total Door uses a turret instead of a stamping press), the punch usually just cuts one door skin per sheet, which makes cycle times consistent. And the punching and forming cycle times do not exceed the line’s average takt time.

A worker transports a blank onto Total Door’s turret punch press, which is integrated within a single-piece flow line.

Most important, because programs for the LVD punch and press brake are downloaded directly from engineering, and because the brake tooling setup usually remains consistent from job to job, setup time for both processes is minimal or nonexistent. All this meant that they could actually put the punch press and press brake on the build line itself—with no WIP buffer between punching, bending, and the next downstream process.

Today metal sheets of various sizes, grades, and gauges are stored by the punch press, at the point of use. Operators load sheets, which are automatically unloaded as punched skins, and then loaded immediately on the adjacent press brake. The forming technician bends the part, then places it directly on a roller conveyor, where it moves on to the next station where it is made into a complete door body, constructed to order. It’s next hung on the main overhead conveyor for further processing.

About 80 percent of the equipment in the shop is now new. In fact, the manufacturing process has changed to such an extent that Total Door has had to revalidate its product line to ensure its fire doors and other products meet building code requirements.

New processes include an electrostatic coating and ultraviolet curing system, which works even on the company’s complicated shapes. The doors flow through an electrostatic coating chamber then through an oven with 10-inch UV lamps that cure both sides of the door at the same time.

The system reduced energy consumption and, because of its quick cycle times, reduced WIP. And with increased throughput in coating, the entire manufacturing line is faster.

Some processes do need to be set apart from the main build line. This includes the company’s new roll forming line. When the line was designed, consistency was key. So the system has more rolling stands and roll tools than absolutely needed, just to make setups easier and more consistent. The line also includes three stations—before the rolls, in the middle, and at the end—that incorporate secondary operations, such as the stamping of cutouts.

What’s Next?

At this writing the people at Total Door are developing and testing a new high-strength brazing process that will improve quality; reduce cycle time; and complement the company’s other joining processes, such as conventional arc welding and spot welding. The company is also working toward being a paperless environment. The process scrutiny, Yulkowski said, never stops.

“If you come back next year, the company will look very different,” she said.

In one sense, change at Total Door has become the status quo. But with change, Yulkowski knows there’s an element of risk. She quoted a study from Conner Partners, a firm specializing in transformational change, saying that any major change at a company—be it quality-driven, cultural, or driven by a new software installation or new processes —has a failure rate of between 63 and 81 percent. “And when we moved into our new building [in 2010], we went through all of those changes.”

Walk through the plant and you can see evidence of those changes. You spot the key tenets of visual management, including clearly marked signs, labels, and documented procedures. It’s easy to see exactly where the product is coming from and where it’s going. And when Yulkowski walks the shop floor, she can tell within a few seconds just how much WIP is in the build line. The old facility had two to three weeks’ worth; today the line has just two days. “Our goal is to get the WIP down to four hours,” she said.

Total Door recently brought roll forming in-house. Doing so gave the company more control over quality and delivery.

She added that running with so little WIP requires a lot of planning and good machine maintenance.

“If the turret is down, the line is down. We are not fabricating things in advance. It’s really the process that initiates the flow, with a single piece of steel.”

It also requires close supplier relationships, which is why the company works almost entirely with local suppliers. Yulkowski said that working with local suppliers isn’t just the ethical thing to do, it’s good business.

With so little WIP, it also doesn’t take long for a single piece to flow through the facility and ship. And as Yulkowski explained, the proof of such increased productivity is in the results. At 50 employees, the company has grown its head count by 20 percent over the past year. They all work in a smaller space than they did before 2010—but again, they have quadrupled production capacity.

Five-year Relevancy

Yulkowski and her team take a methodical problem-solving approach. They don’t make changes to improve things for the next quarter or even the next year.

As a baseline, any change needs to have what Yulkowski calls a “five-year relevancy.” That is, any change made today ideally needs to be relevant for at least the next five years. “We build for the long term, and continually evaluate every department to improve our performance,” she said.

“The staff is very involved in the process, too, in terms of layout and new equipment,” she continued. “It’s not just carried out by a few people in management. It’s a team approach to problem solving, which is why we’re so successful.”

She added one more coda. “Problem solving is not a singular project. It’s a process—a way of life, and now just how we think and work.”

Photos courtesy of Ara Howrani.

Total Door Systems, 248-623-6899, www.totaldoor.com

A part emerges from Total Door’s new roll forming line.