Design for manufacture and assembly (DFMA) does well as a stand-alone methodology for simplifying product designs and lowering production costs. However, DFMA should also be hailed as a pathway to lean manufacturing.
To explain, let’s consider the main goal of lean manufacturing. It’s not cost reduction. Lean is mainly about reducing lead times and cycle times. It’s about responding quickly and flexibly up and down the value chain. Lean manufacturing attempts to harness the pull of customer demand to set operational activities in motion back through the chain.
Given that as lean’s calling, let’s presume that basic lean principles—such as pull production, small lots and kanban—did not exist. DFMA could, by itself, fill much of the void. It does that through order-of-magnitude reductions in what manufacturing would otherwise struggle to cope with: a multitude of sizes and types of parts and assemblies.
A Vital Component of Lean
It should be obvious why reducing part counts is fundamentally lean. However, the two methodologies are typically viewed as separate disciplines. To clarify why DFMA deserves a central place in the lean agenda, we need to bore into some of lean’s core principles.
High on the list is quick changeover. Lean adherents see quick setup and changeover as lean’s primary method of delivering fast, flexible response to customer demand.
Conventionally designed products call for extensive quick-changeover efforts, because they typically contain an outsized array of parts. By decreasing part count, design for manufacture (DFM) eliminates the need for many setups, and design for assembly (DFA) eliminates the need for many changeovers.
One of the earliest and most successful adopters of lean manufacturing was Bruce Hamilton, former general manager of United Electric Controls Co. and current president of the Greater Boston Manufacturing Partnership. He explains why quick changeover is necessary—but not sufficient: “Through our use of SMED [single-minute-exchange-of-dies],” he says, “we reduced many lot sizes to one—but even for that one piece, we had to activate our entire production system.”
DFMA avoids the need to activate the production system. It does this in two ways. One is by standardizing parts. For example, Renishaw Inc. maintains a library of standard part features. This allows its entire suite of components to be set up and manufactured with approximately 70 different tool assemblies, vs. hundreds a decade ago. The main reason Renishaw implemented the library was not cost, but lead time.
At its best, DFM can reduce a multipart design to a single part, requiring no setup adjustments at all. In some cases, the manufacturer could even opt to give this no-setup part its own dedicated machine tool—perhaps an ancient conventional machine that had been collecting dust. When the machine is cleaned up and rigged to make just one important but sporadically needed part, no one cares if it operates only two hours a week. After all, the machine was fully depreciated decades ago.
DFA goes one step further. It redesigns the product to eliminate certain parts entirely. An early, widely cited example is the IBM Proprinter. It had no screws, springs or belts. The parts were designed to snap together as the printer moved down a robotic assembly line. In another famous example, NCR engineers designed a new cash register with so few parts that a person could assemble it in less than two minutes—blindfolded!
DFMA and the “Lean Core”
This discussion could end satisfactorily right here. The point—that DFMA should be seen not as an adjunct to lean, but as a bona fide lean practice—has been made. But the discussion is worth continuing, because DFMA achieves several more of lean’s core principles.
DFMA paves the way to cellular manufacturing and one-piece flow. By shrinking part counts, DFMA does away with space-consuming storage and handling equipment. It may clear room for two or more cells, each compact enough that one-piece flow is within reach. Similarly, low part counts favor kanban as an efficient way to deliver parts to the cells, either from stores or directly from outside suppliers.
Part-number congestion can stymie cellular configurations. Getting all the parts to the right station in the cell and finding space for them widens its footprint. That puts distance between productive stations, nullifying the advantages of a compact cell. Non-value-adding conveyors and storage apparatus may consume as much space as value-adding equipment. One way of coping with this is the common, but un-lean practice called kitting, which requires extra people and double-handling of parts.
Kanban can act as a queue limiter. By reducing the variety of parts in a queue, DFMA may enable manufacturers to implement a concept known as cardless kanban or kanban squares. The concept is simple: When a square is empty, produce parts to fill it. When it’s full, don’t produce. If the kanban square between two workstations involves only one part number, there’s no need for identifying information. If it involves more than one part number, then simply color-coding locations or containers may be enough to identify the parts.
On the other hand, when a queue handles a large variety of items, kanban gets complicated. To prevent mix-ups, each part needs its own kanban card printed with part number, quantity, and source and destination stations. Each item also needs its own container. Color-coding containers becomes impossible with too many different parts.
Removing conveyors, forklifts and pallets is popular sport in the lean game. Years ago at Emerson Electric, the late William A. Rutledge, then executive vice president, issued an edict to all the company’s business units: If they wanted to buy forklifts, they would be charged, say, $200 for the first one, $1,000 for the second, $5,000 for the third, and so on. The amounts are wrong, but you get the idea—and so did those business units. As DFMA shrinks part numbers, it also reduces the variety of containers to hold them and the devices to move them.
Keeping myriad sizes and kinds of parts in stock requires myriad sizes and kinds of containers to put them in. It also requires more complex and costly material-handling devices. Lean copes with this by converting widely scattered shops into compact cells. With shortened handling distances, the need for powered conveyors, forklifts and tugger trains may give way to smaller containers, gravity-fed conveyors, and manually pushed dollies and carts.
Besides aiding with cellular manufacturing and kanban, DFMA can also help manufacturers reduce supplier count, source locally, and get frequent, small-lot deliveries. Maintaining a large variety of purchased parts requires sourcing from numerous suppliers.
By standardizing designs, manufacturers can maintain fewer parts. And that, in turn, enables manufacturers to whittle down the number of suppliers to the lean ideal of “a few good ones.” Then, as the volume of purchased parts from each supplier increases, they could opt to relocate closer to their best customer. With transport distances greatly shortened, suppliers may no longer need to ship infrequently in full truckloads. Instead, it becomes economical to work with small lots and to deliver them daily or more often, just in time.
The best known and most visible marker of leanness is the absence of inventory. By reducing part numbers, DFMA makes inventory—raw, in-process and finished—disappear.
Another widely used lean metric is space reduction. As DFMA standardizes parts, the space needed to hold and process them shrivels. This applies in supply and distribution, as well as within manufacturing. That is no small consideration. In most industries, supply and distribution channels are loaded with inventory. It’s the greatest unmet challenge of lean manufacturing.
The Vision Thing
For many years, I have been compiling an electronic database of best practices in manufacturing. The database now totals some 1,100 entries. Recently, I searched the database for “DFMA.” Incredibly, it came up in just 35 of the reports.
How can there be so few references to so powerful a process-improvement and lean methodology as DFMA? Here are a few speculations.
First, the DFMA community sells itself short. DFMA gets meager recognition because it is promoted mainly for its cost-reduction benefits. So many other initiatives claim to cut costs that DFMA gets lost.
Second, DFMA’s milieu of design engineering is narrow. At many manufacturing companies, departments function as silos, rarely reaching out to other departments.
R.A. Jones & Co., a manufacturer of packaging machines, found an antidote. In the early 1990s, the company found itself maintaining thousands of part numbers. Engineers would design a new part rather than search through massive files of existing parts. To solve the problem, the company moved its five design engineers and their drafting tables to the factory floor. By closely interacting with production associates, engineers refocused their talents on standardizing parts and simplifying assembly.
In contrast to DFMA, lean has become an industry. It has spread amorphously across the enterprise and up and down the value chain. I once made a list of practices that are part of lean manufacturing. It consumed an entire page. Of course, DFMA was on the list. In practice, however, it gets lost in the mix.
Finally, lean “grew up” in operations, and it remains easier for lean teams to expend energy there than to reach out to the design engineering silo.
Lean practitioners tend to obsess excessively over lower-level waste-reduction pursuits. Though that is valuable, lean’s higher purpose revolves around doing what’s important to the customer—at the next process and all along the value chain. Specifically, that purpose is to deliver products quickly and dependably in response to changing customer needs. DFMA is a potent methodology for doing just that.