June 2009 eNews

Lean cell basis in aerospace

70-hour setup shrinks to less than 15 minutes; level-load energy pays off, too

Brad Hart, president of Roberts Tool Co. in Chatsworth, CA, and dynamic spokesman for Supplier Excellence Alliance (SEA), said he sometimes feels he’s talking to a brick wall.

“But more and more, the message is getting through,” he noted. “Suppliers are seeing that the Lean-cell approach is the simplest, yet most effective way to keep aerospace manufacturing in North America.”

Hart aims to convince allies and competitors alike that industry changes dictate a change in production methods.

“An efficient ‘Lean and green’ American supply chain benefits us all,” he said. “Otherwise, we all lose out to low-wage countries.

“Take a step back,” Hart suggested. “View things from a broader perspective and it becomes obvious.”

The integrated approach

As integrated-component designs mature, suppliers face much greater competition for parts contracts.

A few years ago, Parker Hannifin, the large motion-control technology icon, approached Roberts Tool Co. with an offer to help streamline its business. In particular, Parker wanted to teach its established supplier the basics of Lean manufacturing.

“The concept really rang a bell with me,” Hart remembered. “I recognized that if we could standardize and document how we did things, we could expand without having to add much expense to our payroll.

“We embraced the idea so fully, that we ended up hiring away Parker’s ‘Lean guru,’ and flying him from Utah to California every week for the next four years,” he said. “That important change in perspective inevitably led us to [develop] manufacturing cells.”

The building blocks

A cell is a highly efficient self-contained manufacturing entity, Hart explained.

Raw material goes in one end, and finished parts come out the other. The size of different cells can vary, depending on the quantity demands of the customer. Technically, a single machine can be a cell, if it can completely make the part, and has the capacity to meet volume requirements.

“However, we design a lot of our cells around four machines,” Hart said. “We consider a single, well-defined ‘family of parts’ — for example, hydraulic-systems components — and then develop a basic cell process that can manufacture as many of those parts as possible.

“We typically aim for at least 80 percent of a given family,” he continued. “This carefully designed process, balanced with capacity requirements of the contract we’re going after, determines the machines, tools, and fixtures that make up the cell.

“Then, if we have leftover capacity, we go after additional parts that match the process,” Hart said. “Here, we’re matching parts to the process, but initially we are designing the process to best fit a family of parts.”

The primary goal of this high-mix, low-volume process is “near-zero” set-up time. This drastically cuts turnaround times and allows any size run to be profitable — even unity flow. With this degree of production flexibility, there’s no need to inventory any in-process or finished parts.

“With a good cell, you can consistently produce Six Sigma quality with less-experienced labor operating less-expensive equipment,” Hart noted. “You’ll stop wasting material, time and energy — and, of course, you’ll make a lot more money.

The idea is not a revolutionary one — except for the aerospace industry, Hart conceded.

“If you go to the automotive guys, or maybe the medical industry, these techniques are commonplace, but since volumes are so much lower in aerospace, people have been slow to implement dedicated cells in this industry,” he said.

The Lean perspective

Hart contended that the traditional high cost of equipping cells was no longer an excuse.

“In recent years, Haas Automation machines have pretty much set the industry standard for both affordability and reliability,” he said. “As much as possible, we now design around Haas equipment. When you can build reliable cells with dramatically less capital investment, your profit goes way up.

“Staying Lean means buying no more machine than you need,” he continued. “You’re tempted to spend a lot of money for extra bells and whistles because you don’t know what type of work is going to come along. But ‘just-in-case’ thinking is terribly inefficient.

“With manufacturing cells, we know exactly what we’re going to be doing, so we purchase the exact capability we need to meet our process,” Hart explained. “Matching the right machine to the job makes a lot more sense.

Hart said the company carefully designs its process to take advantage of four spindles instead of two, and make twice as many dollars per hour, for half the capital expense.

“When we turn many inefficient processes into a single efficient one — using less energy and producing less waste — we‘ve advanced our company’s ‘green quotient,’ and we’ve inevitably saved money,” he said.

“Based on our ability to build these reasonably-priced cells, we think we can make aerospace parts cheaper than anybody else,” Hart noted. “We find we’re now competitive with China on [Boeing] 787 components.

“The only thing China has over North America is its lower cost of labor — and our processes and cells reduce the labor requirement to a minimum,” he said. “Since we’re closer to the customer and more flexible, we’re finding there’s no way we should be beat by foreign labor.”

The cell advantages

Minimum setup is key. In cells using four 5-axis Haas VF-4 VMCs configured to produce hydraulic pump parts, Roberts’ operators average 90 minutes to set up production.

“Compared to the average 60 hours it used to take, that’s essentially zero,” Hart said.

The company uses quick-change fixtures, unique for each casting or forging, that mount in a few minutes. Tool sets dedicated to each part are stored in rolling carts, so they can be quickly loaded into the carousels.

Roberts’ cells are designed to efficiently balance machine use. A stainless steel “trumpet bell” pump housing illustrates the nature of this balancing act. Most machinists would say it’s an obvious turning application; but here, it’s done on a VF-4 vertical machining center. There’s no lathe in the cell. The unusual milling operation is used because it best fits the cell design, and optimally balances the cycle times of the cell’s four machines.

“When true-position accuracy is not demanded, jobs normally single-mounted may be broken into multiple ops to better balance the cell,” Hart said. “Again, in a traditional environment, it wouldn’t make sense to re-mount, but here, it’s a viable way to maximize the productivity and profit of each cell.”

Process control is continually checked within the cells, and can be monitored via the Internet.

Besides quality control and set-up time, the other key metric Roberts watches closely is inventory turnovers. While most aerospace suppliers typically have three or four inventory turns annually, Roberts Tool turns its inventory 12 to 15 times per year. With the hydraulic-parts cells in production, average lead times fell from 16 weeks to less than four. Now, they only produce the exact number of parts their customer needs.

“We get castings at the beginning of the month,” Hart said. “We often machine, ship and receive payment for the parts before we’re even billed for the raw material. In the old days, we’d have to buy four or five months’ worth of castings, and carry that large expense.”

The competitive edge

In a new single-machine cell designed to produce aluminum wing clips for Cessna’s Mustang business jet, Roberts challenged Cessna to test its capabilities. With a twin-pallet Haas EC-300 horizontal machining center and a carefully designed process, Roberts quickly proved the value of their Lean-cell concept. Cessna gained flexibility and saved money.

Soon, the original contract was widened into an all-inclusive agreement for all Mustang clip kits.

Setup time fell from Cessna’s expected 70 hours per part, to less than 15 minutes. Lead time, including processing, dropped from 87 days to four. Cessna’s costs were cut 10 percent initially, with an additional 10 percent reduction scheduled over the next five years. While Cessna’s previous suppliers made about $75 per machine-hour on these parts, Roberts now makes $286 per hour.

“Since the in-house-trained operator can effectively run three machines in parallel, his contribution to the company is worth more than $850 per hour,” Hart pointed out. “Hopefully, these metrics will convince others that manufacturing cells work for aerospace.

“Cutting lead times, setup times, and batch size variations cuts waste across the board,” Hart noted. “Our Haas cells allow us to level-load our energy and resource demands throughout the shop. I’m convinced anytime a company becomes more efficient it becomes ‘greener’ — and it all ties back to profit.

“In 2000, when Parker Hannifin first approached us about Lean manufacturing, we were a $5-million company with 50 people,” Hart said. “Today, we’ve grown to become a $20-million company with 75 people.

“I feel that if my competitors can do the same thing, it will benefit both me and my customers by keeping aerospace work in North America.”

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Haas Automation Inc.

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