Lean assembly line built using aluminium profiles

C & D Zodiac of Ontario, California, designs and manufactures multiple components for commercial aircraft cabin interiors, though the company specialises in aircraft seats, producing 1200 per month.

Recently C & D converted its production line from a batch and queue system to a one-piece, continuous flow line. Now, a finished seat ranging in price from $1000 to $3200 comes off the assembly line every 18 minutes, packaged and ready to be shipped. This Lean assembly line utilises assembly station carts and fixtures constructed entirely of aluminium structural framing components and systems supplied by the Linear Motion and Assembly Technologies group of the Bosch Rexroth Corporation.

In the one-piece flow line, also called a continuous flow line, seats move through the production line from station to station for sub-assemblies to be installed onto the seat. Following Lean manufacturing principles, assembly work is divided among the stations equally, so each station has exactly 18 minutes' worth of work.

Sub-assemblies feed directly into the main assembly line, while custom sub-assembly workbenches are positioned close enough to enable the operator to place the finished sub-assembly directly onto presentation carts on the main line, or onto the final assembly stations.

In total, the passenger seat line comprises approximately 211 steps using some 311 parts. There are nine final assembly stations and ten sub-assembly stations.

Easy to modify

Ryan Newham, the C & D Zodiac industrial engineer behind the one-piece flow line, explains that Rexroth components were used not only for the carts and fixtures, but also for workstations and tool holders: "The Rexroth tool rack presents the hand tools in a natural, handle-first manner, and, because it is modular, it is easy to add or remove tools at a later date."

Newham describes how the production used to be: "When we used batch and queue, we had mountains of sub-assembly parts everywhere on carts and shelves, but we would never seem to have the actual parts we needed. We would build all of the seats up to a certain point and store them on the floor waiting for the next step. All of the work-in-progress seats occupied limited floor space and were not producing any profit. And, while the seats waited for a next step or parts, they were susceptible to damage, as workers and equipment were forced to move around them."

In addition, the seats were only partially completed, which saddled C & D with the burden of trying to track their progress and made it difficult to manage timely inspections and quality control.

Since conversion to the continuous flow line, C & D now has only eight or nine work-in-progress seats that are all actually being worked on, instead of just waiting for the next step that might be a day away. Overall, conversion to the continuous flow line has led to nearly a 200 per cent increase in production.

Why Rexroth?

Newham states: "When we decided to convert the line from batch and queue to continuous flow, we chose Rexroth aluminium framing because of its ease of construction, its vast flexibility, and its fit and finish. There is no welding or painting involved, so it greatly simplifies and speeds up construction to keep production moving. Because everything is bolted together, we have the ability to make adjustments or add on more features as the needs of the line change."

"I cannot tell you how many times I have designed something in AutoCAD, then when I actually built it, I realised maybe a shelf should be a little bit lower, or a tool holder should be a little bit higher for a person who is shorter. Or, once I realised the person I made a workbench for was left handed, and I had put all the tools on the right. Rexroth aluminium framing gives me the confidence that I have the flexibility to make my designs work. And, when I am all done, I have equipment that is custom built for my exact needs, and it looks stunning and very professional."

Tool rails and holders allow easy movement of tools from one side to the other in order to address operator handedness and other space issues, reduce worktable space, and enhance personnel safety and ergonomics. Finally, end caps provide a clean, finished appearance.

In addition to aluminium structural framing, C & D Zodiac is also using the new Bosch lithium-ion 10.3V electric screwdriver, which, despite its compact size, delivers the required torque and features precision variable-speed control, even at very slow speeds.

Follow the link for more information about Rexroth's Manual Production System workstations and Aluminium Structural Framing system.