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Nortel engineers dramatically lower product costs using DFX principles and design

Boothroyd Dewhurst : 04 November, 2006  (Company News)
Nortel engineers dramatically lower product costs using DFX principles
and design for manufacture and assembly, a design analysis tool
developed by Boothroyd Dewhurst, Inc.
Recently, Nortel product engineers in Electronic Systems Packaging utilized Boothroyd-Dewhurst DFMA to redesign two products in the companyís broadband portfolio, the S/DMS TransportNode OC-3 Express and the S/DMS TransportNode OC-192 ('OC' is 'optical carrier'). The function of the TransportNode family of products is to carry voice, video and data transmissions along an interconnected synchronous optical network. Established as a U.S. standard for fiber-optic transport of communications traffic, the SONET backbone supports speeds from just over 50 megabits per second to almost 10 gigabits per second.

Given the varied requirements its customers have for the volume of transmissions that must be carried, Nortel designs an array of transport products with different characteristics. The systems-packaging engineers have the task of devising housings for the electronic circuitry inside the TransportNode products. The OC-3 Express and the OC-192 stand at either end of Nortelís TransportNode product line. The redesign projects presented unique challenges to the packaging engineers as they embarked upon DFMA.

Beat the competitorís price
A compact unit contained in a single armload-sized shelf, the TransportNode OC-3 Express shelf carries 2,016 calls per optical fiber at a speed of 155.52 megabits per second. It provides a low-cost way of extending SONET capabilities to small and medium applications, such as an office park, a school setting up for distance learning, or a neighborhood organization of telecommuters. The modular OC-3 Express, the 'one-shelf solution' to transport-system needs, is essentially a six-sided sheet-metal box containing telecommunication components. It measures 14.75 in. across by 11 in. deep by 14 in. high, including a removable air deflector and fiber storage tray. The original shelf had a front cover, back cover, and welded shell for the sides, top, and bottom and cost $276 each to make (U.S. dollar amounts).

The original OC-3 Express was a successful design, but it did not reach the market soon enough. It offered more features and flexibility than the competitorís version and promised broader marker penetration, but the competitor soon lowered the price on its more mature product. In response, Nortelís product designers began to look for ways to reduce costs to match the competitorís tactic.

'We had a couple of different ideas to get at,' explains Dean Flockton, mechanical systems design engineer. 'We wanted to make cost reductions, and we wanted to make the unit more environmentally friendly.' For the latter requirement, a major goal was to eliminate 8 feet of beryllium-copper gasket and to find an alternative to the zinc chromate plating used to control corrosion of the sheet metal. Flockton also had to discover a way to double the fiber-carrying capacity of the unit.

The engineering team targeted the shelf mechanics, the box itself, for cost reduction. Following Boothroyd-Dewhurst DFMA principles, the project team disassembled the original OC-3 Express shelf and analyzed the function of each part. Flockton quickly realized that the front cover of the shelf was a strong focus for redesign. A DFA analysis of the original design showed that the hinged aluminum front cover of the box alone consisted of 53 parts and cost $78 to make. A majority of the parts were fasteners. As the analysis process continued, with feedback solicited from vendors and customers, a redesign strategy evolved: tool the front cover in plastic and replace fasteners with snaps where possible. The redesigned cover consisted of only 17 parts and took only 95 seconds to assemble, versus 378 seconds for the original cover. The total parts cost for the new cover was $26, a savings of $52 per unit.

Flockton offers a memorable example of DFMA yielding productive collaboration with suppliers. In a visit to the sheet-metal vendor, the Nortel team discovered that a stainless-steel gasket used in the front cover was being cut with a laser at a cost of $20. Because the gasket was only 0.005' thick, the group decided to use a steel-rule die operation instead, which lowered the cost of the gasket to $5.

Redesign efforts for the remainder of the shelf resulted in similar savings. After learning from customers that access through the rear of the unit was not needed, Flockton incorporated the separate back cover into the welded shell, which eliminated $32 of beryllium-copper gasketing no longer necessary for electromagnetic interference shielding. He redesigned the welded shell itself into C-shaped main and subshelves that nest for easier assembly. The subshelf, which integrates the electronic components, now slides into the main shelf, and the sides of the box weld on at slotted mounting tabs. Much of Flocktonís redesign was aimed at reducing assembly complexity. He explains, 'I changed the way the welded box went together so it required less spinning around to assemble. It used to have welds on four sides, but now there are welds only on two. The front cover is also now all one-axis assembly.'

In all, DFMA-guided redesign of the OC-3 Express shelf mechanics resulted in a total cost of $136, a considerable reduction as compared to the original cost of $276. The expected savings to Nortel in assembly and manufacturing costs are estimated at $700,800 annually.

Reduce the cost of a standard assembly
The TransportNode OC-192 is a seven-foot, closet-sized cabinet of equipment that provides the most sophisticated bandwidth management available in the communications industry today. The OC-192 carries 129,024 calls on each optical fiber at a speed of 9.95 gigabits per second. With wave division multiplexing, which expands the number of light wavelengths that a single fiber can carry, the OC-192 can transport over 250,000 calls per fiber at speeds up to 160 gigabits per second. Forming part of the worldwide telecommunications backbone, the device is used to interconnect supercomputers in business and education and to consolidate and direct huge volumes of transmissions.
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