||NAVSO P-3687: Producibility System Guidelines
Satisfaction Through Design for Manufacture/Assembly and Six Sigma
The LRAS3 design IPT used DFMA and Six Sigma analyses to provide a solid
basis for reducing variation, maintaining process control, minimizing cost
drivers, and maximizing performance. The Army customer demanded higher quality
and performance at cheaper prices with less time to deliver. DFMA and Six Sigma
were used to ensure that the designs were manufacturable and that the production
processes were capable, predictable, and in control. The following analyses
results are highlighted as well as the impact on the design for the GPSIS Cover
Process / Tools Approach
Results of DFMA and Six Sigma Design
- IPT Team Meetings - DFMA / Six Sigma design iterations on seven design
- Listed pros and cons of design options
- Worked with the functional shops
- Documented decisions and trade studies
- Applied the Boothroyd & Dewhurst, Inc. Design for Assembly tool<
- Used Six Sigma analysis tool
- Applied Sigma roll up
The DFMA and Six Sigma analyses had a significant
impact on cost, quality, and schedule. As a result, the following design
recommendations were incorporated into the design:
- Fabricated parts were simplified to make the GPSIS Cover Assembly.
- A foam core was used as a structural member of a composite cover.
- The GPSIS Cover Assembly was made up of four major fabricated parts. The
top and bottom skins and the foam core were a simple design with a Sigma value
greater than six.
- The rubber plaster mold casting required minimal machining as it was
designed before assembly with the cover. Only three mill cuts were needed to
make the surface flat.
- Off-the-shelf mounting hardware was used. Eight Shur-lock inserts were
used, as well as 12 Click Bond inserts for mounting the GPSIS Antennas and the
CCAs. Historically, machined mounts would be used that would be bolted or
welded in place to mount the CCAs and the Antennas.
- Composite laminate used a foam core, eliminating FOD from foam and
resulting in a rigid structure.
- The system was shielded from electro-mechanical interference/radio
- The cover was made flat to minimize tooling cost.
- Marking was minimized. "Bagged and tagged" was used where possible.
- Wherever possible, hardware standardization was applied, using 4-40 Allen
head cap screw type hardware to minimize issues with torqueing of the screws,
and one drive type was used to minimize tooling required to assemble.
- The need for adding a solar shield assembly was eliminated.
- Silk screen or label assembly part number on main housing was used on
assemblies to reduce rubber stamping effort at the higher levels (label
marking was not acceptable for exterior surfaces).
- Used rubber stamp Manufacturer Serial Numbers (MSN) at the assembly level.
Historically, the company would mark every fab part and assembly that goes
into a system, using the rubber stamp process, which required almost one hour.
To minimize the cost of the system, only assembly MSNs on the assemblies were
- Marking height (0.109" through 0.140") was used to reduce smearing,
smudging, etc., which in turn drove up the defect rate, affecting the part's
- Silk screen marking at fabrication levels was used to reduce the defect
rate and assembly cycle time.
- Foam core was used as a structural member of a composite cover, with an
aluminum top and bottom skin. Initially, the design team was looking at using
a casting or a sheetmetal weldment to isolate the insulation foam bonded to
the bottom side of the cover. With age, the exposed foam would cause FOD or
foam particles getting onto optics. These particles would degrade the optical
performance of the system; therefore, by laminating the foam into the cover
the team alleviated the potential damage to system