In an assembly tour-de-force, mechanical engineers at Delphi Automotive
significantly reduced assembly time through the development of an injection
molded plastic radio housing.
"The biggest advantage is the reduction in weight. There is
a 1.2 pound, or 22 percent, weight
savings," says Vineet Gupta, who led the engineering team that developed the
technology.
The new radio case is being used first on the mid-year model
of the GM Tahoe, but will be part of all premium navigation and entertainment
systems, referred to internally at Delphi as
the "black tie" systems.
The plastic case replaces a formed sheet metal case
assembled with screws and cooled with fans. The new plastic case achieves
required EMI and RFI shielding by completely enclosing electronics with a mesh Faraday cage that is insert
molded. Faraday cages are named for English scientist Michael Faraday, who
invented them in 1836.
For a radio, Faraday cages shield external electromagnetic
radiation if the conductor is thick enough and the holes that create the mesh
are significantly smaller than the radiation's wavelength. Electrical charges
within the cage's conducting material will redistribute themselves so as to
cancel the field's effects in the cage's interior. This phenomenon is also
employed to protect electronic equipment from lightning strikes and other
electrostatic discharges.
A big part of the Delphi
trick is how the cage is placed in a mold cavity, and then held in the right
position while plastic is injected at high pressures. Much of the specifics of
the manufacturing technology is proprietary and is covered by 29 pending U.S. patents.
Magnetic Tooling
"The cutting of mesh, the folding of mesh and inserting the
mesh into the mold requires innovative magnetic tooling and the use of robots
to transfer the formed mesh into the mold," says Gupta.
Gupta says the new plastic case provides even better
shielding than the previously used metal cases. There are lower emissions over
a range of 150 Hz to 430 MHz. OEMs are seeking improved electromagnetic
interference to avoid any internal cross talk, such as interference with
electronic engine controls.
The system cost to assemble the radio is reduced by
one-third with the new technology. Gupta declined to provide a specific dollar
savings per radio. Twenty-nine screws are completely eliminated. Use of
injection molding allowed incorporation of design features not possible with
the sheet metal case. For example, Delphi
designed slide lock and snap lock features that allow fast snap assembly. Other
mechanical features are also integrated into the design.
Mechanical part reduction includes ESD grounding clips,
fasteners and main board grounding. Assembly parts eliminated included a separate
assembly fixture and use of torque feedback screwdrivers.
As a result, the case is also more rigid, reducing rattle
noises. "There's also a significant increase in natural frequency," says Gupta.
Natural frequency is the frequency at which a system naturally vibrates once it
has been set into motion. Vibration testing on the new plastic case radio
showed a 25 percent increase in natural frequency.
Recycled Plastic
Delphi is used reprocessed
plastic to make the case. MRC Polymers of Chicago
supplies 16 percent glass-filled PC/ABS for the part, which is produced by Amity
Mold of Tipp City,
OH. The plastic comes from post
industrial and post consumer sources. The PC/ABS blend had to be optimized to
meet environmental requirements and reduce warpage.
The design of the plastic case lowered the internal
temperature. One reason for the improved thermal management is insulation of
the heat sink from the interior of the radio. The cooling fan was eliminated
due to the insulative properties of the plastic. As a result, electric current
used is also reduced, improving vehicle mileage.
Other Advantages Include:
·
The weight of the structural support for the
radio can also be reduced;
·
Safety is improved because injuries from metal
cuts are reduced. Protective gloves are not required for assembly;
·
Condensation is eliminated during temperature
cycling. The reason is simple - dewpoint temperature is not achieved so no
moisture drops on the circuit board; and
·
There's also lower dust intrusion during
standard testing.
Gupta says Delphi will also
be used for "interior black boxes" for Asian OEMs. "It's going to be used
across the board at Delphi ultimately," he
says. "Wherever we're currently using sheet metal we are going to use this
technology. It is quite broad based. We can use that competitive advantage for
all of our product lines."
Widespread Application
Gupta says it applies to any automotive interior electronic
packaging. The same advantages apply: part
and weight reductions, integration of mechanical and electrical features, and
improved air cooling with no loss of shielding. Gupta says Delphi
will also explore non-automotive consumer applications.
The Delphi plastic radio
case could replace a wide range of shielding approaches besides sheet metal
cases. These include die cast metal cases, conductive coatings (paints and
plating), board-level shielding for individual metal cases, conductive plastics
and conductive additives.
The Society of Plastics Engineers Automotive Div. announced
Oct. 19 that the plastic case radio is a finalist for its 39th-annual
Automotive Innovation Awards Competition, the oldest and largest recognition
event in the automotive and plastics industries. Winners will be announced Nov.
12 during the Automotive Innovation Awards Gala,
which will be held at Burton Manor in the suburbs of Detroit.
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