In an assembly tour-de-force, mechanical engineers at Delphi Automotivesignificantly reduced assembly time through the development of an injectionmolded plastic radio housing.

"The biggest advantage is the reduction in weight. There isa 1.2  pound, or 22 percent, weightsavings," says Vineet Gupta, who led the engineering team that developed thetechnology.

The new radio case is being used first on the mid-year modelof the GM Tahoe, but will be part of all premium navigation and entertainmentsystems, referred to internally at Delphi asthe "black tie" systems.

The plastic case replaces a formed sheet metal caseassembled with screws and cooled with fans. The new plastic case achievesrequired EMI and RFI shielding by completely enclosing electronics with a mesh Faraday cage that is insertmolded. Faraday cages are named for English scientist Michael Faraday, whoinvented them in 1836.

For a radio, Faraday cages shield external electromagneticradiation if the conductor is thick enough and the holes that create the meshare significantly smaller than the radiation's wavelength. Electrical chargeswithin the cage's conducting material will redistribute themselves so as tocancel the field's effects in the cage's interior. This phenomenon is alsoemployed to protect electronic equipment from lightning strikes and otherelectrostatic discharges.

A big part of the Delphitrick is how the cage is placed in a mold cavity, and then held in the rightposition while plastic is injected at high pressures. Much of the specifics ofthe 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 themesh into the mold requires innovative magnetic tooling and the use of robotsto transfer the formed mesh into the mold," says Gupta.

Gupta says the new plastic case provides even bettershielding than the previously used metal cases. There are lower emissions overa range of 150 Hz to 430 MHz. OEMs are seeking improved electromagneticinterference to avoid any internal cross talk, such as interference withelectronic engine controls.

The system cost to assemble the radio is reduced byone-third with the new technology. Gupta declined to provide a specific dollarsavings per radio. Twenty-nine screws are completely eliminated. Use ofinjection molding allowed incorporation of design features not possible withthe sheet metal case. For example, Delphidesigned slide lock and snap lock features that allow fast snap assembly. Othermechanical features are also integrated into the design.

Mechanical part reduction includes ESD grounding clips,fasteners and main board grounding. Assembly parts eliminated included a separateassembly fixture and use of torque feedback screwdrivers.

As a result, the case is also more rigid, reducing rattlenoises. "There's also a significant increase in natural frequency," says Gupta.Natural frequency is the frequency at which a system naturally vibrates once ithas been set into motion. Vibration testing on the new plastic case radioshowed a 25 percent increase in natural frequency.

Recycled Plastic

Delphi is used reprocessedplastic to make the case. MRC Polymers of Chicagosupplies 16 percent glass-filled PC/ABS for the part, which is produced by AmityMold of Tipp City, OH. The plastic comes from postindustrial and post consumer sources. The PC/ABS blend had to be optimized tomeet environmental requirements and reduce warpage.

The design of the plastic case lowered the internaltemperature. One reason for the improved thermal management is insulation ofthe heat sink from the interior of the radio. The cooling fan was eliminateddue to the insulative properties of the plastic. As a result, electric currentused is also reduced, improving vehicle mileage.

Other Advantages Include:

·      The weight of the structural support for theradio can also be reduced;

·      Safety is improved because injuries from metalcuts are reduced. Protective gloves are not required for assembly;

·      Condensation is eliminated during temperaturecycling. The reason is simple - dewpoint temperature is not achieved so nomoisture drops on the circuit board; and

·      There's also lower dust intrusion duringstandard testing.

Gupta says Delphi will alsobe used for "interior black boxes" for Asian OEMs. "It's going to be usedacross the board at Delphi ultimately," hesays. "Wherever we're currently using sheet metal we are going to use thistechnology. It is quite broad based. We can use that competitive advantage forall of our product lines."

Widespread Application

Gupta says it applies to any automotive interior electronicpackaging. The same advantages apply:  partand weight reductions, integration of mechanical and electrical features, andimproved air cooling with no loss of shielding. Gupta says Delphiwill also explore non-automotive consumer applications.

The Delphi plastic radiocase could replace a wide range of shielding approaches besides sheet metalcases. These include die cast metal cases, conductive coatings (paints andplating), board-level shielding for individual metal cases, conductive plasticsand conductive additives.

The Society of Plastics Engineers Automotive Div. announcedOct. 19 that the plastic case radio is a finalist for its 39th-annualAutomotive Innovation Awards Competition, the oldest and largest recognitionevent 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.