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Plastic Radio Case Slashes Assembly Costs

Plastic Radio Case Slashes Assembly Costs

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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