Blade System Puts Ribs Into Structural Blow Molded Parts

A novel blow molding process incorporates movable blades within the tool to create a ribbed structure for load-bearing automotive parts. Auto-parts supplier Lear Corp., Southfield, Mich., developed the technology and worked with toolmaker Fremont Plastic Molds, Fremont, Ohio, to produce a lid assembly for an award-winning cargo-management system on the 2006 Ford Escape SUV.

The process, which includes insert-molding a carpet cover, is said to offer major cost advantages over the previous fiberboard lamination process. The so-called “blade” blow molding technology eliminates multiple adhesive bonding steps, cuts secondary operations, and reduces labor. The entire cargo-management system won top honors in the Performance & Customization category at the 2005 SPE Automotive Div. Innovation awards.

 

Blades in the tool

The lid assembly is blow molded of 10% glass-filled PP on a single-head extrusion blow molder. A polyester carpet cover is hung inside the cavity on pins and clamps close around it. Nine 30-in.-long blades are hooked to an internal platen within the tool. As the mold closes around the parison, the part is partially preblown, and air cylinders actuate all nine blades simultaneously from the core half.

These 2-mm-wide blades push the plastic to the “B” side of the cavity and touch and then retract, forming an I-beam structure, according to engineering manager Eric Mansor. As the blades pull back and blowing is completed, the plastic self-seals and forms a ribbed structure. The blades leave no witness lines and create a strong inner structure that can also be grained on the back side if a reversible part is desired, says Mansor.

During the one-shot process, the polyester carpet is melt bonded to the plastic substrate. All tooling functions, including the blade activation, are controlled at the press. The entire blow molding process takes about 2.5 min.

The 25 x 34 in. part is removed from the mold and flash is trimmed in a robotic cell. In a finishing fixture, a latch is installed and a warning label is applied.

 

Load requirements are met

The lid assembly holds 530 lb and meets Ford’s tough load/deflection requirements. A previous version of the product used a labor-intensive fiberboard lamination system that required numerous secondary operations, two tools, and several adhesive bonding steps.

Lear has used the blade blow molding technique in the past three to four years for similar applications, mostly load floors. The lid assembly is the only commercial application right now, although Lear says it is examining other potential uses. The current volume level for the cargo-management system is about 110,000/yr.

While this Ford application is partially recyclable (about 90%), Lear envisions all-olefinic systems consisting of a PP carpet and PP substrate that could be 100% recyclable.