Bottle blow molding applied to car headrests

To produce no-sew automotive headrests, a blow moulding machine builder redesigned molds, changed material formulation and ran 40,000 parts on lab machine to 'fast track' production.

What do milk bottles and automotive headrests have in common? They are both produced on Uniloy Milacron reciprocating blow molding machines.

While Uniloy invented the process for blow molding plastics milk bottles back in 1966, the automotive headrests were a recent application challenge.

Uniloy Milacron found its expertise at turnkey process engineering put to the test in 2004 when a leading tier one supplier of interiors to the automotive industry approached it about blow-molding headrests for a top-selling cross-over vehicle.

"We got the call after a different group failed to produce headrests to the customer's requirements," said Dave Skala, vice president-general manager, Uniloy Milacron North America.

"We were given the mold and asked to make it work.

Within a day we were producing good parts with that mold." The interiors company conceived the blow molded design to save on costs, particularly for labor, over traditional cut-and-stitch headrests.

"The customer is saving about US$3.50 per headrest, US$7 per vehicle," said Skala.

The concept called for the headrest shape to be blow molded from a flexible vinyl, then filled with foam for shape and shock absorption in a collision.

"The blow-molded vinyl provides a seamless, one-piece outer covering, eliminating any need for material cutting and sewing," noted Skala.

"The headrests are molded in several different colors to coordinate with interior schemes for the vehicle." Uniloy's engineering staff at its Tecumseh, Michigan, USA, headquarters worked with the customer to improve the mold design, then modified the mold.

Sample headrests were molded for color and texture approval.

The material was reformulated with the resin maker to get the right colors and gloss.

The material is one used mainly for injection molding, so the maker couldn't provide a shrink rate for blow molding.

Uniloy engineers had to work out the shrinkage and adjust the mold dimensions.

Overall, it took Uniloy only about 25-30 days to do the engineering and get production approval, Skala said.

A supplier of integrated automotive cockpits, the customer recognized that blow molding was not a core competency.

At its request, Uniloy helped in recruiting a processor with the capabilities to produce and deliver the parts on demanding production schedules.

To fast-track production, Uniloy ran 40,000 parts in six weeks on a Tecumseh test lab machine while a Uniloy UR2X24-8 reciprocating blow molding machine was being built at Milacron's Batavia, Ohio plant for the selected supplier's production facility in Mexico.

Plant personnel were brought to Tecumseh for hands-on training during the production run.

"We are not a commercial molder," stressed Skala, "But were able to use our Uniloy 350R2 lab machine to meet the interim need for production headrests." The run also gave Uniloy an opportunity to tweak the process.

For example, it added a drier to the line.

The material is not rated as hydroscopic, he notes, but Uniloy found it runs best at a precisely controlled temperature and dew point.

Each headrest requires a 3 lb shot.

Two headrests are produced per molding cycle.

Steel mounting posts for the headrests are inserted into the flexible vinyl envelope, then energy-absorbing foam is injected into the cavity.

Two different headrest configurations are produced - one for the North American market and another for vehicles destined for sale in Europe.

Uniloy is working with the interiors supplier on headrest projects for two upcoming vehicle models, reported Skala.

"This new process offers some vital benefits in terms of cost economies and lean manufacturing efficiencies," he stated.

"We think the process should be easily adaptable to other products and industries.

It will be interesting to see what product designers come up with as they become familiar with the concept.".

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