Seven 'firsts' for automotive plastics.; they trim weight and costs.

They Trim Weight and Costs

Processing and materials innovations demonstrate new ways to lighten up vehicles and cut costs of both interior and exterior auto components.

Bumpers, fascias, body panels, and instrument panels are just some of the places to look for new achievements by plastics designers and processors in making cars, light trucks, and specialty vehicles more durable and economical. Many of these new parts introduce processing innovations that cut cycle times, improve part appearance, and simplify tooling. Besides taking out weight and cost, several of these new parts give something back in higher performance than previous structures.

Here are seven examples - some already commercialized, others still in prototype - that may be trend-setters in large interior and exterior parts. These applications include new bumper systems aimed at displacing traditional metal/PP-foam structures, a new high-impact TPO that results in big weight savings on front fascia while increasing impact resistance, and an all-urethane instrument panel that dramatically reduces weight while simplifying assembly. Also, engineering plastics are making their way into "super-size" exterior body panels, made possible by thermoforming new coextruded combinations of glass-reinforced and unfilled sheet.

1 Blow Molding Beats Bumper Standard

Engineered blow molding has posed its first challenge to metal/foam bumper systems, which account for 75% of today's passenger cars built in North America. The first blow-molded bumper in the U.S. has been specified by General Motors for its 1997 Chevrolet Malibu and Oldsmobile Cutlass models. The front bumper system is molded of untilled Xenoy 1402B PC/PBT alloy from GE Plastics. It weighs about 11.7 lb - 45% lighter than the steel/PP foam system it replaces - and reduces the number of parts from 26 to 10. (GE's Xenoy was also used for the first-ever blow molded bumper system, which appeared on the 1989 Hyundai Sonata, which was made in Korea and in Canada.)

Maria Grosser, industry manager for GE Plastics' Automotive Marketing Department in Southfield, Mich., says the new bumper withstands a 5-mph impact - double the speed required by the Federal Motor Vehicle Safety Standard - and resists cracking over a temperature span from -20 F to 140 F. Grosser adds that the bumper also takes up less "package" space in the front end, providing more air flow and enabling use of a larger engine. The next phase in blow molded bumper development will be to combine the fascia and structural members into one part.

The bumper is blow molded by Carlisle Engineered Products, Lapeer, Mich., on a dual-head machine, producing two beams every 150 sec. The machine includes an automatic bolt-feeding and loading system that improves productivity and keeps operators out of the tool area. The machine is also equipped with a grinder to remove flash.

After molding, bumper beams are cooled on an indexing conveyor. An automated drilling fixture gang-drills 16 holes per beam and attaches one of five possible fascias, plus fog lamps, fascia supports, and splash shields. The drilling fixture also checks molded-in stud locations, assuring that all parts will fit on a vehicle.

2 One Part Replaces 19

A one-piece injection molded rear bumper beam for the 1997 Saturn Coupe is the first of its kind in the North American market and is the first injection molded bumper beam to exceed the FMVSS 2.5-mph performance requirement and pass a 5-mph test. The beam also passes the Insurance Institute for Highway Safety (IIHS) 5-mph rear pole test. Molded of GE Plastics' Xenoy PC/ABS alloy, the beam replaces 19 parts and is 3 lb lighter than the aluminum/PP foam system it replaces.

The beam is molded for Saturn by the Conix Div. of Magna/Decoma at the company's Nascote Industries plant in Nashville, Ill. The 14.55-lb shot is molded on a 3175-ton press. The valve-gated hot-runner mold reportedly allows filling to be quickly balanced and knit lines to be moved as needed. The tool also incorporates porous metal inserts to eliminate gas entrapment.

Process flow simulation was performed using C-Mold software to optimize flow, balance the last areas of fill, and provide uniform pressure distribution. Simulation allowed knit lines to be moved away from high-stress areas.

3 Bumper Combines Looks & Structure

A prototype injection molded rear bumper system, designed for minivans, light trucks, and sport utility vehicles is believed to be the first all-thermoplastic one-piece integration of a structural bumper beam with a fascia having a Class-A surface. Previous all-thermoplastics bumpers for passenger cars consisted of a "bonded box" configuration in which a separate injection molded structural beam and fascia are glued together. Designed by GE Plastics, the Step Pad bumper combines the ribbed structural beam with Class A fascia "ears" in one piece. A separate cover plate snaps on (without adhesive) to hide the ribs. There is also a replaceable step pad, which allows the bumper to be used as a loading platform.

The prototype, molded of Xenoy 1102 PC/PBT alloy (except for the TPO or TPU step pad), is a cost-competitive system that offers a 30-50% weight reduction over traditional steel/foam bumper systems. The new Step Pad system has a manufacturing cost range of $61.45-$75.45, compared with $63.15-$91.75 for a generic steel/foam/fascia system, according to an estimate by GE Plastics.

The prototype system weighs in at around 23.24 lb.

The system reportedly passes 3-mph impact tests on 5000-lb vehicles and 5-mph tests on 4200-lb vehicles. GE aims to demonstrate 5-mph impact on 5000-lb vehicles, according to Grosser.

The prototype part is molded by Polycon Industries, Guelph, Ont., a joint venture of Ford and Magna International. Both cover plate and beam are molded simultaneously on a press of 2500-3000 tons. (The cover plate can be molded separately, reducing tonnage requirements to around 1500 tons, says Grosser.)

Filling analysis was conducted with C-Mold software. The hot-runner part has five equally sized gates that are fired sequentially at three different times. Opening of the two valve gates that feed the edges of the smaller and thinner (3 mm) cover plate are delayed so that the material reaches the end of fill simultaneously with the larger and thicker (5 mm) beam.

4 Never Too Light Or Too Thin

A new TPO bumper fascia for the Ford Windstar minivan is the lightest ever molded in proportion to its surface area, according to Jim Krebs, product development engineer for Ford's Automotive Products Operations in Dearborn, Mich. The fascia weighs a full 5 lb, or 20%, less than the TPO fascia it replaces. The large part integrates grille and air openings and fog lamps. It rides on the only minivan to receive the five-star top frontal-crash rating of the National Highway Traffic Safety Administration.

The new Windstar fascia is injection molded of a new TPO grade, Hifax HSBM F752 from Montell North America, Wilmington, Del., which is made by the company's Catalloy process. The new material has a higher flexural modulus (200,000 psi) than the previous TPO, so that wall thickness of the part could be reduced from 3.5 mm to 2.5 mm, which saved weight without sacrificing stiffness, Krebs reports. The new material contains a small amount of filler to control mold shrinkage resulting in a specific gravity slightly higher (0.97) than the material it replaced.

According to Krebs, the new material cycles about 25% faster than typical front fascias, which generally take in 90100 sec. The new material has 15 MFR, minimizes flash, and allows a 40% reduction in mold pressure, which improves part appearance by reducing lifter line read-through, according to William Windsheif, marketing manager for Montell's Automotive Business Group in Troy, Mich. Machinery wear is also reduced due to a 30% reduction in hold pressure.

The part is molded by Polycon Industries in Guelph, Ont. Although the new fascia was slightly larger than the part it replaced, it had to run on the same 3000-ton presses, notes Bill Ferris, Polycon's Windstar program manager.

The tool was designed with sequential valve gating and six drops. Bemuse of the part's thin wall, a key issue in the tool design was keeping thickness consistent. Ferris says the wall thickness varies a maximum of 0.15 mm. C-Mold flow-analysis software was used to work out gate placement and knit lines. Extra runner drops were placed in the fog-lamp opening of the fascia in order to provide the shortest flow distance and result in a high-temperature, high-pressure knit line. Sequential valve gating helped to reduce the number of molding trials necessary before getting a production part, Ferris says.

5 All-Urethane I.P. Carries Its Own Weight

General Motors' EV1 electric passenger car is not only the first production vehicle of its type in North America but also the first on this continent with an all-polyurethane instrument panel. The light but stiff I.P. measures 56 x 36 in. and has a 4-mm structural-foam backing (1.2 specific gravity) beneath a 1-mm soft, non-reflective PUR skin. Both materials were supplied by Bayer Corp., which also supplied materials for the world's first all-PUR I.P. on the 1996 BMW 5 Series cars. GM's panel was originally molded by Delphi Interior & Lighting Systems, Warren, Mich., which has since outsourced production to Spearhead Development Technology, Inc., Walled Lake, Mich.

Although PUR is more expensive than traditional thermoplastics such as PP, urethane was chosen primarily for its high stiffness and light weight, offering advantages in assembly and performance, according to Tom Ruster, Interiors Manager of GM's Advanced Technology Projects in Troy, Mich. "The I.P. not only supports itself, but also all of the other elements attached to it," he says.

The huge one-piece panel weighs 25% less than conventional I.P.s, and reduces the number of parts from eight to just one, according to Bayer. The one-piece design eliminates trim plates and hardware and also does not use closure panels for areas such as the steering column and knee blockers. Components such as the radio and instrument displays simply snap into place. It is light enough to be installed by just one assembly-line worker and is held in place by six threaded fasteners, says Ruster.

The PUR skin reportedly offers more than 10 years' durability - three times the life of vinyl, says Ruster. Another advantage of the urethane skin is its ability to faithfully reproduce microdotting (grain within grain) so as to provide low reflectivity.

Also, Ruster notes that the cast-aluminum tooling cost 50% less than traditional I.P. injection tooling. The I.P. is molded in a two-step process. In the first step, the IP's skin is created by spraying PUR into an open mold. Once cured, the skin is placed in a separate female mold, followed by a glass mat and the Baydur 250 IMR structural-foam system, which is then compression molded. Cure time for the foam is about 3 min. The Baydur system's internal mold release reportedly provides fast demolding. Water-jet trimming of the parts is said to be relatively slow but adequate for the low production volumes of the EV1 vehicle (expected to be less than 500 this year).

A second example of a "first" polyurethane I.P. was molded by Tempress in Seattle for the new Kenworth T-2000 truck. (The I.P. on the previous generation Kenworth truck consisted of integral-skin urethane foam molded around a structural foam PC insert.) The vinyl-clad I.P., molded of a proprietary version of BASF Elastolit M50190R LD-RRIM polyurethane is the first commercial application of Tempress' proprietary T-RIM process that was developed for structural interior-trim applications. The T-RIM process uses wollastonite filler to raise the HDT above 160 F at 66 psi in wall sections of 0.25-0.50 in. and reduce the CLTE to less than 3.0 x [10.sup.5] in./in./[degrees] F. T-RIM material, which has a flexural modulus of greater than 95,000 psi, also reportedly provides exceptional stiffness-to-weight ratio: For their weight, T-RIM parts are 100% stiffer than thermoformed ABS, 700% stiffer than steel, and 75% stiffer than aluminum, says Tempress.

The four-piece Kenworth T-2000 I.P. measures over 72 in. long and 8 sq ft in area. Before molding, a vinyl skin is placed in the mold cavity, where it is held in place by vacuum. The skin adheres to the substrate without adhesive. Mold pressure for the T-RIM process is approx. 35 psi. Total system cost is reduced by incorporating backside enhancements such as molded-in bosses, grooves, and slots that facilitate assembly. To reduce secondary operations, Tempress designed a large rotating fixture for single-station drilling and assembly.

6 TPO I.P. Cover Saves Cost

What's said to be the first TPO instrument-panel cover in North America has been specified by Saturn Corp. for all of its 1997 models. The integrally colored TPO panel, which replaced a painted polycarbonate part, resulted in an overall cost saving of 30-40%, resulting from lower material cost and eliminating paint, according to Beth Wodrich, OEM account manager at D&S Plastics International, which supplied the material for the part.

The trim panel spans the width of the vehicle interior, 49.84 in. from A-pillar to A-pillar. A key material property is dimensional stability, enabling the part to withstand temperatures up to 230 [degrees] F without distortion, according to Deborah Thornton, Saturn's release engineer on the project.

The TPO grade, Sequel 1700, was developed specifically for applications requiring low coefficients of linear thermal expansion, a factor in preventing warpage. The material has a CLTE value of 2.8 x [10.sup.-5] in./in./[degrees] F, which is exceptionally low for a TPO, according to Wodrich. The material also has a relatively high flexural modulus of 295,000 psi and a specific gravity of 1.05 - much lower than other materials of comparable stiffness. As a result, the 3.75-lb part weighs 10-20% less than the one it replaced.

Wodrich says the TPO was a drop-in replacement for the polycarbonate and was able to fill the part using the original tool. The switch to TPO, which has a MFR of 14 g/10 min, enabled Saturn to reduce the number of gates from four to one.

7 'Super-Size' Thermoplastic Body Panels

Engineering-thermoplastic panels are poised to make their mark on the large vehicle market, offering properties such as high load-bearing capabilities and high stiffness-to-weight ratios. One prime example is the prototype "Concept 2000" fire rescue vehicle developed by Emergency One, Inc. of Ocala, Fla., and featured by GE Plastics at the NPE show in June. The truck's large multi-layer polycarbonate body panels - such as the 6 x 7 ft roof panel - result from the "Supersize" program at GE Plastics to develop new processing technologies for extremely large (10 sq ft or more) structural thermoplastic parts on outdoor vehicles. The panels were thermoformed on conventional equipment by Thermoform Plastics, Inc., White Bear Lake, Minn.

GE worked with sheet extruder Spartech Plastics to develop a three-layer coextrusion of two untilled Lexan polycarbonate skins and a core of 20% glass-filled PC. "The outer skin supplies the smooth surface. The glass gives the dimensional stability and stiffness. And the inner skin balances the system out," says Doug Apicella, GE's industry manager for outdoor vehicles and devices. Spartech sells the sheet under its Millennium trade name.