Modular systems, more resins make news at SAE '89.
Modular systems and new resins were the hot topics at February's Society of Automotive Engineers conference in Detroit. In addition to entire subassemblies and a spate of new resin systems, plastics processors and resin producers showed off some unique new blow molded parts and also predicted major advances in thermoplastic body panels.
NEW RESINS ABOUND
There was a super-abundance of new automotive resins in evidence again this year. Over 30 new and developmental resin types were introduced by some 19 different materials suppliers (see chart). What's more, fully one dozen of these product introductions represent entirely new product lines for their suppliers. And furthermore, three of these new lines are, generically speaking, entirely new materials: a polyphenylene sulfide sulfone (PPSS) resin from Phillips 66, a PBT/ASA blend from BASF, and a PPO/PS-based expandable bead foam from GE/ Huntsman.
While last year the emphasis was on materials for auto interiors, this year the bulk of new materials were once again aimed at exterior fascia and body panel markets. BASF, Dow, Du Pont, Hercules, Hoechst Celanese, ICI, Mobay, and A. Schulman all had something new to offer. ICI, long a player in polyurethanes, chose SAE '89 to introduce its new family of polyurea systems, showing three grades for fascia and body panels. Hercules presented a DCPD RIM system that's reportedly capable of producing Class-A horizontal body panels.
Du Pont and GE Plastics both reported advances with their competing thermoplastic body panel resins (see below), but polyureas from BASF, Dow, and Mobay, and now ICI, continue to mount a challenge to thermoplastic materials, thanks to new technologies that permit use of existing RIM equipment (due to slower gel times) and allows for processing at ever lower mold temperatures. Texaco, a supplier of polyurea polyols, chose SAE to introduce a new product that, if adopted by polyurea systems suppliers, would provide even further progress in that direction.
That's all not to say that interior and under-the-hood materials were neglected, however. New and developmental materials included high-heat ABS resins by Dow and Monsanto, new foams by Mobay, Huls (and GE/Huntsman), new TPE's from Shell and Teknor Apex, and new underhood resins from Occidental and ICI Fiberite, among others.
For a quick look at materials introduced at the show, see the accompanying chart, and for further descriptions of some of the new products, see New Products section.
MODULAR IP CONCEPT
GE Plastics, Pittsfield, Mass., took the wraps off its long-awaited "new concept" instrument panel (see PT, Oct. '88, p. 41), which the company is calling AIM, or Advanced Instrument Panel Module.
The module includes three structural components compression molded from GE's glass-reinforced/PP Azdel sheet and then electro-magnetic bonded into a box-beam shape that can accommodate HVAC units, ducting and other fixtures, as well as brake pedal, accelerator pedal, and steering column supports. (The plastic "assembly platform," as GE calls it, is further reinforced by a steel bar). The Azdel retainer is combined with a Noryl blow molded upper and energy-absorbing knee-bolster pad made from GE's new GECET expandable low-density PPO/ PS foam bead product (the steering column cover is also made from GECET).
Two of the three reinforced plastic components of the AIM assembly platform, a carrier and a cowl panel, are molded from standard Azdel sheet (PP with 40% random glass reinforcement). However, GE proposes molding the cross-car brace from a "second-generation" Azdel that includes unidirectional fiber placed between plies of continuous strand mat, upping the flexural modulus of the composite sheet from about 800,000 psi to about 1.4 million psi. (This Azdel version reportedly has 2 1/2 times the tensile strength of the random fiber product at no increase in density).
GE sources say an even stronger unidirectional version of Azdel, with a 2 million psi modulus (at about 60% glass loading), should be available later this year. This newest material could permit designers to drop the metal cross-car-bar from the AIM concept or let them make bumper beams that don't require shock-absorber backups. A prototype bumper beam made from unidirectional Azdel also was on display at SAE.
GECET low-density foam was the result of a two-year joint development program between GE Plastics and Huntsman Chemical Corp. Huntsman is manufacturing the foam using GE's PPO resin, and GE is marketing the product. GECET is processed via steam chest molding, which is similar to molding of expandable polystyrene, but at higher temperature and pressure. Pentane-saturated PPO resin-based beads are heated to the desired density, then blown into a tool and fused using high-temperature steam. The process is said to be able to produce parts ranging in density from 3-15 lb/cu ft, and the resins can be molded into 2-3 in. thick sections without sink marks common to some injection molded parts. Currently, three grades of the PPO/PS blend resin are available, corresponding to three different maximum end-use temperatures ranging from 221F to 250F.
NO PROTOTYPES YET
Although the AIM concept was unveiled with considerable enthusiasm by GE Plastics, there are currently no plans to produce any prototypes. A key GE engineer conceded that SRIM IP retainers (Dow Chemical and Arco Chemical both have development programs on these, see PT, Oct. '88, p. 37), using polyurethane resins, can achieve a similar box beam concept in a one-piece construction. However, GE officials stressed the "standardization" of the AIM system, which is designed to be pre-assembled and installed robotically through the windshield opening, and which can accommodate several different blow molded upper panels styles (the uppers carry injection molded instrument clusters). However, automated production of the Azdel components was not included as part of a proposed nine-station automated production system for AIM.
GE officials told PLASTICS TECHNOLOGY that the AIM concept would have no trouble meetings heat deflection test standard for IP retailers (no more than 0.0001 in deflection at 220 F and 264 psi is permitted, and this threshold may be increased to 250 F), despite the relatively low transition point of PP. Some observer had expected the AIM concept to involve a one-piece blow molded IP, but GE engineers indicated that blow molding of IP retainers thus far has not been proven feasible, primarily due to the complexity of the part. (CIRCLE 100)
NEW BLOW MOLDED FUEL TANK
Hedwin Corp., W. Bloomfield, Mich., exhibited the first blow molded HDPE fuel tank to be mounted forward of the driving axle in a U.S. car. Developed jointly with Ford Motor Co., the HDPE tank for 1989 Thunderbird/Cougar models is being produced at a rate of 400,000/yr at Hedwin's South Bend, Ind., plant. The unique design of the blow molded part permits the drive shaft to pass through the middle of the fuel tank (see photo, p. 23).
Hedwin is producing the 21-lb tanks in 2 min, 50 sec cycles on Bekum BAT 1000 blow molding machines, each equipped with a 165-ton clamp and a Moog Inc. programmable wall-thickness distribution system (PWDS). The PWDS is a radial parison programming system with flexible die rings (see PT, May '87, p. 68) that enables Hedwin to mold parts with unequal circumferential wall thicknesses. The wall thicknesses in the T-Bird tank vary from 2.8 to 4.5 mm.
The PWDS system features servohydraulic, closed-loop die gap control with adjustable mandrel/die gap profiling and programmable ovalization. The flexible die rings are deformed according to the profile set by a programmer in a manner similar to that of an axial wall-thickness control system. Two servoactuators with integral position transducers are attached directly to the die ring to affect ovalization - effectively the rings can be pushed or pulled separately from either side during the shot. The stroke of the PWDS actuators can be set separately via the die gap and each actuator is controlled by its own parison programming unit.
Deformation of the flexible die ring can be adjusted using hands tools, without removal from the head. "The system offers an infinite number of programming possibilities, and the shape of the mandrel can be adjusted by moving about a dozen bolt and screw attachments with a wrench. Prior to this, you had to take it out and cut it to shape," says Michael E. Kanouse, assistant manager of automotive operations at Hedwin.
The Ford tanks are being molded at about 400 F. After molding and in-mold flourination, the tanks go through an automated finishing line. Holes are cut for fittings, and a dual heater heats both the surface of the fitting and the surface of the tank to about 380 degrees. The fittings are then pressed onto the tank.
Before specification by Ford, the HDPE fuel tanks were subjected to 61 consecutive drop tests from 20 ft at -40 F. "We needed the (Moog) controls not only to control the thickness and the overall weight of the tank, but to give us the kind of distribution needed to pass these performance tests," says Kanouse.
NEW TEST FOR BARRIER MATERIAL
Du Pont Co., Wilmington, Del., announced at SAE the first U.S. licensee for its Selar RB nylon barrier system for blow molded HDPE automotive fuel tanks. Kuhlman Plastics, Bronson, Mich., currently the largest producer of blow molded fuel tanks, will pay Du Pont an unspecified licensing fee and per-tank royalty for use of the Selar laminar barrier. Kuhlman currently uses post-mold sulfonation as a permeation barrier on its tanks (see PT, Jan. '89, p. 27). Kuhlman and Du Pont say the first U.S. cars with tanks containing Selar laminar barriers will be 1991 models, making it likely that the first Selar application will be on GM's Saturn car. GM has previously indicated that Kuhlman will mold the fuel tanks for Saturn, which currently is set to debut as a 1991 model. (CIRCLE 101)
Du Pont also introduced at SAE a new non-destructive test that makes use of spectral analysis and ultrasonics to measure the barrier effectiveness of HDPE fuel tanks made with Selar RB. The test, which can be applied to each tank as it comes off the production line, uses a fiber optic probe to analyze barrier resin concentrations and geometric formations within the container wall. Probe data is correlated by computer with permeability values based on varying resin concentrations, wall thicknesses and processing conditions. "The computer matches what it observes with the data in its memory and predicts the permeation of the container. Testing to date indicates an accuracy of 90% of the actual barrier value," says Richard Bell, development engineer for engineering materials at Du Pont. In addition, ultrasonic testing was used to determine the presence of laminar barrier platelets.
TP OVERCOMES CTE PROBLEM
Last year at this time, it was widely anticipated that thermoplastics would make major inroads in automotive exterior body panels, particularly in so-called "friendly fender" applications. However, low-volume TP fender programs on the Buick LeSabre and Reatta models (both using GE's Noryl GTX PPO/nylon 910 resin) reportedly experienced difficulty overcoming thermal expansion, and required extensive secondary finishing operations to overcome weld or knit lines. General Motors Corp. opted for polyurethane RIM fenders on its new A-van and an expected announcement of thermoplastic panels for the Saturn car thus far has not materialized.
Last summer, GE said it had a new continuous film gating technique (developed jointly with GM's B-O-C Group; a tool with six tabgates and 15 pinpoint tunnels gates had been used in the original Buick program) for the GTX panels that eliminated the weld and knit-line problem, and it announced that injection molded Noryl GTX 910 fenders would be used on the 1989 Cadillac De Ville and Fleetwood C-body models (see PT, Aug. '88, p. 27). In a technical paper at SAE on the development of the TP fenders for Cadillac, B-O-C Flint Automotive Div. engineer Gerald L. Whitacre revealed that during the LeSabre program a special "slip fastener" system was developed by GM to permit the Noryl fenders to "grow" in two directions during the heat cycle.
The LeSabre fenders exhibited a tendency to grow uniformly from the middle of the panel toward the front and rear. "After many attempts to artificially control the growth phenomenon, it was decided that it's not nice to fool Mother Nature," Whitacre says.
The fenders upper mounting bracket was retained to the motor compartment side rails with a series of spring tension fasteners; this kept the fender in its relative position to the car body, but permitted the 50-in. long panel to expand about 16 mm and then return to its original shape after cooling.
GM also had to adjust its prime coat baking temperature to set the shrinkage of the Noryl resin properly. "The shrink rate of the material is consistent at 0.017 in./in., but full substrate shrink is not achieved until the material is subjected to 280 F. This fact was not initially known, and the learning curve taught us we needed to bake the prime coat at 30 degrees higher than that required to cure the paint to set the shrink at a predictable rate," says Whitacre.
The LeSabre fenders reverted to a steel back-up after about 5000 cars were fitted with the plastic part, but when Reatta successfully ran up to 20,000 Noryl fenders/yr, GM gave the green light on the Cadillac program, according to Whitacre.
MORE TP PANELS PREDICTED
At SAE, GE officials said more than 40,000 Cadillac fenders have been molded without any recurrence of the thermal expansion problem (the resin is said to withstand 375 F paint ovens), and they expressed optimism that the program would exceed 200,000 pts/yr, making it the first successful high-volume thermoplastic fender application. GE also says it has "commitments" for five additional TP fender programs that will come on line between now and 1992.
The Cadillac C-bodies also feature rear fender extensions molded from GE's Lomod 1320 elastomer, said to exhibit superior paint-bake capability over RIM resins, and side claddings of Xenoy 1101. Tooling for the Noryl fenders cost about $1.2 million, compared to an estimated $4.6 million for comparable sheet metal tooling. According to Whitacre, thermoplastics are now candidates for door outer skins, and non-structural quarter panels and rocker panels. He suggested that development work needs to be done in paint systems with lower temperature requirements, resins lower CTE's and in assembly systems reprocessing, which would allow plastic body panels to avoid unnecessary steps in processing.
Du Pont, meanwhile, said at SAE that its Bexloy K reinforced thermoplastic polyester material is now the final candidate in a Chrysler project to study E-coat-capable plastic (Apr. '88. p. 122), and Bexloy panels are undergoing road tests on Chrysler vehicles.
HOT-AIR BONDING GETS A BOOST
High-speed bonding of SMC parts using hot-air curing of adhesives got a positive review in a paper presented by GenCorp Automotive, Marion, III. Joseph Wilks and Vinod Arora of GenCorp's Materials Technology Group reported that 20-sec cycle times were achieved with a high-velocity hot-air impingement (HVHAI) system, with excellent fiber tear and no bond line read-through on the Class A surface.
Although the cost of an HVHAI fixture is expected to be equivalent to that of a conventional conduction heating unit, Wilks says that since fewer HVHAI fixtures would be required to do the same job, the per-part cost could be lowered from about $1.25 to about 62 [cent]. "The HVHAI system is much more than efficient as the time constant of the system is much smaller; the system responds almost instantaneously to the changes in the operating conditions and initials heatups is no more than 20 min," Wilks says.
GenCorp found that the hot-air system requires only about a third of the energy that is used in a conventional bonding system, and greater efficiency is achieved because the part is only heated at the bonding surface. Repeatability of the process was proven, with the temperature profile over a period of 2 min. varying by only 5 [degrees F] for 10 trial runs under the same conditions.
GenCorp set up a scale model experimental impingement heat transfer apparatus consisting of multiple jets connected to a compressed air line via an air dryer, filter and an electrical heater. Air from the heater passes into a compact distributor section, equipped with flow control valves and flow meters. The flow is then divided into 16 streams that enter both ends of eight tubes. Four tubes were located above and four tubes below the four bond lines on the 14 x 14 in flat panel and 12 x 4 in hat section test specimens used in the experiment. The 1/2-in diam. air tubes have holes 0.64 mm through which the hot air impinges on the part.
The heat transfer coefficient of the hot-air system was affected by several factors, including the ratio of open area to the bond area, ratio of the noozle distance from the part of the noozle diameter, and the part thickness. GenCorp determined that a high heat transfer coefficient requires high impingement velocities, with relatively large air quantities set in motion. To avoid an unnecessary load on compressor and circulation duct-work a compact air supply manifold and effective energy transfer zone has to be designed to minimize pressure losses and cross currents, Wilks says.
BLOW MOLDED BUMPER IS SHOWN
Autopolymer Design Inc., the joint venture between GE Plastics and Masco Industries in Rochester Hills, Mich., exhibited the blow molded bumper system it developed for the 1989 Hyundai Sonata. Produced at a rate of about 150,000 bumpers/yr in-house by Hyundai in South Korea and also at ABC Group in Canada, the bumper system consists of a hollow, blow-molded beam and an injection molded fascia, both made from GE's Xenoy polycarbonate/ polyester blend. The total weight of the system is 45 lb, compared to 85 lb for the design it replaced.
The bumper system is attached directly to the face of the car without any shock absorber system. The blow molded component, which consists of three hollow lobes that flex upon impact (the bumper system has passed 5-mph impact tests), is attached to the fascia via heat stakes, adhesives and ultrasonic welding (CIRCLE 104)
Du Pont also touted a new bumper application at SAE. The company said its Hytrel polyester elastomer is being used as an energy-management unit on the bumper system of the 1989 Dodge Daytona. A sleeve of Hytrel slides on a steel tube upon bumper impact. Two of the Hytrel sleeves are installed behind the front and rear bumpers and are fastened to the vehicle's frame by metal brackets. (CIRCLE 105)
ROCKWELL INTO MODULAR, LCM
Rockwell International highlighted two SMC hood-and-fender assemblies for heavy trucks as part of a major thrust into modular vehicle systems outlined at SAE by William F. Rebone, president of Rockwell's Light Vehicle Components unit. The firm has nine modular assembly programs under way (in both metal and plastic components), and is actively seeking more modular work, including an SMC roof assembly, Rebone says.
Rockwell began making a three-panel, 5.6-ft-long, 7.8-ft-wide hood-and-fender assembly for the new Mack CH-600 truck in January, and last year started manufacturing a similar three-piece system for a Freightliner cab. Both programs are being undertaken at Rockwell's Centralia, Ill., composites center, and both involve the use of automated bonding systems.
Also on display at the Rockwell booth was a modular door assembly, with an SMC outer skin and an SMC structural inner panel bonded by a polyester compound. The door assembly includes Rockwell's proprietary door system mechanism module (which encapsulates all mechanical components for the door and its window). Rockwell also exhibited its 6-ft-long SMC Sportside pickup truck fender (for Chevrolet and GMC) that incorporates fender, fender well, rear quarter panel, gas filler pipe access and tail lamp openings in one piece.
When asked if the push toward modular systems and parts consolidation would lead Rockwell into LCM processes like resin transfer molding and structural RIM, Rebone revealed that Rockwell is in the process of acquiring an LCM molder. [Tabular Data Omitted]
PHOTO : Among Mobay's offerings at the show were a new RIM polyurea system, Bayflex 120, and a high-performance SRIM polyurethane system, Baydur STR-400. Bayflex 120 is said to offer dramatic productivity improvements: the molding speed for producing fron fascia prototypes (top) translated into a 40% productivity gain. Baydur STR-400 is designed for high-strength applications like bumper beams (bottom).
PHOTO : GE Plastics' Advanced Instrument Panel Module (far right) features three structural components compression molded from Azdel glass/PP sheet, a metal cross-car support bar, a GECET foam knee bolster, and a blow molded Noryl upper panel (all shown in near photo).
PHOTO : Hedwin Corp. used a Moog Inc. programmable wall-thickness distribution system to blow mold this HDPE fuel tank for 1989 Thunderbird and Cougar models. The tank is located forward of the rear axle and is shaped to fit around the driveshaft.