The ins and outs of automotive materials

DN Staff

October 7, 1996

10 Min Read
The ins and outs of automotive materials

No matter whereyou examine today's automotive design--inside or out--things are changing for the better. Ask the experts and you will find that many of these innovations relate to materials. More important, most of these material challenges don't apply to "skin deep" cosmetics--something employed only to differentiate the design of one automaker's line from the competition, although the end result might just do that.

Basically, the material breakthroughs address such critical design challenges as lowering weight and cost, improving durability, reducing maintenance, and priming future designs for tougher air-quality, safety, and environmental regulations. You will find these material innovations everywhere--under the hood; in the instrument panel; on interior trim; and in body panels, bumpers, and facia. Less apparent, but perhaps even more challenging, are components that most people don't see--seals, lamp housings, switches, and latches, to name a few.

Here's a look at some of the latest challenges that materials have tackled, as well as areas where designers might expect materials to solve even more demanding problems in the near future.

Instruments of life. With the advent of airbags, instrument panels (IPs) have become the focus of design challenges.

For instance, how do you assure performance while making a passenger airbag door virtually invisible? Can you cut cost and weight from a glove box and still meet energy absorption and fit and finish requirements? Is it possible to minimize squeaks and rattles, while keeping the overall instrument-panel system affordable?

Those were the challenges faced by Chrysler Corp.'s Minivan Platform Engineering group when it began development of the instrument panel for the new minivan. "We met every challenge," says Fred Daris, supervisor of re-straint and steering control for the group.

The result is an IP with a passenger airbag door that is virtually invisible in the assembled vehicle, and a glove box that combines a honeycomb "ribbed" construction for energy absorption with a one-time living hinge on the door. The molder for the retainer and the glove box is Textron Automotive Co., with Dow Automotive supplying the substrate material--Pulse(R) PC/ABS resin.

"PC/ABS resin was the logical choice for the substrate due to its excellent ductility," reports Susan Mileski, program manager for instrument panels at Dow Automotive. "Steel use would need to be extremely limited in terms of meeting customers' abuse criteria for this application," adds Randy Ryszewski, the group's manager of restraint and steering control. "There was too much denting and sharp edges."

Concurrently with substrate development, Textron worked on an insert-molded process to create a seamless top pad that would allow the airbag to deploy, yet have a vinyl surface that would create no large projectiles on impact. The resulting proprietary process was used for the first time on the minivan.

Instrumental redesign. Environmental considerations also come into play when designing instrument panels. Recently, GE Plastics, Pittsfield, MA, awarded the University of Rhode Island's Industrial and Manufacturing Engineering (IME) Department a contract for redesign studies of two high-volume IPs. The goal: to explore the potential of advanced thermoplastics that are environmentally feasible, highly manufacturable, and cost-effective.

The IME/GE research will use the latest design for assembly, disassembly and environment (DFA/D/E) analyses to quantify the ability of certain thermoplastics to meet the environmental challenges. The project's first objective: to evaluate the quality of IP designs from the mid-1980s and mid-1990s for end-of-life disassembly and material recovery, or safe disposal. Following this segment, IME will work with automotive industrial designers to develop future concepts for IP designs that incorporate the study's results.

"We picked the instrument panel because it represents a large-scale automotive system with a significant volume of thermoplastic parts of high recycling value," explains Greg Jones, GE Plastics' manager of design development. "Comparing two instrument panels also allows us to make judgments about the changes in past design practices on disassembly and disposal costs. If the benefits are as far reaching as we think, then accelerating the use of engineered thermoplastic designs will justify their material cost, both from a design and recycling perspective."

Impacting design. Such designs also can get an assist with a new data acquisition system that measures how automobile IPs respond to high-speed impacts. ARCO Chemical Co., Newtown Square, PA, in conjunction with VI Engineering, Farmington Hills, MI, de-signed the system.

PC-based data ac-quisition hardware and LabVIEW graphical instrumentation software from Na-tional Instruments, Austin, TX, form the base system. The high-frequency analysis expands the scope of the data captured in high-speed crashes, such as airbag deployment and knee intrusions, which previously generated only crash-test-dummy and head-impact data.

The system generates actual component pressure, stress, and strain data during the test, which are then used to correlate to FEA simulations of the test. Once a successful correlation is made, the simulations help optimize the system so that the results have a high degree of confidence. Once the IP system has been modeled, the loading profile of the system is generated.

Now fog free. If it's a low-outgassing, no-fogging, environmentally friendly material you require for instrument panels, check out four new PoronTM cellular urethane materials produced by Rogers Corp.'s High Performance Elastomers Div., Rogers, CT. The materials are also flame retardant.

"The new formulation meets the requirements of both General Motors and the Ford world specifications on fogging," says Dave Belden, the Poron Materials Unit's marketing manager. They are part of Rogers' overall revamping of its product offering with fewer material grades, making it simpler for customers to order and inventory products.

The materials have excellent compression set resistance, Belden adds. In addition to IPs, they should prove ideal for seals, cup-holder padding, glass mounts, gaskets, airbag devices, vibration isolators, and gas-tank mounting pads.

Closing the gap. Ford turned to a thermoplastic polyurethane (TPU) to reduce lamp housing costs 20% and cut taillight installation time in the Mercury Sable. The savings came from a new gap improvement part (GIMP) injection molded onto the tail-lamp housing. The GIMP, which fills in the gap between the lamp housing and the car's sheet metal, consists of Texin(R) 985-U TPU from Bayer's Polymers Div., Pittsburgh.

The challenges involved finding a material with the right blend of properties. Ford needed a UV-resistant material that was pliable so the GIMP would conform to the housing and sheet metal. But the material couldn't be too soft or it wouldn't retain a constant shape necessary for aesthetics. The rubber-like TPU offers the processing efficiency of thermoplastic resins, yet has the physical properties of elastomers.

Ford molds the tail-lamp housing and GIMP using family molds in a two-station process. The first station molds just the ABS lamp housing, with the GIMP cavity closed. The tool then moves to the second station, where the GIMP cavity is opened and the TPU shot. Combined cycle time for both components: about 60 seconds.

A switch for the better. High heat deflection temperature, low moisture absorption, and dimensional stability. Those were the key reasons that GMC and Chevrolet selected a 33% glass-filled polyphthalamide (PPA) for headlamp switches in C/K full-size trucks. The resin: Amodel(R) AF-1133 V-O grade from Amoco Polymers, Alpharetta, GA.

The switches contain precision insert-molded contact elements made by Acro-Matics Plastics Corp., Leominster, MA. In producing the components, Acro-Matics uses a valve-gated hot runner system for maximum efficiency. "Cycle time is optimized and waste material minimized," says George Doumani, the firm's vice president for sales and engineering.

Resting easier. Every time the user adjusts the head rest in a seat, the latch is subjected to friction wear and impact, which is repeated over many cycles of operation. However, owners of Chrysler vehicles don't face this problem. Adjusting latches made with a glass-fiber-reinforced, heat-stabilized, toughened nylon makes changing head-rest positions a breeze.

"Thermotuf VF HS from LNP Engineering Plastics (Exton, PA) gives the latch the high impact strength needed to withstand being pushed from position to position," says Sal Dorsa, senior plastics engineer at Thomson Industries, the firm that makes the latches. "The impact strength of the material gave us the toughness we needed to be able to perform within the range of temperatures (-40 to 250F) expected in this application. It also gave us the temperature resistance that would maintain the integrity of the part for hardness and durability."

Dorsa adds: "The combination of a stamped metal latch overmolded with Thermotuf VF HS allows greater design freedom, while maintaining stiffness."

Grand Prix seal. When Grand Prix drivers Mika Hakkinen and David Coultard accelerate through corners and thunder down straightaways at 214 mph, the powerful Mercedes-Benz V-10 Phase III engines in their McLaren car approach engine speeds of over 16,000 rpm. Pneumatically operated valves on the 700-plus-hp engine respond to these demands, opening and shutting up to 135 times per second.

IImor Engineering, Northampton, England, designers and builders of F1 and Indy race engines, contacted Advanced Products, North Haven, CT, to help develop a pneumatic seal that would thrive in the engine's punishing environment. The solution: a filled polytetrafluoroethylene (PTFE) spring-energized, 5-mm, high-performance seal. The PTFE polymer material offers wear, temperature, and pressure resistance, and the seal is spring-energized for resiliency and fatigue resistance.

Endurance tests verified a life of four to six hours for the PTFE seals. Changed after each race, which lasts up to 70 laps or about two hours, the seals have performed in the brutal and demanding environment of the Grand Prix circuit without a single failure.

Tire technology. Not even tires escape the materials revolution. For example, whenever a flat tire could spell danger, a tire insert made with an engineering thermoplastic elastomer (TPE) adds security.

"A vehicle fitted with our 'composite run-flat' (CRF) insert can travel 30 miles or more without air in one or more tires," says Greg Marcussen, product engineer at Hutchinson Industries, Trenton, NJ.

Hutchinson engineers the CRF to fit into the plenum space of a conventional tubeless tire mounted on a drop-center wheel. The device consists of two semi-circular components bolted together. The parts are injection molded from a proprietary compound containing Hytrel from DuPont Engineering Polymers, Wilmington, DE.

"The compound has structural strength to support vehicle weight under run-flat conditions, and it resists temperatures of 250F or more generated during run-flat and braking conditions," Marcussen reports.

Springless seats. What will the car seat of the future look like? It won't have foam or springs. It will be about two inches thick, not five inches, and will weigh 10 lbs less. And it will be recyclable.

That's how Hoechst Celanese Corp., Summit, NJ, and Milliken & Co., Spartanburg, SC, picture the next-generation seat. And, they predict, it will be made from a new self-supporting fabric called Gemstone, which they developed. The 360-de-gree stretch of the fabric permits an even weight distribution for comfort, while reducing the weight and size of the seat.

The Gemstone family of structural seating fabrics includes Amber Flex, a warp knit fabric; Crystal Flex, a knit fabric with a weft insertion; and Emerald Flex, a woven fabric. Each offers a distinct set of properties to meet specific seating needs.

What will the future hold? Look for more plastic materials to replace metal parts as the need to make vehicles lighter and more energy efficient expands. Also, plastics' flexibility will enable engineers to further shorten the design cycle. And more plastics producers will join forces to make resins more compatible for recycling efficiency. The result: longer-lasting, less gas-guzzling, more environmentally friendly vehicles with a dazzling array of special components designed to keep the customer coming back for more.

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