Defense engineers target Balkan war, peace efforts
For designers of military products, war is both the ultimate proving ground and consummate design driver. Already, NATO forces in Bosnia have benefited from technologies born of needs defined in such recent events as the Gulf War and the Balkan conflict itself.
For NATO troops, limited-engagement actions create their own special headaches. Operating as a peace force under the microscopic lens of television, they must greatly limit collateral damage to civilian targets. Surveillance of unfamiliar territory, in poor weather, with ever changing borders, proves difficult. And countries willing to play policeman are often less willing to tolerate the loss of even one soldier.
To address each of these restrictions, engineers have developed new devices that locate downed pilots, warn of mine fields or borders, transform dumb bombs into smart bombs, and provide superior surveillance. Some are seeing first action in Bosnia, others will be out in a few years.
Bird's eye view. Take Eagle Vision and Powerscene. The world's first lightweight, deployable ground station for receiving commercial satellite imagery, Eagle Vision hatched from problems identified in the Gulf War. First used over Bosnia, it downlinks 180km-wide by 2,500k-long images from French SPOT satellites, and processes them for use as complex 3-D charts. It took five months to acquire and process graphics of Kuwait in 1990. Eagle Vision provided forces flying over Sarajevo with imagery in 21 days.
Prime contractor Matra Cap Systemes (V‚lizy, France) builds the ground station. Datron/Transco (Simi Valley, CA) supplies the 3.6-m antenna. A separate data processing van from ERIM (Ann Arbor, MI) mixes the SPOT satellite photos with Landsat or other image sources and overlays them on a digital terrain database to yield true 3-D. All of the equipment fits within a C-130 transport for deployment anywhere in the world.
Powerscene, a complimentary technology, works like an advanced video game to allow pilots to fly virtual missions on a computer prior to the actual mission. Three-D images from Eagle Vision or other sources can be put together and displayed on a Silicon Graphics Indigo workstation. An aircraft-like control stick and throttle maneuver the user through the scrolling virtual world, complete with heads-up display and instrument readouts. "You can attack targets from any altitude, any direction," says Lt. Col. James "Snake" Clark, USAF executive assistant for modeling and simulation. "It gives a déjà vu feeling of flying the actual mission."
Recently, peace negotiators holed up at Wright Patterson AFB in Dayton, OH, used Powerscene to help define territorial boundaries. "With Powerscene, there were no arguments between the two sides about where things were," says Clark. "It was very critical when deciding safe passage routes into some villages."
A better Predator. Not all of NATO's new surveillance capabilities originate in space. Predator, a medium altitude UAV (Unmanned Aerial Vehicle) built by General Atomics (GA), San Diego, CA, is virtually silent and invisible to the naked eye from as little as 2 mi. Deployed over Bosnia as an R&D exercise, it uses electro-optical sensors and a Westinghouse synthetic aperture radar for unequaled target identification.
To improve its infrared capabilities, GA contracted DigiVision (San Diego) to supply its proprietary V-LACE™ digital video enhancement processor. "It was an experiment to see if we could enhance the video quality and deal with the haze over (Bosnia)," says a GA engineer.
First developed for medical imaging, V-LACE uses patented algorithms to emphasize high frequency information and improve contrast in real time. It also helps prevent loss of high-frequency data when Predator flies beyond line of sight and has to transmit compressed signals via satellite. Does it work? "In my opinion, a kindergartner could see the difference," says the GA engineer.
Smart bombs, stupid. So-called "smart" weapons are especially critical in a limited-engagement conflict to avoid collateral damage. But the current inventory of laser-guided missiles and bombs ran into a problem when the sky over Bosnia turned grey: They were grounded.
To address this type of situation, the Air Force awarded in October the JDAM (Joint Direct Attack Munition) contract to McDonnell Douglas (St. Louis, MO). "It turns dumb bombs into smart bombs," says Lt. Col. Jim McClendon, USAF spokesman.
A high-tech replacement for the tail section of current free-fall 1,000- and 2,000-lb munitions, JDAM adds GPS, ring-laser Inertial Navigation (INS), a guidance computer, and actuator-driven, moveable tail fins to steer the bombs with 13m target accuracy, in all weather, from as far as 20 miles away when dropped from 40,000 ft.
Advantages: Autonomous guidance means pilots can launch-and-leave; modifying existing bombs means easier certification; JDAM costs just $18,000 ea., $22,000less than proposed; and redundant guidance--if the GPS is jammed, INS alone will guide the bomb to within a 30m radius.
Key to keeping the cost down was the complete absence of mil spec requirements in the contract. "This is the first time this has ever been done, I believe," says Charlie Dillow, program manager for JDAM. "It allowed us to substitute plastic commercial parts and still meet requirement."
Soldier in distress. Another GPS-based device emerged from a request by forces in Macedonia patrolling the tense border with Serbia. Called Soldier 911, the custom units use a modified Motorola (Phoenix, AZ) GPS-112 military radio to provide situational awareness and geolocation capability.
GPS provides soldiers with their exact location within 15m. The shoulder-worn unit, weighing just 2.2 lbs, is powered by lithium batteries for 6 to 8 hrs. It generates a beep when within a specified distance of a border or other hazard, such as a mine field. Object coordinates are programmed into an onboard database. In Macedonia the device is used to prevent inadvertent border crossings and political "incidents."
The 911 capability consists of a button that, when pushed, transmits a signal for up to 100 mi that contains the soldier's position and possibly a code for the type of situation. The unit can also be used to keep track of troop positions. Lt. Col. Robert Kocher, ARPA program manager, estimates that 40% of communications are simply to identify where a soldier is and what is going on.
An obvious potential use for Soldier 911 is locating downed airmen--such as pilot Scott O'Grady, shot down over Bosnia--or aiding troops under fire. "When you're being shot at, typically you have to pull out a map, plot your position, and call it in," says Kocher. "With (Soldier 911), all you have to do is push a button."
Medical manufacturer embraces DFA/DFM
Newton, MA--While medical companies may wrestle with the prospect of dramatically altering their life-saving products, one electronic medical device manufacturer, Indianapolis-based United Medical Manufacturing Co. (UMM), is open to embracing concurrent engineering and idea-building to help produce more reliable products at a lower cost.
UMM established a strategic initiative to develop Design For Assembly (DFA)/ Design For Manufacturability (DFM). To assist with the management training, research and development, manufacturing engineering, and quality services, the medical manufacturer has drawn upon Munro & Assoc., Inc., Troy, MI-based DFA/DFM consultants.
"The most obvious benefits that we have reaped from our training are product designs that are easier to build and service," said UMM's Vincent Fisher, program manager, Advanced Systems Development. "But Munro & Assoc. also helped us to establish a new mindset and an effective approach in both the design and implementation phases."
For example, the BioLogic DT demonstrates UMM's success with implementing DFA/DFM principles. Originally developed by West Lafayette, IN-based HemoCleanse, the BioLogic DT helps treat comatosed drug-overdose patients and is in clinical studies for the treatment of AIDS patients. By applying DFA/DFM to the original "core" prototype, the UMM team produced a redesigned unit that had:
Reduced parts count up to 25 to 30%. c Saved assembly time by about 3 hours.
Some of the parts, cost, and cleanability savings were realized by incorporating a new technology--twin-sheet vacuum forming--to the unit's two plastic doors. Previously, the doors would have been manufactured using "laid-up" fiberglass skins mounted on a metal frame.
Twin-sheet vacuum forming, according to David Storvick, mechanical engineer for UMM, requires a cavity that is the shape of the part you want to create. By heating up two thin sheets of plastic, putting the cavity over the flat sheets, creating a vacuum, and letting the suction from the vacuum pull the plastic into the tool, a plastic part can be created. The twin sheet vacuum process forms two cavities simultaneously, thus a door with a front and a back is formed without using fasteners.
To address serviceability of the BioLogic DT, the UMM team eliminated threaded fasteners and replaced the nuts and bolts with elastic tie downs. Plus, the top portion of the enclosed unit is now hinged rather than bolted, providing easier accessibility.
"While serviceability was not a part of our initial program, it was easier to emphasize because the DFM training provided by Munro & Associates helped to change our attitudes," Fisher said. "The requirement we have set is that any component must be serviceable within 15 minutes--and all indications are that this requirement will be met."
Ford front end wins SPE Grand Award
Detroit--More than 80 automotive products vied for the 1995 Society of Plastic Engineers (SPE) Automotive Div. awards. Only one, however, walked off with the Grand Award--the integrated front-end system (IFES) on the 1996 Ford Taurus and Mercury Sable.
Each year's awards program honors the "most innovative use of plastics technology" in seven categories. The IFES also took the top spot in the chassis/hardware category. The highly integrated subsystem assists radiator, bumper fascia, and headlamp support functions. It allowed for a reduction of 22 parts to two or three, and eliminated 27 fasteners.
Manufacturing flexibility of the composite structures also provided for a high level of component integration. The upper and lower supports serve as locators for the hood latch, hood slam bumpers, headlamps, wiring, radiator system, A/C condenser, cooling fan motors, and shrouds, as well as various sensors. The Budd Co. and Autodie International Tooling Tech Center were also involved in the development effort.
Other categories and their winners:
Body Interior. Blow-molded knee bolster, "the first blow-molded part for use in a structural application, that saved weight and parts for the 1996 Astro and Safari." The component replaces a multi-piece steel and plastic panel with a tunable part. Design partners included: Dow Chemical, General Motors North American Truck Group, and the LCF Div. of the ABC Group.
Body Exterior. Single-sided encapsulated glazing process for the Chrysler Town and Country, Caravan, and Voyager Minivans provided a design with a "flush" look, aerodynamic appearance, and no visible hardware. The process uses Dow Plastic's Pellethane™ TPU. Design partners included Dow Automotive, Chrysler, and Donnelly Corp.
Process. (two winners) Exterior door handle and bezel assembly for the 1996 Chrysler NS/GS Minivans, "reflecting the first use of a multiple-cavity (4), air-assist molding process, that opens new fields for plastics in applications previously limited to metal." The part uses AlliedSignal's Capron™ nylon 6. Chrysler and Siegel-Roberts, Inc., were also involved.
The interior trim package for the 1996 GMC Savana and Chevy Express, which "debuted a unique hot-runner system gated directly onto the backside of show surfaces." This allowed pigmented molding of large ABS parts, without paint, cutting costs. The process used Monsanto's Lustran™ ABS, and was developed with Venture Industries, GM, and several manifold suppliers.
Powertrain. Transmission accumulator piston for the 1996 GM 4L60E and 4T40E transmissions, that features "tight tolerance, low weight, and low cost." It uses regrindable, recyclable Hoechst Celanese FortonLinear PPS thermoplastic. GM and Webster Plastics were also involved.
Environmental. Fuel tank for the 1996 Chrysler Jeep Grand Cherokee, that is "the first plastic fuel tank in the industry to meet California Air Resources Board (CARB) 95 hydrocarbon emission laws for all fuels." The main material consisted of BASF's Lupolen™, as well as a 1.5% adhesive tie layer and a EVOH barrier material. Other design partners included Chrysler and Kautex Corp.
Materials. PolySwitch polymeric resettable fuse in the 1996 Chrysler NS Minivans, that "uses polyethylene to ensure greater component life, while protecting against circuit overload." Chrysler and Raychem Corp. worked on the project.
Software fine tunes guitar design
Corona, CA--In a move that brings high tech to an area usually thought of as pure art, Fender Musical Instruments will produce within the next year a line of its bass guitars developed with solid modeling and analysis software.
"The integration of analysis, solid modeling, and pre- and postprocessing makes it possible to create better designs more quickly, while maintaining greater control over the development process," notes Mark Carlson, a Fender mechanical design engineer and classical guitarist. Using MSC/ARIES and MSC/NASTRAN, from the MacNeal-Schwendler Corp., Carlson is evaluating the necks on the current line of bass guitars, as well as performing other design optimization studies.
The guitars are made of wood, which, Carlson says, can behave "very strangely. We needed extremely flexible solver software that could handle a long solution process, which is why we selected MSC/NASTRAN." He uses MSC/ARIES for building solid models and automatic meshing for analysis. The hardware he uses is a Silicon Graphics Indy R4600SC workstation.
The workstation's graphics capabilities make it easy for him to explain designs to non-engineers on the staff, he says. He uses SGI's Mindshare™ software to turn the solid models into presentation form.
Carlson is using the MSC/NASTRAN-MSC/ARIES combination to study how much a new graphite-reinforced neck would move when string forces are applied and moisture content changes take place. That will allow him to try different reinforcement scenarios to increase neck stability, he says. He generates the stress contour plots with MSC/ARIES.
He is using MSC/NASTRAN to analyze the truss rod, a long, thin piece of steel that runs through the neck of the guitar. Turning a screw at the end of the rod tenses the cable and forces the neck to move. "Through nonlinear, slideline contact analysis, we can optimize the slot to determine what yields the best adjustment," Carlson says.
"The software is helping us save time in prototypes, and gives us the opportunity to try many more design iterations on the computer,"says Carlson. "In that sense, it's an idea tester."
Other analysis tasks Carlson plans involve ways to eliminate dead spots--notes that sound dead or don't resonate like others; "fret buzz," the sound that results when guitar strings are too close to the fret board; changes in moisture content of the wood, which affects stabilization; acoustic analysis; and the possibility of replacing wood with composite materials.
FEA, rapid prototyping slash verification time
Bayport, MN--Andersen Corp. has combined rapid prototyping with finite element analysis to cut design-verification time by up to 85%.
The company, a manufacturer of windows and patio doors, needs to design extrusions such as aluminum and vinyl snap covers for its products. Engineers used to test their designs by first building model dies, and then fabricating sample parts. However, those prototype dies cost thousands of dollars and took several weeks each to produce.
Now, Andersen engineers model an extrusion profile using Computervision CADDS 5 software. Then, the design is analyzed using ANSYS FEA software, allowing them to calculate surface deflection that occurs when force is applied to the part.
"We can optimize and test many more design concepts than with traditional methods," says James Wyman, CAE technical support. On one recent window-sill project, engineers were able to test 11 profiles in less than three weeks.
FEA results are verified by creating a 10-in extrusion-profile model out of ABS using an FDM 1600 rapid-prototyping machine from Stratasys Corp., Eden Prairie, MN.
Stratasys software converts the CAD data into a format understood by the prototyping machine. The model is built layer upon layer, from the bottom up, by a controlled-temperature head extruding resin.
Those models are physically tested on a force-deflection measuring machine. If results correspond with the computer model, engineers then go back to ANSYS to evaluate how using different materials would affect the design.
"It has had a major impact on how w do business," Wyman says. "This technoogy is a perfect fit for what we do."
Polymer makes aerobic step bench 'one step better'
Austin, TX--In designing its new aerobic step bench, Power Bench, Inc. knew the key to the bench's safety and success would lie in selecting the right material. Engineers needed a material with the proper combination of stiffness and toughness, along with a high environmental stress crack resistance (ESCR) rating. Without these key ingredients, the bench would fail prematurely.
After making an initial production run, Power Bench knew it had found that material in Marlex® C590 HDPE (high-density polyethylene) from Phillips Chemical Co., Houston. The new blow-molding grade HDPE not only provided the density needed to make the thin-walled bench strong, it also delivered the high ESCR that would negate material failure.
Choosing the HDPE resin fits Power Bench President Gail Fisher's philosophy of being "one step better" than competitors. "We are developing a reputation as a manufacturer of high-quality step benches for health clubs and individuals," she explains. Fisher, a former furniture designer, taught aerobics for several years before sketching her own step bench. She also interviewed "at least 500 health-club managers" to find out what they liked or didn't like about the benches they were using.
"Their foremost concern was safety," Fisher reports. "The interviews also confirmed my observation that the platform needed to be large enough to accommodate a man's foot and provide the optimum stepping area." The Power Bench has a 36- by 189-inch platform.
"Our exclusive non-tip design and single snap-in extension make the bench comfortable and easy to use," Fisher adds. "It also features a molded-in, skid-proof top, and an amazingly engineered grid pattern support underneath."
What do users think about the bench? "My students and I have found a vast difference among benches," says certified aerobics instructor Megan O'Grady, who teaches at World Gym in Killeen, TX. "Many are slippery, and that's dangerous and more likely to cause a hyperextension of the knee. The foot grips better on the Power Bench, reducing the risk of such injuries.
Analysis shortens design time for shuttle-engine part
West Palm Beach, FL--Using finite element analysis software, engineers at Pratt & Whitney (P&W) cut the time to produce a critical shuttle-engine component from one-and-a-half years to two months.
With ANSYS software from ANSYS, Inc., they simulated the thermal response of a duct in the liquid oxygen turbo pump as it would occur throughout an entire mission. The duct experiences temperature swings of 1,500F during a shuttle mission. The analysis showed there were about 21 locations on the duct with stress points that could develop into cracks. Analysts fed the results back to the design engineer, who used Parametric Technology Corp.'s Pro/ENGINEER CAD to modify the duct to withstand the temperature swings.
"To build and test a part like this normally takes about one-and-a-half years, but we were able to do it in two months," says Joe Metrisin, senior analytical engineer at P & W. "It's difficult to instrument a part like this with strain gauges."
The nickel alloy duct has 22 aerodynamic struts that support a center turning vane between two flow-turning end walls. It turns the turbine exhaust flow to radially exit the liquid oxygen turbine assembly. The pump itself boosts the pressure of the liquid fuel from 420 to 4,300 psi as it enters the engine's combustion chamber.
Turbo pumps are only active when the engines are active--during the approximately eight minutes from launch until the shuttle enters the pre-orbital phase. During the first five seconds of that time, the temperature inside the engines goes from about 300F to more than 1,200F.
The original design of the nickel alloy duct was produced in Pro/-ENGINEER CAD, and Metrisin did his analysis based on that model. "I chose ANSYS in part because it was easy to interface to Pro/- ENGINEER CAD," he says.
Metrisin applied thermal boundary conditions to the duct that he got from P&W's own computational fluid dynamics programs. He performed a transient thermal analysis, then converted the heat transfer model to a stress model, then did a structural analysis of the part at five time points during a mission. The results: The area with the highest stress was at the front end of the flow path, where hot gas exits the turbine. There were 20 other locations that were stressed severely enough to potentially develop cracks, engineers surmised.
After the redesign of the duct, engineers put the part through another similar set of ANSYS analyses. After five iterations of redesign, engineers reviewed the test results from an earlier duct design to verify the analysis results. "The review confirmed our results," Metrisin says. "It cracked in every place the analysis predicted."
NASA has certified the pump to fly ten missions without an overhaul.
Nylon helps uncover mysteries of the universe
Rome, Italy--A mile underground, in a lab about 70 miles from Rome, a co-polyamide resin faces the ultimate test of purity. The international scientific experiment involves invisible particles called neutrinos.
The project: the Borexino Solar Neutrino experiment. The material: Durethan® C38F from Bayer's Polymers Div., Pittsburgh, PA.
Neutrinos, produced by nuclear fusion reaction in the sun, easily pass through stars, planets, people, and objects. Research to detect and study the particles will determine if they have mass, and whether or not they change form as they pass through cosmic objects. The experiment links some of the best scientific minds from the U.S., Italy, Germany, and Russia. The results could change science's view of the universe.
Essential to the experiment is a liquid scintillator that detects the neutrinos as they pass through the earth. As the neutrino hits the scintillator--a gasoline derivative--a flash of light is given off. The scintillator is suspended in a sphere of the Durethan polyamide resin, which, in turn, is surrounded by ultra-pure water where the phototubes that detect heat are located. Other causes of light flashes, such as cosmic rays or impurities in the scintillator, require the experiment to be performed underground in an apparatus with extremely low radioactive impurities.
"The material containing the scintillator is crucial to the success of this experiment," says R. Bruce Vogelaar, assistant professor of physics at Princeton University. "We went through at least a dozen plastics before we selected Durethan for its purity, optical clarity, strength, chemical compatibility, and ease of fabrication."
Copper conductor helps shrink portable phones
Tokyo, Japan--In the past, Taiyo Yuden Co. Ltd., a leading producer of power amplifiers for portable phones, used a silver/palladium alloy for its hybrid circuit conductors. The silver/palladium compositions were reproducible and easy to handle, allowing their use in high-volume applications.
However, the 100-micron line- and space-width limit of the composition didn't allow Taiyo Yuden to use smaller integrated circuits that provide the needed size reductions and electrical efficiency. To address this problem, the company turned to DuPont for a low-temperature copper composition.
Taiyo Yuden found it could achieve 75-micron line widths, within a 10% tolerance, using the copper composition from DuPont. This enabled the company to reduce the power amplifiers' size from 1.2 to 0.4 cc. The highly conductive copper composition also provided better resistivity, the company says, offering a resistance value 1/5 that of the silver/palladium. This better resistivity allows the phone to work at the necessary high frequency and gives it the power to operate for up to 150 hours continuously.
The low-temperature copper composition is fired in nitrogen in a 600C furnace, compared with the 850-900C firing of traditional conductor compositions. Low-temperature firing allows the circuit designer to combine the high conductivity and fine-line printability of copper conductors with the high precision and reliability of thick-film resistors that fire in air at 850C. Taiyo Yuden produces its hybrid circuits using high-technology bare-chip assembly.
Currently, Taiyo Yuden is working on similar products for the 1.5-GHz bandwidth. The company expects to reduce the 0.4-cc size of its modules even further.
Thermoelectrics chill portable cooler
Houston, TX--What's a cooler without ice? For engineers at Igloo Corp., finding a thermoelectric (TE) module that could deliver a big enough temperature drop to replace ice was a top priority.
"They worked like the devil with existing TE modules to try to get the performance," comments Tellurex Corp. President Charles Cauchy, "but they could only get a 40C change in temperature. With the Tellurex module, they achieved a change in temperature of 46C."
The patented Z-Max™ module from Tellurex, Traverse City, MI, now powers the heart of Igloo's premier "active cooling" product line. Igloo and Tellurex engineers teamed up to redesign the cooling system of the new Kool Mate™ line. The coolers also feature a dual-fan configuration for improved air-flow, brushless motors, and modular sub-assemblies for more powerful and reliable performance, say Igloo engineers.
"We improved the TE module substantially, and that allowed Igloo to make ice--which was pretty much unheard of with a thermoelectric device before," adds Cauchy.
Central to the Z-Max module's improved performance is a patented semiconductor fabrication process. Rather than conventional "sliced and diced" thermoelectric semiconductor crystals, the module uses a polycrystalline semiconductor ingot. "We grind it into a powder and press and sinter it--it's almost a powder metallurgy process for a semiconductor product," explains Cauchy. "We projected that would improve the material and it did."
The resulting TE module is more powerful and also more robust, says Cauchy. This gives Igloo engineers added manufacturing flexibility for torquing pressures during assembly. Additional applications for the Z-Max module include electronics cooling for microprocessors, medical, automotive, and other consumer products.
Vacuum cashes in with improved motors
Luton, England--Can fan motors make a difference when it comes to vacuum-cleaner sales? In the case of Electrolux it did--after the company redesigned the motors to use housings and air guides made of a thermoplastic polyester.
The Electrolux Group's UK-based plastics facility revamped both its design and manufacturing methods for the company's twin-fan models with outputs of 550, 1,000, and 1,500W. A chief component, the input air guide for the motors, formerly included 10 stamped metal parts. The new guide consists of a simple metal plate and a plastic part with integral guide vanes molded from Crastin® PBT thermoplastic polyester supplied by DuPont Engineering Polymers, Wilmington, DE. With its smooth surface finish that combats turbulence, the redesigned guide helped improve fan efficiency 3% over the earlier motor.
The new guide also cut assembly costs. It snap-fits onto the lower housing component made of DuPont's Rynite® PET. In contrast, the metal guide it replaces required six mechanical attachments around the aluminum housing's rim.
Replacing the die-cast aluminum housing is a two-piece component also injection molded from Rynite. With the change, manufacturing steps dropped from 12 to four, eliminating metal trimming, machining, and degreasing operations, as well as an extra inspection. Material costs also decreased 5% in the case of the 1,500-W motor. Moreover, the switch to PET eliminated the need for separate brush holder insulators required with the aluminum housing. The result: Electrolux continues to ring up major cost and performance benefits--and, most importantly, sales.
Plastic slims Jeep Wrangler stoplight
Grand Rapids, MI--When Chrysler turned to molder ADAC to help redesign the '97 Jeep Wranger's center high-mount stoplight, the solution involved plastics. Not only did the light's performance improve, but cost savings were significant.
The metal housing bracket for the stoplight, positioned above the Wrangler's spare tire, proved labor-intensive to produce. The challenge: Find a material that could match or exceed the part's present flexural strength while significantly improving torsional stiffness. ADAC investigated several alternatives. In addition to performance considerations, ADAC knew Chrysler wanted a more modern design.
With these goals in mind, ADAC called on AlliedSignal Plastics' Modulus™ Group for design, computerized performance evaluations, and materials guidance. The design group took the part through finite element analysis to analyze structures, stresses, and deflections, as well as natural frequency in a modal analysis. Actual part testing measured vibration, flexural strength, torsional characteristics, and load.
The result: a new, streamlined design that, in testing, performed better than the original housing. Moreover, the design reduced parts from 19 to nine.
ADAC chose AlliedSignal's Capron® 8233 for the main structure of the bracket, and Capron 8267 for the bracket's bezel portion. The materials, in combination with the design change, resulted in a thermoplastic part with equal or slightly superior stiffness to the original steel part. "More important, the two materials showed torsional stiffness that was significantly better than the previous part," says Bill McMaster of the Modulus Group.
For the main stoplight bracket, the weather-resistant, 33% glass-reinforced, nylon 6 Capron 8233 has a tensile strength of 40,000 psi, a stiffness of 1.35 million psi, and a heat-deflection temperature of 410F.
Capron 8267, a weather-resistant 40% mineral- and glass-reinforced nylon 6 used for the bezel, also features a heat stabilizer system. And, it has a tensile strength of 30,000 psi, a stiffness of 1.11 million psi, and a heat-distortion temperature of 395F.
The jet-black part needs no paint and its UV resistance prevents color fading. Overall cost savings for the part were excellent, says Dave Stuart, ADAC's engineering program manager.
ADAC took the prototype into production in less than two months. "The end result of the switch," says AlliedSignal's McMaster, "was an aesthetic, high-performance part that was produced ahead of schedule at a very big cost savings."