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Articles from 1995 In February

Elastomers: More design bounce to the ounce

Elastomers: More design bounce to the ounce

Consumer products, sporting goods, automotive components, wire and cable, industrial equipment, and biomedical devices. These, indeed, represent a diverse range of products. But, in many instances, they have one important element in common-thermoplastic elastomers (TPEs).

The reasoning behind TPEs' choice is not hard to understand. They are a versatile group of resins. Consider, for example, some of their innate property characteristics:

These linear segmented polymers consist of hard and soft ingredients. By varying the relative amounts of the hard and soft components, the resins can meet a wide range of flexibility and performance requirements. This choice alone lets engineers optimize the material to match design criteria when it comes to everything from color or clarity to indoor or outdoor uses.

  • They are environmentally friendly. Recent resin introductions have expanded this friendliness to include improved recyclability and non-toxin-containing formulations.

  • Advances in processing technology enable TPEs to be tailored to meet almost any design need, while improving product quality and cost.

Wrap these features in a package and it's little wonder that TPEs have become an increasingly popular entry on the design engineer's material list.

To better illustrate this adaptability, let's look at two industry areas-automotive and medical-where TPEs are making serious inroads as replacements for metals or to complement other plastic materials.

Automotive electronics provide a perfect example of how TPEs can adapt to the changing design needs. The explosion of electronic features in today's automobiles has caused a corresponding increase in the size of electric wiring harnesses. Packaging constraints due to this trend are driving a downsizing of electrical systems. Engineers have accomplished this in two ways: reducing conductor wires, which results in higher operating temperatures, or reducing the thickness of the insulating materials, which requires the need for greater insulating efficiency.

DSM Engineering Plastics has introduced a series of TPEs, Arnitel(R) V, that addresses the needs of both problems. Arnitel UM551-V, a non-halogenated, flame-retardant grade, answers the primary wire insulation obstacle, while Arnitel UM552 fulfills the need for components that require high-temperature resistance, but not flame retardancy.

DSM, the Netherlands-based parent of DSM Engineering, acquired the Arnitel product line from Akzo in 1991. In Europe, Arnitel U has replaced PVC and cross-linked polyethylene based on its environmental, process, recycling, and performance advantages. Relative to other polyester elastomers and typical wiring insulation materials, says Steve Hartig, DSM Engineering Plastics' automotive industry manager, Arnitel can offer:

Continuous-use temperature capability for natural materials up to 338 degrees F (170 degrees C), and for non-halogenated, flame-retardant grades up to 302 degrees F (150 degrees C).

  • Twice the abrasion resistance.

  • Excellent UV stability and color fastness.

"We have the expertise of our TPE division here in the U.S., and the experience of thermoplastic manufacturing in Europe," Hartig adds. "This will enable Arnitel UM551-V to find an important niche in automotive under-hood cabling systems."

And when it comes to heat- and oil-resistant materials, particularly for such automotive applications as O-rings, seals, and gaskets, don't overlook a new class of specialty elastomers from DuPont. The Advanta 332 degrees and 365 degrees materials consist of compatible alloys of proprietary polar ethylene copolymers and fluoroelastomers. They are peroxide-curable, whereby the same cure system co-crosslinks both components.

Using the new SAE standard J2236 for determining continuous upper temperature resistance, Advanta 332 degrees qualifies as a 165 degrees C material, and Advanta 355 degrees as a 175 degrees C material, with intermittent excursions to 200 degrees C. "Current lab work promises further improvements in long-term heat resistance," says Eric W. Thomas, senior development specialist at DuPont Elastomers. Processing includes standard compression, transfer, and injection molding techniques. Bonding metal and plastic substrates is possible using commercial primers and bonding agents.

There's also a new family of highly cross-linked, dynamically vulcanized TPE compounds for the automotive market. Introduced by the Plastics Div. of Teknor Apex Co., the Uniprene(R) 7000 TPE olefin-based compounds "have physical characteristics, appearance, and feel similar to vulcanized rubber, but offer superior performance versus competitive products in a wide range of demanding environments," says Thomas Moccia, TPE market development manager.

The materials come in hardness grades of 55 Shore A to 40 Shore D. And, because these products are not hygroscopic, they require no drying. "Additionally, they are readily curable, 100% recyclable, and heat stable up to 232 degrees C," Moccia adds.

Airbag advantage. The increasing popularity of airbags is another automotive area where TPEs' "elastic" properties play a major role. In one case, it helped Chrysler save $12 million a year in the production of driver-side airbags.

For this project, Chrysler worked with Advanced Elastomer Systems (AES) and other team members that included Morton International and Venture Industries. The design involved converting the airbag door from a thermoset to a thermoplastic. The savings resulted primarily from a 40% decrease in the weight of the doors and lower resin costs. However, the simplified design also proved a key factor in the cost savings.

The doors had been made out of reaction-injection-molded, SCRIM-reinforced urethane. They were riveted onto the airbag module. Morton developed a design that uses AES' Santoprene(R) thermoplastic rubber to injection-mold a lighter, easier-to-assemble door that snap-fits to the module.

"Morton reviewed 26 thermoplastic materials before selecting Santoprene as offering the best balance of properties for the application," says Bonnie R. Bennyhoff, AES's account manager for Chrysler. "Specifically, Chrysler was impressed with the "look' and "feel' of the material, and with its ease to process. And we have already delivered test samples that will lead to the next generation of airbag door materials."

And TPEs have one other thing going for them in the automotive world. "This market has a focused priority to address recyclability issues, with elastomeric products one focal point," Bennyhoff explains. "It is expected that the activity in this market segment will carry over into other durable goods markets in setting the pace for dealing with the afterlife and reuse of products."

What's next? "People want to "drive their living room,'" says Mark Wright, director of AES' North American automotive sales. "The focus is on trying to make cars quieter on the inside and outside. In Europe, for example, cars will have to pass a "drive-by' noise limit. Some of this results from engine noise falling down to the ground and vibrating back up."

To counter this, according to Wright, people are adding belly pans or bottom enclosures to quiet the noise. "TPE makes up an important part of that system," Wright explains. "Basically, what you have is flaps that allow opening and closure as the car's velocity picks up. This enables good circulation in the engine compartment as needed, and it also helps to seal off some areas."

The medical arena also affords an opportunity for TPEs to show off their attributes. And they are winning a lot of followers.

The objective here, says Scott Fuson, Dow Corning's manager of medical devices, is for resins producers to help medical-device makers lower user health-care costs. But they also must prove that these materials can stand up under the rigors of chemical attacks, sterilization, and a barrage of lengthy tests required by the FDA.

To help make these tasks easier, Dow Corning introduced a new family of biomedical-grade silicones. The Silastic(R) materials not only meet the Tripartite Guidance standard, but ISO standards. Test results apply to all categories of medical devices that come into contact with tissues, fluids, or blood inside the human body for periods of up to 29 days.

"We wanted to clearly meet the most rigorous standards of testing for our elastomeric materials, even though some of them may be used for external applications," says Fuson. "In the long term, we expect that these criteria will be incorporated into FDA requirements for medical devices." Fuson also notes that new Silastic biomedical grades with improved yield and tear properties will debut shortly.

Polyether thermoplastic urethanes (TPUs) also make good candidates for biomedical products. As a group, these materials resist hydrolysis and fungus attack, as well as the effect of lower temperatures for medical products that require refrigeration.

"The biocompatibility of polyurethane tubing minimizes or eliminates necrotizing dermatitis and reduces platelet damage," says Mike Marasch, senior marketing manager for BF Goodrich's Estane(R) TPU. "Its inherent flexibility resists shrinking, cracking, and kinking-and the tubing can be sterilized. It's also chemical- and solvent-resistant, transparent, and has a high tensile strength. This makes it useful for catheters, connectors, and shunts."

Softness, plus. A "soft touch" also has its advantages in the medical field. With this in mind, GLS Corp. has introduced two Dynaflex(R) medical-grade thermoplastic elastomers: Dynaflex G-2707 and G-27711. With a 32 Shore A hardness, the transparent, high-gloss G-2707 is claimed to be mar resistant, while exhibiting improved puncture and resealing qualities. The G-2711 grade, a translucent resin of 44 Shore A hardness, offers high re-silience, good clarity, and can be resealed.

"Both grades are easily sterilized using gamma radiation, with no significant loss in performance," says John Marshall, GLS market development manager. Typical uses: tubing, EKG pads, mouthpieces, facemasks, hemostat clamp cushions, and syringe plunger tips.

Also, don't overlook thermoplastic vulcanizates (TPVs) when it comes to softness. "TPVs are leading the way over all other thermoplastic elastomers as the "soft touch' material of choice," enthuses Malcolm Thompson, sales and marketing manager for DSM Thermoplastic Elastomers. Thompson considers TPV to be an ideal replacement for EPDM, neoprene, and other mid-performing rubbers, as well as self-skinning urethanes.

Thompson cites DSM's Sarlink 2000 and 3000 TPVs as popular materials for overmolding applications where material compatibility becomes an issue. Overmolded onto polyolefin-based thermoplastics, such as polypropylene, "they achieve excellent thermal bonding, while maintaining recyclability properties and ensuring a soft, rubbery feel," he explains.

Processing breakthroughs. Advances in polyolefins based on new technologies have spurred the production of a new class of elastomeric materials. One of the most recent advances involves the development of homogeneous (single-site) catalyst systems.

One such system, Insite from Dow Chemical, has resulted in elastomeric copolymers of ethylene and octene. Dow sells them under the trade name Engage polyolefin elastomers (POEs). The Dow catalyst process walked off with two major design awards last year: the National Inventors of the Year honor from the Intellectual Property Owners Association, and an "R&D 100'' award from R&D Magazine.

In a paper presented at last fall's technical meeting of the American Chemical Society's Rubber Div., Dow project leader Jeff E. Brann reported that the Engage POEs "have significant advantages versus EPDM/EPM compounds in heat aging, UV stability, mechanical properties, and processing." These enhancements, he adds, make the POEs well suited for such applications as cable insulation, belts, automotive hoses, seals, and other electrical uses.

From an environmentally improved processing perspective, Lord Corp. has developed a method to better bond waterborne elastomers to metal. The single- and two-coat aqueous adhesives for vulcanization bonding "have demonstrated comparable, and often improved performance, compared to existing solvent-borne adhesives," says Lord spokesperson Tony Ciampa. "They provide end users with an excellent alternative to VOC-containing, solvent-borne adhesives."

In a series of tests, the Chemlok aqueous adhesives demonstrated "excellent adhesion to natural rubber, styrene-butadiene, neoprene, nitrile, and butyl rubbers," Ciampa notes. In some cases, they maintained this level of performance after a five minute pre-bake, as well as severe environmental analyses.

"Concerns for the environment; federal, state, and local government regulations; health insurance; and worker safety all serve as impetus to use aqueous adhesives," Ciampa adds. Considerable lab work and production trials have been conducted to help facilitate this transition. Lord recently completed an applications lab that can perform all the operations found in a production plant. Customers can evaluate the adhesive in production conditions that match actual plant operations.

But what really excites those at Lord are the opportunities that will be created by a new line of products based on Lord's controllable fluid technology. These so-called MR fluids are free flowing until they encounter a magnetic field, which converts them to a non-flowing, near-solid consistency. Their application in devices such as exercise equipment will allow the user to "dial in" a desired program of physical intensity. In the automotive arena, seats suspended on MR dampers will pamper operators of off-road vehicles.

There's yet another new trend in the polyurethane elastomer industry, reports Wally Cutler, administrative manager at Innovative Polymers, Inc. His firm has formulated a system for use in rapid prototyping. The 75 Shore D, ultrafast-cure material is meter-mixed and injected into the mold. "This new concept of liquid injection molding holds great promise to produce parts with very little lead time," Cutler adds.

And this is only a sample of even greater things to come. From their meager beginnings in the realm of natural rubber, elastomers, especially the TPE variety, will enjoy a sales gain of at least 7% a year through 1997. That's the prediction of TPC Business Research Group, Lancaster, PA. And of particular interest to design engineers, TPC forecasts that "many new types of TPEs will be developed during that time."

Close-up view of electrodeless lighting

Close-up view of electrodeless lighting

Fluorescent lights are commonplace mysteries-the physics of the interaction of electrodes, electric field, and the photon-emitting plasma they produce isn't completely understood. It is known that efficiency improves with increasing distance between electrodes. Thus, the most efficient bulb would have infinite distance between electrodes. In effect, it would be "electrodeless."

Enter the Genura lamp from GE Lighting, Cleveland, OH. Although the electrodeless design was patented in 1970, it's taken a quarter century for the necessary power-conversion electronics to shrink to the point where the bulb can fit into conventional incandescent cans. The bulb produces as much light as a 75-W incandescent but uses only 23 W and has a rated life of 10,000 hrs. On sale now in Europe (where, due to the higher supply voltage, the efficiency is even higher), Genura will debut in the U.S. this spring for commercial and industrial use.

Phosphor coating on the bulb's inner surface converts UV photons from energized plasma into 1,100-lumens of 3,000K-color, visible light.

Electron/ion plasma results from interaction of high-frequency electromagnetic field with a proprietary bulb-gas mixture.

Induction Coil resides completely outside the pinched-sphere-shaped bulb, generates electromagnetic field. The bulb itself comes from a GE Lighting plant in Nagykanizsa, Hungary. The glass-blowing technology is reputedly among the world's best.

VALOX(R) housing from GE Plastics supports and protects two-piece bulb, serves as chassis for electronic and Edison-base power connector.

Electronics package converts service-line electricity to 2.65-MHz power for induction coil. Its compact circuits were designed concurrently by GE Lighting operations in the U.S. and U.K. as well as engineers from the GE R&D Center, Schenectady, NY.

Open architectures coming to factory automation

Open architectures coming to factory automation

Robert P. Collins, President and CEO,
GE Fanuc Automation North America, Inc., Charottesville, VA

Collins joined GE in 1960 after receiving an electrical engineering degree from Manhattan College. He spent 20 years with GE's aerospace operations, specializing in radar, electrical systems, and instrumentation products. He received a patent for liquid crystal displays. Before taking his present position, he was vice president and general manager of GE's electric automation controls operations.

Proprietary automation technology is a noose around the neck of factories, says Collins. He sees open architectures as the wave of the future.

Design News: What trends do you see in factory automation and manufacturing?

Collins: Programmable logic controllers (PLCs) and computer numerical controls (CNCs) are the main solution for real-time control. The most noticeable trends in both areas are open-architecture systems, higher level programming languages, and pervasive application of man-machine interfaces-all windows-based. As control products' power and performance continually increase, cost and equipment size are continually decreasing. In addition, diverse interfaces and I/O options, especially intelligent ones, are increasingly available and popular.

We also see growing use of personal computer hardware and operating systems, but those systems haven't matured enough for true real-time control applications. We believe it will be only after the year 2000 that they will be used for real-time control, and even then it will make sense only in selected applications.

Q: When will American manufacturing adopt a true open architecture for automation equipment?

A: The short answer is-when other suppliers are willing to step forward and truly embrace this concept. Open architecture and open systems have been a key strategy that GE Fanuc has embraced for many years to improve our customers' productivity. Other market leaders in factory automation are holding their customers back by forcing them to use proprietary systems for applications that would benefit greatly from an open architecture solution. In reality, customers are allowing the proprietary-driven supplier to tighten the noose of proprietary technology on their factories by this approach.

Q: We hear a lot about partnerships these days. What are the greatest benefits of partnerships between OEMs and their suppliers?

A: Shorter design and manufacturing cycles that benefit both OEMs and their suppliers are key benefits. We've found partnerships helpful in breaking down the barriers to a faster time-to-market cycle. Partnerships allow the OEM to gain access to technology, and in turn, allow the supplier to add value to the design of the machine. For example, our partnership with Husky, a world leader in injection-molding machines, calls for us to provide controls and software for their equipment. Our boundary-less design team, composed of people from both companies, has cut through traditional sup-plier/vendor barriers, speeding up the work while keeping its cost down.

Q: How will the consolidation among large end users in the defense industry affect automation-equipment suppliers like GE Fanuc?

A: Our relationships and strengths have been with the large defense firms, so this additional consolidation will just serve to further strengthen those relationships. The remaining defense contractors' main mission will be to help the DOD stretch the ever-shrinking defense budget dollars further. This country will have to maintain a smaller, smarter, more mobile defense force. Because like it or not, we are the stabilizing force around the globe and that role will not diminish in the short term.

Q: What role do you see for government in encouraging investment by industry in productivity-enhancing equipment?

A: Manufacturing remains the prime driver of our economy and standard of living. We cannot get the productivity improvement needed for long-term economic growth simply by shrinking, cutting, and tightening our manufacturing infrastructure. The lack of investment capital is acute among small-to-medium-sized manufacturers (less than 500 employees). Companies this size represent the vast majority of all U.S. manufacturing establishments and generate the majority of new manufacturing jobs. We need a bold new national agenda to nourish our manufacturing base and to train our people, before we lose our position of strength in the industrial world.

Designer's Corner

Designer's Corner

Clean polyurethane mixer

Polyurethane-molding processors traditionally rely on high-pressure counter-current mixheads to completely combine polyol and isocyanate prior to injection. But liquids emerging turbulently from the mixhead can splatter, reducing the quality of finished parts. The lightweight MX mixhead virtually eliminates that problem: Its flowpath downstream from the mixing chamber includes two divergent volumes to reduce fluid pressure and velocity, ensuring laminar mixture flow.

The mixhead's shot-control piston and its coaxial throttling sleeve and cleaning piston can all be operated separately via integrated hydraulic valves. Full extension of each element cleans out all reaction spaces in the mixhead. Separate constituent-flow throttles allow precise pressure control for difficult mixtures.

Marketing Communications Group, Hennecke Machinery, Polymers Div., Miles, Inc., Mobay Rd., Pittsburgh, PA 15205-9741, (412) 777-2000.

Ambidextrous switch

Captive terminal screws, accessible from beneath or from either side, help the 8400K2 rocker switch reduce inventory needs for power-tool or appliance manufacturers. Available in 7-A, 125-V or 4-A, 250-V versions, the switch accommodates screw-mount or trap-mount applications. Its all-plastic housing resists corrosion, dirt, and sawdust.

Customer Service Center, Eaton Corp., Aerospace and Commercial Controls Div., 4201 North 27th St., Milwaukee, WI 53216, (800) 735-6265.

Non-contacting speed sensor

Not a Hall-effect device, this newly introduced sensor registers time-varying magnetic fields as the voltage across two elements of proprietary alloys. According to its manufacturer, the design resists stray magnetic fields better and thus delivers an order-of-magnitude improvement in accuracy over Hall-effect sensors.

That improvement in accuracy lets the device handle field oscillations between 1 and 15 kHz. Depending on the peak magnetic field strength, the sensor may be placed as far as 0.75 inch from its target.

Wolfgang Eggert, Vacuumschmelze Div., Siemens Components, Inc., 186 Wood Ave. South, Iselin, NJ 08830, (908) 494-3530.

Programmable pins support PCBs during screen printing

Programmable pins support PCBs during screen printing

Franklin, MA--Electronics manufacturers create solder pads on PC boards using high-speed screen printers. In MPM Corp.'s new high-volume, Ultraprint-3000-Series precision printer, the downward force exerted on a board by the squeegee can range from 1 lb to 50 lbs.

To keep boards from bowing under that load, users typically use blocks fixed to the printer's bed beneath the board. Workers must place the supports manually, changing the block set for each new board.

Design engineer Pat McCormick, Product Manager Steven Hall, and their colleagues at MPM found a better way to support boards in the new 3000 Series. Their system employs a set of magnetic pins stored in the screen printer. A gantry, positioned by "H'-Block and Power Block rod-cylinder slides from Tol-O-Matic Inc., Hamel, MN, picks the pins out of their storage position and locates them on a steel plate beneath the PC board.

  • Grinding

  • Plasma and waterjet cutting

  • Machine tools

When a board first enters the 3000-Series screen printer, it takes up a position on a queuing conveyor. A scanner reads a bar code on the board, and transmits that information to a 486-based motion-control board. Capable of simultaneously controlling seven of the 22 independent axes on the 3000 Series, the motion controller checks a lookup table, determines the pattern of support pins needed by the board, and instructs the gantry to deliver those pins to the printer's workbed. (A second on-board computer handles documentation and diagnostic data.)

The 3000 Series can store as many as six stencils, automatically selecting the one needed by the incoming board. After the support pins and stencil are in place, the board passes onto a process conveyor that locates it beneath the stencil. An optical sensor provides feedback that allows precise adjustment of board location. Paste is placed on the stencil by a dispenser positioned by an Axidyne stepper/ball screw assembly and a band cylinder (both from Tol-O-Matic). The printer's squeegee then delivers the paste to the fully supported board in a two-stroke sequence. A laser system then uses triangulation to measure the height and location of as many as 14 solder pads per second.

If 45-degree printing is required to ensure accuracy or make some downstream operation easier, a gearbox can position the printer's bed at 0 to 90 degrees relative to the squeegee's centerline. After the printing operation, the board moves to a pickup conveyor, and remains there until downstream equipment can receive it. Able to process as many as five boards per minute, the 3000 Series can also work with lot sizes as small as a single piece.

Additional details, 3000 Series...Contact Robin Alan Rhodes, MPM Corp., 10 Forge Park, Franklin, MA 02038, (508) 520-6999.

Additional details, Tol-O-Matic Automation products...Contact Douglas C. Moore, Tol-O-Matic Inc., 3800 County Road 116, Hamel, MN 55340, (800) 328-2174.

This Leopard claims a new spot

This Leopard claims a new spot

Herts, England--Using a suite of software packages, engineers at Chichester-Miles Consultants Ltd. (CMC) are designing a four-seat jet that will travel at 500 miles per hour. The company says the plane, which it calls the Leopard, will be the first production jet of that size.

Critical to the plane's design is the extensive use of engineering software. Among the programs playing a key role: Algor, AutoCAD, and NISA II.

A marketable idea. During his 30 years in the British aerospace industry, Ian Chichester-Miles, chairman and chief executive of CMC, witnessed the development of jet airplanes ranging in size from large aircraft to executive jets. In 1980, he decided to take jet propulsion technology one step further by applying it to a basic four-seat plane.

Armed with several pencil drawings, he set out to create an airplane nimble enough to get in and out of small airfields easily, yet powerful enough to achieve full-scale jet performance. His goal was to fly 500 miles/hour at 40,000 ft or above.

But meeting those requirements wasn't enough. Chichester-Miles also wanted to ensure a high comfort level for passengers. That meant reducing noise and vibration, and providing sufficient space-features that are difficult to incorporate in small planes. "You can't just scale down a big airplane unless you are designing to carry babies," he says. "People don't just change size as they go from big aircraft to small ones."

To reduce internal noise, Chichester-Miles designed the Leopard with the engines placed at the rear of the plane, well behind the passenger cabin. But he still needed a compact airplane configuration that could accomodate four people and the necessary operating equipment at a low cost. The solution: model the plane's interior in a style similar to a high-performance sports car.

The influence of automobile designs does not stop there. CMC looked at environmental control systems on several large aircraft to determine how they could be simplified and made less costly. Typical air cycle systems found in large aircraft are both light and efficient, but are also very expensive. The final decision was to use a fluid cycling system similar to those used in cars.

Back to basics. The Aircraft Research Association Ltd. (ARA) in Bedford, England, was responsible for the 3-D shaping of the wings on the original prototype aircraft (001) for CMC. ARA used their in-house 3-D Full Potential Flow method to create an aerodynamic design; while the structural design was done largely by hand. Mainly a crude, proof-of-concept prototype, the 001 was first flown in December 1988 at the Royal Aircraft Establishment in Bedford, England. The plane completed some 100 test flights with only one real problem emerging: a pitching instability that was easily fixed by changing the pivot axis position of the horizontal stabilizers.

Since then, CMC has been hard at work updating and redesigning the Leopard. The new version has an increased payload and much higher performance than the 001, and it is pressurized. This means engineers can no longer rely on hand calculations to achieve the highly efficient and reliable structural design they need. As a result, engineering software has played a crucial role in the design process.

Engineers used Algor's Linear FEA software with Composites add-on to do a stress analysis of the Leopard's stabilizers. Chris Burleigh, chief designer at CMC, needed to know the distribution of the internal loads among the ribs and spars of the stabilizer structure. He was also interested in the overall bending and torsional stiffness of the stabilizer, as well as the magnitude of the local bending effects in the skin panels due to the distributed pressure loading.

Since the stabilizer's structure is mostly stitched carbon-fiber fabrics in an epoxy resin matrix, Burleigh chose to analyze the area as orthotropic plates, knowing the laminate properties could easily be calculated by hand. He calculated the thickness and modulus of the plates to give the same membrane and bending stiffness as the equivalent composite. He obtained the panel bending by separating panel membrane loads and bending moments, and correcting for each layer of material.

The analysis of the roof of the pressurized passenger cabin also required the use of Algor software. "By this time I had gained enough confidence in Algor and my ability to use it to go straight into the Composites modeler," says Burleigh. He put the roof's honeycomb sandwich panels with glassfiber/epoxy skins into the Algor model as thick sandwich elements, using the actual properties of each layer. A simple laminate analysis provided stress output that indicated areas of weakness. Burleigh eliminated these areas one by one by adjusting the skin and core construction until he was satisfied with both the deflections under load and the stresses.

He also used Algor to model solid components and combine them with composite element models. Case in point: A large fitting at the inboard end of the wing flaps that is used to transmit the flap actuator load into the flap structure. The flap itself was represented by thin composite plate elements, and the fitting by solid brick elements. The models were constructed by creating the geometry in Algor's Superdraw and then pulling out each component to create separate, smaller models. Burleigh decoded and recombined each of these models. "This made the models and their input data easier to handle. It also allowed modification and deletion of pieces of the model without interfering with the whole thing," he explains.

Surface modeling steps in. When designing the engine pods at the rear of the aircraft, the goal was to minimize the frontal area by fitting the cowlings as closely as possible around the engines. Burleigh was equally concerned with providing a smooth streamlined shape and incorporating an "S"-shaped intake duct.

The engine and pod were first drawn by hand to scale. Burleigh constructed the basic cross sections and lines in Algor's Superdraw as arcs and circles, and converted them into smooth closed NURB splines. After dividing the closed splines and deleting one half, he transferred the remaining parts to Algor's Supersurf and created a NURBS surface over them. He then used a mirror image to replace the missing half.

Burleigh checked the clearance above the engine by observing cross sections at strategic points along the pod surface. He modified splines and constructed new surfaces to attain the 0.25-inch clearance required at the critical points. Several cross sections were plotted full-size so a "negative" mock-up of the available space could be created in wood. When the mock-up showed modifications were still needed, Burleigh reconstructed the surface and adjusted the model. He made prototype tooling directly from the full-size plots by sticking the plots to fiberboard and cutting them out with a bandsaw. "Overall," he says, "Supersurf has proven to be extremely useful."

Carlton Matthew, an outside consultant to CMC, conducted an analysis of the wing structure using NISA II FEA software from Engineering Mechanics Research Corp. (EMRC). He created a complex model of the wing using thin composite plate and orthotropic composite brick elements. Matthew ran several analyses to develop the design and to establish correlation with prototype test results. Eventually, he created an entirely new model for the wing design.

Back at the drawing board. Electrical and avionics designers at CMC use AutoCAD LT to produce wiring diagrams and drawings for sheet metal brackets. Burleigh notes the package has been very cost-effective and is adequate for even fairly complicated components.

Meanwhile, other engineers have been using AutoCAD Release 12 to produce most of the 2-D drawings for the Leopard. The company claims its techniques are not very advanced because it doesn't use solid models or complex assemblies, but that hasn't been a problem. According to Burleigh, "With AutoCAD we can produce good working drawings very quickly, and modify them if required without delay." The best part, he says: "We're doing it without a huge investment in equipment or manpower."

Moving forward. The 001 prototype featured two low-power NPT301 turbojets from Noel Penney Turbines (NPT) Ltd. in Coventry, England. The converted missile engines were intended solely for the 001, and NPT was slated to develop new engines for the final version of the aircraft. But when NPT went bankrupt, the entire Leopard project was delayed for one year until CMC teamed up with Williams International Corp., Walled Lake, Michigan.

Williams developed the FJX-1 engine for CMC's first production-configured aircraft, the 002, now under construction at the Designability R&D Center in Dilton Marsh, England. Rated at 680 lb-thrust, the FJX-1 has more than twice the power of the NPT301. That's okay for the 002, but it's not quite enough for the final aircraft. Williams is currently researching the proposed 1,000 lb-thrust engine for the final jet.

Material sacrifices. The 002 is made of all composite parts, mostly carbon or graphite epoxy. To keep tooling costs down, CMC is using low-temperature curing resins instead of high-temperature ones. But not without penalty: the efficiency of the structure in terms of strength-to-weight is not as good as with high temperature resins, so the plane weighs more. Still, the company says the ratio is better than with the equivalent metal structure.

The Leopard seems to offer everything a business traveler could want: speed, comfort, and the convenience of a personal plane. But what about safety? Chichester-Miles insists the Leopard will be just as safe as any other properly certified aircraft. In fact, he says the plane's design parallels that of larger executive jets, right down to its standard anti-icing system for the wings and tailplanes.

X-31: Prelude to tailless flight?

X-31: Prelude to tailless flight?

Mission: Demonstrate the use of thrust vectoring-coupled with advanced flight controls-to provide enhanced flight maneuverability at very high angles of attack. Mission accomplished: Flight tests yield an almost 10:1 kill ratio, far surpassing the optimistic 3:1 ratio predicted by simulation.

The slower the speed, the smaller an aircraft's radius of turn. As any fighter pilot knows, tighter turns mean earlier weapons launch. Unfortunately, conventional aircraft offer limited control at slow speed, and they can fall out of control at stall speed-just when achieving the smallest turn radius.

The X-31 program at Edwards Air Force Base, CA, demonstrates how the ability to maneuver beyond stall limits-allowing very high attack angles-improves a fighter's chances of winning the close-in-combat dogfight. Two design components contributed to the program's success: aerodynamics optimized for post-stall maneuvering and multi-axis, thrust-vectoring capability.

Based on the European Fighter Aircraft, with refinements developed by Rockwell International and Deutsche Aerospace AG (formerly Messerschmitt-Bolkow-Blohm GmbH), the X-31 features a delta/canard configuration. Its center of gravity sits aft of the subsonic center of lift, making the layout unstable in pitch at subsonic speeds. In combination with the delta wing's large surface area and high leading edge sweep, however, the design offers superior supersonic performance.

The "long-coupled" canards, located further from the wing than "short-coupled" configurations, also function differently than conventional canards. Designed for pitch control and trim rather than lift, they move into the wind at increasing angle of attack, maintaining control effectiveness throughout post-stall maneuvers. Should the thrust-vectoring system fail, the canards assist in aerodynamic recovery.

Fixed aft and nose strakes complete the aerodynamic package. The aft strakes supply extra nose-down pitch-control authority from very high angles of attack, while the small nose strakes help control side slip.

Thrust-vectoring control. General Electric's 404 engine-powerplant of the F-18, F-117, X-29, and F-20-provides the thrust-to-weight ratio needed for supermaneuverability. It also resists flow distortion resulting from high angles of attack, large yaw rates, and big sideslip angles. Combined with a belly intake, the engine allows full-power operation, even at extreme angles of attack.

At the program's start, thrust vectoring presented a problem, since no multi-axis nozzle was available. The X-31's solution: three composite vanes arranged 120 degrees apart. Mounted on the aft fuselage with nimonic alloy fittings, the vanes deflect into the exhaust to generate as much as 17% engine thrust in any lateral direction. Constructed of lightweight, heat-resistant carbon-carbon material, the vanes can sustain temperatures as high as 1,500 degrees C for extended periods of time. When not being used for maneuvers, the vanes trail outside the exhaust plume, automatically tracking the jet plume boundary during power changes and change-of-flight condition to minimize effectiveness deadband.

Because the vanes, actuators, and support structure were designed into the aircraft from the beginning, overall effect on weight remains minimal. Moreover, no added aircraft ballast is needed. In fact, says Harvey Schellenger, X-31 chief engineer at Rockwell, the net weight of the vane system totals about the same as the added weight of an integral nozzle. "Without the need for ballast," he points out, "the X-31 thrust-vectoring system is hundreds of pounds lighter than either the F-18 HARV (external steel vanes plus ballast) or the F-16 MATV (integral nozzle plus ballast)."

Flight controls. The digital flight control system hardware, designed by Honeywell Defense Avionics Systems, uses both conventional and thrust-vectoring control surfaces to maintain precise control of the aircraft throughout its flight envelope. Based on pilot input and feedback signals, the control laws (developed by Deutsche Aerospace) calculate the required thrust deflection in pitch and yaw. The flight-control system translates this deflection command into single-vane deflections. For example, if a yawing moment to the right is required, the left vane moves into the exhaust jet. The upper vane moves into the plume enough to compensate for the pitching moment created by the left vane. The right vane moves out of the plume.

In general, direction of thrust can be deflected at an angle of more than 15 degrees around centerline. In the event of system failure, or if the pilot chooses to disengage thrust vectoring, the flight-control system automatically redistributes commands to the conventional aerodynamic surfaces. "Even if one of the vanes falls off," says Hannes Ross, pre-design department director, Deutsche Aerospace, "it wouldn't put the pilot in jeopardy."

No tailless fighter design has ever been flight tested, and no vertical tailless aircraft has flown supersonically. However, the X-31's all-digital, fly-by-wire flight control system with integrated thrust vectoring readily lends itself to "quasi-tailless" flight experiments. These tests measure in flight the requirements needed to maneuver and control a tailless aircraft.

The quasi-tailless mode uses the plane's aerodynamic surfaces, primarily the rudder, to cancel the stabilizing effect of the vertical tail. This, explains Schellenger, directionally destabilizes the aircraft so it behaves as though all or part of the vertical tail has been removed-without really removing the tail.

Instead, thrust vectoring stabilizes the destabilized aircraft and performs yaw control for maneuver coordination. Moreover, variable destabilization gains permit selection of varying degrees of tail removal. If undesired aircraft motions occur, or if the pilot disengages the mode, the flight-control system quickly reverts to its normal mode of operation. "That's the real attraction of the quasi-tailless feature," says Ross. "Many different tailless designs can be aggressively tested in complete safety."

A special feature of the quasi-tailless control mode provides the option to use the rudder to both destabilize and to emulate the effects of another yaw-control device. Such non-rudder aerodynamic controls, Ross points out, are likely to be part of an aircraft designed to be tailless.

Historic flight. On March 17, 1994, the X-31 climbed to 37,000 feet above the desert floor of Edwards Air Force Base, accelerated to Mach 1.2, and engaged the quasi-tailless mode-a significant first in aviation history. The degree of tail removal was increased incrementally up to full tail off. Performing maneuvers, including 2g turns, the aircraft responded well.

Quasi-tailless experiments at subsonic cruise speeds, and at low approach and landing speeds, will be the next step. These tests will allow investigation of the relationship between degree of destabilization, aggressiveness of maneuver, and aerodynamic yaw control required at selected flight test points. A new control law version that incorporates added logic to emulate a tailless aircraft throughout the entire X-31 flight envelope will follow. The new version will add thrust control of the engine to the thrust-vector control, further enhancing aircraft response in the quasi-tailless mode.

After all quasi-tailless flight data have been evaluated, the X-31 will proceed with the next step in the follow-on program: physically reducing the size of the present vertical tail and rudder. Ability to control the aircraft should thrust vectoring fail will determine the new size of the tail and rudder. These tests will verify the quasi-tailless results with flight data from a truly destabilized airframe.

Finally, after installation of a deployable/retractable stabilization and control device, such as a flip-up, all-moving vertical fin, plans call for removing the vertical tail completely.

Where does this all lead? Post-stall performance has already attracted the attention of air forces around the world. Now, the possibility of replacing aircraft surfaces with vectored thrust capability promises substantial reduction in aircraft weight, aerodynamic drag, fuel consumption, and radar signature. While the latter is important to military personnel, less weight, drag, and fuel consumption are of significant interest to the commercial airline industry.

Militarily or commercially, if the results prove as good as they look, the X-31 program could eventually result in increased employment for aerospace engineers worldwide.

AutoCAD, Release 13

AutoCAD, Release 13

Considering R13 has been rewritten from the ground up, I was happy to find myself comfortable with it from the beginning. I loaded my old AutoLISP command shortcuts, and was immediately at home. Autodesk has taken pains to ease us into this next stage of AutoCAD. I'm slowly increasing my usage of the customizable icon interface, and expect a new operating style to develop naturally.

3-D modeling. Since much of my current work involves conceptual designs using AME, I started with the 3-D modeler. Operations seemed familiar even though the internal operation of the ACIS kernel is totally new. R13's 3-D editor uses commands similar or identical to those of AME, and new features are easy to learn. The real difference comes with the NURBS-based definition of curves and true ellipses. Now, complex shapes are defined compactly and accurately.

I was particularly pleased with the successful construction of a hydrodynamic shape that I had been unable to generate with AME. R13 easily filleted edges defined by elliptical and other non-circular, curved intersections.

Since R13 doesn't retain solid primitives which have been used for booleans, it can't support an equivalent of the AME SOLCHP command. Modifying completed solid features can be performed only through additional construction. In the long run, Designer will more than fill this loss. But for now, some discrete SAVEs and use of AutoCAD's still exceptionally robust UNDO are satisfactory.

2-D drafting. The 2-D drafting improvements in R13 are extensive. Associative boundary hatching is intuitive and efficient, and hatch edits have eliminated erasing and re-hatching. Trimming is a breeze. Intelligence has been added to dramatically reduce the number of steps needed for complex trims. I found these editing improvements, along with projected and implied intersections for both trim and extend and relaxed UCS restrictions, among the most productive in R13.

AutoCAD, Release 13
The Windows version reviewed uses Win32sfor high performance and a customizable Windows interface. The ACIS kernel provides accurate representation of 3-D geo- metry. R13 offers 2-D drafting enhancements, improved solid modeling performance, and advanced rendering capabilities. The Windows version requires a 386 or better, 16M bytes of RAM, 35M bytes of hard disk space, and a permanent swap file of 64M bytes.

List Price: $3995 diskettes $3750 CD-ROM

Autodesk, Inc., 2320 Marinship Way, Sausalito, CA 94965; ph: 415-332-2344.

Dimensioning offers a wealth of new and improved features. All dimensions are associated with easily edited, expanded styles; and style overrides permit custom formatting at the single-dimension level. I found nearly any visual effect was possible.

The new linear dimensioning command permits rapid construction of both vertical and horizontal dimensions without additional commands. Additions such as multi-line text entry, expanded baseline and continuous dimensioning, and improved drafting standards support offer everything I need at present.

3-D to 2-D transition. Although the manuals offer no equivalent of AME's SOLPROF command, proper setting of the DISPSILH silhouette control variable produced a reasonable facsimile-adequate enough to provide clear, facet-free isometric views.

However, I would like to see improvement in this area. I think a projection command should be added to provide flat, explodable, clean views suitable for efficient dimensioning.

AutoCAD's built-in rendering capability continues to grow, with materials, more lighting options, and Phong shading producing a significant improvement in realism. I found rendering fast enough to use frequently, now competing with HIDE and SHADE as an interactive tool. File export of rendered images was invaluable for image editing and for compilation into other Windows documents. I used the direct .3ds file export to 3D Studio and was pleased to bypass the .dxf file export/import methods used earlier. I had to make some surface normal adjustments within 3-D Studio, but found the overall process very satisfactory.

All-in-all, R13 met, and in many cases exceeded, my expectations. I'm particularly pleased with the new ACIS capability, and am impressed with the general stability and robustness of code which has been so extensively revised.

Application Digest

Application Digest

Saving energy through pump speed control

Bruce Widell, Senior Applications Engineer,
Danfoss Electronic Drives Division, Danfoss, Inc.

Some of the most commonly used methods for controlling pump flow rely upon throttling and restrictive devices. All of these devices dissipate power by friction and heat diffusion, thus wasting energy. So the obvious question arises: How can you minimize the losses?

An adjustable-frequency drive may be the answer. Adjustable-frequency drives can be implemented in a way that optimizes system efficiency, thus offering the potential for greatly improved energy savings.

How does an adjustable-frequency drive save energy? Well, most of the electrical energy in today's industrial plants operates centrifugal loads, such as pumps, fans, blowers, and compressors. Constant-speed ac motors, sized for maximum loads under worst conditions, power most of those loads. A high percentage of pumps, fans, and blowers also have fluctuating output requirements, so they need an external means to adjust flow. That's why users employ throttling and restrictive devices-such as valves, bypass lines, orifices, and recirculation loops.

Using an adjustable-frequency drive instead of a constant-speed ac motor typically eliminates the need for the throttling and restrictive devices. As a result, power losses are minimized.

The accompanying figure shows the input power and flow for a standard centrifugal pump using a throttle valve. Factors affecting energy are the percentage of flow cutback, running time at reduced volume, and cost of electricity. The power curve for the adjustable-frequency drive is based on an average amount of static head, or lift, in the system. Total head equals the sum of the static head and the friction head.

Choose the Right Slide For Maximum Performance

Gary Murphy, Applications Engineering Manager, PHD, Inc.

Selecting the right slide can be a nightmare. With so many models to choose from, consider these variables to determine the right slide for your application:

Bushing load capacity: First, decide which type of bushing best suits your application. Linear ball bushings are the most common and give good performance in a variety of applications. Fluoropolymer-composite bushings are a more recent development. These new maintenance-free, self-lubricating bushings carry greater static loads, cost less than linear ball bushings, and are ideal for working in harsh environments.

Shaft deflection: Shaft deflection affects the accuracy of the slide's tool-plate location and, therefore, the accuracy of the slide application. This deflection is a function of the shaft's diameter, material, travel length, load, and distance between the linear-bushings. Other factors that can affect accuracy are: shaft straightness; shaft weight; and linear bushing alignment. Most slide manufacturers have deflection graphs and calculations available to ensure proper application.

Air cylinder thrust: The amount of cylinder thrust depends on the cylinder size, available air pressure, and safety factors related to horizontal or vertical applications. The cylinder must generate the force required to move the load.

Kinetic energy: You should consider unit speed and the ability to stop loads to ensure that the slide can handle the amount of kinetic energy produced. To increase ability to stop a load, some manufacturers offer to provide cushions and shock absorbers.

Once you've determined these elements, the rest is easy. Your requirements can be matched with the exact slide for your application.

Engineering News

Engineering News

Pentium flas could spark scramble
for bug-coping strategies

Experts advise cross-checking critical designs using different processors and software. The tradeoff? Time to market.

Newton, MA--By now, engineers worried about potential Pentium division errors have contacted Intel and swapped their flawed chips for new ones. But while that problem may be "solved," the Pentium flap has raised a broader question: Are other chips or software also making errors that some mathematics professor may not catch until next year? Should engineers consider strategies for overcoming potential flaws, including delaying time to market while checking a design one more time?

"Microprocessors have become so complex that it is no longer possible to completely debug them, or even to determine every bug that exists in one," according to Dr. Thomas R. Nicely, the mathematics professor at Lynchburg College, VA, who discovered the Pentium flaw. His advice: Perform "mission-critical" computations multiple times-preferably with different CPUs, operating systems, and software algorithms.

"This is a direct assault on speed to market," says Michael Schrage, a research associate for the Sloan School at MIT who also writes the Innovation column for the Los Angeles Times. "But you retain no market-share advantage if you're being sued for $250 million by 10 of your largest customers for a flawed product."

The potential for hardware flaws shouldn't be overstated. After all, chips and software go through multiple quality-control checks before hitting the market. Still, caution is advisable. "There's probably a greater chance of error in formulating the problem and writing the code than there is in a microprocessor," says Rich Partridge, a microprocessor market analyst with D.H. Brown Associates, Port Chester, NY. "But they're all tied together. If you can't trust anything, what do you do? You do cross checking."

Pandora's box. The catalyst for this uneasiness is Intel Corp.'s Pentium microprocessor. Its floating-point unit had a flaw that caused it to return reduced-precision results for division involving certain numerators and denominators. The flaw was due to five missing entries in a 4,000-entry look-up table the iterative algorithm uses to perform the divide instruction.

Intel officials say that for 1 in 9 billion possible divides, any digit from the fifth digit on could be incorrect. However, the error could be magnified by multiplying the result by a large number or subtracting two numbers that have been divided.

The impact of the flaw varied by the rate of use of floating-point instructions, the input data fed to them, the use of the results in further calculations, and the accuracy needed. One of the most intensive uses of floating-point math is in engineering software.

"CAE users need to be jolted into the realization that computers are not infallible," says Charles Foundyller, president of CAE market research firm Daratech in Cambridge, MA. He doubts that engineers will be doing CAE on multiple platforms because of the time involved, and advises moving to the latest computer technology with caution.

Schrage predicts that companies will be sharing more hardware testing data and publishing the results. Disclosures from such companies as Boeing, Ford, GM, and HP on their own tests would help speed the discovery of hardware and software bugs.

Validating designs. Testing is an increasingly critical issue for microprocessor designers and manufacturers. Partridge says that as chip densities climb, designers will be devoting more internal hardware to detecting and correcting errors. In 18 months to two years, we may see more chips with error-correcting caches, residue checking, or instruction retry.

Such features would catch errors due to manufacturing problems, but not design problems. For example, the Pentium had a basic design problem that required extensive testing to catch. "Our ability to successfully test microprocessors has been outstripped by the product's inherent complexity," notes Schrage. Adds Partridge: "You won't find every problem using brute-force testing of trillions of combinations. You have to have a more rigorous approach where the engineer who designed the chip needs to defend the mathematics involved in how he or she has implemented the logic."

As a result of the Pentium embarrassment, companies may take the time to do such design walkthroughs-even though that may delay microprocessor introductions. Walkthroughs will be especially crucial with superscalar processors, such as RISC chips, which can execute more than one instruction at a time. These chips are ripe for instruction sequencing problems that would be much more difficult to find-no matter what the method-than the Pentium flaw.

It's not just the chip. Dr. Julian Palmore, principal investigator at the U.S. Army Construction Engineering Research Laboratories (CERL) in Champaign, IL, and professor of mathematics at the University of Illinois, points out that errors caused by a processor chip are only one way computer simulations can become flawed. "In any discipline using computer models, especially where safety is concerned, it's absolutely essential to verify and validate the model using exact arithmetic."

That means writing software that is machine-independent for calculations. For example: In statistics, researchers use exact arithmetic by employing an integer-based random-number generator, so there's no rounding.

  • Computer hardware and software can introduce design errors.

  • For critical work, devise a strategy to offset the chance that your design work will be compromised.

  • You'll have to make tradeoffs between design cross-checking and speed to market.

Palmore's work at CERL on battlefield simulations has revealed many specific opportunities for errors in timing, interfacing, and computations. "Depending on how sensitive a process is, such as in an aircraft controlled by very small signals, these errors can have devastating consequences."

A real-world example of such impact occurred during the Persian Gulf war, when a Patriot system failed to engage a SCUD missile. A U.S. General Accounting Office report found that the computer's binary arithmetic, which introduced small errors over about 100 hours, resulted in a timing mismatch between the computer program and the radar system. The 1/3-second calculation error caused a shift of about 700 meters in the radar range gate, which was enough to make the system fail to recognize the incoming SCUD as a missile to engage.

Warns Palmore: "Errors occur and accumulate when you have any sort of algorithm that's being used iteratively, with the output from one calculation feeding the next. You have to watch out for and understand how errors affect the calculation."

Of course, the ultimate quality-control check is engineering training and common sense. "You can analyze things to death," says Bob Riccomini, lead engineer on Apple Computers' PowerBook 270c. "You have to go with your engineering judgment."

-Deana Colucci, New Products Editor

Hannover aids search for European products, customers

As competition in U.S. industries increases, more and more companies are taking their products to the international marketplace. And with good reason: The European Community's single-market economy represents more than 345 million consumers and $6 trillion of purchasing power. But for would-be customers, finding the right products can be both confusing and time-consuming.

One place to turn: The Hannover Fair tradeshow in Hannover, Germany. Europe's leading industrial trade show, it covers nine sectors ranging from factory equipment and automation to environmental technology.

Last year's show hosted some 6,800 exhibitors from 60 countries and filled more than 12 million square feet of space. Nearly 400,000 attendees traveled from 110 countries in Europe, the Americas, Asia, and Africa.

In addition to the individual company exhibits, attendees can visit special USA Pavilions and group exhibits organized by region or association.

"The show's organization and planning are first-rate," says Bill Taylor, vice president of sales and marketing for Jeffrey Chain Corp., Morristown, TN. "We made good contacts, and we're very happy we went."

Snorkel solves aerial balancing act

St. Joseph, MI--Balance is critically important to Snorkel Economy, a maker of self-propelled aerial work platforms. Their devices move workers in the air up to four-stories high-without using outriggers, special extensions, or braces. "Our machines have to be stable in any position of articulation," engineer Dave Engvall explains.

During one recent project, Engvall analyzed an articulated boom with 27 junctions known as pin joints, where sections of the boom connect and move. Two aspects of the design were crucial: stability of the overall vehicle, and the load on each pin joint.

Engvall imported his CAD files into Working Model, a dynamics/kinematics analysis package from Knowledge Revolution, San Mateo, CA. To find the most unstable aspect of his design, he focused on the lifting structure-the boom, engine, and counterweight, all set on a rotating turntable.

The hardest balancing problem in the design was side tip stability, he says, with the boom extended at a right angle to the vehicle. The key point of balance or "tipping fulcrum' in this position was the tire. In a few seconds, a simulation revealed at what point the mobile lifter was stable: When the force on the separator was less than zero, the machine tipped over; when it was greater than zero, it didn't.

He also used the software to measure the load stress or static force balance on individual pin joints. "If I did the static force balance analysis myself, I would have to describe a free body diagram of each component, write equations for the translations and rotational elements for each link, and solve them all simultaneously."

Instead, he used Working Model to assign the proper weight to each component, put a pin joint at each location so the components could move, and let the simulation run.

The savings? It used to take him more than a week to create models and do static load calculations. Now he finishes those tasks in a few hours.

Composite cuts weight in multi-function printer

Dayton, OH--Fax/telephone/modems. Photocopier/scanner/faxes. Analysts predict a new surge of these "one-man-band" products for 1995, especially in the electronics and computer marketplaces. With that in mind, engineers are struggling to produce multi-function machines that are not large and bulky.

Monarch Marking Systems recently entered this foray with a portable four-in-one printer. The hand-held thermal bar code printer-which includes a label applicator, data collector, and laser scanner-is the only one of its kind on the market, says Tom Keller, senior mechanical design engineer at Monarch.

Keller and his team examined several materials options to reduce the printer's size and weight. They settled on Lubricomp RCL, a carbon-reinforced, internally lubricated nylon 6/6 thermoplastic composite.

"Especially in portable products, weight and ergonomics have become so important, you have to get as much function as you can out of each part," Keller explains. "So, the more characteristics you can squeeze from a given material, the more you can do with that particular part."

Lubricomp's stiffness and strength enabled the printer's drive frame to become the central structural skeleton of the unit, with the outer housing bolted over the top.

The composite also gave the drive frame the rigidity, dimensional stability, and lubricity Monarch sought. The printer, weighing about 38 oz, can survive ten drops from one meter onto concrete in various orientations.

"We also needed good wear resistance," Keller says. "Because two posts in the drive frame support rotating gears, we chose a material with PTFE lubrication."

Using Lubricomp also resulted in a substantial cost savings, according to Keller. "We were able to cut down considerably on weight and volume. After all, those are the two most important criteria when designing a portable unit."

Inhaler gets an upgrade with CAD

Madison, NJ--Pocket inhalers, those small devices used to administer metered medical dosages for treatment of asthma and other bronchial ailments, seem uncomplicated to users. However, assuring their reliability can create a problem for their designers. So, when Schering-Plough Corp. decided to redesign an existing model, it wanted to improve performance as well as embellish the inhaler's look.

Three parts make up the inhaler. They include: a clear housing that holds the canister of medication, an actuator to administer the required dosage, and a dustcap that fits over the nozzle spout to protect it from outside contamination.

"In addition to aesthetics, we wanted to use the redesign as an opportunity to improve the snap-fit between the canister and the actuator," explains Keith Bishop, Schering-Plough's associate principal scientist. "This would eliminate any chance of an inadvertent separation of the two parts-something that had happened with the old design."

To help in the redesign, Schering-Plough called on Phillips Plastics Corp., Prescott, WI. During preliminary design stages, Schering-Plough fed Phillips' CAD designers with concepts used to create a design database. Phillips CAD Engineer Mark Sponsel reports that Pro/ENGINEER (Pro/E) solids modeling software helped model the parts in CAD.

"Pro-E is a perfect fit where no existing design database exists," says Sponsel. "It allowed us to perform interference checks and formed a perfect foundation for stereolithography (SL) work needed to prove out elements of the design."

Improving the fit of the housing and actuator was achieved by incorporating a proven snap-fit design into the inhaler. "Incorporating that snap-fit ultimately saved design time and aided in the SL process," Sponsel adds. It also enabled the use of a two-cavity production tool to build the final eight-cavity production mold.

The redesigned inhaler incorporates several subtle design refinements. Among them: the addition of textured grips in the dustcap, and the placement of the company's logo into the part. The snap-fit design provided the appropriate degree of resistance, alleviating virtually all separation concerns. Moreover, part consistency and tolerances between the canister and actuator were improved. Adds Bishop: "The result is a far better product in today's marketplace."

Intake manifold wins SPE Grand Award

Detroit, MI--A thermoplastic composite intake manifold on the 1995 Cadillac Northstar V-8 engine walked off with top honors in the 1994 Society of Plastics Engineers' (SPE) Grand Award for the "Most Innovative Use of Plastic." The component also won the powertrain award category.

Production of the manifold makes use of the lost-core manufacturing method. It allows several pieces to be integrated into the same molding. The result: elimination of more than 80 components required in the earlier design.

"Along with the performance benefits of increased power, as well as improved idle stability and driving range, the thermoplastic manifold significantly reduces part complexity and mass, which simplifies manufacturing and assembly," reported Sam Winegarden, chief engineer of the Northstar engine, in accepting the award. "Moreover, the nylon 6/6 material can be recycled."

Freudenberg-NOK's Plastic Products Div., Plymouth, MI, designed and produced the manifold. It consists of glass-fiber-reinforced Ultramid nylon from BASF. The 6/6 nylon was specially formulated to resist engine temperatures and attacks from oil, fuel, and underhood fluids.

The manufacturing process required eight metallic intake runner cores die-cast from a soft solder-type material. The cores are locked on a mandrel, set into a plastic injection mold, and the nylon 6/6 injected into the mold.

The mold and cores are immersed in a hot oil bath to melt the cores, creating hollow tubes inside the manifold. This results in very smooth inner walls for optimum air flow and distribution. The low thermal conductivity of the nylon also serves to insulate the air inside the manifold from engine heat to help increase air flow.

"The SPE recognition underscores the great contributions that plastic composites can make in solving the complex challenges automakers now face," says Robert C. Hange, senior vice president & general manager of Freudenberg-NOK's Plastic Products Div. "This means enhanced mileage and performance, while cutting manufacturing cost and reducing automotive noise."

Workstations help patients avoid surgery

San Jose, CA--With medical tools such as laparoscopes, doctors can perform minimally invasive procedures on patients, greatly reducing the need for extensive surgery. Stryker Endoscopy, a designer and manufacturer of medical equipment, knows how important it is to design better and smaller instruments.

To improve its product designs, the company used a computer system that ran 2-D geometry applications, but had poor 3-D wire frame capabilities. Engineers had difficulty detecting interference between parts, and their system was unable to effectively simulate the motions of instrument parts. Often, construction problems could not be detected until the prototype stage. And, Stryker had only one PC for CAD work, while all others were reserved for word-processing tasks. The result was a bottleneck and unacceptably long design cycle.

With a goal of reducing the entire product-design cycle by at least 40%, the company installed a network of SPARCstation workstations and servers. In addition, 18 PCs used for word processing and less demanding design tasks now share files with the SPARCstations through PC-NFS(R). Among the programs running on the system: Pro/ENGINEER, AutoCAD, MECHANICA, and Optical Research Associates' Code V software.

"Since installing the network," says William Chang, vice president of research & development at Stryker, "we have more than met our goals. In addition to reducing the overall design cycle time by approximately 50% and generating prototypes that work the first time, we've increased productivity by almost 70%."

Turbocharger bearing retainers take the heat

Tokyo, Japan--NSK, a large bearing manufacturer, wanted to lower costs and improve productivity in the production of turbocharger bearing retainers. However, machined components made from compression molded polyimide stock shapes proved too expensive. The solution: a switch to an injection-molded polyimide.

Polyimides resist high temperatures, wear, and solvents. Until recently, they also resisted conventional processing. For the most part, they required the fabrication of parts by machining stock shapes, or compression molding powders under high heat and pressure. Enter AURUM JCN 6230 polyimide from Mitsui Toatsu Chemicals, New York, which lays claim to being "the world's first injection-moldable polyimide."

Before making the switch to the injection-molded poly-mide, NSK put the high-performance thermoplastic to a 500-hr simulated under-the-hood test. According to Mitsui officials, the only modification to the processing equipment involves the need for a nozzle that can tolerate temperatures of 75 degrees to 79 degrees F.

Test conditions included: maximum velocity of 135,000 rpm, temperatures of about 300 degrees C, and use of a steel mating material with oil lubrication. Not only did the material pass the test, but it helped NSK lower production costs and increase productivity and moldability. The retainers also have a longer life at high temperatures in oil, according to test results.

Garrett Turbo, Inc., a unit of AlliedSignal, Inc., makes the turbochargers. You will find them in certain models produced by "a large Japanese automaker."

Protective coating keeps superconductors running

Wilmington, DE--Advanced superconductors are moving out of the lab and into practical applications, thanks in part to ultrathin protective coatings of amorphous fluoropolymer.

The coatings, made of Dupont Teflon(R) AF, are applied in a solution only 2 microns (0.08 mils) thick. They protect superconductive metal-oxide films against damage from traces in the atmosphere.

The superconductors, also products of a DuPont new business venture in superconductivity, can function in real-world conditions. Conventional niobium superconductors only work at temperatures near absolute zero. However, the metal-oxide films, pioneered by DuPont, become superconductive at temperatures as "high" as -143 degrees C (-243 degrees F). Cooling can be accomplished with liquid nitrogen or by using mechanical refrigeration.

With no electrical resistance, the "high-temperature" superconductors (HTS) provide the basis for ultra-efficient electronic devices. Among their potential uses: microwave-frequency, broad-band antennas; low-loss filters; and high-quality resonators and oscillators.

The superconductor bases consist of yttrium, barium and thallium, barium, calcium, and copper. They are deposited on wafer substrates of lanthanum aluminate or sapphire. Circuit patterns are etched in the films using the same patterning proccesses employed for semiconductors.

"Because our films are oxides, they can be damaged by traces of acid in the atmosphere, and, in many applications, have to be protected or passivated," says Daniel Laubacher, product development manager for DuPont Superconductivity. "We tried standard polyimide passivation coatings, but they didn't adhere well, and they picked up acidic moisture."

Superconductor devices using the new coating benefit from the low dielectric constant of Teflon AF: 1.89 to 1.93. This is the lowest dielectric constant for any polymer, Laubacher claims. In one HTS design, Teflon AF serves as an adhesive. Circuits now being explored will use the fluoropolymer in a resist layer for reactive-ion etching, and as a coating that makes other resist layers easy to remove.

Oxygen process boosts glass quality

Somerset, KY--Inject pure oxygen into a glass-melting furnace, and what have you got? A whole list of benefits, according to GE Lighting.

By providing better control over glass quality, oxygen fuel firing reduces the incidence of cord (an inclusion of glass of a different composition), and stones (crystalline inclusions). And the method being used by GE Lighting, 92% oxygen fuel firing, promises cleaner flue emissions.

There are other direct benefits. Since GE Lighting converted from regenerative air to the oxy/fuel process, melting capacity has increased by 20%, while gas use has dropped by half on a day-to-day basis. Counting gas and electricity, utility costs have decreased by $45,000 a year.

The inexpensive and accessible oxygen has completely changed the economics of glass melting, according to Dan Cico, GE Lighting's manager, glass marketing. GE had a number of systems to choose from in making its conversion. It finally settled on a vacuum swing adsorption (VSA) system built by Air Products and Chemicals. Because of its success, another GE glass plant switched to the process late last year, with two more plants scheduled to come on line by mid-1995.

Concept cars get serious at '95 auto show

Detroit, MI--What will you be driving in the year 2000? Concept cars at the North American International Auto Show propose future vehicles with interactive electronics and an emphasis on safety.

With climbing attendance rates and an ever-more-international audience, the annual NAIAS is on the grow. In January, representatives from some 30 countries attended the introductions of more than 40 vehicles.

The concept designs-typically a mix of pre-production and fantasy-favored realistic technologies. "In past years the concept cars were almost theatrical," commented one industry analyst. "This year, they're less show and more business."

Witness the Buick XP2000. With interactive electronics and eight airbags, this idea car explores what interior options might be most appealing to future drivers. For example, the XP2000 features a "smart-card" instrument panel and memory chip that would let drivers insert a credit card to automatically pay for tolls, fuel, food, and other services. The card could also store driver preferences to tailor automatic seat settings, transmission shift pattern, and suspension response.

The instrument panel includes a flat-panel color display suitable for future intelligent vehicle highway systems and a color heads-up display. The flat panel is linked to sensors that indicate diagnostics such as low air pressure in the tires.

Anxious to avoid a "showbiz" label, Buick General Manager Edward Mertz described the car as "a realistic preview of Buicks of the future." Some technologies that look promising for the near-term: a single high-intensity discharge lamp to deliver all interior lighting via fiber optics, as well as side and front airbags for front and rear passengers. The car's computers can be programmed to automatically dial local emergency services if an accident activates the airbags, say Buick engineers.

But eight wasn't the record for airbags. The Mercedes X-bag research car uses 17 airbags, including kneebags under the lower dashboard, rear-passenger airbags, side bags in front- and rear-door panels, B-pillar roof bags for side collisions and rollovers, and bags built into the head restraints to protect in rear-impact accidents. Although many are design exercises, some airbags from the X-bag, such as the side bags, will find their way into '96 production Mercedes. They are already offered in '95 Volvos.

In the X-bag concept car, sensors work with a computer chip to inflate whichever airbags are needed to protect the occupants. Engineers hope the car will be a precursor to an "anticipatory crash-analysis system" that would use electronic object recognition to establish the size and weight of an oncoming vehicle based on pre-programmed data. Engineers predict such a system would calculate impact angle and speed, as well as the expected severity of the collision, then trigger the appropriate airbag several centimeters prior to a collision-thus improving airbag performance.

Big ideas. In many stands, the theme was BIG. For example, at just under 17 feet in length, the Chrysler Atlantic concept car unabashedly recalls the heroic proportions and profiles of luxury coupes from the 1930s. Modern touches include an all-steel unitized body and neon stop and taillights.

At Ford, big was to the tune of a 6.0-l, V-12 engine. The design of the GT90 concept car, from the multi-beam, high-intensity discharge headlamps to the stainless-steel exhaust, was completed in six months. Although Ford has "no plans" to build a production version, Vice President of Design Jack Telnack pointed out that "because of extensive use of CAD tools and rapid prototyping, GT90 is very repeatable-unlike most show cars."

The GT90's deliberately un-retro styling includes unconventional lighting such as fluorescent stop lamps and gauge illumination, and ion-charged taillights. Equally unconventional is the mid-ship, turbo-charged, aluminum-block engine with a 720 horsepower rating. The car, which takes its name from the GT40 racer, boasts a zero-to-sixty acceleration of 3.1 seconds and a top speed of 235 mph.