Engineering News

Welding makes strong connections

New fluxes and sophisticated welding techniques solve joining problems in metal-to-metal connections

Newton, MA--When engineers think of joining methods, adhesives and fasteners are typically the first technologies that come to mind. Welding, however, is the joining technique of choice in metal- to-metal applications from microelectronics to medical devices. Although once considered a black art, modern welding offers a world of opportunities.

At the Edison Welding Institute (EWI), engineers are working with the Navy Joining Center (NJC) in Columbus, OH, to improve an arc-welding process used to join pipes, fittings, and components used in fabricating submarines and ships. The process, called gas tungsten arc welding (GTAW), is widely used in industrial applications for single-pass welds and as the base or "root" pass of multiple-pass welds.

Weld penetration gives the joint integrity and is therefore essential, say NJC engineers. However, problems often arise because of shallow and inconsistent weld penetration, particularly for stainless steel, copper-nickel, and nickel-based alloys. Inconsistent penetration in these materials is known to be influenced by small variations in minor alloying elements in the base material.

To eliminate the effects of such variations, EWI and NJC engineers are developing new welding fluxes. Using new inorganic flux compounds on the surface of the component to be welded can increase penetration by as much as 300% on stainless and carbon steels, copper-nickel, nickel-based alloy, and titanium, says project spokesman Troy Paskell. An evaluation is also underway to determine corrosion resistance, weldability, and metallurgical and mechanical properties of welds made using the fluxes.

On the road. In some applications, a harsh operating environment calls for sophisticated welding techniques. For example, trailer-component manufacturer Tramec Corp., Iola, KS, makes an electrical harness that conducts electrical current between trailers and cabs. Consumers expect the plug to deliver long life, but the connection is exposed to salt spray and almost constant vibration. "One of the main problems in the past was corrosion," explains Tramec material control manager Patrick Meyer. "This is a long-standing product, and a change of design is very difficult."

The connection is between a multiple-stranded copper wire conductor and a nickel-plated pin that is molded to a socket. In the past, the contact involved putting the wire into a plastic insert with a flat pin, and using a small number-10 screw to make the connection. Engineers found that the screw was breaking some strands of wire, causing loss of current conduction and accelerating deterioration due to salt spray.

To add to the challenge, Tramec engineers also had to meet the specifications of the OEM trailer manufacturers. One of the most difficult: A minimum pull test designed to simulate what happens when the owner forgets to unhook the plug before separating the cab and trailer. "It needs to come apart at a certain pull without tearing the connection off," explains Meyer. "That's where the strength is really needed, because that actually happens quite often."

After evaluating several alternatives, Tramec engineers chose an ultrasonic welding process. Using a WS2025 ultrasonic welder from Sonobond Ultrasonics, West Chester, PA, engineers increased the bonding strength and life of the connection, as well as adding corrosion resistance to the component. The result: The Sonogripplug eliminates failures due to corrosion and vibration loosening.

"We couldn't find any other way to get a very solid contact that would bond copper wire to nickel-plated brass--which are good conductors--without changing the materials to bad current conductors," says Meyer. The plug's molded body uses a sealed strain relief to further strengthen the assembly and block moisture.

--Andrea Baker, Associate Editor

Resin improves quality of fuel-pump solenoid

Waterford, MI--By re-designing a solenoid for automotive fuel pumps, Pontiac Coil, Inc. improved quality, increased temperature resistance, and simplified assembly.

The former design used a single-polyester bobbin with two sets of windings separated by insulation tape. Now, the solenoid has two coil bobbins injection-molded from DuPont ZytelHTN high-temperature nylon resin by Plasti-Coil, Inc., Woodstock, IL.

"The two-bobbin design improves quality by ensuring complete isolation of the solenoid's two sets of windings," says Steve Hojnacki, an engineer at Pontiac. The bobbins nest together. The inner bobbin holds the power coil that generates a magnetic field to move the solenoid's armature. The outer bobbin supports a coil that senses armature position. An electronic circuit switches the power coil off when the armature completes a stroke, and switches the armature on when a spring returns the armature to the starting position.

Using Zytel® HTN for the bobbins promotes reliability in demanding automotive environments. "HTN's heat-deflection temperature of 500F gives us an extra margin of high-temperature performance," Hojnacki says. The resin's low thermal-expansion coefficient minimizes wire stress during high-temperature operation. HTN also absorbs relatively little moisture and thus has good dimensional stability.

"The material's toughness, strength, and excellent moldability allow us to use molded-in features and thin sections to improve our design," adds Hojnacki. To protect lead wires against damage, for example, the bobbins have molded-in channels to hold them.

Larry Rowe, Director of Engineering at Plasti-Coil, says the good melt flow and toughness of Zytel make it an asset in molding the bobbins as well. "HTN flows well through thin sections to fill the tool, and these thin areas are tough to help prevent damage during handling and assembly."

AMG soups up Mercedes-Benz sedan

Watertown, MA--In an appeal to younger, hipper buyers, Mercedes-Benz has adopted an old Janis Joplin tune for commercials--and introduced a limited edition of its C-class sedan jazzed up by AMG.

This is not your staid, status-symbol Mercedes. This is one understatedly sexy vehicle. During my travels, one fellow rushed out of a real-estate office to ask me about it: He'd never seen a Mercedes looking like this one and it was love at first sight (with the car, not me). You probably haven't seen one either--only 1,000 of the $49,800 cars will hit the roads between the 1995 and 1997 model years. But if you do get the chance to drive one, jump at it.

The ride was so firm and smooth, I was going 80 mph on the highway before I knew it. Acceleration time from 0 to 60 mph is 6.4 seconds thanks to the 6-cylinder, 24-valve DOHC engine with electronically controlled variable intake valve timing. By increasing displacement from 2.8 to 3.6l and using a longer-stroke crankshaft and larger-diameter forged pistons, engineers got the engine to deliver 280 ft-lb of torque at 4,000 rpm. Electronics restrain the top speed to 150 mph, so there was a limit to how much trouble I could get into.

AMG--one of Germany's top automotive customizers and race "tuners"--extensively modifies the base Mercedes C280 sedan. Its contributions to the C36 include: the 3.6l engine, engine-management control units, automatic transmission, intake and exhaust equipment, low-profile 17-inch tires, shocks, front brakes, side skirts, rear apron, and front spoiler with integrated fog lights.

My one quibble is that the climate-control system has too many buttons and is not at all intuitive. But once you've figured that out, you can race wherever you want to go in supreme comfort.

--Julie Anne Schofield, Associate Editor

CAD quickens speaker design

Canoga Park, CA--Audio speakers require precise engineering to produce the best quality sound. But when the speaker's "look" is also of key importance--and you've got less than 12 weeks to go from concept to final product--speaker design carries additional challenges.

"Half of the speaker is the enclosure," explains Ravi Sawhney, president of RKS Design, since a specific amount of air is required for proper acoustics. But Harman/JBL was also seeking an eye-catching design--quickly--to win a bid from Digital Equipment Corp. to manufacture speakers for its multimedia computer systems.

A team from RKS and Harman generated several hundred hand-sketches in two days. After the initial design concept was refined, the engineers used Alias software running on Silicon Graphics workstations.

"We were able to look at surfaces much more rapidly than you ever could by hand," he says. While designers can sketch curved surfaces with lighting and shadows, the shading could be wrong. "By developing through technology, you have greater fidelity." The Alias design was transferred into SolidDesigner software to develop 3-D CAD models.

CAD technology also helped engineers check for critical angles and complex ribbing, as well as ensure accurate tooling. Because the speaker had no constant, straight parting line (where a part comes out of the tool), the tooling needed to be virtually perfect. "It would be impossible to build a tool like that from drawings," Sawhney says. RKS used stereolithography (3D Systems) to validate the design, and then silicon molds were made from those prototype parts. The parts were stuffed with speaker components, painted, and finished to simulate actual production parts. The result: JBL won a multi-million OEM contract for the speakers from those realistic prototype parts, and went from concept to full production in 2.5 months.

"This was the end-all of accelerated programs," Sawhney says.

Compact receiver pulls in GPS data

Sunnyvale, CA--Manufactured by Trimble Navigation Limited, the Lassen™-SK8 OEM GPS module for embedded applications offers engineers a compact, board-level means of providing GPS capability for products. The new GPS board employs 8-channel and ASIC technology. Measuring 0.040 × 3.25 × 1.25 inches, the Lassen-SK8 board consumes 0.75W at 150 mA. With its antenna, the unit consumes 0.88W at 175 mA.

Joel Avey, Trimble's OEM product manager, says this new GPS receiver can acquire satellite signals in less than two minutes from a true cold start. It can capture signals in less than 20 seconds if satellite position data has been saved, and shutdown was of short duration. Reacquisition of satellites after signal loss takes less than two seconds.

Requiring +5V dc, ±5%, the Lassen-SK8 can provide differential GPS accuracy to two meters. If an application does not require differential accuracy, the unit provides position location within 25 m. An optional RF shield permits users to protect the new OEM receiver in severe RF environments, and Trimble offers three different antennae to accommodate various applications. Weighing 0.7 oz without its optional shield, the unit can function in temperatures from -10 to 60C, and options expand the temperature range from -40 to 85C.

Priced at $995, a starter kit provides engineers with equipment needed to experiment with the new board, and begin integrating GPS into an application. An interface motherboard in a metal enclosure comes with the Lassen SK8 board. Software and dual DB9, RS232 interface make the receiver computer-ready. Basically, the kit permits users to quickly evaluate the new board, and explore the value of GPS technology.

Potential applications for the new receiver include car navigation systems, fleet vehicle tracking, agricultural-control systems, instrumentation systems, and various mobile tracking devices.

Hydrojet ferries French at 40 knots

Saint-Malo, France--Travel between the south coast of France and the island of Corsica, a 125-mile trip, has become faster and more comfortable. Making it possible is a new high-speed hydrojet vessel (NGV), the Corsaire 11000.

Leroux and Lotz built the fast ferry for SocieNationale Corse Mèè (SNCM). Using hydrojets to pump in sea water and push it out with force, the NGV can travel as fast as 40 kt (46.6 mph) versus 22 to 24 kt for most modern ferries. As a result, what was normally an overnight ferry ride averaging 10 hours now takes between 2½ and 3½ hours.

Measuring 335 feet long and 50.5 feet wide, the NGV can carry 500 passengers and 148 vehicles, and has a crew of 12. Its four diesel engines, with a combined power of 24,000 kW, feed the four hydrojets--two stationary and two which can be directed to aid in the steering of the vessel.

The NGV features new, high-technology stabilizers (five skegs) especially adapted to this type of ship. The design will help the vessel maintain stability in rough seas.

The stabilization, or Ride Control System (RCS), controls both the vertical-plane (pitch and heave) and lateral-plane (roll and yaw) motions. System specifications called for pitch and heave motion control with vertical acceleration at the center of gravity not to exceed the 2, 5, and 10% Motion Sickness Incidence (MSI). The MSI applies to three hours exposure during head and bow seas operation at two speeds above 30 kt with 1.5 to 3.25m wave heights. In the lateral plane, the hull design and the vessel's high speed increase the roll stiffness and roll damping, which provides good roll motion characteristics.

The T-foil, key to the system's design, uses both incidence and flap control, a design used successfully on several catamaran ferries. Its mechanism, including the rotation axis, resides inside the ship for easier maintenance. The thin shape of the T-foil is optimized from a hydrodynamic point to minimize appendage resistance.

An integrated controller pilots the five appendages. The T-foil and trim tabs are used for the pitch and heave motion control; the fins, in combination with waterjet steering, improve directional control under autopilot operation; and the fins and trim tabs in combination reduce roll motions.

Most attractive of all, however, is the fare. Ticket prices remain the same even though the trip takes one-third as long as that on the old-style car ferries.

Cockpit approach helps automakers meet cost, customer targets

Detroit, MI--More content is being packaged into today's instrument panels (IPs) than ever before--sophisticated navigation, security, safety, and other system components, for example. But it's just the beginning--according to Dow Automotive officials.

"At the same time, consumers are saying 'don't complicate things,'" says Dick Giba, application development manager for IPs at Dow Automotive. "They want ease of access to everything and a feeling of simplicity, comfort, and spaciousness in their vehicles."

To address these concerns, Dow has under development a "cockpit" approach for IP design. It envisions the integration of the HVAC system, steering column, and pedals (clutch and brake), as well as audio, security, cellular, safety, and navigation systems.

Giba sees one possible solution as an "on-command" multi-function screen, rather than several instrumentation displays showing all functions at all times. By simplifying what the driver sees and replacing a range of displays with one, occupant comfort is improved while still meeting instrumentation requirements, Giba adds.

One design Dow visualizes treats the IP as an integrated system that encompasses the vehicle interior from the front of the dash to the passenger compartment. Critical to the design, Giba feels, is making the most effective use of materials, as well as design engineering.

"Faster time to market, reduced system and assembly cost, and lower weight are some of the key elements of the development focus," adds Karen Fennessy-Ketola, Dow Automotive market manager. "Many OEMs have indicated that IP development is an area where they are looking to Tier I suppliers for an ever-increasing amount of innovative, up-front solution development and engineering support. This means that companies such as Dow must bring more to the equation than their traditional material approach."

Self-clinching nuts simplify assembly

Hingham, MA--For GFX Corp., using conventional nuts and bolts to attach the top cover on its SUPER SPLIT log-splitting machines was awkward because of loose parts and hindered access during assembly. Removing the cover for service in the field also proved cumbersome. To solve the problem, GFX switched to PEM self-clinching nuts from Penn Engineering & Manufacturing Corp., Danboro, PA.

The PEM nuts are permanently installed by the company's fabricator on each backplate, reducing the number of handled parts. "The assembly process is no longer awkward or inconvenient because we don't have to hold the nut in place while inserting a screw," says Richard McCann, general manager of GFX. "It's also much simpler to remove and re-attach the backplate cover for service because only the screw on the outside needs to be handled while the nut holds tightly in place," he adds.

The backplates support the cover over the operating mechanism on all SUPER SPLIT models. Four PEM carbon-steel nuts with a ¼-20 thread size are installed inside every backplate using a standard press that embeds the nuts' clinching ring and knurled collar into the thin 12-ga. sheet metal backplate. The displaced sheet metal flows into a back-tapered shank, locking the fastener permanently in place. The embedded knurled ring provides the high torque-out resistance.

The PEM fasteners provide the desired load-bearing threads for easy insertion of screws from the front of the backplate to complete the attachment process, says McCann. Service personnel can remove the cover by simply taking out each screw without any worry that the nut will fall out or loosen. And despite expected wear-and-tear in the field, McCann reports no problems since switching to the PEM nuts.

Corrosion-resistant magnesium improves helicopter

Mesa, AZ--For a new helicopter transmission, engineers at McDonnell Douglas have pioneered the use of what is said to be the most corrosion- and abrasion-resistant coating yet developed for magnesium.

Tagnite 8200 is a nonchromated anodized finish developed by the Technology Applications Group, Grand Forks, ND. Applied over WE43 magnesium and finished with a Rock-Hard coating, the material gives a gearbox housing the corrosion properties of aluminum at just two-thirds the weight.

"We discovered during the Advanced Rotorcraft Transmission program with NASA that the WE43 alloy with Tagnite and Rock-Hard showed great promise," says Gary Craig, team leader for the 600N helicopter's drive system. "The material and coatings do a triple whammy on the corrosion problem."

The "corrosion problem" Craig speaks of was so troublesome that many designers stopped using magnesium. The material was still found, however, in the MD 500's transmission. When time came to redesign this gearbox for extended life and improved corrosion resistance, the new coatings offered a way to stay with the lightweight metal. Ultimately, engineers opted to increase the model-500 gearbox's capacity from 425-hp to 600-hp--thus enabling the development of the eight-seat MD 600N.

ASTM salt-spray tests confirm the new coating's benefits. A sample of the previous magnesium and coatings changed from a rating of 10 (no corrosion migration) to a 2 in 1,000 hours. By contrast, the Tagnite-treated specimen showed no change, says Craig. "We're now looking into using (the new material) for a tail-rotor transmission as well."

WE43 magnesium is a product of Magnesium Elektron, Lakehurst, NJ. Rocklin Manufacturing, Sioux City, IA, supplies the Rock-Hard coating.