New Demands, New Solutions
By Michael Legault
Molders involved in the automotive electronics market, the bulk of which consists of connectors, switches, sensors, housings and other unnoticed but essential parts, can console themselves with the kn...
Molders involved in the automotive electronics market, the bulk of which consists of connectors, switches, sensors, housings and other unnoticed but essential parts, can console themselves with the knowledge that while their business may be out of sight, it is not out of mind. If anything, it is increasingly on the minds of designers, as new trends in the architecture of the car are requiring more and better-made electrical/electronic parts.
In many vehicle lines, space is being minimized while power is being maximized, meaning designers are looking for smaller, thinner parts often subjected to high heat environments. Under-the-hood environments can be especially harsh in today’s cars and trucks.
“There’s a horsepower race between car companies right now with new generations of sports cars and muscle cars back in style,” says Ticona’s Jim Dutchik, automotive market specialist. “This generates a lot of heat in a small space, so that in some cases the standard requirement has been pushed from Class III (125C) to Class IV (155C).”
Dutchik is referring to the United States Council for Automotive Research’s (USCAR) specification which classifies part performance after exposure to high humidity and increasing temperatures. USCAR’s Class III rating specifies 40 cycles at 90C/95% relative humidity for six hours, raised to 125C for two hours, then cooled to -40C. Class IV is identical with the exception that the temperature is raised to 155C for two hours. Parts, such as connectors, are subjected to a variety of tests after exposure to determine their compliance with a particular rating.
Dutchik says Ticona has introduced three new grades of hydrolysis-resistant PBT to meet the emerging needs of the automotive connector market. The grades are Celanex 2003 HR, unfilled PBT, and Celanex 3200HR and Celanex 3300HR, which are 15% and 30% glass-filled, respectively. Conventional PBT grades are most susceptible to a loss of elongation at break under hydrolysis conditions. According to Dutchik, Celanex 3300HR retains its elongation under both Class III and Class IV conditions. The Celanex grades also have faster crystallization rates, which improves cycle times as a result of faster set-up in the mold.
Paul Cane, DuPont Automotive engineering polymers’ development program manager, acknowledges that hydrolysis-resistant connectors and housings have become a priority with car designers, noting the OEMs want to keep moisture out of electrical connections and ensure the materials used will not crack under high humidity/heat conditions. Dupont’s Crastin PBT comes in two hydrolysis-resistant grades, a 15% and a 30% glass-filled version. Cane cautions that molders must be careful when evaluating hydrolysis-resistant PBTs.
“Not all hydrolysis-resistant PBTs are alike,” Cane says. “With some grades of HR PBT you can get severe mold deposits.”
LEAD-FREE SOLDERING RAISES HEAT REQUIREMENTS
A new lead-free soldering technique being adopted by connector manufacturers is significantly raising the high temperature requirements for materials. The technique, widely used in Europe, is called infra-red (IR) reflow soldering. Temperatures of IR reflow soldering are in the range of 230C to 260C, compared to about 180C for lead-based soldering. Cane observes that this temperature exceeds the performance range of PBT. DuPont has developed a high-temperature polyester, called Thermx PCT, with an upper-end temperature exposure that exceeds that of PBT by 50-60C. With a shrinkage rate nearly identical to PBT, Thermx PCT can be used as a drop-in replacement for PBT, allowing the molder to make the part on the original tooling. Thermx is currently being used by a Tyco Electronics’ facility in Greensboro, NC, to manufacture a connector used in an automotive seat control module. The material selected by Tyco, Thermx CGT33, is a 30% glass-filled grade with a heat deflection temperature of 259C and good dimensional stability, a critical factor in the connector’s precision pin spacing.
GE Advanced Materials’ offering for IR reflow soldering applications is LNP Thermocomp HT resins, materials with a heat deflection temperature of over 260C. Thermocomp HT Solder UF-1006 and Thermocomp HT Solder ZF-1006 are comprised of a matrix of resin blends and 30% glass-fibre. The former is based on polyphthalamide (PPA) resin, while the latter features a matrix of modified polyphenylene ether (MPPE). Both materials are formulated with a halogen-free flame retardant.
According to Keith DuPont, GE’s global marketing director, automotive, GE has invested significantly more resources in its automotive technical support group to help suppliers fight cost pressures through design and materials innovations.
“This is a real area of change right now,” says DuPont. “Instead of looking just at cost-cutting in a narrow sense, more customers are striving for technical innovations.”
DuPont says there’s still a lot of metal under the hood, but that the easy conversions have already been done. This is where design and material formulation expertise come in, he notes.
One way to meet the simultaneous goals of taking up less space and lowering cost is to make connectors with thinner walls.
“There are real estate problems under the hood in today’s vehicles,” says Rob Crowell, vice president marketing, DSM Engineering Plastics. “Thinner walls make the parts more susceptible to breaking during assembly.” DSM’s Stanyl glass-filled polyamide 46 combines high-temperature resistance, toughness and high flow to give it an advantage over competing materials, says Crowell.
THE FUTURE IS NOW
“We’ve had more enquiries on applications for hybrid gas-electric vehicles than ever before,” says DuPont.
Two areas of special interest for hybrid designers and suppliers are EMI/RFI shielding and sound/noise dampening. The need for shielding materials arises from the electromagnetic signals generated by a hybrid car’s multiplicity of motors. GE’s LNP Faradex DS-1003 FR HI is a stainless-steel-filled compound that offers both EMI shielding and electrostatic dissipative properties in a custom-colorable, halogen-free, flame retardant package.
Dampening noise in hybrids is an engineering objective because, to the human ear, hybrids sound noisier. Ironically this is because the engine runs more quietly. Engineers are investigating ways of reducing noise through use of lubricated polymers in gears, bearings, bushings, cams and other moving parts. LNP Lubricomp wear-resistant compounds contain internal lubricants such as silicone, graphite, PTFE, aramid or molybdenum disulfide, eliminating the need for external lubricants.
Another area of intense interest that is just coming onto the radar screen for manufacturers and suppliers is an electronic-based suspension system. General Motors has committed to installing electronic stability control systems on its vehicles by 2010, according to Ticona’s Dutchik, with other OEMs not far behind. According to early reports released by one manufacturer, the suspension design replaces shock absorbers with a system of sensors and ultra-fast linear electric motors. Dutchik says the new suspension will be a boon for sensor applications.
“Some of these sensors would be in hot areas, and some would be located away from hot areas, so the material requirements could change with the setting.”
Engine and drive train sensors typically combine metal thermocouple or transducer elements with thermoplastic protective shells. The shells protect the sensor, seal access points and provide assembly and mounting bosses for attachment to the engine block or transaxle.
Stanyl TW200F6 is used in a broad range of automotive sensor applications, according to DSM’s Crowell. In one open oil-level application, Stanyl replaced a 40-percent, glass-filled polyphenylene sulfide. The grade of Stanyl had superior melt flow and allowed the processor to use a lower mold temperature of 80C.
Such performance factors, as well as the versatility of
an engineering resin, will play an important role in deciding which material is used in these cutting-edge electronic applications.
INSTRUMENT DIAL REPLACES ALUMINUM RING WITH PLASTIC
Speedometer dials are often surrounded by a decorative aluminum ring. Engineers have eliminated the ring from the current Volkswagen Golf by a unique application involving Bayer’s Makrofol DE 1-4 polycarbonate film. The speedomater dial is made of printed Makrofol that is formed at the circumference edge to have a matte metallic appearance. The 0.015 in. thick film is printed on both sides with more than 10 layers of ink using the screen printing method. The translucent symbols are gray and backlit by colored LEDs. The metallic edge is formed using the “high pressure forming” method patented by Bayer MaterialScience. The process permits the film to be formed with great precision well below the glass transition temperature of polycarbonate, retaining the matte surface finish.