High strength, unusual designs, and cost savings, characterize winners in an annual powder-metal design competition.
The typical U.S. passenger car contains more than 36 lb of powder-metal (P/M) parts. This figure is expected to rise even higher within the next few years. So it's not surprising that several prize winners in the annual Metal Powder Industries Federation (MPIF) competition operate in the automotive arena. However, other P/M entrants garnering top awards included those making parts for rifles and shotguns, power tools, surgical instruments, laser diodes, and motors.
The MPIF is an umbrella organization for powdermetallurgy trade organizations. Member companies produce parts using conventional P/M processing, powder forging (PF), metal injection molding (MIM), hot isostatic pressing (HIPing), direct powder rolling, and gravity sintering.
- GKN invested $20 million beefing up PF production, including two new automated hot-forging lines and an expanded plant totaling about 200,000 ft2. Each line makes more than 10,000 PF connecting rods daily.
- Hoeganaes Corp. introduced five binder-treated powders. Three of them target high-performance P/M parts designed to replace malleable and ductile irons. The other two are said to provide binder-treated premixed alternatives to similar diffusion-alloyed products.
- The Powder Metal Products Group, Brush Wellman Inc., Tucson, Ariz., has received a U.S. patent for improvements to net-shape or near-netshape copper/tungsten composites.
- Dynamet Technology Inc., Burlington, Mass., has received a U.S. Dept. of Energy research grant to commercialize its titanium matrix-composite material for die-casting tooling. The material has the potential to increase the service life of tooling by a factor of five, Dynamet reports.
- Pacific Sintered Metals (PSM) establishes the Polyalloys Div. to make metal-injection-molding (MIM) parts at its Los Angeles, P/M parts plant. The new division will focus on medical and aerospace markets and reports interest from current automotive customers.
- MPIF has produced two new ASTM standards: the 988-98 Standard covers hot isostatically pressed stainless-steel flanges, fittings, valves, and parts for high-temperature service; the 989-98 Standard covers hot isostatically pressed alloy steel flanges, fittings, valves, and parts for high-temperature service
- The "Aluminum and Light Alloys for Automotive Applications" conference sponsored by MPIF, Nov. 2-3 in Detroit will focus on precision parts made from aluminum and aluminum-alloy powders and composites.
NONFERROUS GRAND PRIZE
The competition's nonferrous grand prize went to Ceromet Div., Metal Powder Products Co., Anaheim, Calif., for a P/M bronze inertial active shock absorber valve. The valves have a radial crushing strength range of 39,750 to 41,950 psi and critical tolerances on the inside diameter of ± 0.0005 in. The castle height of 0.010 ± 0.001 in. is necessary for valve lift-off. The parts are formed to a density of 7.8 gm/cm3 and must exhibit little sliding friction.
The shock provides variable-damping rates depending on the type of force it sees. The valve opens and closes bypass ports to control hydraulic pressure through the piston. The OEM, Edelbrock Corp., Torrance, Calif., runs them through a 10 million cycle durability test to verify their impact toughness.
The valves were designed as original P/M parts. Two diameters are available. The first, at 1.811 in., is designed for heavier vehicles in the SUV and truck aftermarket. The second with a 1.417-in. OD goes into performance and street cars such as Mustangs and Camaros as well as motorcycles.
The only other practical way of making such valves would be to machine them out of bronze bars. With P/M the only secondary operations needed are coining and machining the valve's 0.920 to 0.923-in. ID.
THE P/M PROCESS
In contrast to other metalforming techniques, P/M parts are shaped directly from powders. The basic P/M process uses pressure and heat to form nearnet-shape parts. Metal powder is squeezed in a rigid precision die at pressures up to 50 tons/in.2 After the powder is compressed into shape, it's ejected from the die and fed slowly through a high-temperature, atmospherically controlled furnace. At temperatures below the melting point of the metal, the particles bond, metallurgically fusing or sintering together.
Although P/M is used to fabricate parts from just about any metal, the most common come from iron-based alloys, nickel, tin, copper, or refractory metals such as tungsten or tantalum. Other metals available include aluminum, stainless steel, and nickel, or cobalt-base super alloys. Powder particles are specific in shape and size ranging from 0.1 to 1,000 m.
High precision P/M parts have been available for years, but limitations in their mechanical properties once restricted their use. A porous, lowdensity part will not be as strong or as corrosion resistant as its wrought-metal counterpart. Now, however, this is no longer true for P/M parts that undergo hot forging in closed dies or are produced using hot isostatic pressing (HIPing), or those metal injection molded (MIM). P/M parts forged, HIPed, or injection molded to 100% theoretical density in production conditions are said to be equal and sometimes better than their wroughtsteel counterparts.
For example, relatively complex carbon or lowalloy steel parts in large quantities are ideal candidates for powder forgings (PF). And although PF is not a particularly new process, it along with HIP and MIM have sparked the most interest in recent years. Automakers, were among the first to realize the merit of fully dense PF parts. The precision-forged components now operate in a wide variety of transmissions, accessory mechanisms, and engines.
Another means of boosting performance is the addition of carbon to P/M steel. Doing so makes the P/M parts heat treatable. Heat treating increases hardness, toughness, wear resistance, and strength of the component. Likewise, the addition of alloying elements to the iron-powder mix further enhances the properties of heat-treated steel P/M parts.
FERROUS GRAND PRIZE
A copper-infiltrated-steel compressor-valve plate walked away with the ferrous grand prize. Made by Metal Powder Products (MPP), Metal Powder Specialties Div., Logan, Ohio, the P/M valve plate replaces a machined four-piece, copper-brazed stamping. The unusual geometry of the MPP parts comes from sinter-bonding the three-part assembly into a single unit. The mating parts — plate body and two valve seat inserts — are also copper infiltrated which makes a stronger part. The finished part is flat and parallel to within 0.0005 in./in.2 of surface area.
The valve plate is formed to a typical density of 7.3 gm/cm3 has a hardness of 90 RB and carries tensile and yield strengths of 80,000 and 60,000 psi, respectively.
The valve plate is used in UL-certified compressors for diesel truck air-conditioning systems and stationary refrigeration systems. P/M provided a 30% cost savings over the former stamped plate.
ADVANCED-PARTICULATE GRAND PRIZE
An axial flux stator for brushless motors won the grand prize in the advanced-particulate materials category. The net-shape P/M part, manufactured by Mii Technologies LLC, West Lebanon, N.H., is made from iron powder that is encapsulated with a proprietary magnetic-oxide coating. The coating insulates and acts as a magnetic coupling between the powder particles.
Several innovative tooling and manufacturing techniques are employed to form the part. A patented powder-filling system coupled with better die lubrication helps Mii control the stator's pole pieceheights to within 0.002 in. This accuracy reduces the stator rotor gap, giving the motor more power. ShurFlow Pump Manufacturing Co., Santa Ana, Calif., uses the dc motors in small-diameter centrifugal pumps.
A LITTLE HISTORY
Powder metallurgy was practiced long before ancient artisans learned to melt and cast iron. Egyptians made iron tools using P/M techniques as far back as 3,000 B.C. Precious metal powders also were used to form ancient Incan jewelry and artifacts. Tungsten filaments for electric light bulbs in the early 1900s were the first modern P/M products. They were followed by tungsten-carbide cutting tool materials in the 1930s, automobile parts in the '60s and '70s, aircraft turbine engine parts in the '80s and parts made by powder forging (P/F), metal injection molding (MIM) and warm compacting in the '90s.
OVERSEAS GRAND PRIZE
The overseas grand prize went to a complex four-level copper-nickel-steel injection-pump sprocket by AMES S.A., Barcelona, Spain. The P/M part has tensile, yield, and fatigue endurance limits of 79,000, 55,000, and 34,000 psi, respectively. The sprocket operates in diesel-engine injection pumps from Nissan Motor Iberica, S.A., Spain.
A copper-tungsten substrate made from a functionally graded-powder material (FGM) won the first award of distinction in the advanced-particulate-materials category. The substrates operate in highpower microelectronics and optoelectronics packaging and heat sinking for cellularphone base stations, ground-based radar, and laser diodes. They are made by the Electronics Div., Brush Wellman Inc., Tucson, Ariz.
A 85% tungsten — 15% copper surrounding-body is compacted and sintered in a hydrogen atmosphere. Then a 50% tungsten-50% copper core is inserted into the body and sintered again in hydrogen. Heat sinks made this way are thermally efficient and cost comparatively little to make.
MIM GRAND PRIZE
A body assembly in a current-to-pressure (I/P) converter module for chemical and oil flow control valves topped the list in the MIM category. Made by Advanced Materials Technologies Pte. Ltd., Singapore, the complex MIM part replaces a fourpiece assembly of two conventional P/M parts and two machined parts.
The MIM part comes from a 50% nickel/50% iron alloy. It has a final sintered density of 8.05 gm/cm3 and a 55 RB hardness. Along with an elongation of 25%, the part carries tensile and yield strengths of 65,250 and 24,650 psi, respectively.
The high-precision sensor mounts inside the control valve. Magnetic flux is applied through the body assembly. The assembly is integrated, greatly reducing resistance for the magnetic path compared to the previous design. Reduced hystersis loss is said to make calibration of the sensor more accurate and consistent. Secondary operations include machining and threading. The part is made for Fisher Controls International, Marshalltown, Iowa.
MIM AWARDS OF DISTINCTION
The first MIM award of distinction went to ironnickel safety buttons and a lock tumbler used in a new integrated security system for shotguns and rifles. Manufactured by the Powder Metal Products Div., Remington Arms Co. Inc., Ilion, N.Y., the safety buttons replace external locks such as cables or trigger guards.
The parts have a density of 7.5 g/cm3, an assintered ultimate tensile strength of 55,000 psi, a 30,000-psi yield strength, and a 25% elongation within a 2-in. gage length. The iron-nickel P/M safety buttons and lock are case hardened to a microhardness range of 50-60 RC. Secondary operations include centerless grinding, machining, black oxiding, and painting.
A disposable assembly of scissors blades, clevis, and actuator for endoscopic Metzenbaum surgical scissors won the second MIM award of distinction. The 17-4PH stainless steel parts come from FloMet LLC, DeLand, Fla. They replaced blades previously machined from 303 stainless steel.
The scissors are used during minimally invasive cardiac, general, and plastic/reconstructive surgery. They have minimum yield and ultimate tensile strengths of 140,000 and 155,000 psi, respectively, and density on the order of 7.5 gm/cm3.
Developers say their biggest challenge was in getting the proper geometry for blade curvature. The blades must have the correct preload against each other and maintain single-point contact throughout their length. The blades are curved in pairs by FloMet and then sharpened by the OEM, Genzyme Surgical Products, Genzyme Corp., Tucker, Ga.
FERROUS AWARDS OF DISTINCTION
A hot-forged steel 64-tooth power take-off drive gear used in transmissions of gas and diesel pick-up trucks and utility vehicles won the ferrous award. The highstrength part is made by GKN Sinter Metals - Romulus, Romulus, Mich., for GMC's Allison Transmission Div., Indianapolis, Ind. A new application, the PF part costs an estimated 40% less than machined steel. It weighs 3.3 lb, has a 136,300-psi tensile strength, and features minimum case and core hardnesses of 58 and 20 RC, respectively. Gear teeth need no secondary operations.
The drive gear diverts torque from the engine through the Allison 1000/2000 Series automatic transmission into a power take-off gear box. The gearbox runs a hydraulic pump that drives accessory items such as power tailgates, dump beds, or snow blades. The gear also has an auxiliary function of monitoring shifting speed. The transmission operates in GM, Ford, and DaimlerChrysler trucks, ambulances, and buses.
A shaft-output used in a four-wheel-drive shifting system won the other award of distinction in the ferrous category. Made by ASCO Sintering Co. in Commerce, Calif., the system operates in trucks and sport-utility vehicles. The shaft-output supplies torque via a planetary gear composed of 15 P/M gears and 3 P/M carriers. The shaft is made from a proprietary high-impact copper-steel to a density of 7.7 gm/cm3. It has an unnotched Charpy impact strength above 100 ft-lb, elongation of more than 8%, and a tensile strength of 95,000 psi. Secondary operations include heat treating, deburring, and oiling.