GKN Sinter Metals of Auburn Hills, MI won a grand prize in an annual powder
metal design competition for a carrier and one-way rocker clutch assembly made
for Ford Motor.
Designed for powder metal (PM), the assembly uses fewer components
compared to alternate designs and manufacturing methods, reducing the mass of
the assembly, improving fuel efficiency without sacrificing performance.
Used in the new Ford Super Duty TorqShift six-speed automatic
transmission, the hybrid assembly contains five powder steel parts weighing a
total of 17 lb. The sinter-brazed subassembly consists of four multi-level PM
parts, of which three parts (cage, spider, and carrier plate) are made to a
density of 6.8 g/cm3.
The rocker plate is sinter-hardened during the sinter- brazing phase
and has a density of 7.0 g/cm3. The assembly also has a
doubled-pressed and double-sintered cam plate made to 7.3 g/cm3
density with an ultimate tensile strength of 170,000 psi and a mean tempered
hardness exceeding 40 HRC.
To form the parts and maintain precision tolerances, special tooling
was developed and used with unconventional press motions. Ford subjected the
assembly to ultimate torsional torque loading at a minimum of 8,000 ft-lb and
fatigue testing at a minimum of 299,000 cycles at 1,730 ft-lb.
"The application provided an estimated 20 percent cost savings over competitive
processes," according to a statement from the MPIF.
GKN Sinter Metals won another grand prize in the automotive chassis category
for a differential bearing adjuster made for American Axle & Manufacturing
and used in the GMT 900 rear differential on GM Tahoe and Yukon models.
Other winners are:
A porous bronze filter made by Capstan California, Carson, CA. for
Chase Filters and Components received the grand prize in the aerospace/military
Parmatech Corp., Petaluma, CA, earned the grand prize in the hand
tools/recreation category for a 420 stainless-steel, metal injection molded (MIM)
hunting arrowhead made for Optek Precision Tooling Ltd.
A PMcopper-steel outer hub
exit spindle used in electronic door locks won the grand prize in the
hardware/appliances category. Made by ASCO Sintering Co., Commerce, CA, for
Ingersoll Rand Security Technologies (Schlage), the part connects a standard
lock and an exit device.
FloMet of Deland, FL earned the grand prize in the medical/dental
category for a housing cup and lid used in an audio device with magnetic
Awards of Distinction
Cloyes Gear & Products Inc., Paris, AR - intake sprocket gear and
an exhaust gear used in a coupling assembly.
Megamet Solid Metals Inc., Earth City, MO - a rear sight used on
sporting and military rifles.
Indo-US MIM Tec (P) Ltd., Bangalore, India - a 17-4PH stainless steel
Webster-Hoff Corp., Glendale Heights, IL - a PM sinter-hardened steel
cam and bushing used in a manual paper hole punching machine.
Lovejoy Sintered Solutions, Downers Grove, IL - a PM diffusion-alloyed
Burgess-Norton Mfg. Co., Geneva, I- a PM steel crimp retainer operating
in a valve assembly.
Kinetics Climax, Wilsonville, OR - a 17-PH stainless steel distal
channel retainer formed via the MIM process.
Powder metal parts can cut costs, but (as with any material or process) it's important that there be a good match between the application and the material. The award-winning parts seem to be good examples of this.
Unfortunately, I've also seen examples of parts which never should have been powder metal. For example, I was once involved in a failure analysis for a mechanical brake actuator which consisted of a hub with a long shaft. Since the compaction direction was along the axis of the shaft, and the length of the shaft was more than twice the diameter of the hub, it was difficult to achieve a high density in the shaft. The shaft was subjected to torsion and bending loads. Depending on the exact size and location of porosity, fatigue cracks would initiate at the base of the shaft. With repeated actuations, the shaft would snap off, rendering the brake inoperable.
Making the part out of powder metal may have saved money in the short term, but this could have been a very expensive problem if anyone had been injured or any property had been damaged (fortunately, this never happened). As it was, a significant sum of money needed to be spent on this issue.
Of course, there are PM techniques which could have been used to solve this problem. For instance, double press / double sinter would have made it possible to achieve a higher density. Powder forging would have allowed an even higher density. But once the part was already in production, either of these options would have required significant new tooling expenditures. Ultimately, after examining a number of options, it was found that it was cheaper to machine this part from an inexpensive forging.
There are many applications for which PM is a great option. However, design engineers need to make sure that it is a good fit for the application. PM suppliers should also be careful to bring up any potential areas of concern during the design review process, so that any potential issues can be resolved before the part goes into production.
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