Intermet Leads Joint Development of Enhanced Compacted Graphite Iron
1 March 1999
Intermet Leads Joint Development of Enhanced Compacted Graphite Iron
TROY, Mich., March 1 -- Intermet Corporation
and DaimlerChrysler presented findings today on the development of a new
modified compacted graphite iron which combines much of the strength,
ductility and toughness of ductile iron with the better damping and
machinability of gray iron. The new product, Enhanced Compacted Graphite Iron
(ECG), was developed, evaluated and launched in production as a joint Intermet
and DaimlerChrysler Corporation project for use in the new 4.7 L, V-8 engine
introduced in the 1999 Jeep Grand Cherokee.
According to Dr. Robert J. Warrick, Intermet vice president of Materials
Research and Development, the development of ECG came about when
DaimlerChrysler engineers found they needed a bedplate material for their
engines that was significantly stronger and stiffer than gray iron to help
meet engine weight objectives. The material also had to provide good NVH
(noise, vibration and harshness) characteristics, be cost effective and
machinable.
"As their casting supplier," Warrick explains, "we saw the need for an
additional material that was significantly tougher than gray iron, could be
cast sound in complex sections and could be reliably produced on a cost
effective basis."
Although ductile irons are stronger and tougher than gray irons, the gray
irons were superior in the areas of damping capacity, casting soundness, mold
yield and machinability. The other choice, compacted graphite iron,
unfortunately didn't have as much ductility, toughness or stiffness as
desired. As a result, Intermet suggested evaluating a modified compacted
graphite iron with an increased nodularity of up to 50 percent. This material
proved to be a winner.
"The major factor in developing ECG was taking a new look at the ratio of
nodular to compacted graphite forms in the iron," says Warrick. "The 'normal'
limits of 20 or 30 percent maximum nodularity for compacted graphite and 80
percent minimum nodularity for ductile iron have been set by individuals, not
by nature. Materials in this 20 to 80 percent nodularity range can certainly
be produced. So, working with DaimlerChrysler, we decided, rather than work
with some preset definition, we would first let the engine decide what
nodularity range it needed from the iron and then follow up with the best
limits for the foundry and engine plants consistent with those engine
requirements."
The resulting ECG has met and/or exceeded the project requirements:
* ECG has been shown to have much higher strength, stiffness and
toughness than Class 30 gray iron.
* This enhanced strength and stiffness aided in meeting engine weight
objectives and provided superior engine characteristics. It has eliminated
the need for 100 percent magnetic-particle inspection for cracks common for
gray iron bedplates.
* The material has now been shown to be "production feasible" for a high-
volume automotive application.
* And, in its 4.7L V-8 engine bedplate application, ECG casts sound
without risers and has a high mold yield.
Warrick presented an overview of the development and application of ECG at
this week's 1999 Society of Automotive Engineers Expo at Cobo Conference and
Exposition Center in Detroit, Michigan. The presentation was one of two given
this year by Intermet at the annual SAE event.
With headquarters in Troy, Michigan, Intermet Corporation and its
subsidiaries design and manufacture precision iron and aluminum cast
components for automotive and industrial equipment manufacturers worldwide.
Intermet also produces precision-machined components and manufactures cranes
and specialty service vehicles. The company has more than 6,900 employees at
19 operating locations in North America and Europe. The company's Internet
address is http://www.intermet.com.