Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02384221 2002-04-30
6206-Bequette et al.
METHOD OF MAILING COPPER INFILTRATED FERROUS METAL PRODUCTS
BACKGROUND OF THE INVENTION
1. . Field of the Invention.
The present invention relates to the manufacture of powder metal products, and
more
particularly, to a method of making copper infiltrated ferrous metal products.
2. Description of the Prior Art.
It is known to produce metal products by compacting metal powder into a green
powder
metal compact and then heating the green powder metal compact to sinter the
metal particles to
produce the metal product. Due to inherent limitations in the manufacturing
process, the densities
of the metal products typically are below theoretical density; in other words,
the green powder
compacts and the metal products are typically porous.
The properties of such porous metal products are commonly improved through a
technique
known as infiltration. :In infiltration, the open pore structure of the
sintered powder metal product is
infiltrated by another metal having a lower melting temperature. This second
metal is commonly
referred to as an infiltrant.
A typical prior art infiltration process is illustrated schematically in FIG.
1. As there shown,
a mass of powdered metal 10 is pressed and sintered to form a sintered porous
powder metal
product 12. The sintered porous metal product 12 has a contact surface 14, and
an interior with
pores, shown enlarged and schematically at 16, with the sintered metal shown
in cross-hatch at 17.
An infiltrant is provided in the form of a green powder metal compact 18. This
infiltrant compact is
made from powder metal in a typical pressing operation. The green infiltrant
compact 18 is placed
on the contact surface 14 of the sintered powder metal product 12. The
combination is then placed
in a furnace at a temperature high enough to melt the metal in the green
powder metal infiltrant 18
but lower than the melting temperature of the metal in the sintered powder
metal product 12. The
metal of the infiltrant 18 melts, and the liquid infiltrant metal flows into
the pores of the metal
product 12 through capillary action. After the process is complete, the pores
16 are theoretically
filled with the metal infiltrant, which solidifies. The infiltrated metal
product is shown at 20 with its
CA 02384221 2002-04-30
pores filled with solid metal infiltrant; the sintered metal is shown at 17 in
the cross-hatch angled
upward toward the right, and the solid metal infiltrant is shown at 22 in the
cross-hatch angled
upward toward the left.
Typical infiltrants are metal or metal alloy powders that have been formed
into a green
<;ompact shape to mate generally with the shape of the contact surface of the
metal product to be
infiltrated. Copper or copper based alloys have commonly been used as
infiltrants for ferrous
powder metal product.
One problem with the infiltration technique is known in the powder metallurgy
art as
c;rosion. In erosion, some of the metal of the powder metal product or compact
at or near the
<;ontact surface with the infiltrant compact dissolves in the infiltrant. With
such erosion, the
dimensions of the metal product may change during infiltration. If the
dimensional change is great
enough, the infiltrated product may need to be subjected to another
manufacturing step, such as
sizing, to reach final design dimensions. With the increased density of the
infiltrated product after
infiltration, it may be difficult to use a pressing step to size the
infiltrated product. Machining to
final dimensions is an expensive alternative.
Another problem with the infiltration technique relates to the handling of the
green infiltrant
compacts. Particularly for small parts, the green infiltrant compact is
commonly of small size. The
small size green infiltrant compacts are more delicate and more difficult to
handle: movement of the
small green infiltrant compacts in a production operation results in breakage
of some of the
compacts. The metal powder in the broken compacts is generally not reusable,
so this breakage can
add significantly to the cost of producing the finished infiltrated metal
products.
SUMMARY OF THE INVENTION
The present invention is directed to increasing efficiency in the manufacture
of infiltrated
powder metal products.
In one aspect, the present invention provides a method of making an
infiltrated ferrous metal
product. The method comprises the acts of providing a ferrous metal powder and
forming the
ferrous metal powder into a porous ferrous metal product having a contact
surface. An infiltrant
pre-form is provided. 'The infiltrant pre-form is selected from the group
consisting of metal wire
material and sheet metal material. The infiltrant pre-form is placed on the
porous ferrous metal
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powder product contact surface. The combination of the infiltrant pre-form and
the porous ferrous
metal product is heated so that at least some of the metal in the infiltrant
pre-form infiltrates into the
porous ferrous metal product to form the infiltrated ferrous metal product.
In another aspect, the present invention provides a method of making an
infiltrated ferrous
metal compact. A ferrous metal powder is formed into a porous ferrous metal
product having a
contact surface. A metal wire infiltrant pre-form is provided. The infiltrant
pre-form comprises
cropper and at least about 2.5% iron by weight. The metal wire infiltrant pre-
form is placed on the
porous ferrous metal powder product contact surface. The combination of the
infiltrant pre-form
and the porous ferrous metal product is heated so that at least some of the
metal in the infiltrant pre-
form infiltrates into the porous ferrous metal product to form the infiltrated
ferrous metal product.
In another aspect, the present invention provides a method of making an
infiltrated ferrous
metal compact weighing less than 5 ounces. The method comprises the acts of
providing a ferrous
metal powder and forming the ferrous metal powder into a porous ferrous metal
product having a
contact surface and weighing less than 5 ounces. An infiltrant pre-form is
provided, the infiltrant
pre-form is made of a material selected from the group consisting of metal
wire material and sheet
metal material. The infiltrant pre-form weighs less than about '/2 ounce. The
infiltrant pre-form is
placed on the porous ferrous metal powder product contact surface. Then, the
combination of the
infiltrant pre-form and the porous ferrous metal product is heated so that at
least some of the metal
in the infiltrant pre-form infiltrates into the poraus ferrous metal powder
product to form the
infiltrated ferrous metal product.
In another aspect, the present invention provides a method of making an
infiltrated ferrous
metal compact weighing less than 5 ounces. The method comprises the acts of
providing a ferrous
metal powder and forming the ferrous metal powder into a porous ferrous metal
product having a
contact surface and weighing less than 5 ounces. The method further includes
providing a metal
wire infiltrant pre-form comprising copper and about 2.5% iron by weight. The
metal wire infiltrant
pre-form weighs less than about 1/2 ounce, and is shaped to be supportable on
the porous ferrous
metal powder contact surface. The infrltrant pre-form is placed on the porous
ferrous metal powder
product contact surface. The combination of the infiltrant pre-form and the
porous ferrous metal
product is heated so that at least some of the metal in the infiltrant pre-
form infiltrates into the
porous ferrous metal product to form the infiltrated ferrous metal product.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, like numbers have been used for like parts and:
FIG. 1 is a schematic drawing showing a prior art infiltration process, with
the porous
ferrous metal powder product, green infiltxant compact and infiltrated ferrous
metal product shown
schematically in a perspective view, and with portions of the porous ferrous
metal powder product
and the infiltrated ferrous metal product shown schematically in cross-
section;
FIG. 2 is a schematic drawing showing the infiltration process of the present
invention, with
the porous ferrous metal powder product, infiltrant pre-form and infiltrated
ferrous metal product
shown schematically in a perspective view, with portions of the porous ferrous
metal powder
product and the infiltrated ferrous metal product shown schematically in cross-
section;
FIG. 3 is a perspective view of an alternate infiltrant pre-form on a porous
ferrous metal
powder product; and
FIG. 4 is an elevation of a third embodiment of an infiltrant pre-form.
DETAILED DESCRIPTION
The present invention provides an efficient method of making infiltrated
ferrous metal
products. A schematic illustration o.f the process of the present invention is
shown in FIG. 2. As
there shown, a ferrous metal powder 30 is provided. Commercially available
metal powders may be
used, such as, for example Ancorsteel 1000, available from Hoeganaes Corp.,
Cinnaminson, NJ.
The ferrous metal powder 30 may then be pressed to produce a ferrous metal
compact. The ferrous
metal compact may then be sintered in a furnace to form a porous ferrous metal
product, shown at
32 in FIG. 2. The compaction and sintering steps may employ standard
techniques, and it is
f;xpected that techniques that are developed in the future may also be used.
If the porous ferrous metal product 32 is to be infiltrated, it will typically
have a contact
surface. The contact surface may comprise an annular surface of the metal
product, as shown at 34
in FIG. 2. The contact surface 34 is provided as a surface for supporting the
infiltrant pre-form, and
should have a shape that will enable it to perform that function. Since there
is a possibility of some
erosion of this contact surface, it should be designed as part of an area of
the metal product where
dimensional control is less critical.
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T o illustrate the process of the present invention, a portion of each porous
ferrous metal
product 32 is shown schematically in cross-section in FIG. 2. As there shown,
the porous ferrous
metal product comprises areas of sintered metal shown at 36, and pores shown
at 38. It should be
understood that these features are enlarged and shown schematically in FIGS. 2-
3 for purposes of
illustration.
In the present invention, instead of a green powder metal compact as in the
prior art, the
infiltrant is provided in the form of a solid metal alloy pre-form. The
infiltrant pre-form may
<;omprise a metal wire material shaped to mate generally with the shape of the
contact surface of the
metal product, as shown 40 at in FIG. '<?. Altern tively, the infiltrant pre-
form may comprise a sheet
metal material cut into a shape to mate with the shape of the contact surface
of the metal product, as
shown at 42 in FIG. 3. Most typically, the shape of the infiltrant pre-form
40, 42 will comprise an
annulus, although it may be desirable to form the solid metal material into a
helical shape, for
example, as shown at 44 in FIG. 4, if the metal product is of larger size
requiring a greater quantity
of infiltrant. If annular, the ends of the infiltrant pre-form 40, 42 need not
meet; there may be some
;,mall space between the ends, or the ends may overlap slightly. Other shapes
of infiltrant pre-forms
may be used as well, and the invention is not limited to any particular shape
unless the claims
expressly so require.
The infiltrant pre-form is preferably made of a copper alloy material that
includes more than
0.8% iron by weight. A particularly useful alloy includes copper and iron, the
iron comprising
about 2.5% by weight of the alloy. This solid metal alloy material is a
commercially available one.
la is designated alloy C 19400. The higher iron content of this alloy is
desirable in reducing erosion
of the porous ferrous metal product during infiltration.
Because of the higher iron content, this copper alloy is not typically
available in wire form.
'The increased iron content affects the formability of the alloy into wire and
into a usable pre-form.
Accordingly, it may be desirable to obtain the copper alloy material in sheet
form, and to cut the
pre-form from the sheet, like the embodiment shown at 42 in FIG. 3. A suitable
sheet material for
copper alloy C 19200 is available from ABC Metals, Inc., of Logansport, IN in
thicknesses of about
0.064 inch. However, a wire form of copper alloy C 19400 is commercially
available from Lewis
Spring, Niles IL, and is suitable for forming the infiltrant pre-form shape
shown at 40 is FIG. 2, as
swell as the pre-form shape shown at 44 in FIG. 4. Typical wire diameters for
the pre-forms will be
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on the order of about 0.08 inch. It should be understood that the present
invention is not limited to
this particular alloy or to this particular suppliers. It should be understood
that different alloys may
be chosen, with constituent elements selected to reduce the solubility of the
iron in the copper alloy.
For example, an alloy containing manganese may also be possible. Generally,
the alloy should
include an element that limits the solubility of iron during the infiltration
process, in an amount that
allows for efficient forming of a wire form of the alloy or that allows for
efficient cutting of a sheet
metal form of the alloy to produce the desired pre-form shape. The amount and
identity of the
clement used to limit solubility of iron may be selected based on known
criteria, such as the location
of the contact surface, and the degree of dimensional control needed for the
contact surface, for
example.
The characteristics of the material for the infiltrant pre-form may generally
be selected with
cost-effective processing in mind. For example, the thickness or diameter of
the material should be
such that allows the raw material to be economically shaped into the desired
pre-form shape, such as
the annulus or helix shown at 40 and 44 in FIGS. 2 and 4, and for the sheet
product, for the desired
shape to be cut from the sheet metal. Other alloying elements that improve the
formability of the
solid metal could be used, although they preferably do not increase the
solubility of iron in the
infiltrant.
The infiltrated ferrous metal product is produced by placing the infiltrant
pre-form 40, 42 or
44 on the contact surface 34 of the porous ferrous metal product 32, as shown
in FIG. 2. The
<;ombination of the infiltrant pre-form and the porous ferrous metal product,
shown at 46 in FIG. 2,
is then heated in a furnace in the usual manner. At least some of the metal in
the infiltrant pre-form
40, 42 or 44 will infiltrate into the pores 38 of the ferrous porous metal
product 32 and solidify to
form the infiltrated ferrous metal product. The infiltrated ferrous metal
product is shown at 48 in
FIG. 2, with the solid infiltrant shown at 50, in what previously were the
pores 38.
With the level of iron content of the pre-form 40, 42, or 44, erosion of the
contact surface 34
of the porous ferrous metal product 32 during infiltration should be reduced.
With the use of a solid
metal pre-form 40, 42, or 44 instead of a green powder compact 18 as the
carrier for the infiltrant,
breakage during handling of the infiltrant pre-form should be minimized.
The method of the present invention is expected to be particularly useful in
the production of
relatively small products. For mid-size to large porous ferrous metal
products, it is expected that
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use of the standard prior art process will be most cost-effective; the copper
infiltrant can be provided
in the form of a green powder metal compact that is formed using traditional
powder metal
processes. Powder metal mixes with relatively high concentrations of iron are
commercially
amailable, and standard practices may be used to minimize erosion of critical
areas of the product.
However, for producing smaller infiltrated ferrous metal products, such as
products up to
about 4 ounces in total weight (or less than about 5 ounces), the method of
the present invention
should be more cost effective. Generally, in the infiltrated product, the
amount of copper will be
about 10% by weight. A green powder metal copper infiltrant compact weighing
'/2 ounce or less is
difficult to handle in a manufacturing operation without incurring breakage.
Since a green powder
metal infiltrant compact, once broken, cannot be reused, breakage leads to
increased costs.
However, with a solid metal form of infiltrant, either in the form of a wire
or sheet metal pre-form,
breakage of the infiltrant pre-form will generally not be an issue even if the
pre-form weighs less
than '/z ounce. Thus, for the production of smaller infiltrated ferrous metal
products, the method of
the present invention should thus be more cost effective than the traditional
prior art method.
An example of a small infiltrated ferrous metal product that may be
advantageously made
using the method of the present invention is a shoe for a diesel engine fuel
pump. The product so
made should meet industry standards, such as standard MPIF FX 1008.
It should be understood that standard commercial practices may be employed
with the
present invention. For example, prior art methods for determining the
preferred area of contact
between a green infiltrant compact and the contact surface of the porous metal
product may be used
in determining the preferred area of contact between an infiltrant pre-form of
wire of cut sheet metal
and the contact surface of the porous metal product.
While only a specific embodiment of the invention has been described and
shown, it is
apparent that various alternatives and modifications can be made thereto.
Those skilled in the art
~,vill recognize that certain modifications can be made in this illustrative
embodiment. It is,
therefore, the intention in the appended claims to cover all such
modifications and alternatives as
may fall within the true scope of the invention.
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