U.S. patent application number 10/588328 was filed with the patent office on 2008-05-08 for sheet material infiltration of powder metal parts.
This patent application is currently assigned to GKN SINTER METALS, INC.. Invention is credited to L. Kent Byrd Jr., Alan Taylor.
Application Number | 20080107558 10/588328 |
Document ID | / |
Family ID | 34860278 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080107558 |
Kind Code |
A1 |
Byrd Jr.; L. Kent ; et
al. |
May 8, 2008 |
Sheet Material Infiltration of Powder Metal Parts
Abstract
A powder metal part infiltration process uses a stamped metallic
sheet as a source of metal for infiltration to achieve a high
strength powder metal part. A powder metal is compacted, and an
infiltrant blank is formed from a wrought metal sheet. The
infiltrant blank is placed on top of the compact, and the compact
is sintered at a temperature sufficient to form a sintered compact
with a matrix having pores and to melt the wrought metal such that
the melted wrought metal infiltrates the pores of the matrix. The
infiltrant blank may be formed with a locating element for engaging
a corresponding locating element on the compact to improve
positioning of the blank on the compact. Also, the compact may be
separately sintered, and the infiltrant blank may then be placed on
the sintered compact. The wrought metal is then melted such that
the melted wrought metal infiltrates the pores of the matrix.
Inventors: |
Byrd Jr.; L. Kent; (New
Albany, IN) ; Taylor; Alan; (New Albany, IN) |
Correspondence
Address: |
QUARLES & BRADY LLP
411 E. WISCONSIN AVENUE, SUITE 2040
MILWAUKEE
WI
53202-4497
US
|
Assignee: |
GKN SINTER METALS, INC.
ROMULUS
MI
|
Family ID: |
34860278 |
Appl. No.: |
10/588328 |
Filed: |
February 4, 2005 |
PCT Filed: |
February 4, 2005 |
PCT NO: |
PCT/US05/03767 |
371 Date: |
August 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60542271 |
Feb 4, 2004 |
|
|
|
Current U.S.
Class: |
419/8 ;
419/2 |
Current CPC
Class: |
B22F 3/26 20130101 |
Class at
Publication: |
419/8 ;
419/2 |
International
Class: |
B22F 7/00 20060101
B22F007/00; B22F 3/12 20060101 B22F003/12; B22F 3/11 20060101
B22F003/11 |
Claims
1. A process for manufacturing a metal-infiltrated powder metal
part, the process comprising: compacting a powder metal to form a
compact; forming an infiltrant blank from a wrought metal sheet;
placing the infiltrant blank on top of the compact; and sintering
the compact at a temperature sufficient to form a sintered compact
with a matrix having pores and to melt the wrought metal such that
the melted wrought metal infiltrates the pores of the matrix.
2. The process of claim 1 wherein: the powder metal is selected
from iron, iron alloys and mixtures thereof; and the wrought metal
is selected from copper and copper alloys.
3. The process of claim 2 wherein: the wrought metal sheet has a
thickness of less than 1 millimeter.
4. The process of claim 1 wherein: the infiltrant blank is formed
by a method selected from stamping, fine blanking and abrasive
water jet cutting.
5. The process of claim 1 further comprising: forming the
infiltrant blank with a locating element that is suitable for
engaging a corresponding locating element on the compact; and
placing the infiltrant blank in contact with the compact such that
the locating element of the blank engages the corresponding
locating element on the compact.
6. The process of claim 5 wherein: the locating element of the
blank is a section of the blank extending outwardly from a body of
the blank.
7. A process for manufacturing a metal-infiltrated powder metal
part, the process comprising: compacting a powder metal to form a
compact; sintering the compact at a temperature sufficient to form
a sintered compact with a matrix having pores; forming an
infiltrant blank from a wrought metal sheet; placing the infiltrant
blank on top of the sintered compact; and melting the wrought metal
such that the melted wrought metal infiltrates the pores of the
matrix.
8. The process of claim 7 wherein: the powder metal is selected
from iron, iron alloys and mixtures thereof; and the wrought metal
is selected from copper and copper alloys.
9. The process of claim 8 wherein: the wrought metal sheet has a
thickness of less than 1 millimeter.
10. The process of claim 7 wherein: the infiltrant blank is formed
by a method selected from stamping, fine blanking and laser
cutting.
11. The process of claim 7 further comprising: forming the
infiltrant blank with a locating element that is suitable for
engaging a corresponding locating element on the compact; and
placing the infiltrant blank in contact with the compact such that
the locating element of the blank engages the corresponding
locating element on the compact.
12. The process of claim 7 wherein: the locating element of the
blank is a section of the blank extending outwardly from a body of
the blank.
13. A process for manufacturing a metal-infiltrated powder metal
part, the process comprising: compacting a powder metal to form a
compact; forming an infiltrant blank from a wrought metal sheet,
the blank having a locating element that is suitable for engaging a
corresponding locating element on the compact; placing the
infiltrant blank in contact with the compact such that the locating
element of the blank engages the corresponding locating element on
the compact; and sintering the compact at a temperature sufficient
to form a sintered compact with a matrix having pores and to melt
the wrought metal such that the melted wrought metal infiltrates
the pores.
14. The process of claim 13 wherein: the powder metal is selected
from iron, iron alloys and mixtures thereof; and the wrought metal
is selected from copper and copper alloys.
15. The process of claim 14 wherein: the wrought metal sheet has a
thickness of less than 1 millimeter.
16. The process of claim 13 wherein: the infiltrant blank is formed
by a method selected from stamping, fine blanking and laser
cutting.
17. The process of claim 13 wherein: the locating element of the
blank is a section of the blank extending outwardly from a body of
the blank.
18. A process for manufacturing a metal-infiltrated powder metal
part, the process comprising: compacting a powder metal to form a
compact; sintering the compact at a temperature sufficient to form
a sintered compact with a matrix having pores; forming an
infiltrant blank from a wrought metal sheet, the blank having a
locating element that is suitable for engaging a corresponding
locating element on the sintered compact; placing the infiltrant
blank in contact with the sintered compact such that the locating
element of the blank engages the corresponding locating element on
the sintered compact; and melting the wrought metal such that the
melted wrought metal infiltrates the pores of the sintered
compact.
19. The process of claim 18 wherein: the powder metal is selected
from iron, iron alloys and mixtures thereof; and the wrought metal
is selected from copper and copper alloys.
20. The process of claim 19 wherein: the wrought metal sheet has a
thickness of less than 1 millimeter.
21. The process of claim 18 wherein: the infiltrant blank is formed
by a method selected from stamping, fine blanking and laser
cutting.
22. The process of claim 18 wherein: the locating element of the
blank is a section of the blank extending outwardly from a body of
the blank.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/542,271 filed Feb. 4, 2004.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates to manufacturing powder metal parts,
and in particular to the infiltration of powder metal parts with a
metallic material such as copper.
[0005] 2. Description of the Related Art
[0006] Powder metal parts are used to produce many automotive
components that have a need for net-shaped components. Powder metal
components are typically produced by pressing a powder metal in a
die into a compact of a desired shape and thereafter sintering the
compact to increase the strength of the part.
[0007] It has been reported that conventional powder metal parts,
produced by pressing and sintering, have inferior impact and
fatigue strength because of the presence of pores in the sintered
parts. Accordingly, methods have been proposed to remove porosity
and achieve nearly full density in the parts. One method for
obtaining nearly full density is to infiltrate the powder metal
parts with a metal such as copper. See, for example, U.S. Pat. Nos.
6,676,894, 6,551,373, 6,500,384, 5,925,836, 5,574,959, 5,031,878,
4,976,778, 4,861,373, 4,836,848, 4,769,071, 4,734,968, 4,731,118,
4,606,768, 4,485,147, 4,424,953, 4,412,873, 4,168,162, 4,008,051
and 3,829,295.
[0008] Infiltration is the process of filling the interconnected
pores of the powder metal compact with a molten metal or alloy (the
"infiltrant") of lower melting point by capillary action. For
example, copper infiltrated steels are manufactured by compacting
iron or iron-base powder (with or without graphite powder) into a
finished shape and infiltrating the interconnected pores with a
copper base material during the sintering operation. This may be a
single pass or two stage infiltration. The result is a steel-copper
structure unique to the powder metallurgy process. Compared with
as-sintered iron or carbon steel powder metal parts, copper
infiltration can improve tensile strength, fatigue strength,
elongation, hardness, and impact properties.
[0009] In the past, the source of copper for infiltrating a powder
metal part was a powder metal copper compact, i.e., a part made
from copper powder that is pressed together to maintain its shape.
However, using a copper powder metal compact as the source of
infiltrating copper has drawbacks. For example, (1) residue may
remaining after infiltration; (2) erosion of the base metal surface
at the point of infiltrant entry may occur; (3) infiltration
localization may be difficult because certain shapes may not be
practical via conventional powder metal infiltrant compacts; (4)
breakage associated with fragile powder metal infiltrant compacts
may occur; and (5) positioning of the powder copper compacts may be
difficult.
[0010] Therefore, there is a need for an improved process for
infiltrating porous powder metal parts with a metallic material
such as copper.
SUMMARY OF THE INVENTION
[0011] The present invention meets the foregoing needs by providing
an alternative to using a powder metal compact as the infiltration
source. An infiltration process according to the invention uses a
stamped metallic sheet material as a source of metal for
infiltration to achieve a high strength powder metal article. In
one form, an infiltration process according to the invention uses a
stamped wrought copper sheet material as a source of copper for
infiltration to achieve a high strength powder metal iron or steel
article.
[0012] In one aspect, the invention provides a process for
manufacturing a metal-infiltrated powder metal part. In the
process, a powder metal is compacted to form a compact, and an
infiltrant blank is formed from a wrought metal sheet. The
infiltrant blank is placed in contact with the compact, and the
compact is sintered at a temperature sufficient to form a sintered
compact with a matrix having pores and to melt the wrought metal
such that the melted wrought metal infiltrates the pores of the
matrix to form a metal-infiltrated powder metal part. Location of
the blank on top of the compact improves infiltration of the
wrought metal. In one embodiment, the powder metal is selected from
iron and iron alloys, and the wrought metal is selected from copper
and copper alloys. It can be beneficial for the wrought metal sheet
to have a thickness of less than 1 millimeter. The infiltrant blank
may formed by a method such as stamping, fine blanking or abrasive
water jet cutting.
[0013] In another aspect of the invention, the infiltrant blank may
be formed with a locating element that is suitable for engaging a
corresponding locating element on the compact, and the infiltrant
blank may be placed in contact with the compact such that the
locating element of the blank engages the corresponding locating
element on the compact. For example, the locating element of the
blank may be a section of the blank extending outwardly from a body
of the blank. As a result, positioning of the blank is improved on
the compact.
[0014] In yet another aspect of the invention, the compact is
separately sintered at a temperature sufficient to form a sintered
compact with a matrix having pores, and an infiltrant blank is
formed from a wrought metal sheet. The infiltrant blank is then
placed in contact with the sintered compact, and the wrought metal
is melted such that the melted wrought metal infiltrates the pores
of the matrix to form a metal-infiltrated powder metal part.
[0015] Some advantages of utilizing wrought metallic sheet instead
of a powder metal compact for the infiltration material are: (1) a
reduction in the amount of residue remaining after infiltration;
(2) a reduction in the amount of erosion of the base metal compact
surface at the point of infiltrant entry; (3) improved selective
infiltration localization because the sheet stamping process
facilitates shapes with geometry not practical via conventional
powder metal infiltrant compacts such as thin webs, and missing
areas; (4) improved infiltration process quality due to the
elimination of the breakage associated with fragile powder metal
infiltrant compacts; and (5) improved positioning of the stamped
sheet blanks due to the stamping processes' ability to form
locating features to interlock or engage with the component to be
infiltrated.
[0016] These and other features, aspects, and advantages of the
present invention will become better understood upon consideration
of the following detailed description, drawings, and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a top view of a copper infiltrant blank resting
on an iron base compact before sintering in accordance with one
version of the invention.
[0018] FIG. 2 shows the details of experimental test pieces after
sintering and infiltrating.
DETAILED DESCRIPTION OF THE INVENTION
[0019] In an example process for manufacturing a metal infiltrated
powder metal part according to the present invention, an iron or
iron alloy powder is introduced into a die having the desired shape
of the final part. The powder metal is then compressed in the die
to a higher density article commonly known as a "green compact".
Typically, iron-based green compacts have a density of 6.0 g/cc to
7.3 g/cc. (Theoretical density for iron is 7.88 g/cc.) Next, the
desired amount of copper or copper alloy wrought sheet is formed
into the desired shape for the infiltrant blank, and the blank is
placed in contact with the green compact such that the copper may
infiltrate the pores of the compact upon heating.
[0020] The compact and the copper blank placed in contact with the
compact are subjected to a conventional sintering process performed
at a predetermined temperature above the melting point of copper
(e.g., 1100.degree. C.) for a fixed amount of time (e.g., 15
minutes) in a suitable atmosphere (e.g., a reducing atmosphere
having hydrogen). Typically, the sintering process promotes the
bonding or diffusion between the iron or iron alloy powder
particles to create a sintered compact with a matrix having pores.
During the sintering process, the melted copper flows into the
pores in the matrix. The melted copper wicks, via surface tension,
gravity and capillary action, into the open porosity of the matrix.
Therefore, molten copper fills the pores of the matrix, thereby
increasing the density and integrity of the matrix. The amount of
copper infiltrated depends on the physical and mechanical
properties that are desired in the matrix. When only a partial
infiltration into the matrix is desired, the amount of copper is
reduced. Porosity measurements of the green compact can be used to
determine the amount of copper infiltrant needed.
[0021] In an alternative process, the compact alone is first
subjected to a conventional sintering process to form a sintered
compact with a matrix. In a second step, the copper infiltrant
blank formed from the wrought sheet is placed in contact with the
sintered compact and the copper sheet and the sintered compact are
heated at a predetermined temperature. During the second step, the
copper melts and flows into the pores in the previously sintered
porous matrix. The copper melts and wicks, via surface tension,
gravity and capillary action, into the open porosity of the
matrix.
[0022] FIG. 1 shows an example combination of a compact and an
infiltrant blank suitable for use in a process of the invention. A
copper infiltrant blank 10 about 0.032'' (0.8128 mm.) thick in the
form of a ring is shown resting on the top 22 of a tubular iron
base compact 20 before sintering. The top 22 of the compact 20 has
recessed areas 24a, 24b, 24c and 24d that receive tabs 14a, 14b,
14c and 14d that extend outward from the perimeter edge 12 of the
body of the blank 10.
[0023] The tabs 14a, 14b, 14c and 14d provide locating features to
interlock with or engage the recessed areas 24a, 24b, 24c and 24d
in the compact 20 to be infiltrated with the copper of the blank
10. In the embodiment shown, the tabs 14a, 14b, 14c and 14d extend
outward from the blank 10 and engage recessed areas 24a, 24b, 24c
and 24d in the compact 20. However, in an alternative
configuration, the blank may include recesses that engage outwardly
extending locating features of the compact.
[0024] The copper infiltrant blank 10 may be formed by stamping,
fine blanking or abrasive water jet cutting wrought copper or
copper alloy sheet material. By "wrought", we mean a material
shaped by a mechanical action such as rolling, forging, extrusion
or drawing. A wrought material typically has a density greater than
99% theoretical density. Thus, compacted powder materials are not
considered to be wrought materials as compacted powered materials
typically have a density of 93% or less of the theoretical density.
Exemplary wrought copper materials have thicknesses of 0.001 to
0.250 inches (0.0254 to 6.35 mm.). Wrought copper materials having
thicknesses of less than 0.039 inches (1 mm.) are particularly
advantageous. Suitable copper alloys include brass and bronze.
EXAMPLES
[0025] The following Examples have been presented in order to
further illustrate the invention and are not intended to limit the
invention in any way.
1. Experimental Methods
[0026] Three infiltration techniques were compared versus a
non-infiltrated control test. Standard test rings measuring
nominally 2.0'' (50.8 mm.) outside diameter.times.0.75'' (19.05
mm.) inside diameter.times.1.125'' (28.575 mm.) long were used,
made of a material meeting specification Std 35 FC-0208 of the
Metal Powder Industries Federation (MPIF). MPIF Std 35 FC-0208 is
as follows: Elemental Iron powder 93.2-97.9 weight percent;
Elemental Copper powder 1.5-3.9 weight percent; Carbon (as graphite
powder) 0.6-0.9 weight percent; and Other Elements 2.0 weight
percent maximum.
[0027] The base compacts were pressed to a density of 6.95 g/cc.
Eighteen test rings were manufactured for the infiltration.
[0028] The three infiltration techniques explored were: (1) a
not-infiltrated (control) based on MPIF Std 35 FC-0208; (2) a
standard powder metal copper infiltration as described in MPIF Std
35 (FX series), i.e., using a powdered copper infiltrant material
and pressing it to form a compact of a shape suitable to lay on the
top of a compacted iron or iron-base powder metal article for
subsequent copper infiltration during sintering; (3) a dual feed
process where copper powder was mixed with MPIF STD 35 FC-0208
material, the die was then lowered and a second fill with copper
infiltration material was added and compacted; and (4) infiltration
using a 0.032'' (0.8128 mm.) thick copper stamping material cut
using tin snips to produce a shaped copper source the same area as
the test ring.
[0029] All test pieces were sintered in a 24'' muffle furnace at
normal sintering conditions, that is, at 2050.degree. F.
(1121.degree. C.) for 15 minutes in a 90% nitrogen -10% hydrogen
atmosphere.
[0030] FIG. 2 shows the details of the test pieces after
sintering/infiltrating. The top row is of the Dual Feed process.
The second row from the top is the standard ring with pressed
powder copper compact rings set atop. The second row from the
bottom is the standard ring with a pre-fabricated copper stamping
set atop. The bottom row is the standard ring. Notice the amount of
skull left on the top two rows. The pre-fabricated stamping leaves
no skull.
2. Test Results
[0031] Density measurements were taken and are shown in Table
1.
TABLE-US-00001 TABLE 1 Processes Density (g/cc) (1) Control base
process non 6.88 infiltrated (2) Conventional Copper Infiltration
7.57 Using Copper Powder Compacts (3) Dual Feed Material 7.57 (4)
Infiltration by Copper Stamping 7.62
[0032] The infiltration by copper stamping according to the
invention produced the highest density and is therefore a suitable
replacement for powder metal infiltration. It may also be possible
to use a wrought sheet material other than copper as the source of
the infiltration material.
[0033] Erosion/Cleanliness readings were taken and are shown in
Table 2.
TABLE-US-00002 TABLE 2 Process Comments (1) Control base process
non As sintered infiltrated (2) Conventional Copper Infiltration
Normal residue and erosion Using Copper Powder Compacts for this
process (3) Dual Feed material Dual Feed creates the effect of more
erosion compared to conventional copper infiltration (2) (4)
Infiltration by Copper stamping Reduced erosion and minimal residue
compared with conventional copper infiltration (2)
3. Conclusions
[0034] Dual feeding of material was not a suitable method for
infiltration of powder metal articles.
[0035] Conventional copper infiltration produces significant
residue and erosion. It is difficult to align the pressed copper
infiltrant slug causing inconsistent infiltration. Due to the
fragile green strength of the pressed infiltrant material, the
infiltration process is subject to high scrap when the infiltrant
slug is thin due to handling breakage.
[0036] Infiltration by copper stamping is a unique process and has
the following advantages: (1) the process is a low erosion
infiltration process; (2) the process is a low residue infiltration
process; (3) the process is a selective infiltration process by
stamping shapes with geometry not practical via conventional powder
metal infiltrant slugs such as thin webs and missing areas; (4) the
process uses thin gauge copper materials and therefore eliminates
the breakage associated with powder metal infiltrant slugs, thereby
reducing scrap and improving quality; and (5) the process allows
for the use of stamping location features such as "ears", "lips" or
"tabs" or other readily stamped orientation features.
[0037] Thus, the invention provides an alternative to using a
powder metal compact as the infiltration source. An infiltration
process according to the invention uses a stamped metallic (e.g.,
copper) sheet material as a source of metal (e.g., copper) for
infiltration to achieve a high strength powder metal (e.g., iron or
steel) part.
[0038] Although the present invention has been described in
considerable detail with reference to certain embodiments, one
skilled in the art will appreciate that the present invention can
be practiced by other than the described embodiments, which have
been presented for purposes of illustration and not of limitation.
Therefore, the scope of the appended claims should not be limited
to the description of the embodiments contained herein.
INDUSTRIAL APPLICABILITY
[0039] The invention relates to a process for producing stronger,
higher density and improved surface texture powder metal parts.
* * * * *