U.S. patent application number 10/136247 was filed with the patent office on 2003-10-30 for powder injection molded metal product and process.
Invention is credited to Clark, Ian Sidney Rex, Harvey, Ronald, Reed, Jeffrey Lance.
Application Number | 20030202897 10/136247 |
Document ID | / |
Family ID | 29249615 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030202897 |
Kind Code |
A1 |
Clark, Ian Sidney Rex ; et
al. |
October 30, 2003 |
Powder injection molded metal product and process
Abstract
A powder injection molding process for making hard to make parts
having internal cavities and hard to make parts made by the
process. Metal powders having a variety of shapes and sizes are
mixed with binder to make a feedstock. The feedstock is molded into
at least two raw molded parts which are then sintered to join the
parts together to form the hard to make part. This process
eliminates all secondary operations in parts having internal
cavities where core withdrawal is not possible. In preferred
embodiment two raw parts are joined together during the sintering
step without adding any materials to assist the bonding. This
methodology can be used to make assemblies that have complex
internal cavities such as filter sections and wave-guide components
that are a low cost critical solution for the communications
industry.
Inventors: |
Clark, Ian Sidney Rex; (San
Diego, CA) ; Reed, Jeffrey Lance; (San Diego, CA)
; Harvey, Ronald; (Escondido, CA) |
Correspondence
Address: |
John R. Ross
Ross Patent Law Office
P.O. Box 2138
Del Mar
CA
92014
US
|
Family ID: |
29249615 |
Appl. No.: |
10/136247 |
Filed: |
April 29, 2002 |
Current U.S.
Class: |
419/6 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 5/10 20130101; B22F 2998/00 20130101; B22F 2201/013 20130101;
B22F 3/1007 20130101; B22F 3/225 20130101; B22F 9/082 20130101;
B22F 2999/00 20130101; B22F 2999/00 20130101; B22F 7/062 20130101;
B22F 3/22 20130101; B22F 3/225 20130101; B22F 2998/00 20130101;
B22F 7/062 20130101; B22F 2998/10 20130101 |
Class at
Publication: |
419/6 |
International
Class: |
B22F 007/06 |
Claims
What is claimed is:
1. A powder injection molding process for making hard-to-make parts
having internal cavities comprising the following steps: A) metal
powders having a variety of shapes and sizes are mixed with binder
to make a feedstock, B) the feedstock is molded into at least two
raw molded parts, C) the at least two molded parts are then
sintered to join the parts together to form the hard-to-make
part.
2. A process as in claim 1 wherein said metal powders comprise
copper.
3. A process as in claim 1 wherein no material is added between the
at least two parts to assist in the bonding.
4. A process as in claim 1 wherein said at least two parts are two
parts.
5. A process as in claim 1 wherein said hard-to-make part is a wave
guide component.
6. A process as in claim 4 wherein said hard-to-make part is a
filter section.
7. A process as in claim 1 wherein said process is a part of a mass
production process for making said hard-to-make parts.
8. A process as in claim 1 wherein said raw molded parts taken
together are about 15 percent to 35 percent larger than the
hard-to-make part.
9. A process as in claim 1 wherein said raw molded parts taken
together are about 28 to 30 percent larger than the hard-to-make
part.
10. A process as in claim 1 wherein said metal powders of various
sizes are prepared using a water atomization process.
11. A process as in claim 1 wherein each of said raw molded parts
comprise at least one location pin or pin hole for assuring proper
positioning of the parts.
12. A process as in claim 1 wherein a compressive force is applied
to press the at least two parts together during the sintering
process.
13. A process as in claim 11 wherein one of the at least two parts
is on top of another part and said compressive force is applied by
adding a weight on top of the top part.
14. A process as in claim 1 wherein said sintering takes place in a
sintering furnace and a strong reducing gas is added to the
sintering furnace during the sintering process.
15. A process as in claim 13 wherein said strong reducing gas is
hydrogen.
16. A process as in claim 2 wherein said molded parts are sintered
at temperatures about 2 to 10 degrees C. below a melt point for the
metal powders.
17. A process as in claim 16 wherein said powders are copper
powders and said melt point is about 1083 C.
18. A hard-to-make part having an internal cavity comprising: A) a
first sintered part, B) a second sintered part solidly bound to
said first sintered part at an interface forming said internal
cavity with no added material at said interface.
19. A hard-to-make part as in claim 18 wherein said hard-to-make
part is a copper part.
20. A hard-to-make part as in claim 18 wherein said hard-to-make
part is a wave guide component.
21. A hard-to-make part as in claim 20 wherein said hard-to-make
part is a filter section.
Description
[0001] This invention relates to metal products with complicated
internal cavities and to techniques for making them in particular
when the metal is copper.
BACKGROUND OF THE INVENTION
[0002] Powder injection molding is a well-known process for making
metal parts having complicated shapes. A metal is converted to fine
powder. The powder is mixed with a binder to form a feedstock. The
binder typically includes one or more binder materials that can be
removed at temperatures lower than the melting point of the metal.
Using an injection-molding machine the feedstock is injected into a
mold cavity having the shape of the desired product except the
shape is about 15 to 30 percent larger than the finished product.
The molded parts are then placed in a solvent bath to dissolve the
soluble components to make the molded material porous. The porous
parts are next sintered to remove all of the remainder of the
binder material leaving a part that is in the desired form and
almost 100 percent metal. The sintering step typically reduces the
size of the part by about 20 to 30 percent. A detailed description
of a good powder injection molding process is included in U.S. Pat.
No. 4,197,118, incorporated by reference herein.
[0003] Several prior art techniques for joining of two injection
molded components parts are known. One known technique involves
shrinking one injection molded component part around a second
component part. The second component part may be fully dense or may
be sintering at the same time. Conventionally, component parts have
been joined by adding to the interface between the parts, an
intermediate material such as a brazing material, solder, welding
alloys, glues or epoxies.
SUMMARY OF THE INVENTION
[0004] The present invention provides a powder injection molding
process for making hard to make parts having internal cavities and
hard to make parts made by the process. Metal powders having a
variety of shapes and sizes are mixed with solvent and binder to
make a feedstock. The feedstock is molded into at least two raw
molded parts, which are then sintered to join the parts together to
form the hard to make part. This process eliminates all secondary
operations in parts having internal cavities where core withdrawal
is not possible. In preferred embodiment two raw parts are joined
together during the sintering step without adding any materials to
assist the bonding. This methodology can be used to make assemblies
that have complex internal cavities such as filter sections and
waveguide components that are a low cost critical solution for the
communications industry. This methodology eliminates expensive
secondary operations such as fixturing and eliminates any need for
intermediate-bonding materials such as braze compounds, epoxies and
glues. This invention also permits inspection of the critical
internal features before the components are joined into the
assembly. This technology can be used to make filter sections,
wave-guide components and other parts with similar complex internal
shapes for the communication and other industries at lower costs
than other assembly methods. Assemblies can be made quickly and
inexpensively with a very high yield comparable to that in the
process for regular powder injection molded parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIGS. 1A and 1B show two views of a part made pursuant to
the present invention.
[0006] FIGS. 2A, 2B and 2C show three views of a mold pattern for
the FIGS. 1A and 1B part.
[0007] FIGS. 3 through 7 show examples of hard to make parts.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0008] Hard to Make Part
[0009] FIG. 1A is a cross section view and FIG. 1B is a front view
along the axis of a typical hard to make copper part (such as high
frequency wave-guides or high frequency filters that are very
difficult to fabricate with accurate dimensions. Attempts were made
by Applicants to mold a part such as this as one piece using a
copper powder technology. This effort was only partially
successful. After repeated efforts by Applicants, precise
dimensions on the inside surfaces could not be provided. The part
could be made by die casting two aluminum halves, machining the
halves to tolerance and then brazing, welding or gluing and
mechanically fastening the two halves together. Applicants' have
developed a better method of making parts like the part shown in
FIGS. 1A and 1B.
[0010] Preferred Powdered Injection Molding Technique
[0011] Applicants have proven the feasibility of the present
invention by making samples of a wave-guide filter section in high
purity copper. The bond strength of the two joined components was
demonstrated by a water pressure test at 100 psi without leakage or
separation. These samples have been tested and found to meet the
radio wave requirements.
[0012] Making the Metal Powder
[0013] In this preferred embodiment of the present invention, the
metal powders used to make the components are pure copper to
achieve the desired high electrical conductivity and are produced
by water atomization to provide low cost and irregular particle
shapes. The preferred water atomization process is described in
detail in U.S. Pat. No. 4,080,126, issued Mar. 21, 1978. That
patent is incorporated by reference herein. The powder is screened
to minimize particles larger than 44 microns and to ensure
sufficient fine particles in the powder lot size distribution so
that the molded parts will sinter to sufficient density, typically
at least 95% of full density, to provide strength and prevent
leakage. The water atomization process produces very small
irregularly shaped particles suitable for powder injection molding.
Furthermore, Applicants have discovered, surprisingly, that these
irregular shaped particles are important in effecting the joining
of two separate component parts during sintering by providing
interlocking pressure points at the joint interface, which enhances
diffusion across the interface between the components being
joined.
[0014] Making the Raw Parts
[0015] In this preferred embodiment parts such as the part shown in
FIGS. 1A and 1B are made by injection molding two separate
component parts and then joining the parts in a sintering process.
To make the part shown in the figures, one mold cavity is prepared
using an injection block and a top moving part to provide an
enlarged cavity image of one half of the part shown in FIGS. 1A and
1B. The mold cavity is 28 percent larger than the finished part and
each part comprises two small location pins (1.0 mm long and 1.0 mm
in diameter) and two matching location pinholes having
corresponding dimensions. FIG. 2A is a cross section of the mold
with the mold closed showing the mold cavity 10, the mold runner 12
and the mold gate 14. FIG. 2B shows a side view of the moving part
of the mold showing at 30 the location of the location pins and the
location pin cavities. FIG. 2C shows a side view of the mold insert
block with phantom outlines showing the location of the core
forming elements in the moving part of the mold. Since the part is
symmetrical, only one mold is needed. The powder is screened and
tested to assure that the particle sizes are as desired. The powder
is mixed with a binder material including soluble binding materials
to produce the injection molding feedstock. The feedstock is then
fed into a conventional injection-molding machine and raw component
parts are produced in the conventional powder injection molding
process. Applicants are able to produce as many as 60 to 180 raw
parts per hour from one cavity using a Model 270S injection-molding
machine available from Arburg, Inc.
[0016] Sintering and Joining in One Step
[0017] After the raw component parts are inspected a first part is
placed on top of a second part. The top and bottom parts are
processed through the solvent to remove the soluble binder
components and then placed in an oven for sintering at a
temperature slightly below the melting point of copper. The
sintering step removes the remaining binder material, shrinks the
parts to the desired size and permanently joins the top to the
bottom part.
[0018] It is preferred that the components to be joined have
interfaces that fit together as closely as possible in order to
enhance the diffusion of copper between the two components. Some
force perpendicular to the join interface is required. In many
applications the weight of the top part applies sufficient force.
Alternatively, a secondary inert weight can be used while some of
the binder components are being removed in the solvent step and
during sintering.
[0019] It is also preferred that shrinkage during sintering is at
the maximum end of the spectrum normally used for powder injection
molded parts. For example a scale-up multiplier from drawing to
mold size in the order of 1.28.times. to 1.30.times. or more is
preferred to aid bonding at the interface between component
parts.
[0020] Initial sintering of the copper powders starts before the
backbone binder component is burned off and during this time the
structure of the components is weakest and the interface relaxes to
accommodate small irregularities between the joining components.
The sintering step encourages the diffusion of the copper atoms to
not only fill spaces between the copper particles but also to cross
the interface between components and thereby causing the components
to become one assembled part. The preferred atmosphere in the
furnace is a strong reducing gas to reduce oxides and any other
surface films from the particle surfaces during sintering. Hydrogen
gas is a preferred atmosphere for the copper powders. The heating
profile in the furnace must follow a series of temperature rises
and holds as for conventional metal powder injection molded
components. This removes the backbone binder slowly and without
breaking the components. A maximum sintering temperature is
preferred to achieve the highest density and the strongest joint.
For pure copper components there is a single melt point at 1083 C.,
which cannot be exceeded. A temperature about 2 to 10 C. below the
melt point is a practical preferred maximum temperature. The
preferred time at the maximum temperature for the water atomized
copper powders is four hours.
FIRST PREFERRED EXAMPLE
[0021] 1. Feedstock Preparation
[0022] Two mixes of copper feedstock, identified as 2002-059 and
2002-060 were made using the following procedure. A 4,553-gram lot
of water atomized pure copper powder was placed in a V-cone
blender. The particle size distribution of the powder after
blending was analyzed by Microtrac as follows:
[0023] 99.9% was less than 88.0 microns
[0024] 92.9% was less than 44.0 microns
[0025] 68.4% was less than 22.0 microns
[0026] 49.1% was less than 15.6 microns
[0027] 27.0% was less than 11.0 microns
[0028] 10.6% was less than 7.8 microns
[0029] 3.0% was less than 5.6 microns
[0030] Stearic acid, at 3% of the binder system, was added to the
copper powder and all was blended together for 30 minutes.
[0031] The binder system consisted of 447 grams of the following
constituents:
[0032] Polypropylene at 40%
[0033] Paraffin wax at 48%
[0034] Carnauba wax at 9%
[0035] Stearic acid at 3%
[0036] The binder components except for the Stearic acid were
melted in a preheated sigma blade mixer. When the copper powders
and Stearic acid had completed the blend cycle they were slowly
added to the molten binders and the whole mixture was heated to 180
C. to ensure complete melting of all binder components. Then the
temperature was lowered to 165 C. and held for one hour. Finally
the mixer was evacuated with a rough vacuum pump for five minutes
to pull out entrained air as the mix temperature was lowered to 155
C. After the five minute cooling period the mixer was stopped, the
vacuum removed and the mix was unloaded from the mixer and cooled
to room temperature. When cooled, the chunks of mix were granulated
in a conventional granulator of the type used for regrinding
plastic screws and runners. The resulting small pea sized particles
are the feedstock for the molding machine.
[0037] 2. Molding Parts
[0038] The copper feedstock was fed into a conventional
injection-molding machine and injected into a mold cavity that was
larger than the final component by 28%. The molded component
contained two locating pins on one side and two matching pinholes
on the other side. Two such parts could then be assembled together
with the self-locating pins in the pinholes.
[0039] 3. Solvent Debinding
[0040] The molded copper assemblies were placed in a tank
containing 1,1,1-Trichloroethane to remove the waxes and the
Stearic acid from the binder system. The solvent was heated to 46
C. to shorten the binder removal time. The time to remove the
soluble components was determined by weight loss from the as-molded
parts and 14 hours was used. Other equivalent solvents also can be
used to remove the soluble binder constituents.
[0041] 4. Sintering
[0042] The debound copper assemblies were removed from the solvent,
dried and placed on ceramic furnace shelves. Additional ceramic
setter pieces were placed under a raised section of the assembly
for further support so it would not sag during sintering. The
ceramic setter shelves were loaded into the furnace. The furnace
was purged with nitrogen for 25 minutes to remove air and then
hydrogen was introduced. The furnace was heated with a 100%
hydrogen atmosphere in a series of ramps and holds as follows:
[0043] Ramp from room temperature to 490 C. in 70 minutes
[0044] Hold at 490 C. for 110 minutes
[0045] Ramp to 525 C. in 90 minutes
[0046] Hold at 525 C. for 90 minutes
[0047] Ramp to 590 C. in 90 minutes
[0048] Hold at 590 C. for 60 minutes
[0049] Ramp to 1081 C. in 130 minutes
[0050] Hold at 1081 C for 230 minutes
[0051] Furnace cool to room temperature
[0052] Importance of Water Atomized Copper
[0053] The concept of joining water atomized copper PIM components
was conceived on Dec. 18, 2001. Although attempts at joining PIM
parts in the sinter furnace had been tried previously with limited
success, the use of PIM parts made from water atomized copper
powders had not been tried in joining experiments. However, the
authors thought that it might be possible to improve the join
between two components by sintering the highly irregular copper
powders across the interface between two components.
[0054] Applicant's Experiments
[0055] The first attempt to join two copper components was done by
placing one separately molded part on top of another in the sinter
furnace and sintering the assembly along with other production
parts made of the same copper material. After sintering in the
conventional production cycle it was found to Applicant's surprise
that there was a very strong bond between the two components which
could not be broken by striking one component with a hammer while
the assembly was fixed in a vice. Subsequent sinter joining tests
confirmed Applicants' surprising discovery. Next a special mold was
built to make a component part that could be joined into one
assembly using self-locating V-shaped grooves and ridges. However,
it was found during sintering that one component would shift with
respect to the other and ride up on the V-shaped grooves causing
the joint to separate at various locations. Therefore, the mold was
rebuilt without the V-grooves but used two pins and two pinholes to
self-locate each component. Assemblies of these components with
self-locating pins were sintered and found to make very uniform,
strong leak-tight joins. It was also found that critical design
features within the assembly cavity and measured across the join
could be held to tolerances of approximately +/-0.001 in. which
made the process practical for many types of assemblies.
[0056] Hard to Make Parts
[0057] Cross sections of several examples of hard to make parts are
shown in FIGS. 3 through 7. Parts like these are easily and
efficiently produced using the present invention. FIG. 3 shows a
connector with a 90-degree bend. FIG. 4 shows a similar connector
with a U bend. FIG. 5 shows an electrical connector housing for a
sensor system. FIG. 6 shows an example of a part which is made
hollow merely to reduce weight and/or save material costs. FIG. 7
shows a technique for making internal threads using a molding
process.
[0058] While the present invention has been describer in terms of
the above descriptions of preferred embodiments, the reader should
understand that the present invention is not limited to those
embodiments and that many modifications and variations of the above
embodiments are possible without departing from the spirit of the
invention. The scope of the invention should be determined by the
appended claims and their legal equivalents.
* * * * *