HIGH VELOCITY ADIABATIC IMPACT POWDER COMPACTION
A method and apparatus for powder compaction using high velocity adiabatic impact. A quantity of powder material is impacted with a power ram at a controlled velocity in a single controlled impact on the powder material at a controlled specific impulse or specific kinetic energy to adiabatically compact the powder material into a workpiece with a relative density of 95% or above without additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts.
This application claims benefit of the filing date of U.S. Provisional Patent Application No. 61/104,173, filed on Oct. 9, 2009 and entitled “High Velocity Adiabatic Impact Powder Compaction.” The entire contents of said application are fully incorporated herein by this reference.
BACKGROUND1. Field of the Invention
The present invention is directed to powder metallurgy. More particularly, the invention concerns high density powder compaction processes. Still more particular, the invention relates to compaction and article formation of powders comprising materials such as metal, ceramic, plastics, woods, and combinations thereof using high velocity adiabatic impact methods and machinery.
2. Description of the Prior Art
By way of background, high density powder metal compaction is a technique whereby a powder metal is compacted to high density in order to form near net or net shapes of finished articles. For many applications, the technique offers a viable alternative to conventional forming operations such as milling, machining, forging, casting and extrusion, which are generally more time consuming, costly and wasteful of raw material. Moreover, for materials such as titanium, the ability to process articles from powder metal means that manufacturers are not dependent on foundries that use conventional pyrometallurgical industrial processes. For example, the Kroll process is commonly used to produce titanium sponge that is melted into titanium billets for subsequent shape forming. Instead, titanium powder produced by alternative techniques may be utilized, as can scrap material. Ground sponge material may also be used.
Unfortunately, the performance and properties of an article formed from powder metals are highly dependent on the relative density of the article that can be achieved in manufacturing. The relative density of a powder metal article is defined as the ratio (usually expressed as a percentage) of the article's density to that of its pore-free (wrought) equivalent. Increasing the final relative density of a powder metal article above 95% of maximum has been shown to significantly improve tensile strength, fatigue strength, elongation, and toughness/impact strength. Traditional process methods for compacting powder metal use cold isostatic pressing, which achieves relative densities of 85% to 90% of maximum. This is typically followed by vacuum sintering to raise relative densities to 95%, and finally hot isostatic pressing to push relative densities to 99% or better. Process times are significant. Isostatic pressing typically lasts several seconds to a few minutes, and sintering can take several hours. An alternate method known as pneumatic isostatic forging utilizes a rapid gas pressurization technique to reduce processing delays, but still requires cycle times of 10 to 120 seconds to achieve high densities.
High velocity adiabatic impact (HVAI) processing is a metal forming technique whereby high energy is delivered very rapidly to a metal target using a pneumatically-driven, spring-driven or hydraulically-driven ram. The energy delivery is performed without significant heat transfer to the target or the tooling. The technique is well suited for applications such as precision cut-off, zero clearance blanking, and net shape forming. HVAI processing has also been shown to be viable for adiabatic coalescence of powder metal to form articles of high relative density, as well as articles made from combinations of powder metal and other materials, such as powder ceramic. Densification is achieved by intensive shock waves delivered by the high speed ram traveling at velocities ranging from 2-10 meters/second (with higher speeds up to 30 meters/second also being mentioned in the literature).
Unfortunately, conventional HVAI powder metal compaction techniques have several intrinsic limitations that contribute in large measure to high costs, less than ideal finished part properties and performance, and a limited variety of materials that can be successfully compacted to high relative densities without secondary process operations such as sintering and multiple impacts. For example, bouncing of the high-speed ram has been difficult to control. Such bouncing shortens tool life. A further limitation of conventional HVAI powder metal processes is that special density enhancement techniques are used in order to achieve relative densities to levels above 95%. One such technique is to combine HVAI compaction with post-compaction sintering. Another technique is to combine HVAI compaction with preliminary (conventional) compaction, pre-compaction sintering and post-compaction sintering. According to this technique, preliminary conventional compaction is performed, followed by pre-sintering, followed by HVAI compaction, followed by post-sintering. Additional processing, such as warm compaction and die wall lubrication has also been used in combination with the foregoing HVAI compaction techniques to further increase workpiece density. Multiple impacts have also been used to increase workpiece density.
The need for such density enhancement techniques substantially lengthens processing time and increases manufacturing costs. Moreover, applicant has observed that the above-discussed techniques cannot adequately compact large masses of materials in a single impact. Nor can they provide extremely high process repeatability and extremely low part defect rates irregardless of the material and the component shape and features.
SUMMARY OF THE INVENTIONIt is an object of the invention to provide a powder compaction technique using high velocity adiabatic impact that produces relative densities of at least approximately 95%, and preferably at least approximately 99%, without a need for additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts, thereby reducing overall process time and minimizing tooling wear.
It is a further object of the invention to provide a powder compaction technique using high velocity adiabatic impact that produces near net shape to net shape compacted workpieces.
It is a further object of the invention to provide a powder compaction technique using high velocity adiabatic impact that reduces sintering time and temperature for applications where sintering is desired.
It is a further object of the invention to provide a powder compaction technique using high velocity adiabatic impact that can be used with many different powders, including but not limited to powders comprising metals, ceramics, metal-ceramic mixtures, plastics and woods.
It is a further object of the invention to provide a powder compaction technique using high velocity adiabatic impact that is energy efficient.
It is a further object of the invention to provide a powder compaction technique using high velocity adiabatic impact having quick die change capability.
The foregoing objects and advantages are provided by a method and apparatus for compacting a powder using high velocity adiabatic impact. A quantity of powder material is impacted with a power ram at a controlled velocity in a single controlled impact on the powder at a controlled specific impulse or specific kinetic energy to adiabatically compact the powder material into a workpiece with a relative density of 95% or above without additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying Drawings, in which:
Applicants have determined that high quality powder compacted parts may be formed by impacting a quantity of powder material with a power ram in a single high velocity adiabatic impact that delivers a controlled specific impulse or specific kinetic energy of appropriate magnitude to the powder. Impulse represents the change in momentum (I=mΔv) of the power ram as it impacts the powder sample. The quantity “m” represents the effective mass of the power ram and the quantity “Δv” represents the change in ram velocity resulting from the impact. Because the final ram velocity is zero, the quantity “Δv” (vinitial−vfinal) becomes the ram velocity immediately prior to impact. It will be appreciated that the impulse “I” with respect to time (mΔv/Δt) provides a measure of the force (F=ma) imparted by the power ram to the algae. Everything else being equal, a sharp impact producing rapid power ram deceleration tends to increase the force, and visa versa. Kinetic energy is given by E=½mv2, where “m” represents the effective mass of the power ram and “v” represents the ram velocity at impact.
The amount of compaction that will result from a given impulse or kinetic energy delivered by the power ram is a function of the powder mass. The larger the powder mass, the larger will be the impulse or kinetic energy that needs to be delivered to the powder. Specific impulse is a quantity representing the impulse delivered by the power ram per unit mass of the powder. Specific kinetic energy is a quantity representing the kinetic energy delivered by the power ran per unit mass of the powder. Controlling the power ram to deliver an appropriate specific impulse or specific kinetic energy leads to successful powder compaction for different sizes of workpiece to be produced.
Using the high velocity adiabatic impact technique disclosed herein, powder metal and other materials can be compacted into a workpiece having a relative density of at least 95%, and as high as 99% and above. If additional compaction is required, a power stroke may be applied following initial ram impact but before ejecting the workpiece. Although not required, conventional processing operations, such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication and multiple impacts, may be used to achieve further densification. Advantageously, these operations may be performed more efficiently than in prior art powder compaction processing due to the ability of the disclosed compaction technique to achieve high relative densities using a single power ram impact.
Turning now to drawing figures, wherein like reference numerals indicate like elements in all of the several views,
As can be seen in
As can be seen in
As discussed above, the specific impulse or specific kinetic energy delivered by the power ram is determined by selecting the mass and velocity of the power ram according to the mass of the powder. The material type, particle size and particle size distribution of the powder material may also affect compaction.
Following are examples to illustrate the selection of power ram effective mass and velocity to deliver an impulse and specific impulse, or a kinetic energy or specific kinetic energy, according the mass, material type, particle size and particle size distribution of the powder material:
Experimental Setup And Test Results
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- Test machine: Model SIP 100 adiabatic press, built by LMC Inc (DeKalb, Ill.); incorporates vertical ram design (see FIGS. 3A and 7-18).
- Die & punch design: 1.5 inch diameter circular die with mating crankshaft-driven spring-loaded ram punch having effective mass of approximately 2.15 kg (see '493 patent and
FIGS. 9 and 11 herein). - Powder Material: titanium CP-2 powder, nickel 123 powder, coarse copper powder, fine copper powder.
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- 1. Select and adjust machine ram speed at impact by adjusting and setting stroke engagement of the ram prior to impact.
- 2. Weigh a given amount of powder material.
- 3. Deliver room-temperature powder material into pre-located die on machine platen using powder feeder to drop powder into die.
- 4. Align die containing powder material by centering it under the ram.
- 5. Release ram for single impact and compaction of powder material in die.
- 6. Remove compacted workpiece from die.
- 7. No power stroke was used.
- 8. No preliminary (conventional) compaction, pre-compaction sintering or post-compaction sintering was used.
In this experiment, a sample of titanium CP-2 powder was compacted in a single impact having an impact impulse of 107.36 Newton-seconds, a kinetic energy of 2,712 Joules, and a ram velocity of 50 meters/second. The mass of the powder material was approximately 7.15 grams. The specific impulse was 15.02 Newton-seconds/gram. The specific kinetic energy was 379.3 Joules/gram.
Results for Experiment #1:
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- 1. The titanium CP-2 powder sample was compacted to 99.2% of the density of wrought titanium.
In this experiment, two samples of type 123 nickel powder were compacted using the same ram velocity, impulse and kinetic energy applied in Experiment #1, namely, v=50 meters/second, I=107.36 Newton-seconds and E=2,712 Joules. The mass of the powder was varied in order to test how density is affected by changes in specific impulse and specific kinetic energy.
Results for Experiment #2:
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- 1. A 5.93 gram sample of type 123 nickel powder was compacted to 96.4% of the density of wrought nickel. The specific impulse was 18.1 Newton-seconds/gram, and the specific kinetic energy was 457.34 Joules/gram.
- 2. A 27.90 gram sample of type 123 nickel powder compacted to 72.0% of the density of wrought nickel. The specific impulse was 3.84 Newton-seconds/gram, and the specific kinetic energy was 97.20 Joules/gram.
In this experiment, two 5.93 gram powder samples were compacted using the same ram velocity, impulse and kinetic energy applied in Experiment #1, namely, v=50 meters/second, I=107.36 Newton-seconds and E=2,712 Joules. One sample was type 123 nickel powder and the other was coarse copper alloy powder in order to test how density is affected by changes in material type while the specific impulse and specific kinetic energy is the same. The specific impulse was 18.1 Newton-seconds/gram, and the specific kinetic energy was 457.34 Joules/gram.
Results for Experiment #3:
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- 1. The 5.93 gram sample of type 123 nickel powder was compacted to 96.4% of the density of wrought nickel.
- 2. The 5.93 gram sample of coarse copper alloy powder compacted to 98.6% of the density of wrought copper.
In this experiment, two copper powder samples were compacted using the same ram velocity, impulse and kinetic energy applied in Experiment #1, namely, v=50 meters/second, I=107.36 Newton-seconds and E=2,712 Joules. One sample was coarse copper powder with a mass of 5.874 grams having a first set of characteristic particle sizes and PSD of d(0.1)=99.8 micrometers, d(0.5)=579.6 micrometers, and d(0.9)=1117.2 micrometers. The other sample was fine copper powder with slightly less mass of 5.811 grams (1.1% less than the coarse copper sample), having a second set of characteristic particle sizes and PSD of d(0.1)=18.2 micrometers, d(0.5)=33.8 micrometers, and d(0.9)=69.3 micrometers. The specific impulse was 18.28 Newton-seconds/gram and 18.48 Newton-seconds/gram for the coarse and fine powders, respectively, and the specific kinetic energy was 461.70 Joules/gram and 466.70 Joules/gram for the coarse and fine powders respectively.
Results for Experiment #4:
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- 1. Fine copper powder: achieved 97.8% of the density of wrought copper.
- 2. Coarse copper powder: achieved 95.7% of the density of wrought copper.
In this experiment, 7.025 gram and 7.080 gram samples of titanium CP-2 powder were compacted using a ram velocity of 50 meters/second, an impulse I=98.37 Newton-seconds and a kinetic energy E=2,278 Joules. The 7.025 gram sample was given one impact and the 7.080 gram sample was given two impacts spaced approximately 10 seconds apart. The specific impulses were 14.00 and 13.89 Newton-seconds/gram respectively, and the specific kinetic energies were 324.3 and 321.75 Joules/gram respectively.
Results for Experiment #5:
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- 1. The 7.025 gram sample receiving one impact was compacted to 97.04% of the density of wrought titanium.
- 2. The 7.080 sample receiving two impacts was compacted to 99.22% of the density of wrought titanium.
Conclusions from Experimental Data
Experiment #1 demonstrates that it is possible to compact a powder metal such as titanium to better than 99% of the metal's wrought density in a single stroke, without additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts, using a controlled power ram velocity (e.g., 50 meters/second) and a controlled specific impulse (e.g., 15 Newton-seconds/gram) or specific kinetic energy (e.g., 380 Joules/gram).
Experiment #2 demonstrates that increasing the specific impulse and specific kinetic energy increases workpiece density. As shown, a specific impulse of approximately 18-20 Newton-seconds/gram and a specific kinetic energy of approximately 457-520 Joules/gram was sufficient to produce workpiece density of 96.4% for the nickel material tested. On the other hand, lowering the specific impulse to approximately 4 Newton-seconds/gram, and the specific kinetic energy to approximately 97 Joules/gram, dramatically lowered the workpiece density to only 72%.
Experiment #3 demonstrates that workpiece density varies somewhat by material. In this example copper achieved higher compaction density than nickel for a given specific impulse and specific kinetic energy. If Experiment #1 is considered, unalloyed titanium achieved higher compaction density with less specific impulse and specific kinetic energy than either copper or nickel.
Experiment #4 demonstrates that workpiece density is affected by particle size and particle size distribution of the powder. The slight difference in mass between the two copper powder samples can only explain a density difference of approximately 0.3%, whereas the actual density difference achieved was 2.1%.
Experiment #5 demonstrates that performing at second impact can increase workpiece density. Again, the slight difference in mass between the two samples only accounts for a density difference of approximately 0.3%, whereas the actual density difference achieved was 2.18%. If multiple controlled impacts are used, the total specific impulse delivered by the multiple impacts of the power ram may be determined according to the number of impacts and the specific impulse delivered by each impact.
Using the disclosed compaction technique, final workpieces having a mass of approximately 0.01 grams to 30 kilograms or more may be produced, depending on the size of the power ram apparatus. The power ram preferably travels at a velocity above approximately 8 meters/second, for example, in a range of approximately 30-50 meters/second or more. If necessary, higher velocities up to and exceeding 200 meters/second may be used. The specific impulse is preferably at least approximately 15-18 Newton-seconds/gram and the specific kinetic energy is preferably at least approximately 380-520 Joules/gram. If necessary, higher values of specific impulse and specific kinetic energy may be used to increase workpiece density for some materials.
It should be noted that the powder material may comprise materials in addition to metal, such as plastic, wood or combinations of the foregoing. The workpiece may be an intermediate shaped workpiece for use in final forming by further adiabatic processing or by conventional methods, including turning, milling, forging, grinding, honing, electrical discharge machining (EDM), electro-polishing, polishing or other techniques. Alternatively, the workpiece may be a near net shape workpiece for use in final forming by further adiabatic processing. The workpiece may also be a final net shape component that requires no further forming, polishing or finishing operations.
If desired, one or more additional processing operations may also be performed, including conventional preliminary compaction of the powder material, conventional pre-compaction sintering, post-compaction sintering or other heat treatment of the workpiece, pre-heating of the powder material (warm compaction), lubrication, multiple impacts. Further processing operations include final forming of the workpiece, component machining, ingot manufacturing, and mill processing to produce sheet, plate, strip, bar, wire, forging billets, extruded shapes, pipes, and tubing in one or more unalloyed or alloyed grades. As previously stated, these operations may be performed more efficiently than in prior art powder compaction processing due to the ability of the disclosed compaction technique to achieve high relative densities using a single power ram impact.
Turning now to
The construction of the power ram unit is additionally shown in
As can be seen in
Turning now to
Accordingly, a high velocity adiabatic impact powder compaction technique has been disclosed. While various embodiments of the invention have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.
Claims
1. A method for compacting a powder material using high velocity adiabatic impact, comprising:
- impacting a quantity of powder material with a power ram at a controlled velocity in a single controlled impact on said powder material at a controlled specific impulse or specific kinetic energy to adiabatically compact said powder material into a workpiece with a relative density of 95% or above without additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts.
2. A method in accordance with claim 1, wherein said relative density is 96-99% or above.
3. A method in accordance with claim 1, wherein said relative density is 99% or above.
4. A method in accordance with claim 1, wherein said power ram velocity and impulse delivered by said power ram are determined according to one or more of a mass, material type, particle size and particle size distribution of said powder material.
5. A method in accordance with claim 1, wherein said power ram delivers a specific impulse of at least approximately 15-18 Newton-seconds/gram or a specific kinetic energy of least approximately 380-520 Joules/gram to said powder material.
6. A method in accordance with claim 1, wherein said workpiece has a mass within a range of approximately 0.01 grams to approximately 30 kg.
7. A method in accordance with claim 1, wherein said power ram velocity is not less than approximately 8 meters/second when impacting said powder material.
8. A method in accordance with claim 5, wherein said power ram velocity is at least approximately 30-50 meters/second when impacting said powder material.
9. A method in accordance with claim 1, wherein said powder material comprises one or more of metal, ceramic, plastic, wood or combinations of the foregoing.
10. A method in accordance with claim 1, wherein said workpiece is one of an intermediate shaped workpiece for use in final forming by further adiabatic processing or by conventional methods, a near net shape workpiece for use in final forming by further adiabatic processing, or a final net shape component that requires no further forming, polishing or finishing operations.
11. A method in accordance with claim 1, wherein said method is performed with an additional ram power stroke applied following said single controlled impact and prior to ejection of said workpiece.
12. A method in accordance with claim 11 wherein said ram power stroke has a duration of up to approximately 100 milliseconds and a magnitude of up to approximately 2500 tons.
13. A method in accordance with claim 1, further including one or more processing operations of preliminary compaction of said powder material, pre-compaction sintering, post-compaction sintering or other heat treatment of said workpiece, final forming of said workpiece, component machining, ingot manufacturing, and mill processing to produce sheet, plate, strip, bar, wire, forging billets, extruded shapes, pipes, and tubing in one or more unalloyed or alloyed grades.
14. A method for compacting a powder material using high velocity adiabatic impact, comprising:
- impacting a quantity of powder material with a power ram at a controlled velocity in a single controlled impact on said powder material at a controlled specific impulse or specific kinetic energy to adiabatically compact said powder material into a workpiece with a relative density of 95% or above without additional processing such as preliminary compaction, pre-compaction sintering or post-compaction sintering;
- said impacting being performed by a powder compaction apparatus, comprising:
- a power ram;
- a crankshaft and spring system adapted to control power ram motion;
- a die disposed in the path of said power ram;
- a power feeder adapted to deliver powder to said die; and
- a workpiece ejector adapted to eject a workpiece compacted from said powder.
15. A method in accordance with claim 14, wherein said crankshaft and spring system are adapted to deliver a power stroke to said power ram following said controlled impact and prior to ejection of said workpiece.
16. A method in accordance with claim 14 wherein said power ram comprises a ram punch disposed in a punch middle part.
17. A method in accordance with claim 14 wherein said power ram is slidably disposed in punch holder.
18. A method in accordance with claim 14 wherein said power ram comprises one or more punch guiders.
19. A method in accordance with claim 14 wherein said power ram apparatus comprises a tool holder holding a tool outer and a tool inner that collectively comprise said die, said tool inner being supported by an anvil flush and an anvil plate.
20. A method for compacting a powder material using high velocity adiabatic impact, comprising:
- impacting a quantity of powder material with a power ram at a controlled velocity in a single controlled impact on said powder material at a controlled specific impulse or specific kinetic energy to adiabatically compact said powder material into a workpiece with a relative density of 99% or above without additional processing such as preliminary compaction, pre-compaction sintering, post-compaction sintering, pre-heating of the powder material (warm compaction), lubrication or multiple impacts;
- said power ram delivering a specific impulse of at least approximately 15-18 Newton-seconds/gram or a specific kinetic energy of least approximately 380-520 Joules/gram to said powder material;
- said power ram velocity being at least approximately 30-50 meters/second when impacting said powder material; and
- said method further comprising an additional ram power stroke applied following said single controlled impact and prior to ejection of said workpiece, said ram power stroke having a duration of up to approximately 100 milliseconds and a magnitude of up to approximately 2500 tons.
Type: Application
Filed: Oct 9, 2009
Publication Date: Apr 15, 2010
Inventors: Glenn Thomas (East Amherst, NY), Lennart Lindell (Dekalb, IL)
Application Number: 12/576,897
International Classification: B22F 3/24 (20060101); B22F 3/02 (20060101); B22F 3/12 (20060101);