Title:
HIGH VELOCITY ADIABATIC IMPACT POWDER COMPACTION
Kind Code:
A1


Abstract:
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.



Inventors:
Thomas, Glenn (East Amherst, NY, US)
Lindell, Lennart (Dekalb, IL, US)
Application Number:
12/576897
Publication Date:
04/15/2010
Filing Date:
10/09/2009
Primary Class:
Other Classes:
419/38, 419/66, 419/1
International Classes:
B22F3/24; B22F3/02; B22F3/12
View Patent Images:



Primary Examiner:
ZHU, WEIPING
Attorney, Agent or Firm:
WALTER W. DUFT (CLARENCE CENTER, NY, US)
Claims:
What is claimed is:

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.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

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.

BACKGROUND

1. 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 INVENTION

It 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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a graph plotting power ram displacement vs. time in a prior art high velocity adiabatic impact powder compaction process;

FIG. 2 is a graph plotting power ram displacement vs. time in an example powder compaction process using high velocity adiabatic impact in accordance with the present disclosure;

FIG. 3 is detailed graph plotting power ram displacement and ram crankshaft motion vs. time in an example powder compaction process using high velocity adiabatic impact in accordance with the present disclosure, and further illustrating an optional power stroke;

FIG. 4 is a graph plotting relative tensile strength, fatigue strength and elongation vs. relative density of a compacted powder workpiece formed using high velocity adiabatic impact in accordance with the present disclosure;

FIG. 5 is 2000× magnified photograph of a compacted powder workpiece that has been compacted using high velocity adiabatic impact power compaction in accordance with the present disclosure;

FIG. 6 is 5000× magnified photograph of the compacted powder workpiece shown in FIG. 5;

FIG. 7 is a perspective view of an example high velocity adiabatic impact powder compaction apparatus;

FIG. 8 is a front elevation view showing the powder compaction apparatus of FIG. 7;

FIG. 9 is a cross-sectional view taken along line 9-9 in FIG. 8;

FIG. 10 is a side elevation view showing the powder compaction apparatus of FIG. 7;

FIG. 11 is a cross-sectional view taken along line 11-11 in FIG. 10;

FIG. 12 is an exploded view of the powder compaction apparatus of FIG. 7;

FIG. 13 is perspective view of the powder compaction apparatus of FIG. 7 during a powder measuring phase of high velocity adiabatic impact powder compaction;

FIG. 14 is perspective view of the powder compaction apparatus of FIG. 7 during a powder charging phase of high velocity adiabatic impact powder compaction;

FIG. 15 is perspective view of a power ram portion the powder compaction apparatus of FIG. 7 during an initial impact phase of high velocity adiabatic impact powder compaction;

FIG. 16 is perspective view of the powder compaction apparatus of FIG. 7 during a power stroke phase of high velocity adiabatic impact powder compaction;

FIG. 17 is perspective view of the powder compaction apparatus of FIG. 7 during a power ram release phase of high velocity adiabatic impact powder compaction; and

FIG. 18 is perspective view of the powder compaction apparatus of FIG. 7 during a workpiece ejection phase of high velocity adiabatic impact powder compaction.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

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, FIG. 1 is a graph plotting power ram displacement vs. time in a prior art high speed adiabatic impact powder compaction process. As can be seen, the power ram is subjected to repeated bouncing, which introduces excessive shock loading that reduces tool life and wastes energy. Ram bouncing is caused by excess energy being delivered to the target due to improper power ram press design and/or setup. The power ram press should guarantee delivery of minimum energy to complete the work cycle. Excess energy has to be absorbed by the press. This results in the bouncing illustrated in FIG. 1. Excess energy also reduces tool life, causes variations in part quality, places extra strain on equipment, and wastes power. FIG. 1 also shows that the power ram velocity at initial impact is fairly low. The ram drops 15 millimeters in 6 milliseconds, producing an impact velocity of 2.5 meters/second.

FIG. 2 is a graph plotting ram displacement vs. time in an exemplary powder compaction process performed using high velocity adiabatic impact in accordance with the present disclosure. This graph illustrates that there is no bouncing of the power ram during any portion of the compaction operation. The power ram velocity is also higher in order to deliver a larger impulse and kinetic energy, and a short ram power stroke is also shown (see below). The ram drops 13.75 millimeters in 1.25 milliseconds, producing an impact velocity of 11 meters/second. Higher power ram velocities may also be used.

FIG. 3 is an additional graph plotting both power ram displacement and power ram crankshaft motion vs. time. The crankshaft motion refers to a crankshaft that is used to control the position of a spring-loaded power ram that may be used to impact the workpiece. An example crankshaft-driven, spring-loaded power ram (used for adiabatic cutting and blanking) is disclosed in U.S. Pat. No. 4,245,493, entitled “Impact Press” (the '493 patent). The entire contents of the '493 patent are hereby incorporated herein by this reference. According to the '493 patent, a reciprocating crankshaft drives the power ram toward and away from the workpiece in cyclic fashion. Throughout most of the crankshaft's reciprocating motion, the power ram is locked in a retracted position within a sleeve that is coupled to the crankshaft. A compressed spring is biased against the back of the power ram while the latter is retracted. As the crankshaft rotates and drives the sleeve and power ram toward the workpiece, the spring is released and the power ram is forcefully driven from its retracted position into contact with the workpiece. Continued rotation of the crankshaft while the head of the power ram remains in contact with the workpiece pushes the power ram back to its retracted position within the sleeve while recompressing the spring for the next impact.

As can be seen in FIG. 3, the power ram may be spring-released from its sleeve just as the crankshaft begins to drive the power ram toward the powder. Other release points may also be used. The ram position is controlled by the crankshaft so that there is no bounce following initial impact and compaction of the powder. In many cases, full compaction occurs within not more than approximately 1 millisecond following of the power ram first contacting the powder material. As further shown in FIG. 3, an additional power stroke may be applied by the crankshaft following the power ram impact and prior to ejection of the workpiece, while the compacted powder is still warm or hot. Using the apparatus of the '493 patent, the power stroke may be implemented by designing the crankshaft, sleeve and power ram components so that the crankshaft continues to move toward the workpiece for a short time after the power ram has been recaptured back in the sleeve. The continued motion of the crankshaft will be transferred through the power ram into the workpiece with high mechanical advantage and large forces. The ram power stroke may be completed in approximately 10-100 milliseconds or more, delivering a short duration squeeze of up to 2500 tons or more, depending on equipment capabilities. The power stroke can be used to further compact the powder so that the final workpiece density is virtually or near 100%. The power stroke is most preferably delivered without removing the power ram from the workpiece following initial impact. FIG. 3 also illustrates that the pre-compacted powder may be at room temperature, or it may be modestly preheated to a desired temperature. An example preheat temperature would be 300° F., and a preheat temperature range likely to be used in practice would be 200° F. to 900° F. depending on the mass of material and the material properties.

As can be seen in FIG. 4, compacting a powder metal to 95% of its wrought density dramatic improvements in workpiece structural properties may be achieved by increasing relative density to 99% and above using the disclosed technique. For example, applicant has observed that tensile strength increases by 11%, fatigue strength increases by 25%, and elongation capability increases by 50%. As can be further seen in FIGS. 5 and 6, a compacted workpiece having a relative density of 99% or better has almost no porosity.

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

    • 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.

Test Procedure:

    • 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.

Experiment #1—Proof of >99% Density

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:

    • 1. The titanium CP-2 powder sample was compacted to 99.2% of the density of wrought titanium.

Experiment #2—Effect of Specific Impulse and Specific Energy On Density

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:

    • 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.

Experiment #3—Effect of Material Type On Density

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:

    • 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.

Experiment #4—Effect of Mean Particle Size and Particle Size Distribution (PSD) on Density

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:

    • 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.

Experiment #5—Effect of Multiple Impacts on Density

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:

    • 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 FIGS. 7-12, a high velocity adiabatic impact powder compaction apparatus 20 is provided. In FIG. 7, the apparatus 20 is shown as comprising a power ram unit 22 and a powder hopper 24. The powder hopper 24 dispenses powder through a hopper discharge pipe 26. As additionally shown in FIGS. 8 and 9, the power ram unit 22 includes an automated powder feeder 28 that receives powder from the discharge pipe 26. The powder feeder 28 includes a rotatable and reciprocally driven powder feed rod 30 having a powder receptacle 30A. A workpiece push-out knife 29 is disposed below the power feeder 28.

The construction of the power ram unit is additionally shown in FIGS. 10-11, and in the exploded view of FIG. 12. Starting from the top of FIG. 12, the power ram unit includes a punch cap 32, a ram punch 34, a punch middle part 36, a punch holder 38, a punch guider 40 (two or more), a tool holder 42, a tool outer 44, a tool inner 46, an anvil flush 48, and an anvil plate 50.

As can be seen in FIGS. 9 and 11, the ram punch 34 is seated in the punch middle part 36. The punch middle part 36 is slidably mounted in a large central bore of the punch holder 38. Although not shown in the Drawings, the ram punch 34 can be driven by a crankshaft and spring-loaded as per the '493 patent. The punch middle part 36 is retained in the punch holder 38 by the punch cap 32, which is bolted to the punch holder 38. The bottom of the punch holder 38 is bolted to the top of the tool holder 42. The bottom of the tool holder 42 is bolted to the anvil plate 50. Each punch guider 40 is slidably received in a corresponding bore formed in the punch middle part 36. The bottom of each punch guider 40 rests on an internal annular shoulder of the tool holder 42. This annular shoulder is located at the base of a first central bore of the tool holder 42. The tool outer 44 rests on the same annular shoulder. The tool outer 44 has a central bore that receives the tool inner 46. The top of the tool outer 44 and the top of the tool inner 46 are configured to collectively provide a die 52 where powder is received and a workpiece is formed. The bottom of the tool inner 46 is received in a central bore of the anvil flush 48, which in turn is slidably positioned in a second central bore of the tool holder 42. The anvil plate 50 supports the tool inner 46 and the anvil flush 48.

Turning now to FIGS. 13-18, an example operation of the compaction apparatus will be described. In FIG. 13, the punch 34 and the punch middle part 36 are raised, the powder feeder 28 is retracted, and the die 52 is empty. In FIG. 14, the powder feeder 28 is feeding a load of powder into the die 52. In particular, the entire power feeder 28 has moved closer to the punch holder 38 and the powder feed rod 30 has advanced into the interior of the punch holder so that the powder receptacle 30A is positioned above the die 52. FIG. 14 shows the powder receptacle 30A facing upwardly, just prior to the powder feed rod 30 being rotated 180 degrees to dump the powder from the powder receptacle 30A into the die 52. In FIG. 15, the punch 34 and the punch middle part 36 have been accelerated downwardly so that the punch 34 adiabatically impacts the powder. In FIG. 16, an optional power stroke is applied to the punch 34. In FIG. 17, the punch 34 and the punch middle part 36 are raised to their starting position to expose the compacted workpiece. In FIG. 18, the push-out knife 29 is advanced to eject the workpiece.

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.