WO2003008131A2

WO2003008131A2 - Apparatus and method for high-velocity compaction of multiple-level parts

Info

Publication number: WO2003008131A2
Application number: PCT/US2002/022499
Authority: WO
Inventors: Gerd Hinzmann
Original assignee: Hawk Precision Components Group, Inc.
Priority date: 2001-07-20
Filing date: 2002-07-16
Publication date: 2003-01-30
Also published as: WO2003008131A3; AU2002354920A1

Abstract

A method for the high-velocity compaction of a part from particulate material is disclosed. The method includes the steps of providing a cavity that is at least partially formed by at least one bottom punch, inserting a pre-form that includes at least two levels into the cavity and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part. A multiple-level part from particulate material and a high-velocity compaction press are also disclosed.

Description

Apparatus and Method for High-Velocity Compaction of Multiple-Level Parts

Background of the Invention

Field of the Invention

The present invention relates to the art of particulate materials. More particularly, the present invention relates to the compaction of particulate materials. Still more particularly, the present invention relates to the high-velocity compaction of multiple-level parts composed of particulate materials, such as metal powder, by utilizing high ram velocities.

Description of Related Art

Traditional powder metal compaction uses powders with admixed lubricants in a percentile range of 0.4% to 1.2%. The lubricant is required to reduce die wall friction during the compaction and the ejection of the components to be manufactured as well as to avoid excessive die wear. The admixed lubricants reduce the compressibility of the powder, however, and limit the density of the final product to 90% to 92% of the theoretical density of the material. Typically, a density as close as possible to the theoretical density of the material is desired, because with increasing densities the mechanical properties of powder metal parts improve. These properties are characterized by tensile strength, modulus, elongation, and apparent hardness. A different lubrication technique, die wall lubrication, allows densities of parts to rise to 93% to 95% of the theoretical density of the material. Still, densities closer to 100% of the theoretical density of the material are desired. High-velocity compaction, a recently developed technique, yields parts with further increased densities when used in conjunction with admixed lubricants or die wall lubrication. In traditional compaction, the top tooling, consisting of one or more punches, is constantly connected to the main ram of a compaction press. Hydraulic cylinders, crank drives or knuckle drives actuate the motion of the ram, resulting in force control or position control of the main ram. The compacting speed reached in traditional compaction is in a range of about 0.02 m/s to about 0.1 m/s. In contrast, high-velocity compaction reaches speeds substantially greater than 0.1 m/s, in a range of at least 1 m/s and up to about 100 m/s at impact, an average of about two orders of magnitude greater than traditional compaction. This is accomplished through the use of a ram that is not connected to the top tooling.

In high-velocity compaction, a ram with a discrete mass is accelerated and impacts the top tooling, i.e., the top punch, which is in contact with the powder charge in the die. The mass of the ram and the force of acceleration of the ram, which is typically actuated by hydraulic pressure, are kept constant and the acceleration distance is altered to control the kinetic energy of the ram. The main ram is therefore energy controlled rather than force or position controlled. An exemplary high-velocity compaction press using a hydraulic drive is described in U.S. Patent No. 6,202,757, issued to Dahlberg. A high-velocity press using a mechanical drive is described in U.S. Patent No. 4,245,493, issued to Lindell.

Using high-velocity compaction, densities of 95% to 97% of the theoretical density of the material are possible when admixed lubricants are employed. This rises to 98% and greater with the use of die wall lubrication rather than admixed lubricants. Moreover, the process allows a uniform density distribution along the length of the part.

In the prior art, high-velocity compaction has been applied only to single-level parts for reasons to be detailed below. Processing of multiple-level parts has been performed by traditional compacting only. In the compaction process, the apparent density of the powder in the die when it is initially filled is typically about 37% to 42% of the theoretical density of the material. The powder starts to pre-compact, that is, the particles start to mechanically bond, once the density of the powder reaches approximately 58% to 66% of the theoretical density of the material. This pre-compaction necessitates the use of multiple punches for multiple-level parts in conventional compaction.

Each level subsequent to a first level in a multiple-level part constitutes a drop. The compaction ratio, i.e., the ratio of the length of a part as filled in the die to the length of that part as finally compacted, is typically greater than two. Such a high compaction ratio and the restricted ability of the powder to flow between sections after pre-compaction dictates a change in the drop height in the tooling during the compaction cycle to achieve a uniform density distribution, minimum part geometry distortion and/or crack prevention in the part. This change of drop height in the tooling is achieved by moving multiple punches relative to one another.

In traditional compaction, drop heights of about 5% or more of the overall length of the part typically require the use of multiple punches. The timing of the motion, speed and travel of each punch in a multiple punch tool is determined by the part geometry and the compaction ratio in relation to the main ram motion. Punch motions are either speed controlled or force controlled. At different phases of the compacting cycle, alternating control of force and speed can also be used.

The compaction of multiple-level parts with multiple punches through traditional compaction is known in the art. However, high-velocity compaction has been applied only to single level parts, because the control of timed punch motions relative to the high main ram speed and deceleration of the main ram while releasing the impact energy is extremely difficult. Notwithstanding such difficulties, if the desired density of a part can be achieved with a specific amount of energy from a single impact, the same density should be achieved when this same energy is released by multiple impacts of lesser energy.

Accordingly, it is desirable to develop a method and a device to allow the compaction of multiple-level parts with a higher density than that allowed by the procedures and devices of the prior art. Specifically, this invention is directed to a method and a device to enable the compaction of multiple-level parts using the principle of high-velocity compaction.

Summary of the Invention

The present invention provides a method and apparatus for the high- velocity compaction of multiple-level parts. In accordance with one exemplary embodiment of the present invention, a method for the high-velocity compaction of a part from particulate material includes the steps of providing a cavity that is at least partially formed by at least one bottom punch, inserting a pre-form that includes at least two levels into the cavity and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part. In accordance with another exemplary embodiment of the present invention, a multiple-level part is formed from particulate material by a process including the steps of providing a cavity that is at least partially formed by at least two bottom punches, inserting particulate material into the cavity, moving a main ram in one of force and position control toward the particulate material to compact the particulate material to form a pre-form having at least one step and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part.

In accordance with yet another exemplary embodiment of the present invention, a press for high-velocity compaction of a part from particulate material includes an energy controlled, high-velocity mode for a main ram and an alternate operating mode for the main ram.

Brief Description of the Drawings The invention may take form in certain components and structures, preferred embodiments of which will be illustrated in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a tool set in accordance with an embodiment of the present invention in an open position; FIG. 2 is a sectional view of the tool set of FIG. 1 in a fill position;

FIG. 3 is a sectional view of the tool set of FIG. 1 after a first compacting motion in a standard mode;

FIG. 4 is a sectional view of the tool set of FIG. 1 after a first compacting motion in a standard mode after retracting the bottom punches to a mechanical stop; FIG. 5 is a sectional view of the tool set of FIG. 1 after a final compacting motion in an energy controlled, high-velocity mode;

FIG. 6 is a sectional view of the tool set of FIG. 1 in an ejection position; FIG. 7 is a sectional view of a tool set in accordance with another embodiment of the present invention in an insertion position;

FIG. 8 is a sectional view of the tool set of FIG. 7 after a compacting motion;

FIG. 9 is a sectional view of the tool set of FIG. 7 in an ejection position;

FIG. 10 is a sectional view of a tool set in accordance with another embodiment of the present invention in an insertion position;

FIG. 11 is a sectional view of the tool set of FIG. 10 after a compacting motion; and FIG. 12 is a sectional view of the tool set of FIG. 10 in an ejection position.

Detailed Description of the Preferred Embodiments

As described above, metal powders start to pre-compact, i.e., mechanically bond, at a density of about 58% to 66% of the theoretical density of the material. Pre-compaction occurs in both traditional compaction and high- velocity compaction. When very high densities, i.e., beyond approximately 97%, are approached the adverse effects of pre-compaction include substantial part distortion and, to a lesser extent, inhomogeneous density distribution. To overcome these adverse effects, the present invention involves multiple punches that are pre-lifted and then retract to compact a pre-form by force or position control, similar to traditional compaction. The pre-lifted punches may be stationary during a high-velocity impact or impacts. The retraction of a punch below the shape of the pre-form prior to a subsequent high-velocity impact may facilitate material flow during the subsequent impact.

As previously mentioned, in many applications, the speed profile of the high-velocity compaction may not allow for adequate timing of the punch motion. The present invention overcomes such difficulties by compacting a part at high velocity only after a pre-form is made. For example, the first ram compacting motion that forms a pre-form may be force controlled or position controlled rather than energy controlled.

Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting the same, FIGS. 1-6 show an exemplary embodiment of the present invention utilizing multiple punches at various steps of a compaction method. FIG. 1 depicts a tool set in an open position. The set includes a top punch 10 that defines a central orifice 12, a die 14, a bottom inner punch 16, a bottom outer punch 18 and a core rod 20 that is disposed in an inner circumference of the bottom inner punch 16. The die 14, bottom inner punch 16, bottom outer punch 18 and core rod 20 cooperate to define a cavity 22. The lower limit of the movement of the bottom punch 16 is defined by a first mechanical stop 24, while the bottom outer punch 18 has a lower limit defined by a second mechanical stop 26. Turning now to FIG. 2, particulate material 28, also known as a powder charge, is inserted into the cavity 22. The powder charge may be pre- weighed. A representative height of a first level of the particulate material 28 is used to illustrate the stages of compaction and is shown at a fill height of the first level A. The bottom inner punch 16 is pre-lifted as known in the art in the fill position and is then at least partially retracted upon the first compacting motion. As known in the art, a main ram (not shown) of a compaction press (not shown) is activated and moved to cause the top punch 10 to move and compact the particulate material 28. With reference to FIG. 3, the tool position after a first compacting motion is shown. This tool position is arrived at by force or position control of the main ram, where the compacting speed is in a range of about 0.02 m/s to about 0.1 m/s.

The particulate material 28 after this first compacting motion has become a pre-form 32. The representative height of the first level has decreased to a distance B in the pre-form 32 that is significantly lower than the height A of the first level in the fill stage (referring back to FIG. 2).

During this first compacting motion, the bottom inner punch 16 has been moved toward its mechanical stop 24, but not onto the stop 24. A gap 36 is thereby created between the first mechanical stop 24 and the bottom inner punch 16. This movement of the inner punch 16 relative to the outer punch 18 during the first compacting motion of the ram assures uniform distribution of the particulate material.

As shown in FIG. 4, a gap 38 may be present between the inner punch 16 and the pre-form 32. The gap 38 is created by the retraction of the inner punch 16 below the pre-form 32 onto its mechanical stop 24 after the first compacting motion to maintain an equal compaction ratio for both levels during a subsequent high-velocity impact.

As an alternative to the retraction of the bottom inner punch 16 of FIG. 4, the bottom inner punch 16 may reach its mechanical stop 24 at the end of the first compaction motion. In this case, the fill heights of the particulate material and the pre-lift travel of the bottom inner punch 16 are set to allow the density of the section of the pre-form 32 above the bottom inner punch 16 to be lower than the remainder of the pre-form 32. This in turn allows a uniform density distribution in the pre-form 32 after the subsequent high velocity compaction impact or impacts.

In accordance with this first embodiment of the invention, after at least one compacting motion through force or position control, the main ram is operated at high velocity with energy control. As mentioned above, the energy control of the main ram is typically through the use of a ram with a given mass and a constant acceleration force, such as hydraulic pressure. The acceleration distance of the ram is altered to achieve different ram energies. However, it is also anticipated that the acceleration distance may be constant and the acceleration force may be altered to change and control the energy of the main ram. The pre-form 32 is further densified through one or more impacts at high velocity, i.e., a main ram velocity that is substantially greater than 0.1 m/s at impact. Preferably, the main ram velocity is in a range of at least 1 m/s and up to about 100 m/s at impact. More preferably, the main ram velocity is in a range of from about 10 m/s to about 30 m/s at impact.

After the final high-velocity compacting impact, as illustrated in FIG. 5, the pre-form has become a part 40. The representative height of the first level has decreased from its previous height B (referring back to FIG. 3) to a final, smaller height C of the first level. During the high-velocity impacts, there has been no relative movement between the bottom inner punch 16 and the bottom outer punch 18. The high-velocity impact or impacts increase the density and homogenize the density distribution in the multiple-level part 40 beyond levels accomplished through traditional compaction.

When the compaction process is complete, the part 40 is ejected, as shown in FIG. 6. The top punch 10 is raised to allow access to the part 40 and the core rod 20 is retracted or lowered to allow the part to be pushed out of the cavity 22 by the bottom outer punch 18 with minimal resistance.

In a second embodiment of the method of this invention, rather than actuating the main ram of a press in a force control or position control mode to form a pre-form and then actuating the main ram in an energy control mode, an existing pre-form may be inserted into the tool. In this instance, an energy control mode allowing for high-velocity compaction may be the sole mode that is used.

Turning now to FIGS. 7-9, various stages of compaction are illustrated using an existing pre-form and only a high-velocity, energy controlled mode for the main ram. The tool set includes an upper punch 44 that may include a step 46 to complement the multiple-level configuration of a pre-form. The tool set also includes a die 48, a bottom inner punch 50, a bottom outer punch 52 and a core rod 54 that is disposed on an inner circumference of the bottom inner punch 50. The bottom inner punch 50 has a lower limit defined by a first mechanical stop 56 and the bottom outer punch 18 has a lower limit defined by a second mechanical stop 58. The die 48, bottom inner punch 50, bottom outer punch 52 and core rod 54 cooperate to define a cavity 60. A pre-form 62 is inserted into the cavity 60. The pre-form can be made by any means known in the art, such as by forming in a traditional compaction press. The pre-form may be pre-sintered to burn off lubricant or fully sintered. The pre-sintering or full sintering of the pre-form constitutes a sizing or coining operation rather than a compacting operation, but also serves the objective to form a high-density powder metal part.

For the purpose of illustration, a representative height of a central level of the pre-form 62 is at a distance D. A gap 66 is shown between the bottom inner punch 50 and the pre-form 62. The gap 66 allows an equal compaction ratio for all levels to be maintained after one or more high-velocity impacts.

Once the pre-form 62 is inserted into the cavity 60, the main ram is moved at high velocity by energy control to increase the density of the pre-form 62 through one or more impacts.

Turning to FIG. 8, after the final compacting impact, the pre-form has become a part 68. The representative height has decreased from its previous height D (referring back to FIG. 7) to a final, smaller height E of the central level. During the high-velocity impacts, there has been no relative movement between the bottom inner punch 50 and the bottom outer punch 52.

The use of high-velocity impact or impacts has increased the density and homogenized the density distribution in the multiple-level part 68 beyond levels accomplished through traditional compaction. When the compaction process is complete, the part 68 is ejected, as illustrated in FIG. 9. The top punch 44 is raised to allow access to the part 68 and the core rod 54 is retracted or lowered to allow the part to be pushed out of the cavity 60 by the bottom outer punch 52 with minimal resistance. It is to be noted that more than two bottom punches may be included in a tool set in accordance with the present invention.

With reference to FIGS. 10-12, the use of a single, stepped bottom punch with a pre-form and only a high-velocity, energy controlled mode for the main ram is illustrated. As in FIGS. 7-9, the tool set includes the die 48 and the upper punch 44 that may include a step 46. In this embodiment, however, a single bottom punch 70 includes a step 72 with an appropriate draft angle 74 between the step 72 and the lower level 76 of the punch 70 to allow removal of a finished part. The core rod 54 is disposed in an inner circumference of the bottom punch 70. The bottom punch 70 has a lower limit defined by a mechanical stop 78. The die 48, bottom punch 70 and core rod 54 cooperate as in the above embodiment to define the cavity 60.

The pre-form 62 with the representative height D of the central level is inserted into the cavity 60. The gap 66 between the bottom punch 70 and the pre-form 62 may again be present to allow an equal compaction ratio to be maintained for all levels after one or more high-velocity impacts. Once the preform 62 is inserted into the cavity 60, the main ram is moved at high velocity by energy control to increase the density of the pre-form 62 through one or more impacts. Turning to FIG. 11 , after the final compacting impact, the pre-form has become a part 68. The representative height has decreased from its previous height D (referring back to FIG. 10) to a final, smaller height E of the central level. When the compaction process is complete, the part 68 is ejected, as illustrated in FIG. 12. The top punch 44 is raised to allow access to the part 68 and the core rod 54 and the die 48 are lowered to allow the part 68 to be removed from the top of the bottom punch 70. The part 68 may also be removed by raising the bottom punch 70, as described above.

Another embodiment of the present invention includes a compaction press to be used for high-velocity compaction of a part from particulate material. The press includes a ram drive that is energy controlled and capable of high velocity, also known in the art as a high-velocity compaction press, and an alternate ram drive mode that may be position controlled or force controlled. In accordance with the above description, the press may perform at least one compacting motion in a force controlled or position controlled mode and then perform subsequent high-velocity compaction in an energy controlled mode.

As is apparent from the foregoing detailed description, a method for the high-velocity compaction of a part from particulate material, such as powder metal, is also disclosed. The method comprises the production of parts in accordance with the steps that are presented in the process detailed in FIGS. 1- 12 above.

The invention has been described with reference to the preferred embodiments. Values given for apparent, pre-compacted and final densities apply to most ferrous particulate materials; the invention however is not limited to those, but also applies to other particulate materials such as non-ferrous metals, ceramics and composite materials. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

What is claimed is:

1. A method for the high-velocity compaction of a part from particulate material, comprising the steps of: providing a cavity that is at least partially formed by at least one bottom punch; inserting a pre-form that includes at least two levels into the cavity; and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part.

2. The method for the high-velocity compaction of a part from particulate material of claim 1 , wherein the pre-form is one of partially sintered and fully sintered.

3. The method for the high-velocity compaction of a part from particulate material of claim 1 , wherein the cavity is at least partially formed by at least two bottom punches.

4. The method for the high-velocity compaction of a part from particulate material of claim 1 , wherein the at least one bottom punch is a stepped punch.

5. The method for the high-velocity compaction of a part from particulate material of claim 1 , wherein the velocity of the main ram at a compacting impact is substantially greater than 1 m/s.

6. The method for the high-velocity compaction of a part from particulate material of claim 1, wherein the velocity of the main ram at a compacting impact is in the range of from about 10 m s to about 100 m/s.

7. The method for the high-velocity compaction of a part from particulate material of claim 1 , wherein the velocity of the main ram at a compacting impact is in the range of from about 10 m/s to about 30 m/s.

8. The method for the high-velocity compaction of a part from particulate material of claim 1 , further comprising the step of ejecting the part from the cavity.

9. A method for the high-velocity compaction of a part from particulate material, comprising the steps of: providing a cavity that is at least partially formed by at least two bottom punches; inserting particulate material into the cavity; moving a main ram in one of force and position control toward the particulate material to compact the particulate material to form a pre-form having at least one step; and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part.

10. The method for the high-velocity compaction of a part from particulate material of claim 9, wherein at least one of the bottom punches moves upon compacting the particulate material to form a pre-form.

11. The method for the high-velocity compaction of a part from particulate material of claim 9, wherein the particulate material includes a pre- weighed powder charge.

12. The method for the high-velocity compaction of a part from particulate material of claim 9, wherein the velocity of the main ram at the high- velocity compacting impact is substantially greater than 1 m/s.

13. The method for the high-velocity compaction of a part from particulate material of claim 9, wherein the velocity of the main ram at the high- velocity compacting impact is in the range of from about 10 m/s to about 100 m/s.

14. The method for the high-velocity compaction of a part from particulate material of claim 9, wherein the velocity of the main ram at the high- velocity compacting impact is in the range of from about 10 m/s to about 30 m/s.

15. The method for the high-velocity compaction of a part from particulate material of claim 9, further comprising the step of ejecting the part from the cavity.

16. A multiple-level part from particulate material formed by a process comprising the steps of: providing a cavity that is at least partially formed by at least one bottom punch; inserting a pre-form that includes at least two levels into the cavity; and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part.

17. The multiple-level part from particulate material of claim 16, wherein the cavity is at least partially formed by at least two bottom punches.

18. The multiple-level part from particulate material of claim 16, wherein the at least one bottom punch is a stepped punch.

19. The multiple-level part from particulate material of claim 16, wherein the pre-form is one of partially sintered and fully sintered.

20. A multiple-level part from particulate material formed by a process comprising the steps of: providing a cavity that is at least partially formed by at least two bottom punches; inserting particulate material into the cavity; moving a main ram in one of force and position control toward the particulate material to compact the particulate material to form a pre-form having at least one step; and moving an energy controlled main ram toward the pre-form at a high velocity to increase the density of the pre-form and form the part.

21. The method for the high-velocity compaction of a part from particulate material of claim 20, wherein the particulate material includes a pre- weighed powder charge.

22. A press for high-velocity compaction of a part from particulate material, comprising: an energy controlled, high-velocity mode for a main ram; and an alternate operating mode for the main ram.

23. The press for high-velocity compaction of a part from particulate material of claim 22, wherein the alternate operating mode for the main ram is one of position control and force control.

24. A press for high-velocity compaction of a part from particulate material, comprising: a tool set for high-velocity compaction of a multiple-level part from particulate material, including a die forming at least a portion of a cavity, at least one top punch capable of extending at least to the cavity from above the die, and at least one bottom punch capable of extending at least to the cavity from below the die; and a main ram moveable toward the tool set including a velocity that is substantially greater than 1 m/s at impact with the top punch of the tool set.

25. The press for high-velocity compaction of a part from particulate material of claim 24, wherein the velocity of the main ram at a compacting impact with the top punch is in the range of from about 10 m/s to about 100 m/s.

26. The press for high-velocity compaction of a part from particulate material of claim 24, wherein the tool set includes at least one core rod that is disposed within a center of at least one bottom punch and extends into the cavity.

27. The press for high-velocity compaction of a part from particulate material of claim 24, wherein the tool set includes at least two bottom punches.

28. The press for high-velocity compaction of a part from particulate material of claim 24, wherein the at least one bottom punch is a stepped punch.