WO2008061342A1

WO2008061342A1 - Method and apparatus for die wall lubrication

Info

Publication number: WO2008061342A1
Application number: PCT/CA2007/002057
Authority: WO
Inventors: Roger Lawcock; Mark Haiko
Original assignee: Stackpole Limited
Priority date: 2006-11-20
Filing date: 2007-11-16
Publication date: 2008-05-29

Abstract

An apparatus for forming a powder metal article includes a die having a die cavity and a pair of opposing punches for compressing a powder metal. The apparatus includes a lubricant spraying tube with a porous nozzle, the tube being associated with one of the punches. The nozzle being retractable so as to be exposed only when the die cavity is to be sprayed.

Description

METHOD AND APPARATUS FOR DIE WALL LUBRICATION

FIELD OF THE INVENTION

[0001] The present invention relates to the field of manufacturing articles using powder metallurgy (PM). More specifically, the invention relates to methods and apparatus for lubricating the dies used in PM processes.

BACKGROUND OF THE INVENTION

[0002] In the manufacture of articles by the powder metallurgy (PM) process, metal powders are pressed or compacted in a die cavity to form a "green compact". The die and associated pressing equipment is commonly referred to as "tooling". The green compact is then sintered to form bonds between the powder particles, thereby imparting mechanical strength properties to the component. After sintering, the component may be re-pressed, using tooling similar to the original compaction tooling, to meet desired dimensional requirements.

[0003] To prevent wear of tooling during pressing operations, lubricants are commonly employed, which serve to reduce friction between the die wall and its contents (i.e. the powders or the compressed product). The lubricants commonly used with compaction tooling comprise particulate lubricants that are usually added to the powder metal formulation. Such lubricants are commonly referred to as "admixed lubricants". Typical particulate lubricants used comprise metallic (lithium (Li) or zinc (Zn)) stearates or similar stearic acid compounds. Re-pressing tools are usually lubricated with a liquid mineral or synthetic oil spray.

[0004] One common goal in manufacturing PM structural parts is to increase the strength of the manufactured parts. Typically, the strength of the formed components will increase with its density (i.e. reduced porosity content). Hence methods that can be used to manufacture components of higher density are desirable.

[0005] It is commonly known in the PM industry that a disadvantage to the use of admixed lubricants is a limitation to the maximum density to which the component can be pressed. Specifically, since the admixed lubricants generally comprise low specific gravity materials, even a relatively a small percentage fraction by weight (levels of 0.5 to 1 wt% are commonly used) will occupy a significant volume within the compacted article. In addition, during the sintering step, the lubricant is often completely evaporated, thereby leaving a void or pore within the internal structure of the sintered compact. In the result, the final density of the pressed component is reduced. [0006] Thus, to produce parts with high density it is desirable to minimize or eliminate the amount of particulate lubricant added to the starting powder formulation. However, simply reducing the lubricant content without providing an effective alternative to tool lubrication will result in impractical tool wear consequences.

[0007] Various apparatus and methods have been previously proposed to address the issue of die wall lubrication. However, such methods often involve complex devices and/or increased cycle time. In both cases, the overall cost of the process is increased. Examples of such prior methods are taught in the following US Patents: 6,299,690; 5,855,321 ; 5,842,510; 4,380,052; and 3,857,363.

[0008] In some of the known methods, lubricant is sprayed into the opening of the die cavity from the top opening of the die. However, such method is more suited to the commercial manufacture of simple shaped components and is difficult to apply to components that have significant powder fill depth requirements. Also, since the lubricant is sprayed from the top of the die, if a component requires a narrow powder fill cavity, the top sprayed lubricant will not effectively cover the lower extremities of the die cavity. A potential solution to this die coverage problem is offered by US patent number 6,299,690, wherein a spray plug, having the generally the same shape as the article being formed, is inserted into the die cavity to ensure coverage of all die surfaces. However, the mechanism and apparatus taught by this patent is complex. Further, the time required for insertion of the plug, spraying the lubricant, and withdrawal of the plug greatly increases the process cycle time of the compacting operation.

[0009] The present invention seeks to overcome at least one of the deficiencies associated with the prior art methods and/or apparatus. For example, the invention provides a method of lubricating tooling such that admixed lubricants can be reduced or eliminated. The method therefore allows the advantageous manufacture of higher density components. The invention may be used in repressing operations so as to eliminate the requirement for liquid spraying, which also has associated disadvantages.

SUMMARY OF THE INVENTION

[0010] In one aspect, the present invention provides a method for lubricating die walls during the manufacture of a powder metal (PM) component. Such method avoiding the need for relatively complex equipment and/or unduly increased cycle times.

[0011] In another aspect, the invention provides a method for lubricating repressing tools.

[0012] In another aspect, the invention provides an apparatus for the efficient application of lubricant within a die. [0013] Thus, in one aspect, the invention provides an apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- a first punch located at one end of the die cavity and a second punch located at an opposite end of the die cavity, wherein at least a portion of the first and second punches are extendable into the die cavity;

- the second punch being reciprocatably moveable into the die cavity and with respect to the first punch;

- the first punch being fixed in position with respect to the die cavity and including a bore opening into the die cavity;

- a lubricant injection tube extending through the bore in the first punch and including a nozzle portion at first end thereof, the nozzle portion extending into the die cavity, the opposite second end of the injection tube being connected to a source of pressurized lubricant and the nozzle being operable, when in use, to spray the lubricant into the die cavity;

- a sleeve coaxially provided over the injection tube, and extendable through the bore in the first punch, the sleeve being reciprocatably extendable over the nozzle portion of the injection tube.

[0014] In another aspect, the invention provides an apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- a lubricant injection tube reciprocatably extending through the bore in the first punch and having a first end extendable into the die cavity;

- the injection tube first end comprising a plug portion and having a nozzle portion proximal to the plug portion;

- the injection tube being moveable between a spraying position, wherein the injection tube is advanced through the bore in the first punch until the nozzle portion enters the die cavity, and a non-spraying portion, wherein the injection tube is withdrawn through the bore in the first punch until the nozzle portion is contained within the bore and wherein the plug portion in contained in the die cavity;

- the injection tube including a second end opposite the first end, the second end being connected to a source of pressurized lubricant and the nozzle being operable, when in use, to spray the lubricant into the die cavity.

[0015] In another aspect, the invention provides an apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- the first and second punches being reciprocatably moveable into the die cavity and with respect to each other;

- the first punch including a bore opening into the die cavity;

- a core rod extending through the bore in the first punch and into the die cavity, the core rod being stationary with respect to the die cavity;

- the first punch including a first end extendable within the die cavity, the first end including a nozzle portion, wherein the nozzle portion is in fluid communication with a source of pressurized lubricant and the nozzle being operable, when in use, to spray the lubricant into the die cavity.

[0016] In a further aspect, the invention provides an apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- the first punch including first bore and the second punch including a second respective bore, the first and second bores opening into the die cavity;

- a core rod extending through the first bore in the first punch and into the die cavity, the core rod being reciprocatably moveable within the die cavity;

- a lubricant injection tube reciprocatably extending through the second bore in the second punch and having a first end extendable into the die cavity, wherein the injection tube first end comprises a nozzle portion, and a second end connected to a source of pressurized lubricant, the nozzle being operable, when in use, to spray the lubricant into the die cavity;

- the injection tube being moveable within the second bore between a spraying position, wherein the injection tube is advanced through the second bore until the nozzle portion enters the die cavity, and a non-spraying portion, wherein the injection tube is withdrawn through the second bore until the nozzle portion is contained within the bore.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:

[0018] Figures 1a to 1d are schematic cross sectional elevations of a tooling configuration according to one embodiment of the invention.

[0019] Figures 2a to 2d are schematic cross sectional elevations of a tooling configuration according to another embodiment of the invention.

[0020] Figure 3 is a cross sectional elevation of the lubricant discharge nozzle of Figure

2.

[0021] Figure 4 is a plan view cross section of the nozzle of Figure 3 through the line A-

A.

[0022] Figures 5a to 5d are schematic cross sectional elevations of a tooling configuration according to another embodiment of the invention.

[0023] Figures 6a to 6d are schematic cross sectional elevations of a tooling configuration according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] In the present disclosure, the terms "upper" and "lower" are used to facilitate the description of the apparatus illustrated in the accompanying drawings. However, it will be understood that such terms are used for convenience only and are not meant to limit the invention to any specific orientation or configuration.

[0025] The present invention provides, in one aspect an apparatus incorporating tooling design features incorporating lubricating members or channels that may be integrated with the compaction tooling itself. The disclosed tooling design facilitates die wall spraying particularly, but not exclusively, of shallow and deep filling tooling situations. The invention avoids the need for a complex plug or plunging device. The new tooling design also facilitates lubrication of the tooling during the normal tooling motions; hence no disadvantageous increase in cycle time is introduced. An economic method for the production of high density powder metal components is therefore described. [0026] In the present invention, the lubricant used may be either solid (i.e. particulate) or liquid. In a preferred embodiment, the lubricant is provided in a particulate form and is applied to the die walls of the tooling. Preferably the lubricant particles have a size of 100 μm or less. Any known lubricants may be used in the present invention and examples of available commercial grades that could be used are Zn-stearate, Acrowax™, and Kenolub™.

[0027] Figures 1a to 1d illustrate an apparatus for lubricating a die cavity in accordance with one embodiment of the present invention. The apparatus comprises a die 10 having a die cavity 12 bounded by die wall 14 and, typically, by a lower punch 16. The die cavity 12 and/or die wall 14 will generally have any desired shape corresponding to the component to be made. For convenience only, the die wall 14, and, therefore, die cavity 12 are shown in a generally cylindrical geometry.

[0028] The apparatus also includes a core rod 18 extending through the lower punch 16 and into the die cavity 12. The core rod 18 includes a lower, generally solid portion 20 and an upper spray end 22. The lower portion 20 includes a fluid conveying channel (not shown) that extends into the upper spray end 22. The fluid channel is used to convey lubricant material (comprising, as described herein, either a solid or liquid material in a fluidic form) to the spray end 22. The spray end 22 includes a generally porous tip 24 that permits passage of the lubricant material there-through. The porous tip 24 may, in one embodiment, comprise a porous collar secured generally co-axially to the core rod 18. Lubricant is fed through the conduit provided in the lower portion 20 of the core rod 18 and is discharged through the porous tip 24. As will be understood, and as described further below, the core rod components can be provided in various different configurations as will be apparent to persons skilled in the art.

[0029] A sleeve 15 is also provided with the apparatus of Figure 1. The sleeve 15 is generally coaxial with the core rod 18 and is able to slide over the core rod 18 and into the die cavity 12.

[0030] In the initial position as shown in Figure 1a, the die cavity is empty, that is, it does not contain any powder metal or finished (i.e. pressed) component. In this state, the sleeve 15 is in a lowered position whereby the porous tip 24 of the core rod 18 is exposed. A lubricant material, as described above, is then supplied to the fluid channel provided in the lower portion 20 of the core rod 18, with such material subsequently exiting through the porous tip 24. The tip serves to disperse the lubricant 26 throughout the die cavity as illustrated in Figure 1a. For this reason, the porous portion of the tip is preferably sized and designed to adequately coat the die cavity. As will be understood, the size and dimensions of the porous tip would therefore vary from one application to another. In the result, the die surface 28 of the die wall 14 becomes coated with the lubricant. During this step, a cover plate 30 may optionally be provided in order to prevent loss of lubricant outside of the die cavity 12.

[0031] As shown in Figure 1b, once a sufficient volume of the lubricant is provided into the die cavity (i.e. sufficient to form a mist of lubricant within the die cavity or to coat the walls thereof), the sleeve 15 is extended over the core rod 18 and into the die cavity 12. As shown in Figure 1b, the sleeve is extended to overlap and cover the porous tip 24 of the core rod 18. It will be understood that in this stage, the lubricant supply is switched off. It will be understood that as the sleeve 15 is raised into the die cavity 12, the outer surface of the sleeve in the portion within the die cavity 12 may also become coated with lubricant (in cases where the die cavity contains a lubricant mist).

[0032] As shown in Figure 1c, when the sleeve is fully extended into the die cavity 12, and when the porous tip 24 is covered by the sleeve, a powder metal (PM) mixture 32 is supplied into the die cavity 12. The PM mixture will have any desired composition depending upon the final characteristics of the component being formed. As shown in

Figure 1 c, due to the presence of the sleeve 15, the porous tip 24 does not contact the PM mixture.

[0033] Figure 1d illustrates the final step of the process wherein a top punch 34 is used to compress the PM mixture to form a green compact 36. Again, during this step, the porous tip 24 is covered by the sleeve 15.

[0034] After the green compact 36 is formed, the upper punch 34 is retracted and the compact is ejected from the die cavity in a conventional manner.

[0035] Thus, as taught in the above description, the invention allows the relevant die cavity surfaces to be coated with a sufficient amount of lubricant without having to admix the lubricant in the PM mixture.

[0036] In the embodiment of Figure 1 , it is noted that the core rod 18, which may also be referred to as a lubricant discharge tube, is fixed in position with respect to the die cavity 12 and a reciprocating sleeve 15 is provided thereon to cover the porous discharge portion during the PM compression step.

[0037] As is known in the art, the various channels used to convey the lubricant may be formed from or coated with any insulative material so as to reduce or avoid the build-up of static charges resulting from the high speed flow of the lubricant particles. For example, such channels may be formed from or coated with polytetrafluoroethylene (PTFE), or

Teflon™. Alternatively, such channels and other equipment may be grounded or connected to an oppositely charged by means of applying a suitable current. Various other means for reducing or avoiding static charge build-up can be used for the same purpose. [0038] Another embodiment of the invention is illustrated in Figures 2a to 2d where elements that are similar to those described above are identified with like reference numerals.

[0039] As shown in Figure 2a, which represents the starting position, the die 10 generally has the same components as in Figures 1a-1d. Specifically, the die 10 includes a lower punch 16, a die wall 14, and a die cavity 12 formed there-between. The apparatus of Figure 2 varies from the previously described apparatus with respect to the core rod 18. Specifically, as shown in Figure 2a, a core rod 40 is provided generally axially through the lower punch 16. The core rod 40 includes a lower portion 42 having a generally axially extending lubricant supply channel 44. The opposite upper end 46 of the core rod 40 comprises a porous discharge portion 48 through which lubricant is supplied into the die cavity 12. The terminal end of the core rod 40 comprises a non-porous cap 50. In a preferred embodiment, the height of the cap 50 generally corresponds to the height of the die cavity 12, the purpose of which is described further below.

[0040] The upper end 46 of the core rod 40 is illustrated in more detail in figures 3 and 4. As shown in Figure 3, the upper end 46 includes the cap 50, which is positioned above the porous discharge portion 48. Below the discharge portion 48, the rod stem 47 includes a support shoulder 49 for supporting a generally cylindrical porous collar 52. The stem 47 includes a generally axially extending lubricant channel 51. The channel 51 opens into a discharge opening 53 through which lubricant passing through the channel 51 is discharged through the porous collar 52. Figure 4 illustrates the rod 40 taken through section A-A of Figure 3.

[0041] Returning to Figure 2a, the apparatus is shown in the starting position when lubricant 26 is discharged through the discharge portion 48 into the die cavity 12. In this way, the die cavity walls are coated with the lubricant, which also fills the die cavity 12 in the same manner as described above. As with Figure 1 , a cover 30 may be used to prevent lubricant from being discharged outside of the die cavity 12.

[0042] As shown in Figure 2b, after a sufficient volume of lubricant is discharged into the die cavity 12, the core rod 40 is partially withdrawn downwardly through the lower punch 16. In this manner, the porous discharge portion 48 of the core rod 40 is withdrawn into the lower punch and is no longer exposed to the die cavity. In the result, the cap 50 occupies the previous position of the discharge portion 48 within the die cavity. As the cap 50 enters the die cavity, its outer surface may be coated with the lubricant mist in the same manner as the sleeve discussed with respect to Figure 1 b.

[0043] In Figure 2c, the die cavity 12 is shown as being filled with a desired volume of PM material 32. [0044] Figure 2d illustrates the advancement of an upper punch 34 to compress the PM material in the die cavity 12 to form a green compact 36.

[0045] Thus, in Figure 2, the core rod, or lubricant discharge tube is movable between a first lubricant discharge position and a second compression position. [0046] Figures 5a to 5d illustrate another embodiment of the invention wherein elements that are similar to those described above are referred to with the same reference numerals. In the embodiment of Figure 5, the lower punch is adapted to incorporate a lubricant discharge system.

[0047] Specifically, as shown in Figure 5a, the die 10 includes a die wall 14. The die also includes a generally centrally located core rod 60 that is generally maintained in position with respect to the die cavity 12 (as shown in Figure 5b). The apparatus also includes a lower punch 62 having a generally cylindrical shape with an upper, die cooperating portion 63 and an opposite lower portion 64. The upper portion 63 of the lower punch includes a generally annular shaped porous discharge nozzle 66. The upper portion 63 also includes a preferably solid bearing surface 65. The lower portion 64 of the lower punch 62 includes a generally annular space 68 in fluid communication with the nozzle 66. A lubricant material is injected through the annular space 68 and discharged through the nozzle 66 as shown in Figure 5a. As can be seen, the bearing surface 65 effectively closes the die cavity 12 during the lubrication step. Also, during lubrication, it will be observed that all surfaces of the die cavity 12, including the outer surface of the core rod 60, are coated with lubricant during this step.

[0048] Figure 5b illustrates the next step in the process wherein, after a sufficient volume of lubricant is discharged, the lower punch 60 is lowered to vacate the die cavity 12. [0049] As shown in Figure 5c, the next step involves filling the die cavity 12 with a desired volume of PM material 32.

[0050] Figure 5d illustrates the advancement of the upper punch 34, which compresses the PM material to form a green compact 36. The compact 36 is then discharged from the die cavity.

[0051] Figures 6a to 6d illustrate a further embodiment of the invention wherein die wall lubrication is applied through an upper punch of the die. Elements of Figures 6a to 6d that are similar to those referred to above are identified with the same reference numerals. [0052] As shown in Figure 6a, the die 10 of the apparatus includes a lower punch 16 and a die wall 14. The die 10 also includes an upper punch 70 that is modified from those mentioned above. Specifically, as shown in Figure 6a, the upper punch 70 is provided with a generally centrally extending lubricant nozzle 72. The nozzle 72 includes a lubricant channel 74 extending there-through and a porous discharge end 76 for discharging lubricant into the die cavity 12. The die 10 also includes a core rod 78 that is axially moveable with respect to the die cavity 12.

[0053] As illustrated in Figure 6a, during the lubrication step, the core rod 78 is withdrawn from the die cavity 12 and the nozzle 72 is extended downward so as to allow the discharge end 76 to be positioned within the die cavity 12. In this position, lubricant 26 is sprayed into the die cavity 12, thereby coating the die walls. The positioning of the upper punch 70 serves to effectively close the upper end of the die cavity 12 so as to prevent lubricant from spraying outside of the cavity 12.

[0054] After a sufficient volume of lubricant is sprayed into the die cavity 12, the nozzle

72 is withdrawn upwardly and the core rod 78 is advanced into the die cavity 12. In this process, the upper portion of the core rod 78 is covered with lubricant remaining in the die cavity 12. This step is illustrated in Figure 5b.

[0055] As shown in Figure 5c, once the core rod 78 is fully extended into the die cavity

12, a desired volume of PM material 32 is added to the cavity 12.

[0056] Finally, as shown in Figure 5d, the upper punch 70 is advanced into the die cavity

12 so as to compress the PM material to form the green compact 36. The compact is subsequently ejected from the die cavity 12.

[0057] As indicated above, the present description is not meant to limit the apparatus to any particular shape or orientation. As will be understood by persons skilled in the art, the apparatus and method of the present invention can be used to form compacts of many shapes and sizes. In particular, since the lubricant is added with a specialised nozzle or discharge system that extends into the die cavity, the invention can be used to effectively and economically lubricate any length or size of die cavity. Further, as will be noted by persons skilled in the art, the tooling motions described above are generally the same as those used in a conventional compaction cycle. That is, the present invention does not include any extra steps for conducting the lubrication that would unduly increase the cycle time of the pressing process.

[0058] It will be noted that two of the features of the invention lie in the tooling design for providing the lubricating channels and the controlled tooling motion for the lubricating cycle.

[0059] In addition, although the above description has illustrated the use of the invention in forming green compacts, it will be understood that the invention may equally be adapted to re-pressing operations wherein a sintered compact is formed to desired dimensions.

[0060] The present invention can be used to compact or repress products such as, but not limited to, spur gears, helical gears, sprockets, clutch plates, connecting rods, planetary carriers, main bearing caps and various other components. [0061] As mentioned above, various known particulate lubricants can be used with the present invention. However, it should be pointed out that the invention can also equally be used with liquid lubricants.

[0062] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined and claimed herein. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.

Claims

WE CLAIM:

1. An apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- a lubricant injection tube extending through the bore in the first punch and including a nozzle portion at first end thereof, said nozzle portion extending into the die cavity, the opposite second end of the injection tube being connected to a source of pressurized lubricant and the nozzle being operable, when in use, to spray said lubricant into the die cavity;

- a sleeve coaxially provided over the injection tube, and extendable through the bore in the first punch, said sleeve being reciprocatably extendable over the nozzle portion of the injection tube.

2. The apparatus of claim 1 wherein the nozzle comprises a porous metal portion.

3. An apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- the injection tube first end comprising a plug portion and having a nozzle portion proximal to the plug portion; - the injection tube being moveable between a spraying position, wherein the injection tube is advanced through the bore in the first punch until the nozzle portion enters the die cavity, and a non-spraying portion, wherein the injection tube is withdrawn through the bore in the first punch until the nozzle portion is contained within the bore and wherein the plug portion in contained in the die cavity;

- the injection tube including a second end opposite the first end, the second end being connected to a source of pressurized lubricant and the nozzle being operable, when in use, to spray said lubricant into the die cavity.

4. The apparatus of claim 3 wherein the nozzle comprises a porous metal portion.

5. An apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- the first punch including a bore opening into the die cavity;

- the first punch including a first end extendable within the die cavity, the first end including a nozzle portion, wherein the nozzle portion is in fluid communication with a source of pressurized lubricant and the nozzle being operable, when in use, to spray said lubricant into the die cavity.

6. The apparatus of claim 5 wherein the nozzle comprises a porous metal portion.

7. An apparatus for forming a powder metal article, the apparatus comprising:

- a die cavity having a die wall;

- the first and second punches being reciprocatably moveable into the die cavity and with respect to each other; - the first punch including first bore and the second punch including a second respective bore, said first and second bores opening into the die cavity;

- a lubricant injection tube reciprocatably extending through the second bore in the second punch and having a first end extendable into the die cavity, wherein the injection tube first end comprises a nozzle portion, and a second end connected to a source of pressurized lubricant, said nozzle being operable, when in use, to spray said lubricant into the die cavity;

8. The apparatus of claim 7 wherein the nozzle comprises a porous metal portion.

9. The apparatus of claim 7 wherein the core rod is extendable through the die cavity and into the second bore on the second punch.