CA1095679A - Apparatus and method for producing spherical articles - Google Patents

Abstract

APPARATUS AND METHOD FOR PRODUCING SPHERICAL ARTICLES
Abstract of the Disclosure An apparatus and method for compressing powder material into at least partially spherical articles, comprising a die and upper and lower reciprocally movable punches. The die has a center bore through which the lower punch is reciprocable. The wall at the upper part of the die bore is enlarged to form a spherical zone portion of a hemispherical cavity. The end face of the lower punch has a concave shape to form a segment of the hemispherical cavity when the face of the lower punch is flush with the die cavity wall. The lower face of the upper punch de-fines a hemispherical cavity which mates with the hemispherical cavity of the die. In operation, the bore and die cavity are charged with powder material and the upper punch is brought into engagement with the die. A compaction stroke by the lower punch then forces the powder material into the spherical cavity. The upper punch is then withdrawn and the compacted spherical article is removed from the die. Alternatively, the end face of the lower punch may be flat, convex, or any other appropriate shape to compact partially spherical articles. A portion of the mold-ing cavity may be coated with an elastomeric material.

Description

11~95679 The present invention relates to powder material com-pacting apparatus and methods and, more part~cularly, to an im-proved apparatus and method for compacting powder material into spherical and similar shapes.
The present invention is concerned with improved tooling for use in powder-compacting presses such as are disclosed in U. S.
patents 3,826,599; 3,775,032; 3,730;659; 3,726,622; 3,~45,658;
3,574,892; 3,561,056; 3,415,142; 3,344,213; and 3,328,840, all of which are assigned to the same assignee as the present application.
In the powder-compacting presses disclosed in the afore-mentioned U. S. patents, the articles are compacted and formed in a multi-cavity die forming part of a punch and die set, with the finished articles being automatically ejected from the die cavities, picked up by a vacuum pick-up head, and conveyed into suitable receptacles. The work station positioner assembly, which is part of the press, is mounted angularly movable transversely over the die plate and carries a powder dispenser, an anvil and the pick-up head. The powder dispenser, which is supplied with powder from a primary powder supply means connected thereto by means of a flexible tubing or the like, is first positioned over the die cavity or cavities which are thus filled with powder as the punches are displaced downwardly so as to draw a predeter-mined amount of powder into the die cavity or cavities. The dispenser is then removed from above the die cavity or cavities by the subsequent angular motion of the station positioner assem-bly, and the anvil is, in turn, positioned over the die cavities.
The anvil is clamped over the die cavity by means of a pivotable clamp supported above the anvil and actuated in timed relation with the movement of the punches. The anvil is held down with sufficient pressure to perm~t the compaction of the powder against the anv~l as a result of an up~ard motion of the punches into the die cavit~ or cavit~e~. The anv~1 i5` then removed from its `` -1 ~k , 1~95679 position over the die cavity or cavities and is replaced by the pick-up head by a further angular motion of the work station posi-tionex transversely across the face of the die plate. The punches are d:isplaced upwardly so as to bring their upper ends in sub-stantial flush alignment with the upper surface of the die plate, such that the finished compacted articles are ejected from the die cavities and picked up by the pick-up head. As the result of a return angular motion of the work station positioner to the initial fill position, the pick-up head is removed from over the die cavity and is disposed over one or, if a plurality of die cav-ities are employed, a series of discharge apertures arranged in a disposition similar to the arrangement of the die cavities in the die plate, and the finished compacted article or articles are drawn, as by vacuum, through the discharge aperture or apertures into a container or separate containers.
The tooling used in the prior art in compacting powder materials into spherical forms consists of a die having a center bore, and upper and lower punches the faces of which define a spherical cavity. Typically, powder material is charged in a measured quantity into the die bore and hemispherical cavity of the lower punch. The upper punch is then moved through the bore and compacts the powder material in the spherical cavity defined by the end faces of upper and lower punches. It is necessary to make the ends of the walls of the punch members thick enough at the equator of the spherical cavity to prevent distortion or breakage of the walls by the compacting forces. As a result, a portion of the powder material is squeezed in the equatorial space and the end faces of the punches do not make contact with each other. The compacted material then has an equatorial ring or bulge of greater diameter than the d~ameter of the spherical cav-it~, T~e excess m~ter~al ~:n t~is ring has to be removed by a tum~ling or similar proce~ i~ order to obtal'n a spher~cal article.

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~t~gs6;79 The present invention provides a method and apparatus for producing a compacted spherical article without an equatorial ring or bulge.
In accordance with the present invention, a spherical mold cavity is defined primarily by an upper punch member and a die with a center bore. These members are brought into engagement prior to the time a compaction stroke is started.
The compaction stroke then takes place by reciprocation of the lower punch through the die bore which has a diameter less than the diameter of the spherical cavity.
One aspect of the present invention relates to an apparatus for compacting powder material into ~enerally spherical articles, the apparatus comprising a punch and die assembly comprising a die plate, a bore in the die plate, a punch disposed reciprocably in the bore, a compacting face on the end of the punch, a progressively enlarged end portion in the bore, the enlarged end portion forming with the compacting face a first half-mold cavity, a counterpunch having a flat end face engageable with the die plate, a second half-mold cavity disposed in the counterpunch end face, the second half-mold cavity being alignable with the bore, and means for reciprocating the punch to a position whereby the face of the punch forms with the enlarged end portion of the bore the first half-mold cavity for compacting the powder material in a molding cavity formed by the first and second half-mold cavities.
Another aspect of the present invention relates to the method of compacting powder material in a mold into generally spherical articles which comprises filling by gravity with said powder material a first partial mold having an open upper end, displacing a movable portion of said first ~.

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rw/-Y - _ 3 _ 1~95~79 partial mold during filling in a direction and to a prede-termined position increasing the volume of said first partial mold, leveling said powder material in said first partial mold to a level corresponding to the level of said open end, placing over the open end of the first partial mold a second partial mold having an open cavity therein, the first and second partial molds having correspondingly engageable interferring faces preventing one of the partial molds from penetrating into the other, displacing in an opposite direction the movable portion for transferring part of the powder material from the first partial mold through the open end into the cavity in the second partial mold and for compacting the powder material in a mold defined by the first and second partial molds for forming one of the articles, removing the second partial mold from over the open end of the first partial mold, and further displacing the movable portion in the opposite direction for ejecting the article from the first partial mold through the open end.
FIG. 1 is a broken sectional view of a die with upper and lower punches illustrating the prior art apparatus and method of forming spherical articles from powder material;
FIG. 2 is a view of a spherical article produced by the prior art apparatus and process illustrated in FIG. l;
FI~. 3 is a broken sectional view of a die and lower punch according to the present invention showing the charging of ~' - rw/- - 3a -1()95679 powder material to the die cavity;
FIG. 4 is a broken sect~onal view of the apparatus in accordance with the present invention showing the upper punch clamped over the die cavity prior to the powder material compac-tion step;
FIG. 5 is a broken sectional view similar to FIG. 4 but with the lower punch in the position it occupies after compaction of the material;
FIG. ~ is a broken sectional view similar to FIG. 5 but with the upper punch withdrawn after compaction of the material;
FIG. 7 is a broken sectional view of the die and lower punch with the lower punch in ejection position and pick-up head in place;
FIG. 8 is a broken sectional view of a vacuum-powered system for collecting spherical articles in a receptacle;
FIG. 9 is a schematic partial elevation view of means for cleaning the end face of the upper punch; and FIGS. 10 and 11 are schematic representations of modi-fications of lower punch shapes and corresponding articles made thereby.
Referring to FIG. 1, which illustrates the prior art, a die 10 of cylindrical configuration has an axial bore 11. The die 10, which is sometimes referred to as a "die bushing", is nor-mally composed of a very hard material such as cemented tungsten carbide. The die bushing 10 is supported by being press-fitted or otherwise fastened in a bore of a die plate 12 which may be made of carbide but which is normally made of a less costly material than tungsten carbide, such as steel or the like. The die plate is mounted in the table or bed of a press apparatus (not shown~.
The die bore 11 accommodates an upper punch 13 and a lower punch 14 which are rec~procally mova~Ie therein. The end ~4~

l(~gS679 faces of the punches 13 and 14 define a hemispherical cavity.
With the upper punch 13 out of engagement from within the die 10, a measured portion of powder material is poured in the hemispher-ical cavity of the lower punch 14 and in the bore 11 of the die 10. The upper punch 13 is then moved into the die bore 11 and the lower punch is moved upwardly into compacting engagement with the powder material to compact it into a spherical form as shown at 15. During the compacting stroke, a portion of the powder is caused to project between the flat portions of the end faces of the upper punch 13 and lower punch 14, thus forming an equatorial bulge 16 which prevents engagement of the surfaces of the punches 13 and 14. This equatorial bulge must be factored into the design in order to provide a uniform diameter in a longitudinal direction of the sphere. The product removed from the press is as shown in FIG. 2. It is necessary to remove the bulge 16 by a tumbling or similar process, in order to obtain a generally spherical article.
Referring now to FIGS. 3-7, there is shown, in a sche-matic manner, an apparatus according to the present invention for molding a generally spherical or partly spherical article without an equatorial bulge. The molding apparatus comprises a die con-sisting of a die bushing 20 press-fitted, cemented or otherwise disposed in a bore 22 in a die plate 24. The die bushing 20 is preferably made of a hard material, such as tungsten carbide or the like, and the die plate 24 may be made of a tool steel, but is preferably also made of carbide with a highly polished upper sur~ace 25. The die bushing 20 is provided with a longitudinal bore 26 accepting for reciprocation therein a lower punch 28.
In the example of structure illustrated, the lower punch 28 has a concave end face 3Q shaped substantially as a spherical seg-ment, and the upper end of the die bushing bore 26 is provided with an enlarged portion shaped ~u~stantially as a complementary spherical zone, as- s~own at 3I, such that together they define a 1(~95~;79 first half-mold cavity.
The lower punch 28 is reciproca~le by means of an appropriate ram 29 forming a part of the press apparatus, not shown, as di.sclosed in detail in the aforementioned patents, and an upper punch member 32, or counterpunch, (FIGS. 4-6) is provided recipro-cable towards, and away from, the die plate 24 and die bushing 20 by being mounted on the end of a ram 33 ~FIG. 4), reciprocated by appropriate means by the press mechanism, not shown, as dis-closed, for example, in aforementioned Patent No. 3,826,599. The end face of the upper punch 32 is provided with a hemispherical cavity 34, defining the second half-mold cavity, surrounded by an annular flat surface 36. When reciprocated towards and away from the die plate 24, the upper punch 32 is guided by an anvil member 38, having a lower surface 39 at all times in engagement with the upper surface 25 of the die plate 24, but displaceable from posi-tions away from over the die cavity to a position over the die cavity, the latter position being illustrated at FIGS. 4-6. The upper punch 32 is reciprocable through a vertically disposed bore 40 in the anvil member 38, and has an abutment surface 42 engage-able with the top end surface 44 of a coil spring 46, or other biasing means such as superimposed Belleville springs or the like, disposed over a reduced diameter portion 48 of the anvil member 38.
A radial slot 50 is disposed through the wall of the anvil member 38 to provide appropriate clearance for the finished part, when the anvil member 38 is laterally displaced from above the die cavity by means of the operation of the station positioner of the press apparatus as disclosed and explained in detail in the hereinbefore referred-to patents, and more particularly Patent Nos. 3,726,622; 3,645,658; 3,574,892; 3,561,056 and 3,145,142.
In operation, the die cavity is gravity filled with powder material 52 as illustrated at FrG. 3 by means of a powder .

hopper 54 disposed over the die cavity. During filling of the die cavity with powder material, the lower punch 28 is retracted so as to draw into the die cavity an appropriate amount of powder materi.al 52.
Subsequent to filling of the die cavity with powder material, the powder hopper 54 is laterally displaced, with the result that the edge of the powder hopper 54, in contact with the upper surface 25 of the die plate 24 and the end face 21 of the die bushing 20, wipes the surfaces clean of any powder particles and at the same time levels the charge of powder material 52 evenly flush with the end face 21 of the die bushing 20. The anvil member 38, supported and driven by the station positioner of the press apparatus, is then displaced to its position over the die cavity, and the upper punch 32 is advanced by the ram 33 into the guiding bore 40 of the anvil member 38, thus compressing the spring 46 and forcing firmly the anvil member against the die plate 24 until the annular face 36 of the upper punch 32 engages the end face 21 of the die bushing 20, as represented at FIG. 4.
Although not absolutely necessary for successful opera-tion of the apparatus of the invention, the height of the anvil member 38 and the length of the upper punch 32 are preferably e~ual, such that, in the position shown at FIG. 4, the punch abutment surface 42 engages the top end surface of the anvil mem-ber, therefore apply.ing the anvil member lower face 39 with great pressure against the die plate upper surface 25.
The lower punch 28;is then advanced to the position in-dicated at FIG. 5 until the recess 30 at the end of the lower punch forms with the spherical zone portion 31 of the die bore wall a complete hemisphere, thus compacting the powder ~aterial 52 into a spherical article 56, The press apparatus i5 adjusted such that the force applied for reciprocat~ng the lower punch 28 i5 slightly smaller than the force h~ldl~ng the upper`punch 32 with its annular face 36 in engagement with the die bushing end face 21. The upper punch 32 is subsequently withdrawn from within the bore 40 in the anvil member 38, as illustrated at FIG. 6, and the anvil member 38 is laterally displaced to a position away from above the die cavity, the slot 50 in the wall of the anvil member providing appropriate clearance for the spherical article 56 dur-ing displacement of the anvil member.
A vacuum pickup head 58, also supported by the press apparatus station posi.~ioner, is subsequently placed above the die cavity, and the lower punch 28 is advanced upwardly such as to eject the spherical article 56 from the spherical zone wa~l 31 of the die into the vacuum pickup head 58. ~,~
In the structure illustrated at FIG. 7 and in more de-tail at FIG. 8, the vacuum pickup head 58 has an orifice 60 placed in communication by means of a flexible tubing 62 with a recep-tacle 64 connected by way of a line 66 to a source of vacuum (not shown). In this manner, the spherical articles 56 ejected from the die cavity are propelled within the tube 62 to the receptacle 64. It will be appreciated that other means of ejecting the fin-ished part, such as mechanical wiper means or vacuum pickup heads provided with a screen to which the finished articles remain ad-hering until the pickup head is displaced over an appropriate ejection aperture through the die plate communicating with an àppropriate receptacle, may also be used in conjunction with the apparatus of the invention as disclosed in the aforementioned patents.
It has been d~scoYered that when forming certain types of powder material into spherical articles, according to the pre-sent invention, some powder particles ma~ find their way betweén the upper punch annular ~ux~ace 36 and the end face 21 of the die hu~fi~ng 2a~ The d~e ~ush~ng end f~ce 21 ~9` ~ept clean by the ~ng act~on of the powder a~penser edge and, in order to pre~

1~95679 vent an accumulation and build-up of powder particles on the end annular face 36 of the upper punch 32, means may be provided, as illustrated at FIG. 9, for wiping the annular surface 36 of the punch clean between compacting operations. As illustrated, such wiping operation is effected by means of a vacuum brush 68, having a length corresponding substantially to the diameter of the punch 32, mounted on the end of an arm 70 pivotable about a~ipivot point 72 disposed on a side of the upper ram 33. A cam follower 74 sup-ported on one side of the arm 70 is engageable with a stationary cam surface 76 when the ram 33 and the punch 32 are reciprocated, so as to move the vacuum brush 68 from the position shown in phan-tom line at FIG. 9 when the upper punch 32 is advanced, to the position shown in full line when the upper punch 32 is retracted.
Appropriate biasing means, such as a spring 78, are provided for urging the arm 70 and the brush 68 in the position shown in phan-tom line, such that during reciprocation of the upper punch 32, the vacuum brush 68 is caused to traverse the face of the punch, thus removing any powder particles that may remain adhering to the punch face. Other convenient means, such as the rotary brush arrangement disclosed in Patent No. 3,328,840, may be used for wiping clean the end face of the upper punch.
It will be readily appreciated that the compacting apparatus of the present invention may be modified to provide compacted articles other than strictly spherical articlesO For example, as shown at FIG. 10, by using a lower punch having a flat face an article 56' is obtained of generally spherical shape but provided with a flat face 80 corresponding to'the f~at end face of the lower punch. With a lower punch 28 having a convex end face, a generally spherical article 56" is obtained, as shown at FIG. 11, having a concave recess 82.
The present invention also contemplates that at least a portion of the wall of the molding cavity may be coated with an ~C~95679 adhering layer of elastomeric material. For example, the wall of the hemispherical cavity 34, FIG. 4, in the upper punch member 32 may be provided with a surface layer varying in thickness from a few microns to a few millimeters, which is made of a material such as natural rubber, neoprene, polysiloxane elastomers, polyurethane, polysulfide rubber, polybutadiene, buna-S or like material.
It is to be understood that the example of the present invention as disclosed herein constitutes one preferred form and that other forms might be adopted. For example, the term "~pheri-cal" should not be considered unduly limiting, but should include other shapes within the spirit of the invention and the scope of the appended claims.

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Claims (21)

Canada The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for compacting powder material into generally spherical articles, said apparatus comprising a punch and die assembly comprising a die plate, a bore in said die plate, a punch disposed reciprocably in said bore, a compacting face on an end of said punch, a progressively enlarged end portion in said bore, said enlarged end portion forming with said compacting face a first half-mold cavity, a counterpunch having a flat end face engageable with said die plate, a second half-mold cavity disposed in said counterpunch end face, said second half-mold cavity being alignable with said bore, and means for reciprocating said punch to a position whereby the face of said punch forms with the enlarged end portion of said bore said first half-mold cavity for compacting said powder material in a molding cavity formed by said first and second half-mold cavities.

2. The apparatus of claim 1 wherein said bore is in a die bushing disposed in said die plate and the flat end face of said counterpunch is engageable with an end of said bushing.

3. The apparatus of claim 2 further comprising support and guide means for said counterpunch provided with an end face for engagement with said die plate, means for applying a clamping force to said counterpunch in engagement with the end of said bushing and abutment means on said counterpunch for engagement with said support and guide means for transmitting said clamping force to said support and guide means.

4. The apparatus of claim 3 wherein said clamping force is transmitted by said abutment to said support and guide means by spring bias means.

5. The apparatus of claim 1 further comprising means cleaning said counterpunch end face from powder particles when said end face is disengaged.

6. The apparatus of claim 1 wherein said powder compacting face is concave and forms a spherical segment, said bore enlarged end portion forms a spherical zone, said spherical segment and zone defining a hemisphere, and said second half-mold cavity is a hemisphere.

7. The apparatus of claim 1 wherein at least a portion of said molding cavity is coated with an elastomeric material.

8. An apparatus for compacting powder material into a generally spherical article, said apparatus comprising a punch and die assembly comprising a die plate, a die in said die plate having a vertically disposed bore, an enlarged upper end portion in said bore of progressively increasing diameter forming a first partial generally spherical molding cavity, a punch reciprocably movable in said bore and having an upper end face forming a second partial molding cavity, said first and second partial molding cavities forming a first half-mold cavity, a counterpunch in axial alignment with said die bore and having a flat end face engageable with said die plate reciprocably movable for closing said bore upper end, a partial cavity defining a second half-mold cavity in the end face of said counterpunch of the same diameter as the said enlarged upper end portion of said bore, and means for reciprocating said punch to a position whereby the face of said punch forms with the enlarged end portion of said bore said first half-mold cavity for compacting said powder material in a molding cavity formed by said first and second half-mold cavities.

9. The apparatus of claim 8 further comprising support and guide means for said counterpunch provided with an end face for engagement with said die plate, means for applying a clamping force to said counterpunch in engagement with said die plate and abutment means on said counterpunch for engagement with said support and guide means for transmitting said clamping force to said support and guide means.

10. The apparatus of claim 9 wherein said clamping force is transmitted by said abutment to said support and guide means by spring bias means.

11. The apparatus of claim 8 further comprising means cleaning said counterpunch end face from powder particles when said end face is disengaged.

12. The apparatus of claim 8 wherein said punch compacting face is concave and forms a spherical segment, said bore enlarged end portion forms a spherical zone, said spherical segment and zone defining a hemisphere, and said second molding cavity is a hemisphere.

13. The apparatus of claim 1 wherein at least a portion of said mold wall is coated with an elastomeric material.

14. The method of compacting powder material in a mold into generally spherical articles which comprises filling by gravity with said powder material a first partial mold having an open upper end, displacing a movable portion of said first partial mold during filling in a direction and to a predetermined position increasing the volume of said first partial mold, leveling said powder material in said first partial mold to a level corresponding to the level of said open end, placing over the open end of said first partial mold a second partial mold having an open cavity therein, said first and second partial molds having correspondingly engageable interferring faces preventing one of said partial molds from penetrating into the other, displacing in an opposite direction said movable portion for transferring part of said powder material from said first partial mold through said open end into said cavity in said second partial mold and for compacting said powder material in a mold defined by said first and second partial molds for forming one of said articles, removing said second partial mold from over the open end of said first partial mold, and further displacing said movable portion in said opposite direction for ejecting said article from said first partial mold through said open end.

15. The method of claim 14 further comprising wiping clean the engageable faces of said first and second partial molds prior to placing said second partial mold over said first partial mold.

16. The method of claim 14 further comprising picking up said molded article by vacuum pickup means for transportation to a discharge station.

17. A method for compacting powder material into a generally spherical solid article, said method comprising filling with powder material an open first half-mold disposed in a die plate and having a vertical bore provided with an enlarged upper end portion of progressively increasing diameter forming a first partial generally spherical molding cavity, a unitary punch reciprocably movable in said bore and having a concave upper end face forming a second partial molding cavity, placing a unitary counterpunch in axial alignment with said open first half-mold, said counterpunch having an end face movable toward said first half-mold for closing said first half-mold in overlapping position therewith without penetrating into said first half-mold and the end face of said counterpunch having a third partial molding cavity of the same diameter as said enlarged upper end portion of said bore whereby said partial molding cavities when in mating relationship define a complete and closed mold for compacting said powder material, displacing said punch toward said counterpunch for displacing part of said powder material into said third partial molding cavity and compacting said powder material into said generally spherical solid article in said mold while limiting the displacement of said punch to a position whereby said first and second molding cavities are in mating relationship, removing said counterpunch from overlapping position over said first half-mold, and advancing said punch to a position ejecting said article from said second partial molding cavity.

18. The method of claim 17 further comprising providing support and guide means for said counterpunch with its end face in engagement with said die plate, applying a clamping force to said counterpunch causing said counterpunch end face to engage firmly with said die plate, and transmitting said clamping force from said counterpunch to said support and guide means for causing a corresponding end face of said support and guide means to engage firmly with said die plate.

19. The method of claim 18 wherein said clamping force is transmitted to said support and guide means by spring bias means.

20. The method of claim 17 further comprising cleaning said counterpunch end face from powder particles when said end face is disengaged from said die plate.

21. The method of claim 17 wherein said punch compacting face is concave and forms a spherical segment, said bore enlarged end portion forms a spherical zone, said spherical segment and zone defining a hemisphere, and said third partial molding cavity is a hemisphere.