US3897184A - Apparatus for making bars from powered metal - Google Patents

Abstract

Powdered metal is continuously introduced into a die cavity in discrete quantities and compacted into bar segments to form a bar. The cavity has a fixed cross-sectional area and is open at both ends, except during the initial compaction when one end is closed. After formation of a length of the bar, the frictional resistance between the bar and the cavity wall is relied on so that the bar remaining in the cavity serves as a stopper for subsequent compactions of the discrete quantities of powdered metal to form the continuous bar. The bar is forced out of the cavity and may be passed through an induction furnace for sintering, and through a swager, all preferably in a continuous operation. Also provided is means for varying the compaction so that the bar lengths formed from the discrete quantities of powdered metal are compacted and bonded into a bar of substantially uniform physical characteristics along its length.

Description

United States Patent Woodburn, Jr. et al.

APPARATUS FOR MAKING BARS FROM POWERED METAL Assignee:

Filed:

Inventors: James Woodburn, Jr., Wheaton;

Gordon Russell Lohman, Glen Ellyn, both of 111.

Amsted Industries Incorporated,

Chicago, 111.

Mar. 7, 1974 Appl. No.: 448,819

U.S. Cl. 425/79; 425/78; 425/258;

Int. Cl.....B29c 3/00; B30b 11/06; B30b 15/22 [58] Field of Search 425/78, 79, 149, 258, 260

[56] References Cited UNITED STATES PATENTS 1,806,300 5/1931 Lemming 425/78 X 2,289,787 7/1942 Kaschke et a1. 425/79 X 2,389,561 11/1945 Stokes et a1. 425/78 2,499,980 3/1950 Stokes et a1. 425/78 2,651,952 9/1953 Leavenworth 425/79 2,904,835 9/1959 Thomas 425/78 2,984,866 5/1961 Schwabe.. 425/78 X 3,264,388 8/1966 Roach 425/78 X 3,491,407 1/1970 Gustafson 425/78 3,579,741 5/1971 Schwartz 425/149 3,734,663 5/1973 Holm 425/149 3,788,787 1/1974 Silbereisen et al.... 425/78 3,819,774 6/1974 Eggenberger et a1 425/149 X Primary ExaminerJ. Howard Flint, Jr. Attorney, Agent, or Firm-Andrew .1. Bootz; Ralph M. Faust; Fred P. Kostka [57] ABSTRACT Powdered metal is continuously introduced into a die cavity in discrete quantities and compacted into bar segments to form a bar. The cavity has a fixed crosssectional area and is open at both ends, except during the initial compaction when one end is closed. After formation of a length of the bar, the frictional resistance between the bar and the cavity wall is relied on so that the bar remaining in the cavity serves as a stopper for subsequent compactions of the discrete quantities of powdered metal to form the continuous bar. The bar is forced out of the cavity and may be passed through an induction furnace for sintering, and through a swager, all preferably in a continuous operation. Also provided is means for varying the compaction so that the bar lengths formed from the discrete quantities of powdered metal are compacted and bonded into a bar of substantially uniform physical characteristics along its length.

2 Claims, 11 Drawing Figures PATENTEDJUL 2 91975 SHEET SHEET PATENTED JULZQ 197s APPARATUS FOR MAKING BARS FROM POWERED METAL BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to an apparatus for making a rod from powdered metal, and more particularly to a new and novel apparatus for continuously forming the rod from powdered metal and to a new and novel apparatus.

One method and an apparatus for continuously forming rod from powdered metal is described in US. Pat. No. 2,097,502 granted Nov. 2, 1937. This method comprises generally the compaction and compression of successive lengths of rod in a mold including die members which are separable to release pressure radially applied by the die members and thereby to release a length of rod from the mold. The rod thus formed is subsequently sintered.

By the present invention it is proposed to provide an improved apparatus for continuously forming a bar from a powdered metal wherein successive separate quantities of powdered metal are axially compacted by compacting means axially movable in a unitary die having a cavity of fixed cross-sectional area into bar segments bonded to each other to form a green compact bar. The green compact bar is incrementally forced out of the die such that a length thereof is frictionally retained within the die to serve as a stopper against which a succeeding quantity of powdered metal is compacted. The frictional resistance force between the cavity wall and the length of the bar defining the stopper is measured. This measurement is used to determine if the frictional resistance force corresponds to the compacting force required to compact the quantity of powdered metal into a bar segment having desired physical characteristics. If the frictional force deviates from the required force, the length of travel of the compacting means and the volume of powdered metal are varied relative to each other until the measured resisting force corresponds to the required compacting force whereby the powdered metal is compacted into a bar segment having the desired physical characteristics.

In accordance with the present invention the compaction is accomplished by a punch which is reciprocable within the die cavity. The required frictional force is maintained by controlling the length of travel of the punch in the cavity so that the quantity of powdered metal is compacted to provide a green compact rod of substantially uniform physical characteristics along its length.

The green compact rod formed in the continuous manner as described above is then sintered to improve the physical characteristics after emerging from the die. Preferably the sintering is performed by induction heating means.

After sintering the rod may also be swagged or otherwise hot worked to further increase the density thereof.

Further features of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of an apparatus, for carrying out the invention.

FIG. 2 is a fragmentary rear elevational view taken from the right of FIG. 1 showing the upper portion of the apparatus.

FIG. 3 is a view partly in section taken generally along the lines 3-3 of FIG. 1 showing the die with the die closure plug in assembled posit-ion.

FIG. 4 is a schematic diagram of the control system utilized in the apparatus for controlling the length of stroke of the ram.

FIG. 5 is a top plan view of the induction means for sintering the rod taken generally along the lines 5-5 of FIG. 1.

FIG. 6 is a view similar to FIG. 3 but showing the ram punch prior to the compaction of a further quantity of powder and before removal of the closure plug in the lower end of the die.

FIG. 7 is a view similar to FIG. 6 but with the closure plug removed and a length of the rod emerging from the die.

FIG. 8 is an end view of a press punch showing one pattern on the end surface.

FIG. 9 is an end view of a press punch showing another pattern.

FIG. 10 is a view of a portion of a rod showing schematically a joint between adjacent segments of the rod.

FIG. 11 is a view showing several selected crosssectional shapes of die cavity, each oriented along the lines 11-11 of FIG. 3.

Referring now to drawings, there is shown an apparatus orpress 20 including aframe 22 having alower frame unit 24, abed 26 and a superstructure frame unit 28. Supported in theupper unit 28 is a cylinderram device orjack 30, preferably hydraulic, for applying the compacting pressure to form the rod from powdered metal. The jack includes aram 32 having apunch 34 attached thereto. Theram 32 carries aswitch actuator 33 which may be in the form of a plate, as shown. Incorporated in thebed 26 is a die unit 36 (see also FIG. 3) and located below thebed 26, is asintering unit 38. Below thesintering unit 38 is a conventional rotaryswager creeping spindle 40. A continuous bar take-up orsupply holder 42, as schematically illustrated, is located at the base of the apparatus.

Mounted on thebed 26 is afeed shoe 44 having an opening 46 which defines a feed aperture, through which powdered metal is adapted to flow. Thefeed shoe 44 is slidable on thebed 26 between a retracted position shown in full lines and an advanced or feeding position as shown in FIG. 2. Thefeed shoe 44 is moved between the retracted and feeding positions by a hydraulic cylinder-ram device orjack 48.

The press is preferably operated by conventional built-in controls (not shown) so that thefeed shoe 44 advances and retracts as thejack 30 reciprocates between its limit positions. Thefeed shoe 44 is provided with limit switches (not shown) preventing lowering of thejack 30 when thefeed shoe 44 is in advanced position.

Mounted on and slidable with thefeed shoe 44 is afeed hopper 50 having a bottom outlet communicating with the aperture 46. Above thefeed hopper 50 is astationary supply hopper 52 having aspout 54 leading into thefeed hopper 50. Thepowdered metal 56 from which the continuous rod is formed is stored in thesupply hopper 52 and flows through thespout 54 into thefeed hopper 50 and from there through the aperture 46 in thefeed shoe 44 into thedie unit 36. Thefeed hopper 50 is constructed so that thespout 54 remains in continuous communication therewith as thefeed hopper 50 moves between the retracted and advanced positions.

The arrangement as shown in FIG. 2 also includes a pair of vertical control switches including an up"limit switch 60 and a down limit switch .62. Theswitch 60 is mounted on astationary frame element 64 while thedown limit switch 62 is mounted on alever arm 66 pivoted at 68 on a suitable stationary element such as theframe element 64. Thelever arm 66 and thus theswitch 62 is controlled by a cylinder-ram device, orstroke adjustment jack 70. The up and downlimit switches 60, 62 are actuated by the actuator orplate 33, mounted on theram 32 for movement thereby to limit the length of the stroke of the ram, and reverse the direction of the ram. The downlimit switch 62 is adjustable vertically, as hereinafter described.

Thedie unit 36 includes a die 72 (FIG. 3) and aholder 74 therefor, the holder being secured in thebed 26 in any suitable manner as by a shoulder indicated at 73 and a retainer ring 73a. The die 72 may be made from hardened steel and includes acavity 76 which may be any of various fixed cross-sectional shapes such as shown in FIG. 11, for example, round, square, and triangular designated respectively as 76a, 76b and 760. Thedie 76 is open at both ends and thecavity 76 is ground to a smooth finish. Preferably, the grinding is performed in the direction of compaction of the powdered metal. Thedie holder 74 has a threadedcounterbore 78 in line with thecavity 76 for receiving a stopper or closure plug 79 which is placed in position in the initial portion of the forming operation as explained hereinbelow, and later removed. Such a plug is shown in position in FIGS. 3 and 6, and removed therefrom in FIG. 7, wherein a portion of the formed bar or rod extends beyond thedie cavity 76 and through the threadedcounterbore 78.

In the operation of the press, a supply of thepowdered metal 56 is maintained in thesupply hopper 52 and the powdered metal flows through thespout 54 into thefeed hopper 50 and feed aperture 46 of thefeed shoe 44. The feed aperture 46 is closed-off by the base until theshoe 44 moves to advanced position and is aligned with thedie cavity 76. When in alignment, the powdered metal flows through the feed aperture 46 until thecavity 76 is filled. In this manner the quantity of powder introduced into the die is controlled or determined by the volume of the space in thedie cavity 76 above thestopper 79 or rod segment remaining in the die as more fully to be described hereinafter. It is also possible to control the quantity of powdered metal by other means. Upon retraction of thefeed shoe 44, thepress cylinder 30 is pressurized through line 85 (FIG. 4) to actuateram 32 so that thepunch 34 enters thedie cavity 76 to compact the powdered metal against the stopper or rod in thecavity 76. Successive quantities of powdered metal are introduced and compacted and bonded to the preceding compacted powdered metal to form thebar 94 as more fully to be described hereinafter. As the bar orrod 94 is formed, it is forced downwardly out of thedie 36 and into thesintering furnace 38 through acentral opening 82, and after the rod passes through the sintering furnace, it continues through therotary swager 40. This swager is of known construction and need not be described in detail. Generally, it is of the creeping spindle type, which prevents rotation of thebar 94. The swager reduces the diameter of the bar to a suitable extent, such for example as one-half of the cross-sectional area at 76, and as the bar passes through the swager it is wound on thereel 42 or placed in other suitable supply holders. Thesintering furnace 38 includes a body (FIGS. 1 and 5) with thelongitudinal opening 82 therein. The furnace is heated by induction coils 84 (FIG. 5) of suitable number and capacity to provide the desired temperature as referred to hereinbelow.

In the initial compaction of the powder to form thebar 94, theclosure plug 79 is inserted in thecounterbore 78 and a quantity of powdered metal is placed in the die cavity and compacted against the plug to form a segment of the bar. If the segment, thus formed has the desired physical characteristics and frictional resistance with the cavity wall to serve as a stop, theplug 79 is removed. The compacted segment of the bar in the cavity now serves as a stop means or stopper. If necessary, a plurality of quantities of metal powder may be compacted prior to removal of theplug 79 to achieve a length of bar having the requisite frictional engagement with the cavity wall to serve as a stopper. Another quantity of powder is introduced and another compaction performed. This quantity is compacted against the last formed segment of the bar in the cavity and bonded thereto. When the ram approaches the end of its stroke the force transmitted through the compacted segment is sufficient to overcome the frictional forces between the rod and the cavity wall so that thebar 94 is projected at least partially out of the die cavity. This process is repeated until the bar is of a desired length.

FIGS. 8 and 9 show non-planar end surfaces of the punch, FIG. 8 showing a corrugated waffle pattern 80' while FIG. 9 shows acorrugated ripple pattern 82. These corrugations form a corresponding configuration in the end of the segment thereby causing bonding of the succeeding quantity of powdered metal thereto during compaction in the die 72 as a further segment of the bar.

FIG. 4 shows an electro hydraulic system for controlling the length of the stroke of thepress ram 32 to compensate for the changes in volume in thedie cavity 76 for reasons which will become apparent hereinafter. The press cylinder ofjack 30 is incorporated in ahydraulic circuit 85 which also includes high andlow switches 86, 87, respectively. These switches are ordinary pressure actuated switches and are responsive to the pressure forces sensed in thecylinder 30. FIG. 4 also shows ahydraulic valve 88 actuated by solenoids 89-89 which in turn are activated by internal controls (not shown) in the press for reciprocating the cylinder orjack 30 as referred to above. This valve and the actuation thereof by the solenoids are well-known in the art.

Thestroke adjustment ram 70 is associated with thehydraulic valve 88 andsolenoid 89 for controlling the length of the stroke of the ram. Controlling thestroke adjustment ram 70 is ahydraulic valve 90 also of known kind and which may be of the same kind as thevalve 88, actuated by an upsolenoid 92 and adown solenoid 95 controlled, respectively, by the high and low pressure switches 86, 87. As thepress ram 32 descends to engage thedown limit switch 62, theswitches 86, 87 sense the pressure applied by the ram. If the pressure so sensed is higher than a predetermined maximum value thehigh pressure switch 86 senses the pressure in thehydraulic line 85, and energizes the upsolenoid 92 which thereby actuates thevalve 90 which controls thejack 70, retracting the piston therein and lowering thedown limit switch 62. This lengthens the extent of the travel of thepress ram 32. On the other hand, if the pressure is less than a predetermined minimum value thelow pressure switch 87 senses that pressure, and actuates thedown solenoid 95 which actuates thejack 70 in the opposite direction. This results in raising thedown limit switch 62 to shorten the travel of ram 32 (FIG. 2).

Thus the force exerted by the punch in compacting the powder in the die against the previously formed length of bar remaining seated in the die is measured. This compacting force also equals the resisting frictional force between the previously formed length of bar remaining in the die and the die wall. As heretofore mentioned, the frictional force between the previously compacted slug and the cavity wall serve to retain the bar within the die to provide a stop means against which the powdered metal is compacted. The compacting and the corresponding ejecting force must therefore be greater than the frictional force existing at the cavity wall. At the same time the force must not be of a magnitude that causes compacted powder to be wedged within the cavity so that it cannot be extracted without either damaging the bar or the die. On the other hand, the force applied must be such that the powdered metal is compacted and bonded to the previously formed length of bar. In establishing the prerequisite force, the initial pressing force or pressure is critical in order to produce a bar having the desired green compact characteristics, primarily density. Preferably, such green compact bar should have about a 70 percent density so as to be self-supporting and capable of withstanding the handling forces imposed thereon during transfer to a sintering or swaging station or the like.

Further factors in the carrying out of the method of the present invention are die design, surface area of the formed bar remaining in the die, powder properties, and lubrication.

The die is made from a material having a hardness and surface finish which minimizes galling. Preferably, the die surface or cavity wall is ground in the direction in which the rod is pressed or forced through the die. The die is also provided with aradius 76a at the punch entrance end thereof to serve as a punch guide. A short distance at theexit end 76b of thecavity 76 is tapered or flared outwardly to the extent that the compacted rod is permitted to expand gradually. The gradual taper allows the rod to expand as the compacted material attempts to relieve itself of the stresses developed during compaction. In the absence of taper the rod may crack due to a sudden or abrupt expansion.

The powder properties such as particle size, hardness, and particle size distribution may affect the friction developed at the cavity wall during compaction. These properties will affect the pressing pressures and the slug length.

The metal powder mix also includes a lubricant. The lubricant will affect the frictional characteristics along the cavity during compaction.

The above factors are all considered for producing a rod of substantially constant density along its length. However, because of variations in the metal powder properties, lubrication and the like, it is not possible to precisely predict the total length of the bar which remains in the die after each compaction. The total area of the rod remaining in the die directly determines the frictional resisting force and the compacting force whichmust be applied to eject the rod from the die. When the die is filled to the end of the cavity an increase or decrease of the volume remaining in the die results in corresponding decrease or increase in the volume of metal powders to be compacted. Under these conditions there is also coresponding increase or decrease in the compacting force sensed by thehigh pressure switch 86 andlow pressure switch 87. This causes the stroke adjustment ram to be adjusted as above explained to achieve the desired uniform physical characteristics. This measurement and adjustment is not only made during the initial formation of the bar, but is also made whenever the physical characteristics of the bar deviate from the desired characteristics.

In carrying out the method, powder of the material desired, e.g., iron, stainless steel composition, etc. of a size of less than 500 microns is generally utilized. A lubricant which may for example be --Acrawax C-- made by Glyco Chemical Co., or any of various other kinds of prior art lubricants, is thoroughly admixed with the powder.

In one practical example of utilizing the method, a stainless steel powder was compacted in the die to about one-half its original volume. The stainless steel was a type 316 stainless steel having the following composition:

The above stainless steel composition was admixed with Acrawax C to about l%% of the powder by weight.

The powder was introduced into the die cavity filling a length of the latter of about 3 inches, and after compaction it formed a segment of the bar of about 1% inches.

The adjacent segments were compacted and bonded together as mentioned above, forming a continuous integral bar, identified at 94, the segments being individually identified 96 (FIG. 10) and the bond therebetween at 98. In actual practice, theline 98 was substantially undiscernible. When the bar was subjected to bending stresses during test there was no greater tendency for the bar to break at 98 than at any other location stressed to the breaking point.

As each new quantity of powder was introduced and a segment formed, the continuous integral bar was forced out of the lower end of the die and continuously through the furnace as noted above, and in the sintering operation, the lubricant was burned out of the bar.

In the initial compacting step, when theclosure plug 79 was in place, a compaction pressure of about 20-25 tons per square inch (tsi) was utilized. After the plug was removed, and a subsequent quantity of powdered metal was introduced into the die cavity, a greater compacting pressure was utilized, such as between 30 and 40 tsi, and at an average of about 35 tsi.

The continuous bar thus formed was sintered at a temperature of the order of about 2,150 F., preferably for a period of about one-half minute.

Thebond 98 was along an irregular or non-planar conformation formed by a correspondingly shaped end surface of the punch, as shown in FIG. 9, the bond including overlapping extensions or elements which enhances bonding. It has been found that the strength at the bond is substantially the same as in other portions of thebar 94 both after green compaction and after sintering.

The pressure utilized creates substantial green strength in the bar, i.e., strength after compacting but before sintering, so that the bar can be handled in its green state without disintegration particularly when forcing it out of the die' and through the sintering furnace.

Metal powders of A.I.S.l. M-2 tool steel, Eatonite, Copper l-RXN, aluminum type 60l-AS (Alcoa), stellite-6B, and iron powder of A. O. Smith Inland 300M were compacted in a manner generally similar to the method described above. The metal powders of each of the different ferrous and non-ferrous metals were continuously formed into a green rod of a desired length and capable of being self-supporting and handling.

What is claimed is:

1. A press for continuously forming continuous bar comprising a die having a cavity, means for introducing a selective amount of powdered metal into the die cavity, a ram and punch reciprocable toward and from the die, lengthwise spaced limit means engaged by the ram for controlling and reversing the movement of the ram in response to engagement by a respective one of the limit means, the ram being operative on advance stroke to move the punch into the die cavity, the engagement of the punch with the powdered metal in the die cavity developing reaction pressure, and means for relocating one of said limit means and thereby adjusting the length of each advance stroke of the ram and punch in direct proportion to said reaction pressure during that stroke.

2. A press according toclaim 1 wherein the means for adjusting the length of the stroke is operative for increasing that length in response to higher reaction pressure than a predetermined value and reducing that length in response to a lower reaction pressure.

Claims (2)

1. A press for continuously forming continuous bar comprising a die having a cavity, means for introducing a selective amount of powdered metal into the die cavity, a ram and punch reciprocable toward and from the die, lengthwise spaced limit means engaged by the ram for controlling and reversing the movement of the ram in response to engagement by a respective one of the limit means, the ram being operative on advance stroke to move the punch into the die cavity, the engagement of the punch with the powdered metal in the die cavity developing reaction pressure, and means for relocating one of said limit means and thereby adjusting the length of each advance stroke of the ram aNd punch in direct proportion to said reaction pressure during that stroke.

2. A press according to claim 1 wherein the means for adjusting the length of the stroke is operative for increasing that length in response to higher reaction pressure than a predetermined value and reducing that length in response to a lower reaction pressure.

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