Fluid-conducting Hot-forging Die And Method Of Making The Same

Abstract

A foraminous ordinary-duty hot-forging die is provided with minute fluid passageways therethrough for the conduction of a coolant, a lubricant or a protective atmosphere under high pressure. A porous hot-forging die is made by forming a briquette of coarse powdered tool metal or carbide, sintering the briquette, machining a die cavity or die bore therein, and heat-treating the thus-formed die for the required hardness and wear resistance.

Description

A modified heavy-duty fluid-conducting hot-forging die is formed from powdered material by loading the die cavity of a briquetting press with a charge consisting of alternate layers of powdered tool metal or carbide and fusible wire inserts extending thereacross and compressing this charge into a briquette. This briquette is then sintered at a temperature below the melting point of the insert material, hot-forged to density it so as to produce a substantially solid die forging of approximately 100 percent density, annealed, and bored to form a central pilot hole therethrough. The die forging is then vacuum-sintered at a temperature higher than the melting point of the insert material with a sufficiently low vacuum to vaporize the insert material and withdraw it from the body, leaving perforations therethrough. The sintered perforated die forging is then machined to provide the desired shape of die cavity or die bore and finally heat-treated to obtain the necessary hardness and wear resistance. Either form of die is mounted in a bore in a die-holding block having a chamber therearound. During hot-forging operations, this chamber is supplied with a coolant, a lubricant or a protective atmosphere agent under a sufficiently high pressure to force it through the pores of the porous die or through the perforations in the solid die while the die is being used to hot-forge, extrude or otherwise form workpieces.

BACKGROUND OF THE INVENTION.

Hitherto, hot-forging dies of solid metal have possessed short working lives and have been subject to considerable oxidation as a result of the high pressures and high temperatures to which they have been subjected during use. The present invention enables an ordinary-duty die to be formed from powdered metal or carbide with pores sufficiently large for the passage of a coolant, a lubricant or a protective atmosphere agent, increasing the working life of the die. The substantially solidified sintered powdered metal perforated heavy-duty hot-forging die of the modification of the invention enables higher temperatures and higher forging pressures to be employed yet with increased working life than in previous hot-forging dies.

In the drawings:

FIG. 1 is a central vertical section through an ordinary-duty fluid-conducting hot-forging die of sintered powdered metal or carbide, according to one form of the invention;

FIG. 2 is a central vertical section through a hot-forging or extrusion press showing the hot-forging die of FIG. 1 at the start of a hot-forging or extrusion operation;

FIG. 3 is a view similar to FIG. 2, but showing the position and shape of the workpiece at the conclusion of the hot-forging or extrusion operation;

FIG. 4 is a central vertical section through a heavy-duty fluid-conducting hot-forging die of densified sintered powdered metal or carbide, according to a modification of the invention;

FIG. 5 is a top plan view of a fusible wire insert employed in making a heavy-duty solidified hot-forging die, according to the modification of the invention shown in FIG. 4;

FIG. 6 is a central vertical section through the die bore of a briquetting press showing the formation of the briquette for the heavy-duty die of FIG. 4 at the start of the briquetting operation;

FIG. 7 is a view similar to FIG. 6 but showing the briquette at the end of the briquetting operation;

FIG. 8 is an enlarged central vertical section through the presintered briquette of FIG. 7 after a pilot hole has been drilled therethrough;

FIG. 9 is a cross-section taken along the line 9--9 in FIG. 8;

FIG. 10 is a central vertical section through a hot-forging or extrusion press showing the hot-forging die of FIG. 4 at the start of a hot-forging or extrusion operation;

FIG. 11 is a fragmentary cross-section taken along the line 11--11 in FIG. 10; and

FIG. 12 is a view similar to FIG. 10 but showing the shape and position of the workpiece at the conclusion of the hot-forging or extrusion operation.

Referring to the drawings in detail, FIG. 1 shows a porous ordinary-duty hot-forging die, generally designated 20, according to one form of the invention, as consisting of a porous body 22 of sintered powdered metal or carbide preferably with a slightly tapered side surface 24 and with top and bottom surfaces 26 and 28 respectively interconnected by a die cavity 30. The die cavity 30 is shown by way of example to have a shape adapted for the production of a poppet valve workpiece 32 (FIG. 3), such as is used in the manufacture of internal combustion engines and in this instance consists of an approximately cylindrical upper cavity portion 34, tapered intermediate cavity portion 36 and a straight cylindrical lower cavity portion 38.

The body 22 is first formed as a briquette or compact by conventional briquetting or compacting methods and apparatus known to those skilled in the powder metallurgy art, using a preponderance of a coarse metal or carbide powder, such as 150 mesh tool steel, or tungsten carbide, titanium carbide or silicon carbide powder with or without the addition of a finer mesh powder thereof, depending upon the porosity desired for the die. This powder is mixed with other necessary ingredients, such as graphite, and a lubricant in order to obtain a homogeneous blend of the component materials possessing the proper chemical composition. The charge of this powder mixture is placed in a conventional briquetting or compacting press and compacted at a pressure higher than the pressure to which the die is expected to be subjected in service. For example, if the die 20 is expected to be used in hot-forging service at pressures not exceeding 50 tons per square inch, it would be compacted at a pressure of about 70 tons per square inch.

The compact or briquette is then removed from the briquetting press and sintered in the conventional manner for the particular die material employed, and in a protective atmosphere, such as a hydrogen or dissociated ammonia atmosphere if oxidizable ingredients, such as chromium, are present. After the briquette has been sintered, it is bored or otherwise machined to form the die cavity or die bore 30 with the shape required for the production of the particular workpiece 32 to be produced. The die 20 thus formed is heat-treated in a conventional manner to provide it with the necessary hardness and wear resistance. If, during machining, the porosity of the die body 22 has been impaired, such as by wholly or partially closing up the pores, these may be re-opened by the use of a conventional chemical etching agent.

The porous hot-forging die 20, thus produced, is mounted in a conventional hot-forging or extrusion press or machine, generally designated 40, shown diagrammatically in FIG. 2. This is shown, in its working parts adjacent the die 20, to include a press bed assembly 42 consisting of a lower punch support 44 mounted on a lower bolster plate (not shown), a back-up plate 46 resting on the lower punch support 44, and a die holder plate 48 disposed above the back-up plate 46. The lower punch back-up plate 46 is provided with a stepped bore 50 in which is mounted a correspondingly-flanged lower punch 52 containing an elongated central bore 54. The bore 54 slidably receives the upper end portion of an ejector or knockout rod or plunger 55 and opens into an enlarged bore 56 in the lower punch support 44, which contains a counterbore 58 snugly receiving the lower portion and lower end of the lower punch 52, which has an upper end surface 60 upon which the lower end surface 28 of the die 20 rests.

The die holder plate 48 contains a bore 62 which is tapered according to the taper of the side surface 24 of the die 20 so as to fit snugly therewith. Intermediate the opposite ends of the tapered bore 62 there are provided upper and lower annular passageways 64 and 66 respectively interconnected by circumferentially-spaced fluted fluid transmission grooves collectively constituting a flock chamber 68, similar to those shown in FIG. 11. Extending outward through the body 70 of the die holder plate 48 is a passageway 72, the outer end of which is threaded to receive the correspondingly-threaded high pressure coupling 74 connecting the passageway to a high-pressure conduit 76 which at its opposite end is connected by a high pressure elbow coupling 78 to a high pressure fluid accumulator, generally designated 80. The accumulator 80 is adapted to contain a lubricant, a coolant or a protective atmosphere agent subjected to a standing pressure indicated on a pressure gauge 82 communicating therewith by a Tee fitting 84 which in turn is connected to a conduit 86 leading to a pressure-regulated pressure source (not shown).

The hot-forging or extrusion press or machine 40 also includes an upper platen or ram 88 (FIG. 2) which is provided with a socket 90 receiving the upper or butt end 91 of an upper punch 92 having a lower end surface 94 with a nose portion 95 thereon and also having an annular tapered portion 96 thereon urged toward the upper platen 88 by its engagement with the correspondingly-tapered bore 98 in retaining plate or ring 99 bolted or otherwise secured to the upper platen 88.

In the operation of the hot-forging or extrusion press or machine 40 employing the ordinary-duty fluid-conducting hot-forging die 20, let it be assumed that the upper platen 88 and upper punch 92 have been moved upward to their retracted positions so as to leave open for loading the die cavity 30 in the hot-forging die 20. Let it also be assumed that the latter and its die holder 70 and back-up plate 46 have been heated to a suitable pre-heating temperature between 600.degree. and 1,000.degree. F. by conventional means (not shown). Let is also be assumed that the accumulator 80 has been placed in operation to cause a flow of coolant or lubricant, as the case may be, through the passageway 72 into the chamber 68 whence this fluid surrounds the body 22 of the hot-forging die 20 and penetrates the pores thereof to reach the die cavity 30. This contemplates the use of a pressure within the range of 100 pounds per square inch up to 5,000 pounds per square inch, depending upon the size of the pores in the die body 22 and the viscosity of the fluid being transmitted therethrough.

A workpiece slug or bland B having been heated to a suitable forging temperature, is now dropped into the die cavity 30 of the now-heated porous hot-forging die 20 and the platen 88 then made to descend, causing the upper punch 92 to enter the upper portion 34 of the die cavity 30. The lower end 94 and the nose portion 95 thereof engage the hot slug or blank B and push it downward, causing the material thereof to undergo flow and to be extruded through the tapered intermediate bore 36 into the straight cylindrical lower bores 38 and 54 (FIG. 3). The foregoing action forms a workpiece W having a head H with a recess R and an elongated stem S interconnected by a tapered neck N. It will be understood, however, that the workpiece W is merely one form of workpiece which may be hot-forged by the porous die 20 of the present invention and that many other forms of workpiece may also be hot-forged thereby in a similar manner according to the configuration of the workpiece W/and the consequent shape of the die cavity 30 required to produce it.

The upper platen 88 and punch 92 are now retracted upward away from the die cavity 30. The workpiece W, which for purposes of illustration has been illustrated and described as for a poppet valve for an internal combustion engine, is now caused to be ejected from the die cavity 30 by moving the ejector rod or plunger 55 upward in the bore 54 so as to engage the lower end of the workpiece W and first dislodge it and then push it upward out of the die cavity 30. Meanwhile, the high pressure coolant or lubricant fluid reaching the die cavity 30 through the conduit 72, chamber 68 and pores of the die body 22 cools or lubricates, or both cools and lubricates the wall of the die cavity 30 and also cools the hot-forging die 20, inhibiting oxidation, deterioration and wear and greatly increasing the life of the die 20. In the alternative, a gaseous protective agent reaching the die cavity 30 through the pores of the die body 88 from the passageway 72 and chamber 68 prevents oxidation of the heated workpiece slug or blank B and the workpiece W forged or extruded therefrom.

The modified heavy-duty fluid-conducting hot-forging die, generally designated 100, shown in FIG. 4 is also adapted to be cooled, lubricated or supplied with a protective atmosphere but is employed for heavy-duty hot-forging where the pressures involved are beyond the capacity of the porous ordinary-duty hot-forging die 20 of FIGS. 1, 2 and 3. Unlike the porous hot-forging die 20 of porous sintered powdered material, the densified fluid-conducting hot-forging die 100 is composed of sintered powdered material which has been subjected to hot-forging itself in order to compress its particles, close up its pores and densify it so as to render it substantially solid with a density approaching 100 percent. Instead of fluid-conducting pores of the porous die 20 of FIG. 1, the heavy-duty die 100 of FIG. 4 is provided with elongated minute fluid-conducting passageways or channels 102 extending from its external surface 104 to its die cavity 106 through/its body 108.

To produce the densified substantially solid hot-forging die 100, powdered material, such as powdered metal or powdered carbide, with conventional sizes of particles is briquetted or compacted in a conventional briquetting press 112 shown diagrammatically in FIGS. 6 and 7. The briquetting press 112 is shown as including a briquetting die 114 containing a briquetting die cavity or bore 116 with a lower punch 118 entering the lower end thereof and an upper punch 120 movable into and out of the upper end thereof. The upper punch 120, like the upper punch 92 of FIG. 2, is connected to an upper platen (not shown) which, at the start of operation, is retracted upward away from the briquetting die 114. The die cavity 116 is then filled with a charge 122 consisting of alternate layers 124 and 126 of metal or carbide powder and fusible inserts respectively.

Each fusible insert 126 (FIG. 5) possesses the configuration of the pattern of holes or perforations desired in the finished die 104 and consists of multiple fusible wire arms 128 arranged in a wheel-spoke or star shaped pattern and secured at their midportions to one another in any suit-able manner as by solder 130. The inserts 126 are conveniently formed from copper wire because of its ease of soldering and convenient melting point of 1,980.degree. F., but it will be understood that other suitable fusible materials may also be employed for this purpose. The powder layers 124 of the charge 122 are conveniently composed of so-called high speed steel or tool steel powder or of carbide powder, such as tungsten carbide, titanium carbide or silicon carbide. The loading of the briquetting die cavity 116 with the charge 122 is performed by placing the lowermost layer 124 of powder on the top surface 132 of the lower punch 118, whereupon an insert 126 is placed on top of the powder layer 124. A second layer 124 of powder is then placed on top of the first insert 126, followed by another insert 126 in a slightly rotated position (FIG. 9) and so forth until the die cavity 116 is filled to the extent necessary to produce the desired size of die 100 with the arms 128 of the inserts 126 offset relatively to one another in different layers of the charge 122 (FIG. 9).

The briquetting press 112 is then operated to cause the upper punch 120 to descend and enter the die cavity 116 (FIG. 6), compressing the charge 122 therein (FIG. 7). Meanwhile, the lower punch 118 is held stationary or, if the die 114 is mounted upon a conventional die cushion (not shown), the assembly of die 114 and lower punch 118 descends slightly, The result is the compressed insert-equipped briquette 134 shown in FIG. 7. The upper punch 120 is then retracted upward, whereupon the briquette or compact 134 is ejected from the briquetting die cavity 116 by moving the lower punch 118 upward.

The briquette or compact 134 is then pre-sintered in a suitable atmosphere such as hydrogen or dissociated ammonia at a temperature sufficiently below the melting temperature of the inserts 126 to prevent melting thereof yet at the same time sufficient to pre-sinter the entire briquette 134. The pre-sintered briquette is then normally re-heated to the presintering temperature to still avoid melting the inserts 126 and is then subjected to hot-forging to convert the pre-sintered compact into a substantially solid die forging 140 (FIG. 8) approaching 100 percent density. In the alternative, the hot working of the forging 140 can also be accomplished without reheating if the pre-sintered compact is removed quickly from the pre-sintering furnace and hot-forged immediately before it has had time to cool. The forging operation upon the sintered compact distorts the cross-section shape of the inserts 126 very slightly from their original shape, thereby converting the wires 128 from circular cross-section to approximately oval cross-section.

The hot-forged sintered compact or die forging 140 is then annealed in a conventional manner to soften it sufficiently to permit the drilling of a central pilot hole 136 (FIG. 8), whereupon the insert-equipped forging 140 is then fully sintered in a vacuum at 2,000.degree. to 2,500.degree. F. depending upon its material. This action melts and vaporizes the material of the inserts 126 and withdraws it by suction, leaving the perforated hot-forging die blank forging 140 (FIG. 8) provided with the holes, passageways or channels 102 radiating outward from the pilot bore 136 to the external surface 144 of the die blank 140. If the inserts 126 are made from copper wire which has a melting point of 1,980.degree. F., the hot-forging is performed at approximately 1,900.degree. F. and a 1-micron vacuum at a temperature of 2,100.degree. F. The procedure just described melts, vaporizes and removes the copper material of the inserts 126.

The die forging 140 thus equipped with multiple passageways 102 is now machined to form the heavy-duty substantially solid fluid-conducting hot-forging die 100 by boring or otherwise producing its die cavity 106. This die cavity or die bore 106 can also be produced by so-called electrical discharge machining and can be of any suitable configuration. The particular die cavity 106 shown in FIG. 4 is presented solely by way of example for forming a poppet valve workpiece similar to the workpiece W shown in FIG. 3. In the event that the mouths of the perforations or passageways 102 become partially or wholly clogged during the machining operation which produces the die cavity 106, these openings can be cleared by the use of a conventional etching agent, such as an etching acid.

In the use of the perforated heavy-duty die 100, the latter is mounted in a conventional hot-forging or extrusion press or machine, generally designated 148, shown diagrammatically in FIGS. 10, 11 and 12 and includes a press bed assembly 150 having a lower punch 152 mounted in a lower punch back-up plate 153 above a lower bolster plate (not shown) in a manner similar to the arrangement shown in FIGS. 2 and 3. An outer die 154 is provided with a tapered outer surface 156 and is mounted in the correspondingly-tapered bore 158 of a pre-stressed annular die holder 160 which in turn is provided with a tapered outer surface 162 mounted in a tapered bore 164 in a die holder plate 166.

The outer die 154 is provided with an upper die bore 168 snugly receiving an upper punch 170 and is also provided with a counterbore 172 snugly receiving the outer surface 108 of the die 100 at its upper and lower ends. The counterbore 172 intermediate its upper and lower ends is provided with a pair of vertically-spaced annular upper and lower fluid passageways 174 and 176 interconnected by grooves 178 (FIG. 11) extending therebetween and sufficiently therebeyond to reach all of the passageways 102 in the die 100. From the lower annular fluid passageway 176 a fluid passageway 180 extends upward within the outer die 154 and at its upper end is threaded to receive a high pressure elbow fitting 182 connected to the coupling 184 of a high pressure fluid supply line 186.

The operation of the hot-forging or extrusion press 148 employing the perforated solid hot-forging die 100 is sufficiently similar to that of the hot-forging or extrusion press or machine 40 described above as to require no repetition, hence is not repeated in order to avoid duplication. The high pressure fluid reaching the annular passageways 176 and 174 by way of the passageway 180 and elbow coupling 182, 184 from the high pressure fluid line 186, whether a coolant, a lubricant or a protective agent, passes through the minute perforations or passageways 102 in the hot-forging die 100 and cools, lubricates or protects both the die 100 and the workpiece therein (FIG. 12) as the heated or blank B is forced downward through the die cavity or die bore 106 to become the elongated workpiece W. The upper punch 170 is then retracted upward and the knockout rod or ejection plunger (not shown, but similar to the member 55 in FIGS. 2 and 3) is then moved upward to eject the workpiece W from the die cavity 106 and die bore 168.

Claims

I claim:

1. A fluid-conducting porous hot-forging die device, comprising

a die holder having a bore therein,

a porous die body composed of particles of sintered powdered heat-treated tool steel and having a die cavity therein and an outer peripheral surface therearound spaced outward from said die cavity and spaced inward from said die holder bore and defining therewith a fluid chamber,

means for supplying a lubricant fluid under high pressure to said chamber,

fluid-conducting means in said porous die body consisting of a multiplicity of minute fluid-transmissible passageways formed by the pores between said particles and extending continuously from said fluid chamber outside said outer peripheral surface to said die cavity with their opposite ends open to said chamber outside said outer peripheral surface and to said die cavity respectively,

said die cavity having an elongated substantially cylindrical upper cavity portion, a substantially cylindrical lower cavity portion of smaller diameter than said upper cavity portion, and a tapered intermediate cavity portion connecting said upper and lower cavity portions and merging smoothly at its junctions with said upper and lower cavity portions,

and an elongated power-operated substantially cylindrical punch of substantially the same diameter as said upper cavity portion reciprocably movable into and out of closely-fitting but relatively-sliding telescoping relationship with said elongated cylindrical upper cavity portion.