US 3680354 A
A die assembly for use in forming operations, such as hot extruding wherein the forming insert is frustoconical in shape and is cold pressed into a sleeved support which is contained within a casing with the major base of the insert facing the exit side of the assembly and supported under axial load by a backer bushing affixed to the support casing, said forming insert being substantially radially supported within that section of the sleeved support and casing which is subject to longitudinal anneal by the heat generated in the extruding operation.
Claims available in
Description (OCR text may contain errors)
United States Patent Phillips, Jr.
 DIE ASSEMBLY  Inventor: William H.
 Assignee: Allegheny Ludlum Steel Corporation, Pittsburgh, Pa.
 Filed: March 23, 1970  App]. No.: 21,634
 U.S. Cl ..72/467, 72/481  Int. Cl. ..B2lc 3/00, B2ld 37/04  Field of Search ..72/467, 481
 References Cited UNITED STATES PATENTS 1,952,245 3/1934 Garner ..72/467 3,296,848 1/1967 Murphy ..72/481 3,420,085 l/1969 Pratt ..72/467 [451 Aug. 1,1972
Primary Examiner-Charles W. Lanham Assistant Examiner-R. M. Rogers Attorney-Richard A. Speer, Vincent G. Giola and Howard R. Berkenstock, Jr.
[ 5 7] ABSTRACT A die assembly for use in forming operations, such as hot extruding wherein the forming insert is frustoconical in shape and is cold pressed into a sleeved support which is contained within a casing with the major base of the insert facing the exit side of the assembly and supported under axial load by a backer bushing affixed to the support casing, said forming insert being substantially radially supported within that section of the sleeved support and easing which is subject to longitudinal anneal by the heat generated in the extruding operation.
4 Claims, 3 Drawing Figures DIE ASSEMBLY BACKGROUND OF THE INVENTION al, currently available are subject to one or more of the following failure modes: (1) radial cracking of the insert; (2) laminar cracking of the insert; (3) wash out of the extrusion contour and the die bearing; (4) heat checking; and (5') closing of the die bearing. Failure of the insert in any category occurs in conventional use, generally after extruding one to five billets. If the cracking is not too severe, the die is run to destruction; however, it maybe necessary to recut the dies a small amount after a few pushes to re-establish the forming surfaces. Recutting is a costly operation. Press efficiency is reduced by frequent replacement of dies. In addition to introducing nonuniformity in size of the ex truded product by frequent recutting, the quality of the product is poor until the crack die is recut. By way of example, dies for extruding copper and brass rod composed of a stellite insert, shrunk-fit into a hardened, high temperature steel. casing crack radially after only three to five pushes: following 25 to 50 pushesthese radialcracks open up necessitating a recut of about 0.020 inch. This recut cycle continues throughout the use life of the die.
A further problemis experienced in that the operating temperature during extrusion rangesapproximately 1-,200to 2,100F. With the die insert conventionally shrunk-fit at room temperature to about 0.003 inch per inch of its outside diameter, operation at the-extrusion temperature causes the casing supporting the die to expand more than the. insert allowing the insert to become unsupported. The result of extruding with the unsupported die is a radial failure. A severe cracking of the insert often results in break-up of the die.
serts as well as the new ceramic type inserts, discloses a die body fit into a retainer sleeve before assembly into the support casing. While the die assembly described in that application provides a superior mounting for the die body by subjecting it to a compressive loading throughout the forming operation, its use has pointed up other disadvantages shortening the service life of the die body. The invention described herein provides a die .structure more uniformly supported compressively within the die assembly, having service life many times longer than conventionally known.
SUMMARY OF THE INVENTION This invention. relates to a die assembly for use. in forming operations such as the extruding of metals under high temperature and pressure, in a die body of generally frustoconical shape, having a forming surface aligning an axial opening therethrough. The die body is loaded into. a-retainer casing within a sleeve, the die body being'supported in compression by the sleeve and casing, in the portion of the sleeve and easing subject to anneal by the heat generated in the forming operation. Backing means support the die body and sleeve against the axial forces developed in the forming operation.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the die assembly of my invention.
FIG. 2 is a sectional view of my invention along the line IIIl.
FIG. 2a .is a fragmentary section of an alternative embodiment of the insert support structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referringnow to the drawings, reference numeral. 2
Ceramic and other high-hardness die materials came into limited use recently and exhibit good wear-resistant characteristics. However, they are relatively brittle and have low tensile strength. It is critical to keep such dies under compression or very low tensile stresses throughout their use. Failure to provide an adequate loading on such brittle die materials permits radial and/or laminar cracking, at least causing the finish of the extruded product to be marred. As with the previous alloy die bodies, the recent low tensile dies have been mounted in the die assembly structure by a conventional shrink-fitting procedure. Thus, the ceramic type die inserts in conventional assemblies suffer a similar loss of compressive loading due to the ness material, such as a nickel binder carbide available from the Carmet Company under the tradename AMET-X. The insert 2 in the-disclosed example has an opening defined by forming surfaces 3 for extruding round, brass rods three-fourths inch in diameter. Insert 2 is frustoconical in shape, having a major base4 of approximately 1.450 inches in diameter and a minor base 6 of approximately 1.4107 inches in diameter and a depth of 0.375" inch. Sides 8 of insert 2 exhibit a slope of 3from the axis of the die in the example The degree of slope may be varied so long as there is suffi, cient slope to eliminate the shear loading in the insert. Insufficient taper results in placing the insert inshear' when either hot-shrunk or cold-pressed into retainer casing. 1 0, a cause is previously discussed. Containing insert- 2 is a sleeve 12 which in the example is A.I.S.I. Type H-2I steel, hardened to a hardness of 46 to 48 RC. In the. example, the sleeve has a taperedinner wall 14 at an angle of 3 from the axis complementary to side'8 ofinsert 2. Outer'wall l5ofsleeve. l'-2'is cylind'ri-- cal or of uniform diameter matching the complementary shape of cylindrical wall 16 of 'casing 10. In the example, disclosed, sleeve 12 hasv a diameter of 2.220 inches and is of the material A.I.S.I. Type M-2 steel,
hardened to a hardness of 54 to 56 RC. The depth of. sleeve 12 is approximately 0.500 inch. Insert 2 and? sleeve 12 are contained in retainercasing 10 which has a generally cylindrical shape with an opening 20 to accommodate the sleeve-containing insert. In theembodiment disclosed wherein side 15 of sleeve 12 is cylindrical, the opening 20 has a diameter of 2.2177 inches. The overall dimensions of retainer casing in the disclosed embodiment are 1.750 inches in thickness I 46 to 48 RC. As shown in FIG. 2a the sleeve walls 14 and 15 may also exhibit corresponding slope as disclosed in my previous application Ser. No. 864,841.
In the preferred embodiment a backer bushing 22 is contained within the opening of casing 10. It will be noted that the diameter of the backer bushing is equal to that of the sleeve, i.e., 2.220 inches. Opening 26 in bushing 22 corresponds to that defined by forming surfaces 3 of insert 2. So positioned, bushing 22 supports insert 2 and sleeve 12 across the back of said insert and sleeve absorbing. the axial load placed thereupon by the extruding operation.
As previously discussed, ceramic and other highhardness die inserts are exceptionally weak under tension and shear loads. The die assembly of the invention offsets these weaknesses and takes advantage of the high compression capacity of the material to utilize the extruding wear-resistance of these materials at extrusion temperatures. Thus, the dimensions of the assembly elements; insert 2, sleeve 12, casing 10, and bushing 22 are interrelated to take advantage of these desirable characteristics of the materials involved. In the assembly of the various comments, these charac teristics of the materials must be considered so as not introduce unwanted stresses. In the disclosed invention, sleeve 12 is cold-pressed into casing 10. It will be noted that the preferred embodiment of sleeve 12 contains a. slight chamferas at 28 to facilitate the pressing of sleeve 12 having a slightly larger diameter into the slightly smaller diameter of hole 20 of casing 10. Insert 2 is then compressed into .the sleeve contained within the casing 10 at room temperature to an interference fit between the insert 2 and the sleeve 12 of 0.008 inch per inch of the outside diameter of the insert, providing a high compressive loading. This figure maybe varied for different materials other than AMET-X insert and thev tool steels utilized in the example to produce the desired loading. It willbe noted that the dimensions of sleeve 12 and insert 2 are such that the insert is received into sleeve 12 such that the back faces of the insert 2 and the sleeve are flush prior to any interference fit being accomplished. A projection is contained on the face 30 of backer bushing 22 measuring some 0.096 inch in the preferred embodiment. The height of the projection 30 is coordinated to provide the amount of interference fit necessary which in the instant example is 0.008 inch per inch of outside diameter of insert 2 when shoulder meets sleeve 12. It will be noted that the projection 30 substantially sup ports the back surface or major base of insert 2 such that upon interference fitting; i.e., pressing the insert 2 into the sleeve 12 the back of major base of insert'2 is totally supported by the backer bushing projection 30 and the sides 8 of insert are fully within sides 14 of sleeve 12. As the backer bushing is compressed into the casing 10 and contacts sleeve 12 as at 32 the insert 2 is within the sleeve 12. Such an assembly method avoids any shear loading on the insert during the loading process. In the example described above, the interference fit prescribed produces a tangential compression preload in the insert inside diameter of the insert 2 of about 185,000 psi. Conventional assemblies using stellite inserts using a hot-shrink fitachieve a total interference fit of only about 0.003 inch per inc. The use of sleeve 12 in the assembly drastically reduces the tangential tension load at the inside diameter of the casing 10 which in the example is approximately 76,000 psi. It has been observed that insertion of an insert directly into a casing without interposition of. a sleeve 12 therebetween would result in a tangential tension load ing, the jointure of the insert and the casing of approximately 98,000 psi. Heating the assembly structure to an extruding temperature of l,200 F. yields a compression preload in the inside diameter of about 104,500 v psi, thus, illustrating that the insert is maintained in a high compression loading configuration. The tangential I tension loading at this temperature in the casing inside the diameter of the sleeve 12 with the sleeve 12 incorporated is about 48,000 psi, without the sleeve 12 observations show tension loading in the casing to be approximately 55,000 psi. The tension loading in both the sleeve and the casing is maintained approximately equal, i.e., 48,000 psi. This equalization of stresses avoids overload and resulting creep rupture. Minimization of case stress by the use of sleeve 12 eliminates 7 case creep rupture permitting the use of high compresproperly preloaded under a complete compressive load sion loading in the inserts. As was previously noted, the sleeve 12 in insert 2 is assembled in a 3 per side taperin the example. Such a tapered assembly eliminates shear loading as previously described in insert during the assembly operation allowing the forces of loading to be uniformly transferred across the sloping surfaces 8 of the insert to the surfaces 14 of the sleeve during cold pressing. As was previously noted, the backer bushing in 22 supports the insert 2 as well as the sleeve 12 under the axial loading during the extrusion operation. Supporting the insert 2 and sleeve 12 in such a manner prevents deflection of the insert of the load which would otherwise induce laminar cracking in the insert and deterioration on the surface of the extruded product.
. 0f further importance in the invention is the limitation of mounting of insert 2 into sleeve 12 and casing 10 within that area of the die assembly which is subjected to the anneal of the penetration of the high heat generated during the forming operation. It has been discovered in die structures of the type and size illus trated that the anneal of the forming operation penetrates to a depth of approximately three-eighths of an inch toward the backer bushing along the line between the surface 8 of the insert and 14 of the sleeve from the front face of the die insert. The anneal penetrates to a depth of approximately five-sixteenths inch in the disclosed example along the intersection of the sleeve 12 in casing 10. Within this area of anneal, the high hardness of the supporting materials is severe ly affected being reduced as much as one half or less of the original cold values. This penetration of anneal may be determined by cutting a radial section from the sleeve and casing and hardness measurements made. The profile of these sections may then be tested for hardness at intervals throughout the section and an evaluation of the penetration of the anneal made therefrom. The insert 2 may then be dimensioned such that it is entirely supported within that area of the sleeve which is annealed by the heat of the forming operation. It may now be appreciated that further loading of an insert spanning across this hardness differential of the supporting materials would result in a transverse shear being set up at this abrupt differential. Such loading of a differentially supported insert results in laminar cracking at the shear point. I have discovered that by restricting the insert 2 to being supported within the area of the anneal this abrupt shear may be avoided. By so avoiding the abrupt shear within the die insert, the laminar cracking formerly experienced may be eliminated.
It may now be appreciated by those familiar with the art that every element of the assembly interacts with each and every other element of the assembly to provide an insert completely supported in compression which reduces tension loading in the casing and eliminates shear loading within the die insert. It will also be evident with those familiar with the art that variations in tool steel and size of the elements may be made without departing from the scope of the invention disclosed herein. Adaptations of the teachings may be made to accommodate excluding a plurality of rods or the like in a single assembly or to accommodate different cross-sections to shape tubings and the like, as hexagonal rather than round extrusion.
1. A die assembly for use in forming operations comprising casing means having a bore therethrough, a sleeve press-fit within one end portion of the bore, said sleeve having an interior diameter uniformly increasing inwardly of the adjacent end of the bore, a die body having a frustum shaped exterior complementary to the interior of the sleeve, said die body being press-fit within said sleeve and including a forming opening longitudinally therethrough, said die body being complete- 1y received within said sleeve, and a separate backer bushing within said casing bore inward of the sleeve and die body and in supporting engagement therewith, said backer bushing having an opening longitudinally therethrough corresponding in size to and aligned with the die body forming opening, said backer bushing presenting a face coextensive with and engaged with the inner ends of the sleeve and die body between the die body opening and the casing.
2. Apparatus of claim 1 wherein the sleeve and die body engaging face of said backer bushing includes an inner projection coextensive with said die body, said projection being received within the sleeve to orientate the die body inward of the bushing engaged end of the sleeve.
3. A die assembly for use in forming operations comprising casing means having a bore therethrough, a sleeve press-fit within one end portion of the bore, said sleeve having an interior diameter uniformly increasing inwardly of the adjacent end of the bore, a die body having a frustum shaped exterior complementary to the interior of the sleeve, said die body being press-fit within said sleeve and including a forming opening longitudinally therethrough, said die body being completely received within said sleeve, and a separate backer bushing within said casing bore mward of the sleeve and die body and in supporting engagement therewith, said backer bushing having an opening longitudinally therethrough corresponding in size to and aligned with the die body forming opening, said backer bushing presenting a face coextensive with and engaged with the inner ends of the sleeve and die body between the die body opening and the casing.
4. Apparatus of claim 2 wherein the sleeve and die body engaging face of said backer bushing includes an inner projection coextensive with said die body, said projection being received within the sleeve to orientate the die body inward of the bushing engaged end of the sleeve.