US2783504A - Method of forming articles from comminuted material - Google Patents

Description

March 5, 1957 H. J. HAMJIAN ET AL METHOD OF FORMING ARTICLES FROM COMMINUTED MATERIAL 2 Sheets-Sheet 1 Filed May 6, 1955 mm r Z V d u, m H

fali/r /V. Dormant BY 12a 41%? ATTORNEYS March 1957 H. J. HAMJIAN 1-:- AL 2,783,504

METHOD OF FORMING ARTICLES FROM COMMINUTED MATERIAL Filed May 6, 1955 2 Sheets-Sheet 2 Fig 10 m/l/r/vrons Harry J- Ham/i017 Fa/ih N. Darmara BY %&, W zfi/w 454%,

ATTORNEYS United States atent' JMETHODOF FORMING ARTICLESITROM COMMINUTED .MATERIAL iHarry.S-J..:Harnjian, Whitesboro, andfFalih N. lhi'rmara, :tNew EHartford, .Nuy rassignors' to .Utiea Drop Forge & Tool Corporation, Utica, N. Y., a corporationoi ,NewXork =ApplicationfMay 6, 1953, Serial No. 353,386

2 Claims. (CRIS-59.5)

metalloid powders. "It 'shouldbe-borne'inmind, accord- 'ing'ly that "when 'we "describe the *formation of articles fnom such powders"wedo not 'intendto be limited :thereto, the scope of the invention being defined 'by theclaims *herinafter'appended- 'Asi's known tothose skille'd in this art, the formation ermine from compressed powders of the refractory metals andca'rbideshas followedtwo general methods of e .ppm: a'ch. "In one such method the powders were compressedby a 'ram operating'in conjunction with a die enclosure, and the powders 'were thus compressed into cylindricah polyhedral, or similar blocks. These blocks were then-sintered at high temperature. The 'ultimatedesired shapes were "then 'carved out :of such blocks by grinding or machining steps.

-Ina second methoda the 'was provided wherein the inner wall of the cavity-wasshaped to generally conform 'to the-ou-ter *wall of the ultimate article, as in a'mold ---formolten"metal,-and the powdered or comminuted par- .ticles were then pressed into the die cavity by a ram capable of *exerting tremendouspressure. Obviously for a shape of even average complexity the die must be a multi part one, so as tobe separableto permit removal of ithe article, and undercutcontours are extremely difiicult to :make in this way without multiplying inordinately the number of die parts. Again, in this method, the pressed aarti'clei iszsintered.

.As is alsorwelhknowniin this art there is a shrinkage tiactor on "sintering which results i in .a linear shrinkage of the article'to ran extent varying witha numbenof .factors, .iincluding the particular axis on which the :shrinkage is measured with relation to the direction of'ram pressure, the particle .size, the temperature of sinteriug, etc, and this shrinkage .in the case of carbides may amount :to *betweenfifteen and eighteen percent, linearly, "or forty Iotfifty percent, volumetrically. This-must be :compensated for incalculating the die dimensions.

-Even when vanarticle was made to thedesired shapein ametal .dieunder ram. pressureapplied either directly on an exposed surface of the powder .or on a. movable die part, a substantial. am-ountnof 'iinish grinding -.or.rnachiningwas always required inithe prior art practices.

One 'of th'e' disadvantages of article production as above described was the tremendous cost of the'final shaping operaticnspwhether doneby oneor the other'o'fthe. meth- -ods described. "The-cemented carbides areextre'mely'ha'rd 2,783,504 *Fatented Mar, 5, 1.957

.32 after sintering, "andmust be machined or ground by .spe-

cial tools or 'grindingw'heels which are "themselves :31 least as hard as the object on whichthey operate. .The portion of "the workpiecewhich 'isIgr un'dor cutaway constitutes .anexpensive loss, and thetools do 'notfhav e a long working life. w l

In an obvious admissiomt'hat these methods were. economically unsound, one'rnanufacturer has attempted To solve the problem, at least in part, byfirst compressing the "powders, fthen g'iving the"compressedblock or shaped article 'an initial partial fsinterin'g, 'then shaping the partially sintere'd material "to -approximately "the final contour, then finishingthe sintering, and finally completing the "machining operation. "Since afinaih machining step is not "avoided, at least "where "accuracy of tdlerancesis needed, the solution is not completely satisfactory a'lthough'somesto'ck can be-removed While in a relatively soft-condition.

Further, as is known to those skilled inthis art, *ih use of mechanical pressure, as"'heretofore characterized, produces 'uneven surface hardness, 'and unevenpenetra- *t'ionof the 'hardening'force-along di'iierently oriented axes with respect *to the "direction *of rampres'sure application and the shape of the article. This is especially true-Where *articles 'are being" for m-ed' incontoured metal dies wherein certain surface zones of the article are sheltered from the maximum pressure by die projections, etc.

last-named difiiculty by putting therefractorypbwdersin "a' flexible bag 1 and subjecting the bag to hydrostatic 'pres- "sure, but =here-agalin the final lump of =material-required expensive machining or grinding operations, and as the material is cut-away there arises considerable variationin surface hardness. p

The main reason why this particular arthasmaintained a commercial position despite the above-namedjand other difiiculties is that there exist situations *in which the physical properties of an article formed from cemented carbides or -refractory metals .are so necessary in some specific application that the customer will 'pay practically any .askingprice for the finished article.

An object of the present invention is to provide a method of forming articles directlyfrom metal powders with such dimensional accuracy that theycon'form tonormal dimensional tolerances, and 'final finishing steps, if ever required, are'ofsuch'minorcharacter that they=do not materially add to the cost of the article. "Usually, the accuracy of dimension of.articles made by our process is in the order of hundredths of an inch, with excellent accuracy of detail. Occasionally, if accuracy in thousandths .is required, a minor amount of'finish grinding suffices.

A further object of the invention isto provide "a method ofproducing articles as-defined inithe lastprecedingpara graph Wherein the density'throughout the finished article is uniform to a high degree.

A further objectuof theinvention is to produce-articles as defined in .the last two preceding paragraphsby'means oihydrostatic pressureefiective peripherally on a flexible die or mold, the interior contour of which is shaped to conform to the exterior contour of the ultimate article.

A further object of the invention is to produce shaped articles with undercuts and intricate contours, directly from comminuted powders in 'such way that the compressed article can 'be readily removedfrom the :die.

A further object of the invention is toproducezshaped articles directly from metal powders by hydrostatic pressure in molds of such character that die costqand' die wear are reduced toa minimum.

Further objects and advantageswillbe apparent from a study of the following 'desc'riptionoffthe invention, in conjunction with the accompanying drawings, in which die 10 so as to compress the material.

Fig. "1 is a diagrammatic sketch, in simplified form, showing structural elements such as were used in the compression of metal powders in the prior art.

Fig. 2 is a pictorial-representation of density variation in the cross section of a polyhedral block made by means of the apparatus shown in Fig. -1.

Fig. 3 is a diagrammatic showingof a specimen under hydraulic pressure in accordance withthe principle outlined in the description hereinbelow.

Fig. 4 isa diagrammatic sectional showing of a hollow flexible mold having a powder charge therein, and closure means thereon.

Fig. 5 is a diagrammatic showing of a metaldie, a cavity for hydraulic fluid, a powder-containing mold in the cavity, and means for applying hydrostatic pressure within the cavity.

Fig. 6 is a perspective view of a four-bladed helical cutter of a type susceptible of ready manufacture by our invention.

Fig. 7 is a fragmentary perspective view of a flexible mold and closure suitable for use in making the cutter shown in Fig. 6.

Fig. 8 is a perspective view of a chuck wrench susceptible of ready manufacture by our invention.

Fig. 9 is a fragmentary perspective view of a flexible .mold and closure suitable for use in making the wrench ,shown in Fig. 8. g

Fig. 10 is a showing similar to Fig. 5, but in which a resilient insert has been substituted for a hydraulic fluid.

Referring now to the drawings, in generally numerical order as this description proceeds, we show a metal die 10 which has a bored aperture 11 therein, adapted to slidingly receive a lower plunger or ram 12 and an upper plunger or ram 13. Asexemplary of one preferred proccss of the prior art, comminuted metal powder 14 is bond between the particles.

Fig. 2 pictorially represents one such block 15 which has been sintered, cut vertically, and suitably etched to I indicate the effect of the ram pressure on the internal structure, the pressure having been applied in the direction of the arrows P. The zones 15a and 1517 are of roughly piano-convex shape, which may here be termed for convenience lenticular, and plainly indicate that the pressure at the center was effective to a maximum extent, the effect falling off gradually towards the peripheral face 15c of the block. The central zone 15d, of double-concave contour, represents an area of reduced density;

From a consideration of Figs. 1 and 2 it will be evident that in the prior art process just described the powdered material around the inner die periphery, by reason of friction on the die wall, and because there is only a limited number of'directions to go, namely in a 90 ,quadrant downwardly and towards the center, will tend inevitably to take .on vthe lenticular density characteristics just described. Obviously when an article of irregular shape is. carved from the block 15, the cuts or ground outhollows extending to varying depths, there will re- -sult an article-of varying surface hardness depending on the depth of penetration and the location of penetration.

This is quite undesirable where a uniform hardness is required by the particular application.

Fig. 3frepresents, pictorially, a very desirable type 4 of pressure application such as has been used in the prior art to achieve an even surface density in a lump of'material. The cube 16 in this case represents a pliable closure such as a bag filled with comminuted metal powder and dropped into a strongly built die or closure 17 filled with liquid 18 such"as'6il' or the like. Pressure is then. applied to the liquid by means of the piston 19 and, the pressure being hydraulic, is effective equally in all directions as indicated by the arrows. As previously explained,'even' this method is expensive, since the final article must be machined or ground out of the block thus produced. j

The economies which we have as one of our objects result from the achievement of a fully compressed structure in an article formed to final shape during the initial pressing operation, the density being uniform throughout at points equidistant from the article surface.

Since it is apparent that one of the most fundamental problems of this art is that of compacting the powder to final shape, with uniform internal structural density, and since it has been impossible in the past to achieve the final shape of the article without extremely expensive final shaping operations on the more refractory and harder metals and alloys, it occurred to us that what was needed was to develop an inexpensive but accurately contoured mold upon which hydrostatic pressure could be used in such way that the pressure is as fully effective on the comminuted metals as if the mold did not intervene.

After extensive study and experimentation we have developed a process which greatly extends the field of powdered metal compression into accurately formed yet inexpensively produced articles.

Our process comprises the use of a soft elastic mold made from rubberor rubber-like material. Such mold may be formed around a pattern identical in shape with the article to be formed except of course that compression shrinkage and eventual sintering shrinking must be allowed for, and the pattern and mold made sufficiently oversize to compensate for such shrinkages.

In one method of making the mold liquid rubber was cast around the pattern, and stripped off after solidification. Obviously an aperture must exist to permit removal of the pattern and insertion of the powdered material, and the mold wall must be sufficiently strong to retain its contour when filled with comminuted materials. This method of manufacturing the mold permits the existence of undercuts and other surface irregularities which would be economically impractical to form in a rigid mold, and thereafter it would be impossible to remove the compressed article from a rigid mold.

The pattern may be made from a number of rigid materials such as wood, ferrous metal, the low melting point metals such as lead, bismuth, antimony, tin, etc., and alloys thereof, or even wax. In case of the low melting point alloys or wax, the pattern can be removed from the mold by melting, which permits even more intricately-shaped contours with involved undercuts to be used for the manufacture of the pliable mold.

Fig. 4 shows, in vertical section, a rubber mold 20 having a comminuted metal charge 21 therein. It is shown as provided with offsets or ears 21a and 21b which would render it impossible to remove the final article from a rigid die, but an inexpensive rubber mold can be stripped or cut therefrom. This showing of Fig. 4 is merely diagrammatic, and the rubber wall is made thick enough to hold its shape in actual practice, and flexible enough to allow sufiicient compression of the powder to the pressed shape of the final article.

When the mold of Fig. 4 is filled with powder, it may be placed in a vacuum chamber and air evacuated therefrom since air in the interstices of the powder forms voids or porosity in the final article. A closure 22 is then sealed thereon, or otherwise attached was to seal against hydrostatic pressure. The sealed mold is dropped into a dead end bore 23 of a die 23a (Fig. in which there is a hydraulic fluid. Above the fluid is a piston 24 propellable by a plunger 25. Between the plunger and piston is a sealing washer 26. The manner of use is obvious from what has just been described. When heavy pressure is applied to the hydraulic fluid it produces hydrostatic pressure on the yieldable mold and consequently on the powdered material in the mold. The effect of such pressure has been discussed hereinabove. Again, as in previous drawings, the showing in Fig. 5 has omitted many mechanical details necessary in practice, but not at all necessary for an understanding of the present invention.

Fig. 6 shows a rotary cutter 28 with helical teeth 29, obviously diflicult or impossible to produce by using a rigid die, but well adapted for forming in a flexible:- shaped die such as shown in Fig. 7. Fig. 8 shows a chuck wrench having a plain cylindrical shank 31 and a bevelgear nosepiece 32. This is easily reproducible from the mold 33 in Fig. 9. The mold cavities of Figs. 7 and 9 are shown a noticeable amount oversize with respect to the articles respectively formed therein, merely as an indication that a predeterminable relationship exists, having in mind the known compression shrinkage and sintering shrinkage of the particular material. In the sintering process, of course, a true inter-molecular bond develops between the closely packed metallic particles.

A remarkable and useful feature of our process as above described is that the article which emerges from the sintering step is an exact replica of the pattern, except for the linear and volumetric shrinkage.

Fig. shows an embodiment wherein a conventional steel die 35 has a shaped insert 36 therein of rubber or rubber-like material. There can then be a lower anvil or plunger 37 and an upper plunger 38. Compression of the powder 39 produces a quasi-hydrostatic pressure in the material compacted into the mold aperture. Die wear costs can be reduced by this method since the insert 36 is replaceable at any time.

The method above described is the most economical method so far developed for reproducing small parts, of accurate contour and even density and in large numbers. Non-miscible metals may be alloyed, the porosity may be controlled, the chemical analysis may be very accurately fixed, and laminated combinations and metalceramic mixes may be achieved. As suitable materials we may mention molybdenum, tungsten, the carbides of said metals, titanium, zirconium, etc. These can be satis- Y factorily sintered at about two-thirds of their respective melting points, and eutectic temperatures should be borne in mind in mixing and sintering mixtures of metals.

In the manufacture of intricate parts in large numbers, savings of about ninety percent may be effected under the cost of the older method of using rigid dies and mechanical rams which must be followed by tedious shaping steps.

Not much has been said so far of the manufacture of articles from the non ferrous metals, for example aluminum and its alloys. In prior art methods aluminum was not usually used as a materal for powder compression, since the pressing problem caused by material sticking to thedies makes powder metallurgical methods more expensive than conventional casting or mechanical deformation methods. Recent developments have shown t at the oxide layer on aluminum particles, if properly controlled, allows the fabrication of a new aluminum alloy from such powder which has exceptional high-temperature mechanical properties above the softening point of the normal aluminum alloys.

With this most recent development, attention has been given to the development of new techniques for pressing this material in order to eliminate the die sticking problem. Our solution lies in the hydrostatic pressure of preforms and articles in pliable molds.

The equipment problem is simplified since one hydro static die of adequate capacity, equivalent to the die 23a of Fig. 5, can accommodate simultaneously a number of molds for articles of varied sizes and shapes.

As in previous practices in compressing of articles from comminuted metals there is a practical upper limit to the size of articles which can be produced, of adequate overall density and uniform hardness at points equidistant from the outer surface.

In the present application the term refractory material is intended to include carbides such as silicon and tungsten carbide, as well as the high melting point metals such as molybdenum, tungsten, titanium and vanadium and their alloys and compounds and mixtures thereof.

What we claim is:

1. A process of forming an article having surface irregularities such as undercuts and the like, comprising providing a hollow mold formed from resilient material, said mold having walls of a thickness adequate to be self-supporting, forming the wall of the casting cavity of said mold to be complementary in contour to that of the article surface with respect to said irregularities and undercuts, but sufficiently oversize to compensate for article shrinkage during formation thereof, filling said mold with comminuted refractory material, placing said mold in a closure with suflicient liquid to immerse said mold completely, applying hydrostatic pressure to said liquid until said comminuted material is compressed to solidity and to the size of the final article, and stripping said mold from said article while maintaining said mold intact.

2. A process of forming an article having surface irregularities such as undercuts and the like, comprising providing a hollow mold formed from resilient material, said mold having walls of a thickness adequate to be self-supporting, forming the wall of the casting cavity of said mold to be complementary in contour to that of the article surface with respect to said irregularities and undercuts, but sufficiently oversize to compensate for article shrinkage during formation thereof, filling said mold with comminuted material of the class consisting of ferrous metals, refractory metals and refractory compounds, placing said mold in a closure with sufficient liquid to immerse said mold completely, applying hydrostatic pressure to said liquid until said comminuted material is compressed to solidity and to the size of the final article, and stripping said mold from said article while maintaining said mold intact.

References Cited in the file of this patent UNITED STATES PATENTS 1,081,618 Madden Dec. 16, 1913 1,226,470 Coolidge May 15, 1917 1,981,719 Comstock Nov. 20, 1934 1,983,602 Daubenmeyer Dec. 11, 1934 2,220,018 McKenna Oct. 29, 1940 2,298,908 Wentworth Oct. 13, 1942

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