US2479364A

US2479364A - Method of making molds

Info

Publication number: US2479364A
Application number: US624495A
Authority: US
Inventors: Douglas L Jocelyn
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-10-25
Filing date: 1945-10-25
Publication date: 1949-08-16
Anticipated expiration: 1966-08-16

Description

D. L. JOCELYN METHOD OF MAKING MOLDS Aug. 16, 1949.

2 Sheets-Sheet 1 Filed 0G12. 25, 1945 &\\

IN VEN TOR.

Aug. La, 1949.y

Filed oct. 25, 1945 D. L. JOCELYN METHOD 0F MAKING MOLDS 2 Sheets-Sheet 2 f24 if ///'//1 INVENTOR.

Patented Aug. 16, 1949 PATET oFFlCE This invention relates to molds for useV in the production of cast or molded articles and particularly to so-called permanent type molds which may be used repeatedly for the production of relatively large numbers of castings in the same mold. An important object of the invention is to provide a metallic mold which is permeable in character thereby permitting the rapid escape of gases from the mold cavity during the casting operation and as a consequence enabling superio castings or molded articles to be made. A further object of the invention is to provide a sintered metal mold formed of powdered metal which, before sintering, is pressed through the medium-of dies under great pressure to produce the casting cavity, the mold having substantially all of the advantages of a conventional permanent mold yet'capable of being produced at a fraction of the cost theerof, thus enabling many articles to be cast by permanent mold methods which otherwise would not be possible owing to the great cost of conventional type permanent molds.

Still another object of the invention is to provide a sintered powdered metal mold which is self-venting due to the permeability thereof and which is thus capable of producing a casting having a smoother surface than ordinary molds.

A further object of the invention is to provide a permanent metal mold of relatively inexpensive character in which the portions of the mold having the casting cavity or cavities are formed of and having a high degree of uniformity in the y density of the walls of the mold.

Still another object of the invention is to produce a powdered metal foundry mold of substantially uniform density for casting an article of irregular contour, such as an article having protruding bosses `or stepped portions forming different levels, as a result of which uniform density and freedom from distortion during heat treatment of the mold brlquette are not possible by the use of conventional methods of forming the -briquette from powdered metal. AIn accordance with the present invention, however, I introduce into the die cavity containing the loose or un.

compacted powdered metal one or more preformed briquettes of powdered metal which has been partially compressed to predetermined density, the pre-formed -briquettes of required size andshape being positioned in the die cavity at localities where different levels are present in the punch. Upon compression of the material between upper and lower punches the pre-formed briquettes' are consolidated with the powdered mass and augment the density of the final briquette at the localities where variations in density would otherwise occur due to the different levels on the punch. Thus, by the use of these preformed briquettes it is possible to compensate for variations in density which otherwise would occur in the formation of a powdered metal mold.

A further object of the invention is to produce a powdered metal mold having sumcient permeability to cause the mold to be self-venting during the casting operation, and invaddition to provide a metallic surfacing of chromium, or other high heat resistant metal, on the mold permitting molten metals to be poured at higher temperatures in the mold while reducing the tendency of the pores of the mold to become closed or blocked as the result of fusing of the surface of the mold in contact with the molten metal. Such metallic surfacing of the mold renders the mold highly wear resistant and more durable while at the same time providing a smoother, harder surface capable of producing smoother surfaces on the castings.

This application is a. continuation in part of my application Serial No. 572,117, filed January 10, 1945, now abandoned.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specication wherein like reference chaarcters designate corresponding parts in the several` views.

Fig. 1 is a side elevation of a mold unit or section constructed in accordance with the present invention, this view being taken substantially through lines I-I of Fig. 2 looking in the direction of the arrows.

Fig. 2 is an enlarged section of the assembled mold units or sections taken substantially through lines 2-2 of Fig. 1 looking in the direction of the arrows.

Fig. 3 is a sidevelevation of the assembled mold shown in Fig. 2.!

Fig. 4 is a fragmentary sectional view of a punch and die apparatus for forming the powdered metal mold unit.

Fig. 5 is a view similar to Fig. 4 illustrating the position of the upper punch at the commencement of a pressing operation.

Before explaining in detail the present infention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology -employed herein is for the purpose of description and not of limitation.

It will be understood that the invention is capable of use in casting or molding a wide variety of articles from dierent materials. principally metal and its alloys, thermoplastics and thermosetting resins. Any suitable number of articles may be cast simultaneously in the same mold and in the present embodiment I have shown a mold constructed to cast two articles, each of which is cast in a mold cavity formed partly in one mold section, such as the cope, and partly in the other mold section, such as the drag.

In the drawings, wherein one embodiment is illustrated by way of example, the mold comprises two sections I and II, preferably in the form of cast iron blocks, assembled along a lpart-- ing line I2. The block II) is provided with a pair of similar bores I3 and in like manner the block I I is provided with a pair of bores I4. These bores preferably extend entirely through the supporting blocks III and II, the bores I3 being adapted to receive. cylindrical powdered metal mold inserts I and the bores I4 being adapted to receive cylindrical powdered metal mold inserts I 6. The corresponding pairs of mold inserts I5 and I6, when positioned within their respective bores, meet at the common parting line I2. In the present instance, each mating pair of -powdered metal mold inserts I5 Aand I6 are formed to provide a common casting cavity C, as shown in Fig. 2. As hereinafter described, the mold inserts are formed of sintered powdered metal such as ferrous metal or an alloy thereof, and the cavities C are shaped so as to produce the desired articles when the molten metal congeals within the cavities after the pouring operation. In the present instance, each insert I6 is formed with a portion I1 of a riser extending upwards from the cavity and communicating therewith. Each riser portion I1 communicates with a riser portion I8 formed in the supporting block I I for the inserts I6. Also each mold insert I6 is formed with a portion I8 of a runner gate leading into the cavity C from below.

The supporting block II is cast or otherwise fabricated to provide diverging runner gate portions 20, as clearly shown in Fig. l, register with which leads upwards to the sprue passage 22 into which the molten metal is poured. The gateportions 20, as clearly shown in Fig. 1, registers with the gates I9 through which the metal enters the cavities C.

The powdered metal mold inserts I5 and I6 have a smooth sliding fit within their respective bores I3 and I4 in the supporting blocks I II and II. Thus, when assembling the mold, the mold inserts will slide cinto the bores until flush with the inner upright faces of the blocks I0 and II 4 l at the parting line I2. They are then rigidly clamped in place by means of retainer bolts 23 extending through tapped holes in the blocks III and II and engaging the inserts. The blocks Il! and II, with their assembled mold sections. are then assembled as illustrated in Fig. 2, being clamped together in tight abutting relation at the parting line I2 in any conventional mannen after which the castings are poured. lSuitable knock-out pins (not shown) of any conventional kind may be mounted in the inserts I5 and I6 for ejecting the castings after the mold sections have been separated. Thereafter the riser and gate portions of the castings are removed to -provide the finished article.

The mold inserts I5 Yand I6 are prepared from powdered metal, preferably ferrous metal or an alloy thereof, and are shaped under high pres- 'sure and then sintered. In Figs. 4 and 5 there is illustrated a press designed for the purpose of forming the mold inserts I5, it being understood that the mold inserts I5 will be formed in substantially the same manner as the inserts I5. As illustrated in Figs. 4 and 5, the press herein utilized to prepare the powdered metal mold inserts comprises a bed or bolster 2l and a side die 25 supported upon the bed by means of removable blocks 26. The die 25 has a central vertical bore 21 corresponding in diameter to the bore I3 or I4 in the mold Supporting block III or II.- Suitably anchored to the bed 2l of the press Ais a lower punch 28 having a vertically extending cylindrical portion fitting into the bore 21 in the die 25 and in the present instance terminating in a flat top surface 29. The press also comprises an upper vertically' reciprocable punch 30 of a diameter to have a sliding t within the bore 21 of the side die 25. The working end of this punch is shaped to produce, in cooperation with the bottom punch and side die, the powdered metal mold insert I5 with its portion of the casting cavity C. Accordingly, the punch has an annular surface 3l which produces that portion of the mold insert I5 lying along the parting line I2. 'I'he nose of the punch, which protrudes downwardly below the surface 3i, is formed with

sections

32, 33 and 34 which lie at diierent levels, the portions 32 and 33 vlbeing joined by an upwardly curving or inclined surface 35. a

In order to obtain as high a degree of accuracy as possible in respect to shape and dimensions of the casting cavity C, it is important that the.

cavity'in the insert will also have these corre-v sponding levels, as indicated by the

levels

32, 33 and 34 in Figs. 4 and 5. If it is attempted to prepare the mold insert by compressing a mass of powdered metal introduced between the

punches

28 and 30, the powder at the different levels of the punch 30 will be pressed under different pressures and the densities of the compressed powder will correspondinglyvary. In other words, uti-` lizing the punch 30 shown in Figs. 4 and 5, the powdered metal after compression would normally be compacted to the greatest extent so as to produce the greatest density opposite the' highest level 32 of the punch. The density of the powdered m'etal would decrease opposite the curved surface and would be increasingly less opposite the successive

lower levels

33, 34 and 3| in proportion to the distances of these levels from the level 32. Thus, in the absence of mold compensating means in accordance with the present invention for increasing the density of the powdered metal opposite the different levels 3|, 33, 34 and 35, the finally compressed powdered mold would have widely varying densities and would not produce a satisfactory mold after the sintering operation. This variation in compactness and density arises from the fact that the metal powder will not flow under pressure as in the case of flowable or plastic materials, and hence, the compression of the powder opposite different levels of the punch will vary.

According to the present invention, therefore, I obtain a high degree of uniformity in density of the pressed metal powders by compensating CII for the lower levels in the punch through the medium of pre-formed powdered metal briquettes. These briquettes are pre-compressed to the desired extent and are so dimensioned that they may be positioned within the die before the pressing operation commences and arranged opposite and coextensive with the lower levels of the punch so as to increase the density of the final mold to the desired extent. Thus, as illustrated in Figs. 4

and 5, an annular or ring-shaped pre-compressed powdered metal briquette 3l is positioned opposite the annular flat surface forming the lowest level 3| in the punch 30. A pre-compressed powdered metal briquette 38 is positioned opposite the surface forming the next lower level 34, the adjacent surfaces of briquette 38 and level 34 being coextensive. A pre-compressed powdered metal briquette 39 is positioned opposite the next lower level 33, and a pre-compressed briquette is positioned opposite the curved level 35, the adjacent surfaces of these briquettes and the associated portions of the punch being coextensive.

With the lower punch 28 and die 25 positioned in the press as illustrated in Fig. 4, and the upper punch 30 retracted, a mass of powdered metal 4| is introduced into the bore 21 ov'er the lower punch, the level of ll of the powder being indicated by the line 42. Thereafter the pre-formed and pre-compressed powdered metal briquettes 31-40 lare embedded in the powder 4| and arranged opposite the various levels of the punch 3D, as clearly illustrated in Fig. 4. After the preformed briquettes have been properly positioned and firmly embedded in the powder, an additional small amount of metal powder may be sprinkled over the briquettes in order to ll any crevices, cracks or voids therebetween and provide a slight covering therefor. Thereupon the upper punch 30 is caused to descend so as to position the same in the shaped cavity formed between the pre-formed briquettes 31-40 and the intervening level of powder 42, as in the manner shown in Fig. 5. With the lower punch in stationary position on the bed 24 and the die 25 in like manner supported on the removable blocks 26, the descent of the'upper punch is continued so as to apply pressure and compress the powders, resulting in consolidating the pre-formed briquettes intimately and homogeneously with the mass of loose powder 4|. Thereupon the pressure of the upper punch is released to permit removal of the blocks 26, after which the upper punch is caused to descend again. Inasmuch as the die 25 at this time is unsupported it will move in unison with the upper punch relative to the lower punch 28 thereby resulting in upward pressure being exerted by the stationary lower punch against the bottom of the compressed briquette equalizing the density of the powder. The briquette thus compressed under predetermined pressure will be of substantially uniform density throughout and may thereafter be heat treated or sintered to produce the nal mold unit I5 Without danger of any appreciable buckling, warping or distortion. It will be understood that the mold unit 16 or any other selected mold unit or section may be produced in accordance with the foregoing described method utilizing pre-compressed briquettes at regions where variations in levels exist so as to increase the amount of powder at these regions and compensate for variations in density of the compressed powdered metal which otherwise would occur by the use of conventional methods.

It will be manifest that the dimensions as to width, height and shape of the pre-compressed or pre-formed briquettes 31-38 will be governed by the dimensions of the low level areas of the upper punch, or the complementary areas of the article being formed, as well as the differences in height of the several levels. The densities of the precompressed briquettes may of course vary but should be selected in advance in order to determine the correct heights or thicknesses in a vertical direction of the briquettes. The amount of pre-compression of the powder' to form the briquettes 31-39 should preferably be such as to give as low a density as possible while permitting safe handling thereof without disintegration or crumbling of the briquette. Assuming that the selected density of the finally compressed -mold is on the order of grams per cubic centimeter, and

the compression ratio is approximately three tol one, the pre-formed briquette may be satisfactorily formed with a density on the order of approximately 70 grams per cubic centimeter. The height or vertical thickness of the briquette may be readily calculated by the following formula:

where D1 is the desired density of the final briquette, D2 is the selected density of the

pre-formed briquette

31, 38, 39 or 40; H is the distance between the highest level and the level opposite which the briquette is to be placed; and T is the vertical thickness of the pre-formed briquette.l Assuming that 'the distance between levels 3| and 32 is three inches, and using the density values mentioned above by way of example, then the vertical thickness of briquette 3l would be calculated as follows: f

g-X 3= 4.07 inches It will be understood that the densities of the pre-formed briquettes may be varied to suit condit-ions and that small amounts of suitable binders, such as sugar water, syrup or any other material which on heat treatment will char or reduce to a harmless carbon residue, may be added to the metal powder in order to facilitate handling of the pre-formed briquettes. Irregular Aor odd shapes of pre-formed briquettes may be formed in suitably shaped dies or may be cut from pre-formed plates, slabs, cylinders, rings, etc.

From the foregoing it will be seen that substantially uniform density distribution, equalization of strength throughout all sections of the nnal briquette, freedom from distortion during heat treatment or sintering, and greater accuracy in detail of contour and shape are achieved by virtue of the present invention. As a consequence the molds I5 and I6 produced from sintered briquettes ln accordance with the present method will not only be highly permeable but will be stronger, more durable and lasting and more accurate in all respects.

Although castings produced in ferrous metal molds embodying the present invention will have relatively smooth surfaces free from excessive pitting, even superior results may be achieved by providing a metallic surfacing or coating over the inner surfaces of the molds I5 and yI6. A thin film of chromium, or other high heat resistant metal, is deposited over the mold surfaces by ordinary electrolytic procedure. However, the deposition of the chromium is conducted so as to eliminate the absorption of hydrogen by the metal which, in carrying out the4 process, is in effect de-hydrogenated. 'I'he chromium film will not obstruct or Iclose the minute pores which permeate the mold but instead form thin protective walls or layers around the pore openings at the surface of the mold, and due to its high heat resistance properties will prevent over prolonged periods of use any tendency of the metalpf the mold to fuse at the surface thereof and close oif the pore openings. The pores in the surface of the chromium film provide a multitude of tiny expansion areas enabling the chromium film to expand and contract sufdciently to resist cracking, aking or peeling during the casting operation. A chromium surface powdered ferrous metal mold in accordance with the present invention may be used advantageously for casting various metals, such as' aluminum and brass. In fact, highly successful results have been obtained in making repeated runs of steel castings in a powdered ferrous metal mold surfaced with chromium. Even though the molten steel was poured at a temperature on vthe order of 2800 F. no destructive effects on the surface of the mold were discerned.

I claim:

1. The method of making a powdered metal mold utilizing a forming punch contoured with different levels, including the steps of supporting a loose mass of powdered metal in a confined space opposite said punch, positioning a pre-compressed powdered metal briquette in said mass opposite a lower level of the punch, and consolidating said mass and briquette together by pressure exerted vthereon by said punch.

2. The method of making a powdered metal mold utilizing a forming punch contoured with diierent levels, including the steps of supporting a loose mass of powdered metal in a confined space opposite said punch, positioning a plurality of pre-compressed powdered metal briquettes of different thicknesses in said mass opposite the different lower levels of the punch, and consolidating said mass and briquettes by pressure of the punch.

DOUGLAS L. JOCELYN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,809,872 Solderberg June 16, 1931 2,042,635 Schellens June 2, 1936 2,048,222 Rehmann July 21, 1938 2,121,448 Ritzau June 21, 1938 2,298,885 Hull Oct; 13, 1942 1 2,299,192 Tormyn Oct. 20, 1942 2,397,831 Bellamy Apr. 2, 1948 FOREIGN PATENTS Number Country Date 330,018 Great Britain June 5, 1930