US1491817A - Method of casting - Google Patents

Description

April 29, 1924.

. C. PACK METHOD OF CASTING Filed Dec. 1, 1922 2 Shee'ts-Sheet 1 lllll INVENTOR.

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CHARLES PACK, OF ELMHURST, NEW YORK, ASSIGNOB TO DOEHLER DIE-CASTING- COMPANY, A CORPORATION OF NEW YORK. 4

METHOD or cas'rme.

Application filed December 1, 1922. Serial no. 604,128.

To all whom it may concern:

Be it known that 1, CHARLES PACK, a citizen of the United States, residing at Elmhurst, in the county of Queens and State of 6 New York, have invented certain new and useful Improvements in Methods of Casting, of which the following is a full, clear, and exact description.

While my method is of general applica- 10 tion in the casting art it is particularly applicable and will have its chief use in the art of die-casting,

An object of my invention is to provide a practical method for making castings having internal undercuts, where because of the size or shape of the cavity or for other reasons a collapsible core cannot be employed advantageously.

In accordance with my invention I cast directly upon a metal core which is suificiently soft to yield orflow when forcibly pressed against a part formed of the casting metal, and I then forcibly extract the core from the casting, thereby causing the metal of the core behind the undercut of the casting to yield or give way and let the core come out. Just what happens to the metal of the core depends upon the depth and shape of the undercut. In some cases the trapped'part of the core will be sheared ofi' in others the metal will be gouged out or will be displaced while in others it will -progressively be conformed to the cavity as the core is being withdrawn, as where the cavity includes a series of reverse bends.

Where'the design calls for sharp lines or edges, of for small protuberances or other like features on the molding surface of the core which are easily blurred'or eradicated 40 by partial fusing, it is generally preferable to use for the core a metal having at least substantially as high a fusing point as has the casting metal. For many purposes a metal of even lower fusing'point may be employed for the core. The specific heat of the casting and also its masswhich determines rough y the quantity of heat contained in it will be considered in selecting the metal for the core. Generally speaking to the heat interchange'must not be suflicient to raise any part of the core to the fusing point, and this depends upon several factors, such as the specific heat of the core metal, the contour of its surface, and its size or mass. In carrying out my method I re date the temperature of the casting meta so as to keep it below that which would effect a heat transfer to the core sufficient to cause surface fusion, while the temperature is generally maintained as high as conditions will warrant to assure perfect fluidity.

It is well known that alloys of metals generally fuse at apoint substantially lower than that of either of their constituents.

For example, pure aluminum, which is rela- For example, the fusing point of an alloy of 75% aluminum and 25% copper is substantially 1080 F. while that of aluminum is substantially 1250 F. In practice that alloy could be cast at even 1300 F. upon an aluminum core for cavities of the ordinary size and shape without any fusion of the surface of the core, and at that tem erature or even lower such an alloy casts per ectl As an illustration of the use of my method, I shall describe it as employed in the diecastin of a golf ball mold, although it will .be un erstood that the application of my invention is not limited except as, pointed out in the appended claims.

As is well known, the surface of substantially all golf balls is charaterized by a design formed of dimples or small depressions symmetrically and closely arranged.

One of the last operations in the formation of the balls is the molding of this design in.

the surface, the mold consisting! of two hemispherically recessed mold parts the molding-surface of which has small rounded elevations complementary to the dimples in the surface of the ball.- Heretofore these molds have been machined out at comparetively large expense, but my method provides a way to die-cast them, thereby'very materially reducing their cost..

I first make the core, for example, from aluminum, of the necessary size, shape and surface configuration, and then with a proper die make the cast about the core, using a suitable aluminum-copper alloy, for example, for the casting. The casting with the core locked therein is then removed from the die and with a suitable appliance the core is bodily drawn out of the casting. If necessary to do any machining on the casting, this may conveniently be done before the core is removed.

I shall now describe my method with the aid of the accompanying drawings in which I show apparatus suitable for one adaptation of my invention, and shall thereafter point out my invention in claims.

Fig. 1 is an elevation of a core for use in die-casting a golf ball mold.

Fig. 2 is a cross section of the same on line 2-2 of Figure 1.

Fig. 3 is a section of an assembled die with the core in place.

Fig. 4 is an outside elevation of the half die carrying the core.

v Fig. 5 is an elevation of the casting and core.

Fig. 6 is a section of thesame after the casting has been machined.

Fig. 7 is a section of the casting and a partial section and partial elevation of the core showing the core withdrawn sufficiently to be free of the casting.

While the core element shown in detail in Figures 1 and 2 may be formed in any suitable way, I prefer to turn it from bar stock for reasons which will hereinafter appear, and then machine the dimples in the molding surface. A. suitable metal for this purpose is aluminum. The core, as shown, has a hemispherical end 1 in which the depressions or dimples 2 are formedin any suitable way, as by machining, the diameter and surface configuration of the portion 1 being a replica of one half of a golf ball. This hemispherical end merges into a plain, cylindrical zone or band 3 of proper width, the forward limitation of which is indicated $1 the dotted diametral line in Figure 1. he purpose of this band will presently appear. Back of the zone 3 the diameter is reduced to form a shank or stem 4: for anchoring in the die.

The two halves of the die are shown in Figure 3, the one half 5 containing the mold cavity 6 and carrying the core, and the other half 7 containing the gate or sprue opening 8. The mold cavity 6 is shown as undercut, being of substantially frusto-conical shape. Therefore, the mold 9, as shown in Figures 5 to 8, has its side walls thicker at the top than would be the case if the top diameter were the same as the bottom diameter. Due to the ressure to which these molds are subjected to the molding ofgolf neei'erv balls, it is desirable to provide this substantial thickness of wall throughout.

To enable the removal of the mold 9- from the die, the half 5 of the die is made in two parts, dividing on the central transversealine 5", as shown in Figures 3 and 4.

A. suitable metal for the casting is aluminum-copper alloy such as commonly used in die-casting since this possesses the requisite strength and hardness and casts easily, and also has a substantially lower melting point than aluminum.

Following the casting operation, the core and casting are removed from the die, appearing at that point as shown in Figure 5. The round bosses or elevations 10 on the upper part of the surface of the concavity of the mold 9 interlock with the corresponding dimples in the core face. The mold may now be mounted for machining with respect to the shank or stem 1, and since the core was originally turned, it follows that the mold may be accurately machined about the axis of the core as a center. In this operation the face of the mold surrounding the core is machined down to'the diametral line of the core, which is the dotted line indicated in Figure 1, leaving the zone 3 of the core protruding beyond the face of the mold. This condition is shown in Figure 6.

Finally while the mold 9 is firmly held a pull is exerted on the core suficient to extract it from the casting. This causes the dimples 10 in the upper rows to shear or gouge the metal between the rows of dimples 1n the core, mutilating the core to this extent as shown in Figure 7. l have found that the metal of the mold stands up well without any appreciable deformation from its action upon the core during this with drawing operation.

llt is obvious that my invention is in no wise confined to the particular details of the steps as explained above, but that the details may be variously modified by those skilled in the art to adapt the method to particular conditions without departing from the spirit and scope of my invention as pointed out in the appended claims.

ll claim:

1. The method of making castings with an internal undercut consisting in casting about a suitably shaped and relatively soft metal core, a materially harder metal having its fusing point and specific heat so related to those of the core metal that the heat transference during the casting operation will he insuflicient to raise the core surface to the fusing point, allowing the casting to set, and then forcibly extracting the core from the casting.

2. The method of making castings with an internal undercut consisting in casting a relatively hard metal about a relatively soft metal core having a complementary lid undercut, and extracting the core by applying a pulling force thereto sufiicient to cause the metal of the core behind the internal undercut of the casting to give Way as the core is withdrawn.

3. The method of makin castings with an internal undercut consisting in casting a relatively hard metal about a suitably shaped core composed of substantially softer metal having a higher melting point, and extracting the core by applying a pulling force thereto suflicient to cause the metal of the core behind the internal undercut of the casting to give way as the core is withdrawn.

4:. The method of making castings with an internal undercut consisting in forming a suitably shaped core of a substantially pure and comparatively soft metal, casting upon this core a comparatively hard alloy of the metal, and extractin the core by applying a pulling force tiereto sufiicient to cause the metal ofthe core behind the internal undercut of the casting to give way as the core is withdrawn.

5. The method of making castings with an internal undercut consisting in casting a hardaluminum-copper alloy about a suitably shaped core of substantially pure aluminum, and extracting the core by applying a pulling force thereto sufiicient to cause the metal of the core behind the internal undercut of the casting to give way as the core is Withdrawn.

6. The method of making castings with an internal undercut consisting in forming a suitably shaped core of comparatively soft metal, casting about the core a harder metal capable of shearing the metal of the core, and shearing off the portion of the core behind the undercut by exerting a direct pull on the core to withdraw the core from the casting.

In witness whereof, I hereunto subscribe m si ature.

y gn CHARLES PACK.

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