US2256913A - Manufacture of wire-drawing dies - Google Patents

Description

Sept. 23, 194 E. B. WELCH MANUFACTURE OF WIRE'DRAWING DIES Original F iled May 2, 1959 INVENTOR Patented Sept. 23, 1941 MANUFACTURE OF WIRE-DRAWING DIES Elmer B. Welch, McKeesport,- Pa., assignor to Firth-Sterling Steel Company,

Pennsylvania.

Original application May 2,

a corporation of 1939, Serial No.

271,318. Divided and this application September 16, 1940, Serial No. 356,928

1 Claim.

This invention relates to the manufacture of wire-drawing dies, and consists in improvements in apparatus for the manufacture of such dies. The object is to produce a die of superior quality, a die more certainly secure against accidental breakage, and, accordingly (the average product being considered) a dieof enhanced durability.

The application for this patent consists in a division of my application Serial No. 271,318, filed May 2, 1939.

In the accompanying drawing Fig. I is a view partly in elevation, partly in vertical and axial section, of a press and of the parts that go to make up the die assembly in position in the press, ready to be acted on; Fig. II is a like view of the same collocation, after the press has operill ated upon the parts in place within it; Fig. HI

is a view in perspective of the nib of the die, before assembly with its carrier; Fig. IV is a view in perspective of the completed die; and Fig. V

is a view in axial section of a finished die.

A wire-drawing die includes a nib and acarrier. The nib is formed of a very hard metal composition of relatively high melting-pointsuch a composition, for example, as may be prepared by sintering a mixture of a hard metal carbide with a binding metal, such as cobalt. The nib is essentially a small cylindrical body having (ultimately) an axial perforation through it. It is initially prepared for the purposes of this invention as a cylindrical block 2 (Fig. III) having in one head a central conical recess, 15, but being otherwise of unmodified cylindrical shape. The carrier is a heavy walled casing, and consists essentially of a cylindrical block of softer metal (and of lower melting-point) having an axial bore of diameter sufficient to receive the nib. The bore is shouldered within, and upon the shoulder the nib rests and in such position the nib is secured to its carrier. The casing serves to carry the nib and in the wiredrawing operation to re-enforce the nib, and to prevent the cracking of the nib under the stressesof service.

It has heretofore been proposed to mount such a wire-drawing nib in a steel casing by assembling the nib within a sleeve of steel, heating the assembled nib and sleeve, and then placing the assembly in a die and forging or rolling it so as to fold the upper edge of the sleeve over the nib and so to lock the nib in place. Other methods such as shrinking and pressing of the nib in place are also used.

I have found that, in forging or rolling a steel sleeve around the nib in this manner, the portion of the sleeve whichis folded over or upset over the nib is strained, and is likely on cooling to crack the nib or to be cracked itself. must also be exercised in fitting the nib to the steel sleeve. Wire-drawing dies are subject to great pressures during use, and unless the hard metal carbide is reinforced by intimate contact with its sleeve throughout all adjacent portions, there is danger that the nib will crack in service. Shrinking and pressing of the nib into place also require very close work in fitting, and there is danger of cracking the nib and the sleeve in the operation.

Another method of preparing the assembly of nib and carrier is that proposed in the Schultz patent, No. 1,922,178, a patent that is owned by the company by which I am employed and to which the invention of this application is this day assigned. According to that method the tungsten-carbide nib isplaced in a mold cavity, and a suitably compounded iron is cast around it to form the carrier, embedding the nib within the cast metal body. My company has encountered difficulty in centering the nib in the mold in following the Schultz method. The nib has a tendency to be forced off center when the melted iron is poured into the mold. Another disadvantage of this method is that blow-holes are likely to form in the casing, particularly at the surfaces of contact with the nib. This results in an insufficient support for the nib. The formation of holes or porosity in the cast-iron casing, when operating according to the Schultz teaching, is believed to be due largely to the fact that when the molten cast iron makes contact with the cold nib within the mold, gases are released which are entrapped in the cast iron, particularly at the surfaces of the contact with the nib. Furthermore, if any of the cast iron spatters in the pouring and falls upon the cold nib, it solidifies immediately, forming pellets that may not be completely liquefied and merged with the remainder of the cast iron as it is poured into and fills the mold; and this may result in imperfections in the casing metal.

According to the present invention a nib 2 is provided that in this blank stage may, as has been said, consist'merely of a small cylindrical block having a conical depression sunk centrally in one of the heads of the cylinder. This block may be formed of tungsten carbide bonded with cobalt, or of another hard metal composition, of high melting-point. The carrier 4 is essentially a cylindrical block of relatively soft metal, of relatively low melting-point, such as steel, cop- Great care per, or modified cast iron. The modified cast iron that I prefer for this purpose is that known commercially as Meehanite. It is a product of methods described in United States patents, Nos. 1,499,068; 1,683,086; 1,683,087; and 1,731,346. It is obtained by adding to the better grades of molten commercial cast iron a small amount of a silicide of an alkaline earth metal, such as calcium or magnesium, or by adding metallic calcium. This cylindrical carrier block 4 is penetrated by an axial bore that from the upper face of the block downward (as seen in Fig. I) is cylindrical, and of a size snugly to receive, when the parts are cold, the nib 2. This cylindrical portion oi the bore is of greater extent longitudinally than the length of the nib; it terminates in an inward extending ledge or shoulder; and from this ledge or shoulder the bore continues with downward flare, as Fig. I shows.

The nib 2 is introduced into the bore of the block 4 and rests upon the ledge with that head uppermost that bears the central conical depression, as shown in Fig. I.

A press is provided whose members 9, 9 are electrodes in an electric circuit of suitable current strength and voltage, and, as is conventional in such case, these electrodes are of copper and are water cooled. They are faced with work-engaging blocks and II, of graphite. The graphite blocks 5 and II have work engaging faces that carry in relief a certain design- -in this case circular bosses or projections .50 and H0, respectively, somewhat less in diameter than the heads of the block 4, and these bosses are encircled by steps or shoulders of less eminence. Thus the blocks are mold members, or die members, whose function in this respect will presently be made more clear.

Both blocks 5 and II are axially perforate and in the perforations are set pins 1 and i3 (also of graphite) and of such snug fit within the perforations as to be carried frictionally and to slide in the perforations when in the pressing operation stress is exerted upon them. Normally they project from the perforations in the blocks 5 and I I. At their ends they are shaped, the pin 1 to register with the flaring lower end of the bore through block 4, the pin I: to register with the conical depression I5 in the head of nib 2.

The assembly of block 4 and nib 2 is brought to place in the press and the press is closed, the pin 1 in engagement with the bore in block 4, the pin l3 in engagement with the depression l5. Thus the assembly is trued and held true in the ensuing operation. The press is closed, and contacts are established by pressure. Current is then turned on, and this current, flowing through the central body portion of the block 4 (the body portion that extends immediately between the bosses and III! of the work-engaging blocks 8 and II), heats the central body portion of the block 4 until it comes to a semi-molten or plastic condition. (The outer side wall of the block 4, exposed to the cooling eifect of the surrounding atmosphere, remains rigid.) Under pressure (increased if need be) the substance of block 4 (within such rigid side wall) is minutely shaped. The walls of the bore close upon the adjacent walls or nib 2, in a bond that is intimate and continuous, and without fault or flaw; the bore above the nib closes in upon the pin ll, iorming an annular shoulder it that overhangs the upper head of the cylindrical nib 2; and the bosses upon the faces of the blocks 5 and II sink into the surfaces of the heads of block 4, forming centered countersunk recesses. The boss-encircling depressions upon the faces of blocks 5 and II provide clearance for the upper and lower pcripheries of the rigid side-wall portion oi the block, and form at the margins of the heads of the block I desired upstanding rims. These operations of shaping and die-casting will be understood on comparing with Fig. I (which shows the initial positions) Fig. II (which shows the ultimate positions).

In the operations as I have conducted it I have employed with success a current of from 2,000 to 10,000 amperes on the secondary, using a 120 kva. transformer, cycle, 1 phase, with a primary of 115, 230, and 330 volts.

When the press is opened the die is removed. It consists of a cylindrical carrier with outstanding terminal rims l7, and having an axial bore within whose walls is embedded and bonded the accurately aligned nib 2. It remains only to shape in conventional manner the eye I! through the nib, through which the wire-drawing operation is effected.

I claim as my invention:

In a press for shaping upon a nib for a wiredrawing die a carrier softened by the passage ing frictionally a work-truing pin movable lon- ELMER B. WELCH.

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