US2235532A - Method for shearing normally brittle sheet metal - Google Patents

Description

METHOD FOR SHEARIHG NOKIALLY BRITTLE SHEETv METAL Inventor: @Obert 1T Reardon,

R. 1'. REARDON Filed Sept. 29;. 1938 ngnnn 'wuwwuauuusu March 18, l1941.

by )if 4c".

Hi Attorney Patented Mar. 18, 1941 PATENT OFFICE METHOD FOR SHEARING NORMALLY BRITTLE SHEET METAL Robert T. Reardon, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application September 29, 1938, Serial No. 232,326

3 Claims.

The present'invention relates to a method for shearing normally brittle sheet metal, and more particularly to a-methodI `olsproducing punchings from sheet silicon'fsteelsi'and the like that are brittle under normal temperature conditions.

It is an object of this invention to provide a method of obtaining smooth-edged, accurately dimensioned, sheared products formed of sheet ferro-magnetic metal such as silicon steel.

It is a further object of the invention to provide a method of improving the magnetic properties of punchings of normally brittle ferromagnetic material, and to obtain such punchings with less breakage than heretofore has been possible.

Another object of the invention is to increase the useful shearing life of shearing tools as, for example, the punching or stamping dies used in producing steel laminations.

The novel features which I believe to be characteristic of the invention are set forth in the appended claims. The invention itself, however; will bes be understood from the following description when considered in connection with the accompanying drawing wherein Fig. l is a diagrammatic view illustrating one form of apparatus adapted for use in carrying this invention into effect; and

Fig. 2 is a view similar to Fig. 1 of another form of apparatus that may be employed in practieing this invention.

Ferrous alloys containing, for example, about 2 to 8% silicon have low hysteresis and eddy-current losses. Such alloys, commonly known as silicon steels, therefore are widely used in thin sheet form in manufacturing magnetic strucl tures of electric apparatus, for instance motor stators-,-.rotors, transformer cores, etc. In makmg sueistruetures the sheet stee1 is punched tov form laminations of a desired size and shape. These punched laminations are superposed t form a magnetic core. The addition of silicon to iron or steel imparts hardness and brittleness thereto, increasingly so above 3% silicon. The

punching operation sets up stresses and strains in silicon steels, both .hot rolled and mill annealed,

detrimentally affecting their magnetic properties and often resulting in considerable damage.

4It has been suggested heretoforethat silicon steel to be punched or otherwise mechanically worked should be' heated prior to such mechanical alteration, for instance within the temperature range of 30 to 200 C. Such heating of thel steel produces ductility therein, but removes advantages sought in using high silicon steel as core material of audio, power or reactor transformers, and in motor applications. For example, when the steel is hot and the punching dies are cold, variations inthe dimensions of the punched laminae occur due to the unequal expansion between the work-and the tool. These variations, in turn, result in air gaps in magnetic cores made from such laminae and a material decrease in the effectiveness of the magnetic structure. Further; particularly when a high speed punch press such as a Wright stamping machine is used, the'non-uniform expansionl and contraction between the work and the cutting portions of the press, cause binding in the dies. As a result, breakage of the laminae is relatively high, even after satisfactory punching, as the work moves through the pressl to stacking devices. Also, in

`punching either cold or preheated silicon steell or the like, frequent re-grinding of the cutting edges of the punch is necessary in order to obtain clean-cut laminae.

I have discovered that the above diculties inshearing, as by punching or stamping, metals such as ferrous alloys which in sheet form are highly brittle, for example silicon steels containing from 3 to 8% silicon, can be avoided by punching or otherwise shearing the sheet metal while both the metal and at least the cutting edges of the shearing tool are at a temperature well above room temperature'but materially below a visible heat (500 to 550 0.). Generally, the tool and the work at the time o'f shearing are at a temperature not exceeding substantially 200 C; but well above room temperature, specifically above 40 C. v

With further reference to the drawing there is shown by way of illustration in Figs. 1 and 2 a chamber or oven which is designated in Fig. 1 by the numeral I0 and in Fig. '2 as Illa. This oven envelops the work Il and, also, all or a substantial portion (and in any event the cutting portion during punching) of the punch press I2. In Fig. 1 I have shown the work II in the form of stacked sheets, one of such sheets being shown at IIa as removed from the stack and passing through the rollers I3 to a point beneath the cutting edge I4 of the hammer I5 of the punch press I2. In Fig. 2 the work I I is shown as being of continuous length and in coil form upon a reel I6. With the aid of the rollers I3a the work is withdrawn from the reel I6 and led to the punch press as above described with reference to Fig. 1. The work II is usually slit sheet steel, specifically silicon steel, for example 14 to 25 mils thick, and of a width such that it will pass I through the punch press I2 and will yield a maximum number of laminae per surface unit with ings being separately withdrawn by any suitable means (not shown). A

In Fig. 2 the oven I0a is shown asbeing provided with an elongation I1 tting Within the press frame. A suitable opening in the upper portion of this elongation permits the downward thrust of the hammer I and engagement of the cutting edge I4 withthe work IIa when the latter is in position for punching. The oven design shown in Fig. 2 provides somewhat lower installation and heating costs as compared with that of Fig. 1.

'I'he oven I0, Ilia may be heated by any suitable means as, for example, by gas heat, electric heat, a combination of gas and electric heat, etc. For DuI'pOse of illustration I have shown the source of heat as being the electric heaters I8.

Suitable openings or windows are provided in the oven I 0, I 0a for introduction of the work and for observation during its passage through the press. For illustrative purposes I have shown the oven I0 as being provided with an opening I9 in the side wall of that portion of the fur- Anace Where the work is initially heated. This opening may take any suitable form` as, for example, a hinged or slidingdoor which may be entirely glass-encased or may be of metal with smaller openings therein for observation of the work and for removing the individual sheets,

with the aid of a suitable device from the stacked device and introducing the same between the rollers I3.. I have also shown a window 20, which may be encased. with glass or other suitable transparent material, in the side Wall of that l part of the furnace I0 Where the press is located.l

'Ihis window permits visual observation of the punching operation, and may be slidably aris supplied from the chamber toat least the cutting edges of a shearing tool such, for example, as the'punch press I2. then sheared while both the metal and the cutting edges of the shearing tool are at a temperature well above room temperature but below a visible heat. stamping die orfother shearing tool employed should be heated to approximately the same elevated temperature. The temperature employed may vary considerably, depending, for instance, upon the particular metal being sheared'and the resistance of the shearing tool to heat. In most casesthe work and the tool are heated and maintained during shearing at al temperature within the range-of 40 to 200 C. In producing silicon steel laminations from sheet silicon steel containing 3 to 8% silicon, the optimum temperature of heating the steel and at least the cutting edges of the shearing tool is within the range of 100 to 200 C. The higher the silicon content of the steel, the more brittle the material and the higher, for best results, should be the temperature of the work and the tool during shearing. Temperatures during shearing ranging from about 200 C. up to a'visible heat are not The metal is For best results the work and the objectionable provided the tool is formed of a heat-resisting alloy capable of withstanding successfully such temperatures.

If desired, the work initially may be brought to a. temperature somewhat higher than its temperature during shearing. For example, the metal may be preheated to 100 to 550 C. Thereafter, by suitably regulating the heating means and varying the operating speed of the Ipunch press or other shearing tool employed, the metal can be cooled during its passage to the tool so that at the time of punching its temperature is ,of the orderof 440" tol200 C. In this way advantage canube taken of the higher temporary ductility created in the metal by reason of the higher preheating temperature, which ductility decreases relatively slowly as the metal cools to punching temperature. v

In-certain'cases, for example in treating normalized, hot rolled or semi-mill-annealed sheet silicon steel or other ferro-magnetic material, I may apply a stabilizing anneal for improving the magnetic properties of the metal in conjunction with the production of punchings therefrom. This may be done by heating the sheet material at a temperature above 400 C., usually above 450 C., and below a temperature which would materially deform the sheet, for a period of time sufiicient to improve itsmagnetic properties. lI Ihereafter the heated' sheet material is suitably-cooled to a temperature ranging from well above room temperature to 200 C. or above. The cooled metal is directed to a punch press at least the cutting edges of which have been heated to approximately the same temperature as that of the sheet metal immediately before being punched, and the thus treated material is thenpunched to form punchings thereof.

The maximum annealing temperature to which the sheet metal is heated will depend upon the particular steel being processed. For example, with silicon steels such as those containing from v 3 to 8% silicon the maximurntemperature to which the sheet material is heated to improve its magnetic properties advantageously is Vof the order of '800 to 860 C. With other ferro-magnetic materials, for instance iron-nickel alloys, the maximum annealing temperature may be as high as l100 to 1200 C. Such annealing operation may be carried out in an oxidizing, reducing or inert atmosphere, as desired or as conditions may require. When an oxidizing atmosphere is used in annealing steel not already having an oxide film thereon, the treatment results in forming a tightly adhering insulating oxide lm on the metal surface. Such treatment may be modified as described in my co-pending application Serial No. 127,405, filed February 24,

.1937, and assigned to the same assignee as the present invention. 4

While I have shown the work I I in Fig. 2 in the form of a coil and in that same ligure the oven IIla as being adapted to encase only the operating portions of the press II, it will be understood, of course, that the work may be introduced in coil form into the oven I 0 of Fig. 1 and in the form of stacked sheets into the oven I0a of Fig. 2.

applicable to other metals which in thin sheet form, as, for instance, 14 to 25 mils in thickness, are excessively brittle at room temperature (20 to`25 C.). Examples of such metals are 3 tools chrome and tungsten magnet steels, high man'- ganese steels, iron-cobalt steels, etc.

Th'e present invention materially increases the period of usefulness of the shearing or cutting before regrinding becomes necessary. thereby decreasing unit costs of `producing laminatidns. The magnetic properties of the metal are improved, since fewer stresses and strains are produced` therein vduring punching Breakl age is reduced to'a negligible amount. Further. products of this invention have new utility.

For example, high silicon steel laminae produced as herein described can be used in cores of electro-magnetic devices in lieu of the higher l 15 priced iron-nickel and similar alloys heretofore ,required wherel minimum noise duringoperation of the completed device is an important factor, for example in radio transformers.

What I claim as new and desire to secure by 30 Letters Patent of the United States is:

-1. The method of improving the magnetic properties of punchings of ferro-magnetic material which comprises heating such material in sheet form at a temperature above 400 C. and

25 below a temperature which would materially deform the sheet for a period of timefsulcient to limprove its magnetic properties, cooling the heated sheet material, toatemperature ranging its magnetic properties, cooling the heated steel the range of 40 to 200 to a. temperature within a stamping die C., and then shearing it with heated to approximately the same temperature as the said steel within 200 C.

` 3. The method of treating sheet silicon steel which comprises annealing said sheet steel at a temperature above 400 C. and below a temperature at which the jsheet would materially deform for aperiod of -time sulcient to improve its magnetic properties, Acooling the heatedsheet steel to a temperature within the range of 40 to 200 C. and then shearing it with a die heated to approximately the same temperature as the said steel within the range of 40 to 200 C.

the range of 40 to ROBBERT Ti REARDON.

temperature to 200 VC.,

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