US2622456A

US2622456A - Method of making dies

Info

Publication number: US2622456A
Application number: US142991A
Authority: US
Inventors: Gyuris John
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-11-01
Filing date: 1950-02-08
Publication date: 1952-12-23
Anticipated expiration: 1969-12-23

Description

3 Sheets-Sheet 1 Original Filed Nov. 1, 1946 a h a 2 W INVENTOR Dec. 23, 1952 Original Filed f-lov. l, 1946 J. GYURLS METHOD OF MAKING DIES 3 Sheets-Sheet 2 Dec. 23, 1952 J. GYURIS METHOD OF MAKING DIES 5 Sheets-Sheet 5 Original Filed Nov. 1, 1946 INVENTOR Patented Dec. 23, 1952 UNITED STATES PATENT OFFICE DIETHOD OF MAKING DIES V 2 John Gyuris, New York, N. Y.

Original application November 1, 1946, Serial No.

707,106, now Patent No. 2,543,527, dated February 27, 1951. Divided and this application February 8, 1950, Serial No. 142,991

, 3 Claims. 1 This application is a division of my application, Serial No. 707,106, filed November 1, 1946, which matured as Patent No. 2,543,527, dated February 27, 1951.

This invention relates to a heating element adapted for use in an electric iron or other electrical appliance and to a method for making such a heating element.

This invention further relates to a terminal construction which is particularly adapted to make contact with a flat, conductive portion of a heating element.

This invention has further reference to a die constructed and arranged to form a heating element in a single operation and to a method for making the same.

This invention also embraces the construction of an electric iron or appliance embodying the novel heating element or terminal structure, alone or in combination. I

Heretofore, heating elements for electric irons and other electrical appliances have ordinarily consisted of a ribbon or spiral of resistive material embedded in a mass of insulating material, this element being secured between two metal plates constituting the body of the iron. Aside from the inherent difliculties of constructing and assembling such a, structure, the prime disadvantage of this type of heating element resides in the poor heat conduction between the heating element and the body of the iron. This arises from the thickness of the insulating material which is necessary to enclose a spiral or ribbon of resistance material and adequately insulate it from the body of the iron, such insulating materials normally being poor conductors of heat. As a result, the heating element is ordinarily operated at a temperature of several hundred degrees above the operating temperature of the iron, resulting in rapid deterioration of the heating element and formation of an oxide film thereon which is in itself a poor heat conductor, thus causing a further increase in the temperature differential between the heating element and the body of the iron.

It has been proposed to substantially minimize this temperature differential by utilizing a substantially flat heating element in which a number of slots are punched to define the respective segments of a heating element. However, dini- 2 culties have been encountered with such structures in that it is extremely difficult to provide an element with suflicient rigidity and mechanical strength to prevent buckling and the contacting of adjacent resistance-segments. In addition, difiiculty is also experienced in the manufacture of such elements in that a large number of closely-spaced slots must-be formed in the heating element, usually by cutting one slot at a time, with the result that the process is quite expensive and diflicult to perform.

In accordance with my invention, a heating element is provided in which both the resistance portions lie in a single plane and in which the resistance portions are bonded to a sheet of heat resistant insulating material to provide the requisite mechanical strength and rigidity. In manufacturing my novel heating element, grid like resistance elements are formed by suitable cutting or etchingoperations from a thin plate of resistance material. The resistance elements are interconnected, during the initial stages of the process, by portions of the plate of sufiicient size to provide enough mechanical strength and rigidity to prevent buckling. While in this stage, the resistance elements are bonded to a thin sheet of heat resistant insulating material, such as, for example, mica, to positively retain the respective segments of the resistance element in their proper relation. Thereafter, the interconnecting portions are severed. to provide a resistance element bonded to the sheet of insulating material with flat plate-like terminal members extending from the respective ends' thereof; I may then complete the resistance unit by bonding a second insulating sheet to the exposed surface of the plate.

In this manner, I eliminate the difficulties arising from an excessive'temperature differential between the heating element and the metal plates associated therewith. This is explicable on the basis that my heating element is entirely flat throughout and free from buckling so that it may be placed in intimate contact with the adjacent metal plates, separated therefrom only by extremely thin sheets of heatresistant insulating material. The advantages resulting from the use of such thin sheets of insulating material may be better understood by reference to the following tabulation which compares the temperature differential with the thickness of the interposed insulating material where the operating temperature is maintained constant at 250 C.

Conventional heating elements utilize insulating plates ranging from about 0.013 inch to about 0.016 inch in'thickness and the temperature differential, which is an index of the heat transfer eificiency between the heating element and the iron, varies from about 400 C. to about 550 C. It will be observed that the heating elements of such irons are operated at temperatures on the order of 650 C. to 787 C. which approaches red heat for Nichrome wire. This results in rapid deterioration and oxidation of the heater structure. When the novel heating elements of this invention are utilized, the thickness of the insulating material may be reduced to a thicknessin the range from 0.001 inch to 0.010 inch with a temperature differential of as little as 1 to 244 C. Preferably, I utilize insulating material having a thickness of 0.004 inch to 0.005 inch with a temperature differential of 13 C. to 25 C. It will be noted the element may be operated, in accordance with the invention, at temperatures of about 250 C. to 300 C. which is insufficient to cause deterioration or excessive oxidation of the heater element even when it is used for extended periods. I have verified these facts by extensive life tests and found that the novel heating elements of this invention, after prolonged operation, show no signs of deterioration and preserve a bright untarnished surface. These results may be attributed to the fact that the heater element is under the protection of the heated body as a result of the intimate heat exchange relation therebetween.

Another factor contributing to the low temperature differential and increased efiiciency of my heating units is the novel terminal construction therefor. By the use of this structure, the terminal portions of the heating element may consist of plate-like members integrally formed with and lying in the same plane as the grid-like resistance structure. I have found that the use of such terminal portions contributes substantially to the low temperature differential of the heating element and I have devised a terminal structure for making efficient contact with such flat plate-like terminal members.

Another aspect of the invention relates to an improved die for forming, at a single operation, one or more rows of slots in a metal plate defining grid-like resistance portions and terminals. With this die, a large'number of extremely thin, accurately positioned slots may be formed in a single operation and, in order to accomplish this result, I provide a plurality of die members each comprising a row of stacked metal plates with corresponding plates in each row being of identical thickness and having accurately aligned slots therein for receiving and guiding a cutting tool.

I prefer to make the respective sets of corre' sponding plates by placing the plate portions of each set in side by side position, machining the plates to uniform thickness and forming aligned transverse slots in the plates while they are in such side by side position. Thereafter, I assemble the plates in rows to form a plurality of die members with the plates of each set occupying corresponding positions in the respective rows.

In view of the foregoing discussion, it will be seen that I have provided an efiicacious solution to many of the problems confronting the manufacturer of electrical appliances, such as electric irons and heating units.

It is an object of this invention to improve the construction and operation of heating elements.

It is a further object of the invention to set forth a novel method of making a heating element.

It is a still further object of the invention to provide an improved terminal structure for a heating element.

The invention further aims to provide an electrical appliance, such as an iron, embodying the novel heating element from a plate of resistance metal in a single punching operation.

It is another object of the invention to describe an improved method for making such a die.

Other objects of the invention will be apparent from the following description and. accompanying drawings taken in connection with the appended claims.

The invention accordingly comprises the features of construction, combination of elements, arrangement of parts, and method of manufacture referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawings, the scope of the invention being indicated in the appended claims.

For a fuller understanding of the nature and objects of the invention as well as for specific fulfillment thereof,- reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a perspective view of an electric iron embodying the novel heater element and terminal structure;

Fig. 2 is a plan view showing a metal plate prepared for an etching operation;

Fig. 3 is an end view of the plate shown in Fig. 2;

Fig. 4 is a plan view of a metal plate having a series of slots formed therein by a punching or etching operation;

Fig. 5 and 6 are plan views of a partially coinpleted heating element;

Fig. '7 is a plan view illustrating the resistance unit bonded to a sheet of heat resistant insulating material;

Fig. 8 is a sectional view taken along the line 88 of Fig. '7;

Fig. 9 is a fragmentary perspective view of the completed-resistance unit;

Fig; 10 'isa planview of a complete heating element of modified structure;

Fig. 11 is'a vertical sectional view of the novel terminal construction; V

Fig. 12 is a front elevational view, partially in section, of a die constructed in accordance with this invention;

Fig. 13 is a side-elevational view of the die shown in Fig.- 12; r

Fig. 14 is a plan view of the stationary die assembly; e 1

Fig. 15 is a sectional viewtaken along the line Il5 of Fig; '14; v I

Fig. 16 is a perspective view showing a ste in making the die of Fig. 12;

Fig. 1'7 is a sectional view which is descriptiv of another step in making the die of Fig. 12; and

Fig. 18 is a front elevational view showing a modification of the step illustrated by Fig. 17.

In each figure, the size of the slots shown therein is greatly exaggerated for clarity.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variations may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. .Inthe' following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring now to the drawings in detail, Figs. 2 to 9 illustrate successive steps in the method of making my novel heating element. In Fig. 4, a thin plate l0 of resistance metal, such as Nichrome, is shown" having two rows of slots A, B formed therein in the manner to be hereinafter explained. Each row comprises a series of parallel, closely spaced slots which are arranged in staggered formation so that each slot is laterally offset from. the two slots adjacent thereto. Accordingly, each row may be said to consist of a group of slots II, the inner ends of which define the inner edge of a grid-like re-- sistance element l2, Fig. 6, together with a group of slots l3, laterally offset from slots II, the outer ends of which define the outer edge of grid-like resistance element 12.

It will be observed that the outer ends of the respective groups of slots 13 define substantially the outline of an electric iron, the slots being shorter and more closely spaced adjacent the tip portion 14 than the'slots adjacent the other endportion I5. Closer spacing of the slots will increase the electrical resistance of the grid portions defined thereby and thus will increase the temperature of the electric iron in such regions. If it is desired to manufacture a heating element adapted for use in an appliance other than an electric iron, the slots maybe formed to define any desired shape of heating element, as will become clearl-y'apparent-from the following description. For the purpose of supporting and aligning the elementwith the die during successive stages of the manufacturing operations,

In a preferred embodiment of the invention, the slots are stamped in the plate by a'single-operation of my novel die which is described in detail hereinafter. -I-Iowever, the method of making a heating element in accordance with the inventioncontemplates the formation of the slots in anyv suitable manner such as, for example, by punching out the slots one at a time or in groups, or by utilizing the etching process now to be described in connection with Figs. 2

and 3.

In forming the slots by etching, the plate I0 is coated on one or both sides thereof by a layer of masking material I9. A plurality of slits 20 corresponding, respectively, to the slots: ll, 13 are formed in the masking layer in any-suitable manner, as by scratching the masking layer with a sharp instrument. The plate is then immersed in a bath of a suitable acid reagent which corrodes the unmaskedportions of the plate forming the slots II and I3. In orderv to carry out the etching in a quick and efficient manner, it is preferred to make the resistance plate the anode in an etching solution which may be a strong mineral acid, such as sulphuric, nitric 'or hydrochloric acid of the desired concentration and to-apply a voltage-of 50-60 volts to the anode and cathode. I have found that in this manner a Nichrome plate having a thickness of 0.003 may be etched through in about 5. to 6 seconds. Instead of providing a continuous coating of the masking material on the resistance plate, it is also possible to apply the masking material in the form of a waxy film having the desired configuration by means of a printing or lithographic process which eleminates the necessity of scratching in the slots by a separate operation. The masking material is then removed leaving the plate in the condition shown by Fig. 4.

The slotted plat e of Fig. 4, whether produced by etching or stamping, is then placed in a suitable die and a central channel 22, Fig. 5, is formed therein, the longitudinal edges 23 of which define the respective inner edges of the grid-like resistance elements [2, Fig.6. Precisely, the edges 23 areformed along the extreme inner ends of the slots II but some tolerance is permissible in the width of channel 22, the essential feature being that each slot -II communicates with the channel 22 to prevent a short circuit being formed between adjacent segments of the resistance grids. It will be observed that the slots and the channel are shaped to form circular passages 24 constituting openings for receiving supporting bolts to secure the heating element in proper position with respect to the structure associated therewith. The end of channel 22 may terminate ata short slot 25 at the tip portion I4 to provide uniformlthickness of the heating element in this region.

The structure of the grid-like resistance units I2 isthen. completed by cutting away portions 26 of the plate, thus defining the outer edges 2'1, Fig.6, of grid-like resistance structures i2. The edges 21 are preferably formed along the :ex-

treme outer ends of slots l3 but may extend inwardly .a short distance beyond such outergends, the essential feature being that the slots 13 separate and prevent a" short circuit between adjoining outer ends of, the segments of grid-like resistance elements l2. It will be observed'ithat the ends I5 of resistance elements I2-,terminate in integral fiat plate-like portions 28,,29 .constituting terminals for the heater element, such terminals lying in the .same plane as resistance elements 112.

The structure shown in Fig. '6 has sufficient mechanical strength and rigidity to prevent buckling and bending :of .the resistance segments into short circuiting contact with each other. This is due to the fact that the grid-like ,resistance elementis interconnectedat the end M thereof by a plate portion 32 which serves to connect elements l2 in series. The mechanical strength and rigidity is also due to the interconnection of terminalmembers'28 and 29 by plate portion v33. It will be understood. however, that plate portion .33 forms ashort circuit between portions f the grid-like structure .at this'time and, accordingly,imust be'subsequently removed.

In accordance with the invention, while the grid-like structure isstill .interconnected this manner, I bond it to a sheet of .heat resistant insulating material, such as-mica. Referring to Fig. 7, the element is shown .with the grid-like resistance elements 12 'securedto amica sheet 35 by bonding material 36, Fig. 8. More specifically, the grid-like elements I2 may be bonded or 'heat sealed to the surface of mica sheet 35 by means of a layer 35, Figs. 8 and-11, of thermoplastic resin, such as a suitable vinyl resin. This may be accomplished by coating the mica surface with a suitable thermoplastic'resin, such as vinylseal, placing the resistance-grid thereon and then applying heat and pressure to the said plateby means of a metal surface, such as steel, which is heated to a. temperature of 180-220 C. Preferably, the application of heat and pressure-stops short 'of the terminal regions of'the plate, which are initially integrally connected so that such regions are not bonded to the insulating surface. This permits-the terminal regions to be slightly lifted up so that the short portion 33 of the metal plate bridging the terminal portions may be cut out. Thereupon heat and pressure maybe applied to the entire surface ofthe resistance plate so thatthe terminal-regions are also firmly bonded to the mica plate by the layer 36. Thebonding material serves to afford suflicient-strength andrigidity to preserve the flatness and configuration or theheater element, atleast until it is'rigidly mounted in an iron or other electrical appliance. Once the element is mounted in this fashion, it is immaterial whetherthe bond between the heating element and insulating sheet 35 persists or whether the bonding material is decomposed during operation of the iron.

After the bonding has been completed, I fill the slots I I, I3 with a semi-refractory insulating compound or mass 31, Figs. 8 and 11, which-remains in position after assembly and at all times, positively insulates adjoining segments of the resistance elements fromeach other. A suitable compound for this purpose is an oxide paste prepared from a refractory metal oxide, such as aluminum, calcium, or magnesiumoxide, a filler such as water glass or uncalcined borax-and water.

After the slots are filled, a second sheet 37a, Fig. 9, of heat resistant insulating material, such as mica, is bonded or otherwise suitably secured to the exposed surface of plate 10, this second sheet having openings 38 therein permitting access to the respective terminalportions28 and 29.

Alternatively, the bondingoperation may be peri'ormed at any .stage of. the :process. so .long

as the grid-like resistance elements are inter connected before the bonding in such fashion that the structure has sufficient ,mechanical strength and rigidity to prevent buckling and contact of adjacent resistance elements. After bonding, the interconnecting portions are severed to define the heater element. Thus, ,for example, the plate 10 of Fig.2 may be coated on one side only, with masking material'after .which the other side thereof may be bonded .toinsulating sheet 35, Fig. 7. The masking material is then removed from thecoated face todefine the finished heater element of Fig. '7 after which the assembly .is etched electrolytically, a potential being applied to ainumber .of points at the same'time. In this manner, the interconnecting portions ,are severedorremoved by the etching and the complete resistance elementis formed in a single etching operation. Thereupon the interspaces between the slots-may be filled, as described, with an oxide ,paste' and ,a second insulating sheet bonded ,to the exposed surface of the metal plateto ,forma completed heater element.

Accordingly, the completed resistance element comprises a metal plate of resistance material I0 having grid-like resistance elements 12, I2 defined therein bythe slots II and I3, inner edges 23 and outer edges 21. The elongated grid-like resistance elements [2 are connected in series by plate portion 32 and terminate, respectively, in fiat integral plate-like terminal portions 28, 29 which lie in the same plane'as grid-like resistance elements l2. The grid-like portions ofthe element are bonded to ,heat resistant insulating sheet 35 to secure the desirable mechanical strength and rigidity, and the insulating compound 31 fills the slots H, l3 to effectively insulate the respective resistance segments from each other. A second sheet of insulating .material, suchas mica,.is appliedorbonded to the exposed surface of theplate, this'second sheet having openings 38 thereinfor-effectingconnection to the terminals Hand 29. ,In its completed form, the heater Lelement is of uniform thickness throughout and free from b0nds,.folds, soldered or welded joints. The insulating layers are likewise completely plane :andofuniform thickness throughoutso that they can'be pressed against the plane heater element substantially in the complete'absenceof any interposed or entrapped airspaces or films. This is of critical importance asevenan air film or gap of 0.0001" may very appreciably reducethe efficiency of heat transfer. In this manner, the concentration of heat in definite regionawhich is characteristicof conventional wire or ribbonwound heater elements, and the-resulting presence of hot spots is completely avoided.

Suitable dimensions for the component parts of the novel heating element are; a thickness of about 0.001 to 0.004 inch fortheplate I0 and a thickness of about 0.004 .to 0.005 inch-for the insulating sheets 35 and..3'la. I prefer to utilize about to slots on each side of the channel 22, thewidth of theslotsvarying from about 0.002 to 0.01 inch and the lengthzthereof' being determined by'the particular. zigzag pattern ,de sired for the heater element.

The widthof the grid-likeportions defined by the slots may vary from about 3 2 to {a inch, this dimension being .is. suitable. for use ina hot plate, is shown. by. Fig.

10. This element is formed in accordance with the principles of the present invention and comprises a plate 40 of resistance metal having generally semicircular grid-like resistance elements ll connected, at one end, by a plate portion 52. and terminating, at the other end, in integral, fiat terminal members 43. The grid-like portions -'are bonded to a sheet 44 of heat. resistant insulat- "ing material and, prior to the bonding operation, the terminals were interconnected by a metal plate portion giving sufficient mechanical strength to prevent buckling, this interconnecting portion being severed after the bonding step. The resistance elementsare defined, as in the case of the element shown in Fig. '7, by slots 45, the inner edges 45 of a channel 41, and outer edges 48. The slots 45 are filled by a suitable insulating compound or paste thus insulating adjacent segments of the grid-like resistance elements.

Referring now to Figs. 1 and 7, an electric iron is shown embodying the heating elementv of the present invention. The heating element is mounted between a pair of metal plates or

bodies

50, 5| which are held together by bolts 52 extending through the respective openings 24 in the heating element and also carrying a handle 53.

In accordance with the invention, I provide terminals of novel construction for making connection to the respective plate-like terminal portions 28 and 29, these terminals making an efficient electrical connection to the plate portions 28 and 29 while permitting them to remain in the plane of the heater element.

Each terminal, as shown in detail in Fig. 11, may comprise a metal sleeve or container member 55 having a lower flanged portion resting on insulating sheet 37a and disposed in a cavity formed in the upper iron member 5|. Sleeve member 55 may be insulated from metal plate 51 by a bushing or grommet 56 which is lapped over the top of plate 5|. A solid body or rod 57 of compressed, conductive, powdered material, such as graphite, is disposed within the container member 55 and a portion of this material extends through the opening 38 into contact with the flat terminal portion 28. rod, pure graphite powder of high electrical con ductivity is glowed while in powder form and compressed into desired cylindrical shape generally without any binder. The resulting pressed graphite body is characterized by high mechanical strength, is unaffected "by elevated temperatures, and has some elasticity to apply resilient pressure to the resistance plate. The compressed body of powdered material or rod is forced into contact with the terminal portion in any suitable :manner, such' for example, as by a set screw 58 which is disposed on interior threads located at the top of sleeve member 55. The set screw 58 :should be formed of material which is non-oxidizing at moderately high temperatures, such as nickel, Monel metal, or silver plated brass.

The member 55 also carries external means for making electrical connection through the sleeve and compressed conductive material 5? to the flat terminal portion 28. This external means may comprise a pair of

nuts

59, 60 threaded to the exterior of the sleeve. The nut 59 may be forced into engagement with grommet 5G and the top of plate member 5|.to hold the terminal firmly in assembled position thereon. The nut ea may be utilized to hold a lead or conductor in contact with sleeve 55 and nut 59 to afford an electrical connection to the terminal portion 28. It is also possible, of course, to clamp or otherwise attach :a conventional contactor pin to the terminal In preparing the terminal which is adapted to"cooperate with a conventional connector at the end of a fleziible cordr Itwill be apparent that the e'ntireheatin'g element, including the grid-like resistance eleinents l2 and the terminal portions 28, ,29 is held in a perfectly flat position between the

metal plates

50,51 and the insulating sheets 35, 31a. Accord= ingly, the insulating sheets may be greatly re duced in thickness, as compared with prior art structure's, thus reducing the operating tempera' ture of theheater element and decreasing the temperature differential between the heater element and the body of the iron. As a result, the heater is placed under the protection or the body of the iron due to the intimate heat ex change relation therebetween. Furthermore, the heating element is absolutely plane, of uniform thickness throughout and free from bonds, folds, soldered or welded joints. The terminals, one of which is provided for eachterminal portion 28 and 29, cooperate with the associated structure to maintain a perfectly fiat position for the entire heating element, and to afford an efficient electrical connection thereto;

Another important aspect of this invention relates to a die for forming the slotted. plate shown in Fig. 4 by a single punching operation and to a method for making such a die. The die is shown by Figs. 12 to 15 in which upper and lower rectangular frame'members and 66, respectively, are mounted on four posts or rods 51 disposed at the respective corners thereof, as by bolts 68. A stationary die assembly 59 is fixedly secured to the frame 66in any suitable manner; for example, by bolts 70. I I

A movable unit generally indicated at "H is mounted for reciprocatory verticalmotion'on the rods 61 and this movable unit is actuated by a reciprocatory shaft 12 connected to any suitable power source, not shown. The movable unit comprises a support or frame 13 to which is secured a tool carrying assembly 14, as by bolts 15. A guide Orheade'r assembly 16 is carried by the movable unit H but is adapted for limited relative movement with respect to the tool carrying assembly 14. To this end, the guide assembly and tool carrying assembly are interconnected by members 11, Fig. 12, each having a circular opening 18 for receiving a bolt 19 which is attachedto guideassembly l5 and a slot, for receiving a bolt 8| attached to tool-carrying assembly 14. Accordingly, it will be apparent that the guide member may slide alo'ng' the posts 61, moving relatively to the tool-carrying assembly a distance determined by the length of slots 80.

The guide assembly is urged to a spaced position with respect to the tool-carrying assembly by a pair of compression springs which are mounted in suitable recesses provided in the aforesaid guideand tool-carrying assemblies.

The tool-carrying assembly, guide assembly,

and stationary die assembly areeach adapted to receive a row of stacked metal-plates intheir stacked position. To this end, each assembly comprises a pair of end frame membersx86 and lateral frame members 81, Fig. 14. "The inner surfaces of frame members 81, are shaped to form longitudinal slots 88, respectively, whichare adapted to receive complementary end portions of the aforesaid metal plates. a} a The tool-carrying assembly carries a rowel] of metal plates, thefguide assembly carries a row 5! of metal plates and the stationary die assem bly carries a row 92 of metal plates, each row being supported, as stated, by the longitudinal slots 88 in frame members 81. In accordance with the invention, corresponding plates in each row are of identical thickness and have accurately machined parallel sides. Aligned slots 93 are formed in each set of corresponding plates, these slots conforming, in size and location, to the slots to be formed in metal plate It), Fig. 4. That is to say, the slots in each assembly are divided into two rows, the slots in each row being in parallel staggered arrangement with their ends defining the edges of the heating element to be formed, which, in the example shown, is an element adapted for use in an electric iron. It will be noted that the plates are of progressively decreasing thickness progressing toward the tip of the heating element defined thereby.

The edges of each slot in the stationary die assembly may diverge somewhat progressing away from the top of the plates to define cutting edges at the top of the plate and permit severed material to be readily ejected from the die.

Each of the slots in the tool-carrying assembly carries a cutting tool or knife 95, Figs. 13 and 15, having a flanged end portion 96 and an angular cutting edge 91. The flanged portion is held between the frame member 13, Fig. 15, and toolca-rrying assembly 14 and the body of the knife extends through the adjacent slot in tool-carrying assembly 14 and into the corresponding slot in guide assembly 16, the cutting edge being closely spaced from the lower end of such corresponding slot.

From the foregoing description, the operation of my novel die may be readily understood by those skilled in the art. A thin metal plate, such as the plate In of Fig. 4, is placed on the upper surface of stationary die assembly 69. Thereupon, the movable unit H is lowered causing the guide assembly to press against and hold the plate in flattened position on the stationary die member. Upon continued movement of the unit H, the tool-carrying member moves downwardly into engagement with the guide assembly. causing the respective cutting edges of the knives to penetrate the plate and move into the slots in the stationary die assembly. In this manner, the slots II and I3, Fig. 4, are formed in th plate by a single punching operation. When the movable unit is retracted, the parts return to the position shown by Fig. 12- and the guide assembly is urged to a position spaced from the tool-carrying assembly by the springs 85.

In order to insure that corresponding plates in the three die assemblies shall be of exactly the same thickness and that the slots therein shall be in precise alignment, I form each set of corresponding plates, which I refer to as a. die element, in a single machining operation. In Fig. 16, I have shown a set of hardened plates 99, constituting a die element, in side-by-side osition upon a hardened steel frame IDB which is secured to the table of a milling or grinding machine, as by a magnetic tool holder or clamp. It will be noted that portions HH have been cut from the sides of the plates, thus defining tongues I02 which fit into the grooves 88, Fig. 14, on the respective die assemblies.

In the machining operation, the plates are formed to identical thickness and transverse slots are formed across the set of plates while they are in the aforesaid side-by-side position. In this manner, I insure that the corresponding plates in each die assembly are of precisely uniform 12 thickness and that the slots 93 therein are in exact alignment.

Preferably, and in accordance with the invention, one end of the plate utilized in the stationary die assembly is elevated while the slot 93 is being formed, Fig. 17. This may be accomplished by placing a spacer I03, which may be about 0.003 inch in height, between one side of the plate and the table of the grinding machine. In this manner, the slot I94 in this plate is of progressively increasing depth and forms a shoulder or cutting edge at I05 against which the plate I0 is positioned after the die is assembled.

Instead of using three plates in side-by-side position, as illustrated in Figs. 16 and 1'7, I may utilize a single piece of metal I06, Fig. 18, having weakened portions l0! along which the metal piece is severed, after the machining operation, to form a set of plates 99. The weakened portions or grooves I01 are preferably formed before the plate I 05 is hardened.

It will be understood that the sets of plates forming the respective die elements are made separately and that a number of such sets are utilized to form the completed die. In assembling the die, the plates are assembled into rows, with the plates of each die element occupying corresponding positions in the rows. Thereupon, the rows of plates are inserted into position in the slotted portions 88 of the respective die assemblies and secured in position therein to form the completed die.

In some cases, where the die is used for cutting relatively thick material, it may not be necessary to provide a guide assembly. In such a structure, each die element will consist of two plates, one for the stationary die assembly and the other for the tool-carrying assembly.

While the present invention, as to its objects and advantages, has been described herein as car ried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims. For example, instead of concentrating the heat at the tip of the iron by decreasing the Width of the element adjacent the tip regions, it is also within the scope of the invention to slightly roll down the tip portion of the heater element blank, thereby increasing the specific resistance of the element in this region.

What is claimed is:

1. A method of making dies, comprising in combination, the steps of placing at least two plates in side-by-side relationship, said two plates constituting a die element; machining said plates to form on each plate smooth plane parallel front and rear faces; machining in the exposed front faces of said plates aligned transverse slots while said plates are in side-by-side relationship; and assembling a group of said die elements with said plates constituting two rows with one of each two plates machined together in one operation located in one of said rows, and the other of said each two plates occupying a corresponding position in the other of said two rows, and with the slots machined together in one operation aligned, each plate in each row of plates abutting with the front face thereof against the rear face of an adjacent plate, each row of plates constituting a die member laminated parallel to said aligned slots.

2. A method of making dies, comprising in combination, the steps of placing at least two plates in side-by-side relationship, said two plates constituting a die element; machining said plates to form on each plate smooth plane parallel front and rear faces; elevating one of said plates on one end thereof; machining in the exposed front faces of said plates aligned transverse slots while said plates are in side hy-side relationship so that the slot in said elevated plate is of progressively increasing depth and an acute angle is formed on the edge on the other end of said plate extending across said slot; and assembling a group of said die elements with said plates constituting two rows with one of each two plates machined together in one operation located in one of said rows, and the other of each two plates having an edge formed with an acute angle occupyin a corresponding position in the other of said rows with the slots machined together in one operation aligned, each plate in each row of plates abutting with the front face thereof against the rear face of an adjacent plate, each row of plates constituting a die member laminated parallel to said aligned slots so that said edges formed with an acute angle are adapted to cooperate as cutting edges with tools mounted in the slots of the first-mentioned rows -2 of plates.

3. A method for making dies, comprising in combination, the steps of placing three plates in side-by-side relationship, said three plates constituting a die element; machining said plates to form on each plate smooth plane parallel front and rear faces; elevating one of said plates on one end thereof; machining in the exposed front faces of said plates aligned transverse slots while said plates are in side-by-side relationship so that the slot in said elevated plate is of progrcs sively increasing depth and an acute angle is formed on the edge on the other end of said plate extending across said slot; assembling a group of said ide elements with said plates constituting three rows, namely, two outer rows and one intermediate row, with one of each three plates machined together in one operation located in one row, the second of each three plates occupying a corresponding position in the second row, and third of each hree plates having an edge being formed with an acute angle occupying a corresponding position in the third row with the slots of each three plates machined together in one oper tier: said third row being an outer row and edge being located adjacent to the corresponding plate in the adjacent intermediate row, each plate in each row of plates abuttin with the front face thereof against the face of an adjac nt plate, each row of plates constitring nher lamii parallel to said a ned slots; mounting cutting tools in the slots r the plates constituting the other outer row, said cutting toois adapted to pass through corresponding aligned slots and cooperatin with formed with acute angles, the same serving as correspond 1 cutting edges; mounting each of rows a frame; and mounting said oa sup ort permitting relative movement .i said frames e said slots remain in aligned position.

JOHN GYURIS.

REFEP ENJES CITED The following references are or record in the e of this patent:

UNITED STATES PATENTS Number