US3753798A

US3753798A - Process and apparatus for the partial or localized tempering of a steel sheet-or the like stock

Info

Publication number: US3753798A
Application number: US00005072A
Authority: US
Inventors: N Komatsu; Y Hara; K Asakura; T Suzuki; T Ito
Original assignee: Toyota Central R&D Labs Inc
Current assignee: Toyota Central R&D Labs Inc
Priority date: 1969-01-25
Filing date: 1970-01-22
Publication date: 1973-08-21
Anticipated expiration: 1990-08-21
Also published as: DE2003305B2; DE2003305A1; DE2003305C3

Abstract

This invention relates to a process and apparatus for the localized temper treatment of a steel diaphragm clutch spring. In the inventive process a pair of die members adapted for cooperation with each other and having each a working surface to cover a local area of the steel diaphragm spring to be locally tempered is heated to a temperature at least a tempering temperature of the diaphragm spring and then the diaphragm spring is placed between the die members and squeezed therebetween under pressure, thereby the diaphragm spring being heated up to its tempering temperature at said local area to be tempered through heat conduction from the dies to the diaphragm spring. The inventive apparatus comprises in combination: a first and second die members relatively movable towards and from each other; heating means attached to each of said die members for heating them at a temperature above the tempering temperature forming to its desired shape when squeezed between the cooled die members under pressure.

Description

I United States Patent 1191 1111 3,753,798 Komatsu et al. Aug. 21, 1973 [54] PROCESS AND APPARATUS FOR THE 3,169,156 2/1965 Johnson a a1. 266/5 R PARTIAL 0R LOCALIZED TEMPERING OF FOREIGN PATENTS OR APPLICATIONS A STEEL SHEET'OR THE LIKE STOCK 218,822 7/1924 Great Britain 148/131 [75] Inventors: Noboru Komatsu; Takatoshi Suzuki;

Takuo Ito, all of Nagoya-shi; Yoshiteru Hera, Chiryu-machi, l-lekikai-gun; Kouichi Asakura, Kariya-shi, all of Japan [73] Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho and Aisin Seiki Company Limited, Nagoya-shi, Aichi-ken, Japan [22] Filed: Jan. 22, 1970 [21] App]. No.: 5,072

[30] Foreign Application Priority Data Jan. 25, 1969 Japan... 44/6130 [52] US. Cl. 148/131 [51] Int. Cl C2ld 1/18 [58] Field of Search 148/131, 11.5, 12, 148/134, 130, 145; 263/2, 5; 266/2, 5

[56] References Cited UNITED STATES PATENTS 972,436 10/1910 Clark 148/145 X 1,429,138 9/1922 Harry 148/130 X 1,183,809 5/1916 Frisbee et a1.. 148/131 3,015,292 l/1962 Bridwell 148/11.5 3,130,089 4/1964 Mellinger 148/13 Primary Examiner-Charles N. Lovell Attorney-Sughrue, Rothwell, Mion, Zinn and Macpeak [5 7] ABSTRACT This invention relates to a process and apparatus for the localized temper treatment of a steel diaphragm clutch spring, In the inventive process a pair of die members adapted for cooperation with each other and having each a working surface to cover a local area of the steel diaphragm spring to be locally tempered is heated to a temperature at least a tempering temperature of the diaphragm spring and then the diaphragm spring is placed between the die members and squeezed therebetween under pressure, thereby the diaphragm spring being heated up to its tempering temperature at said local area to be tempered through heat conduction from the dies to the diaphragm spring. The inventive apparatus comprises in combination: a first and second die members relatively movable towards and from each other; heating means attached to each of said die members for heating them at a temperature above the te1npering temperature forming to its desired shape when squeezed between the cooled die members under pressure.

8 Claims, 7 Drawing Figures Aug. 21, 1973 United States Patent [1 1 Komatsu et al.

PAIENIEDmczu ms 3.753.798

sum 1 or 3 FIG l PATENTED All; 2 1 i973 SHEET 2 0F 3 PATENTED AUSZI I975 SHEET 3 f 3 LEVER NUMBER u mmwz r 0 lo 4o so DISTANCE MEASURED, MM, FROM TIP END OF LEVER ELEMENT PROCESS AND APPARATUS FOR THE PARTIAL R LOCALIZED TEMPERING OF A STEEL SHEET-OR THE LIKE STOCK This invention relates to improvements in and relating to a process for the partial or localized tempering of a steel sheetor the like stock, and an apparatus for carrying out the process.

The term stock" means throughout the specification and appended claims a stock per se, a work, an intermediate product, a finished product or the like, as the case may be.

In manufacturing factories, for mechanical parts, especially those for automotive parts such as diaphragm springs or the like various steel sheet parts, it is frequently required to quench locally part of a steel sheet stock to a substantial hardness and to temper the remaining part of the same stock to a rather soft state. For the realization of such locally different heat treatments, those skilledin the art generally adopt any selected one of the following two generally acknowledged heat treatment techniques The first category of this art resides in such that the steel stock is subjected in its entirety successively to a quenching step and a tempering step and finally that part of the stock which must represent a high value of hardness is. subjected locally to a re-quenching step through the high frequency induction heatingprocess as a representative one. i

The second category resides in such that the stock is subjected in its entirety to a quenching step as before, and then the part of the stock which must have a rather soft nature is subjected locally to a tempering step by the high frequency heating process as a representative way.

In the practice of the first category of heat treatment, it is frequently encountered that in the critical zone between the temperedarea and the requenched area of the stock, a softened marginal zone will appear which represents a grave drawback of the product in viewpoint of its strength, even if the problem of increase of manufacturing cost and labor caused by the repeating number of the heat treating steps be neglected from consideration.

On the other hand, the second category of heat treatmentwillprovide a considerable difficulty in the con trol of the tempering temperature.

- In addition theretofand in commonto the both categories of the heat treatment, there must be provided a tedious equipment forhigh frequency heating suchas those of heating coils and power supply appliances necessary for the practice of the localized heating of the steel sheet stock.

It is further encountered generally that in the practiceof the overall quenching of the steel stock as a whole, a considerable thermal distortion develops unavoidably and that the nextsuccessive and localized heat treatment to be adopted in either of the both processing modes in the above sense can not cure the once developed thermal distortion, yet under most circumstances, it may accelerate the distortion.

It is the main object of the invention to provide a process, as well as an apparatus, for obviating the aforementioned conventional drawbacks. More specifically, the invention provides a highlyimproved process and an apparatus therefor for carryingout a local tempering of a steel sheet stock previously quenched in its entirety, in a possible minimum number of steps and with views of several working constituents of the apparatus.

a substantially improved processing efficiency, while removing substantially the thermal deformation developed in the foregoing quenching step.

For attaining the aforementioned mainobject, the process according to this invention resides in such that a pair of die members adapted for cooperation with each other and having each a working surface to cover a local area of a steel stock to be locallytempered is heated to a temperature higher than the tempering temperature of the stock, and then the stock is placed between the die membersand squieezed there between under pressure, thereby the stock being heated up to its tempering temperature at said local area to be tempered through heat conduction from the dies to the stock. v

For carrying out the process according to this invention, such an apparatus is proposed according to this invention which comprises in combination a first and second die membersrelatively movable towards and from each other heating means attached to each of said die members for heating them at a temperature above thetempering temperature of a steel stock to be locally tempered each of said die members having a working surface having dimensions enough tocover the local area of the steel stock to be locally tempered, and die-actuating means for bringing said die members in their working position where the steel stock is squeezed between the working surfaces of the die members under pressure so as to realize a. pressure vcontactof these surfaces with said local area of the stock, thereby heat being conducted from the die members to the local area of the stock for heating the area to the tempering temperature.

These and further objects, features and advantages of the inventionwill appear more apparent when read the. following detailed description of the invention byreference to the accompanying. drawings illustrative of a.

FIG. 1 is an elevational view of an apparatus adapted.

for carryingout the processaccording tothis invention. FIGS. 2 and 3 are enlarged and partially sectioned shown in'FlG. l.

FlG..4 is a. plan view of a diaphragm spring for-autow motive clutch use, as a representative example of the steel sheet stock to be treated upon by the processaccording to the invention, said spring beingshown man enlarged scale when comparing with that shown in FIGS. 1 and 2.

FIG. 5 is a side elevational view of said diaphragm spring shown in FIG. 4. l

FIG. 6 is a comparative test curves of the diaphrag spring subjected to the processes according to priorxart and the invention, showing its hardness distribution.

FIG. 7 is also a comparative test curves of the diaphragm spring subjected to the process according to prior art and the invention, showing its distortion distributio'ri.

Referring now to the accompanying drawings, especially FIG. 1, a preferred embodiment of an apparatus for carrying out the process according to the invention will be described hereinunder in detail.

In FIG. 1, the numeral represents a rigid base or bed which is mounted rigidly on a floor surface only partially shown at 11. A pair of

columns

12 and 13 is rigidly attached at their lower ends onto the bed 10 by welding, screwing or the like conventional fixing means, although not shown. The uppermost ends of these

columns

12 and 13 are rigidly connected together by an upper tie plate 14 which is fixedly attached thereto by conventional fixing means such as screwing, bolting, welding or the like, although not specifically shown on account of its very popularity.

A ram or slide 15 in the form of a rigid horizontal plate is slidably guided along the

columns

12 and 13 in parallel to the upper surface 10a of the bed 10, the upper plate 14 being arranged equally in parallel to said surface 10a.

A hydraulic cylinder 16 having an upper cover flange 16a and a lower cover flange 16b is rigidly mounted on the upper surface 14a of said tie plate 14 at its center, although the fixing means have been omitted only for simplicity of the drawing.

A hydraulic piston 27 is slidably mounted within the interior space of the cylinder 16, thus the cylinder space being divided thereby into an upper chamber 16c and a lower chamber 16d. A piston rod 17 connects rigidly the hydraulic piston 17 with the slide 15, said rod passing sealingly through the lower cylinder cover 16b and the tie plate 15, although the sealing means have been omitted from the drawing only for simplicity.

The upper and lower cylinder chambers 16c and 16d are hydraulically connected through respective pipings l8 and 19 with a hydraulic pressure control valve unit 20 connected with a motor-pump unit 22 which is rigidly mounted on a reservoir vessel 23. The unit 20 is arranged to be controlled by a manual lever 21 in such a way, that an operator brings the lever 21 at its one end position, pressurized oil which is delivered through the oil-filled interior space of the vessel 23 bythe motor-pump unit 22 via piping 18 to the upper cylinder space 16c so as to lower forcibly the assembly comprising piston 27, rod 17 and slide 15 in the downward direction, while oil is discharged from the lower cylinder chamber 16d through piping 19 and control valve unit 20 into the interior space of the vessel 23. On the contrary, when the operator brings the control lever 21 to its opposite end, the reverse function will be invited. In this case, more specifically, pressurized oil is supplied through the piping 19 to the lower cylinder space 16d, while oil is discharged from the upper cylinder space 160, so as to forcibly elevate the said piston-slide or -ram unit. With the control lever 21 positioned at its neutral position, oil supply is ceased, thus the pistonram unit being held in its stopped position so selected by the operator. Such design and function of a hydraulically operated piston-ram unit is commonly known so that no further detailed analysis would be necessary for better understanding of the invention.

The slide 15 is rigidly attached at its bottom surface with an upper holder plate 24 by means of a plurality of fixing bolts 25 as hinted only schematically by dashdotted lines in FIG. 1, said holder plate being fixedly attached with an upper die element 26 through a thermal insulator plate 27 by means of a plurality of fixing bolts of which only one is representatively shown at 28 in FIG. 2.

In the similar manner, yet in an opposing arrangement, the bed 10 is fixedly attached on its upper surface 10a with a lower holder plate 29 which mounts in turn fixedly a lower die element 31 through the intermediary of a conventional thermal insulator 30, although the fixing bolt means are only representatively shown at 32 and 33 in FIGS. 1 and 2, respectively.

The upper die element 26 is shown in FIG. 2 in a more specific way, and the lower die element 31 is shown more in detail in FIGS. 2 and 3.

The steel sheet stock in the form of an diaphragm spring is shown at 34 in its inverted and ready-fortempering position in FIGS. 1 and 2 and in its enlarged top plan and regular elevational views in FIGS. 4 and 5, respectively.

Referring to FIGS. 2 and 3, the upper die member 26 is formed with a convex working surface 26a corresponding to the dished configuration of the inverted work piece 34, and the lower'die member 31 is formed with a concave working surface 31a corresponding to the bottom surface of the same working piece or diaphragm spring.

The work piece diaphragm spring 34, as specifically shown in FIGS. 4 and 5, has generally a truncated cone shape when seen in its elevation and comprises a pcripheral ring part 34a and a plurality of radially and inwardly directing arm or lever elements 34b which are made integral with said ring part called spring part by those skilled in the art. The diaphragm spring stock has been shaped as such on a forming press in advance of subjecting to the heat treatment. The tempering process according to this invention is to be applied locally onlyto said spring part 34a. The working surfaces 26a and 31a formed respectively on the upper and

lower die elements

26 and 31 are so designed and shaped enough to cover the spring part 34a and to be in registration therewith when the die elements are brought into their operating position kept in pressure contact with the stock. r i

As is commonly known, the innermost tip end 34c of each of the lever element must be highly resistant to wear as encountered in its practical use and thus have a high value of hardness by applying a quenching step. For this purpose, the inner extremities of the working surfaces 26a and 31a are defined by the respective concentrically formed

circular recesses

35 and 36 on the upper and lower die

elements

26 and 31, for keeping the lever elements 34b of the work piece 34 untouched with the cooperating working surfaces 26a and 31a of the

die elements

26 and 31 in the course of the heat treatment according to the inventive process. On the bottom of the relieving recess 35 of the upper die element, a conventional heat insulator sheet 37 is fixedly attached by conventional fixing means such as set screw, not shown. In the similar way, a heat insulator sheet 38 is fixedly attached onto the bottom surface of the recess 36 of the lower die element 31. These

insulators

37 and 38 serve for interrupting disadvantageous heat radiation from the die elements towards lever elements 34b when the work piece is being tempered.

Through the body of the lower die element, a plurality of horizontally extending parallel bores 39 are provided, an insulator tube 40 made preferably of a ceramic material being inserted in each of these bores. An electrically heatable element 41, preferably resistant coil of nickel chromium alloy is inserted in each of said insulator tubes, as most clearly seen from FIG. 3.

One side ends of these heatable elements 41 are electrically connected with a common terminal 42, from which an electric cable 43 extends towards a power source, not shown, said terminal being fixedly attached to an insulator plate 44 covering one side of the related die element. In the similar way, the opposite ends of the heating elements 41 are collectedly connected to a certain common terminal, not shown, which is attached to an oppositely arranged insulator plate 45, an electric cable extending equally towards the power source being seen at 48 in FIG. 3.

A similar electric heating unit is equally fitted to the upper die element, as will be easily supposed by observing the upper half of FIG. 2. Therefore, more detailed analysis in this respect could be dispensed with, without sacrifice of better understanding of the invention.

The upper die element 26 is enclosed by four insulator plates as similar to those denoted 44-47 in FIG. 2, but only an opposingly arranged pair is seen at 44 and 45'.

All these insulator plates serve for preventing any appreciable heat radiation from the respective die elements so as to improve the overall thermal efficiency of the apparatus, some of these being utilized for supporting current distributing or collecting terminals for electrical heating of the die elements proper, as was briefly described above.

In FIG. 2, the numeral 49 denotes a thermocouple 49, preferably Chromel-Alumel type, which is inserted in a blind bore 50 formed perfectly through insulator plate 49 and partially through the material of the upper die member proper, said thermocouple being electrically connected through conductor means to a die temperature control unit 52, shown in FIG. 1.

In the similar way, the lower die element proper is fitted with a thermocouple 49' which is connected through conductor means 51' to the control unit 52.

As the material of the die elements, steel or the like better heat-conducting metal can be employed.

In the following, a preferred example for carrying out the localized tempering of the diaphragm spring 34 on the machine so far shown and described will be described in detail.

The material of the diaphragm spring was of JIS, SK-S. The term JIS is an abbreviation of Japanese Industrial Standard. The outside diameter of the diaphragm amounted to 170 mm, the thickness being 2 mm. The diaphragm had been heated at 830C and quenched in an oil bath as usual.

Then, the resistance elements 41 in the both die elements were energized by closing a switch, not shown, for supplying heating current from the power source,

said conductors 43; 48 for the both die elements being connected in series to each other and through said control unit 52 to the power source. The heating current was so controlled by manipulating suitable control means, not shown, in the control unit 52 that these die elements were kept at 625C which is a desirous tempering temperature for the stock, the latter being then placed on the upper surface of the lower die element. Then, control lever 21 is actuated, so as to supply pressurized oil to the upper cylinder chamber 16c through piping l8 and to discharge oil from the lower cylinder chamber 16d through piping 19, for lowering the hydraulic piston 27 together with rod 17, slide 15, holder plate 24 and upper die element 26. When the upper die was brought into engagement with the lower die through the processing work piece, the die application pressure was regulated to 25 kg/sq. cm, as an example, which did not affect upon the thickness of the stock.

Under these operating conditions, the spring part 34a of the stock 34 was kept in pressure contact with the working surfaces of the upper and lower die elements, and heat was quickly transmitted therefrom to the stock at its spring part which was then heated up rapidly to 625C which was a proper tempering temperature of the stock, while the lever elements were practically not affected thermally on account of effective interruption of the radiant heat from the die elements to these lever elements, indeed, by the provision of

heat insulators

37 and 38. Any practical radiation loss of heat from the die elements to ambient atmosphere was considerably remedied by the provision of the heat insulator plates 44 47 and the like.

The electrical arrangement of resistant element groups of the both die elements was such that they are mutually connected in series to each other, and that the constituent resistance elements of each group are connected in parallel and in a substantially evenly distributed multistage and parallel way, a highly even and quick heating-up of the die element was realized for optimum heat conduction from the die means to the stock.

According to our practical experiments, it was enough to perform the desired temper by keeping the lever elements of the stock under heat conducting and pressure contacting conditions between the both die elements for a short period such as 15 seconds. Upon lapse of this tempering period, the operator manipus lated the control lever 21 to its opposite end position, so as to supply pressurized oil to the lower cylinder chamber 16d through piping l9 and to discharge oil from the upper cylinder chamber 16c through piping 18, for initiating a return movement of the hydraulic piston 27 together with the upper die element 26. When the piston came to its uppermost position, the operator manipulated the control lever to its neutral position so as to stop the upward piston movement. Then, the tempered work piece was taken out from the lower die element and cooled rapidly by immersing the tempered work piece in acold oil bath. As measured, the spring part 34a was tempered to the desired hardness: about I-I C 43, whilethe tip ends of the lever elements 34b maintained the initial quenched hardness of about H C 65.

Then, the thus tempered diaphragm spring was marked with thirty three measuring points along a radial line 53 extending from the tip end of a lever element 34b to the outer periphery of the spring part 340, the pitch between two successive measuring points amounting to 2 mm. Rockwell hardness was measured at each of these points and the results were plotted against the distance measured radially from the minermost lever end, as shown by a curve a shown in FIG. 6. From this curve a, it will be seen that the spring part extending within the range 40 mm distant from the. lever end represents H C 40 45 with no appreciable variation in the hardness, which means that the spring,

part was well and evenly tempered. It can be further seen that the tip end portion extending from nil to about 15 mm from the lever end extremity represents H C 65 66 which means that the quenched hardness in this end area were well preserved in spite of thCl aforementioned tempering treatment. Thus, the desired local tempering was perfectly realized.

It will be further seen that there is no critical zone between the spring part and the lever part which represents a softer hardness to a substantially unfavorable degree.

In FIG. 6, a comparative test curve b is additionally shown. This curve was obtained by making similar hardness measurements on a similar diaphragm spring which has been quenched and tempered in its entirety, and locally subjected only at its spring part to a requenching through conventional high frequency induction heating.

It will be clearly seen in the conventional process that a marginal softer zone appeared between the quenched and the tempered zone, as denoted by a reference symbol b. In addition, the conventionally quenched and tempered product represents substantial variations in the hardness within the tempered zone.

Since the localizedly tempered zone such as the spring part of a diaphragm spring is heated under pressure during the tempering process according to this invention by squeezing the stock between the upper and lower die elements, a considerable effect for obviating a quench distortion developed in the previous quenching step is additionally attained. This will naturally contribute considerably for attaining a distortionless temper.

For determining this effect, the practical heights of the sixteen lever ends from a horizontal plane upon which a quenched diaphragm spring stock in advance of the practice of a temper processing according to this invention was placed were measured. The results were shown by a curve S, representing substantial variations in the height of lever tip ends, said height variations representing a measure of distribution of the quench distortion over the whole area of the diaphragm spring. The maximum difference was measured to about 4.5 mm, thus showing a considerable amount of quench distortion. Whenthis quenched stock was tempered in accordance with the novel teachings of the invention, and similar measurements were made, a substantially straight curve Q was obtained, which means a considerable distortion-reducing effect.

When a similar diaphragm spring stock was as a whole quenched and tempered, and finally locally requenched only at the lever tip ends, the height distribution of lever ends were substantially similar to that shown by the curve S, which means that substantially none of quench distortion correcting effect was obtained.

On the contrary, the curve Q shows only a slight maximum height'difference amounting to about 0.2 mm which means that the quench distortion was reduced to about one twentieth of that appeared in the foregoing quenching step.

As clearly understood from the foregoing, effective and selectively localized tempering of a steel stock, preferably of sheet or the like, may be easily and positively carried into effect within a short time period and without forming a marginal zone of an advantageous soft er nature, as otherwise appearing between the quenched region and the tempered region, when following the novel teachings proposed by the invention.

The thus tempered product represents a favorable strength condition and is relieved of otherwise preserved quench deformation. In addition, the tempering heat treatment can be completed in one and the same processing stage. These advantages represent naturally a considerable progress in the art.

The process and the apparatus may be practiced in somewhat modified manner from those described in the foregoing. As an example, the process can be brought into effect with use of a plurality of pairs of working surfaces which are heated to various different temperatures so as to provide different temper effects to a single work piece.

The temperature of the cooperating die elements for treating steel stock may be higher than the conventional tempering temperatures in order to accelerate the tempering process to a still shorter treating period. This temperature increase may amount to several hundred degrees, depending upon the tempering period and temperature the practical temperature range is between l50-730C. The operating pressure may amount to a value ranging from 1-3 ,000 kgs. per square centimeter according to the thickness of the stock.

We claim:

1. A process for the localized temper treatment of a heat treated quenched steel diaphragm clutch spring generally having a truncated cone shape comprising the steps of:

a. heating at least one pair of die members, consisting of an upper die member and a lower die member generally corresponding to the configuration of the diaphragm spring each having a working surface for engaging a predetermined localized area of the quenched diaphragm spring, to a predetermined temperature at least equal to the tempering temperature of the diaphragm spring being treated;

b. placing said quenched diaphragm spring between said pair of die members;

c. pressing said quenched diaphragm spring between the working surfaces of the die members under pressure;

d. heating the predetermined local area of the diaphragm spring to a tempering temperature by heat conduction from the working surfaces of the die members to the diaphragm spring;

e. removing the heated diaphragm spring from between said pair of die members; and

f. cooling said diaphragm spring, whereby said quenched diaphragm spring is locally tempered at that portion thereof in contact with the working surfaces of said pair of die members, while simultaneously relieving the quenching deformation of the diaphragm spring created during the quenching thereof during the process of the tempering treatment.

2. A process according to claim 1, wherein said working surfaces of the die members are heated to a temperature range from to 730C.

3. A process according to claim 1 wherein said diaphragm spring is pressed between said working surfaces of the die members under a pressure range from 1 to 3,000 kgs/sq. cm.

4. A process according to claim 1, further comprising the step of providing a plurality of pairs of die members, each pair of die members having a working surface to cover a different predetennined local area of the quenched diaphragm spring.

5. A process according to claim 4, wherein the working surfaces of each pair of die members are heated to different temperatures corresponding to the tempering phragm spring is pressed between the working surfaces of each pair of said die members under a pressure range from 1 to 3,000 kgs/sq. cm. i

8. A process according to claim 5, wherein said diaphragm spring is for an automotive clutch.

Claims

2. A process according to claim 1, wherein said working surfaces of the die members are heated to a temperature range from 150* to 730*C.
3. A process according to claim 1 wherein said diaphragm spring is pressed between said working surfaces of the die members under a pressure range from 1 to 3,000 kgs/sq. cm.
4. A process according to claim 1, further comprising the step of providing a plurality of pairs of die members, each pair of die members having a working surface to cover a different predetermined local area of the quenched diaphragm spring.
5. A process according to claim 4, wherein the working surfaces of each pair of die members are heated to different temperatures corresponding to the tempering temperatures of the predetermined local area of the diaphragm spring to be tempered.
6. A process according to claim 5, wherein each pair of said die members are heated to a temperature range from 150* to 730*C.
7. A process according to claim 5, wherein said diaphragm spring is pressed between the working surfaces of each pair of said die members under a pressure range from 1 to 3,000 kgs/sq. cm.
8. A process according to claim 5, wherein said diaphragm spring is for an automotive clutch.