U.S. patent number 3,753,798 [Application Number 05/005,072] was granted by the patent office on 1973-08-21 for process and apparatus for the partial or localized tempering of a steel sheet-or the like stock.
This patent grant is currently assigned to Kabushiki Kaisha Toyota Chuo Kenkyusho and Aisin Seiki Company Limited. Invention is credited to Kouichi Asakura, Yoshiteru Hara, Takuo Ito, Noboru Komatsu, Takatoshi Suzuki.
United States Patent |
3,753,798 |
Komatsu , et al. |
August 21, 1973 |
PROCESS AND APPARATUS FOR THE PARTIAL OR LOCALIZED TEMPERING OF A
STEEL SHEET-OR THE LIKE STOCK
Abstract
This invention relates to a process and apparatus for the
localized temper reatment 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. This invention relates to
improvements in and relating to a process for the partial or
localized tempering of a steel sheet- or 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 skilled in 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 heating process as a representative one. 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 tempered area 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
treatment will provide a considerable difficulty in the control of
the tempering temperature. In addition thereto and in common to the
both categories of the heat treatment, there must be provided a
tedious equipment for high frequency heating such as 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 practice of the overall
quenching of the steel stock as a whole, a considerable thermal
distortion develops unavoidably and that the next successive 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
highly improved process and an apparatus therefor for carrying out
a local tempering of a steel sheet stock previously quenched in its
entirety, in a possible minimum number of steps and with a
substantially improved processing efficiency, while removing
substantially the thermal deformation developed in the foregoing
quenching step. For attaining the aforementioned main object, 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
locally tempered is heated to a temperature higher than the
tempering temperature of the stock, and then the stock is placed
between the die members and squeezed 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. 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
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 of a steel stock to be
locally tempered ; each of said die members having a working
surface having dimensions enough to cover 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 contact of 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 invention will appear more
apparent when read the following detailed description of the
invention by reference to the accompanying drawings illustrative of
a process and an apparatus, by way of example, for the localized
tempering of a diaphragm spring as a representative example of the
steel sheet stock capable of being treated in accordance with the
novel teaching of the invention.
Inventors: |
Komatsu; Noboru (Nagoya-shi,
JA), Suzuki; Takatoshi (Nagoya-shi, JA),
Ito; Takuo (Nagoya-shi, JA), Hara; Yoshiteru
(Chiryu-machi, Hekikai-gun, JA), Asakura; Kouichi
(Kariya-shi, JA) |
Assignee: |
Kabushiki Kaisha Toyota Chuo
Kenkyusho and Aisin Seiki Company Limited (Nagoya-shi,
Aichi-ken, JA)
|
Family
ID: |
11629901 |
Appl.
No.: |
05/005,072 |
Filed: |
January 22, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jan 25, 1969 [JA] |
|
|
44/6130 |
|
Current U.S.
Class: |
148/580; 148/639;
266/128 |
Current CPC
Class: |
C21D
1/34 (20130101); C21D 9/46 (20130101); B21J
5/00 (20130101); C21D 9/02 (20130101) |
Current International
Class: |
B21J
5/00 (20060101); C21D 9/02 (20060101); C21D
1/34 (20060101); C21D 9/46 (20060101); C21d
001/18 () |
Field of
Search: |
;148/131,11.5,12,134,130,145 ;263/2,5 ;266/2,5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lovell; Charles N.
Claims
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 150.degree.
to 730.degree.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.degree. to
730.degree.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.
Description
In the drawings :
FIG. 1 is an elevational view of an apparatus adapted for carrying
out the process according to this invention.
FIGS. 2 and 3 are enlarged and partially sectioned views of several
working constituents of the apparatus shown in FIG. 1.
FIG. 4 is a plan view of a diaphragm spring for automotive clutch
use, as a representative example of the steel sheet stock to be
treated upon by the process according to the invention, said spring
being shown in an 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.
FIG. 6 is a comparative test curves of the diaphragm spring
subjected to the processes according to prior art 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 distribution.
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 10 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 18 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 by the 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 16c, 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 piston-ram 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 dash-dotted 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-for-tempering 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 peripheral 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.
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-5. 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 830.degree.C 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
625.degree.C 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 18 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 625.degree.C 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 manipulated the control lever
21 to its opposite end position, so as to supply pressurized oil to
the lower cylinder chamber 16d through piping 19 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
a cold oil bath. As measured, the spring part 34a was tempered to
the desired hardness: about H.sub.R C 43, while the tip ends of the
lever elements 34b maintained the initial quenched hardness of
about H.sub.R 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 34a, 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 - 70 mm distant from the lever end
represents H.sub.R 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.sub.R C 65 - 66 which means that the quenched hardness in this
end area were well preserved in spite of the 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
re-quenching 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. When this 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 re-quenched 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 softer 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
150.degree.-730.degree.C. The operating pressure may amount to a
value ranging from 1-3,000 kgs. per square centimeter according to
the thickness of the stock.
* * * * *