U.S. patent number 3,848,496 [Application Number 05/323,955] was granted by the patent office on 1974-11-19 for die and spring assemblies having particular application to stripper plates.
This patent grant is currently assigned to Dayton Progress Corporation. Invention is credited to Allan E. Randolph, Sr., Harry A. Stevens.
United States Patent |
3,848,496 |
Stevens , et al. |
November 19, 1974 |
DIE AND SPRING ASSEMBLIES HAVING PARTICULAR APPLICATION TO STRIPPER
PLATES
Abstract
A die for use in a punch press or like equipment embodying
improvements in the mount and suspension of a spring biased
stripper plate. It features stripper springs endowed with a
definite pre-load by virtue of a special cage assembly. The caged
spring assemblies are so constructed and applied that there is
absolutely no pressure on the stripper plate when the die is in an
open position. In preferred embodiments of the caged spring
assemblies, the open spaces between the coils of a contained spring
are reduced to a dimension less than that of the thickness of the
coils themselves. This prevents the coils from winding or screwing
and from materially affecting the prescribed pre-load in event of
spring breakage. The invention further features means to maintain
the stripper spring preload constant and to preserve a constant
relation of component parts of the die when adjustment of the die
tools is required.
Inventors: |
Stevens; Harry A. (Union,
OH), Randolph, Sr.; Allan E. (Dayton, OH) |
Assignee: |
Dayton Progress Corporation
(Dayton, OH)
|
Family
ID: |
23261436 |
Appl.
No.: |
05/323,955 |
Filed: |
January 15, 1973 |
Current U.S.
Class: |
83/133;
83/140 |
Current CPC
Class: |
B21D
45/006 (20130101); Y10T 83/2159 (20150401); Y10T
83/2144 (20150401) |
Current International
Class: |
B21D
45/00 (20060101); B26f 001/14 () |
Field of
Search: |
;83/140,133,139,143,141,142,136 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Meister; J. M.
Attorney, Agent or Firm: Bloom; Jerome P.
Claims
Having thus described our invention, we claim:
1. In a die for use in a punch press or like equipment including a
first die means providing a first die shoe to which is secured a
tool retainer, a second die means providing a second die shoe to
which is fixed a die plate, stripper plate means interposed between
said die means and normally displaced from and mounted for movement
to and from said tool retainer, work being accomplished by the die
in movement of one of said die means relative the other between an
open position of the die in which said tool retainer and stripper
plate are displaced from each other and from said die plate and a
closed position in which work is performed by tools mounted by said
tool retainer, and biasing means positioned between said first die
means and said stripper plate, said biasing means including
compressible spring means and a cage-like housing therefor, said
housing basing on said stripper plate and having a relatively
reciprocable relation to said first die means and there being means
responsive to relative motion of said die means in a closing
movement of the die to compress said spring means independently of
said housing, expansion of said spring means responsive to relative
motion of said die means in an opening movement of the die being
limited by said housing.
2. Apparatus as in claim 1 characterized by said means to compress
said spring means including means positioning, at least in part,
internally of the spring means and projecting from said housing to
be contacted by said first die means.
3. Apparatus as in claim 2 wherein said means positioning, at least
in part, internally of said spring means has a pin-like form and
provides a base for maintaining the line of said spring means and
said cage-like housing is arranged also to maintain the line of
said spring means.
4. Apparatus as in claim 1 characterized by stripper plate mounting
means including screwlike connectors suspending said stripper plate
means from said first die means around the body of each of which
connectors is a sleeve the length of which is governed in dimension
by the desired distance between said stripper plate and said tool
retainer in the open position of the die.
5. Apparatus as in claim 4 characterized by said sleeve having
means at one end thereof positioning normally, in the open position
of the die, on the surface of said tool retainer which is remote
from the stripper plate while the body of the sleeve is adapted to
project from said tool retainer to abut the surface of the stripper
plate most adjacent the tool retainer, said sleeve being axially
displaceable in reference to said tool retainer on the closing of
said die.
6. Apparatus as in claim 5 wherein said sleeve provides means
readily adjusted as to its length to accommodate an adjustment in
the spacing between said stripper plate and said tool retainer
while maintaining the described position thereof in the open
position of the die.
7. Apparatus as in claim 1 characterized by said cage-like housing
limiting the axial length of said spring means and establishing
thereby a required pre-load.
8. Apparatus as in claim 7 characterized by said cage-like housing
having turned over ends containing said spring means and means
within one of its turned over ends to prevent full axial expansion
of said spring means within said cage.
9. Apparatus as in claim 8 characterized by a pin like plunger
inserted within said spring means, which is coiled thereabout
within said cage-like housing, having said means preventing said
full axial expansion of said spring means in connection
therewith.
10. Apparatus as in claim 9 characterized by said plunger having an
extension normally projected in a recess in said first die means
aligned with the related spring means and having the projected
extremity of said extension normally spaced from the bottom of said
recess when the die is in its open position.
11. Apparatus as in claim 10 characterized by said plunger
extension providing means for adjustment of the assembly thereof
with said spring means and the said cage therefore to readily
accommodate the sharpening or adjustment or replacement of tools
mounted to said tool retainer so as to maintain the pre-load
condition established for said spring means to inhibit an
application of stress to said stripper plate in the open position
of the die.
12. Die apparatus according to claim 1, characterized by stripper
plate mounting means including hanger means guiding said stripper
plate in relative approaching and separating motions with respect
to said tool retainer of said first die means in opening and
closing of the die and limiting relative separating motion, said
hanger means including screw means to effect service adjustments in
the projected position of said stripper plate relative to said tool
retainer.
13. Apparatus according to claim 1, wherein said cage-like housing
presents an outer end portion to said first die means and confines
said spring means between said outer end portion and an inner end
portion based on said stripper plate means, said means to compress
said spring means including a free floating plunger having a
portion interposing between said spring means and said outer end
portion of said housing, another portion of said plunger projecting
from said outer end portion of said housing to be contacted by said
first die means.
14. In a die for use in a punch press or like equipment providing
opposing first and second die means movable in relative approaching
and separating motions to die closed and die open positions and
providing an interposing stripper plate means, hanger means placing
said stripper plate means in a connected relation to said first die
means and limiting relative projection of the plate toward said
second die means, means comprised in said hanger means to select a
projected position of said stripper plate and to retract said plate
relatively to said first die means to establish and maintain an
operating position of said stripper plate irrespective of service
adjustments, spring means for biasing said stripper plate to a
projected position, cage means containing said spring means to
establish a predetermined compression thereof which relieves said
stripper plate of pressure thereon in an open position of the die
while establishing and maintaining a pre-load condition of said
spring means, and means, forming a reducible axial extension of
said spring means and projecting beyond one end of said cage means,
for obviating increases in the pre-load of said spring means in
different retracted positions of said stripper plate.
Description
BACKGROUND OF THE INVENTION
This invention relates to die apparatus such as used in punch press
and like equipment. It features improvements in dies which are
particularly related to the mount and adjustment of spring biased
stripper plates.
The stripper plate of a die is intended to serve several important
functions. These functions should include a flattening of the stock
to which the die tools are applied, prior to their impact. If not
properly achieved, the surface of the stock presented to the tool
might be wavy and cause fracture or malfunction of the die tools. A
second desired function of a stripper plate is to prevent lateral
movement of the stock. Failure to achieve this will obviously
result in ruin of the stock. A third desired function of the
stripper plate is to strip stock from the die tools, as a die is
moved from its closed to its open position following a cutting,
perforating, or forming operation by the tools.
In efforts to achieve the desired functions above noted, it has
been the practice in the past to heavily preload the stripper plate
through the medium of its backing or biasing springs. In
conventional practice the mount and preload of a stripper plate is
such that the stripper plate is continuously stressed, even in the
open position of the die in which it is embodied. The stress so
applied creates pressure points which tend, either initially or
eventually, to bow or warp the stripper plate. Moreover, when the
die is open this stress is transferred to the plate hangers in
direct shear. This last introduces a requirement for a considerable
number of hangers in the conventional mount of a stripper
plate.
Further problems encountered in the mount of stripper plates as
practiced in the prior art are evidenced each time the die punches
or other tools must be sharpened or adjusted as to their projected
length. With a shortening of the tools, the stripper plate must be
adjusted. When this occurs, the problems noted above are
compounded. This is self evident since the backing or biasing
springs are normally further loaded, adding to the pre-load and
stressing further the stripper plate and its hangers.
SUMMARY OF THE INVENTION
The present invention obviates the above noted problems as well as
other problems which are inherent in prior art practice referenced
to the subject matter at hand. It provides an improved die
incorporating a spring biased stripper plate, the backing springs
of which are preloaded and so applied that there is no pressure on
the stripper plate in an open position of the die. Means are
provided to facilitate the adjustment of the position of the
stripper plate without affecting the preload of the stripper
springs. Thus, in accordance with the invention practice the spring
preload may be maintained constant.
The improvements noted are enabled by a particular caged housing of
the stripper springs. An extremely important advantage of the
invention is that the construction of the caged stripper spring
assemblies as here provided offers safety in use to a degree not
heretofore possible. Use of a particular type of hanger unit for
the stripper plate further facilitates a simple and inexpensive
precision adjustment of the related parts.
A primary object of the invention is to provide improvements in
dies which are economical to fabricate and render the dies more
efficient and satisfactory in use, adaptable to a wider variety of
applications and unlikely to malfunction.
Another object of the invention is to provide an improved spring
assembly having a particularly advantageous application as a means
for biasing a stripper plate forming part of a die.
A further object of the invention is to provide a die wherein a
stripper plate may be backed by springs which may be maintained
under a constant load which in an open position of the die
apparatus applies no pressure to the stripper plate and thereby
facilitates assembly and maintenance.
An additional object of the invention is to provide simple and
inexpensive means for a compensating adjustment in the position of
a stripper plate in a die without adding load to its spring biasing
means.
A further object of the invention is to provide improved means for
suspension of a stripper plate in a die.
Another object of the invention is to provide improvements in dies
and components thereof and in particular a stripper spring assembly
possessing the advantageous structural features, the inherent
meritorious characteristics and the means and mode of use herein
described.
With the above and other incidental objects in view as will more
fully appear in the specification, the invention intended to be
protected by Letters Patent consists of the features of
construction, the parts and combinations thereof, and the mode of
operation as hereinafter described or illustrated in the
accompanying drawings, or their equivalents.
Referring to the accompanying drawings wherein is shown one but
obviously not necessarily the only form of embodiment of the
invention;
FIG. 1 is a fragmentary view of a die in an open position, shown
partly diagrammatic and in cross section, embodying the various
features of the present invention; and
FIG. 2 is a view similar to that shown in FIG. 1 but illustrating
the die in a closed position.
Referring to the drawings, the portions of the die there
illustrated are embodied in a suitable press to perform punching
and like operations. Only so much of the structure as may be
necessary for an understanding of the invention is shown.
As shown, elements of the die include a tool or punch retainer
plate 10, a matrix or die retainer plate 12 and an interposing
stripper plate 14. The plate 10 is backed by and releasably
attached to an upper die shoe 11. The latter is suitably fixed to
the ram of the press (not shown). Bolts are conventionally applied
to hold the plate 10 in a fixed relation to the die shoe. The die
retainer plate 12 as installed, will have a fixed mount to a lower
die shoe (not shown) and forms a work surface over which a piece of
stock W is positioned for performance of work thereon by suitable
die tools fixed to and projected from the plate 10. The tool
retainer plate 10 and its backing shoe 11, and the die retainer
plate 12 and its backing shoe, may be regarded as providing,
respectively, an upper or first die means and a second or lower die
means.
The tool or punch retainer plate 10 has a plurality of through
bores 16, the upper end of each of which is expanded adjacent the
die shoe 11 by a counterbore 18. Each bore 16 accommodates the
shank of a perforator or punch type tool 20 the head of which is
expanded to provide thereon an external flange which seats to the
annular shoulder provided by the counterbore 18. It will be noted
that the surface defining the head extremity of each punch 20 will
so position that it is flush with the uppermost surface of the
plate 10. Each punch element 20 projects through and beyond the
plate 10 and at the outer projected extremity thereof has a reduced
diameter work engaging portion 22.
The plate 10 has a further plurality of through bores 28, each of
which accommodates the projection therethrough of a hanger device
24. Each device 24 includes a cylindrical sleeve 26 which has a
sliding fit with respect to the wall defining its bore 28. At what
might be considered its upper end, each sleeve 26 projects through
and beyond the bore 28 and has an external flange 27 which has an
annular configuration. The flange 27 is adapted to seat to the
upper surface of the plate 10, about the bore 28 in which the
sleeve is inserted. The opposite end of the sleeve 26 projects, in
each case, through and beyond its bore 28 to orient in a
substantially parallel relation to the punch elements 20. Further
comprised in each hanger device 24 is a socket head cap screw 25.
The threaded shank of the screw 25 is projected through the sleeve
26 to have its lower extremity project through and beyond what
might be regarded as a lower or outer end of the sleeve. The
projection of the screw 25 is limited as its relatively enlarged
head 30 seats on the flange 27. It is noted that the head 30 has a
socket to receive an Allen type wrench.
The plate 10 is formed with a plurality of additional through bores
36, each of which accommodates a caged spring assembly 38. Each
spring assembly 38 has a generally cylindrical configuration which,
as installed, has a generally parallel relation to the punches 20
and the hanger devices 24. The outer housing 44 of each spring
assembly has a generally cylindrical tube form and its respective
vertical extremities are each turned over to define inwardly
projected and radially directed flange-like abutment portions 29
and 31. With reference to the drawings, it may be seen that the
upper abutment portion or flange 29 defines an opening the center
of which lies in the central or vertical axis of the housing 44.
Each housing 44 provides a cage for a coil spring 46 the lower
extremity of which seats to the lower flange or abutment 31 while
its upper extremity positions concentrically about the pin-like
lower end portion of a plunger element 48. The plunger 48 has an
intermediately positioned portion 50 which is enlarged in diameter
to form a shoulder to either face thereof. The shoulder 50 has its
upper surface arranged to limit against the upper abutment 29
formed on the housing 44. The lower surface of shoulder portion 50
provides a limiting surface for the upper end of the spring 46. The
plunger 48 includes an extension 35 which projects beyond the
shoulder portion 50, through the opening defined by the upper
abutment 29. It will be seen that by a suitable selection of the
spring 46, an appropriate selection as to the length of the cage
44, and a predetermined dimension of the shoulder portion 50 on the
plunger 48, in an axial sense, one can provide a definite preload
on the spring elemnt 46. The criteria for obtaining the desired
preload are obviously easy to determine.
Noting the drawings, the upper die shoe 11 is provided with
apertures or recesses to form extensions of the bores 28 and 36
provided in the punch retainer plate 10 to accommodate their
variously related components. For example, formed in the die shoe
11 are openings 32 positioned in correspondence with the bores 28
and forming axial extensions thereof. In each case the bore 32 is
enlarged in diameter with respect to the diameter of the related
bore 28 in the plate 10. This enables the bore 32 to accommodate
the flange 27 on a sleeve 26 which seats to the upper surface of
the plate 10 and the head 30 of the screw 25, which seats in turn
to the flange 27. Further, the die shoe 11 has a series of
cylindrical recesses 40 formed in the bottom thereof each of which
is of like diameter and forms an axial extension with respect to a
related bore 36 in the plate 10. In the case illustrated the upper
end of each cage 44 and the relatively projecting extension 35 of
the related plunger 48 is accommodated in a recess 40. The length
of the spring assembly 38 will preferably be such that the
projected end of plunger extension 35 will have a slight clearance
at its upper surface with respect to what may be considered the
bottom of the recess 40 when the die is in the open position. The
material of the portion 35 of the plunger 48 is such to lend itself
to easy grinding whereby to make specific changes in its thickness
or length, the purpose of which will be further described.
The upper die shoe 11 does not provide recesses to align with bores
16 in the plate 10. Thus, the bottom surface of the die shoe 11
provides for an abutting engagement therewith of the heads of the
punches 20.
Referring now to the stripper plate 14, it will be seen that this
plate has a through bore 52 aligning with each retainer plate bore
16, adapted to receive therein the reduced diameter working
extremity 22 of a punch 20. At the upper extremity thereof each
bore 52 is enlarged by a counterbore to accommodate the entry
therein of a portion of the shank of the related punch, in the
course of a working of the die. The stripper plate 14 also has an
internally threaded aperture 34 arranged to align with each bore 28
formed in the plate 10. The dependent extremity of each screw 25 is
threaded into an aperture 34 and the plate 14 is thereby suspended
from the plate 10. Still further, the stripper plate 14 has a
cylindrical recess 42 in its upper surface aligning with each bore
36 in the plate 10 to accommodate therein and seat to its base the
lower extremity of a stripper spring assembly 38.
The matrix or die retainer plate 12 similarly has a plurality of
through bores 54 respectively aligning with the bores 16 of the
retainer plate 10 and with the through bores 52 of the
intermediately disposing stripper plate 14. Pressed in each bore 54
is a tubular die button 58. The latter has an expanded head portion
which seats in a counterbore 56 in the lower end of the particular
bore in which it is placed.
In an assembled position of the parts, it will be seen that each
punch 20 is aligned with a die button 58 in the die retainer plate
12 and the head thereof is abutted to and backed by the lower die
shoe. (not shown)
The caged stripper spring assemblies (only one thereof being
illustrated) are oriented similarly to the punches to have the
lower end thereof seated in each case in a recess 42 in the
stripper plate 14 and the vertically projected plunger portion
thereof received in a recess 40 in the upper die shoe 11. The head
extremity of the plunger portion 35 will position with slight
clearance thereabove under no load conditions as in the open
position of the die.
Additionally, the hanger devices 24 (only one thereof being
illustrated) will in the no load position of the parts shown in
FIG. 1 have the sleeve portion 26 thereof positioned so its lower
end seats freely on the top of the stripper plate as it is
suspended by virtue of the flange 27 at its upper extremity seating
to the top of the punch retainer plate 10. The screw portion 25 of
each hanger device will engage the stripper plate as described and
have the head 30 thereof abutted to the flange 27 of the related
sleeve.
As mentioned previously, in the first instance, in the caging of
the springs 46, there is applied thereto a preload of a definite
predetermined character, which is readily determined by the
original length of the springs and their contained length as
determined by the thickness or depth of the shoulder portion 50 of
the plunger 48 and the dimension between the flange-like abutment
portions of the cages 44. It should be noted that in each assembly
the spring 46 is not only closely contained and guided by the inner
wall of its cage but the pin-like body portion of the plunger 48
which depends below the shoulder portion 50 will closely guide and
maintain the vertical orientation of the spring. The hanger devices
24 will be dimensioned correspondingly to the spring assemblies as
indicated so that in an open position of the die there will be no
additional load placed on the springs 46 and accordingly there will
be no load or stress placed on the stripper plate 14 in an open
position. The built-in specific preload in the springs 46 per se
determine that the stripper plate assembly will function precisely
as desired in every respect.
Considering the assembly of the die parts as illustrated in FIG. 1,
it will be therefore seen that the stripper plate 14 is effectively
suspended from the retainer plate 10 by hanger devices 24 with the
flanged heads 27 of their sleeves 26 abutting against the upper
surface of the punch retainer plate 10 to define the extent to
which the stripper plate will be projected relative to plate 10. In
such projected position the stripper plate will occupy a position
relative to the punches 20 to house the lower dependent working
extremities 22 of the punches within the bores 52, immediately
adjacent and spaced from the lower surface of the stripper
plate.
Thus, the compression springs 46 are fully contained and their
length and preload basically determined by their respective cages
44. The preload effect on the springs will be such, of course, to
urge their related plungers 48 axially outward and upward in each
case with such motions being limited by the contact of the shoulder
portion 50 with the abutment 29 formed by the inturned upper
extremity of its particular cage. The parts of each spring assembly
as previously noted are so structured and related that with the
spring 46 expanded to its allowable limits and with shoulder 50
engaging the abutment 29, the upper extremity of the plunger
portion 35 is spaced from the bottom of recess 40 thereabove a
distance slightly to clear the same. Thus, in the no load position
of the die shown, no reactant force of a spring 46 is applied to
the upper die shoe and there is no reactant force directed from the
caged spring assemblies to the stripper plate 14. Attention is
directed to the fact that in preferred embodiment for certain
applications the spacing of the coils of each spring are made such
that the axial dimension thereof is less than the thickness of the
wire of which the spring is made. Thus, if during die operation a
spring might break it inherently will not be able to wind or screw
on itself. This insures that there will not be any material change
in the preload.
In the operation of the die apparatus illustrated, when the ram of
the press in which it is installed descends, the die shoe 11, tool
retainer plate 10 and its mounted punch elements 20 descend
simultaneously and vertically therewith, toward the relatively
stationary die retainer plate 12 and the work piece W which is
moved thereon. In the course of such movement, the lost motion
inherent in the spacing between the heads of plungers 48 of the
caged spring assemblies and the bases of the recesses 40 which
contain them is taken up and thereafter the stripper plate spring
assemblies and the stripper plate 14 itself move unitarily downward
with the tool retainer plate 10, the springs 46 providing a
yielding force to maintain the position required of the stripper
plate by virtue of their preload. The relationship of the parts
substantially as illustrated in FIG. 1 accordingly is substantially
retained until stripper plate 14 contacts the work piece W
whereupon the upper die shoe 11 and tool retainer plate 10 move
relatively to the stripper plate, with the extremities 22 of punch
elements 20 being caused thereby to project through and beyond
bores 52 to penetrate the work piece and pass into the die buttons
58 in the lower die plate 12. In the course of this motion, as the
punch extremities pierce the work W they project into the die
buttons the cut slugs, which are allowed to drop free of the die
buttons, through the expanding tapering bores thereof. Downward
motion of the shoe 11 and tool retainer plate 10 relative to
stripper plate 14 as the latter engages the work piece accomplishes
a compression of the springs 46. This is produced by reason of the
reactant load forcing the cages 44 vertically of the plungers 48,
which at this point are abutted to the die shoe 11. Resultingly, as
seen in FIG. 2, the flange portions 29 of the cages will be
displaced vertically, from their no-load position in abutment with
plunger portions 50. Each hanger sleeve 26 will be correspondingly
displaced with its related hanger screw 25. At this time the
stripper plate 14 is powerfully stressed with, however, the applied
load being sustained by the plate 11 and the structure which backs
the same. Due to the uniformity of the preload on the springs 46,
there is a uniform distribution of the applied pressure. The
applied pressure fixes the work piece and insures a condition of
flatness thereof allowing for precise penetration of the punch
elements and the formation of sharp edged openings in the work
piece W.
At the bottom of a closing stroke of the press, the parts assume a
position substantially as shown in FIG. 2. In a return or opening
stroke of the press, retainer plate 10 and die shoe 11 are pulled
away from die plate 12, retracting punch extremities 22 from the
die buttons 58 and from the apertures cut in the work piece.
Facilitating the latter process is the pressure applied by the
springs 46 which hold the stripper plate 14 to the work while the
punch elements are being withdrawn. Again the influence of springs
46 will be balanced. Movement of the tool retainer plate 10
relatively to the stripper plate 14 continues until plate 10 abuts
hanger sleeve flanges 27 whereupon continued retraction of the
upper die shoe and retainer plate 10 is accompanied by a lifting of
plate 14 from the work. The return motion continues until the parts
reach substantially the position shown in FIG. 1, which may be
described as the fully open position of the press and the die. In
the interval during which the press is open or during which it is
opening, the work piece W may be advanced to clear the die or bring
a new section thereof to overlie the die buttons 58 in preparation
for the next closing stroke of the press.
In the early part of the return stroke of the tool retainer plate
10, accomplished relatively to stripper plate 14, the spring or
springs 46 are gradually relieved of their compression and at about
the same time that the plate 10 abuts hanger flanges 27, shoulder
portions 50 of the spring plungers will limit against abutments 29.
The superposed reactant pressure applied on the stripper springs in
the die operation accordingly is released and as the die parts
reach an open position and while they retain such position the
stripper plate 14 is unstressed by the stripper springs 46, though
they inherently retain their preload. Excessive shear force upon
the hanger devices 24 is avoided, as well as warping or otherwise
damaging influences being exerted upon the stripper plate. As long
as the press remains in an open position, the spring or springs 46,
while maintaining a preloaded condition, are ineffective to apply
their stored energy in a stressing of the plate 14.
In use of the die, the punch elements 20 will wear and their
operating portions 22 must be resharpened by grinding. This
naturally has the effect of shortening the overall length of the
punch elements and alters the relationship between the punch
elements and the stripper plate 14 with possible loss of punching
or cutting effectiveness unless the position of the stripper plate
is adjusted. Thus, following a grinding down of punch elements 20,
the stripper hanger devices must be adjusted to retract the
stripper plate 14 in a manner to restore the original relationship
between the plate and the punch elements. As will be evident, in
the invention assembly a rotary motion applied to the heads 30 of
screw means 25 will turn the latter in threaded bores in the
stripper plate. This is necessary to bodily reposition the plate 14
but in accordance with the invention, the screws 25 cannot be
turned into the stripper plate unless there is an adjustment as to
the length of the sleeves 26. In accordance with the invention, the
sleeves 26 will be ground off at their lower end portions an amount
equal to the length of material ground from the operating ends 22
of the punches 20. This will enable a precise adjustment of the
stripper plate 14 on turning the screw means 25 into the stripper
plate in correspondence with the adjustment of the length of the
punches 20. If only this is done, the adjustment of the position of
the stripper plate 14 as to its open position relative the plate 10
can obviously cause an addition to the preload on the springs 46 to
thereby stress the stripper plate in the open position thereof.
This is avoided in accordance with the invention by the provision
that the extensions 35 of the plungers 48 may be easily reduced as
to their length by grinding or other suitable means in
correspondence with the amount of the shortening of the punches 20
and the sleeves 26. Thus, by a corresponding and equal adjustment
of the length of the punches 20, sleeves 26 and extensions 35 of
the plungers 48, once more we have, in a simple fashion, provided
for an unstressed condition of the stripper plate 14 in the no load
or open position of the die. There is no complexity in the
operation of the invention system and the adjustment thereof and
one can readily insure a uniform and constant preload in reference
to the stripper spring assemblies.
In summary, the invention stripper plate spring assemblies enable a
uniform and constant loading of the contained springs in the first
instance. As employed, moreover, the stripper spring assemblies, in
accordance with the invention, will neither distort the stripper
plate or unevenly stress the same. In addition, load in shear on
the hanger devices utilized for the stripper plate is completely
avoided. This enables that a stripper plate may be suspended by
relatively few hanger devices, thereby reducing machining and
number of parts required for a die. An ancillary advantage is the
enabling of an increase in available tool area within a die. It is
obvious, of course, that the involved parts will have a longer
operating life. The fact that the springs 46 can in the first
instance be endowed with precise design specifications and retained
as to specified preload values throughout the operation of die
apparatus is an important factor in the substantial benefits of the
invention. Safety is also inherent in the spring assemblies as here
provided due to both the inner and outer containment of the spring
devices.
While in the spring assemblies illustrated only one spring element
has been shown in each instance, it is of course obvious that
plural spring elements can be utilized in tandem within a cage such
as the cage 44 illustrated without departing from the basic concept
of the invention. Where plural springs are employed within a cage,
there obviously can be a suitable modification of the plunger or
plungers employed such as 48 in a manner well evident to one versed
in the art. Where plural springs are employed within a single cage,
the arrangement could of course also provide for a differential
rating of the simultaneously contained springs. The use of spring
assemblies of this nature may be considered, for example, where one
contemplates a light lead-in pressure and a heavier working
pressure towards the end of a stroke of a die set.
It is also evident that spring assemblies here illustrated can be
employed in a reverse or inverted position with the plunger
abutting against the stripper plate without loss of effectiveness
and still within the concept of the invention.
As is obvious the spring assemblies here illustrated can have a
utility apart from the specific embodiment shown. The assembly will
have advantage in any case where safety, constant preload and
adjustment without changing preload are important and necessary
assets.
From the above description it will be apparent that there is thus
provided a device of the character described possessing the
particular features of advantage before enumerated as desirable,
but which obviously is susceptible of modification in its form,
proportions, detail construction and arrangement of parts without
departing from the principle involved or sacrificing any of its
advantages.
While in order to comply with the statute the invention has been
described in language more or less specific as to structural
features, it is to be understood that the invention is not limited
to the specific features shown, but that the means and construction
herein disclosed comprise but one of several modes of putting the
invention into effect and the invention is therefore claimed in any
of its forms or modifications within the legitimate and valid scope
of the appended claims.
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