FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13) TITLE OF THE INVENTION:
SPRING RETENTION MECHANISM FOR FLOATING STRIPPER
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra. INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to a press tool assembly and particularly to the press tools used for processing coils or strips in progressive punching operations executed during the manufacturing process of sheet metal components used in applications such as electrical/electronic products, automobiles, watches etc. The present invention more particularly relates to spring retention mechanism for holding the compression spring columns with a floating stripper in the top half of the press tool.
B) BACKGROUND OF THE INVENTION
[0002] Press working is one of the major processing techniques for converting a sheet metal into the sheet metal parts of different shapes. The sheet metal parts are required for different applications such as electrical/ electronic products, automobiles, watches etc. The sheet metal is punched between two parts called punch and die. The die profile is the female profile intentionally kept bigger than the punch profile by a uniform gap called cutting clearance.
[0003] The press tool mainly consists of two halves, namely fixed bottom half and moving top half. The fixed bottom half is secured to the stationary bolster plate of mechanical press. The bottom half comprises an arrangement to guide the strip/coil, die cavities, guide pillars for alignment of both halves etc. The top moving half is clamped

to the moving ram of the mechanical press and it comprises a number of circular and non circular cutting and non cutting elements called punches. The punches move up and down along with the moving ram of the mechanical press and they are guided in cavities made in a plate called Stripper plate. During the downward movement, the punches penetrate the sheet metal and enter the die cavity thereby pushing the sheet metal scrap displaced by the cutting punch into the lower half of the tool. One downward and return upward movement of the top half of press tool is called as a stroke of press tool. The surrounding metal clings to the body of cutting punches during the downward stroke. The same is stripped off by the stripper plate during the upward stroke of the punches.
[0004] The press tools are of multi-station type or single station type. In a multi¬station tool, the strip moves from one end of the strip guides to the other end. It moves progressively by a fixed distance called pitch after every stroke of the mechanical press. At each stage during the movement of strip, different punching operations are carried out on the strip / coil leading to the completion of the stamping profile in the last stage. The stripper in the press tools is designed to move as the press ram reaches the bottom of its stroke. Usually the strippers are of two types such as a fixed stripper and a floating stripper. The fixed stripper is fixed to the bottom half of the press tool and the floating stripper is fixed to the top half of the press tool to hold down the stock during the stamping operation and strip the stock.
[0005] In conventional press tool assembly, the spring retainer is provided in the top plate or shank plate to hold the springs in the top half of the press tool. The set of springs

or spring columns are supposed to have sufficient force to help the stripper in doing the stripping action. The spring hole in the top plate or shank plate is blind and it is difficult to ensure identical depth of all the blind holes. The difference in the hole depth leads to non uniform compression of springs and unbalanced load will be exerted on the Stripper during the assembly and during the working of the tool. This unbalanced load is transferred to the Punches which are precisely guided in the Stripper and the Guide Pillar assembly. This results in breakage of thin and delicate punches and damages the Guide Pillar assembly. Moreover, the assembly process of spring retainer in the tool is time consuming, since spring retainer rotates inside the top plate along with the screw. The screw is inserted from the bottom surface of the stripper plate. The stripper will also be stressed during the assembly of the tool and assembly of the stripper is very carefully done as the tilting of the stripper during assembly process may damage or break the Punches.
[0006] Sometimes the assembly of the circlip on the stripper plate below the screw is forgotten. The screw used in the stripper plate for clamping the spring retainer gets unscrewed and falls inside the tool during the working of the tool thereby damaging or breaking the tool elements very heavily. Moreover the manufacturing of the groove for the circlip in the stripper plate is difficult.
[0007] Hence there is a need to provide an arrangement to eliminate the transmission of spring forces to the punches during assembling and working of the press tool and hence to eliminate the breakage of slender and delicate punches. Also there is a need to

provide an arrangement to assemble and dismantle the floating stripper in short time without stressing the stripper plate.
[0008] There is yet another need to provide an arrangement which is accident free and which is easily assembled. Also there is a requirement for an arrangement which ensures that the spring force on the stripper plate is equal on all the regions. Further there is a need for a construction which can eliminate the usage of Circlip and manufacturing of groove for circlip.
[0009] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECTS OF THE INVENTION
[0010] The primary object of the present invention is to provide a spring retention arrangement to hold the compression spring columns for floating stripper in the top half of press tool assembly.
[0011] Another object of the present invention is to provide a spring retention arrangement to eliminate the transmission of the spring forces to the punches during the assembling and the working of the tool thereby eliminating the breakage of slender and delicate punches.

[0012] Yet another object of the present invention is to provide a spring retention arrangement for floating stripper in a press tool assembly to reduce the load exerted or stress on the stripper plate during the assembling of the tool.
[0013] Yet another object of the present invention is to provide a spring retention arrangement to assemble and dismantle the floating stripper in short time without stressing the stripper plate.
[0014] Yet another object of the present invention is to provide a spring retention arrangement to avoid the over tightening of the spring in the press tool due to unbalanced load exerted on the spring.
[0015] Yet another object of the present invention is to provide a spring retention arrangement which is easy to dismantle during repair and maintenance.
[0016] Yet another object of the present invention is to provide a spring retention arrangement to overcome the difficulty in assembling and dismantling the spring retainer inside the top plate.
[0017] Yet another object of the present invention is to provide a spring retention arrangement to make an accident free construction.
[0018] Yet another object of the present invention is to provide a spring retention arrangement to make a construction which is best suited for larger sized tools.
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[0019] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0020] The various embodiments of the present invention provide a spring retention arrangement for a floating stripper in a press tool assembly to retain the compression spring columns in the top half of the press tool and to assemble and dismantle the stripper springs in short time without stressing the stripper plate. The spring retention arrangement is provided to reduce the load exerted on the stripper plate during the assembling of the tool and also to avoid the over tightening of the spring in the press tool due to unbalanced load exerted by the spring.
[0021 ] According to one embodiment of the present invention, a spring retention mechanism for floating stripper plate in press tool assembly has a spring retainer provided in a top plate arranged in a press tool assembly. A set of coil springs is placed in the top plate around the spring retainer. A round spacer is arranged below the spring retainer. A retainer plate is mounted below the top plate. The stripper plate in the press tool assembly is fixed to all the springs separately and the retainer plate holds the coil springs inside the top plate in pre-compressed condition.

[0022] The coil springs are arranged inside the top plate in a pre compressed condition. The total number of springs used for the floating stripper plate depends on the size of the stripper plate. The number of springs arranged in the spring retainer is selected in such a manner that the total force exerted by the springs depends upon the cutting load and thickness of the strip or coil. The springs are selected based on the force required per spring and the deflection required for the spring during the use. The spring has a height based on the free length of the spring and the working deflection of the spring. The working deflection of the spring is decided by strip/coil thickness & configuration of stamping.
[0023] Pluralities of spring retainers are used to hold the respective coil springs. The heights of all the spring retainers are made equal. As a result, the heights of all the spring columns used in the spring retainer system remain the same thereby exerting a balanced or uniform load on the stripper plate. The height of the spring retainer is decided by the free length of the spring and the working deflection of the spring. The round spacer is machined to maintain the relative height of the spring column with respect to the punches, as the height of the punch is reduced after the resharpening process. The retainer plate is fixed to the top plate by a fastener such as an Allen screw. The spring retainer is fixed to the round spacer and to the stripper plate using a fastener like an Allen screw.
[0024] According to one embodiment of the present invention, the press tool assembly comprises of a top plate. A spring retainer is provided in the top plate. A

spring is guided on the external diameter of the spring retainer. A round spacer is connected below the spring retainer. A retainer plate is fixed to top plate bottom surface of press tool. A floating stripper is connected to the upper moving half of the press tool by the guide pillars. The Allen screws are used to fix the retainer plate to the top plate and to retain the spring and spring retainer inside the top plate. An Allen screw is provided to fix the spring retainer and round spacer to the floating stripper plate. A base plate is provided in the press tool assembly. A die plate is clamped to the base plate. A strip or coil is to be guided on the die plate and a fixed stripper plate with a cavity at the centre is mounted on the die plate.
[0025] Initially, the entire tool without stripper springs and cover plate / clamping plate / shank plate is assembled first. The springs are put in the holes provided in the top plate and then the cover plate / clamping plate / shank plate is tightened above the top plate. The variation in the spring force while tightening is directly transferred to retainer plate, cover plate and top plate but not stripper plate. This eliminates the transfer of spring force onto the delicate punches in the assembly. While dismantling the tool, the clamping plate and the springs are removed first thereby eliminating the transmission of spring force on to the punches. The spring retention system supports the press tool, when the guide pillar is mounted both at the bottom half of the tool and at the top half of the tool.
[0026] According to one embodiment of the present invention, the round spacer is provided below the spring retainer. The height of the cutting punches is reduced after

resharpening. This is compensated by machining the round spacer by the same amount so that the relative height of spring column with respect to punches is maintained. The retainer plate is fixed to the top plate bottom surface by using an Allen screw. The retainer plate holds the coil springs inside the top plate in pre compressed condition. The Allen screw at the top is used to fix the spring retainer and round spacer to the floating stripper. The Allen screw at the bottom is used to fix the retainer plate to the top plate and to retain the spring and spring retainer inside the top plate.
[0027] According to one embodiment of the present invention, the floating stripper is connected to the upper moving half of the press tool. The floating stripper plate is aligned with respect to upper half of tool by the guide pillars. A set of coil springs are provided between the top plate of the press tool and floating stripper plate. In an embodiment of the present invention, the spring retainer is provided in the top plate. The spring retainer guides the spring on its external diameter. The height of the spring retainer is decided based on the free length of the spring and the working deflection required. The heights of all the spring retainers in the press tool are made identical. As a result the heights of all the spring columns will remain identical and exert a balanced load on the floating stripper. Even numbers of springs are selected for a floating stripper depending upon the size of stripper plate. The total force of the springs is decided based on the cutting load and thickness of strip/coil. The working deflection of the spring is decided by the thickness of the strip/coil and the configuration of stamping. The spring

criterion is selected based on the force required per spring and the deflection required during the working.
[0028] During the downward movement of the press tool, the floating stripper plate rests on the strip or coil first and the springs start getting compressed. This causes relative movement between the punches and floating stripper. The punches come out of the floating stripper plate, penetrate the sheet metal and enter the die cavity thereby pushing the sheet metal scrap displaced by the cutting punch into the lower half of the tool. The surrounding metal clings to the body of cutting punches during the downward stroke. The same is stripped off by the stripper plate during the upward stroke of the punches. The punches are moved only to the extent of compression of stripper coil springs. Since the floating stripper directly rests on the strip/coil, the cutting punches get guidance very close to the cutting point. This reduces the vulnerability of the punches.
[0029] The spring retention arrangement is provided to ensure identical depth of all the holes in the floating stripper during the punching operation. The spring retention arrangement also reduces the load exerted or stress on the stripper plate during the assembling of tool. The assembling of the spring retention system can be done independent of other elements. The stripper plate can also be fixed to all the spring separately thereby making the bench work easy.

E) BRIEF DESCRIPTION OF THE DRAWING
[0030] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0031] FIG. 1 shows a sectional view of the press tool assembly with spring retention arrangement for floating stripper, according to one embodiment of the invention.
[0032] FIG. 2 shows an exploded sectional view of the press tool assembly with spring retention arrangement for floating stripper, according to one embodiment of the invention.
[0033] FIG. 3 shows an enlarged sectional view of the spring column in a spring retention arrangement for floating stripper in a press tool assembly, according to one embodiment of the present invention.
[0034] FIG. 4 shows a sectional view of the spring retainer in a spring column in a spring retention arrangement for floating stripper in a press tool assembly, according to one embodiment of the present invention.
[0035] FIG. 5 shows a sectional view of the round spacer in a spring retention arrangement for floating stripper in a press tool assembly, according to one embodiment of the present invention.

[0036] FIG. 6 shows a sectional view of the retainer plate in a spring retention arrangement for floating stripper column in a press tool assembly, according to one embodiment of the present invention.
[0037] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0038] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0039] The various embodiments of the present invention provide a spring retention arrangement for the floating stripper in press tool assembly to retain the compression spring columns in the top half of the press tool and to assemble and dismantle the stripper in short time without stressing the stripper plate. The spring retention arrangement is provided to reduce the load exerted on the stripper plate during

assembling of tool and also to avoid the over tightening of the spring in the press tool due to the unbalanced load exerted on the spring.
[0040] According to one embodiment of the present invention, a spring retention mechanism for floating stripper plate in press tool assembly has a spring retainer provided in a top plate arranged in a press tool assembly. A set of coil springs are wound around the spring retainer. A round spacer is arranged below the spring retainer. A retainer plate is mounted below the top plate. The stripper plate in the press tool assembly is fixed to all the springs separately and the retainer plate holds the coil springs inside the top plate in pre-compressed condition.
[0041] The coil springs are arranged inside the top plate in a pre compressed condition. The total number of springs used for the floating stripper plate depends on the size of the stripper plate. The number of springs arranged in the spring retainer is selected in such a manner that the total force exerted by the springs depends upon the cutting load and thickness of the strip or coil. The springs are selected based on the force required per spring and the required deflection of the spring during the use. The spring has a height based on the free length of the spring and the required working deflection of the spring. The required working deflection of the spring is decided based on the thickness of the strip/coil and the configuration of the stamping.
[0042] Pluralities of spring retainers are used to hold the respective coil springs. The height of all the spring retainers is made equal. As a result, the height of all the spring

columns used in the spring retainer system remains the same thereby exerting a balanced or uniform load on the stripper plate. The height of the spring retainer is decided based on the free length of the spring and the required working deflection of the spring. The round spacer is machined to maintain the relative height of the spring column with respect to the punches, as the height of the punch is reduced after the resharpening. The retainer plate is fixed to the top plate by a fastener such as an Allen screw. The spring retainer is fixed to the round spacer and to the stripper plate using a fastener like an Allen screw.
[0043] According to one embodiment of the present invention, the press tool assembly comprises of a top plate provided with a spring retainer. A spring is guided over the external diameter of the spring retainer. A floating stripper is connected to the upper moving half of the press tool by the guide pillars. An Allen screw is used to fix the retainer plate to the top plate and to retain the spring and spring retainer inside the top plate. A round spacer is provided below the spring retainer. Another Allen screw is used to fix the spring retainer and round spacer to the floating stripper plate. A die plate is clamped to a base plate provided in the press tool assembly. A strip or coil is to be guided on the die plate. A fixed stripper plate with a cavity at the centre is mounted on the die plate.
[0044] The Stripper spring retention system eases the tool assembly and eliminates the breakage of slender thin and delicate punches. The entire tool without stripper

springs and cover plate is assembled first. The springs are put in the holes provided in the top plate and then the cover plate is tightened above the top plate. The variation in the spring force during the tightening process is directly transferred to the retainer plate, the cover plate and the top plate but not to the stripper plate. This eliminates the transfer of spring force onto the delicate punches in the assembly. While dismantling the tool, the clamping plate and the springs are removed first thereby eliminating the transmission of spring force to the punches. This stripper spring retention system supports the press tool when the guide pillar is mounted both at the bottom half of the tool and at the top half of the tool.
[0045] The round spacer is provided below the spring retainer. The height of cutting punches is reduced after resharpening. This is compensated by machining the round spacer by the same amount so that the relative height of spring column with respect to punches is maintained. The retainer plate is fixed to bottom surface of the top plate by using an Allen screw. It does the function of retaining all the coil springs inside the top plate in a pre compressed condition. The Allen screw at the top is used to fix the spring retainer and the round spacer to the floating stripper. The Allen screw at the bottom is used to fix the retainer plate to the top plate and to retain the spring and spring retainer inside the top plate.
[0046] According to one embodiment of the present invention, the floating stripper is connected to the upper moving half of the press tool. The floating stripper plate is aligned with respect to the upper half of tool by the guide pillars. A set of coil springs
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are provided between the top plate of the press tool and the floating stripper plate. In an embodiment of the present invention, the spring retainer is provided on the top plate. The spring retainer guides the spring through its external diameter. The height of spring retainer is decided based on the free length of the spring and the working deflection required. The height of all the spring retainers in the press tool is made identical. As a result the height of all the spring columns remains identical and exerts a balance load on the floating stripper. An even number of springs is selected for floating stripper depending upon the size of stripper plate. The total force of the springs is decided on the basis of the cutting load and the thickness of the strip/coil. The working deflection of the spring is decided by the thickness of the strip/coil and the configuration of the stamping. The spring criteria are selected based on the force required per spring and the required deflection of the spring during working.
[0047] During the downward movement of the press tool, the floating stripper plate rests on the strip or coil first and the springs start getting compressed. This causes the relative movement between the punches and floating stripper. The punches come out of the floating stripper plate, penetrate the sheet metal and enter the die cavity thus pushing the sheet metal scrap displaced by the cutting punch into the lower half of the tool. The surrounding metal clings to the body of the cutting punches during the downward stroke. The same is stripped off by the stripper plate during the upward stroke of the punches. The movement of the punches is restricted only to the extent of compression of stripper coil springs. Since the floating stripper directly rests on the strip/coil, the cutting

punches get guidance very close to the cutting point. This reduces the vulnerability of the punches.
[0048] The spring retention arrangement is provided to ensure an identical depth of all the blind holes in the floating stripper during the punching process. The spring retention arrangement also reduces the load exerted or stress on the stripper plate during the assembling of the tool. The assembling of the spring retention system is also done independent of the other elements. The stripper plate is also fixed to all the springs separately making the bench work easy.
[0049] FIG. 1 shows a sectional view of the press tool assembly with spring retention arrangement for floating stripper, according to one embodiment of the invention. The press tool assembly mainly consists of two halves, namely, a fixed bottom half and a moving top half. The fixed bottom half is secured to the stationary bolster plate of a mechanical press. The base plate 2 is clamped to the fixed bottom part. The die plate 4 is clamped on the base plate 2 with the strip or coil to be punched is guided on the die plate 4. The fixed stripper plate 5 is clamped to the die plate 4. The top plate 1 is clamped to the shank plate 3. The top plate 1 holds the spring columns 9 with the retainers. The top plate 1 also includes punches 15 which move up and down along with the moving ram of the mechanical press and they are guided in the cavities made in the stripper. The press tool assembly includes an arrangement to guide the strip/coil, die cavities, guide pillars for alignment of both the halves.

[0050] With reference to FIG.l, the spring retention system comprises of an arrangement to hold the compression spring columns 9 for the floating stripper plate 6 in the top half of the press tool. The floating stripper 6 is connected to the upper moving half of the press tool. The floating stripper plate 6 is aligned with respect to upper half of the tool by a guide pillar 7. A set of coil springs are provided between the top plate 1 of press tool and floating stripper plate 6. The spring retainer 8 is provided in the top plate 1. The spring retainer 8 guides the spring 9 on its external diameter. The round spacer 11 is provided below the spring retainer 8 to compensate the relative height of the spring column with respect to the height of the punches. The Allen screw 12 is provided to fix the spring retainer 8 and round spacer 11. The retainer plate 10 is fixed to bottom surface of the top plate 1 by using an Allen screw 13, which retains the coil springs 9 inside the top plate 1 in a pre compressed condition. An Allen screw 14 is provided to clamp the shank plate 3 on the top plate 1.
[0051] Initially the entire tool without stripper springs 9 and cover plate 3 is assembled. The springs 9 are inserted in the holes provided in the top plate 1 and the cover plate 3 is tightened above the top plate 1. The variation in the spring force while tightening is directly transferred to retainer plate 10, cover plate 3 and top plate 1 but not stripper plate 6. This eliminates the transfer of the spring force onto the delicate punches in the assembly. While dismantling the tool, the shank plate 10 and the springs 9 are removed first, thereby eliminating the transmission of spring force to the punches. This

stripper spring retention system supports the press tool when the guide pillar 7 is mounted both at the bottom half of the tool and at the top half of the tool.
[0052] During downward stroke of the press tool, the floating stripper plate 6 rests on the strip or coil first and the springs 9 start getting compressed. This causes relative movement between the punches and floating stripper. The punches come out of the floating stripper plate 6, penetrate the sheet metal and enter the die cavity thereby pushing the sheet metal scrap displaced by the cutting punch into the lower half of the tool. The surrounding metal clings to the body of cutting punches during the downward stroke. The same is stripped off by the stripper plate during the upward stroke of the punches. The movement of the punches is restricted only to the extent of compression of stripper coil springs. Since the floating stripper directly rests on strip/coil, the cutting punches get guidance very close to the cutting point. This reduces the vulnerability of breakage of the punches.
[0053] FIG. 2 shows an exploded sectional view of the press tool assembly with a spring retention arrangement for floating stripper, according to one embodiment of the invention. The press tool assembly has two halves, namely a fixed bottoms half and a moving top half. The die plate 4 and the fixed stripper plate 5 are assembled with the fixed bottom half of the press tool. The holder plate, punches 15 and guide pillar 7 are assembled with the moving top half of the press tool. The spring retainer system with the floating stripper is assembled with the moving half of the press tool as shown in FIG. 2. The spring retention system includes an arrangement to hold the compression spring

columns 9 for the floating stripper plate 6 in the top half of the press tool. The floating stripper 6 is connected to the upper moving half of the press tool. The floating stripper plate 6 is aligned with respect to the upper half of the press tool by a guide pillar 7. The coil spring is provided between the top plate 1 of press tool and floating stripper plate 6. The spring retainer 8 is provided in the top plate 1. The spring retainer 8 guides the spring 9 on its external diameter. The round spacer 11 is provided below the spring retainer 8. The Allen screw 12 is provided to fix the spring retainer 8 and round spacer 11. The retainer plate 10 is provided to fix it to the top plate 1 bottom surface of the press tool by using an Allen screw 13. An Allen screw 14 is provided to clamp the shank plate 3 on the top plate 1.
[0054] FIG. 3 shows an enlarged sectional view of the floating stripper spring column, according to one embodiment of the present invention. With reference to FIG. 3, the spring retainer system comprises a spring retainer 8 provided in top plate 1. A spring 9 is guided through the external diameter of the spring retainer 8. A floating stripper plate 6 is connected to the upper moving half of the press tool by the guide pillars. An Allen screw 13 is provided to fix the retainer plate 10 to the top plate 1 and to retain the spring 9 and spring retainer 8 inside the top plate 1. A round spacer 11 is provided below the spring retainer. An Allen screw 12is arranged to fix the spring retainer 8 and round spacer 11 to the floating stripper plate. Initially, the entire tool without the stripper spring 9 and cover plate 3 is assembled. The spring 9 is inserted in to the hole provided in the top plate 1 and then the cover plate 3 is tightened above the

top plate 1. The variation in the spring force while tightening is directly transferred to retainer plate 10, cover plate 3 and top plate 1 but not stripper plate 6. This eliminates the transfer of spring force onto the delicate punches in the assembly. While dismantling the tool the cover plate 3 and the springs 9 are removed first, thereby eliminating the transmission of the spring force to the punches. This stripper spring retention system supports the press tool when the guide pillar 7 is mounted both at the bottom half of the tool and at the top half of the tool.
[0055] FIG. 4 shows a sectional view of the spring retainer, according to one embodiment of the present invention. The spring retainer 8 includes a cylindrical protrusion. The cylindrical protrusion is provided on the spring retainer to support the spring guided on the external diameter of the spring retainer. The height of spring retainer 8 is decided based on the free length of the spring and the working deflection required. The heights of all the spring retainers in the press tool are made identical. As a result the heights of all the spring columns will remain identical and hence exert a balanced load on the floating stripper. The spring retention arrangement is provided to ensure an identical depth of all the blind holes in the floating stripper during the punching process. The spring retention arrangement also reduces the load exerted or stress on the stripper plate during assembling of tool. The assembling of the spring retention system is also done independent of other elements. The stripper plate is also fixed to all the spring separately making the bench work easy.

[0056] FIG. 5 shows a sectional view of the round spacer, according to one embodiment of the present invention. The round spacer is provided below the spring retainer. The height of the cutting punches reduces after resharpening. This is compensated by machining the round spacer by the same amount so that the relative height of spring column with respect to punches is maintained.
[0057] FIG. 6 shows a sectional view of the retainer plate, according to one embodiment of the present invention. The retainer plate 10 is fixed to the bottom surface of the top plate by using an Allen screw. It does the function of retaining the coil springs inside the top plate in a pre compressed condition.
G) ADVANTAGES OF THE INVENTION
[0058] The various embodiments of the present invention provide a spring retention arrangement for floating stripper in press tool assembly to retain (hold) the compression spring columns in the top half of the press tool and to assemble and dismantle the stripper in short time without stressing the stripper plate. The spring retention arrangement is provided to reduce the load exerted (stress) on the stripper plate during assembling of tool and also to avoid the over tightening of the spring in the press tool due to unbalanced load exerted on the spring.

[0059] The heights of all the spring retainers in the press tool are made identical. As a result the heights of all the spring columns will remain identical and hence exert a balanced load on the floating stripper. The spring retention system ensures equal pre compression of all the stripper springs in the assembly. The assembling of the spring retention system is done independent of other elements. The stripper plate can be fixed to all the spring separately making the bench work easy. The spring retention system also eliminates the spring force exerted on the punches during the downward stroke of the press tool thereby eliminating the breakage of slender and delicate punches.
[0060] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0061] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.


CLAIMS
What is claimed is:
1. A spring retention mechanism for floating stripper plate in press tool assembly
comprising:
A spring retainer provided in a top plate arranged in a press tool assembly;
A set of coil springs arranged around the spring retainer;
A round spacer arranged below the spring retainer; and
A retainer plate mounted below the top plate;
Wherein the stripper plate in the press tool assembly is fixed to all the springs
separately and the retainer plate holds the coil springs inside the top plate in pre-
compressed condition.
2. The mechanism according to claim 1, wherein the coil springs are arranged inside the top plate in a pre compressed condition.
3. The mechanism according to claim 1, wherein the coil springs are arranged around the external diameter of the spring retainer.
4. The mechanism according to claim 1, wherein the total number of springs used for the floating stripper plate depends on the size of the stripper plate.

5. The mechanism according to claim 1, wherein the number of springs provided in the retainer is selected in such a manner that the total force exerted by the springs depends upon the cutting load and thickness of the strip or coil.
6. The mechanism according to claim 1, wherein the spring criteria is selected based on the force required per spring and the deflection of the spring during the use.
7. The mechanism according to claim 1, wherein the spring has a height based on the free length of the spring and the working deflection of the spring.
8. The mechanism according to claim 1, wherein the springs are deflected based on
the thickness of the coil or the strip and the configuration of the stamping in the
coil or the strip.
9. The mechanism according to claim 1, wherein the spring retainer has a height based on the free length of the spring and the working deflection of the spring.
10. The mechanism according to claim 1, wherein the round spacer is machined to maintain the relative height of the spring column with respect to the punches.
11. The mechanism according to claim 1, wherein the retainer plate is fixed to the top plate by a fastener.
12. The mechanism according to claim 8, wherein the fastener is an Allen screw.

13. The mechanism according to claim 1, further comprises fastener to fix the spring retainer and the round spacer to the stripper plate.
14. The mechanism according to claim 10, wherein the fastener is an Allen screw.

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