FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"A press tool assembly with a floating holder plate mechanism"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: Larsen & Toubro Limited
Electrical & Automation North Wing, Gate 7, Level 0, Powai Campus, Saki Vihar Road, Mumbai 400 072, INDIA
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

A press tool assembly with a floating holder plate mechanism
Field of invention
The present invention relates to press tools, and more particularly to a press tool assembly having a floating holder plate mechanism.
Background of the invention
The use of press tools for progressive punching and cutting operations is well known in the art. A strip or coil is punched, formed, bent, notched and made in to different shapes progressively at various stages in a press tool operation. Finally, components and stampings are separated from the strip or coil either by blanking, parting or by cut off operation.
The press tool assembly consists of two halves, namely a bottom half and a top half. The bottom half is fixed and is secured to the stationary bolster plate of a mechanical press. The top moving half is movable and is clamped to the moving ram of the mechanical press that comprises a plurality of circular and non circular cuttings elements traditionally known as punches.
The punches move up and down along with the moving ram of the mechanical press and are guided in cavities defined in a plate called Stripper. The punches penetrate the sheet metal during their downward movement and enter the die cavity thereby pushing the sheet metal scrap to be displaced by the cutting punch.
However, there is a great likelihood of buckling or breaking of the punches during punching or stamping operations, when the coil or strip is thin and cutting punches are small in cross sections. Moreover, these punches frequently undergo wear and tear due to even minute misalignment of top and bottom halves under the high load working conditions. Generally, use of press alignment means is well known

in the art for facilitating alignment of top and bottom halves of the press. However, presses alignment means fail to accurately align the top and bottom halves, when the punch cross section and the strip/coil thickness are very small.
Therefore, there is need of a press tool assembly that facilitates accurate alignment of the top and bottom halves in stamping operation for the strips/coils having small thicknesses. Also, there is need of a press tool assembly that performs critical stamping operations on the normal stamping press. Further, there is need of a press tool assembly that operates the punches on the normal stamping press without being buckled or broken.
Objects of the invention
An object of the present invention is to provide a pressure tool assembly with a floating holder plate mechanism for press tool.
Another object of the invention is to provide a pressure tool assembly that prevents breakdown of punches having small cross sections thereby increasing the tool life of the press tool.
Yet another object of the present invention is to provide the press tool assembly that makes the press tool generic to be advantageously utilized on all types of presses.
Summary of the invention
Accordingly, the present invention provides a press tool assembly with a floating holder plate mechanism adapted to perform a stamping operation with a plurality of delicate or critical punches mounted thereon, the press tool assembly comprising:

A moving upper half having a top plate, a holder plate and a backing plate, the backing plate connecting to the top plate through the backing plate;
a stationary lower half having a stripper plate;
a first subassembly having a first spring and a first spring retainer, the first spring retainer positioning the first spring between the holder plate and the stripper plate;
a second subassembly having a second spring and a second spring retainer, the second spring retainer positions the second spring within the top plate, the first spring and the second spring performing a floating action for facilitating a dampened pressure load on the punches; and
an auxiliary pillar securing rigidly within the backing plate and the holder plate, the auxiliary pillar moving axially to pass through an auxiliary bush mounted on the stripper plate, the auxiliary pillar facilitating accurate alignment between the first subassembly and the second subassembly for preventing breakage of the punches.
Brief description of the drawings
FIG. 1 is a cross-sectional view of a press tool assembly in accordance with the present invention;
FIG. 2 is an enlarged cross-sectional view of the press tool assembly of FIG. 1; FIG. 3 is a front view of a first spring retainer of the press tool assembly of FIG.
1;
FIG. 4 is a front view of a second spring retainer of the press tool assembly of
FIG. 1;
FIG. 5 illustrates an auxiliary pillar of the pressure tool assembly of FIG. 1;
FIG. 6 illustrates an auxiliary bush of the pressure tool assembly of FIG. 1;
FIG. 7 is a cross-sectional view of the pressure tool assembly of FIG. 1 in an
upward stroke condition;
FIG. 8 is a cross-sectional view of the pressure tool assembly of FIG. lin a first
downward stroke condition; and

FIG. 9 is a cross-sectional view of the pressure tool assembly of FIG. 1 in a second downward stroke condition.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Referring to FIG. 1, a pressure tool assembly 10 adapted for press tools, progressive dies, stamping dies and the like in accordance with the present invention is illustrated. The pressure tool assembly 10 includes a moving upper half 14 and a stationary lower half 16. The moving upper half 14 and the stationary lower half 16 respectively include a top plate 15 and a bottom plate 17. The moving upper half 14 and the stationary lower half 16 mutually include a first sub assembly 18, a second sub assembly 20 and a third sub assembly 22 that assist in performing a critical (small) stamping operation on a strip or coil of predefined height and thickness. However, it is understood here that the pitch and thickness of the coil may vary in other alternative embodiments of the present invention per intended application of pressure tool assembly 10.
As shown in FIG. 2, the pressure tool assembly 10 includes a backing plate 24 and a holder plate 26. The backing plate 24 is connected to the upper half 14 and the holder plate 26 is connected to the backing plate 24. The backing plate 24 and the holder plate 26 are screwed together by a plurality of counter sunk screws. The pressure tool assembly 10 includes an auxiliary pillar 30 mounted within the backing plate 24 and the holder plate 26 that extends at a predefined distance within a stripper plate 32. The auxiliary pillar 30 is adapted to guide the first sub assembly 18 and second sub assembly 2() during the operation of the pressure tool

assembly 10. The auxiliary pillar 30 is positioned within an auxiliary bush 34 defined on the stripper plate 32.
The first and second sub assemblies 18, 20 are floated using a first spring 36 and a second spring 38. The first spring 36 is positioned within the first subassembly 18 through a first spring retainer 40. The second spring 36 is positioned within the second subassembly 20 through a second spring retainer 42. The first spring retainer 40 and the second spring retainer 42 are respectively held in position using a first Allen screw 44 and a second Allen screw 46. A washer 48 is positioned between the first spring retainer 40 and the first Allen screw 44 and having an opening adapted to facilitate passage of the Allen screw 44.
The first spring 36 is positioned between the holder plate 26 and the stripper plate 32 such that the load of the spring 36 is just enough to provide cutting load required for small or critical stamping operations. The second spring 38 is positioned between the top plate 15 and the second spring retainer 42 to withstand the travel of the second sub assembly 20 such that the load exerted by the spring 38 in the pre compressed condition overcomes the load of all the springs accommodated in the stationary lower half 16. The first and second springs 36, 38 are adapted to govern the floating action of the first and second sub assemblies 18, 20 to deliver a low pressure to the cutting punches being mounted in the press tool assembly 10.
In this one preferred embodiment, the holder plate 26 is a soft steel plate that is preferably of a rectangular configuration. The holder plate 26 includes a plurality of threaded holes (not shown) that receive the countersunk screws for clamping the holder plate 26 with the backing plate 28. The holder plate 26 includes a plurality of holes (not shown) adapted to receive the spring retainers 40. The holder plate 26 includes at least a pair of holes (not shown) adapted to receive the auxiliary pillars 30. The holder plate 26 includes a plurality of mounting holes (not shown) adapted to receive a respective plurality of piercing punches.

In this one preferred embodiment, the backing plate 24 is a hardened steel plate that is preferably of rectangular configuration. The backing plate 24 includes a plurality of holes (not shown) that receive the countersunk screws to clamp the holder plate 26 with the backing plate 28. The backing plate 24 includes a plurality of holes (not shown) adapted to receive the spring retainers 40. The backing plate 24 includes at least a pair of holes (not shown) adapted to receive auxiliary pillars 30. The backing plate 24 is adapted to avoid digging mark of the punches.
In this one preferred embodiment, the stripper plate 32 is having a rectangular configuration and is made of a soft constructional steel material. The stripper plate 32 includes a plurality of threaded holes (not shown) adapted to mount the spring 36. The stripper plate 32 includes a plurality of counter holes (not shown) configured to mount a respective plurality of holder springs (not shown). The stripper plate 32 is adapted to guide the punches thereby keeping the thin strip in a substantially flat position during the stamping process. The stripper plate 32 is adapted to strip out the slug during an upward stroke of the press tool assembly 10. The stripper plate 32 includes at least a pair of holes (not shown) adapted to accommodate the auxiliary bushes 34.
As shown in FIG. 3, the first spring retainer 40 is specifically adapted to be used for light holder plate springs in this one preferred embodiments. The first spring retainer 40 includes a top end 52 and a bottom end 54. The top end 52 includes a collar 56 having a rectangular configuration. The collar 56 positions within the backing plate 24 to hold the spring retainer 40 in position within the press tool assembly 10. In addition, the collar 56 creates required gap for the movement of the spring 36. The bottom end 54 defines a threaded hole 58 that receives the Allen screw 44 for mounting the bottom end 54 within the stripper plate 32.

Referring to FIG. 4, the second spring retainer 42 is specifically adapted to be used for heavy stripper springs in this one particular embodiment is illustrated. The second spring retainer 42 includes a body 60 that is preferably made of steel material in this one preferred embodiment. However, it is understood that the body 60 may be made of other materials in other alternative embodiments of the second spring retainer 42, which may be obvious to a person skilled in the art. The second spring retainer 42 includes a thorough hole 62 preferably centrally located within the body 60 of the second spring retainer 42. The body 60 defines an opposed pair of ribs 64 that laterally outwardly extends from the body 60. The ribs 64 help assist the spring 38 to remain in position within the second sub assembly 20 (Refer FIG. 2).
As shown in FIG. 5, the auxiliary pillar 30 includes a body 66 that is made of hardened tool steel in this one particular embodiment. However, it is understood here that the body 66 can be made of other suitable materials per intended application of press tool assembly 10. The auxiliary pillar 30 includes a top end 68 and a bottom end 70. The top end 68 is adapted to be positioned within the backing plate 24 and the bottom end 70 is adapted to be positioned within the stripper plate 32. The auxiliary pillar 30 facilitates accurate alignment of the holder plate 26 and the stripper plate 32 during the operation of the press tool assembly 10. The auxiliary pillar 30 prevents breakage of the punches (not shown) positioned on the press tool assembly 10.
Referring now to FIGS. 5-6, the auxiliary bush 34 includes a body 72 adapted to be positioned within the stripper plate 32 is illustrated. The auxiliary bush 34 includes a top end 74, a bottom end 76 and a central opening 78. The top end 96 defines an opposed pair of shoulders 80 adapted to be positioned above the stripper plate 32. The central opening 78 is having a diameter that is equal to an outer diameter of the auxiliary pillar 30 adapted to guide the auxiliary pillar 30 within the opening 78.

In Operation;
As shown in FIG, 7, the press tool assembly 10, in operation, is in an upward stroke condition that is indicated by an arrow-E. In this condition, the first and second spring retainers 40, 42 attain a top dead centre (TDC, hereinafter) position due to self weight and pre-compression load on the spring 36. In this condition, the backing plate 24 is positioned at a first distance 82 from the top plate 15. In this condition, the collar 56 (Refer FIG. 9) of the first spring retainer 40 is positioned at a second distance 84 from a top face 86 of the backing plate 24.
Referring now to FIG. 8, the press tool assembly 10, in operation, is illustrated in a first downward stroke condition indicated by an arrow-F. In this condition, initially the stripper plate 32 touches the strip or coil to be punched. Subsequently, the backing plate 24 touches to the top plate 15. This transfers the compression load to the spring 38 that upwardly positions the second spring retainer 42 at a third distance 88. In this condition, the third distance 88 in the downward stroke is substantially equal to the first distance 82 (See FIG. 7) in the upward stroke.
Referring to FIG. 9, the press tool assembly 10, in operation, is in a second downward stroke condition that is indicated by an arrow-G is illustrated. In this condition, the press tool assembly 10 is at a bottom dead centre position. In this condition, the first sub assembly 18 (see FIG. 1) touches to the top plate 15. In this condition, the collar 56 (Refer FIG. 3) of the first spring retainer 40 is positioned at a fourth distance 90 from the holder plate 26. In this condition, the ribs 64 (Refer FIG. 4) of the second spring retainer 42 are positioned at a fifth distance 92 from the top plate 15. This allows the spring 36 to absorb a high pressure of the spring 38 and deliver a low pressure to the cutting punches. This low pressure and local auxiliary alignment avoids frequent breakages of delicate or critical punches.
Advantages of the present invention are:

1. The first and second sub assemblies 18, 20 substantially reduce the tool down time for punch breakages.
2. The press tool assembly 10 increases the tool life of the punches.
3. The productivity in stamping operation increases by loading the press tool assembly 10 on high speed presses.
4. The press tool assembly 10 can perform critical stamping operations on the any normal press that makes the press tool assembly 10 generic for all presses.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim:
1. A press tool assembly for performing a stamping operation with a plurality
of punches mounted thereon, the press tool assembly comprising:
a moving upper half having a top plate, a holder plate and a backing plate, the backing plate connecting to the top plate through the backing plate;
a stationary lower half having a stripper plate;
a first subassembly having a first spring and a first spring retainer, the first spring retainer positioning the first spring between the holder plate and the stripper plate;
a second subassembly having a second spring and a second spring retainer, the second spring retainer positions the second spring within the top plate, the first spring and the second spring performing a floating action for facilitating a dampened pressure load on the punches; and
an auxiliary pillar securing rigidly within the backing plate and the holder plate, the auxiliary pillar moving axially to pass through an auxiliary bush mounted on the stripper plate, the auxiliary pillar facilitating accurate alignment between the first subassembly and the second subassembly for preventing breakage of the punches.
2. The press tool assembly as claimed in claim 1, wherein the press tool assembly in an upward stroke positions the first sub assembly at a predefined distance from the top plate to transfer a pre-compression load on the first spring.
3. The press tool assembly as claimed in claim 1, wherein the press tool assembly in a first downward stroke transfers the pre-compression load on the first spring to the second spring.
4. The press tool assembly as claimed in claim 1, wherein the press tool assembly in a second downward stroke mutually operates the first spring and the second spring to deliver a low pressure on the cutting punches.