FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention -

AN IMPROVED PRESS TOOL ARRANGEMENT FOR STRIPPING MATERIALS

2. Applicant(s)
(a) NAME :
(b) NATIONALITY :
(c) ADDRESS :

LARSEN & TOUBRO LIMITED
An Indian Company
L & T House, Ballard Estate, Mumbai 400 001, State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE NVENTION
The present invention relates to a press tools. Particularly the invention relates to an improved press tool arrangement for stripping down materials with minimum or no distortion. More particularly, the invention is concerned about floating stripper bush arrangement in press tools to strip down the material and to avoid the distortion in the component/strip during stripping
BACKGROUND OF THE INVENTION
The manufacturing process for sheet metal component or stamping is by processing a sheet metal coil or strip in a press tool. The sheet metal strip or coil may be of ferrous or non ferrous materials.
Press working is one of the major processing techniques for converting sheet metal into 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 & die. The die profile is the female profile intentionally kept bigger than the punch profile by a uniform gap called cutting clearance.
Press tool mainly consists of two halves, namely fixed bottom half and a moving top-half. The fixed bottom half is secured to the stationary bolster plate of mechanical press. It comprises 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 & it comprises a no. of circular & non circular cutting & non cutting elements called punches. The punches move up & down along with the moving ram of the mechanical press & they are guided in cavities made in a plate called Stripper. During downward movement, the punches penetrate the sheet metal & enter the die cavity thus pushing the sheet metal scrap displaced by the cutting punch into the lower half of the tool. One downward & return upward movement of

the top half of press tool is called as stroke of press tool. Surrounding metal clings to the body of cutting punches during downward stroke. The same is stripped off by the stripper plate during upward stroke of the punches.
Press tool may be of multi-station type (progressive) or single station type. In a multistation tool, the strip moves from one end of 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 of movement of strip, different punching operations are carried out on strip / coil leading to completion of stamping profile in last stage.
Press tools are used for processing coils/strip in Progressive punching operations. The strip or coil is punched, formed, notched, bent and made to different shapes progressively at various stages. Finally the component is separated from the strip / coil either by blanking or by parting operation.
In a progressive die, normally floating type stripper or travelling type stripper is preferred for better flatness of component &. close guidance of punches. This type of construction is expensive & can be justified in case of high volumes of production. In some tools floating stripper is not necessary since the operations like bending and parting/cut off operations are performed in a single station.
Normally for components of less thickness, Spring loaded stripper (Floating stripper) is preferred. In this tool cutoff and bending is done simultaneously. It is difficult to remove / takeout the finished component from the tool when it is a floating stripper. In Fixed stripper plate construction, the stripper plate will be provided up to the area of cut off and bending. So the finished component (after cutoff and bending) is free to be removed / taken out from the tool since stripper plate obstruction is avoided. When some operations like piercing, notching etc. in the component are to be done before cut off and bending, fixed stripper plates are used for guiding punches. In a fixed stripper the strip/coil is fed inside through the slot provided for feeding. This slot is

normally higher by 0.2 to 0.3 mm wider than the strip / coil. The depth of slot is normally 3 to 4 times the thickness. But when the thickness of the stip/coil is very less then 2 to 2.5 mm depth is provided to ensure smoother feeding of strip/coil. Hence during the upward stroke of the press the material (strip/coil) which clings to the punch travels up by around 2-3 times its thickness before getting stripped down. This causes the distortion in the profiles/holes in the component. Hence the stripper plate doesn't hold the material before punching operation in the case of fixed stripper construction.
If the piercing punches are slender with respect to the thickness of stock being punched, the tips of the punches are likely to chip off frequently by buckling in case of Fixed Stripper tool construction. When the strip thickness is very small, the strip / coil gets distorted after piercing/notching during stripping operation. The material surrounding the piercing punch clings to the punch and goes upward along with the punch during the upward stroke. This strip is stripped down by the stripper plate. But since the gap is 2.5 times the thickness of the strip, the surrounding regions of the hole gets disturbed / distorted very badly. In the prior art, floating stripper plate was used for this kind of strip thickness, which is very costly to manufacture and difficult to assemble and maintain.
Thus, there is a need to overcome the disadvantages of the prior art. Therefore, the inventors provided floating stripper bush construction in press tools to strip down the material and to avoid the distortion in the component/strip during stripping. The present invention would provide better guidance of the punch till the cutting zone and proper stripping would achieve with this arrangement. This construction is less expensive compared to the Floating Stripper construction.

OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the
prior art.
Another object of the present invention is to provide an improved press tool
arrangement for stripping down materials with minimum or no distortion.
Another object of the present invention is to provide a floating stripper bush means
arrangement in press tools.
Another object of the present invention is to provide the arrangement for better
guidance of the punch till the cutting zone.
Another object of the present invention is to provide the arrangement for smoother
feeding of coil / strip.
Yet, another object of the present invention is to provide the arrangement for ease of
maintenance
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an improved press
tool arrangement for stripping down materials with minimum or no distortion, said
arrangement comprising:
punch means ;
strip/coil means;
stripper plate means;
stripper bush means ;
clamping plate means;
plurality of spring assembly means comprising first spring assembly, second spring
assembly and third spring assembly;
pusher assembly comprising a pusher means and said third spring assembly;
sleeve means;
screw means;

wherein said stripper bush means being mounted on said stripper plate means for
guiding said punch means and/or stripping of coil means; said first spring assembly
being adapted to place inside said stripper plate means to move upward said stripper
insert means and said strip plate means;
wherein said clamping plate means being mounted on said stripper bush means and
said stripper plate means so as to restrict the movement of said stripper bush means;
said second spring assembly being adapted to place inside said stripper plate means to
move upward said clamping plate means; said clamping plate means adapted to
accommodate said sleeve means with said screw means and adapted to pass through
said punch means;
wherein said sleeve means being mounted between said stripper plate means and said
clamp plate means;
wherein said pusher assembly being adapted to place inside top half of the press tool;
wherein said pusher means comes in contact with said clamping plate means such that
said spring assembly gets compressed to actuate said stripper bush means to be
pushed down during the downward stroke so as to precisely guide the said punch for
piercing/cutting operation;
wherein said punch means moves inside the stripper bush so as to disengage the
strip/coil means from the punch means and disengaging said pusher means from said
clamping plate means and said spring assembly pushing said clamping plate means
and said stripper bush means upward during upward stroke.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates sectional view of press tool assembly
Fig. 2 illustrates strip layout showing the piercing punch size, piercing location and
the strip/coil thickness
Fig. 3 illustrates sectional elevation showing various elements of the tool with
floating stripper bush arrangement

Fig. 4 illustrates enlarged view showing various elements associated with the stripper
bush arrangement in press tools
Fig. 5 illustrates sectional view showing the press tool in the 'stroke up' condition.
Fig. 6 illustrates sectional view showing the press tool taking the downward stroke.
Fig. 7 illustrates sectional view showing the press tool taking the down ward stroke.
Fig. 8 illustrates sectional view showing the press tool in the fully downward stroke.
Figure 9 illustrates planar view of stripper bush
Figure 10 illustrates planar view of clamping plate
Figure 11 illustrates planar view of sleeve
Figure 12 illustrates planar view of pusher
Figure 13 illustrates sectional view of stripper plate
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention there is provided a floating stripper bush construction in press tools comprising stripper bush means (8), clamping plate means (6), pusher assembly (2), plurality of spring assembly means (II) comprising first spring assembly (11a), second spring assembly (Mb) and third spring assembly (lie), stripper plate means (7) as shown in figures 3 and 4. The press tool assembly is shown in figurel.
In the present invention, a stripper bush (8) is mounted in the stripper plate (7). This stripper bush (8), as shown in figure 9, is precisely guided inside the stripper cavity and can move up and down according to the stroke of the press. The stripper bush (8) is made of through hardened steel. As shown in figure 13, the stripper plate (7) is an essential feature in any press tool. It is used for precisely guiding the punches, guiding the strip/coil and stripping the same down during upward stroke. It is normally rectangular in shape and is either hardened or soft. It has provisions for guiding the strip, provisions for accommodating the stripper bush (8) and spring

assembly, provisions for accommodating Socket Head (alien) screw means (10), sleeve means (9) and spring assembly used for clamping plate assembly(6).
The first spring assembly (11a) comprising plurality of light load compression springs. A spring is housed inside the stripper plate (7), between the stripper bush (8) and stripper plate (7). This spring pushes the stripper bush (8) upward in the idle condition, thus the bottom surface of the stripper bush (8) is always in the same level of bottom surface of strip guiding surface of stripper plate (7). As shown in figure 2, strip layout showing the piercing punch size, piercing location and the strip/coil thickness.
A floating clamping plate (6) is mounted above the stripper plate (7) and stripper bush (8). Clamping plate (6) is a rectangular steel plate mounted behind the stripper plate (7) and the stripper bush (8). This is rectangular in shape and has provisions for accommodating alien screws (10) with sleeve (9) and has clear hole for the punch to pass through as shown in figure 10. This plate is always engaged with the stripper bush (8). This plate is also spring loaded and can move up and down according to the stroke of press. This is achieved by the spring mounted inside the stripper plate (7) below the clamping plate (6). The springs always push the clamping plate (6) towards the upward direction thus maintaining a constant gap between the stripper plate (7) and the clamping plate (6) in the idle condition. This is maintained with the help of Socket Head (alien) screw (10) and sleeve (9) arrangement mounted between the stripper plate (7) and clamping plate (6). The upward movement of the stripper bush (8) is restricted by the clamping plate (6). Thus springs housed inside the stripper assembly pushes both the clamping plate (6) and stripper bush (8) constantly upward in the idle condition of the tool.
Normally 10 to 20% of the total cutting load is required for stripping action. The springs provided in the stripper plate (below the stripper bush and clamping plate)

will not be enough to achieve the stripping load. Also there needs to be a mechanism which will push the stripper bush/clamping plate downward till the cutting edge during downward stroke of the press and a mechanism which will ensure that extra downward stroke is taken care of.
Hence a spring loaded pusher assembly (Minimum two numbers) is provided from the top half of the tool. A spring loaded pusher assembly (2) is housed inside the top half of the tool (between top plate means (1), backing plate means (3) and holder plate means (4)). The pusher rod (2a) is directly loaded above the clamping plate (6). The pusher means (2a) is housed inside the top hole provided inside the top plate. It projects outside from the bottom of the holder plate. The spring is also housed inside the hole provided in the top plate means (1) and is guided by the pusher (2a). This spring is selected such that it can provide the required stripping force and it can take care of the extra downward stroke of the press.
As shown in figure 12, Pusher means (2) is cylindrical in shape. The pusher assembly (2) comprises a step profile which operatively communicates with the top plate means (1), backing plate means (3) and holder plate means (4) such that the pusher assembly itself is provided with a resting surface abutting against the backing plate means (3) to further provide resting surface to the spring means. The step in the pusher (2a) acts as a resting surface for spring and for itself when it is assembled inside the top half. The top half of the pusher (2a) acts as a guide for spring. As shown in figure 11, the sleeve (9) arrangement is provided between clamping plate (6) and stripper plate (7). A Socket head (alien) screw (10) is inserted through the sleeve (9) and is clamped to the stripper plate (7). The length of the sleeve (9) is maintained based on the travel required for the stripper bush (8) and the spring selected.
There are 3 different varieties of springs used in the mechanism/ arrangement.

1. The first spring assembly (11a) comprising light load compression spring is used between stripper bush (8) and stripper plate (7). The load of the spring is just enough to overcome the friction during guidance between the stripper bush (8) and stripper plate (7) and to overcome the weight of stripper bush (8). The stroke of the spring is also very less and depends on the strip thickness and the depth of the guiding slot provided in stripper plate (7).
2. The second spring assembly (lib) comprising light load compression spring is used between clamping plate (6) and stripper plate (7). The load of the spring is just enough to overcome the friction during guidance between the stripper bush (8) and stripper plate (7) and to overcome the weight of stripper bush (8). The stroke of the spring is very less and depends on the travel required for stripper bush (8).
3. The third spring assembly (1 lc) used in the pusher assembly (2) requires more travel and the load exerted by it in the pre compressed condition should overcome the load of all the springs accommodated in the bottom half.
Figure 5 illustrates the press tool in the 'stroke up' condition i.e. the stripper bush (8) and the clamping plate (6) are pushed up by the spring force and the bottom of the stripper bush (8) is flush with the stripper plate (7) guiding surface. The pusher assembly (2) is away from the stripper assembly and the spring (lie) in the pusher assembly (2) (top half) is in the pre compressed condition.
During the downward stroke of the press, the pusher (2a) touches the clamping plates (6) and pushes it downward and the springs get compressed. Thus the stripper bush (8) is pushed downward and touches the strip/coil during the downward stroke as shown in figures 6 and 7. The punch also moves down through the stripper bush according to the downward stroke. The movement of the stripper bush is restricted when it comes in contact with the strip / coil. Further downward stroke of the press, engages the piercing punch (5) and strip/coil against the die and piercing operation

gets completed. During this action, the pusher (2a) starts moving upward and compresses the spring inside the top plate (1), thus compensating the extra downward stroke of the press as shown in figure 8.
During the upward stroke of the press, first piercing punch means (5) moves inside the stripper bush (8), thus disengaging the strip / coil with the piercing punch (5). Thus stripping action is completed and hence distortion in the strip/coil is avoided. The spring (11e) in the pusher assembly (2) starts expanding at this time. During further upward stroke, disengages the pusher (2a) and the clamping plate (6). The spring (11e) in the pusher assembly (2) comes to the pre compressed condition. The disengagement of the clamping plate (6) and pusher (2a) takes away the load on the compression springs in the stripper assembly and pushes the clamping plate (6) and the stripper bush (8) upward.
ADVANTAGES OF THE INVENTION
1. The strip/coil is positively stripped down by this mechanism
2. The construction takes care or extra downward movement (extra stroke) of the press
3. Very simple mechanism, less expensive to manufacture (as compared to Floating stripper construction).
4. The distortion of the component /strip/coil is fully eliminated
5. Positive guidance of the punch till the cutting periphery which increases the component accuracy.
6. Easy for manufacturing and maintenance
The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The top plate, punch, die plate, clamping plate , stripper plate, stripper bush, plurality of springs, backing plate ,Allen screw,

pusher and base plate as stated do not limit the scope of the present invention. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.

WE CLAIM
1. An improved press tool arrangement for stripping down materials with minimum or no distortion, said arrangement comprising: punch means; strip/coil means; stripper plate means; stripper bush means ; clamping plate means;
plurality of spring assembly means comprising first spring assembly, second spring assembly and third spring assembly;
pusher assembly comprising a pusher means and said third spring assembly; sleeve means; screw means;
wherein said stripper bush means being mounted on said stripper plate means for guiding said punch means and/or stripping of coil means; said first spring assembly being adapted to place inside said stripper plate means to move upward said stripper bush means and said strip plate means; wherein said clamping plate means being mounted on said stripper bush means and said stripper plate means so as to restrict the movement of said stripper bush means; said second spring assembly being adapted to place inside said stripper plate means to move upward said clamping plate means; said clamping plate means adapted to accommodate said sleeve means with said screw means and adapted to pass through said punch means; wherein said sleeve means being mounted between said stripper plate means and said clamp plate means;
wherein said pusher assembly being adapted to place inside top half of the press tool;

wherein said pusher means comes in contact with said clamping plate means such that said spring assembly gets compressed to actuate said stripper bush means to be pushed down during the downward stroke so as to precisely guide the said punch means for piercing/cutting operation;
wherein said punch means moves inside the stripper bush so as to disengage the strip/coil means from the punch means and disengaging said pusher means from said clamping plate means and said spring assembly pushing said clamping plate means and said stripper bush means upward during upward stroke.
2. Arrangement as claimed in claim 1 or claim 2, wherein said stripper bush is made of hardened steel and the like.
3. Arrangement as claimed in claim 1, wherein said first spring assembly comprising plurality of light load compression springs and the like adapted to be located between said stripper bush means and said strip plate means.
4. Arrangement as claimed in claim 1, wherein said second spring assembly comprising plurality of light load compression springs and the like adapted to be located between said clamping plate means and said strip plate means.
5. Arrangement as claimed in claim 1, wherein said third spring assembly comprising plurality of light load compression springs and the like.
6. Arrangement as claimed in claim 1, wherein said pusher assembly comprising a step profile being adapted to be operatively communicating with top plate means, backing plate means and holder plate means such that said pusher assembly itself is provided with a resting surface abutting against the said backing plate means to further provide resting surface to said spring means.

7. Arrangement as claimed in claim 1, wherein said pusher assembly is substantially cylindrical shape.
8. Arrangement as claimed in claim 1, wherein said stripper plate means is substantially rectangular shape.
9. Arrangement as claimed in claim 1, wherein said clamping plate means is substantially rectangular shape.
10. An improved press tool arrangement for stripping down materials with minimum or no distortion as herein substantially described and illustrated with the accompanying drawings.