EJECTORS AND SHEDDERS
Ejectors and shedders are the tool members serves the purpose of supporting the blank while cutting action, which helps in maintaining flatness and also eject out the component which is struck inside the die opening after the cutting action.
These may use hydraulic or mechanical menace for actuating :-
• In conventional drop through type blanking tools, the punch forces the blank in to the die.
• The blank will be retained within the die cavity till the subsequent blanks push it past the land.
• Then it falls down through the opening in the bottom plate and subsequently through the opening in the press bed.
These may use hydraulic or mechanical menace for actuating :-
• In conventional drop through type blanking tools, the punch forces the blank in to the die.
• The blank will be retained within the die cavity till the subsequent blanks push it past the land.
• Then it falls down through the opening in the bottom plate and subsequently through the opening in the press bed.
Shedders and ejectors are used when it is not possible to remove the blanks in the conventional methods due to the following reasons:
1.0 Size of the blank does not allow it to conveniently pass through the opening in the press bed.
2.0 Contour of the blank is such that it tends to stick and get distorted during its travel through the die cavity.
3.0 Opening in the press bed fitted with die cushion which will interfere with the piece part disposal.
4.0 Close tolerance specified for the flatness of the blank.
5.0 Tools of inverted nature.
1.0 Size of the blank does not allow it to conveniently pass through the opening in the press bed.
2.0 Contour of the blank is such that it tends to stick and get distorted during its travel through the die cavity.
3.0 Opening in the press bed fitted with die cushion which will interfere with the piece part disposal.
4.0 Close tolerance specified for the flatness of the blank.
5.0 Tools of inverted nature.
EJECTORS
In the conventional position. die is the lower member of the tool.
If the expulsion of the blank achieved by forcing it upwards, the action is known as "ejection". The element of the tool which ejects the blank is called an "ejector“.
Ejectors may be actuated by compression springs. Rubber, pneumatic devices or hydraulic devices.
Ejectors if used with spring strippers, always return the blank into the strip due to the simultaneous stripping and ejecting action.
In some progressive tools. the blanking station is provided with an ejector to return the blank into the strip to be carried forward to the next station for further operations known as the cut and carry method.
In the conventional position. die is the lower member of the tool.
If the expulsion of the blank achieved by forcing it upwards, the action is known as "ejection". The element of the tool which ejects the blank is called an "ejector“.
Ejectors may be actuated by compression springs. Rubber, pneumatic devices or hydraulic devices.
Ejectors if used with spring strippers, always return the blank into the strip due to the simultaneous stripping and ejecting action.
In some progressive tools. the blanking station is provided with an ejector to return the blank into the strip to be carried forward to the next station for further operations known as the cut and carry method.
EJECTORS:-
SHEDDERS:-
Another way to accomplish the expulsion of the blanks from the die cavity is by making use of the knockout mechanism on the press. For this purpose, the tool should be of the inverted design.
In inverted tools, die becomes the upper member of the tool,
being clamped to the press ram. The expulsion of the blanks is achieved by forcing them downwards. This action is generally known as "shedding" and the element of the tool which sheds the blanks is known as the "shedder".
TYPES OF SHEDDERS:-
POSITIVE SHEDDERS
Shedders operated by the knockout mechanism on the press are called positive shedders.
The knockout arrangement of the press is usually of a bump type knockout bar, mounted through slot across the press ram. The knockout bar is free to move up and down with in the slot, as well as it could ride up and down together with the ram.
COMPRESSION SHEDDER:-
Shedders backed up by compression springs, hard rubber or disc springs are called compression shedders.
It could be used to produce flatter and neatly sheared blank. They are also used if the blanks are too large to allow the incorporation of an efficient positive knockout system.
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SHEDDING PINS:-
The stock material is usually coated with a rust preventive solution. It is obvious that any liquid or oil deposit left on the stock material will cause the blanks to stick to the face of the shedder. Spring loaded shedding pins are employed to overcome this problem.
Shedding pins will be more effective if applied to one side of shedder face rather than in the centre. All ejection and knockout elements are to be case hardened to 48-52 HRc depending on severity of operation.
KNOCK OUTS:-
Positive knockouts are classified into 2 groups
1.Direct knockout
2.Indirect knockout
1. DIRECT KNOCKOUT
In this knockout system if the knockout rod is directly in contact with the shedder, the system is known as direct knock out system.
In this knockout system if the knockout rod is directly in contact with the shedder, the system is known as direct knock out system.
2. INDIRECT KNOCKOUT SYSTEM:-
As the passage of the knockout rod is through the shank, any punch which comes in line with or near to the centre line of the shank will obstruct the knockout rod from coming in direct contact with the shedder. In such cases an indirect knockout system should be employed. In addition to the shedder and the knockout rod, it consists of a knockout plate and transfer pins as shown in the figure.
The location and number of transfer pins depend on the size and shape of the blank.
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