STOPPERS

STOPPERS

STOPPERS:-

After each and every stroke of the press, the strip has to be fed forward for one pitch length. This can be accomplished by means of stopper.
   The function of the stopper is to arrest the movement of the strip when it is fed forward to one pitch length.
It is essential that two basic definitions be associated with

The fundamental principles of stops,
• Stop position.
• Registry position.

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STOP POSITION:-
This is the location of the actual stopper position surface against which the stock strip is halted.

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Registry position:-
• This is the exact location in which the stock strip must be established in order to obtain dimensionally correct component.
• The work is located by the stop and is registered by the pilots.
• The registry position may or may not be the same as the stop position.
• When a stop functions as an approximation gauge the stop position does not coincide with the registry position
.• If the stop acts as a true gauge the stop position and the registry position are same.
• If a stock strip is piloted the stop need act only as an approximation gauge.
• The strip is overfed against the gauge and is registered by the pilots.
• If the stock strip is not piloted the stop has to function as a true gauge.
• Primary stops act as true gauges, registering the stock strip.
• Secondary stops normally serve as approximation gauges.
• Therefore overfeeding is allowed when installing them.

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Solid stops:-
• A hardened steel block is mounted at the required location.

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Plain pin stop:-
• It is a plain cylindrical pin mounted in the die block.
• A clearance hole for the pin stop in the bottom plate is provided for the  following reasons.
• To permit adjustment of the height of the pin stop without removing the  die lock from the assembly.
• While re sharpening the die the stop pin can be removed.
• The pin can be driven down in the event of miss feed.
• This reduces the chance of damage to the tool.

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Headed pin stop:-
• When the stop is to be very nearer (very small scrap bridge) to the die opening a headed pin stop is used.
• A plain pin stop cannot be used in such cases because the opening made for locating the stop will weaken the die.
• The mounting hole of the headed pin stop will be away from the die opening.

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Spring loaded pin stop :-
• It is a spring pin located at the required stopping position.
• These stoppers do not require clearance in the opposing tool member.
• The pin is pressed down by the opposing tool member during operation.

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Finger stops:-
• In progressive tools designed for manual feeding, finger stops locate the strip for each station except for the final station.
• This stop is actuated manually.
• It is mounted in the stripper plate.
• Provision is made for moving the stopper through a predetermined distance.
• It is pushed inwards to enable the stock material to halt against it.
• After the press stroke the stopper is released.
• When a new stock strip is fed the stopper has to be actuated again.

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Trigger stops:-
Side acting Trigger stops.
• For faster manual feeding, trigger
  stops are  preferred.
• There are two types of trigger stops.
• Side acting.
• Front acting.

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Front acting trigger stopper.:-
• The working mechanism for side acting and front acting trigger stops are same.
• The front acting trigger stop is mounted in the front end of the tool and the side acting trigger stop is mounted in the side of the tool.
• The lever shaped trigger stop fits freely in the slot milled in the guide plate.

• One side of the wall of the slot is machined with a taper angle.
• It gives the necessary movement to the trigger.
• An inclined set spring at the other end of the trigger holds the trigger in position.
• When the strip is pressed against the tip face of a trigger the trigger moves back wards and stops against the non tapered wall of the slot.
• This allows the strip to advance.
• This advancement is equal to one margin width.
• When the tool is tripped, a knocker bar fixed to the top assembly of the tool comes down and knocks tile free end of the trigger.
• This action lifts to clears the strip thickness and then jumps back to its old position to fall on the strip (blanked portion).
• The strip can be fed forward.