Function of Stopper
The function of a stopper is to arrest the movement of the strip when it is fed forward to one pitch length.After each of the press stroke, the stock strip is stopped at definite position in order to perform cutting/non cutting operation on the strip to obtain the component correctly.
Classification of Stopper
Stoppers are classified into three catagories
- Primary
- Secondary and
- final.
The first stop in the tool is called primary stop.The last stop in the tool is called final stop.The stops in between the primary stop and final stop are called secondary stops.
Stop Position
This is the location at which the stock strip is stopped.
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 fuctions 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 iloted the stop need act only as an aproximation 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.
Types of stop
Solid stops
A hardened steel block is mounted at the required location
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 plate from the assembly.
While resharpening the die the stop pin can be removed.
The pin can be driven down in the event of misfeed.This reduces the chance of damage to the tool.
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 thee stop will weaken the die.
The mounting hole of the headed pin stop will be away from the die opening.
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 mmber.The pin is pressed down by the opposing tool member during operation.
Finger stops
In progresive tols designed for manual feeding finger stops locate the strip for each station except for the final station.
This 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.
Trigger stops
For faster manual feeding,trigger stops are preferred.
There are two types of trigger stops.
- Front acting.
- Side acting.
The working mechanism for front acting and side 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 holds the trigger in position.
When the strip is pressed against the tip face of a trigger,thee trigger moves back wards and stops against the nontapered wall of the slot.
This allows the strip to advance.This advancement is equal to one margin wdth.When the tool is tripped a knocker bar fixed to the top assembly of the top assembly of the tool comes down and knocks the free end of the trigger.This action lifts to clears the thickness and then jumps back to its old position to fall on the strip(blanked portion).The strip can be fed forward.