Gauges
In most pres tools the stock material is fed in the form of long strips.For the efficient functioning of the tool the strip should be guided longitudinally during its travel through the tool.This is achieved by employing gauges.When unit stocks are used,pin gauges nest them in the required position.
Gauges used in secondary operation tools locate the pre-blanked or pre-formed component in relation to the operation to be carried out.
Back guage and front gaugeWhenever the stock material is fed in the form of a strip it is fed in between the back gauge and the front gauge.The back gauge is the one which is on the far side of the press operator or located on rear side of press tool.The front gauge is on the near side of the operator or located in front portion of press tool.While feeding,the operator should always keep the strip pressed against the back gauge.
Back gauge is the actual gauging member and the function of the front gauge is only to provide approximate gauging.The required dimensional co-ordinates are maintained from the back gauge to the die opening.
Bulge clearance
Thick and soft materials tend to bulge sidewise as soon as the blanking operation is performed.This makes it difficult to feed as well as to gauge the strip further.A bulge clearance is provided usually in the back gauge only.
Size of back gauge and front gaugeExtended back gage
for easier gauging the back gauge is extended beyond the die on the feeding side.Its length is equal to the strip width for roll feeding and two and a half times the strip width for manual feeding.
Strip support
During manual feeding, to reduce fatigue to the operator a strip support should be provided while feeding pliable(flexible)strips.The strip support should be made wider and brought closer to die block to provide better support and guidence.Roll feed does not require strip support.
Pushers
Pushers are provided to keep the strip firm against the back gauge during its travel through the tool.Spring loaded pushers are used for this purpose.
Nesting Gauges
Nest gauges are used whenever
- secondary operation tools are used
- unit stock is fed into the tool.
The function of the nest gauge is to align the unit stock or the component for the secondary operation in correct relation to the punch and die.The nest gauges should meet the following three conditions to achieve the best result.
Accuracy
The fit between the piece part and the gauge sholud be perfect and consistent throughout the life of the tool.It is not necessary for the nest to locate the entire contour of the piece part.
Only sufficient number of locating points are needed.
But they should be strategically located in relation to the piecepart contour.The number of locating pins depends upon the life and the shape of the piecepart.The minimum requirement are
- Three points for circular and triangular shapes.
- four points for other shapes.
Easy and quick unloading
Nest gauges should facilitate fast and easy loading and unloading of components.to achieve this good visibility and accessibility are required.Adequate lead angle should be provided around the nesting profile for easy loading,unloading is difficult than loading.So through consideration should be given to this point.For low production tools simple pick off slots are machined in the nest.the operator can manually pick the piecepart out of the nest.Pieceparts can be ejected out by means of lever operated ejectors.Thin pieceparts can be expelled from the nest by means of ompressed air jets.
Fool proofing
Possibility of the piecepart being loaded in incorrect manner by the operator should be pevented by the nest.This can be easily achieved by fool proof pins.
Types of nest gauges
Pin type nest gauges
This is the simplest form of nest gauge .It consists of plain or headed cylindrical pins.They are arranged in such a way as to provide enough number of lcating points for the piecepart.The pins are hardened and ground and are press fitted in the die block.The upper end of the pins must be beveled for easy loading and unloading.The opposing tool member should have relief holes to receive these pins.In inverted tools the nest pins are fitted into the travelling stripper.The relief holes are drilled in the die block.If these holes are to be provided near the die opening the die will be weakened.In such cases the pins are spring loaded.They are pushed below the face of the stripper upon contact with the die block.Retracting nest pins are less accurate and should be used only if inevitable.
Plate type nest gauges
This type of nest gauge is a plate into which an opning is machined to receive the piecepart.This opening need not fit the entire contour of the piecepart.The plate nest can be of split construction for easiness in machining andd hardening.They should be perfectly screwed and dowelled into position.All gauging elemnets should be made out of tool steels and hardened to 48 to 53 HRC.