GUAGES

GAUGES

Gauges must be considered in the design of press tool because theses component position the strip longitudinally in its travel through the die. In second operation dies, gauges locate the previously blanked or formed part for further processing operations.

Design consideration includes :
1. Material choice: finished tool steel is used for gauges in first class die. Cold rolled steel should be used only when low production n requirements exists.
2. Adequate thickness: the back gauge and the front spacer must be thick enough to avoid binding of the strip between stripper plate and die block.
3. Good doweling practice: since the gauges locate the strip they should always be doweled in position.
4 Accuracy of location surfaces: The gauging surfaces which actually bear against the strip or part should be ground, and so marked on the die drawing.

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BACK GAUGE AND FRONT GAUGE:-
In passing through at two station piece and blank die the strip is positioned against back gauge by the operator. Strips support helps to align the bottom of the strip with the top surface of the die block to prevent binding. Back gauge is the actual guiding member and the function of the front gauge is only to provide  an approximately gauging. The required dimensional relations are mentioned from the back gauge to the die opening.

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BULGE CLEARENCE:-
Thick and soft material tend to bulge side wise as soon as blanking operation is performed. This makes it quite difficult to feed as well as to gauge the strip further unless a bulge clearance is provided in such stations. Bulge clearance is provided usually in the back gauge only.

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SIZE OF BACK GAUGE AND FRONT GAUGE:-
The gauge should be thick enough to avoid binding of the strip between the stripper and the die block. The recommended thickness of 3mm for sheet up to 1.5mm and strip thickness+1.5mm for heavier(more than 1.5mm) strip is found to be satisfactory if automatic stops are employed in the tool. The space between back gauge and the front spacer is made to strip width+0.5mm if roll feeding is used and strip thickness+1mm for hand feed.

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EXTENDED BACK GAUGE:-
For easier gauging usually the gauge is extended beyond the die on the feeding side. An amount equal to 2and ½ times the strip width for hand feeding and equal to the strip width for roll feeding is sufficient.

STRIP SUPPORT
While hand feeding the strip to reduce fatigue to the operator a strip support should be provided. The strip support should be made wider and brought closer to the die block to provide better support and guidance. Roll feed doesn’t require strip support.

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PUSHERS:-
These are provided to keep the strip firm against the back gauge during its travel through the tool. Spring loaded pushers are often employed to achieve this.

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NESTING GAUGES:-
Nest gauges are used in secondary operation tool or whenever limit stock is fed in to the tool.There are three conditions to be met to achieve the best result.

ACCURACY : The fit between the gauge part and the gauge should be perfect. For gauging purpose it is not necessary of the nest to fit entire contour of the piece part. All that is required to provide sufficient number of locating points. The number of locating points required for certain nest depends upon the size and the shape of the piece part. A minimum of three part for circular and angular shape and 4 points for other shapes are required.

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EASY AND QUICK LOADING AND UNLOADING:-
Nest gauges facilitate fast and easy loading and unloading of the components. The main factor which decide this are good visibility and accessibility to the nest. Adequate lead angle should be provided around the nesting profile for easy loading.
Unloading more difficult than loading. For low production tools simple pick of slots machined in the nest would be sufficient to allow the operator to manually pick the piece out of the nest. Ejection of piece parts out of the nest by means of lever operated ejectors is another solution. If the piece part is thin it can be ejected from the nest by means of compressed air jets.


FOOL PROOFING:-
Any possibility of the piece part being loaded in the incorrect manner by the operator should be prevented by the nest. Fool proof pins could easily accomplish.

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TYPES OF NEST GAUGES:-

PIN TYPE NEST GAAUGES
The simplest form of nest gauges comprises of plains or headed cylindrical pins arranged in such way as to provide enough number o f locating points for the piece part. These hardened and ground pins are press fritted in to the die block. The arrangement of the pins should be such that a total clearance of at least 0.03mm results between them. The upper end of the pins must be doweled for easy loading and unloading. The opposing member should have relief holes drilled in to it to receive these pins.
 

In inverted tools the nest pins are fitted in to the traveling stripper and the relief holes are to be drilled in the die block. If these holes happened to appear in the near vicinity of the die opening the die will be weekend in such case the nest pins should be of the spring loaded type and made to disappear below the face of the stripper, upon contact with the die block. It is obvious that disappearing nest pins are less accurate and should be used only if inevitable.

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PLATE TYPE NEST GAUGE:-
These type nest is a plate in to which an opening is machined to receive the piece part. As mentioned already the opening need not fit the entire contour of the piece part. Plate type nest could of sectional constructions for easiness in machining and hardening. Plate type nest gauges should be perfectly screwed and dowelled in position.
As a general rule, all gauging elements should be made out of tool steels and hardened to 48-52 HRC.

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NESTING IN DIE SET:-
Simplest nesting method is to fit the section in to the pocket that is milled directly in the die set. The die section should be fit tightly into the pocket but the assembly pressure should be so great as to distort the die set. It should be noted that nesting does not eliminate the need for the use of screw.