PUNCHES
CUTTING PUNCHES
These punches perform operations like blanking, piercing, notching , trimming etc.
Punches can be classified into three categories.
• Cutting punches
• Non cutting punches
• Hybrid punches
PUNCH:-
Punch is the cutting element of the tool. Punch gives the hole size and shape of the component. This is made out of high carbon high chromium steel,(D, M grade in AISI) and hardened and tempered to 58-60 HRc
NON - CUTTING PUNCHES :
These punches perform operations like bending , forming, drawing, extruding etc.
HYBRID PUNCHES :
These punches perform both cutting and non cutting operations, like shear and form, pinch-trim etc.
PUNCH GROUPS :
There are two groups of punches :
1. Segregated punches.
Self mounted punches, which are positioned and retained by means of self contained screws and dowels.
2. Integrated punches.
Punches depend on other component such as punch plate, to locate and position them.
TYPES OF PUNCHES :
Plain punches :
Rectangular in cross section.
These are self mounting straight punches.
Advantages
Material saving.
Machine time saving.
Easy mounting.
Pedestal punches :
They are also called as broad based punches.
Load distribution qualities are excellent.
Used for heavy duty work.
Off set pedestal punches:-
• These pedestal punches have their base off set.
• The reason for off setting the base are space consideration for other components in the assembly.
• Machining and grinding accessibility.
• The distribution of cutting forces is non uniform in these punches.
Keyed punch:-
• A key is provided for non circular punches to prevent their rotation.
Punches mounted In punch holders.
Headless punches.
• This is a plain punch except that it does not require dowels.
• The positioning of the punch is done by the opening provided in the punch holder.
• The punch is fastened to the top plate by means of screws.
Beveled head punch-
• When the punch is made with an angular seating it is called bevel head punch.
• The bevel angle is usually between 30° to 45°.
• The beveled portion may be either machined or peened.
Step head punches (Shouldered punches)
• These types of punches are fitted in the punch plate without screws and dowels.
Floating punches
• They are made loose in the punch holder and are guided in the stripper plate.
Perforators:-
• A punch of diameter 2.5mm or below is called a perforator.
Bevel head perforators
• On these type of perforators a beveled seating is machined or peened.
Headless perforators.
• These punches do not have shoulders.
• A whistle notch is milled on the shank of the perforator.
• A screw from the side will fasten the perforator in position.
Step head perforator shank less:-
• These are similar to step head perforators except that the shank diameter is more by 0.025 mm than the point diameter.
Step head perforator:-
• These are the commonly used perforators.
• They have a stepped head shank and a point diameter.
Pyramid perforators:-
• This type of perforator is used when there is considerable disparity between the point diameter and the shank.
Quelled perforators.
• Slender punches are to be protected from buckling.
• Quills are provided to prevent buckling.
Slug ejector perforator:-
• To prevent slug pulling, air pressure or spring pins are sued.
• These are known as slug ejector perforators.
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