III。 GUIDE PILLAR:

Guide pillar is used to conduct the punch accurately while it gets through matrix thereby it sets up on the bolster however it must be symmetric about the major axes of die to be able to distribute the equal loads on the both side。 Wear resistance, easily machining,  thermal  operation ability and high module of elasticity  are required mechanical specifications for guide pillars。 Necessary information for design and selecting  the  type and dimension of pill are thickness of bolsters, weight  of bolsters and the distance between punch and matrix in the case that the die be open so that called  stroke。

IV。 GUIDE BUSH:

Guide bushes are used in order to lead the guide pillars on the dies and their material depends on the material of guide pillar and it must be made of such a material that is softer than the guide pillar。 These members  must  be strong enough in front of wear and has proper thermal operation ability。 In designing these parts the die stroke, bolster thickness and the guide pillar diameter are  important。

V。 SHANK:

Shank is a pipe that is installed on the  upper bolster  and gets inter the hole which is designed for it in the press。 Shanks are available in two groups welded and screwed。 Mechanical specifications which are required for determining the material of shanks are easy  machining, wear resistance, high hardness, impact resistance and high toughness。  For  designing  the  shanks  of  common  dies   a

Design of Variable Pitch Punching Tool

designer should follow some procedures which  are depicted in

VI。 DIE STRUCTURE:

Guiding:

Stock guide, guide rails, guide pins (elastic and  solid), pilots

Stripper:    movable elastic and solid

Stop pin:   solid and elastic, Finger stops: adjustable and fixed Die material

Carbide, rubber, polyester, polyurethane, zinc alloy,  etc。

Variable pitch punching tool:

VII。 PROCEDURE:

Punching tool consists of two dies top die and bottom die。 In this paper we pided the two dies in two parts。 The movement of both the dies are done by the guide way and T slot which are controlled by using lead screw。 The top die is calibrated by arranging it to bottom die the tool bits are placed in exact positions in the given holes  in  the bottom die。 The Lead Screw is now fixed to the slots and the top die is moved。 The required pitch is obtained by aligning the lead screw and pitch calculated using the washers provided just like markings at a distance of 5mm each on both the sides of the guideway。 The bottom die is fixed to the frame using bolts and for maximum accuracy Dowell pins are used in tightening the bolts to the frame。 Huge vibrations are produced when the machine in operation so these vibrations are controlled using the high tension springs。

VIII。 LIMITATIONS:

 Operator should operate accurately while changing the pitch values。 He should identify the how many rounds he need to rotate the screw in order to get the required pitch。

 Operator should change the die pitches (i。e bottom die, top die ) at a time so he can operate  accurately。

 While changing the dies for different slots operator should be careful and he should operate  safely。

 Operator should check pitch  randomly  while punching。