The guide pins or guide post design provide a good alignment between die shoe and punch holder. The guide bushings are mounted in the punch holder and slide over the guide pins. Figure shows the arrangement of guide pins and bushing of the die set. For the average range of die sets, the diameter of guide pins varies from 2.5cm to 7.5cm. Larger pins may be used, if extreme alignment is required.
The different methods of arranging guide pins or guide post in the die set are given below.
Back post design
In this design, the die has two guide posts positioned in the rear side as shown in Figure. This is the most often used design. The design provides a clear view of the moving parts and there is no obstruction from guide posts. It helps the operator when feeding from left to right and leaves a clear space for hand feeding blanks for second operations.
Centre-post or axial-post design
In this design, two guide pins are positioned along the transverse centre line of the die set, as shown in Figure. This design is suitable, when the load is too heavy and the strip feeding is from the front. The major drawback of this design is that it is not possible for feeding.
Posts design – Diagonal
This design is used, when the load is very heavy and end feeding is required. The guide pins are provided along a diagonal line, as shown in Figure. Generally, the left guide pin is in front, but if feed is to be from left to right, the right guide pin is in front.
Four-guide post design
In this design, a guide pin is positioned at each corner of the die-set, as shown in Figure. This design provides a maximum rigidity and accuracy of alignment. This design is used for large, very complicated, or highly accurate stampings and for multi-station progressive dies.
Bushings are available in various lengths made of different materials, removable or press fit. and of plain or ball-bearing type. The guide bushing provides an easy slide to the punch holder and hence, it reduces the operating power.
It also avoids the wear of punch holder and hence reduces the cost of replacement of entire punch holder. Instead of replacement of punch holder, if the bushing is provided between guide pin and punch holder, it can be replaced with less cost and effort.