Calculation and Designing Support Pin or Leader Pin

as we know in previous posting about main construction of mold, there was pin in leader component, this pin will support main construction and cavity plate (3) from deflection and guide the cavity part and core part when mold closing. here the picture of support pin or leader pin in 3 plate mold type.


Support Pin Main Part
we can divide main part of support pin into 3 type
1. Support pin it self, some mold engineer call support pin by leader pin or main support pin.
2. Bushings, how much bushing that we needed depend on type of mold base, for example for 3 plate type of mold base we need at least 2 bushings, one in stripper plate (2) and one another in cavity plate (3). bushings prevent support pin have direct contact with mold base plate, becouse mold base plate usually use more soft material and support pin is harder material, it can cause scratch if use in long time and mass production, bushings always use harder material with good tolerance to support pin. so the other advantage is mold can be opened and closed with precision. and it can use in mass production mold.
3. Collar, it to prevent plate of mold out from leader pin when puller bolt broken or others accident possibility, with collar give the mold construction more safe.
see the main part of support pin in picture below


Deflection Calculation
ok, to learn more how to calculate the deflection in support pin, when support pin receiving the weight of a mold base plate on their tips,support pins may
deflect due to a large amount of bending moment, to choose right diameter and how much the bending first we must know the force that affect support pin, see picture below


yes at 3 plate type minimum load is from weight of stripper plate and cavity plate, with simple calculation of deflection (although isn't precision) like formula below



to calculate more complex and precision add the force from support pin weight, collars weight, and 3 dimensional calculation methods.
below is some list and use full engineering link to calculate the deflection, radius gyration list, derivation of deflection formula and others
http://en.wikipedia.org/wiki/List_of_area_moments_of_inertia
http://www.doitpoms.ac.uk/tlplib/beam_bending/printall.php

then by calculation we can get the fine radius, after calculation I, maximum deflection is about 0.05 mm, more than 50 micro millimeter, use more large radius of support pin. or place more precision guide, like block guide, linear guide and others between cavity plate and core plate, it should be more precision when mold in closed position.