October 24, 2012

 

IPC/WHMA-A-620 includes the following requirements pertaining to
crimping to solid wire.

 

a.     Crimping to solid wire is not allowed except for connector center
contact.

b.     Crimp tool cycle must be completed.

 

We have an OEM who crimps a solid AWG # 8 gage magnet wire (stripped to
remove insulation) to a standard AN-8 (T&B) NAVY type terminal lug using
a manual hydraulic crimp tool that has adjustable pressure settings.  If
the crimp is performed at 90 PSI, one gets a complete tool cycle which
leaves a deep crimp impression on the top surface of the lug and the # 8
impression on the reverse side of the lug.  One can see a bell-mouth at
both ends of the lug.  If a 60 PSI setting is used, the crimp forms and
one can see two small crimp impressions on the top of the lug but
nothing on the back side of the lug.  Both settings result in the lug
barrel forming around the OD of the stripped magnet wire.  The OEM uses
the 60 PSI setting because of the concern of over crimping at the 90 PSI
setting resulting in possible damage to the wire.  At one time the lugs
were brazed rather than crimped but this process caused some lugs to
crack so they changed from braze to crimp.

 

The contract drawing also mandates that the lugs be soldered after
crimping and that the solder must flow to fill any voids inside the lug
barrel.

 

Based on the above, I have the following questions that I would
appreciate a response to:

 

1.     What is the technical basis for not allowing crimp to solid wire
for any solid wire other than for connectors and why would we not have
the same concern for connector crimp?

2.     Would one expect solder to flow into the ID of the lug with the
60 or 90 PSI settings?

3.     Assuming the 60 psi crimp is pull tested and passed, is this a
technically acceptable crimp?  If not, why not? 

 

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