October 25, 2012

I found out some additional information on the crimping process.  The
actual magnet wire size is MW-35-C, AWG 5 per MW 1000.

The terminal lug is a modified M20659-141 Standard NAVY AN-8 lug (# 8
wire size) that had the lug ID machined to an ID of .185 + .005, -.002,
to depth of .37 inches to accommodate the # 5 AWG magnet wire.

AFTER the lugs are crimped, they are hand soldered using Sn60Pb37 RMA
flux cored solder wire.

The magnet wire is used in an Input Filter Inductor and in the
application, the worst case current is around 35 AMP, 60 Hz AC.  The
magnet wire is a self-winding so there is no lead wire used.
Originally, the manufacturer brazed the lug to the magnet wire but since
the lugs are a split type design, the brazing heat caused some lugs to
crack which is why they changed from a braze to a crimp connection.  The
actual lug terminations are on a terminal block located outside of the
envelope of the inductor where the worst case ambient temperature is
significantly lower than the melting temperature of the solder.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, October 24, 2012 5:36 PM
To: [log in to unmask]
Subject: Re: [TN] Crimping to AWG 8 solid magnet wire

Hi,

 Crimping after solder is a terrible idea. You are going to shear the
solder at the copper and terminal surfaces. Solder simply has very
little strength compared to the other materials.

 Solid wire will not crimp into a tight robust joint. Soldering is about
all you can do. Or switch to a fine stranded wire.

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Wednesday, October 24, 2012 4:45 PM
To: [log in to unmask]
Subject: Re: [TN] Crimping to AWG 8 solid magnet wire

Richard,

I don't have any data to support or refute this.  The idea of soldering
the wire BEFORE crimping goes along with the notion of the leaded solder
"relaxing".  If the soldering is done AFTER crimping I don't think there
will be solder relaxing as you had a good mechanical crimp before you
unnecessarily added the solder.  If someone says to me they are worried
about the solder melting I remind them that for the solder to melt it
will require a very high temperature and it is a safe bet they have a
bigger problem to worry about.

Phil

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Wednesday, October 24, 2012 3:28 PM
To: TechNet E-Mail Forum; Phil Nutting
Subject: RE: Crimping to AWG 8 solid magnet wire

Hi, Phil
I understand and totally agree with you and Steve, soldering stranded
wire and then crimping is a bad idea.
The original reason was that the leaded solder would eventually relax
and cause the crimp to fail.
However, is that still true with lead-free solder?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Wednesday, October 24, 2012 10:35 AM
To: [log in to unmask]
Subject: Re: [TN] Crimping to AWG 8 solid magnet wire

Gerald, et. al.,

Maybe this is a case of "if some is good, more has to be better".
Presumable the manufacturer has tested their terminal successfully at 60
psi, but did the end user not use the same gauge and type wire as the
manufacturer tested.  Maybe someone assumed that more pressure would
make a better joint and the idea stuck... "we have always done it that
way".  Solid and stranded of the same gauge will actually have different
wire diameters.

Some folks will assume that by soldering they make a better connection.
Not the case.

Some folks will say that they have to handle a lot of current so it
needs to be soldered.  But the wire/lug combination can only handle the
amount of current it is rated for without potential for failure.

The only place we use solder with crimps is when terminating Litz wire.
Litz is a whole bunch of fine enamel coated wires that each strand must
be stripped to make a connection.  Chemical stripping and solder pot
immersion are the only possible solutions.  Solder pot stripping is the
most environmentally and manufacturing friendly.

Years ago we crimped and then soldered our terminals.  Bad practice!  I
have converted our staff to agreeing that crimp and solder is incorrect.
The theory is that if the wire/lug combination has been properly sized
and properly crimped that it will make a gas tight mechanical weld.
Adding solder does two possible detrimental things, flux wicked up the
wire (not an issue for solid wire) and it makes the wire more
susceptible to breakage due to wire fatigue (not an issue for solid
wire).  Several years ago this discussion came up and I had Steve
Gregory post a document that I had gotten from Amp that clearly stated
that soldering was bad practice and it outlined exactly what I have
listed above.

Just my opinion though.

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerald Bogert
Sent: Wednesday, October 24, 2012 10:26 AM
To: [log in to unmask]
Subject: [TN] Crimping to AWG 8 solid magnet wire

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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