A typical design point for AI is 80%. In order to maintain
the same AI, the crimp height, CH, needs to change in-
versely to the change of crimp width, CW, in approxi-
mately the same proportion. Thus, if the CW increases
+2%, the CH needs to change approximately -2% in order
to achieve the same AI design point. At first glance that
may not seem significant, but in reality it can be very
significant. Using another general industry design rule of
the ratio of CH to CW of approximately 65%, a typical
set of dimensions used as an example may be: CW = 0.110 in, CH = 0.068 in
Cross Sections Showing Min-
imum (a) and Maximum (b)
Area Index perTerminal
Specification—aVariation of
3.5%
(a)
(b)
Therefore, varying the CW by 2% would result in a CH variation of 2%, or 0.0014 in.
At a CH tolerance of 0.002 in, 35% of the total CH tolerance would be used by a
2% variation in CW. Thus, the importance of crimp width control is obvious when
tooling is changed during a production run.
Flash
Most crimp terminations have a requirement to limit flash. Flash is defined as the material which protrudes to the
sides of the terminal down and along the anvil. Flash is normal in the crimping process but excessive flash is very
undesirable. Controlling flash requires a balance of several geometric factors. Other factors influencing flash are
related to surface finish and friction, which will be discussed later in this paper.
A dominant factor in controlling flash is controlling the clearance between the crimper and anvil during the crimp
process. Defining the ideal clearance could in itself be a simple matter were it not for two facts:
• In order to minimize terminals’ sticking in the crimper, the sides
of the crimper are tapered. Thus the clearance between the
anvil and crimper varies throughout the stroke.
• Crimper and anvil sets are typically designed to terminate two
to four wire sizes. This creates multiple crimp heights. Since the
sides of the crimper are tapered to minimize terminal sticking,
the maximum clearance permitted without creating flash must
be assigned to the maximum crimp height specified for the
tooling set. In addition, a minimal clearance must be maintained
for the smallest crimp height specified by the tooling set to
Crimper-to-Anvil Clearance = X +Y
at the Final Crimp Height
prohibit contact between the anvil and crimper.
Crimper to anvil clearance is thus a combination of crimp width, crimper leg taper,
anvil width, and crimp height. The critical design point is at the largest crimp
height. This contribution to the gap is directly dependent on dimensional control.
The following is offered as an example:
Nominal condition: CH = 0.073 in, CW = 0.110 in
Crimper leg taper = 3.0 degree
Anvil Width = 0.109 in
Nominal anvil to crimper total clearance = 0.005 in
The clearance can grow rapidly with small changes to
the nominal dimensions:
(a)
Significant flash can be generated
with excessive anvil to crimper
clearance, as shown by nominal
design condition (a) and +0.003 in
over nominal condition (b)
CH remains unchanged = 0.073 in
Increase in crimp width, CW, = 0.0008 in
Increase in crimper leg taper = 0.8 degree
Decrease in anvil width = 0.0008 in
(b)
The total increase in total clearance is this case =
0.0026 in
This more than a 50% increase in the nominal design
clearance, which can result in unacceptable flash (see right).
Dimensional control is clearly critical.