Surface Treatment
Surface condition can affect the performance of the crimp tooling as well as the longevity of service. As noted in the
previous section, a hard, smooth surface has improved adhesive wear properties and, thus, longer service life. The
other attribute that needs to be considered is friction.
A commonly accepted approach to improved crimp tooling performance and life has been to apply a surface treat-
ment to the crimp area. The wire crimper has been defined in previous discussions as tooling component that is sub-
jected to the severest duty cycle. Thus, applying an appropriate surface treatment to the wire crimper will have the
most benefit to crimp performance and tooling life. These treatments can include hard metal plating or ceramic
coating.
An example of a treatment that has been successful in achieving significant level of performance and life improvements
is hard chromium plating. There are several valid reasons for this success.
First, chromium plating has a very low coefficient of friction. As noted, friction has a significant effect on crimp form.
The static and sliding coefficients of friction for steel on steel are typically 0.30 and 0.20 respectively. Chromium plated
steel on steel can reduce the static and sliding coefficients to 0.17 and 0.16.
The second area that is greatly improved with
chromium plating is wear resistance. Adhesive wear
resistance is improved as surface hardness improves.
Chromium plating typically exhibits a hardness Rc
65+. This hardness level greatly enhances resistance
to adhesive wear. Also, this now frees up the designer
to consider more base metal options. A base material
of reduced wear resistance but greater toughness can
be selected and its wear resistance improved with
chromium plating. Thus, chromium plating can enable
a better tooling solution for the crimp production
process.
Chromium Plated Crimper
Surface after 100,000Termina-
tions. Note there is no visible
build up of material.
Unplated Crimper Surface
after 60,000Terminations.
Note Significant buildup of
material.
Third, and perhaps one of the most significant effects
of chromium plating, is its resistance to adhesion and
cold welding. A side effect of adhesive wear is the
transfer of material from the terminal to the wire
crimper. By definition, adhesive wear is caused by ma-
terial adhering to localized points on the surface.
Some of the adhesion results in the surface material
being worn away and some in the transfer of material
from the terminal to the crimper. As more cycles
occur, more material is transferred. Thus there a re-
sultant buildup of terminal material on the crimper.
This buildup will result in two potentially catastrophic
failures:
Gross Deformation of Crimped
Terminal Resulting from Mate-
rial Buildup in Crimper
Visible Deformation of Outer
Crimp Surface as a result of In-
dentation from Material Buildup
on Crimper
• The built-up material will create deformations in
the terminal surface, resulting in unacceptable
crimps.
• Crimps will be greatly distorted due to significant changes in the friction factor and result in the terminals not
conforming to the desired form. Unacceptable crimp forms, such as unsymmetrical cross-section, excessive
flash, and open barrels can result.
Chromium plating has the ability to be applied uniformly and consistently and exhibits excellent adhesion to the
base metals. The unique benefits of chromium plating, such as ease of application, consistency of plating, adhe-
sion to base metal, extremely low coefficient of friction, very high hardness, and resistance to adhesion, make it
truly difficult to match in crimp performance and durability. However many alternative coatings are being at-
tempted, and some show excellent promise in specific applications.
Summary
This paper has explored four categories of characteristics that are key to high performance tooling. Several exam-
ples have been discussed which demonstrate how minor variations in those characteristics can have measurable
and sometimes significant effects on the resultant crimp form and its compliance to specifications. These same
characteristics can affect tooling service life. It is also a logical extension of these discussions to conclude that
variations of these characteristics from one tooling set to another tooling set can affect process control when
tooling changes are required in production. Maintaining process control may require additional setup time. Quality
tooling that addresses the key characteristics of geometry, materials, surface condition, and surface treatment is
an important component of your total quality control program.
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