1991-02-01

Obtaining LDH Stability 910512

There are quite a few studies on the influences of coatings and base materials on the results of LDH (Limiting Dome Height) test.(1) Although these influences are hard to quantify, and the interdependence of one variable with the other makes interpreting the results even more complicated(2), a basic understanding has been achieved.
The influence of temperature is not clear, but there are some indications that increasing temperatures have a detrimental effect on the LDH values. A previous investigation carried out at Ford Motor Company(3) on a QC LDH machine reveals that the LDH decreases with increasing temperature of the system (basically three temperatures were monitored: punch, binder and hydraulic oil reservoir). Such a behavior can have important consequences in the industrial implementation of the LDH test: if temperature has a significant effect, then the statistical value of the results is reduced.
This investigation was conducted at the Stamping Development Laboratory of Ford Motor Company. Although the LDH test machine used is not a QC type, the general trends obtained are believed to be applicable to other machines.

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