Hard Chroming Molds

Q. I would like to create a mold which overmoulds plastic to a TIN plated Copper terminal. Previous efforts have yielded flaking of the tin coating on the mold surface which is unacceptable for an upcoming project. A colleague of mine mentioned the use of Hard Chroming to the mold surface which comes into contact with the metallic terminal in order to reduce such ill effects.

Therefore I have two questions:

Do you know if hard chroming has such remedial effects to this situation? What base material is most suitable for a hard chrome layer to adhere to?

Many thanks and regards.

A. Chrome plating the working side of molds is common. The best type of chromium for this purpose would be a thin hard "crack free" plating deposit. Also referred to as "thin dense" hard chrome. The base metal would need to be polished to a smooth finish as the chromium coating will mirror that of the base metal.

In addition to providing increased wear resistance, chromium has a low coefficient of friction, and good "release" properties. The successful performance and longevity of the coating would depend on how many cycles, how hot the mold gets and the frequency of inspections, cleaning and maintenance.

For molds, a coating of chromium should be in the ballpark of 0.0002 to 0.0007 thick and be smooth and adherent. This may require special conforming anoding and rack set up which can run into some extra cost.

Electroless nickel coating is a suitable alternative to chromium and may be less costly to apply.

In any case my best advise would be to take the mold to your local chrome plater and discuss your situation. Generally plating shops have the necessary experience to make the best recommendations.

Good Luck,

Randy Taylor