2.1 - Copper Plating

In the manufacturing of steel parts, copper plating is often used as a selective mask. In general, processing is performed in four steps:

1. Part is machined to specification;
2. Entire part is copper plated;
3. Copper plating is removed in selected areas;
4. Heat treatment at high temperature for specific time.

Where the copper has been removed in Step 3, the exposed area is case hardened and carburized by the heat. Where the copper remains, the metal remains soft.

Correct processing to achieve a desired case hardened depth depends on time and temperature. For instance, a baking temperature of 1500 - 1800 F for a time period of 1-16 hours will achieve a case depth ranging between 1/32” to 1/16”.

The thickness of the copper plating needed to hold back the heat is another important consideration. Most commonly, a FINE GRAIN copper plating is used, and applied to the following parameters:

1. .0003/5” - Carburizing at 1500-1600 F for 1- 2hrs.
2. .001/.0015” - Carburizing at 1600-1800 F for 2-16 hrs per specific depth.
3. .002/.003” - Used for additional safety margin when:

   parts are carburized at higher limits of the range for longer time periods.

   parts are not carburized within 14 days of plating because the copper may deteriorate as a mask.

Most often, the application of .001/.0015” will suffice as a quality mask if parts are baked at 375 F for 1 or more hours within 1-4 hours after plating. This holds back deterioration of the copper plating and improves adhesion of the final machining operations after carburizing.

As a rule of thumb, never assume that all copper is applied as FINE GRAIN. A quality plating vendor will perform porosity tests and cross section analysis on his/her plating solutions monthly; assuring the total adequacy of the copper as a heat treat mask. Prudent engineers will be wise in using the least amount of copper plating necessary to get the job done, since both cost and processing time will increase with thickness.

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