How Electroless Nickel Coating Handles Complex Shapes
For many surface finishing processes, parts with complex geometries can be difficult to coat. In particular, features such as holes, internal cavities, and tight tolerance parts and surfaces can present challenges. This article explains how Electroless Nickel coating can provide consistent coating of complex shaped parts.
No Current, No Shadowing
The electroless nickel plating process forms a coating on a part by means of an autocatalytic chemical reaction. As there is no requirement for a current flow, as with conventional electroplating, all surfaces of a part, regardless of their geometry, are coated to a similar extent. As a result, the process is particularly suitable for parts with complicated shapes.
Interior Bores and Blind Holes
For blind holes and interior cavities it is essential that the coating bath is able to penetrate to the deepest point of the component. In the majority of cases it is possible to obtain an even coating on internal surfaces. Agitation within the hole is critical and this can be influenced by racking angle. Parts are racked in a manner to enable solution to flow in and out of holes and to prevent air pockets from forming.
Threads and Tight Tolerances
Electroless nickel coats all surfaces, including corners and edges, at a uniform rate. For this reason, when coating threads, the amount of coating deposited on the thread surfaces (peaks and valleys) is approximately the same for each surface. This usually results in a coating thickness of 5-25 microns per surface. The need to re-tap threads after coating will depend on the tolerance class of the part being coated.
Masking to Protect Critical Areas
Selective coating of complex components, e.g. bearing bores, sealing faces, etc. can be achieved by masking off specific areas of the component with plugs, caps, etc. or by applying a suitable tape-based compound to the relevant areas of the component.
Allowances When Designing for the Process
General coatings can vary from 5-25 microns in thickness, and must be allowed for when working out the finished dimensions for components that have been coated. Coating can be specified on or excluded from individual components features, and it is only by specifying the process in the design stage that finishes will know what to do with specific features (e.g. cavities, bores, holes) on production.
By specifying the process in the first place, you will avoid a lot of rework and will be able to maintain the tolerances for which you have specified the process.
