GlossaryKind of term: Manufacturing termElectroless nickel plating
What is electroless nickel plating?
Electroless nickel plating deposits a nickel-phosphorus layer without current, almost evenly in bores and corners too; the layer changes every coated dimension.
The process is autocatalytic: a chemical reaction in the bath deposits the nickel alloy, usually nickel-phosphorus. As a result the layer grows to almost the same thickness on faces and edges, in bores, in threads and in internal corners, provided the solution is refreshed there. Electroplated nickel stays thinner in exactly those places. The layer is hard and wear-resistant and protects against corrosion. With the right pretreatment, steel, stainless steel, aluminium and copper alloys can all be plated this way.
What decides the properties of electroless nickel?
Phosphorus content sets the properties: low phosphorus gives a harder layer, high phosphorus better corrosion resistance and a layer that is non-magnetic as plated. A heat treatment after plating can raise hardness or improve adhesion, depending on temperature and time. A high-temperature hardening treatment can lower corrosion resistance, make a high-phosphorus layer magnetic and affect the condition of the base material, for example in heat-treated aluminium. High-strength steel may need a hydrogen embrittlement relief treatment after plating. In deep blind holes and narrow gaps the layer can come out thinner where the solution is poorly refreshed.
What does the standard say about electroless nickel plating?
Common specifications are ISO 4527 and ASTM B733. A complete requirement states layer thickness, phosphorus class, any heat treatment and the surfaces on which the thickness applies. If any of these is missing, ask before the preceding machining is fixed.
How does electroless nickel plating work in practice?
Because the layer grows everywhere, every dimension changes: a bore shrinks by twice the layer thickness on the diameter, a shaft grows by the same amount. As an example, a 15 µm layer takes 0.03 mm off the diameter, more than the whole tolerance of a ⌀12 H7 bore, which ISO 286 sets at 0.018 mm. The preceding machining has to allow for that. On a thread with a 60° thread angle, such as a metric thread, the pitch diameter shifts by about four times the layer thickness, so threads get a tolerance class with room for the layer, are masked, or are re-tapped. Plating usually goes to a specialist plater, with a batch price, a minimum charge and added lead time.
What is electroless nickel plating often confused with?
Electroless nickel is not electroplated nickel: electroplating uses current and builds up thicker on edges and thinner in bores. Hard chrome is a different electroplated layer, with its own size correction and often grinding after plating. And layer thickness is not the change in size: on a diameter the layer counts twice.
How do you see electroless nickel plating in Blake?
In Blake electroless nickel appears with the part as a proposal from the drawing, which you confirm or correct. In the estimate the plating is its own line from your subcontract library, left open until it has a price. More on estimating.
Frequently asked questions
How much smaller does a bore get with electroless nickel?
By twice the layer thickness on the diameter, because the layer grows all round. For a tight fit the bore is machined larger beforehand, allowing for the layer thickness and the spread of the plating.
Do threads need masking for nickel plating?
Not necessarily. With a tolerance class that leaves room for the layer, threads can be plated; otherwise they are masked or re-tapped after plating. On a metric thread the pitch diameter shifts by about four times the layer thickness.
Do drawing dimensions apply before or after plating?
The drawing should say. Dimensions often apply after finishing. If it is not stated, ask: the preceding machining depends on it.