Zinc Nickel Plating

Description

The zinc nickel electroplating process is widely used in the automotive industry and is making its way also into the aerospace industry, mainly as a cadmium replacement coating. Several military and civilian organizations are testing and implementing Zn/Ni as a replacement for cadmium, due to environmental regulations for eliminating the use of cadmium.

With most commercial Zn/Ni baths showing a throwing power that is even worse compared to traditional cadmium cyanide baths, maintaining both minimum layer thickness and alloy composition within specifications represents an additional challenge. A dedicated tooling configuration is unavoidable for ensuring a sufficiently uniform current density distribution when dealing with parts of complex geometry and / or considerable size.

Elsyca has a vast experience in Computer Aided Engineering (CAE) projects that encompass the development of Zn/Ni plating tooling for complex components, thereby delivering a complete plug-and-plate solution.

Zinc Nickel Plating: Challenges

A wide range of Zinc/Nickel bath types are commercially available. The majority of these baths has been developed to tackle the needs of the automotive industry, such as ductile coatings, high throwing power and high plating speed. Only in recent years some bath suppliers have introduced Low Hydrogen Embrittlement (LHE) baths specifically designed for the aerospace market.

Besides layer thickness, electroplating of alloys has the additional challenge of maintaining the metal composition within the specification window. In the case of Zn/Ni, corrosion protection increases with nickel content up to a certain level, above which the alloy becomes nobler than the substrate and loses its sacrificial function. Plating performance can vary depending of the type and age of the bath making it harder to ensure a reliable end product. Although the root problem is a non-uniform current density distribution, often the practical action relies on overplating by increasing the imposed current or plating process time. This sort of actions however does not often solve the problem of failing to meet layer thickness specifications, moreover these actions lead to excessive waste of capacity and resources, possibly also to increased scrap rates.

Elsyca's solutions

Elsyca's Advanced Engineering Services (AES) offer different solutions for Zn/Ni plating. Laboratory bath characterization captures the electrochemical behavior of a plating bath sample. Such study provides valuable information on the electrochemical behavior of a plating bath and often explains the origin of unexpected plating defects. Frequently ignored on the plating shop floor, flow conditions can dictate important plating defects and for that reason flow is an important factor during the laboratorial characterization. Many surface properties, such as alloy composition, roughness, hydrogen embrittlement, etc. can be correlated with current density and flow conditions. This way, together with current density and layer thickness distribution, also different surface properties can be predicted from Elsyca's PlatingMaster simulations.

Plateability analysis is a simple and fast diagnostic tool which can be used by an OEM during component design phase. Foreseeing and minimizing plating problem areas not only reduces the production cost of the component but also reduces the chance of future warranty problems.

A Plating Feasibility Analysis provides a quick plating configuration diagnostic. Either for newly designed tooling configurations or for tooling configurations that have migrated from cadmium plating, the performance of a tooling configuration can be quickly evaluated, even before the Zn/Ni bath becomes operational.

Either for rack plating or plating of individual components, Computer Aided Engineering (CAE) projects make use of Elsyca's PlatingMaster to iteratively design or optimize the part load and / or tooling configuration. Optimization generally starts with fine tuning the part arrangement and positioning. In case tooling is required for meeting layer thickness specifications, current robbers, auxiliary anodes and insulating shields can be iteratively defined and improved based on simulation results. For more advanced tooling configuration as developed for landing gears, different rectifiers can be integrated in the electrical circuit, each feeding a separate sub-group of conforming anodes.

A vast number of tooling sets for Zn/Ni has been designed both by Elsyca's Advanced Engineering Services (AES) and costumers using inhouse Elsyca's PlatingMaster software.

Both for aerospace components or automotive parts, Elsyca has developed a vast number of Zn/Ni plating tooling configurations. Practical limitations of both industries, although very different, are a critical factor to the Elsyca tooling design. While automotive platers prefer robust and operator-friendly tooling for their racks, the stricter specifications and lower part volumes in the aerospace sector call for more complex, thus more performing tooling solutions.

For projects that involve the CAE of an optimised tooling configuration, Elsyca also delivers the Bill of Materials and the CAD of the entire rack skeleton or tooling configuration (including supporting fixtures), depending on the application.

Some examples

  • A characterization report of a generic automotive Zn/Ni bath provides essential insight into the challenges as posed by the zinc nickel electroplating process.
  • A plating feasibility example on a rack of brake calipers is presented here.

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