Depending on the application, metal plating can provide a wide range of performance benefits.
Various materials and techniques can be used in the finishing process for custom metal stamping parts that require metal plating ranging from miniature electronic components to large automotive parts, medical devices, injection molding, as well as other applications.
Metal plating on precision stamped parts is frequently required to boost electrical conductivity and strengthen electronic connections.
Metal plating is typically used for corrosion resistance but may also be used purely for decorative purposes.
For example, zinc or zinc-nickel electroplating will not only protect the surface and prevent corrosion that increases the lifetime of a part but will also enhance its appearance.
Cost-Efficient Design of Metal Stampings
When designing metal stamping the material and type of metal plating required to enhance the functionality, wear, and appearance of the part needs to be taken into account.
For example, the cost of plating material, particularly for precious metals, will play a significant part in the overall cost of production.
Metal stamping engineers at metal stamping companies can assist OEM engineers in ensuring that metal stamping is designed in a way that will maximize performance while at the same time minimizing material waste.
Many metal stamping companies provide upfront guidance on DFM and recommendations on the best plating process for a part.
They may, for example, recommend that where the end-user will only see a small portion of the stamping, for appearance purposes, only the visible part of the metal will need to be plated.
Different Types of Metal Plating Used for Stamped Parts
In pre-plating raw material is plated with a continuous metal strip before any fabrication process is undertaken to create individual parts.
Because it is more cost-effective to coat raw material in one large piece than to plate each individual finished part, it allows for significant cost savings in terms of materials and labor.
However, because the die-cut edges or sides of the finished part will be un-plated, pre-plated material will most likely be affected by the stamping process and may require further operations in order to meet specifications.
• Spot Plating
Spot plating is typically used in applications where precious metals are required for electrical conductivity in order to minimize the use of expensive material.
Post plating is the only option when complete coverage of a part is required. It is more expensive than pre-plating as it involves further handling that puts the part at risk from dimensional issues.
Post-plating forms a part of the metal stamping process and is often used for applications in harsh environments or for a seamless finish where the part will be visible to the end-user.
Parts plated on a reel-to-reel carrier have bare areas caused by the carrier cutting away from the part. This should be taken into consideration in the design process.
Some stamped components may need initial stamping before being plated, followed by a further stamping operation.
This process can be used to reduce the cost of precious metals or to reduce the risk of bent terminals when using the barrel plating process.
It will also benefit manufacturers wishing to form and cingulate parts at their facilities before feeding it into their automation process.
Plating with Precious Metals
According to the Director of Technical Sales at Precision Plating Company, Chicago, manufacturers sometimes require metal plating to be used for electrical connections that specify microscopic levels of 50 – 100 millionths of an inch.
Gold, silver, and the ‘noble metal’ in the platinum metal group, palladium, are the most popular spot plating precious metals used for electrical conductivity.
Expert says ‘noble metals’ like palladium are good electrical conductors and are resistant to oxidation.
In some cases, a non-ferrous metal like copper may be used for the metal stamping itself while precious metal plating is used only at the connection point.
These metals are normally only used in applications that require high product safety and reliability such as in automobiles with highly sophisticated electronics that are used for collision mitigation.
In contrast, non-precious metals such as tin, nickel, or copper may be appropriate for plating in applications that require the transmission of signals such as radio switches, turn signals, and headlights.
The Metal Plating Process
The metal plating process involves adding another layer of metal to an existing part.
The optimal process chosen is based on the part type, the material of the stamped metal, and the location.
A reel-to-reel operation is typically used for complex stamped parts, particularly in spot-plating. Barrel plating provides overall plating and is a less expensive process.
• Reel-to-Reel Plating
The reel-to-reel process is typically used for more delicate and intricate stampings provided to a plating company by the metal stamper on a specially designed strip.
This method is ideal for a spot- and micro-plating of precious metals as it minimizes material waste. However, it can also be used for applications that require overall plating.
• Barrel Plating
Large volumes of small, durable parts can be handled quickly and economically with barrel plating.
Loose pieces of stampings are placed in a rotating barrel with an electric current that contains an electrolytic plating solution,
Usually zinc or zinc nickel. As they tumble in the barrel, the parts are burnished in the solution which helps to remove any scale and burrs.
Barrel plating is not only used to prevent wear and corrosion but also for aesthetic purposes.
• Rack Plating
During the rack plating process, parts are mounted on racks that do not move, providing greater protection for stampings.
As it is highly effective in plating complex geometries, the rack plating method is ideal for intricate and delicate stampings.
It also produces high-quality finishes that are critical for medical devices, electronic goods, and the automotive industry.
However, rack plating is more expensive than the barrel-plating process and may require custom racks, depending on the type of stamping.
• Zinc/Zinc-Nickel Electroplating
Both these processes are used to prevent corrosion, increase the lifetime of parts, and to enhance their appearance.
It is suitable for use on a wide variety of surfaces such as steel, brass, copper, cast iron, and others. A thin layer of electroplating is deposited on the surface of the part that provides a barrier that protects against corrosion and moisture.
To prevent rust as the zinc layer corrodes, a chromatic conversion coating is applied to cover the surface of the plating.
This coating continues to protect the surface of the part even when it gets scratched during use.
Zinc-nickel electroplating has a higher resistance to corrosion than zinc plating alone, wears well in exterior applications, and is environmentally safe.
It usually has a silver/blue appearance; however, other colors are available.
• Aluminum Chromating
This is a conversion coating that is primarily used to passivate an aluminum component surface by converting it to chromate via a chemical reaction.
It is typically used on aluminum parts for corrosion resistance and as a coating in electrical conductivity applications.
The chromate finish serves as a good base for adhesion purposes such as painting. It can also be used to enhance the appearance of aluminum components.
Metal Stamped Parts Suitable for Metal Plating
– Stamped metal components used for insert moldings
– Automotive brake parts and brackets
– Lead frames
– Electronic connectors