A die casting surface finish can provide durability, protection, and an attractive appearance. Last month we detailed the most common decorative finishes used in the industry – this article will delve a bit more into two types of plating that can be applied to die castings; electro-plating or electroless plating. What is the difference between the two processes and which would work best for your application?
Electroplating
Electroplating is a process where thin layers of metal are bonded at the molecular level with another metal. An electrical current is passed by two electrode terminals through a carefully prepared electrolyte solution where a metal part has been placed for plating. The electricity changes the surface properties of the part and allows it to bond with the metals in the electrolyte solution.
What types of metals can be plated this way?
• Platinum
• Gold
• Silver
• Chromium
• Copper
• Tin
• Aluminum*
• Zinc
• Cadmium
• Nickel
• Lead
*Aluminum has a tendency to form an oxide that may prevent proper plating adhesion. It is best to apply a zinc undercoating to aluminum parts before any type of plating.
Why choose electroplating?
• Improve appearance
• Improve the abrasion and wear resistance
• Corrosion protection
• Increase lubricity
• Increase the thickness of a part
What parts are commonly electroplated? Here are a few examples:
• Tools and dies
• Aircraft components
• Machine components
• Mechanical assemblies
• Electronics and computer devices
• Enclosures, chassis, and heat sinks
• Medical diagnostic instruments
• And many more
Electroplating is capable of achieving the best cosmetic plating finish on die castings, since multiple layers of plating are applied and buffing/polishing can be performed after each layer. The main downside to electroplating is that it is very difficult to properly and evenly plate parts with complex shapes. The electroplating process also requires very clean conditions, utilizes possibly hazardous equipment, requires filtration, and typically requires multiple applications to achieve the desired look and thickness. In some instances electroless plating is the better alternative.
Electroless Plating
Electroless plating is quickly becoming one of the most widely used forms of plating today because it is more cost-effective and easier to do than electroplating. Electroless plating is used primarily as a protective and/or used to enhance electrical conductivity. In some cases, it can also be used as a decorative coating.
Electroless plating is also known as autocatalytic plating or conversion coating. Simply put, it is a process for plating a part without using an electrical current. The process for electroless plating basically involves dipping a part into a bath of plating solution where a reducing agent (like hydrated sodium hypophosphite) reacts with the ions in the part to deposit another metal alloy onto it (typically nickel).
A wide variety of metals can be plated this way, including (but not limited to):
• Aluminum
• Titanium
• Mild steels
• Stainless steel
• Hardened steel
• Copper
• Brass
• Zinc
Why choose electroless plating?
• Prevents corrosion and wear
• Adds toughness
• Resistance to abrasion
• Uniform deposits with consistent thickness
• Can be used on parts with very complex shapes
Due to the fact that electroless plating tends to create a very hard and non porous finish, this technique is very popular in industries such as oil fields or marine applications where parts are very vulnerable to wear and corrosion.
What other industries commonly use electroless plating? Here are a few examples:
• Oil and gas – barrels, pipes, pipe fittings, valves
• Automotive – gears, brake pistons, shock absorbers, cylinders
• Food service – food processing machine parts, molds
• Plastics and textiles – dies, machine parts, molds, extruders
• Aerospace – rocket parts, pumps, valves, pistons
• Chemicals – mixing blades, filer units, pumps, heat exchangers
• And so many more
In general, plating processes are the poorest at hiding underlying surface conditions and require the most surface prep operations to achieve the desired final finish. It is vital for a die cast part to have both a good internal structure and good surface finish. These are achieved through good design for both the tool and the component as well as the proper post-casting operations to achieve the optimum surface finish for the desired final plating result. Planning ahead for the finish you need can help to potentially minimize surface finish problems as well as any potential porosity issues.
With over 75 years of die casting surface finishing expertise, our engineers will evaluate your requirements to recommend the best approach to achieve the desired finish for your part. Contact A&B Die Casting today!