Electropolishing is often referred to as a “reverse plating” process. Electrochemical in nature, electropolishing uses a combination of rectified current and a blended chemical electrolyte bath to remove flaws from the surface of a metal part.

Since the development of electropolishing in the 1950s, substantial refinements have taken place. Able has numerous electrolytes to allow for electropolishing on a broad range of metals. These newer electrolytes, combined with advanced part handling techniques, have improved production yields on a wide range of metal products.

While the process is best known for the bright polish left on a surface, other benefits include deburring, corrosion resistance, microfinish improvement and others. These metal improvement benefits offer great promise to design and production engineers for cost savings and product improvement.

Able specializes in providing electropolishing services for a variety of common and specialty metal alloys. Here is a partial list of alloys the company can electropolish:

Figure 1: Electropolishing services. Source: Able Electropolishing Company

Learn more about the benefits

Deburring

The electropolishing process is well-suited for deburring. During the process, the transfer of metal ions occurs most rapidly on corners or edges of metal parts. Current density or concentration of electrochemical power is greatest at high points, just as lightning is drawn to tall trees and buildings. This helps explain why plating builds metal faster on an edge or burr, while electropolishing (the “reverse” of plating) removes metal fastest at these points.

Properly controlled, the process can remove burrs from incredibly complex or fragile parts that do not lend themselves to conventional tumbling or vibratory finishing techniques. The process is best suited for parts having fine blanking, milling, broaching, lapping or grinding burrs. Since electropolishing is non-mechanical, it is important to note that the hardness of a metal part has no bearing on the burr removal. The process works equally well on a fully annealed or hardened part. This is one reason why electropolishing is often specified as a final deburring and finishing process after all fabrication and heat treating processes.

Microfinishing

Virtually all metalworking operations, including cutting, stamping, welding and forming, roughen the metal surface. When that metal surface is then forced to work in critical sealing or friction zones, product performance often suffers. One of the traditional instruments used to measure surface roughness is a profilometer.

A profilometer, using a diamond stylus to record the irregularities of the surface, usually gives a readout in microinches or micrometers. This quantifies the roughness of the surface with a larger number indicating a rougher surface. With .001 inch total material removal, electropolishing typically reduces these microinch values by 50% — for instance, a 16 microinch surface before electropolishing will be improved to an 8 microinch surface afterward.

Figure 2: A 16 microinch surface before electropolishing will be improved to an 8 microinch surface afterward. Source: Able Electropolishing Company

Non-coating

Unlike paints, plating or Teflon coatings, an electropolished surface does not peel or abrade. This is especially important where particles from coating abrasion can cause equipment malfunction or other hazards.

Applications where this can occur include food or pharmaceutical processing, high vacuum assemblies, pure gas/water systems and critical switch assemblies.

Non-distorting

Electropolishing can be performed on complex or fragile parts that do not lend themselves to other finishing methods. There is no effect on surface hardness and no stresses are introduced to the part.

Improved weldability

Figure 3: Electropolishing is fast becoming a replacement process for passivation. Source: Able Electropolishing Company

In critical spot weldments, electropolished components are more conductive. The improved conductivity allows better, stronger welds at lower voltage. In other welding or brazing operations, electropolished surfaces generally weld more readily with less weld splatter and surface damage.

Bright finish

Perhaps the best known application for electropolishing is in the area of decorative finishing. While the bright finish is the trademark of electropolishing, the key benefits of the surface cleansing are much more than “good looks.”

Since the process removes surface metal, virtually all surface impurities are removed as well. Embedded scale, rust, foreign debris, oils, grinding compounds and other materials are removed as the base material is dissolved. While the resultant surface is not technically “pure,” it is left at or near original mill specifications, ready for final assembly or plating.

Corrosion resistance

Electropolishing is widely specified to enhance corrosion resistance on a wide variety of metal alloys. Although most commonly used on stainless steels, electropolishing offers corrosion resistance on other alloys as well.

Due to its versatility and superior effectiveness, electropolishing is fast becoming a replacement process for passivation. Passivation is a chemical process that has been used for years to help restore contaminated stainless steel to original corrosion specifications.

Passivation is routinely specified by engineers because of the many sources of contamination. The intent of passivation is to remove free iron and other foreign matter from the surface of the metal and to create a chromium-rich surface that is resistant to corrosion. However, passivation is generally not effective in removing embedded iron and contaminants and will not remove heat tint or oxide scale on stainless steel.

Engineers looking to pass stringent salt spray and humidity tests have turned to electropolishing for a more aggressive replacement for passivation. The electropolishing process dissolves the outer skin of metal, removing deeply embedded contamination. Heavily contaminated surfaces such as machined parts, welded or brazed assemblies, or other components that typically respond poorly to passivation alone, are good candidates for electropolishing. Unlike passivation, all stainless alloys including the 400 series and precipitating grades can be processed without distortion, flash attack or hydrogen embrittlement.

Fatigue life improvement

Electropolishing has become a common metal finishing process used to help improve the life of metal parts that flex, cycle, twist and bend. These components come in various forms, including stampings, wire forms and machined parts.

During the manufacturing process, micro defects on the surface of these components, such as micro-cracks or pits, are often left behind. These defects can become initiation sites for crack propagation or corrosion. By removing these surface imperfections, engineers have found electropolishing to significantly improve the life of components functioning as springs.

Galling prevention

Galling is a surface defect that hinders a smooth fit between threaded parts, often caused by microburrs. These microburrs create resistance and bond between the two surfaces, resulting in sliding and breakdown of the structure underneath, which can lead to metal being stuck or friction-welded to the other surface.

Some alloys, like aluminum, are more prone to galling due to the atomic structure of their crystals, while stainless steel is somewhat more resistant. Manufacturers of fasteners and other metal parts prone to galling have tried remedies such as reducing installation RPM, frequent lubrication or using different grades of stainless steel for nuts and bolts. However, these methods only offer temporary solutions.

Electropolishing, in addition to its other benefits, makes stainless steel fasteners extremely resistant to galling, ensuring long-term performance. This process is particularly effective for threaded parts. By applying a rectified current to metal parts in an electrolytic bath, electropolishing achieves a precise, controllable and consistent level of material removal, targeting the microscopic high points more aggressively. This allows for the precise removal of burrs while keeping the threads intact.

See it in action

Watch the video on electropolishing versus passivation to see the metal finishing processes in action.

Electropolishing for precise, consistent and effective metal finishing

Electropolishing is an electrochemical process for improving the surface finish of metal parts. This is achieved by precisely removing the outer layer of metal, improving the Ra value up to 50%. Able can apply this process to nearly any metal, including Nitinol and titanium. Don’t trust critical parts to anything less.

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