Electropolishing

1. Definition of Electropolishing

Electropolishing, often referred to as electrolytic polishing, is an electrochemical process for treating metallic surfaces without applying thermal or mechanical stress. An exchange of electrical charge takes place between the metal component and a liquid electrolyte, resulting in the removal of microscopic particles from the component’s surface. Electropolishing results in the smoothing, passivation, and finishing of originally rough, matte metallic surfaces, which become shiny after treatment.

The principle of electropolishing is a reverse galvanic process and, according to DIN 8590, is classified as an electrochemically abrasive manufacturing process.

2. How Does Electropolishing Work? Description of the Electropolishing Process

Electropolishing systems consist of heated immersion baths, power supply units with continuously adjustable rectifiers, and cooling units. The heart of every system is the polishing tank, which contains a highly concentrated acid mixture. The exact composition of this mixture—and thus of the electrolyte bath—depends on the material and the surface characteristics of the workpiece to be electropolished. The electropolishing of stainless steel, for example, takes place in a bath consisting of a highly concentrated mixture of sulfuric acid and phosphoric acid with additives that improve efficiency, smooth out surface roughness, and enhance the luster. When no current is applied, the electrolyte mixture does not attack the stainless steel surface.

The component to be processed is secured to a bronze, copper, or titanium frame, connected to the positive terminal of a direct current source, and immersed in the electrolytic bath. Once the direct current is switched on, the electrolytic solution acts as a conductor (anode). Under the influence of the current, minute particles on the metal surface are dissolved. This removes surface roughness, resulting in a metallurgically pure, passivated, bright, shiny surface. Since even microfine structures at corners and edges are removed under the influence of the direct current, electropolishing is also ideal for fine deburring.

A key prerequisite for achieving flawless results is very thorough pretreatment and cleaning of the components to be electropolished. In particular, scale, grease, and paint residues must be carefully removed before electropolishing, as the metal surface cannot otherwise be uniformly covered by the electrolyte. Mechanical damage also has a negative effect on the result, as it becomes significantly more visible after electropolishing due to the greater material removal at corners and edges inherent to the process.

After removal from the immersion bath, the polished parts must be thoroughly rinsed under running water. Depending on the size and geometry of the component, several rinsing cycles are usually required to remove all electrolyte residues without leaving any traces.

Depending on the effort involved in pre- and post-treatment, an electropolishing process takes between five and 20 minutes.

3. Which materials can be electropolished?

In principle, this surface finishing process is suitable for all stainless steels. Exceptions, however, include steels stabilized with niobium or titanium. These are not suitable for electropolishing due to the stable niobium and titanium carbonitrides. Aluminum, brass, and copper can also be processed very well in an electropolishing system.

For an optimal polishing effect, the material condition of the workpiece, in conjunction with the surface texture, is always decisive. At the same time, the alloy’s components and prior material treatments—such as hardening during manufacturing—influence electrolytic material removal. In practice, therefore, the suitability of certain materials and surfaces can often only be determined through targeted testing.

4. Workpieces must meet the following requirements for electropolishing:

Surface with excellent electrical conductivity
A surface that has been mechanically pre-machined to a high standard
Favorable workpiece geometry
Good flowability for mass-produced parts
Sufficient wall thickness
Suitable contact points for applying direct current.

Rolling defects, inclusions, material structures that cannot be electropolished, mechanical damage, and the like cannot be corrected by electropolishing. Electropolishing is always a finishing process applied to metal surfaces that have been carefully pretreated mechanically.

5. Technical Applications of Electropolishing and Electrolytic Fine Deburring

In general, the electrochemical manufacturing process is used for the precision finishing of stamped, turned, and milled parts. Process-controlled electropolishing ensures optimal surface conditions, particularly for surfaces that come into contact with the product. The range extends from functional surfaces with specific target roughness values to purely visually appealing, glossy exposed surfaces. In practice, the desired surface finish and the associated material removal are defined by a precise surface specification.

For electropolishing to be effective in terms of fine deburring, the relationship between the existing burrs and the shape and size of the workpiece is important. Burrs with a large surface area and a narrow burr base relative to their mass—such as grinding burrs—can be removed more effectively by electropolishing than burrs with a pronounced burr base. However, with appropriate mechanical pre-deburring, electrolytic fine finishing also represents a cost-effective solution in this case.

6. Typical applications for electropolished parts include:

Medical and pharmaceutical technology: Surgical instruments, hospital equipment, and items that are exposed to ionizing radiation or are susceptible to microbiological contamination.
Food and Beverage Industry: Water treatment equipment; surfaces that must be protected against the growth of bacteria, germs, fungi, etc.
Urban Development: Dirt hardly adheres to electropolished outdoor furniture, playground equipment, and sports equipment. Graffiti can be easily removed.

Through the use of modern rectifier technology in combination with the optimal electrolyte composition, electrolytic polishing enables high process reliability and reproducible results with regard to the required surface finishes.

7. Benefits of Electropolishing at a Glance

Improving the Appearance

High reflectivity and the resulting gloss enhance the appearance.

Deburring effect

Rounding off sharp edges.

Relieving Tension

Relief of mechanical and thermal stresses in the metal surface.

No polishing residue

A residue-free, metallically pure surface.

Greater corrosion resistance

Thanks to a significantly thicker passive layer, electropolished stainless steel is more corrosion-resistant.

Smoother surface

Electropolishing has a significant effect on surface roughness. The surface becomes smoother, which improves the flow behavior of fluids in reactors or pipelines, for example. Germs and other undesirable substances have a hard time adhering to the surface.

Greater resistance to germs

Electrolytically polished surfaces are germ-resistant to a certain degree. They are easy to clean and disinfect.

Uniform application

Even parts with very complex shapes and recesses are polished evenly.

Benefits for Small Parts

For small parts, electropolishing is faster, more effective, and therefore more cost-effective than mechanical manufacturing processes.

Low coefficients of friction

In addition, electropolished surfaces offer extremely low coefficients of friction, which is of great economic importance, for example, in the case of wear parts.

Are you looking for other editing options?

We deliver the metal components we manufacture for you as raw parts, or machined, finished, or assembled into subassemblies.

Processing / Assemblies

Extensive processing, surface treatment of metal parts ✓ pro-assembly and assembly of modules ✓ Tell us your requirements now!

Talk to us about your needs

Richter Formteile has many years of experience and in-depth expertise in the manufacture of precision metal parts using investment casting, MIM, sintering, or die-forging processes. Our customers value us as a reliable partner who provides guidance and support from the initial project inquiry through to delivery.

Submit a Project Inquiry Find a Contact Person