Electropolishing will smooth and streamline the microscopic surface of most metal objects, improve surface finish, improve corrosion resistance and achieve passivation—typically stainless steel or similar alloys. Electropolishing typically takes off between 0.0002 and 0.0003 of an inch from the surface of an object.

The process may improve the surface finish of your metal part by 10%-40% (depending on part tolerances and surface finish) or more—rendering the surface of the metal microscopically featureless and void of any tiny imperfections. Often, during a standard run, total material removal is limited between 0.0002” to 0.0003” per surface—but the removal rate can be adjusted depending on a part’s tolerances.

It’s important to note that electropolishing only improves the surface of a metal part on a microscopic level. Any macroscopic textures or surface scratches will only result in a smoother texture or smoothed scratch if taken through the electropolishing process. For macroscopic surface imperfections, mass finishing is the more appropriate process for the job.

How do we do it? We first load the parts onto racks, which we dip into a tank filled with a phosphoric and sulfuric acid solution. The tank is lined with metal plates that function as cathodes so we can run a positive electric current through the bath.

We can adjust the removal rate to a specified tolerance, and we check throughout our process to ensure we are meeting the targets we set. This is especially important during electropolishing of large batches of parts, so we ensure that our quality is consistent from the first part to the last.

Can Electropolishing Achieve Passivation? Yes.

Passivation is the removal of free iron from the surface of a part. Electropolishing will remove free iron, as well as de-burr and deeply clean the surface. This can be especially important when you have small parts with trace amounts of free iron and micro-burrs.

ELECTROPOLISHING PROCESS:-

HOW DOES ELECTROPOLISHING WORK?

Electropolishing works by applying direct positive current to a workpiece or anode. Simultaneously, negative current is applied via cathodes. The electrolytic solution coats the workpiece and allows metal ions to be removed from a parts’ surface. As these ions are removed, the micro surface of stainless steel is improved, and small micro burrs are removed on edges and radiuses. A passive oxygen enriched layer is formed on a part’s surface.

Steps of the electropolishing process:

Pre-Treatment/Cleaning:

Upon arrival, parts undergo a pre-treatment and cleaning process to ensure the surfaces are thoroughly treated and prepared for Electropolishing. Pre-cleaning is used to remove machining oils, heat affected zones and other contaminants prior to the Electropolishing process.

Racking of parts:

Depending on the type of part and order, parts are either individually racked or combined in specially designed baskets for bulk electropolishing of small parts. Parts with higher tolerance standards, such as those used in the medical industry are individually racked for best results.

Electropolishing:

Racked parts are slowly submerged into an electropolishing bath containing an electrolyte mixture (A calibrated blend of sulfuric acid and phosphoric acid). A positive electrical current is applied to the rack which is generated from a rectifier. The electrical output (measured by amperage and voltage) is controlled remotely by a digital controller.

Post-electropolishing procedures:

The post electropolishing procedure involves a multistage rinsing process involving as many as ten rinsing stations. Parts see various acids for additional cleaning as well as clean water rinses and multi stage deionized rinsing stations as a final clean. Parts are then dried utilizing various methods depending on part size and sensitivity.

Testing:

Depending on the manufacturer’s needs, the performance of parts can be tested and analyzed through a variety of methods. Many medical parts are measured before and during processing to ensure part tolerances and thickness are maintained. NEE performs copper sulfate testing upon request to ensure parts are passive.

Final Inspection/Shipping:

Upon the completion of the electropolishing process, parts at NEE undergo a final inspection from our quality team before being approved for packaging. NEE utilizes customer packaging such as trays, cells and containers to ensure parts are well protected. Additionally, care is taken to ensure no metal-to-metal contact is made with sensitive parts.

The Benefits of Electropolishing:-

Curious about the benefits of putting your parts through the electropolishing process? Read along below where we break down the top 5 benefits of electropolishing.

1. Smoothing Effect & Good Aesthetics: Electropolishing removes high spots on the surface of metal parts. During the process, the dimensions of the lower spots are barely altered, creating a smoothing effect to the base of the metal’s surface. This means that throughout the entire electrochemical process, the total amount of dimensional change needed to obtain the polish effect is very small.

2. Easier Cleaning & Maintenance: Many metal parts and components are used in environments where it is difficult to physically access them for maintenance. Others as in medical, food and beverage, and semiconductor applications require repeated sterilization and cleaning. The leveling of micro peaks and valleys through electropolishing not only protects against the “collection” of particulates in otherwise grooved surfaces, but also allows for easier sterilization and maintenance.

3. Reduces friction and surface drag, without cracking. A part that has been electropolished properly will experience the performance benefits of reduced friction and surface drag. Visually, the smoothing removes grain boundaries, which significantly reduces the chances of your metal component cracking under stress. In mission-critical applications, you need your parts and components to be operating at their highest level to ensure your business adheres to some of the extremely tight tolerances your end-users require.

4. Exposes defective parts. In electropolishing, there is a built-in fail-safe for performing quality control on your parts. Since the process is carried out under the presence of intense chemicals, when a defective part comes through the process line, the chemicals in the electropolishing solution tend to unmask the defect in the part quickly and obviously. This is a dramatic and effective way of double-checking the quality of your parts being processed before it is sent out to its final destination.

5. Corrosion Resistance: Free-iron is an almost entirely unavoidable consequence of metal forming in manufacturing. Electropolishing removes metallic and non-metallic inclusions introduced during manufacturing. This results in the removal of elemental iron from the surface of stainless-steel alloys and enhances the chromium/nickel content. The result is a dramatically improved resistance to corrosion. Parts that are professionally electropolished can withstand repeated exposure to water or chemicals and will not compromise the finished surface in medical applications, or in outdoor industrial or architectural installations.