How Much Will Electropolishing Improve the Surface Finish of My Part?
The Benefits of Improved Surface Finish
Ra and RMS are both representations of surface roughness. Ra is calculated as the roughness average of a surface’s measured microscopic peaks and valleys. RMS is calculated as the root mean square of a surface’s measured microscopic peaks and valleys. Each value uses the same individual height measurements of the surface’s peaks and valleys but uses the measurements in a different formula.
A single large peak or flaw within the microscopic surface texture will affect (raise) the RMS value more than the Ra value, which is why Ra is more commonly used today as a measurement.
Machining Surface Finish Chart: Ra vs. RMS
A commonly held belief is that the electropolishing process can improve Ra and RMS by up to 50%. Part tolerances and surface finishes generally limit this number, however. In all practicality, electropolishing will reduce a part’s Ra by 10 to 30% depending on the starting finish. Generally speaking, the lower the Ra or RMS is prior to electropolishing, the lower the percentage in Ra and RMS reduction. In cases like this, the electropolishing process will be controlled to remove a limited amount of material. If too much material is removed, the surface roughness can move up on a micro level, leading to a rough and pitted surface visually.
Material removal can vary in the finished part by altering the dwell time during processing—standard ranges can be from .0002” to .0003” per surface. This precise process can improve the surface of finished parts with removal rates of .0001” accuracy. It is important to communicate your dimensional tolerance requirements with your electropolisher.
Improving The Surface
Electropolishing improves the surface of metal in the following ways:
Smoothing effect, good aesthetics. Electropolishing removes high spots on a metal part’s surface. This means that the dimensions of the lower spots are changed very little, which creates a smoothing effect to the base metal surface. It also means that by the nature of the process, the total amount of dimensional change required to obtain the polish effect is very small.
Easier cleaning and maintenance. Some parts and components are used in settings where it is difficult to physically access them for maintenance purpose; others, as in medical, food and beverage, and semiconductor applications, require repeated sterilization or cleaning. The leveling of micro peaks and valleys through electropolishing not only inhibits the “collection” of particulates in otherwise grooved surfaces, it also allows for easier sterilization and maintenance.
Reduces friction and surface drag, with no cracking. The smoothing of the metal also helps reduce friction and surface drag. Visually, the smoothing removes grain boundaries, which also mitigates the incidents of stress cracking. In mission-critical applications, you need your parts and components operating optimally, and always reliably within some of the extremely tight tolerances your end-users require.
Exposes defective parts. There’s a built-in quality control element to electropolishing. Since the process is carried out in the presence of aggressive chemicals, when a defective part comes through the process line, the chemicals in the electropolishing solution tend to uncover the defect in the part. This is a dramatic and effective way of double-checking the quality of material being processed.
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, enhancing the chromium/nickel content resulting in dramatically improved resistance to corrosion. Repeated exposure to water or chemicals will not compromise the finished surface in medical applications, or in outdoor industrial or architectural installations.
At New England Electropolishing, we have highly controlled processes in place that ensure material removal is precise and repeatable every time. Let us help with your next project! Find out how New England Electropolishing can help you with your electropolishing needs. We’ll provide you with our expert analysis, a quote—even a free sample.
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