What Is Superfinishing?

Metals from the mill often have a finish that is not particularly smooth or aesthetically pleasing. Various manufacturing processes – such as sawing or welding – or corrosion can also degrade the surface of a metal. To improve their surface quality and appeal, certain applications require the surface of the metal to undergo finishing processes. But for some applications, finishing processes alone are not enough, and superfinishing processes must be used.

What is Superfinishing?

Superfinishing is a mechanical material removal process that is performed on material surfaces after they have already undergone some type of finishing or other surface modification process. Superfinishing removes the residual amorphous layer that is left from the previous processes. Superfinishing is used for applications in which surface finish is absolutely critical to the success of the component.

The Superfinishing Process

The superfinishing process is carried out through the use of a stone or abrasive tape with an extremely fine grit. Since the grit is so fine, superfinishing cannot remove large surface imperfections and can only be done after previous surface modification techniques are used to bring the surface to an excellent finish. The abrasive stone or tape is rotated or oscillated against the metal, creating a cross-hatched appearance. This cross-hatching is one of the major differences between superfinishing and polishing, since polishing results in a smooth, mirror-like finish. A lubricant is often used during the superfinishing process to reduce the amount of heat produced by the friction. This helps to avoid thermally damaging the metal.

Why Use Superfinishing?

Superfinishing is an excellent process to use when a high degree of aesthetic appeal is required. Materials that have been superfinished typically have an excellent appearance, and the cross-hatching adds another dimension of aesthetic appeal that polishing does not. Superfinishing also helps improve the usable life of moving parts. This is because a superfinished surface results in low friction. Superfinishing also can improve dimensional accuracy of a surface, sometimes more so than other surface modification techniques. This means superfinished surfaces can create better seals and improve ease of assembly than many non-superfinished surfaces.

Disadvantages of Superfinishing

The primary disadvantage of superfinishing is the time it takes to perform. While the process itself may not necessarily be slow, superfinishing is still another operation that must be added to create a finished product. Adding a superfinishing operation can be costly because of this additional time requirement and the additional equipment needed. Another attribute of superfinishing that could be considered a disadvantage is that unlike polishing, superfinished metal surfaces do not have a mirror-like surface. The use of superfinishing would depend on the desired aesthetic appeal.

Applications of Superfinishing

Superfinishing is used in many different industries for a variety of reasons, either for aesthetic appeal or to improve the lifespan of a metal component.

In the automotive industry, high velocity and high cycle parts such as rods and shafts are superfinished to reduce wear and increase usable life. In the aerospace industry, gears and other components at risk of high amounts of wear are often superfinished to improve their time before repair and overhaul is required.

Metal ornaments and display pieces are also superfinished frequently to improve their aesthetic appeal.