Achieving High Quality Superfinishing

The majority of superfinishing operations, those where materials need to be polished to a Ra value below 0.01 µm, raise a number of issues that, up until now, have meant compromise rather than ideal solutions.

Normally, when starting off with a machined component, the main challenge is deciding how to achieve a super finish in the most cost-effective manner. Until now, the solution most commonly applied would require a lapping operation to first create a flat surface with a uniform finish, followed by a further polishing operation which, in the majority of cases, necessitates a polishing pad to produce the super finish.

This may initially seem like an appropriate solution for the majority of machined parts, but one drawback of the pad polishing process is it may buffer any sharp edges down. This is known as roll-off, where the part has sunk into the polishing pad material, and the edges are blunted and softened by the nap of the pad, which is visible across many finished parts.

The longer a part is processed on the polishing pad, the more this effect has an impact. Thus, it is crucial to balance the speed of the lapping stage against the final surface finish in order to minimize the time on the polishing pad.

Image credit: Kemet International

It is becoming increasingly common for a component designer to request that sharp edges remain on the finished part. This is crucial for components that are used for sealing applications where roll-off would result in leaking parts.

The new Kemet PR3 composite plate material, for use in combination with Kemet’s closely graded Liquid Diamond slurries and Diamond Compounds, has been developed to provide a solution to this issue. It can produce a surface finish value better than what you would expect from a purely polishing process but has the ability to remove material at the same time.

The composite has no metal content and so is well-suited for applications where components must not come into contact with metals, for example, in nuclear and electronics applications. The plate’s ceramic-faced conditioning rings mean parts are much cleaner when compared to metal after lapping, especially when using white aluminum oxide-based ceramic materials.

Since the surface finish achieved after the PR3 is of supreme quality on a diverse range of materials, a pad polishing stage is not usually required, but in certain scenarios where secondary pad polishing is required, the polishing time is reduced so that no roll-off is produced.

Surface Finishing of Optical Components

Surface finishing techniques are of extreme importance when it comes to finishing optical components. The atomic concentration, roughness, and other related properties of optical components are optimized in order to achieve the highest reflective, refractive, transmittance, and related properties.

Polishing pads, ultra-polishing pads, contact polishing, and quasi-polishing pads are commonly used for this purpose.

The Kemet PR3 Polishing Plate is an excellent alternative to polyurethane pads when polishing precision optics. The plate is comprised of a thermally stable resin and is suitable for use with aluminum oxide, cerium oxide, and diamond slurries.

The better the surface finishing technique used, the better the optical properties of the prepared material. Due to very specific optical specifications, surface finishing operations of optical components are generally more complex and expensive.

For all customers, including those who already have a process in place, Kemet offers free-of-charge testing for any lapping or polishing application.

This information has been sourced, reviewed and adapted from materials provided by Kemet International Ltd.

For more information on this source, please visit Kemet International Ltd.


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