BEYOND THE SHINE
A Micropolishing Primer
by Ken Barton
Micropolishing has evolved rapidly over the past 30 years and now is understood as a controlled metal removal, surface finishing process. Micropolishing has the ability to enhance bearing characteristics such as roundness, flatness, surface finish and reduced lobing, all of which improve the Micropolished product’s performance and durability.
Typical metal removal during Micropolishing is between .0001” - .0002” with a maximum generally not exceeding .0004”. With this small amount of material to work with, the bearing surface and geometry must be in this range to allow the Micropolishing process enough material to improve the characteristics described above without going below the minimum size tolerance.
Because engine bearing specifications have become tighter to improve engine efficiency, i.e., mileage, durability and performance, the dimensional tolerance, weight and mating surface of a component’s surface also requires further enhancement.
Changing lubricate technology (synthetics and mineral) to reduce heat are designed thinner for tighter clearances increasing the need to control surface finishes and geometries.
To achieve these required higher quality surface finishes, Micropolishing uses a non-compressible abrasive film with a closely graded abrasive crystal in place of the traditional paper or cloth backed abrasives. This non-compressible, closely graded abrasive crystal composition is used in conjunction with a film backing made of a hard and uniform material to support the abrasive film.
With the abrasive film backing or shoe designed to conform dimensionally to each particular diameter and width of the bearing surface, this allows the perfect form of the manufactured shoe to be transmitted onto the part. In combination with the non compressible abrasive film and film back-up we can now generate the improved the bearing characteristic’s.
Using the materials and process consistency described, the Micropolishing process has proven itself to be a significant improvement over chemical, electrostatic, slurry and belt polishing processes.
There have been many names used over the years for describing the surface finishing process. These include: lapping, OD honing, polishing, superfinishing, Microfinishing, and Micropolishing. Most of these descriptive terms are still in use today. However, although they are often used and understood to be describing the same process, they are each in their own way unique.
Other enhancements besides improvements to geometry and surface finish that can be accomplished using the Micropolishing process include: controlled cross-hatch, straight line, tangential fillet radius blend, ferrite cap removal, and in some cases, gauging is also added to this process for sizing.