How To Improve The Surface Finish of CNC Machined Precision Parts

In most cases, surface quality is crucial for mechanical components. For most CNC machining manufacturers, using the correct machining processes can significantly improve the surface quality of CNC machining.

Surface finish is influenced by various factors, including chip load, step-over, tool geometry, and tool inclination. The benefits of high-speed CNC machining include achieving higher machining speeds through lower cutting forces and lower chip loads-both of which will improve surface roughness.

In certain applications, regardless of how fine the average roughness value is, even a single scratch can render the part unacceptable from a design engineering perspective. These same considerations apply to multiple parameters of waviness and total profile.

Therefore, when design engineers specify surface finish parameters and values, they must understand how these will affect the performance of the part. Given the large number of parameters, choosing the ideal ones for a given application can be somewhat complex, but most applications are limited. Most applications can successfully specify using a few well-known parameters.

Of course, smoother is not always better. CNC machining parts as quickly as possible and minimizing secondary processing have obvious economic benefits. Additionally, in some applications, a certain degree of roughness can enhance functionality, and specifications may call for minimum and maximum roughness values. For example, a surface with a certain roughness often enhances the adhesion of paint or other coatings.

Some parts that perform multiple functions require complex surfaces to function optimally. For instance, engine cylinder walls must be smooth enough to provide a good sealing surface for piston rings to promote compression and prevent leakage. At the same time, they must have enough, adequately sized, and well-distributed "pockets" to hold lubricating oil. The Rk series parameters were developed to describe such complex multifunctional surfaces. This is an example of parameters developed as design rather than inspection tools.

 Once the surface has been defined and specified, manufacturing engineers must determine how to produce it reliably and cost-effectively. In cases where the surface is specified solely by the Ra parameter, this is usually straightforward, as the actual shape of the surface can vary significantly while still meeting the given Ra value. Finer Ra values can be achieved through many alternative methods, including slowing down the speed or feed, making shallower cuts, or performing secondary CNC processes such as fine grinding, honing, and lapping after the primary cutting process. If Ra is the only specified parameter, manufacturing engineers can choose the method they consider economical and effective.