The Basics of Finishing CNC Machined Parts: A Comprehensive Guide

Achieving the ideal surface finish for every CNC machining project is more than just an aesthetic choice; it is an important factor that affects the functionality, durability, and performance of machined parts. A-1 Jay’s Machining Inc is able to provide services such as precision machining and product assembly.

This comprehensive guide delves into the nuances of CNC surface finishes, providing insights into processes, comparisons, and surface finish selection for a variety of applications.

1.What is surface finish?

Surface finish refers to the texture and smoothness of the exterior of a machined part. It is a critical parameter that affects not only appearance, but also the mechanical properties and performance of a part. By controlling surface finish, manufacturers can enhance corrosion resistance, reduce friction, improve sealing capabilities, and ensure that parts meet the specifications required for the intended application.

2.What is the difference between surface finish and surface treatment?

Surface finish and surface finishing may sound similar, but they refer to different aspects of CNC machining. Surface finish refers to the inherent texture and quality of the surface of a machined part, characterized by metrics such as roughness average (Ra). In contrast, surface treatment involves applying additional processes to a machined part to change or improve its surface characteristics, including techniques such as anodizing, powder coating, and shot peening.

3.What are some pre-surface treatment processes for CNC machining?

Prior to surface treatment, certain preparation steps are required to ensure that the machined part is ready for finishing. An important process is masking holes and surfaces to protect specific areas from finishing treatments, preserving their original precision and functionality. Other surface preparation processes include cleaning to remove any machining residues, smoothing edges to eliminate sharpness, and surface treatment techniques to ensure optimal adhesion and finishing results.

4.What are the different surface finish levels commonly used for CNC machined parts?

Surface roughness levels are critical in determining the functionality and aesthetics of CNC machined parts. Here is a breakdown of common roughness levels:

①0.4 μm Ra

This ultra-smooth surface finish is often used for high-precision parts that require minimal friction and maximum durability. It is more expensive due to the extensive machining and quality control work required, adding a significant portion of the production cost.

②0.8 μm Ra

Ideal for parts that need to balance cost-effectiveness with performance, this level of smoothness is often sought after for consumer electronics and automotive components, modestly increasing the production cost of the part.

③1.6 μm Ra

This roughness grade is often used for general machined parts and offers a good balance between surface quality and manufacturing cost.

④3.2 μm Ra

For less critical applications where surface smoothness is not a primary consideration, this grade can reduce production costs while still providing adequate performance for many industrial components.

Surface roughness, often expressed by the term “Ra” (average roughness), is a quantitative measurement of the texture or smoothness of a machined part’s surface. It plays an important role in determining how a part interacts with its environment or other components. Let’s take a closer look at the various Ra grades and their applications in CNC machining.

①0.4 μm Ra

From a microscopic perspective, a 0.4 μm Ra surface finish is very smooth, almost mirror-like. This smoothness is essential for parts where minimal friction is critical, such as aerospace applications or high-precision bearings. This finish ensures that the part operates efficiently at high speeds or in environments where any surface imperfections could cause failure. The precision required to achieve this finish means that it is typically the most expensive and is only used for parts where performance cannot be compromised.

②0.8 μm Ra

The 0.8 μm Ra surface roughness level hits the sweet spot in automotive and consumer electronics, where parts need to be smooth enough to ensure reliability and longevity, but not too expensive. This finish strikes a balance between minimizing wear and keeping manufacturing costs in check. It is ideal for visible parts that require a certain level of aesthetics without the extreme smoothness of a 0.4 μm Ra finish.

③1.6 μm Ra

The 1.6 μm Ra surface finish is widely considered the industry standard for a variety of general applications. This level of roughness is smooth enough for many mechanical parts in machinery, where surface finish does not have a significant impact on functionality. It is a cost-effective option for parts that do not frequently come into contact with the human body or where slight roughness does not affect part performance, such as internal machinery.

④3.2 μm Ra

When it comes to 3.2 μm Ra, we are looking at a surface finish that is functional rather than formal. This level is often seen on parts where surface finish is not a primary concern, such as structural parts or parts hidden from view. This is the most economical option for parts that require basic functionality but do not require a high degree of smoothness. Increased roughness can be tolerated in applications where interaction with other parts or materials is minimal or there is little potential for increased wear.

CNC machining surface finishing is a complex field that requires attention to detail from preparation to final finishing. Understanding common problems and how to prevent them ensures high-quality results that meet or exceed expectations.