Understanding the role of surface finish in CNC machining: how to improve part performance and life?

In precision manufacturing, surface finish is one of the core indicators of CNC machining quality, directly affecting part friction performance, sealing, corrosion resistance and fatigue life. Whether it's aerospace gears or medical implants, precise control of surface roughness (Ra value) has become the key to breaking through technological barriers. In this article, we will analyse the definition of surface finish, influencing factors and optimisation strategies, and share how to achieve the ultimate precision of Ra ≤ 0.4μm through technological upgrading.

I. Definition of surface finish and industry standard

1. What is surface finish?

Definition: Surface Finish refers to the microscopic unevenness of the surface of a part after machining, which is commonly quantified by roughness parameters (Ra, Rz, Rq).

Ra value: the arithmetic mean deviation, such as Ra 0.8μm indicates that the average height of surface undulation 0.8 microns.

Rz value: maximum peak-to-valley height difference, more suitable for assessing extreme surface defects.

2. Comparison of Industry Finish Standards

II. 5 core factors affecting surface finish of CNC machining

1. Tool selection and wear state

Tool geometry parameters:

Large rake angle tool (γ = 15°) reduces cutting forces and reduces surface roughness by 20%.

The radius of the tip circle (r=0.4mm) affects the residual height, and small r-value tools are required for finishing.

Wear monitoring:

Ra value rises by 50% when tool back face wear VB≥0.2mm.

2. Cutting parameter optimisation

Golden ratio formula:

Feed (f): f = (Ra × r)/(8 × Re), where Re is the blunt radius of the cutting edge.

Example: carbide tool machining aluminium alloy, f = 0.05mm / r can achieve Ra 0.4μm.

3. Machine vibration and rigidity

Vibration effects:

Spindle radial runout ≤ 0.002mm, to avoid vibration pattern resulting in Ra value fluctuation ± 0.2μm.

Solution:

Use damping tool shank (such as hydraulic tool shank) to reduce vibration by 30%.

4. Cooling and lubrication

Micro Quantity Lubrication (MQL) :

Reduces Ra by 15% compared to conventional cast cooling and reduces cutting fluid consumption by 80%.

Cryogenic cooling:

Liquid nitrogen cooling processing titanium alloy, surface hardness increased by 20%, Ra value stable at 0.6μm.

5. Material properties and heat treatment

Case comparison:

Ra=1.2μm after machining of 6061 aluminium alloy without aging treatment, reduced to 0.8μm after aging.

III. 4 core technologies to improve surface finish

1. High-speed finishing strategy

Parameter combination:

Spindle speed ≥10,000rpm, feed speed F=800mm/min, depth of cut ap=0.1mm.

Effect:

Surface roughness Ra≤0.4μm, machining efficiency increased by 25%.

2. Tool path optimisation

Equal residual height machining:

Automatically adjust the step distance according to the curvature of the surface to ensure that the fluctuation of Ra value is ≤±0.1μm.

Spiral milling:

Continuous cutting reduces the traces of entering and exiting the tool, which is suitable for hole machining and cavity finishing.

3. Surface post-treatment process

Mechanical polishing:

Adopting diamond grinding paste, Ra value is reduced from 1.6μm to 0.1μm.

Chemical nickel plating:

Plating thickness of 10μm, surface hardness HV500, corrosion resistance increased by 3 times.

4. Online detection and feedback control

Technical solution:

White light interferometer real-time measurement of Ra value, automatic correction of tool offset (accuracy ± 0.05μm).

IV. Application cases of surface finish in different industries

1. Medical industry: life guarantee of artificial joints

Technical requirements:

Titanium alloy hip joint ball head Ra ≤ 0.2μm, reduce the release of metal ions caused by friction.

Process solution:

5-axis CNC machine + diamond tool mirror milling.

2. Automotive industry: the code to improve fuel efficiency

Case:

Cylinder block honing process (Ra 0.4-0.8μm), reducing piston ring friction loss and fuel consumption by 5%.

3. Energy industry: durability revolution for wind power gears

Data:

Gear surface carburising and hardening + gear grinding process (Ra 0.4μm), life extended from 10 to 25 years.

V. JLCCNC: Expert in High Surface Finish CNC Machining Solutions

JLCCNC is deeply committed to the field of precision manufacturing, through technological innovation and strict quality control, to provide customers with Ra ≤ 0.4μm ultra-high finish machining services:

Technical Advantage:

Process database: accumulating 100,000+ cutting parameter combinations, quickly matching the best surface quality programme.

Full-process quality control: from roughing to polishing, 100% pass the three-dimensional inspection and white light interferometer re-inspection.

Service highlights:

Industry customisation: support special finish certification needs in medical, automotive, optical and other fields.

Fast response: 24 hours to provide process solution and quotation, 72 hours to deliver the first sample.

Global delivery: as fast as 3 days to the world.

Contact JLCCNC today to push the limits of your parts' surface finish!