When you receive a CNC machined part straight off the machine, you will notice visible tool marks — the characteristic patterns left by the cutting tool’s path. For many prototype CNC industrial applications, an “as-machined” surface is just a starting point. Surface finishing gives machined components the ability to endure demanding applications as well as the the attributes of functional performance and an aesthetically pleasing appearance.
Surface finishing is a post-processing technique that provides machined components with a surface that is more wear resistant, has lower surface roughness, and is more appealing. Surface finishing increases the functionality and the aesthetic of the machined component. For CNC industrial equipment prototypes, the correct surface finishing may be the difference in the component passing field testing instead of failing in the field.
Finishing Surface for CNC Industrial Equipment Prototypes
There are three main reasons surface finishing is performed:
• Finish appearance. This includes coatings that provide color, and gloss as well as patterned finishes.
• Finish durability. This is achieved via coatings that improve resistance to wear, corrosion, abrasions, and impacts.
• Finish functionality. This is achieved by altering the surface and modifying the electrical, thermal, or chemical properties of the component.
As described above, these are the basic reasons for surface finishing. The rest of the reasons pertain to specific engineering problems. For example, raw aluminum parts can corrode if exposed to the environment, and are left anodized as a surface finish. Stainless steel parts can improve their corrosion resistance if they are passivated. Moving components are advantageous to have low friction, and medical devices require finishes that allow for easy cleaning and sterilization.
At YANMEE, surface finishing is one element of a multi-dimensional, engineering-first methodology. With over a decade’s experience in industrial design and manufacturing, YANMEE offers advanced CNC prototyping and precision production solutions, all of which stand up to the most rigorous engineering scrutiny. Every build is subjected to tolerance, assembly logic, and DFM assessments prior to production, so that surface finishes are applied to parts that have been designed to perform in the real world.
Surface Finishing Methods
There are several broad categories of surface treatment methods that can be applied to CNC machined parts, and each works best with different materials and for different applications.
• Mechanical Surface Treatments are an abrasive or impacting physical alteration to the surface. Examples are polishing, brushing, and sandblast/shot peen treatments. These are the best option for producing a superior surface finish and improving the mechanical performance by decreasing micro-cracks.
• Chemical Surface Treatments bring surface and coating protection to the next level by providing a chemical reaction which alters the surface finish. Anodising, phosphating, and chemical passivation are examples of a chemical treatment that prepare the surface for further coatings.
• Electrochemical Surface Treatments are excellent for surface finish when surface hardness, corrosion protection, and esthetics are of primary importance. Treatments such as electroless nickel plating, electroplating, and hard chrome plating are all excellent options.
• Thermal Surface Treatments are also an excellent option when high surface hardness is required but altering the treatment of the core is not desirable. Carburising, Nitriding, and induction hardening are the best options for treating surfaces of parts that are high friction or high stress.
Coatings and Paints consist of many different methods of application (powder coating, PTFE Coatings, liquid paints, etc.), each providing a protective, long-lasting finish. Paints and coatings can also be treated to allow more functional and aesthetic features.
10 Important Surface Finishing Techniques for CNC Industrial Equipment Prototypes
1. As-Machined Finish
This is the direct result from the CNC and is rated at a standard surface finish of an average roughness (Ra) of ~3.2 μm.
• Best For: Prototypes that are functional, internal components, and components that are to be finished further.
• Pros: The cost of further processing is saved and the finished component is produced with the utmost accuracy.
• Cons: Marks from the tools are evident and the finish does not provide protection from corrosion.
✅ YANMEE Capability: With standard machining of ±0.05 mm with a 19-point QC validation and critical dimensions of ±0.01 mm.
2. Bead Blasting (Sand Blasting)
This is achieved by using beads of glass (or ceramic media) that are propelled at high velocity to the part surface.
• Best For: Aesthetic enhancement of surface finish and preparation for a coating. Tool marks are concealed with this finish.
• Pros: This is a quick and cost-effective finish for all metals.
• Cons: This does not provide a protective finish from corrosion. Brittle plastics should be avoided for this process.
This is usually performed prior to anodizing, in which a texture is provided and a coating is provided to protect from corrosion.
3. Polishing
This process of finishing uses an abrasive that does not result in any friction and therefore achieves a reflective finish.
• Best for: Polishing produces a decorative finish and further benefits a component by reducing friction and increasing cleanliness.
• Given the appropriate equipment, polishing can produce a finish with an average roughness of Ra 0.2 μm.
4. Anodizing (Type II)
• Best used for an aluminum component that requires a durable color finish that is more corrosion resistant than a paint finish.
• Benefits: anodizing provides better corrosion resistance than a coating and colors can be chosen.
• Disadvantages: aluminum components only, available colors may not meet a desired standard.
5. Type III/Anodizing/Hardcoat
Type III anodizing produces a thicker anodized layer, which is harder and more corrosion resistant and wear resistant than standard Type II anodizing. Anodizing of 25-75 μm is more common.
• Best used for an anodized component requiring additional durability, especially for gears and robotic joints.
• Benefits: Hardness comparable to steel (350-600 HV), corrosion resistant.
• Industry application: Robotics, industrial, automotive.
✅ YANMEE Capability: Military-grade anodizing is part of YANMEE’s full post-processing service.
6. Passivation
This is the removal of free iron from the surface of stainless steel, and provides a layer of excellent corrosion resistance.
• Best used for corrosion resistant stainless steels, especially medical and food-grade stainless steels.
• Benefits: No dimensional effect, improves treatment of the surface and corrosion, and often assists in meeting standards.
✅ Standards: YANMEE’s ASTM A967 provides passivation.
7. Powder Coating
Powder Coating develops an attractive and durable finish.
• Having a heat-resistant metallic part is ideal for this solution.
• Advantages: It has a high variety of colors and a high thickness of the coating.
• Disadvantages: This solution adds thickness to the part.
8. Electroplating
Electroplating is one of the electrochemical methods to coat a metallic layer on a part.
• Best for: Some cosmetic aspect or electrical and mechanical enhancements.
• Pros: The coating is uniform.
• Cons: Every part has to be pre-treated.
9. Laser Marking/Engraving
This method is the fastest and the most accurate for the permanent marking of a part.
• Best for: Marking company parts and traceability.
• Pros: Engraved marking is precise and permanent. Plus, it’s a no material added process.
• YANMEE Capability: Our capability is marking lots with a 0.1 mm precision and traceability.
10. Brushed Finish
This is a finish that is both uniform and abrades in a directional manner.
• Best for: Decorative parts.
• Advantages: The texture is uniform, aesthetically pleasing, and satin in nature, plus it has a finish that resists fingerprints.
• Disadvantages: This finish is very material and part shape dependent.
Considering the Appropriate Surface Finish
Several variables come into play when deciding the appropriate surface finish.
• What type of material: Certain finishes only apply to certain materials. For example, anodizing can only be done on aluminum, and passivation is for stainless steel. Paint and polish are options for some plastics.
• Function needs: Does a part need greater resistance to wear, corrosion, or does it need to be conductive, or perhaps need biocompatibility?
• Conditions: Will a part be subjected to any of the elements like moisture, or chemicals, or even salt or temperature extremes?
• Look and feel: Will end-users see a part? Does it need to be a certain color or have a certain texture?
• Finishes also affect dimensions and cost: Some finishes can be applied to a part at a lower cost because they don’t require any additional material to be added, whereas other finishes have multiple steps and add material and cost.
At YANMEE, finish selection is part of the extensive DFM review, and takes less than a day with the assurance of ±0.01 mm accuracy. YANMEE manufactures a sleek, aesthetically pleasing, industrial grade, and real production ready (tooling ready) CNC prototype equipment.
Assurance of Surface Finish Quality
Quality control is a necessity to ensure surface finishes meet demands. At YANMEE, quality assurance includes:
• Certification of ISO 9001 and ISO 14001 standards; which act to ensure continual improvement in the quality of products as well as in the environmental management system.
• 19-point QC loop holding tolerances to ±0.01 mm.
• CMM inspection with 0.001 mm accuracy.
• Surface roughness testing to Ra 0.2 μm.
• First-article inspection (FAI) and full lot-traceability systems.
For specialised surface finishing, YANMEE maintains a Class-10,000 cleanroom with a 500-metre fully automated UV-spray line and film-thickness control to ±0.1 μm. Multi-dimensional CMF (Color, Material, Finish) capabilities include micro-etch textures at 0.02 mm, gradient UV coatings with ΔE ≤ 0.5, and functional layers such as anti-fingerprint (AF > 115°) and antibacterial (> 99.9%) coatings.
Closing Words
Surface finishing transforms CNC industrial equipment prototypes into reliable, production-ready components. The appropriate handling for specific factors such as corrosion and wear can provide significant benefits. After 12 years in business and having a portfolio of over 10,000 clients including Fortune 500 companies, we deliver finishing that is backed by engineering in the automotive, medical, and aerospace fields. With services from Design for Manufacturing in 24 hours to CNC and finishing— all done in-house— we provide a competitive advantage. Upload your CAD for a 24-hour review and elevate your project.
FAQs
Q1: What is surface finishing for CNC machined parts?
A: Surface finishing is a post machining process that helps with corrosion resistance, wear protection, appearance, and functional characteristics like conductivity and friction.
Q2: What is the most durable finishing for industrial equipment?
A: For industrial equipment, Type III hard anodizing and powder coating have great wear and corrosion resistance. For steel, the best industrial finishes would be electroplating or passivation.
Q3: Does surface finishing impact dimensional accuracy?
A: Yes, some finishes can be done to a thickness (powder coating, plating) and some finishes can be done to a material removal (polishing). Finishing is done with tolerances in mind. YANMEE can achieve tolerances of ±0.01 mm even with surface finishing.
Q4: Can I request specific colors and textures?
A: Yes you can. Anodizing, powder coating, and painting have an unlimited color selection. Many textures are also available including brushed, blasted, and micro-etch.
Q5: How do I select a finishing for my prototype?
A: You would have to take into consideration material, environment, functional characteristics (wear, corrosion, friction), appearance, and cost. YANMEE offers a 24-hour DFM review which can also provide some guidance.