Finishing and surface treatment services pretreat or finish the surfaces of manufactured components to meet roughness or surface condition requirements.

Finishing and surface treatment service providers improve a manufactured component's surface in various ways.  They may:

• Remove burrs or flashing to improve surface smoothness
• Polish and hone the part to improve finish
• Harden the part's surface to make it wear resistant
• Clean the surface to make it suitable for further processing
• Coat the surface for improved appearance or corrosion prevention

Finish shops work with parts made of a variety of materials, including ferrous and non-ferrous metals, plastics, composites, glass, and ceramics.

After a manufacturer produces components, they may contract a finish shop to perform work that requires specialized skill or finishing equipment. Manufacturers typically submit detailed finish requirements to the shop before sending the manufactured products. Finish shops then schedule the work when the products arrive, often using Just-In-Time (JIT) scheduling to minimize process and set-up times.

Capabilities

Finishing and surface treatment services may involve numerous capabilities that serve different functions during the finishing process.

Abrasive Blasting/Shot Peening

Blasting uses power spraying or a tumble chamber to remove rust, mill scale, paint, and other contaminants from a component's surface. Particularly, sandblasting creates a roughened surface that improves the adherence of paints and other coatings to be applied to the part. Shot peening improves fatigue strength by blasting a part's surface with smooth glass beads or metal shot. Shafts and other components subjected to a high number of load cycles often require shot peening treatment. 

Sandblasting a metal part.  Video credit:  BlastItClean / CC BY-SA 4.0

Abrasive Flow Machining (AFM)

AFM is used to finish the orifices of nozzles, fuel injectors, spray tips, and other parts with very small apertures. A mixture of abrasive grain is passed through the inner diameter of the part to accomplish this.

Anodizing

Anodizing employs electrolytic oxidation of a metal surface to create a protective oxide coating. This coating is typically transparent and may be between 0.1 and 1.0 mil thick. Anodized coatings provide excellent corrosion resistance and are very hard, durable, and will not wear through under normal conditions. 

Anodizing titanium.  Video credit:  earth2willi / CC BY-SA 4.0

Buffing/Polishing

Buffing and polishing processes smooth the surface of a metal part for aesthetic or functional purposes. 

Chemical Finishing

Some finish shops may refine a product's surface using one of a number of chemical processes. Isotropic superfinishing machines (ISF) utilize chemicals to accelerate material removal and finishing. Shops offering chemical finishing may provide a coating produced by chemical or electrochemical treatment of a metal surface.  These functional coatings provide corrosion resistance and improved adhesion of primers or paints. Electropolishing is an electrochemical process which removes cosmetic surface flaws using a combination of rectified current and a blended chemical electrolyte bath.

Corona Treatment

Corona treatment creates improved bonding characteristics between a metal surface and polymer coatings or adhesives.

Corona treatment of roll goods.  Video credit:  Light Fabrications / CC BY-SA 4.0

Deburring/Deflashing

Deburring refers to the process of rounding off sharp corners or edges. Deflashing removes excess material, or flash, from forged, cast, or molded parts.

Adescription of several deburring methods.  Video credit:  dreambuildfly / CC BY-SA 4.0

Hard Coating

Hard coatings are harder and more abrasion resistant compared to other coatings or finishes. Hard coating processes include hard anodizing, hard coating, hard plating, and hard facing. 

Honing/Superfinishing

Honing and superfinishing are precision surface treatment services, offering much greater control over hand buffing, hand polishing, or tumbling. Both processes involve scrubbing the part with an abrasive stone to improve the part's geometric form.

Honing a part.  Video credit:  WinonaVanNorman / CC BY-SA 4.0

Mass Finishing

Mass finishing involves treating parts in bulk. This method typically uses a tumbler, disc, drum, or other vibratory equipment which is filled with abrasive media. The movement of the media against the parts treats and finishes the part. 

A vibratory tumbler.  Video credit:  lee5490 / CC BY-SA 4.0

Oxygen Cleaning

Oxygen cleaning removes materials, including oils and greases, which could ignite or explode when in contact with oxygen. 

Passivation

Passivation treats the surface of stainless steel by removing leftover iron contaminants and depositing a thin oxide coating. Passivation strengthens and preserves the appearance of the metal.

Phosphate Coating

Phosphate coating treats the surface of a metal with a phosphoric acid solution, which reacts with the metal to form a protective coating. Phosphate coating protects the surface from corrosion and improves adhesive bonding. 

Pickling/Chemical Deburring

Pickling uses a strong acid to remove impurities, such as stains, contaminants, rust, or scaling from metals. 

Sanding/Grinding

Sanding and grinding uses abrasive discs, belts, or grinding wheels to smooth rough surfaces. 

Surface Hardening

Surface hardening uses a variety of finishing methods to improve wear and corrosion resistance of specific areas of a machine, such as an earth moving machine's cutting blades. Processes used include carburizing, nitriding, and hardfacing.

Materials

Finishing and surface treatment service providers may work with a variety of materials.

Metals

The GlobalSpec SpecSearch database contains information about numerous types of metals to be finished.

• Aluminum is malleable and ductile, and features good conductivity, high reflectivity, and oxidation resistance.
• Carbides consist of a metal and carbon, and include silicon carbide, tungsten carbide, and titanium carbide. They have excellent wear resistance and good hot hardness.
• Copper is ductile and is an excellent conductor. Copper alloys are easy to work with and machine, feature superior corrosion resistance and conductivity.
• Iron is a heavy, ductile, magnetic element. 
• Precious metals are relatively rare, valuable metals with high corrosion resistance. They include ruthenium, rhodium, silver, and platinum.

• Steels are chemically and corrosion resistant. Stainless steel can also withstand high pressure ratings.

• Titanium is a light, strong, corrosion resistant metal. It is widely used in the aerospace industry and medical fields.

Non-metallic Materials

Finish shops may also work with ceramics, composites, glass, plastic, or wood.

• Ceramics are materials which have been permanently hardened by firing at high temperature, such as clay. They typically resist heat and chemicals.
• Composites consist of two or more constituent materials with different physical or chemical properties.  Examples include fiberglass, concrete, and engineered wood.
• Glass is a hard and brittle mixture of silicates that is typically transparent.

• Plastics are organic, synthetic, or processed polymers that can be made into objects, films, or filaments.

• Wood is a naturally-occurring tissue used for fuel or building material.

Additional Services

Many finish shops offer additional services or processes in addition to finishing and surface treatment.

• Some providers are capable of inspecting and monitoring materials and coatings in the field to determine performance and recommend repair or other corrective actions.
• Providers offering refinishing services can restore damaged coating or surfaces.
• On-site providers are capable of performing the services at the customer's site or field. On-site services typically include cleaning, finishing, or coating of large structures, facilities, tanks, bridges, or ships.

• Providers may offer process selection or design assistance to aid in the material or coating selection and assist in the design parameters for product improvement.

• Some providers offer cleaning, finishing, or coating of new components or original equipment manufacturer (OEM) parts.

References

NEWMOA - Overview of the Metal Finishing Industry