Polishing is a vital finishing process for creating smooth, lustrous surfaces on materials like metal, plastic, glass, and more. There are various mechanical, chemical, and electrochemical polishing methods used across different industries and applications. Here is an introduction to some of the most common polishing methods and tools:

Mechanical Polishing

Mechanical polishing uses physical abrasion to gradually smooth and flatten surfaces. Common techniques include:

Abrasive Tumbling

In abrasive tumbling, parts are placed in a rotating barrel along with an abrasive media like ceramic pellets, plastic pellets, or metal shot. As the barrel rotates, the media abrades the surface through low-stress grinding and burnishing actions. Finer abrasive grits are used in stages to achieve smoother finishes.

Grinding and Lapping

Grinding uses bonded abrasives like grinding wheels, belts, or discs to remove material. The cutting action results from the fracture and dulling of abrasive grains to expose fresh sharp grains. Lapping employs free abrasive particles in a fluid carrier. The abrasive slurry flows between the lapping plate and workpiece.

Buffing and Polishing

Buffing uses muslin cloth wheels charged with polishing compounds. As the wheel spins, it burnishes and smears the surface to make it bright and smooth. Polishing wheels use softer materials like cotton and flannel for final color and gloss polishing.

Vibratory Finishing

Vibratory finishing uses abrasive media mixed with a liquid which is vibrated against surfaces to abrade and deburr them. Machine parameters can be adjusted to control the intensity of the finishing process.

Chemical Polishing

Chemical polishing uses chemical reactions to evenly remove material:

Electropolishing

Electropolishing makes the workpiece anodic in a temperature-controlled electrolytic bath. As current is applied, surface high points and irregularities experience higher current density and faster dissolution compared to valleys. This results in a leveling action that smoothes the surface.

Chemical Bath Polishing

In chemical bath polishing, the workpiece is immersed in a bath containing an acid solution which reacts with the surface material. By controlling bath parameters like temperature, acid concentrations, and immersion times, the acid can be made to dissolve surface material evenly without preferential attack.

Passivation

Passivation refers to the use of acids like nitric acid or citric acid to remove free iron and other surface contamination on stainless steel and other alloys. This leaves a clean passive layer to enhance corrosion resistance.

Pickling

Pickling entails the use of acids like sulfuric acid or hydrochloric acid to remove oxides and scale from metal surfaces prior to further finishing. It helps expose a fresh, clean underlying surface.

Automated Polishing-Automated techniques improve repeatability and batch processing.

• Robotic polishing – Programmable robots with polishing end-effectors.
• CNC polishing – Computer-controlled polishing using rotating heads.
• Orbital polishing – Machine tools with eccentric rotating polishing pads.

Common Polishing Tools

• Buffing wheels – Made from fabrics like muslin, flannel, or synthetic fibers. Used with polishing compounds.
• Grinding wheels – Abrasive discs of composites like aluminum oxide in a resin bond. Designed for high material removal rates.
• Diamond wheels/plates – Diamond abrasive bonded to a metal core or plate for precise lapping and polishing.
• Polishing pads – Soft pads, often of felt or plastic, used to apply polishes and buff surfaces.
• Compounds – Polishing compositions containing fine abrasives suspended in waxy or oily media.

Titanium alloy screw polishing-method and working principle

Titanium alloy screws require polishing to achieve smooth, bright surfaces and dimensional accuracy. Here are some common methods and the principles behind polishing titanium alloy screws:

Abrasive Tumbling

• Screws are placed in a rotating drum with abrasive media like ceramic/plastic pellets or metal shot.
• As the drum rotates, the media gradually knocks off and smooths microscopic peaks and valleys through low-stress grinding.
• Progressively finer abrasive grits are used to achieve a consistent, directionally-uniform finish.
• Final microfinish polishing compounds produce a glossy surface. Media is then cleaned off.

Abrasive Flow Machining

• An abrasive media flows through a fixture holding the screws under pressure.
• The abrasive media mechanically erodes surface asperities through extrusion flow.
• Repeat cyclical flows with finer abrasives remove material layers to polish and refine the surface.
• No residual stressed or surface damage is imparted during smoothing.

Electrolytic Polishing

• Screws are submerged in temperature-controlled electrolytic bath.
• Electric current oxidizes and removes surface high points preferentially.
• Result is a uniform smoothing action without directional scratch patterns.
• Produces bright finishes while maintaining dimensions.

Proper titanium alloy screw polishing achieves required surface quality and dimensional tolerances for precision applications. The method selected depends on factors like batch sizes, surface requirements, cost, and throughput needs.

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