Polishing

Polishing refines surface roughness to achieve low Ra finishes, improved appearance, and better cleanability by controlled removal of a thin material layer.

Overview

Polishing is a surface finishing process that smooths and refines machined, cast, or formed parts by removing a thin layer of material. It ranges from manual abrasive polishing and buffing, to highly controlled lapping and electropolishing for critical surfaces. The goal is usually a lower Ra, improved appearance, reduced friction, or enhanced cleanability and corrosion behavior.

You apply polishing when dimensional geometry is already correct and you need a smoother, more uniform surface—on either the whole part or critical regions. It works well for stainless, aluminum, tool steels, titanium, and many nickel alloys. Tradeoffs: it adds cost and lead time, can soften edges, and slightly changes dimensions. Manual polishing is operator‑sensitive and less consistent; lapping and electropolishing give more repeatable results but need tighter process control and good fixturing. For engineering drawings, specify surface finish (Ra/Rz), zones that matter, and acceptable cosmetic standards so shops can choose the right polishing method and quote accurately.

Common Materials

  • Stainless steel 304
  • Aluminum 6061
  • Tool steel H13
  • Titanium Grade 5
  • Brass
  • Inconel 718

Tolerances

Surface finish to ~Ra 0.01–0.2 µm; dimensional change typically ±0.0005–0.002" depending on process and coverage

Applications

  • Surgical instruments and implants
  • Injection molds and dies
  • Food and pharmaceutical processing equipment
  • Optical and instrumentation housings
  • Turbine blades and aero hardware
  • High-end consumer hardware and enclosures

When to Choose Polishing

Choose polishing when the part is already to size and you need a lower Ra, better aesthetics, or improved cleanability on exposed or functional surfaces. It suits low to medium volumes, higher-value parts, and any component where surface finish impacts sealing, wear, or the customer’s perception of quality.

vs Machined Surface Finishing

Choose polishing when as-machined finishes or standard toolpath optimization cannot meet required Ra, gloss, or cosmetic level. Polishing is ideal for breaking tool marks, removing minor defects, and achieving mirror or near-mirror finishes on critical sealing or aesthetic surfaces.

vs Coatings

Choose polishing when you need a smooth bare-metal surface without adding thickness, changing color, or complicating rework. Polishing is often used before coatings to reduce roughness so thin films lay down uniformly and cosmetic standards are met.

vs Painting

Choose polishing when you want visible metal with a premium look, such as brushed or mirror finishes, or when paint thickness and potential chipping are unacceptable. Polishing is also preferred in hygienic and high-temperature environments where paint would fail or contaminate the process.

vs Surface Texturing & Marking

Choose polishing when you need a low-roughness, low-friction surface rather than functional textures, micro-patterns, or permanent markings. You can polish the bulk surface, then selectively texture or mark limited areas for grip, branding, or identification.

vs Hard Coatings

Choose polishing when primary goals are aesthetics, cleanability, or moderate wear improvement without the cost and process complexity of hard coatings. Often, surfaces are polished first, then selectively hard coated only where high wear or extreme environments justify the added expense.

Design Considerations

  • Specify quantitative surface finish requirements (Ra/Rz and area zones) instead of vague terms like “polish” or “mirror finish”
  • Leave controlled stock (often 0.0005–0.003" per side) in polishing areas so final dimensions land in tolerance after material removal
  • Avoid deep, narrow grooves or sharp internal corners in cosmetic areas; these are hard to reach and drive up manual polishing time and cost
  • Add simple, robust fixturing or clamping features so parts can be held securely during polishing without marring critical surfaces
  • Clearly separate functional and purely cosmetic regions on the drawing, accepting higher Ra where it does not matter to reduce cost
  • Select alloys compatible with the intended process (e.g., good electropolishing response for stainless, adequate hardness for lapping) and flag any heat treatment that will change polishability