Surface Finish of Custom Parts: 7 Types of Polishing

Polishing is one of the methods of surface treatment of parts, which can improve the surface finish of parts, improve surface quality, increase functions, improve accuracy, and extend service life. Polishing not only improves the appearance of the product but also plays an important role in functionality.

Common copper and steel are very easy to oxidize during processing, and various spots and marks will appear on the surface. These phenomena directly affect the appearance and use of the product. After the polishing process, the surface of the product is no longer oxidized and becomes smoother.

The application of the polishing process is not limited to metallic materials. Materials such as plastic, wood, and ceramics are all suitable for polishing. In this article, the relevant knowledge and skills about the polishing process are explained in detail. Share our work experience with you, hoping to be of more help to you in this regard.

7 methods of polishing and their applications

There are many polishing methods. How to choose a more suitable method requires a combination of multiple factors. Each polishing method has its advantages and disadvantages.

Next, there are 7 commonly used polishing processes for you to choose from. Let’s work together to find a surface treatment that’s best for your product.

1. Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) is a surface polishing process that combines mechanical friction and auxiliary chemicals to achieve surface polishing of semiconductor products.

The CMP process requires the use of polishing pads, abrasive particles and chemical slurries to remove surface material.


  • Semiconductor Manufacturing: CMP, or chemical-mechanical polishing, is a crucial step that makes sure we can build complex circuits on perfectly flat silicon wafers.
  • Photovoltaic industry: For solar cell manufacturing, surface irregularities are removed from silicon wafers, thereby improving efficiency by reducing defects that can impede the flow of electrons.
  • Optics: For optical components such as lenses and mirrors, CMP provides the high degree of smoothness and finish required for efficient light transmission or reflection without distortion.
  • Hard drive industry: Used to polish hard drive substrates to obtain an ultra-smooth surface, which is crucial for increasing data storage density and read and write speeds.
  • Integrated circuit interconnection: CMP flattens the dielectric material between metal layers to complete reliable connections within the integrated circuit.


  • Suitable for flat and large area polishing
  • Can meet ultra-high flatness requirements
  • Reduce defective rate and reduce defects
  • Accurately control material removal rate, down to nanometer tolerances
  • Applicable to a variety of materials: dielectric, polysilicon, metal materials
  • Selective local processing
  • Improve electrical performance and achieve better circuit performance


  • Cost factors: CMP equipment and consumables are expensive, and strict cleaning processes are required during the production process
  • Pollution risk: The chemical slurry used in CMP needs to be managed in a compliant and reasonable manner to avoid secondary pollution
  • Low yield rate: During CMP processing, the first pass rate of products is low, the efficiency is low, and the accuracy of the equipment is required to be high

2.Electrolytic Polishing

Electrolytic polishing can also be said to be electrochemical polishing. It is a finishing process that soaks metal parts in a chemical solution and removes burrs and excess material on the metal surface to improve the surface finish.

The metal parts acts as the anode. The cathode is made of lead or stainless steel material and does not contact the parts. When voltage is applied, an anodic reaction occurs on the surface of the metal parts, and oxidation and dissolution occur. The burrs or peaks on the surface of the parts are evenly removed under the interaction of current to achieve a smooth and smooth surface of the parts.

It is different from electroplating, which forms a smooth coating on the surface of the part, while electropolishing removes a thin layer from the metal surface.


  • Medical devices & equipment: surgical instruments, orthopedic implants such as joint replacements, and medical precision equipment parts.
  • Food processing equipment: large mixing tanks, blades for cutting or mixing food, conveyor belts and packaging machinery parts.
  • Aerospace: turbine blades, etc.
  • Auto parts: bearings, precision parts.
  • Consumer goods: tableware, bathroom, jewelry and watch parts.
  • Architectural metalwork: handrails, door handles and elevator panels made of stainless steel.
  • Pipelines: Oil and gas pipelines.


  • Stronger corrosion resistance and long-lasting surface finish
  • There are no requirements on the structure of the parts, meeting the requirements of various shapes of parts
  • Short production cycle and low-cost
  • Reduce the generation of pollutants and have excellent environmental performance
  • Able to detect defects on material surfaces in time


  • Limited to metal materials and cannot be used for surface treatment of plastic materials
  • The investment cost of equipment and tools is high
  • Must meet environmental standards

3. Mechanical polishing


Mechanical polishing is a processing method that uses repeated friction between abrasives and the surface of parts to remove protruding burrs and excess material on the surface to achieve a smooth surface.

Traditional manual mechanical polishing requires the use of sandpaper, cloth wheels, grinding rods, flat grinders, disc polishers, polishing agents, etc.

Since the efficiency of manual mechanical polishing is too low, there are more polishing methods in the metal polishing process. The polishing equipment currently used on the market is very mature, such as centerless internal polishing machine, shaft polishing machine, mirror jet polishing machine, dry polishing machine, Alpha oblique polishing machines, etc.


  • Machining manufacturing: Prototype parts (3D parts) are often mechanically polished to remove surface knives and defects.
  • Automotive industry: wheels, interior trim parts, exhaust systems.
  • Medical devices: joint implants, surgical equipment.
  • Mold manufacturing: mold cavity, mold inserts, mold accessories.


  • Surface changes can be observed at any time
  • There are many options for mechanical polishing equipment
  • Customizable mechanical polishing equipment


  • Longer processing time
  • Large investment in equipment
  • Takes up a lot of space

4. Ultrasonic Polishing


Ultrasonic polishing uses high-frequency ultrasonic oscillation to repeatedly rub the abrasive on the surface of the part to achieve a high-smooth surface. If corrosive and electrolytic materials are added to the abrasive, it will help the surface of the part to be brightened quickly.

Ultrasonic polishing is also a combination of mechanical polishing and chemical polishing, but the principles and abrasives used are different.


  • Moldmaking: Sealing and polishing of blind holes, slits and narrow grooves for injection molds and die casting molds
  • Mechanical parts manufacturing: complex shapes, curved surfaces, irregular parts
  • Electronics manufacturing: Connecting parts often requires smooth contact surfaces


  • Suitable for a variety of metal and plastic materials
  • Automated mass production possible
  • Minimal damage to the surface of parts
  • Suitable for complex geometries


  • High equipment cost
  • Need professional training
  • High maintenance costs

5. Abrasive Flow Polishing(AFF)

Abrasive flow polishing is a precision surface treatment technology of cold processing, also known as extrusion grinding. It is a surface treatment process that uses a mixture of abrasives and high molecular polymers to polish.

It uses hydraulic pressure to push the abrasive flow through the holes and grooves of the part, effectively rubbing the inner wall surface. Suitable for complex internal geometries, ensuring a consistent and refined finish.


  • Medical equipment: precision tubing parts, micro-tube parts, diaphragm valves, flow studios.
  • 3D printing & rapid prototyping: parts with complex curved shapes.
  • Auto parts: stainless steel bearings, flange parts, gears, new energy vehicle motor cooling water channels.
  • Aerospace: blade internal combustion engine parts, valve parts, turbocharger casing.
  • High-precision molds: high-speed stamping concave and convex molds, tungsten steel screw molds, tungsten steel wire drawing molds, aluminum extrusion molds, powder metallurgy molds, ceramic precision molds.


  • Increase productivity
  • Reduce personnel costs
  • Abrasives are recyclable and more environmentally friendly
  • Parts that meet complex internal structures


  • High equipment and process costs
  • Polishing is difficult and cannot meet ultra-high precision surface requirements

6. Magnetic Polishing

The grinding media and liquid solution (brightener) are placed together in a container equipped with magnets. When the equipment is running, the motor drives the magnetic needle in the magnetic field to rotate.

Based on the structure of the product and the parameters required for polishing, set a reasonable time and intensity to perform automated work.

The generated magnetic field causes the grinding media to move and circulate rapidly around the metal parts, resulting in high-speed tumbling and friction.


  • CNC machining: metal prototype parts, lathe joint parts,heat sink.
  • Kitchenware products: stainless steel liner, stainless steel shell, stainless steel bracket, metal shell.
  • Auto parts: die-cast parts, metal LOGO signs.
  • Medical equipment: surgical scissors, metal equipment casings, medicine storage trays.
  • Metal parts: stamping parts, stainless steel parts, precision springs,hardware tools.


  • Ideal for small, complex parts
  • No manual intervention required, saving labor costs
  • Low processing cost


  • Abrasive materials require regular cleaning
  • One-time equipment cost is high

7. Vibration Polishing


Vibration polishing is the most original semi-automatic polishing process. It removes impurities, oxide layers and defects on the surface of materials through vibration and friction.

Polishing work requires the use of polishing abrasives, polishing slurries, polishing brighteners, water, etc. for mixing and friction to ultimately achieve a perfect surface finish.


  • Automobile manufacturing: automobile wheels, batch automobile parts surface treatment
  • Jewelry: gold bracelets, silver rings, jade, silver necklaces
  • Metal casting: bicycle parts, outdoor sports equipment parts
  • Wood products: polishing the surface of wood products
  • Sheet metal stamping: remove burrs and defects on the surface of parts
  • CNC machining: surface polishing of parts


  • Suitable for a variety of materials, metal, plastic, wood and other materials
  • Can process batches of simple small parts at one time
  • Equipment investment is not high
  • Save labor costs


  • Need professional training
  • Not suitable for smaller parts with complex internal structures
  • Generate large amounts of wastewater

TiRapid’s Polishing Solutions

Surface finish is very important in prototyping and low-volume production. Tirapid’s mechanical engineers select the best surface processing solution based on your product requirements. Polishing is also one of the final production processes for prototypes.

Tirapid team help you and your team solve various polishing problems through the manufacturing of thousands of polishing products. Not only is the quality superior to the same industry, but it also has competitive delivery capabilities.

Choosing the best transportation team, safe and fast delivery is also one of our team’s tasks.


Tips for Polishing Prototype Manufactured

In this section, let’s explore some more techniques to achieve a great polish on your prototype parts.

1.The working places of rough grinding and fine polishing must be separated

2.During polishing work, keep the surface of prototype parts clean

3.Use an appropriate amount of polishing fluid during mirror polishing to cool the surface and reduce frictio

4.For coarse polishing, you can choose rotating surface polishing at 35000~40000r/min

5.Semi-finish polishing uses sandpaper and kerosene, from coarse to fine: 400#, 600#, 800#, 1000#, 1200#, 1500#

6.Fine polishing uses a mixture of diamond abrasive paste and polishing cloth

7.Wheel for polishing. The usual sequence is: 1800#, 3000#, 8000#

8.Stainless steel prototype chooses brightener that matches the material

9.Before plastic mold polishing, the surface of the part must be smoothed with sandpaper



1. What materials is the polishing process suitable for?

Most materials can be polished. In CNC machining manufacturing, the most commonly used materials are metal and plastic materials. Common materials include:

  • Metals: Metals such as stainless steel, aluminum, brass, copper, silver, gold and silver are polished to obtain a reflective surface.
  • Plastics: Plastics such as acrylic (PMMA), polycarbonate (PC), ABS, ASA, etc. can be polished to achieve transparency or gloss.
  • Glass: Optical glass and other high-purity silica glasses, finely polished with cerium oxide or other special compounds.
  • Ceramics: Advanced ceramics often require polishing to achieve a smooth surface to minimize friction or wear.
  • Semiconductors: Chemical mechanical polishing of silicon wafers during the production of electronic components.

Each material requires selection of abrasives and polishing processes based on the characteristics of the material to ultimately meet the product’s optimal surface finish and performance requirements.

2. How do you choose the best polishing process for your prototype parts?

Choosing a suitable polishing process is crucial to the surface and accuracy of the product. It can directly affect the appearance and functionality of the product.

  • Make a decision based on the material. If it is a metal part, the optional polishing technologies are: chemical mechanical polishing, mechanical polishing, electrolytic polishing, magnetic polishing, abrasive flow polishing, vibration grinding polishing, etc., covering almost all polishing technology.

Then, for plastic parts, you can only choose mechanical polishing, manual polishing and flame polishing.

  • According to the structure of the part, if it is a flat metal part, all polishing techniques are applicable. If it has a complex structure, is porous, and has a multi-faceted shape, you can choose electrolytic polishing, magnetic polishing, or abrasive flow polishing.
  • According to the function of the part, mechanical polishing can satisfy products with low tolerance requirements. Other polishing technologies have very little impact on the accuracy of the part.
  • According to the surface requirements of the part, magnetic polishing will form a frost-like effect on the surface. If the surface needs to be ultra-smooth and bright, magnetic polishing is not recommended.
  • The shape and size of the product need to be considered. The size of the product determines the size of the equipment and ease of operation.

3. What factors affect the vibration polishing effect?

Whether vibration polishing can achieve the ideal surface effect depends on several major factors: the choice of grinding stone, the choice of abrasive, the proportion of water, and the shape and material of the part.

Grinding stone types:

Ceramic grinding stone: has grinding power and is suitable for rough grinding, medium grinding and fine grinding.

Porcelain grinding stone: no grinding force, suitable for polishing and mirror processing.

Plastic grinding stone: suitable for soft parts, such as copper, aluminum, copper alloy, etc.

Metal grinding media: suitable for steel, mainly stainless steel, mainly used for metal polishing.


Petting technology can help your product surface lift and cleanliness, remove defects, find the problem of material surface, and enhance your function. In the article, 7 polishing processes and their applications are discussed in detail.

In Tirapid team, we have enough practical experience to help you solve the polishing problem. We provide you with a polishing solution that does not increase product cost and improves product surface. Contact us right away and let us work together.

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