Burnishing on hollow cylinder

What is Burnishing?

Burnishing is the process of flattening the surface of the workpiece plastically by using a smooth but hard tool that is rubbed on the surface of the workpiece by applying a certain amount of pressure. This pressure exceeds the yield strength of the material to undergo plastic deformation. Burnishing makes the surface flat, smooth and shiny. In the process, chips or material removal are not taking place from the workpiece. Burnishing is also named a superfinishing process or Ballizing process.

Any machine element or workpiece have lots of peaks and valleys, which causes imperfection in the surface finish. So, to flatten the surface and improve the surface finishing of the workpiece, a burnishing operation is carried out.

By adjusting the tool forces, the height of the peak and depth of the valley can reduce. It enhances surface finishing properties which lead to getting the mirror-like surface finish.

Burnishing is a type of cold working process which performs on softer materials such as aluminum, brass, zinc, plastic, and low-carbon steel. Burnishing improves surface roughness, surface finish, fatigue, and corrosion resistance by undergoing plastic deformation. It does not remove any material or chips which leads to zero wastage of material. It causes a mirror-like surface finish.

The burnishing process is mostly using in the automotive industry to finish pistons, brakes, clutches, and valves.

Inspection and rate of burnishing can be done by following the process.

Direct surface inspection by an opened eye

  • This inspection can perform by just seeing the workpiece with the naked eye. Any hills or roughness on the surface of the workpiece can detect by our open eyes.

Direct measurement by Using appropriate machine

  • In this method, the rate of burnishing can be calculated by measuring the numerical value of the surface finish.
  • The stylus probe is one of the preferable instruments using to measure the numerical value.
  • This stylus moves on the workpiece and depends upon the roughness of the surface. This movement generates a voltage signal and pneumatic element, which measures the actual surface finish.

Two types of burnishing process based on type of tool used.

Roller Burnishing

The roller burnishing process consists of one or many rollers supported by shank as shown in the video. In this case, multiple rollers are arranged in series by keeping a certain distance and supported by a shank.

As shown in the video, a single roller burnishing tool connects to a CNC, milling, or lathe machine. By adjusting the handle of the machine, the burnishing roller tool comes in contact with the workpiece. So, the roller gets rotated and getting rubbed with the workpiece, and a burnishing operation occurs.

In some cases, the workpiece rotates, and the burnishing roller tool gets inserted into the workpiece to do the burnishing operation. This roller burnishing gives excellent flatness and the shininess of the workpiece increases. The main aim of roller burnishing is to get a high-quality surface finish.

Ball Burnishing

As the name suggests, it consists of a spherical ball instead of a roller. This tool consists of one or multiple spherical balls arranged in series, which are supported by shank as shown in the video.

The movement of the spherical ball can be controlled by adjusting the flow of hydraulic fluid. In some cases, spring is using to control the position of the spherical ball.

The above video shows a schematic diagram of a single rollerball burnishing process. In this case, by adjusting the flow of hydraulic fluid, balls come in contact with the workpiece, which causes the spherical ball to press against with workpiece, and a burnishing operation occurs.

The force required to do a burnishing operation may be varies depending upon the flow of hydraulic fluid.

3 Common types of burnishing tools:

There are the following 3 types of burnishing tools that are widely using in the industry.

Diamond Burnishing Tool: 

  • When we talk about burnishing, the diamond burnishing tool is one of the regularly used tools in burnishing.
  • Diamond burnishing tool is suitable for a variety of materials.
  • These tools are cost-effective and produce quicker flatten the workpiece.
  • Due to these types of advantages, it does not require any secondary process like grinding.

Multi-Roll Burnishing Tool

  • As the name suggests, it has multiple rollers on the tool, which offer accurate sizing, and improves the surface finish of the workpiece to the next level.
  • Multi-Roll burnishing tools can produce 2-8 RA micro-Inch in just one stroke.
  • Multi-Roll burnishing tools are using in any type of machines such as CNC or lathe.

Single Carbide Roll Burnishing Tool

  • Single carbide roll tool is using to produce 4-8 RA micro-inch in just one stroke
  • There is no need for any secondary operation so, it saves too much cost.
  • The single carbide roll tool has longer life as compared to others. Because it is made up of carbide.

Advantages

  1. No material removoval from the workpiece so, no chances of wastage.
  2. Less noisy as compared to other surface finishing process.
  3. Time-saving process.
  4. Burnishing workpieces are undergoing strain hardening so, the hardness of the workpiece is increases .
  5. No use of coolant in the burnishing process.
  6. No need of lubrication.
  7. Created loner life tools.
  8. Used in all types of machine tools.
  9. Improves surface finishing and flatness.
  10. The burnished workpiece is corrosive resistant by removing roughness and mini notches.
  11. Low cost of machine and tools.
  12. It completes all processes in just one setting.

Disadvantages

  1. Suitable for certain materials such as aluminum, brass, zinc, or plastic
  2. Require numerical assessment to measure the smoothness of workpiece
  3. The production rate is high so, not suitable for mass production

Application

  1. Automobile Industry
  2. Aircraft Industry
  3. Home Appliances
  4. Motor and pump industry
  5. Machine tool
  6. Hydraulic System
  7. Food Industry
  8. Turbine Blades
Why is burnishing used?

Burnishing is used to make the workpiece surface flat, smooth and shiny. Pressure applied by the burnishing tool deforms the surface of the workpiece plastically to make it flat and shiny.

Does burnishing remove material?

Burnishing is an advanced surface finishing process where no material is removed from the workpiece surface.