Burnishing is a machining process that can be used on a multitude of different materials to improve size and surface finish. Burnishing can eliminate secondary setups that are often needed to achieve a surface finish requirement. Burnishing is most suitable for metals up to 40 HRC. However, harder metals have been successfully burnished. Generally speaking, the harder the material, the greater the tool wear that can be expected. In all cases, burnishing tool wear surfaces can be replaced without replacing the entire tool.
So, to what materials does burnishing lend itself best?
Some high ductility materials that burnishing is used for include: annealed steel, stainless steel, aluminum, brass bronze, and malleable iron. Manufacturers in the fluid power/hydraulics industry have found success burnishing parts such as high-pressure tubes and hydraulic cylinders made from steel. With these parts, surface finish was critical. Burnishing was able to achieve a 6-7 Ra micro inch surface finish.
Some low ductility materials that burnishing lends itself to include: gray iron, nodular iron, heat treated steel, magnesium alloy, and hard copper alloys. There are a lot of different variables that can affect the surface finish outcome when burnishing a part. That being said, in production work involving surface textures having a 100 to 125 microinch machined finish, burnishing tools can produce a 2 to 16 microinch finish in a single pass. In bronze, aluminum, and steel, readings of 2 to 8 microinch can be achieved with a burnishing tool. In cast iron, a 12 to 24 microinch finish can be expected.
Overall, there are multiple materials to which burnishing lends itself. Depending on the application and part material, burnishing is a fantastic way to reduce cycle time, improve quality and eliminate secondary setups. Roller burnishing specifically has resulted in product improvement and cost savings to the hydraulic cylinder industry. Read some of the burnishing case studies linked below to see how burnishing can help you improve your process.