Burnishing tools are used to impart a gloss or fine surface finish, often in processes that involve the cold working of metal surfaces. Burnishing tools are also used for the sizing and finishing of surfaces.

Features

A burnishing tool is used as a finishing tool. A burnishing machine is widely used for tool polishing, metal finishing, and ball burnishing. A burnishing tool develops a finished surface on turned or bored metal surfaces by performing a continuous planetary rotation of hardened rolls. The rotation of the rolls increases the yield point of the soft portion of the metal surface at the point of contact. This point of contact results in the deformation of the metal surface to generate a finished metal surface.

Types

There are many different types of burnishing tools. Examples include a roller burnishing tool and external taper shaft burnishing tool.

• A roller burnishing tool is a cold burnishing working process tool and is used for generating self-feed and non-feed design surfaces.

• An external taper shaft burnishing tool is a burnishing tool used for generating tape shafts in a workpiece.

Other burnishing tools are commonly available.

Specifications

There are several ways in which burnishing tools function. A burnishing tool works on the principle of the planetary system having hardened and tapered rolls, which are placed evenly in a retaining cage of a burnishing machine. A workpiece is tightly held in the burnishing tool and the tool mandrel applies pressure on the hold piece to finish the workpiece surface. Specifications of a burnishing tool vary depending on the type of burnishing tool used for a workpiece. The normal bore diameter of a burnishing tool can range from 5 mm to 26 mm. The adjustment range of burnishing tools depends on bore diameter. The adjustment range for a 5 mm to 7.50 mm bore diameter ranges from -0.1 to +0.20. The shank size for a ball burnishing should be MT-1 and the holder number for a burnishing tool should be H1. Burnishing tools are designed and manufactured to meet most industry specifications.

Applications

Burnishing tools are used in many applications. Examples of burnishing tools usage include:

• valve guides

• valve rods

• motor end covers

• fan rotor shafts

In addition, burnishing tools are also used in brake cylinders, hydraulic, pneumatic, and master cylinders. Burnishing tools should adhere to the standard used in the design of COBUM 3050 burnishing machines.

Different Approaches to Finer Roughness Values

Machining a metal surface leaves microscopic peaks and valleys that are called roughness. Surface finishing, whatever the method, is about reducing the roughness average (Ra) value of the surface. Basically, the Ra value is a formula that measures the average distance between the tops and bottoms of these points relative to the mean line, which cuts through them. The finer the surface finish, the shallower the valleys and shorter the peaks.

The first noticeable difference between abrading and burnishing a surface to accomplish this peak and valley reduction is that the former removes metal from the part while the latter does not. Abrasive finishing cuts or tears away the peaks in the surface, thereby bringing the average peak and valley distances closer together. But Cogsdill says that this also leaves sharp projections in the contact plane of the machined surface. Burnishing doesn’t have this problem. At first glance, a burnished part looks as if the metal surface has been smeared smooth. But that would be incorrect. The burnishing tool’s polished and hardened rollers actually perform cold flowing of the surface and subsurface material, which results in a controlled plastic deformation of the part.