The efficient process has replaced separate time-consuming OD finish grinding and unpredictable manual polishing operations on a customer’s steel forming rolls. The Elliott S2327 single-roll OD burnishing tool allows the roll shaft to be turned and then finish burnished in a single operation, which is now maintaining a surface texture that is half the specified tolerance, repeating a finish within 0.4 Ra.
Says Mollart sales manager Mark Dore: “The customer elected to change processes, due to problems of inconsistency from the manual polishing process and the time taken to achieve the specified finish. We were then able to add the bonus of eliminating the grinding process plus the logistics of moving components around the workshop.”
The Elliott single roll OD burnishing tool is suitable for use in both manual or CNC lathes and machining centres, and is able to create a controlled finish on diameters, angles, radii and faces.The contact roll can be supplied with a selection of radii of between 0.8 and 3 mm to suit the application.As the roll is made from carbide this means production life is extended and the roll can easily be replaced or refurbished. In order to set operational speeds and feeds, these normally bear a close relationship to those applied in the finished pre-sizing cutting operations while the toolpath replicates the finish machining operation.
In addition to surface finish, the roller burnishing tool enables a constant size to be maintained, provided the pre-roll size tolerance is held. The process also increases surface hardness as it plasticises and generates a constant level of surface stress in the material. If this stress is higher than the yield strength of the material, the surface begins to flow and, as the roll progresses across the material, any elastic deformed material springs back pushing the deformed zone into a state of compression.
The surface peaks left from the pre-sizing operation are pressed down almost vertically as the material flows into the valleys, which can typically change the part diameter by 0.01 mm between the peaks as it eliminates surface roughness. Here, the rate of feed applied to the carbide roller suppresses the plasticised material, which also prevents any tendency of the flow reversing. The clearance angle applied to the roller also ensures the surface does not become over burnished.
