Roller Burnishing is a method to make the workpiece, which has passed through the pre-machining, smooth and hard. It is possible to process any kind of metallic material by using this method. The roller burnishing is done by contacting of the rollers on the surface of the workpiece by the help of a precision mechanism. When such a contact is obtained, the workpiece or the tool turns at a specified speed, then the rollers go forward on the workpiece’s surface by rotation. In addition, a pressure is applied on the surface of the workpiece with a certain force thus the process of roller burnishing is achieved.
Part Quality And Process Improvements
Roller burnishing was first applied in American industry in the 1930s to improve the fatigue life of railroad car axles and rotating machinery shafts. By the 1960s, roller burnishing was more widely applied, particularly in the automotive industry, as other process advantages were recognized. The primary benefits, related to part quality, are as follows.
- Very accurate size control (tolerances within 0.0005 inch or better, depending on material type and other variables).
- Fine surface finishes (typically between 1 to 10 microinches Ra).
- Increased surface hardness (by as much as 5 to 10 percent or more).
Other process advantages include:
- Reduced cycle time (parts are processed in seconds).
- It is cleaner than honing or other abrasive finishing methods.
- It can often eliminate slower and more costly finishing processes and secondary operations such as grinding, honing or lapping.
An Array Of Designs
Roller burnishing tools can be designed and built for virtually any part configuration. Standard tools are offered for burnishing inside and outside diameters. Custom tool designs are made to order for faces, internal and external tapers, contours, spheres, and fillets. External burnishing machines are available for burnishing cylindrical surfaces of any length.
The most common burnishing tool designs are rotary tools used to burnish IDs or ODs. Multiple rollers, mounted in a retaining cage, rotate and bear upon a mandrel or race. The tools are adjustable, typically over a range of 0.040 inch for a given nominal size. Adjustments are typically made in 0.0001-inch increments by changing the position of the tapered rollers in relation to the inversely tapered mandrel or race so as to alter the effective tool diameter.
Other tool designs use a single roll so the tool can be more versatile, rather than being limited to one particular part configuration and nominal size. A single-roll burnishing tool can be applied to shafts, faces, tapers, contours or large IDs. Tool designs are offered in both boring bar and turning holder styles. Another versatile burnishing tool design uses a replaceable, polished diamond insert instead of a roller. The diamond insert is mounted in a turning holder. The tool produces low microinch finishes on shafts or faces of any diameter.
Part Preparation And Operating Parameters
Only one fast pass of the burnishing tool is required for simultaneous sizing, finishing and work-hardening of part surfaces, provided that proper attention is given to part preparation and tool adjustment. Because no metal is removed, a consistent and tear-free surface is required so the peaks on the machined surface can flow uniformly into the valleys under roll pressure.
An ideally prepared part surface for burnishing is a bored or turned surface of 80 to 120 microinches (Ra). This allows for greater displacement of material on the work surface than would a smoother prefinish, thereby enhancing the sizing capability of the burnishing tool. It also allows the tolerance on the prefinish to be much greater than it would be on a smoother prefinish.
Any ductile or malleable metal can be burnished (steel, stainless, alloys, cast iron, aluminum, copper, brass, bronze and so forth). Because the metal must be capable of cold flowing under roll pressure, hardness normally should not exceed 40 on the Rockwell “C” scale.
Speeds and feeds are not critical to successful tool operation.
Any standard grade, lightweight, low-viscosity lubricating oil, or any mineral, sulfur or soluble oil compatible with the metal or alloy to be burnished, is suitable for most metals. Coolant filtration is very important to keep metal particles or grit from being rolled into the part surface.
Roller burnishing is a faster, cleaner, more effective and more economical method of sizing and finishing parts to exacting specifications. Parts can often be burnished on the original machine on which they were produced, thereby eliminating secondary operations. RBT Burnishing tools can help the user achieve significant time and cost savings while improving part quality.