What is Burnishing Balls or Ballizing?
It is a metal-displacement process, in which an oversize ball is pushed through an undersize hole. The ball expands the hole by displacing an amount of material equal to the interference fit.
The ball displaces metal by plastic flow leaving a layer of denser metal on the ID wall. In some materials, the ID is work hardened by cold-work ballizing, and wear life of the ID wall increases. Also, because of its burnishing action, the ball improves surface finish and even “fills in” tiny surface imperfections on the ID.
Burnishing in manufacturing
There are several forms of burnishing processes, the most common are roller burnishing and ball burnishing (ballizing). In both cases, a burnishing tool rubs against the workpiece and plastically deforms its surface. The workpiece may be at ambient temperature, or heated to reduce the forces and wear on the tool. The tool is usually hardened and coated with special materials to increase its life.
Ball burnishing, burnishing balls, or ballizing, is a replacement for other bore finishing operations such as grinding, honing, or polishing. A ballizing tool consists of one or more over-sized balls that are pushed through a hole. The tool is similar to a broach, but instead of cutting away material, it plows it out of the way.
Ball burnishing is also used as a deburring operation. It is especially useful for removing the burr in the middle of a through hole that was drilled from both sides.
Roller burnishing, or surface rolling, is used on cylindrical, conical, or disk shaped workpieces. The tool resembles a roller bearing, but the rollers are fixed so they slide against the workpiece surface instead of rolling. It is simultaneously rotated and pressed into the workpiece. Typical applications for roller burnishing include hydraulic system components, shaft fillets, and sealing surfaces.
Burnishing balls also occurs to some extent in machining processes. In turning, burnishing occurs if the cutting tool is not sharp, if a large negative rake angle is used, if a very small depth of cut is used, or if the workpiece material is gummy. As a cutting tool wears, it becomes more blunt and the burnishing effect becomes more pronounced. In grinding, since the abrasive grains are randomly oriented and some are not sharp, there is always some amount of burnishing. This is one reason the grinding is less efficient and generates more heat than turning.
Results you can depend on
The results of burnishing balls are predictable and nearly foolproof. You can use it to size holes to tolerances of ± 0.0002″. This compares favorably to most reaming and grinding operations. Likewise, burnishing balls can finish a hole with a surface finish of 10 micro inch to a 5 micro inch tolerance.
When it comes to accuracy, it’s important to note that the accuracy of a burnishing ball determines results. Industrial Tectonics, precision ball manufacturer, offers balls in a variety of sizes and tolerances. We can help you determine the type of ball you need, taking into consideration your workpiece and the degree of precision you require. Where the toughest materials are involved that must be burnished, ITI tungsten carbide burnishing balls may be the solution you’re looking for.
Because ballizing uses only a precision ball for sizing and finishing, and not a complex tool assembly, small holes often are easier to ballize than to grind, hone, or roller burnish. In fact, you can ballize a hole as small as 0.020″. Defective parts are almost impossible to produce. Since balls arc self centering in holes, there’s no need to guide them. Consequently, the process lends itself to automation.