The Benefits of Burnishing
Burnishing isn’t necessarily bad. If it happens in a controlled manner, it can have desirable effects. Burnishing procedures are used in manufacturing to enhance the size, shape, surface finish, or surface hardness of a workpiece. It’s basically. The advantages of burnishing often include: Combats fatigue failure, prevents corrosion and stress corrosion, textures surfaces to get rid of visual defects, closes porosity, creates surface compressive residual pressure.
There are several forms of burnishing processes, the most frequent are roller burnishing and ball burnishing (a subset of which is also called ballizing). In both scenarios, a burnishing tool runs contrary to the workpiece and plastically deforms its surface. In some cases of the latter case (and always in ballizing), it rubs, in the former it generally moves and rolls. The workpiece can be at ambient temperature, or warmed to decrease the forces and wear on the tool. The tool is hardened and coated to boost its life.
Ball burnishing, or ballizing, is a replacement for other bore finishing operations like grinding, honing, or polishing. A ballizing tool consists of one or more over-sized balls that are pushed through a pit. The tool is somewhat like a broach, but rather than cutting away material, it plows it out of the way.
Ball burnishing is also utilized as a deburring operation. It is particularly helpful for removing the burr in the center of a through hole that was drilled from both sides.
Ball burnishing tools of another type are sometimes utilised in CNC milling centers to follow a ball-nosed grinding operation: the hardened ball is put along a zig-zag toolpath in a holder similar to a ball-point pencil, except the ‘ink’ is pressurised, recycled lubricant. This combines the productivity of a machined finish which is accomplished by a ‘semi-finishing’ cut, using a much better finish than accessible with slow and time consuming finish cuts. The feedrate for burnishing is that correlated with ‘rapid traverse’ rather than complete machining.
Roller burnishing, or surface rolling, is utilized on cylindrical, conical, or disk shaped workpieces. The tool looks like a roller position, but the rollers are usually very slightly tapered so that their envelope diameter can be accurately adjusted. The pliers typically rotate within a cage, like in a roller bearing. Common programs for roller burnishing contain hydraulic system parts, rotating fillets, and sealing surfaces. Very close control of size could be exercised.
Burnishing also occurs to some degree in machining processes. In turning, burnishing happens if the cutting tool is not sharp, if a large negative rake angle is used, in case a tiny depth of cut is used, or if the workpiece material is gummy. As a cutting tool wears, it grows more blunt and the burnishing effect gets more pronounced. In grinding, since the abrasive grains are randomly oriented and some aren’t sharp, there is always some level of burnishing. This is one reason that the grinding is less effective and creates more heat than just turning. In drilling, burnishing happens with drills which have lands to burnish the material as it moves into it. Regular twist drills or straight fluted drills have two lands to direct them through the hole. On burnishing drills there are 4 or more lands, similar to reamers.
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