Burr (metal)

A burr is a raised edge or small piece of material remaining attached to a workpiece after a modification process.

It is usually an unwanted piece of material and is removed with a deburring tool in a process called 'deburring'. Burrs are most commonly created by machining operations, such as grinding, drilling, milling, engraving or turning. It may be present in the form of a fine wire on the edge of a freshly sharpened tool or as a raised portion of a surface; this type of burr is commonly formed when a hammer strikes a surface. Deburring accounts for a significant portion of manufacturing costs.

In the printmaking technique of drypoint, burr, which gives a rich fuzzy quality to the engraved line, is highly desirable—the great problem with the drypoint medium is that the burr rapidly diminishes after as few as ten impressions are printed.

There are three type of burrs that can be formed from machining operations: Poisson burr, rollover burr, and breakout burr. The rollover burr is the most common. Burrs may be classified by the physical manner of formation. Plastic deformation of material includes lateral flow (Poisson burr), bending (rollover burr), and tearing of material from the workpiece (tear burr). Solidification or redeposition of material results in a recast bead. Incomplete cutoff of material causes a cutoff projection.

Burrs can be minimized or prevented by considering materials, function, shape, and processing in the design and manufacturing engineering phases of product development.

Burrs in drilled holes cause fastener and material problems. Burrs cause more stress to be concentrated at the edges of holes, decreasing resistance to fracture and shortening fatigue life. They interfere with the seating of fasteners, causing damage to fastener or the assembly itself. Cracks caused by stress and strain can result in material failure. Burrs in holes also increase the risk of corrosion, which may be due to variations in the thickness of coatings on a rougher surface. Sharp corners tend to concentrate electrical charge, increasing the risk of static discharge. Burrs in moving parts increase unwanted friction and heat. Rough surfaces also result in problems with lubrication, as wear is increased at the interfaces of parts. This makes it necessary to replace them more frequently. Electrical charge buildup can cause corrosion.

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