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A burr is a raised edge or small piece of material that remains 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 Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
operations, such as grinding,
drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...
, milling,
engraving Engraving is the practice of incising a design onto a hard, usually flat surface by cutting grooves into it with a burin. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an in ...
or
turning Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates. Usually the term "turning" is reserved for the generation ...
. 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 A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nails into wood, to shape metal (as wi ...
strikes a surface. Deburring accounts for a significant portion of manufacturing costs. In the
printmaking Printmaking is the process of creating artworks by printing, normally on paper, but also on fabric, wood, metal, and other surfaces. "Traditional printmaking" normally covers only the process of creating prints using a hand processed techniqu ...
technique of
drypoint Drypoint is a printmaking technique of the intaglio family, in which an image is incised into a plate (or "matrix") with a hard-pointed "needle" of sharp metal or diamond point. In principle, the method is practically identical to engraving. The ...
, 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.


Types

There are three types 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.Tool and Manufacturing Engineers Handbook (TMEH), Volume 3, Materials, Finishing and Coating. Society of Manufacturing Engineers, 1985. 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.


Deburring

There are many deburring processes, but the most common are mass-finishing, spindle finishing,
media blasting Sandblasting, sometimes known as abrasive blasting, is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface or remove su ...
, sanding, grinding, wire brushing, abrasive flow machining, electrochemical deburring, electropolishing, thermal energy method,
machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
, water jet deburring, and manual deburring.


Manual deburring

''Manual deburring'' is the most common deburring process because it is the most flexible process. It also only requires low cost tools and allows for instant inspection.. Manual deburring is either done with tools like scrapers, files, sandpaper, stones and reamers or with handheld power tools that use abrasive points, sandpaper, or cutters similar to those used to deburr during machining.


Electrochemical deburring

''Electrochemical deburring'' is the use of
electrochemical machining Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and is used for working extremely hard materials or materials that are difficult to machine using conventional me ...
to deburr precision work pieces and edges that are hard-to-reach, such as intersecting holes. The process uses a salt or
glycol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. The most common industrial diol is e ...
solution and electricity to dissolve the burr. The electric current is applied with a specialized tool to reach the burr location. Burrs are removed in 5 to 10 seconds, while the rest of the work piece is unaffected.


Thermal energy method

''Thermal energy method'' (TEM), also known as ''thermal deburring'', is a deburring process used to remove hard-to-reach burrs or burrs from multiple surfaces at the same time. The process uses an explosive gas mixture to provide thermal energy to burn off the burrs. It is the fastest burr removal process, requiring only 20 milliseconds to remove a burr. The process starts by loading the workpiece into an explosion-proof chamber, which is then sealed and clamped with approximately . The chamber is then evacuated of air and filled with an oxygen and fuel mix; this mixture is pressurized to . An electrical igniter then ignites the mixture, which burns for approximately 20 milliseconds, causing all of the sharp corners and burrs to burn away. The peak temperature reaches .


Cryogenic deburring

''Cryogenic deburring'' is a
cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
process used to remove burrs and flash from
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
and die cast workpieces. The process works by tumbling and/or abrasively blasting the workpieces at cryogenic temperature levels. The low temperatures (approximately ) are achieved using
liquid nitrogen Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wid ...
, liquid
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, or
dry ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily ...
. This low temperature brings the material below its embrittlement temperature, which causes the flash or burrs to be easily removed via tumbling or media blasting. This process has been around since the 1960s to deflash plastic and rubber. Common materials that are typically cryogenically deburred with blast media include PEEK, nylon, Teflon, Delrin, polypropylene, polycarbonate, acetal, PTFE, PET, HDPE, PVC, ABS and many others.


Mechanical deburring

''Mechanical deburring'' is a deburring process that either mechanically grinds a burr off of metal or rolls the edge of the dangerous slit or sheared metal burrs into itself. Rolled mechanical deburring was first developed in the 1960s by Walter W. Gauer from Gauer Metal Product, Inc. as a means to speed up the process of hand deburring strips of metal that were used in bakery racks.


Water Jet Deburring

One of the main benefits of ''waterjet deburring'' is a high level of precision and repeatability - and for this reason, CNC control is used. This eco-friendly process uses high-pressure water to remove loose burrs and chips even in deep holes – all while leaving the parts cleaner and free of debris. Pressurized water is precisely focused via CNC control to remove burrs and chips in and around parts. Depending on the cleanliness specifications, this can be performed submerged or in an open-air environment. Open-air washing/deburring targets specific areas of the part where the water jet is focused. Submerged will clean the entire part, internally and externally.


See also

*
Swarf Swarf, also known as chips or by other process-specific names (such as turnings, filings, or shavings), are pieces of metal, wood, or plastic that are the debris or waste resulting from machining, woodworking, or similar subtractive (material-r ...
* Fillet and
chamfer A chamfer or is a transitional edge between two faces of an object. Sometimes defined as a form of bevel, it is often created at a 45° angle between two adjoining right-angled faces. Chamfers are frequently used in machining, carpentry, ...
, edge features designed to reduce burrs.


References


Bibliography

* *{{Citation , last = Warfield , first = Bob , title = Definitive Guide to Deburring for CNC , publisher = CNCCookbook , year = 2018 , url = https://www.cnccookbook.com/deburring-for-cnc/ , postscript =. Metalworking terminology Printmaking Cryogenics Plastics industry