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June 2009 • www.sme.org/manufacturingengineering 57

Deburring &Finishing

Edge finishing is a relatively new term in manufacturing. It’s a new and deeper focus onwhat many used to call deburring, edge honing, edge preparation, edge prepping, bur-ring, chamfering, or edge blending. Edge finishing goes beyond any of those definitions.Deburring, which is often considered wasted effort by managers, wrongly carries a neg-

ative connotation. In reality, deburring and edge-finishing processes add many benefits toparts—they create highly desirable edge quality—the quality most products need.

Edge preparation iscritical to many parts;in fact, edge prepabsolutely adds qualityto the product

Burrs on commercial miniature ground tap.

LaRoux K. GillespieSecretary/TreasurerSME Executive CommitteeDearborn, MIE-mail: [email protected]

EDGE FINISHING—PRODUCT ENHANCEMENTOR WASTED COST?

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58 www.sme.org/manufacturingengineering • June 2009

quality edge conditions that ensurelong life. But few users ask the ques-tion: “How can I double my productlife by adding quality to part edges?”

Consider parts that have absolutelyno burrs, but have perfectly square,sharp edges. Such parts are simply notacceptable for assemblies other than,perhaps, welded assemblies. These“burr-free,” perfectly sharp edges cutwires, cause plating buildup, accentuateRF disruptions, cut mating parts, gougeparts stacked upon them or in contactwith them, create high stresses, reducefatigue life, etc. As a result, even if therewere no burrs, companies would haveto finish edges (improve edge quality)to improve performance.

The underlying issue is not burrs,but what edge quality companieswant, and what tradeoffs they arewilling to make to achieve both neces-sary performance and low part cost.“Edge finishing” and “deburring” intheir fullest context are two differentviews of the same need—deliveringedges that customers need or want.

What is edge quality? There are fewdefinitions of edge quality as a genericfield. “Edge quality” is a general termexpressing the needed conditions foredges (i.e. the intersection of two sur-faces) of parts. It’s different from sur-face properties and bulk characteris-tics. The elements that constitute edgequality, however, have some of thesame characteristics as the rest of thepart—specifically geometry or topol-ogy and surface integrity. Surfaceintegrity actually includes a number ofsubsurface issues, as can be seen fromthe list in the sidebar titled Attributesof Edge Quality.

The full list of issues is more exten-sive than that in the sidebar, anddepends upon the material beingmachined. My book Mass FinishingHandbook, available from SME, lists42 different flaws that users want toavoid, and all but three are found onedges as well as other part surfaces.

Clearly, users do not want burrs,but most really do not want perfectlysharp “burr-free edges.” Most userswant smooth edges that assemble cor-

rectly and easily—automatically per-haps—and edges that don’t cause pre-mature failure. Many deburringprocesses provide exactly that—high-

Deburr ing & F in ish ing



Koya Takazawa was one of thefirst individuals to discuss the term asa result of his early work on Toyotaair-conditioning compressors. Exactcontrol of the edge configuration ofcritical parts provides a significantincrease in compressor efficiency(5–15%) and performance of otherproducts. Surface integrity issuesaffect the static and dynamic life andstrength of parts.

Conventional metalcutting andgrinding all leave residual stressesbelow the surface. Tensile stresses typi-cally cause early part failure, whilecompressive stresses provide restrainingstresses that fight tensile loading. Inother words, for most applicationscompressive stresses below the surfaceincrease part life, and may somewhatimprove part strength. Readers can seethe effect of these residual stressesinduced by machining by gently polish-ing samples of parts, and looking at thestrain lines near a part edge. In almostevery case, the metal grains arestretched out into bent lines. That dis-tortion of the metal results in residualstresses. It is most easily seen bymachining brass with a rounded orworn cutting edge. The depth of thedisturbed layer can be approximated bythe formula y~1/3(F/K), where y is thedepth of the layer that has residualstresses, F is the magnitude of the result-ant cutting force per unit width, and K isthe static material yield shear stress.

The cutting tool industry is one ofthe most advanced researchers of edgefinishing, and tens of millions of dol-lars are spent each year to finish theedges of cutters. While toolmakershave honed the edges of cutters insome manner for thousands of years,edge “honing” became a standard inthe 1970s with brush honing and pol-ishing. Edge configurations went fromsharp (as-ground), honed (radiused),chamfered, and chamfered and honed,to those with a variety of lands adja-cent to the edge. Correct finishing of

cutting-tool edges reduces edge chip-ping and flank wear, resulting inlonger tool life. The correct cuttingedge also reduces plowing in the work-

piece (which results in smaller forces),improves surface finishes, and reducesresidual stresses in the machined prod-uct. Correct edge preparation depends



on the cutter material properties, workpiece properties,machining parameters, and the many variations in coatings.

Each of the 109 different deburring and edge-finishingprocesses now in use by industry produces a unique set ofedge conditions. Brushing with abrasive-filled fibers, forexample, is widely used to remove damaging, but minute,sharp-edge variations on cutting-tool inserts. In short, thesharp, ground insert edges must be radiused slightly. Most, ifnot all, cutting-tool inserts undergo automated brushing toprovide uniform radii at low cost. In this industry, brushingis noted for providing the needed edge radii—it is a processthat adds quality to the part—and more uniformity in theedge translates into much longer and more uniform tool life.

Cutting-tool makers are also finding that high-energymass-finishing processes translate into beneficial highersubsurface compressive stresses that result in longer toollife. When end mills were submitted to drag finishingtheir life doubled, according to Walther Trowal (Haan,Germany). The longer life is the direct result of removingsharp edges, as well as uniform radius generation and

smoothing of the flutes to allow easier chip flow. In thisapplication, edge radii produced were controllable from15 to 60 µm ±0.5 µm. The 3.5-min of run time resultedin more than double the tool life.

The underlying issue is what edgequality companies want.

Today other companies are investigating the centrifugalbarrel and turbo-abrasive processes, and even high-fre-quency vibratory finishing for improving fluted-tool life.Some of the benefits of these processes are believed to be theresult of not only surface improvements, but subsurfaceissues arising from better compressive residual stresses. End-mills, drills, spade drills, broaches, hobs, and even circularsaw blades are reportedly being finished by some loose-abra-sive or mass-finishing process. Slurries of fine abrasives arealso used, as are abrasives impregnated in rubber wheels,hand stoning, and both dry and wet blasting.




What is true for the carbide insertindustry is not necessarily true forother cutting tools. Perfectly sharpedges are not desired for most carbideinsert tools, as noted above, but sharpedges on single-crystal diamond (SCD)tools are highly desirable. They canimpart mirror surface finishes on alu-minum. Why a difference between toolmaterials? Carbides are made of manysmall particles pressed and boundtogether, while single-crystal tools aremade—as the name implies—from asingle crystal that shears or grindswith far fewer edge nicks.

Polycrystalline diamond (PCD) toolsare often inspected at 50× magnifica-tion. Dave Novak of ST&F PrecisionTechnologies & Tools (Arden, NC)notes: “The best finish a ground PCDcan produce is 15–50 µm Ra when the50× magnification is the acceptance cri-teria, but tools inspected as free of nicksat 150× magnification can produce10–14 Ra surfaces. In contrast, SCDtools produce finishes of 4 µm because

they are free of minute gaps and nickson the edge. Razor-sharp edges on SCDtools are used for manufacturing specialmetal mirrors and optical lenses.” Somesingle-crystal tools show no discernableedge roundness when viewed at15,000× magnification.

Electropolishing with weak acidsenhances the surface finish of many sur-gical instruments. Hypodermic needles,for example, are electropolished by themillions to smooth surfaces, and toremove any burrs or small slivers with-out generating large radii. Large radiicreate more pain when the needleenters your arm.

Other medical applications includethe use of electrochemical edge finish-ing with NaCl and NaNO3. Recentwork shows that this process can beeffective on titanium medical clips andsurgical-steel knives, as well as othertitanium and stainless products. Unliketypical electrochemical deburring(ECD), recent processes utilize ECDwith advanced programmable con-

Attributes of Edge Quality

• Acceptable edge geometry• Lack of burrs• Correct radius, chamfer, sharpness, or other shape• Uniformity along entire edge(s)• Lack of edge chip-out, fracture, or damage of any kind• Acceptable edge-surface finish• Acceptable surface texture• Freedom from foreign surface smeared material• Freedom from foreign imbedded material• Acceptable subsurface integrity• Freedom from cracks• Presence of appropriate residual stresses (usually compressive)• Freedom from molten metal or plastic• Freedom from heat affected zones • Freedom from “white metal”• Freedom from smeared metal• Correct morphology• Correct structure• Correct grain orientation• Freedom from crystallizing effects• Freedom from chemical changes• Freedom from chemical or physical absorption• Freedom from oxidation, hydration, or stains• Uniformity of all attributes across the entire edge

(unless otherwise defined)



trollers to provide tailored waveforms (an asymmetric, inter-rupted voltage waveform). The electrochemically basedprocesses all have one unique characteristic that is useful formany applications—they do not introduce any residualstresses. They often remove harmful tensile stresses whileeliminating sharp projections. This process reportedly finishesknife edges in 2 sec.

Edge quality is an issuenot just for external edges,

but for many internal holes.Magnetic abrasive finishing provides even finer surface

finishes, while removing EDM recast from parts withoutdamaging any surfaces. Magnetic abrasive finishing canproduce finishes of 0.4 µm Ra, while the mass finishingprocesses cited above provide 4–8 µm finishes (Ra). Themagnetic approach also allows removal of as little as0.000001" (0.000025 mm) from surfaces, if necessary.

Edge quality is an issue not just for external edges, but formany internal holes as well. Fuel-injection ports dependupon nozzle configuration, as do many orifices. Orificesaffect the pressures and velocities downstream, as well asspray patterns. Each of these orifices has well-defined edgeconditions. Edge radii or shape, hardness, resistance to ero-sion, and roughness are all issues for heavily used injectionports or orifices. Diesel injection nozzles, for example, use100–200 µm diam holes having 0.1–0.4 µm Ra surfaces. Theentrances also require such precision finishes. The wrongedge configuration on these parts can influence not only fuelefficiency, but emissions into the air. Edges affect the pressuredrop through holes as well as the actual size of the fluidstream coming out of the hole. My CountersinkingHandbook (available from SME) describes 27 benefits ofcareful edge control on holes.

Fatigue life specimens are commonly edge-smoothed toremove the life-reducing impact of edge effects. Sharp edgeson the test sample can provide misleading endurance infor-mation on new projects. ASTM, for example, recommends

using a 0.006" (0.152-mm) radiifor these specimens.

Sheetmetal edges are sometimesdimpled or coined to induce com-pressive stresses. Coining edges ofaircraft materials reportedly hasincreased fatigue life by a factor offour. A variety of edge configurationscan be produced by these two meth-ods, but the benefit lies in increasingthe life of the product, rather than intraditional edge shapes.

Data by R.E. Cohen, D.K. Mat-lock, and G. Krauss of the ColoradoSchool of Mines (Golden, CO) haveshown that rounded edges produce amore uniform case-hardening depthafter carburizing than square cor-ners. Rounding the edges allows uni-form carbon diffusion that reducesscatter in fatigue data. Their 1992work provides several insights intothe metallurgical differences betweensquare and round edge samples.Square-corner samples retainedalmost 50% more austenite at edgesthan did the rounded samples.Hardness at the edge of square edgeswas lower than for rounded edges,and the endurance limit was 13%lower than for rounded samples.


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Edge finishing requires high preci-sion for many parts, but a large por-tion of the processes used to finishedges do not need high-precisiontooling to accomplish that. Brushingand mass finishing are conformalprocesses; they conform to the slightvariations in part location or toler-ances. They do not need precisioncontrol strategies to provide precisionresults. Some remove tarnish, smoothsurfaces as well as edges, and provideother part benefits. In short, edge fin-ishing does more than just removeburrs—it makes the product functioncorrectly, and last for its intendedlifetime. Some processes provide theedge needed during a soft or greenstate, while others will do it for onlyvery hard edges.

Many parts have more mundanerequirements than expressed above.They simply have to assemble easilyinto complex mechanisms, and a radiusor chamfer facilitates assembly. Thus,edge preparation for these parts (asopposed to just deburring) adds qualityto later operations. Appropriate edgesreduce RF emissions and cross talk,prevent plating buildup, and reduce the

chance for corrosion (because sharpedges act like antenna for electrical cur-rents that hasten corrosion). Smoothededges significantly increase the forma-

bility of sheetmetal parts, and dimpledcountersink edges in thin aluminumsheet can increase fatigue strength by asmuch as 58%.■

LaRoux Gillespie has authoredmany books including: MassFinishing Handbook, which pro-vides how-to details of all massfinishing/loose-abrasive finishingprocesses, Deburring and EdgeFinishing Handbook, which pro-vides an in-depth guide to de-burring technologies, and Count-ersinking Handbook, which pro-vides total coverage of issuesrelated to countersinking andchamfering holes. For more in-formation or to place an order,contact SME Customer Service at800-733-4763, 8 am–5 pm Eas-tern Time, Monday–Friday, or goto www.sme.org/store and fol-low the prompts.

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