a Turbo-Abr'asive Machining and Finishing

by Michael Massarsky and David A. Davidson, Turbo-Finish of America Inc., Middlefield, Conn.

eburring and surface condition­ often approaches the cost of the actual terior exposed surfaces. edges, ing of complex machined and fea­ and deburring or surface conditioning op­ tures of the part simultaneously. turned parts Many D is one of the most erations themselves. Industry has long metal parts that are machined by being troublesome problems faced by the had a strong incentive to .seek Ollt held in a rotational work-holding metalworking industry. In many de­ cases mass-finishing methods that could vice (for example, chucks, parts with complex geometric between forms. achieve surface-finish objectives in a centers, rotary which are manufactured tables. etc.) are poten­ with very so­ dry abrasive operation. In contrast with tial candidates phisticated computer-controlled for TAM processes. and equip­ current methods turbo-abrasive finish­ in many cases, ment. are deburred. these final deburring edge finished. and ing (TAM) operations are completely and surface surface conditioned conditioning operations with manual or dry and produce surface effects rapidly can be performed hand-held power in minutes if not in tools. This labor-in­ in single-part operations. (Some parts seconds. tensive manual handling often has a lend themselves to multiple-spindle or considerable negative impact on man­ multiple-fixture operations when sin­ ufacturing PROCESS BENEFITS process flow. productivity. gle-part processing is not an important and unifomlity of features on the final quality-control objective.) • Very rapid deburring, radiusing. and product. as well as part-to-part and surface conditioning of complex lot-to-Iot uniformity. It has been a parts, replacing or minimizing long-standing man­ industry-wide paradox TURBO-ABRASIVE FINISHING lIal dehurring procedures with that con­ the final surface-conditioning op­ trollable machining processes. erations utilized on The TAM method provides many types of pre­ manu­ • No part-on-part contact or impinge­ cision parts have nowhere near the facturers with the ability to utilize a ment. level of sophistication high-speed precision final of the preceding machining • Reduces manual process machining and finishing method or cycle operations. This is some­ that can accom­ times from hours to minutes. thing that needs to change. modate the current trend toward con­ • Unifonnity. Complete abrasive en­ tinuous processing of individual parts. velopment of parts means all ex­ Many larger and more complex rota­ posed exterior surfaces and features CONVENTIONAL MECHANICAL tionally oriented parts. which pose a will be free abrasive machined. Un­ FINISHING METHODS severe challenge for conventional me­ like processes with hand-held tools chanical-finishing methods. can easily Mass-finishing or directional streams of abrasive techniques. such as be processed. Many types of nonrotat­ barrel and vibratory media, all features of the part are finishing. have ing parts can also be processed by long processed unifonnly and simulta­ been recognized as the primary fixturing them on disk like fixtures. tools for neously. metal part deburring and sur­ Increasingly complex parts are be­ face conditioning • Repeatahility. Part-to-part and lot­ and, as such, have ing fashioned in today's four and five wide to-lot variations can be eliminated or application throughout industry. axis turning and m.achining centers. As metalworking minimized. Uniformity of surface techniques have und TAM technology provides the evolved in effects on features of parts is also recent years. it seems that method in which needed surface im­ an increasing enhanced. number of parts require provements .can be made on these more sophisticated • Compressive stresses and metal im­ deburring and sur­ types of parts with a minimum of di­ face conditioning provement can be developed on crit­ methods. Many parts rect labor and tooling costs. TAM as a routinely ical part areas to enhance metal fa­ manufactured now have size surface-conditioning method is a blend and tigue resistance. shape considerations that preclUde of current machining and surface-fin­ the • Special microlcxtured surfaces can use of conventional mass media ishing technologies. Like machining finishing be generated that have enhanced techniques. Additionally. processes the energy used to remove manufacturers bonding receptivity as substrates to of high-value parts now material from the part is concentrated prefer manufacturing many types of coatings and plating. methodologies in in the part itself, not the abrasive ma­ which • Low-temperature material removal. parts are processed singly and terial interfacing with part surfaces, continuously Unlike inany traditional grinding pro­ rather than in hatches, and like many surface~finishing pro­ obviating cesses. physical characteristics of the the possibility that large cesses material removal is not accom­ numbers outer surface layer of metal are not of parts will he scrapped or plished by a cutting tool with a single reworked changed by process-generated temper­ due to human error or pro­ point of contact. but by complete en­ cess maladjustment. ature shifts on surface of metal. velopment of the exterior areas of the Another • Random surface-finish pattern important consideration in part with abrasive materials. As a re­ evaluating means greater compatibility with current mass-finishing pro­ sult deburring. edge finishing. surface cesses coating and plating processes than is their wet waste effluent blending and smoothing, and surface linear patterns developed with stream, the treatment cost of which conditioning are tradi­ performed on all ex- tional grinding methods. METAL FINISHING • JULY 1991 e CopyrIght Elsevier Science Inc. :

TURBO-ABRASIVE MACHINING surface profile than is possible from of abmsives and specially fomlUlated abm­ CONCEPT pressure and impact methods. sive blends available makes it possible to pnxluce a wide arn\y of divcrne surface­ The basic concept underlying TAM finish effects, even more so when sequen­ operations is the placement of a rotat­ RANDOM VERSUS LINEAR tial cycles with differing media combina­ ing or oscillating metal component or GRINDING PATIERNS tions are utilized. workpiece in a low-speed air-abrasive stream (fluidized bed), which is con­ Another very important functional APPLICATIONS tained by a specially designed cham­ aspect ofTAM technology is its ability to develop needed surface finishes in a ber. Surface finishes and effects can be Some of the applications include low-temperature operation (in contrast gencrated on the entire exterior of high-specd precision, deburring, radius with conventional wheel and belt complex parts, and specially fixtured formation, edge finishing, surface en­ grinding methods), with no phase or nonrotational components. (Simple in­ hancement, and metal improvement of structural changes in the surface layer terior channels on some parts can also all types of rotating components in­ of the metal. A further feature of the be processed.) Various surface-finish cluding turbine/compressor disks and effccts can be obtained by control Iing process is that it produces a more ran­ other rotating components, gears, im­ dom pattern of surface tracks than the variables of the process such as rota­ pellers, sprockets, machined turnings more linear abrasive methods such as tional part speed, part positioning, cy­ of all kinds, turbocharger rotors, tur­ cle times, abrasive particle size and wheel grinding or belt grinding. The bine blade root forms, automotive, tex­ characteristics, and others. Additional nonlinear finish pattcrn that results of­ tile, enginc. electrical, pump marine, ten enhances the surface in such a way surface effects can be developed by electrical, and various consumer items. utilizing processes that make use of as to make it much more receptive as a bonding substrate for subsequent coat­ sequential abrasive and/or polishing SUMMARY media combinations. Sevcral machine ing and even plating operations. designs have been developed that can TAM processes can be easily justi­ accommodate parts as small as 2 to 3 METAL IMPROVEMENT fied in many types of applications in. (50 mOl) in diameter to very large where part sile and shape consider­ and cumbersome rotational parts up to TAM processes have strong applica­ ations make applying other surface­ 4 ft (1,200 mOl) in diameter and larger. tion on certain types of parts that have conditioning technologies difficult. critical metal surface improvement re­ The process deburrs and develops quirements of a functional nature. Sig­ needed edge and surface-finish re­ HIGH-INTENSITY ABRASIVE nificant metal improvement has been quirements very rapidly. EFFECT realized in processes with both abra­ Significant process chmucteristics to keep in mind include (I) very mpid cycle Surface-finish effects are generated sive and nonabrasive media. As a re­ times; (2) a high-intensity, small media by the high peripheral speed of rotating sult of intense abrasive particle contact operation that allows for access into intri­ . parts and the large number and inten­ with exposed features, it has been ob­ cate part geometries; (3) a completely dry sity of abrasive particle to part surface served that residual comprcssive operation; (4) metal improvement eftects~ contacts or impacts in a given unit of stresses of up to 400 to 600 MPa can 2 (5) no part-on-part conlact~ (6) modest time (200-500 per mm /sec or be created in selected critical areas. tooling requirements; (7) primarily an ex­ 129,000-323,000 pcr in. 2/sec). These Tests perfomled on rotating parts for ternal surface preparation method--some factors make this equipment capable of the aerospace industry that were pro­ generating one of the highest rates of cessed with this method dcmonstrated simpler interior channels can also be pro­ cessed;and (8) many types of rotating metal removal to be found in any type a 40 to 200% increase in metal fatigue cOlllJX)nents can be processed--nonrota­ of free abrasive surface-finishing oper­ resistance when tested under working tional components can also be processed ation today. Yet with proper media se­ conditions, when compared with parts when attached to disklike fixtures. lection and process adjustments, very that had been deburred and edge fin­ refined finishes can be achieved. Parts ished with less sophisticated manual treatment protocols. References with an initial surface roughness pro­ I. Massarsky, M. L. and D.A. Davidson, file of 2 to 5 J.lm Ra (80-200 rnicroinch "Turbo-Abrasive Machining Theory Ra ) have been reduced to 0.2 to 0.4 J.lrn lOOSE ABRASIVE and Application," SME Technical Paper R" (7-15 microinch. Ra) in a single TECHNOLOGY MR95-271. P!'Oaedin/?s of the I sf In­ operation in time cycles of only a few fe,.,wfional Machining & Grinding minutcs. It should be noted that sur­ TAM technology makes use of a variety COf!!crcna; Society of Manufacturing face-finish effects developed from this of loose abmsive materials and blends of Engineers, Dearborn. Mich.: Sept. 12­ process depart significantly from those abnt<;ive and nonabra<;ive granulates to at­ 14,1995 2. Massarsky. M. L. and D.A. Davidson. obtained from air or wheel blasting. tain various surface finishes ~md effects "Turbo-Abrasive Finishing,"· SME TAM processes can produce much tJmt can vary from abrasive edge finishing Technical Paper. Pro('eedinRs (~l fht' De­ more refined surfaces by virtue of the and surface smootJling to more refined prc­ hllrring llnd Sill/ace Conditioning Sym­ fact that the rotational movement of plate finishes, .l<; well as using an ~l<;sort­ pos;um; Sociely of Manufacluring En­ parts processed develop a very fine ment of nonabrasive media for metal im­ gineers. Dearborn. Mich.: Ucl. 26-27, finish pattern and a much more level provement processing. TI,e large number 19~ MF

METAt FINISHING • JULY <1997 31