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, and fea­ ing of complex machined and deburring or surface conditioning op­ tures of the part simultaneously. Many D turned parts 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 de­ metalworking industry. In many cases mass-finishing methods that could vice (for example, chucks, between parts with complex geometric forms. achieve surface-finish objectives in a centers, rotary tables. etc.) are poten­ which are manufactured with very so­ dry abrasive operation. In contrast with tial candidates for TAM processes. and phisticated computer-controlled equip­ current methods turbo-abrasive finish­ in many cases, these final deburring ment. are deburred. edge finished. and ing (TAM) operations are completely and surface conditioning operations surface conditioned with manual or dry and produce surface effects rapidly can be performed in minutes if not in hand-held power 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 PROCESS BENEFITS ufacturing 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 man­ long-standing industry-wide paradox TURBO-ABRASIVE FINISHING lIal dehurring procedures with con­ that the final surface-conditioning op­ trollable machining processes. erations utilized on many types of pre­ The TAM method provides 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 of the preceding high-speed precision final machining • Reduces manual process or cycle machining operations. This is some­ and finishing method 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 or directional streams of abrasive Mass-finishing techniques. such as be processed. Many types of nonrotat­ media, all features of the part are barrel and vibratory finishing. have ing parts can also be processed by processed unifonnly and simulta­ long been recognized as the primary fixturing them on disk like fixtures. neously. tools for metal part deburring and sur­ Increasingly complex parts are be­ • Repeatahility. Part-to-part and lot­ face conditioning and, as such, have ing fashioned in today's four and five to-lot variations can be eliminated or wide application throughout industry. axis turning and m.achining centers. minimized. Uniformity of surface As metalworking techniques have und TAM technology provides the effects on features of parts is also evolved in recent years. it seems that method in which needed surface im­ enhanced. an increasing number of parts require provements .can be made on these • Compressive stresses and metal im­ more sophisticated deburring and sur­ types of parts with a minimum of di­ provement can be developed on crit­ face conditioning methods. Many parts rect labor and tooling costs. TAM as a ical part areas to enhance metal fa­ routinely manufactured now have size surface-conditioning method is a blend tigue resistance. and shape considerations that preclUde of current machining and surface-fin­ • Special microlcxtured surfaces can the use of conventional mass media ishing technologies. Like machining be generated that have enhanced finishing techniques. Additionally. processes the energy used to remove bonding receptivity as substrates to manufacturers of high-value parts now material from the part is concentrated many types of coatings and plating. prefer manufacturing methodologies in in the part itself, not the abrasive ma­ • Low-temperature material removal. which parts are processed singly and terial interfacing with part surfaces, Unlike inany traditional grinding pro­ continuously rather than in hatches, and like many surface~finishing pro­ cesses. physical characteristics of the obviating the possibility that large cesses material removal is not accom­ outer surface layer of metal are not numbers of parts will he scrapped or plished by a cutting tool with a single changed by process-generated temper­ reworked due to human error or pro­ point of contact. but by complete en­ ature shifts on surface of metal. cess maladjustment. velopment of the exterior areas of the • Random surface-finish pattern Another important consideration in part with abrasive materials. As a re­ means greater compatibility with evaluating current mass-finishing pro­ sult deburring. edge finishing. surface coating and plating processes than cesses is their wet waste effluent blending and smoothing, and surface linear patterns developed with tradi­ stream, the treatment cost of which conditioning are 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