FEBRUARY/MARCH 2001 ABRASIVES MAGAZINE14

OVERVIEW Turbo-Abrasive Machining [TAM] isan emerging technology originally de-veloped and proven in the former So-viet Union. It represents a significantdeparture from conventional me-chanical finish equipment design andprovides manufacturers with a newand versatile tool for deburring, edgecontouring and surface finishing com-plex rotational parts. As the processesdeveloped for the equipment use onlydry media or dry free abrasive materi-

als, the equipment and attendantprocesses are environmentally in-nocuous, especially when comparedwith systems utilizing “wet” media,water and compounds. As a result,waste disposal costs over the life of theequipment are negligible. Despite thedry nature of the interaction of metalpart surfaces and abrasive, material re-moval and radiusing of exterior edgesare significant. Cycle times can be ex-tremely fast with some rotating partsbeing processed in as little as three

minutes. Fine surface finish profilescan also be achieved with specializedmedia utilization, surfaces as fine assingle-digit Ra have been achieved.Additionally, significant compressivestresses are imparted to critical metalpart surfaces as an aid to preventingpremature part failure as a result ofmetal fatigue.

In some edge and surface finishingapplications such as turbine disks,compressor disks, gas-turbine en-gines, textile machine parts, gears,

sprockets, bearing cages and others,manual deburring methods havebeen traditionally used because of thedifficulty of adapting other finishingtechnologies to large, awkward orcomplex shapes. This labor intensivemanual handling and finishing ofparts and components has had a neg-ative impact on manufacturingprocess productivity and the unifor-mity of edge and surface finish quali-ty in these types of deburring and sur-face conditioning applications.

TAM Mechanics – The Fluidized BedTurbo-Abrasive machining (TAM -technology) is based on using of flu-idized bed of free abrasive grain andthe creation of a fluidized bed intowhich the part to be machined is sub-merged. A low speed air stream is fedinto a specially designed chamber inwhich there are abrasive grains. Air-flow speed achieves its critical valueat the moment when the carrying ca-pacity of the airflow is equal to theabrasive layer gravity and as a resultthe process of fluidization is started.

(Re cr. * Ya) V air flow critical = ——————— ,

Dgr.Where: Re cr. – Reynold’s criterion at which

the layer is suspended Υa – kinematic air viscosityDgr. – medium size of abrasive grain

Reynold’s criterion is calculated byformula:

ArRe cr. = --———————— ,

1400 + 5.22 * √Ar

Where:Ar – Archimedes criterion

q * D3gr. ∫d - ∫aAr = ————––– * ————––– ,

Υ3a ∫a

Where:q – free fall acceleration ∫a – air density ∫d – abrasive grain density

An air flow speed increase leads to alayer volume expansion and abrasiveparticles start an impulsive move-ment in mainly a vertical direction.Abrasive particle interaction givesrise to particle rotation and as a con-sequence to the development of Mag-nus transverse force.

Fm = _∫a * π* D3gr. * _ * V ,

Where:_ – grain angular velocity

TTurbo-Abrasive Machiningurbo-Abrasive MachiningDr. Michael L. Massarsky – Turbo-Finish Corporation – Barre, MA

David A. Davidson – PEGCO Process Laboratories – Bartlet, NH

Model TF-500 Turbo-Abrasive Machining Center

VaV ≈ —–— ,

εWhere:ε – a void volume between the abra-

sive particles which is one of theprincipal characteristics of flu-idized beds, equal ε = 1 - τ, whereτ - volume concentration ofsolid particles for filling layer τ =0.6; ε = 0.4.

For fluidized bed- 0.35 < τ < 0.6; 0.4 < ε < 0.7

The transverse force acts in the direc-tion perpendicular to the air force andis the principal source of chaotic par-ticle movement in the fluidized bed.

The surface of a part to be machinedis placed in such a fluidized bed andis effected the pressure of abrasivegrain movement. Metal removal in-tensity and surface quality depend onthe pressure magnitude and thephysical and mechanical propertiesof a machined material. The value ofabrasive particle pressure on a surfacepermits us to calculate the design ele-ments of Turbo-Abrasive machines,to design fixtures and calculate thepower consumption for machiningprocess as well.

Theoretical Model of Interaction of Factors in the Turbo-Abrasive Machining ProcessSince the Turbo-Abrasive process is anew abrasive technology in principle itis necessary to determine the correla-tion of the principal factors influenc-ing the machine results. After ananalysis of that correlation there wasmade the following assumption: abra-sive particles are sphere simulated, thegrain aggregate is characterized by theaverage values of Dgr., grain mass-Mgr., and abrasive grain speed - Vgr.

The grain pressure (fluidized bed “ in-strument”) on a surface being ma-chined is chosen as a parameter influ-encing the main technological fac-tors. The abrasive particle pressurevalue can be shown as follows:

P (fd) = Igr. * Ngr., (1)

Where:Igr. – impulsive force passed by

grain.Ngr. – statistical average of the

number of grains interacting with a surface square unit pertime unit.

Taking as a basis the impact theorywe can calculate the value of Igr.

Igr. = (K+1) * Mgr. * (Vgr. + Vn), (2)

Where:K – recovery coefficientVn – speed projection of grain

contact point to normal vector in relation to surfacemicro-unevenness.

It is also essential to take into consid-

eration the metal microrelief forma-tion and direction of surface micro-unevennesses of surface roughnessprocess. Consequently the formula(2) will be:

Igr. = (K + 1) * Mgr. * (Vgr. +Vp * sinθ * sinß),

(3)

Where:q – is the angle of side inclination

of micro-unevennesses;ß – is the angle between the direc-

tion of micro-unevennesses andpart speed vector;

The grain number Ngr. is determinedas a part of the number of grain n(gr)is in a volume unit of fluidized bed.Calculations based upon the gas mol-ecular theory show that

Ngr. = _n(gr) * (Vgr. + Vp * sinθ *sinß),

(4)

The number of grains in a volumeunit is as follows:

1 ∫d * (1 – ε)n(gr) = –––––– * ––––––—— , (5)

Lgr. Mgr.

Where:Lgr. – abrasive particle distance in

fluidized bed and is equal to:

1 – εLgr. = √ –––––––– * Dgr. (6)

1 – ε

Where: (1– ε); (1– ε) – abrasive particle con-

centration in a fillingbed (layer) and flu-idized bed respective-ly.

Continued on pg. #

FEBRUARY/MARCH 2001ABRASIVES MAGAZINE 15

Edge and Surface Finish Improvement by TAM Methods

Tam Processes Excel in Dealing with Deburring and Edge ContourProblems Associated with Complex Rotating Shapes Such as This

FEBRUARY/MARCH 2001 ABRASIVES MAGAZINE16

Taking into consideration the formu-las (2) – (6) the calculations showthat:

P(fd) = (k + 1) * ∫d * (1 – ε) * (Vgr. + Vp * sinθ * sinß)2

(7)

Obtained mathematical models per-mit us to value the effectiveness ofvarious Turbo-Abrasive machine de-signs. Reliability of the model is con-firmed experimentally. The calcula-tions carried out by the above men-

tioned model show the value of abra-sive particle pressure on a surface andfunctionally depending intensity ofmetal removal.

Theoretical definition of the metal re-moval intensity of Turbo- Abrasivemachining is carried out by formulaas follows:

– Qm = Υm * Vavg. * Ngr. * P(fr), (8)

Where: Υm – material density to be ma-

chined;Vavg. – an average volume of a sin-

gle microscratch;P(fr) – a coefficient to bear in mind

in correlating of cutting andfriction processes of Turbo-Abrasive machining;

The volume of a single microscratchis determined by considering a singlemicroscratch as a part of ellipsoid.The calculations carried out by for-mula (9) have shown, that _ π _ _ _Vavg. = – * l * b * h, (9)

8Where:_ _ _l, b, h – average values of length,

width, and depth of a micro-scratch respectively.

The microscratch depth is deter-mined by the impact theory. The cal-culations carried out by formula (10)show:_ _ _h = 1.7K(h) * b (m) * D gr. * (Vgr. + Vp * sinθ * sinß),

3/4(10)

Where: K(h) – proportionality coefficient b(m)– metal plasticity constant.

The microscratch length is deter-mined as a path passed by grainduring the contact. The calcula-tions carried out by formula (11)show:

(2 – K(h)) * h * Φ * cosθl = ———————————- ,

Vgr. * sinθ(11)

Where: Φ – tabulated function in terms of

metal plasticity constant valueb(m).

_ The width of a microscratch “b” bymodeling the apex angle with round-ing cone based upon the correlationb = 4h.

TURBO-ABRASIVE Continued

Typical Burr Condition Prior to TAM Processing

Turbine Disc After TAM Processing

Taking into consideration the ob-tained formulas for h, l, b, Vavg. andNgr. the calculations show the metalremoval intensity as follows:

Qm = 33 * Υ * K3 (h) * (2-K(h)) _ _* P (fr)* cosθ* b (m) * D gr. *

* (Vgr. + Vp * sinθ * sinß)

(12)

The Table 1 shows the data of Qmvalues, obtained for steel machiningby abrasive grain of Al O and size 36US Mesh.

Rated and experimental values of _ _ _parameters of h, l, b, and Qm.

Rated and experimental discrepancyof microscratch values is equal to11% – 16% and Qm parameter – 14%– 18%.

Obtained mathematical models ofTurbo-Abrasive machining permits usto determine the interaction betweenthe principal technological parame-ters and forecast the Turbo-Abrasivemachining results (metal removal in-tensity) depending on machiningtime, abrasive particle characteristics,physical and mechanical properties ofa machining material.

Turbo-Abrasive MachiningTechnologyObtained theoretical analysis and ex-perimental investigations of Turbo-Abrasive machining has shown thecorrelation between the technologi-cal parameters of Turbo-Abrasive ma-chining (rotational part speed, size ofabrasive particles, physical and me-chanical properties of grain, machin-ing time, pressure (air discharge), netresults of metal removal intensityand machining quality).

One of the principal technologicalfunctions of Turbo-Abrasive machin-ing is the reduction of surface rough-ness of complex part shapes (turbineblades, compressor and turbine disks,cylindrical and conical gear wheels,and a number of parts used in pneu-matics and hydraulics). Different ex-periments were carried out concern-ing the sample machining from dif-ferent steels and alloys after lathemachining to determine the techno-logical correlations.

Turbo-Abrasive machining canachieve the surface roughness values:

Ra = 0.6 –1.0 µm 30 US Mesh

Ra = 0.4 – 0.6 µm 36 US MeshRa = 0.2 – 0.3 µm 46 US Mesh

Microroughness is reduced 30%–50% after machining parts madefrom Ni and Ti alloys.

The Turbo-Abrasive machined sur-faces typically have dull surfacescaused by the specific impact forcesof abrasive particles. TAM surfaces(substrates) are characterized by theirability to develop a strong bond withvarious coatings (electrodepositions,plasma coatings, etc.)

Given the condition that (1) the rota-tional speed of a component is high(Vp = 20-30 m/s) and (2) there is in-tensive abrasive particle – part sub-strate contact, an important techno-logical condition of the process is theabsence of the abrasive particleimplantation into the surface metallayer.

In order to determine the presence ofimplanted particles into metal sur-faces here was used a specially devel-oped spectral control method withmoving cathodes – sample. The sam-ples were controlled following the in-tensity of spectral line S – 2506 A(abrasive - particles silicon carbide).

That intensity was characterized bythe degree of blackening, measuredwith photometer. The values of S (fortesting the sample after grinding) wasequal to 1.44. Analysis of two seriesof samples after Turbo-Abrasive ma-chining (Vp = 20-30 m/s) showedthat the values of S for above men-tioned samples were within 1.40-1.48, i.e. the deviation from etalon(test) sample was not more than 2-4%, which stays within the range ofmeasurements and demonstrates theabsence of implantation into the sur-face layer by abrasive particles. Mi-croscopic analysis of the surface inpolarized light and with the help ofelectronic microscopy did not re-vealed the presence of abrasive parti-

cles either.

This testing data allows us to come tothe conclusion that there is no im-plantation into steel sample surfaceswhile being treated by Turbo-Abra-sive machining due to insignificantnormal strength of abrasive particleinteraction and also due to the smalldepth of implantation of abrasiveparticle into the metal.

Equipment Performance:Both experimental data and informa-tion based on production related ex-perience indicates that process cycletimes run from three to eight min-utes on most components.

The reduction in surface texture pro-files generated by this equipment issignificant. Both experimental andproduction related experience indi-cates that the high rotational speedimparted to parts [up to 20-30 m/s(meters per second) or 3,900 – 5,850s.f.p.m. (surface feet per minute)]generates an abrasive particle to partsurface contact rate of 200-500 persecond/per square mm. (129,000 -323,000 per in2/sec.). Surface re-moval rates on steel, stainless steel, ti-tanium and other alloys have beenrecorded as high as 2-5µm (.08 - .2thousandths) per minute. Theseforces make TURBO-FINISH equip-ment capable of generating one ofthe highest rates of metal removal tobe found in any type of surface fin-ishing equipment today. Yet with ap-propriate media and process parame-ter selection very refined finishes canbe achieved. Turbo-Abrasive produc-tion experience indicates surface re-duction values from 2-5 µm down to0.2-0.4µm (78-200 µinch down to 7-15µinch) is commonly achieved in 3-8 minute cycles.

A number of other desirable surfacefinish characteristics are attributed tothe TURBO-ABRASIVE method. The

Continued on pg. #

FEBRUARY/MARCH 2001ABRASIVES MAGAZINE 17

_ _ _ _ _ _ Vp h(cal) h(exp) l(cal) l(exp) b(cal) b(exp) Qm(cal) Qm(exp)m/s µm µm µm µm µm µm mm3/min mm3/min

5 0.49 0.63 23.2 19.8 1.92 2.40 0.37 0.30

10 0.61 0.65 41.4 30.6 2.44 2.51 1.01 0.86

15 0.75 0.68 59.4 57.0 3.0 2.60 1.76 1.55

Table 1:

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ability to impart compressive stresses,an important element in developingmetal fatigue and wear resistance incritical parts for the aerospace andautomotive industries, is one out-standing trait. Testing and analysishas shown that TURBO-ABRASIVEprocesses “increased fatigue strengthon some critical parts from 40% to 2times.” It has also been noted that “asthe process is a low temperature one“phase structural changes in themetal surface layer are absent,strengthening a thin layer and devel-oping 400-600 MPa of residual com-pression stress.” This is a very impor-tant surface integrity consideration.

The process also develops a unique“micro-relieved” or “micro-textured”surfaces that are highly compatible

with a large variety of coatings in-cluding: electroplating, galvanic, var-nish, color and plasma coatings.Heat treat scale is also easily removedfrom complex part shapes.

SUMMARY:The Turbo-Abrasive Machiningprocess is a significant new processfor developing important edge con-tour and surface finish effects on awide variety of complex and difficultmachined parts. These kinds of ma-chined parts currently pose a chal-lenge that can not be fully met byconventional finishing methods, andoften require tedious and labor-in-tensive manual methods. Turbo-Abrasive Machining is a method thatallows for automation of these diffi-

cult tasks in a dry abrasive environ-ment that minimizes waste disposaland the incidence of deburring oper-ation related repetitive motion in-juries. It also significantly improvesproductivity and feature-to-feature,part-to-part, and lot-to-lot uniformi-ty, while at the same time enhancingthe surface integrity and service func-tionality of critical hardware.

REFERENCES:1. Dr. M. L. Massarsky and D. A. Davidson,

“Turbo-Abrasive Machining Theory andApplication,” SME Technical Paper MR95-271, Proceedings of the 1st InternationalMachining & Grinding Conference; Societyof Manufacturing Engineers, Dearborn, MI,Sept. 12-14, 1995

2. Dr. M. L. Massarsky and D. A. Davidson,“Turbo-Abrasive Finishing,” SME TechnicalPaper, Proceedings of the Deburring andSurface Conditioning Symposium; Societyof Manufacturing Engineers; Dearborn, MI.;Oct. 26-27, 1993

3. Massarsky, Dr. M. L., Davidson, D. A.“Turbo-Abrasive Machining and Finishing”,METAL FINISHING, White Plains, NY:Elsevier Science, p. 29-31, July, 1997

4. Massarsky, Dr. M. L., Davidson, D. A.“Turbo-Abrasive Machining — Dry ProcessMechanical Finishing for Today’s ComplexComponents”, FINISHER’S MANAGEMENT,August 1997

5. “Dry Mechanical Finishing for RotatingComponents”, SURFACE ENGINEERING,England: Institute of Metals, p. 363-364,1997, Vol 13, No. 5

6. Massarsky, Dr. M.L., The Peculiarities ofPart Treatment in Fluidized Bed of AbrasiveGrains. - In collection “Progressivnyemethody of obrabotki detalej”. - LDNTP,[Russian],1977, p.79-84.

7. Massarskiy Dr. M.L., Guzel V.Z., SurfaceQuality at a New Method of Part Treatmentis Turbo-Abrasive Grinding. - In collection“Physika i Tchnologia UprocheniaPoverchnosti Metalla”. - Materials of semi-nar, L., Physicotechnical Institute namedafter A. F. Joffe, [Russian]1984, p.69-70.

8. Kremen Z.I., Massarskiy Dr. M.L., Turbo-Abrasive Grinding of Parts is a New Methodof Finishing. - “Vestnik mashino-stroyenia”,[Russian] 1977, #8, p.68-71.

9. Davidson, D. A., “Mass FinishingProcesses”, 2000 METAL FINISHINGGuidebook and Directory, White Plains, NY:Elsevier Science, 2000

10. Davidson, D. A. “Current Developments inDry Process Mass Finishing, Finisher’sManagement, Vol 33., No. 7, September,1988, p.43-46

11. Davidson, D. A., “Refining Plastic Surfacesby Mass Finishing Methods”, PlasticsEngineering, April, 1986

TURBO-ABRASIVE Continued

12. Davidson, D. A., High Energy Dry ProcessFinishing, SME Technical Paper MR90-389,International Manufacturing TechnologyConference, Sept 6-10, 1990, Dearborn, MI:Society of Manufacturing Engineers

13. Davidson, D. A., “Developments in DryProcess Mass Finishing”, SME TechnicalPaper MR89-147, SME - DSC’89Conference, San Diego, CA., Feb. 13- 16,1989,

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