Power Skiving

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It has long been known that the skivingprocess for machining internal gears ismultiple times faster than shaping, andmore flexible than broaching, due to skiv-ings continuous chip removal capability.However, skiving has always presenteda challenge to machines and tools. Withthe relatively low dynamic stiffness inthe gear trains of mechanical machines,

as well as the fast wear of uncoated cut-ters, skiving of cylindrical gears neverachieved acceptance in shaping or hob-bing until recently. Indeed, the latestmachine tools with direct drive trainand stiff electronic gearboxes, complextool geometry and the latest coating tech-nology now present an optimal oppor-tunity for the skiving process, includingthe soft-skiving of cylindrical gears.

The Power Skiving Machine

Setup DefinitionsThe geometric setup of a skiving cutterrelative to an internal ring gear is shown(Fig. 1). The front view of the generat-ing gear system is shown in the upperleft graphic. The ring gear is oriented inthe main coordinate system with its axisof rotation collinear to the Y4 axis. Thecutter center (origin of Rw) is positionedout of the center of Y4in the X4 -Z4 planeby a radial distance vector Ex. The pitchcircles of the cutter and the ring gear con-

tact tangentially at the lowest point of thepitch circle. The top view, which showsthe tool inclination angle or shaft angle,is drawn below the front view. In case of aspur gear the stroke motion is directed inline with the Y axis. The relative velocityrequired as cutting motion is generatedwith a shaft anglearound theX4axis ofthe coordinate system shown in Figure 1.In case of a helical gear, the cutter incli-nation can be chosen independently from

the helix angle. However, a helix angle of20 or greater offers the possibility to bematched with the shaft angleand to usea simplified spur gear-style shaper cut-ter for the skiving operation. Also in thiscase, the stroke motion is oriented in Ydirection but an incremental rotation 2,which depends on the stroke feed, hasto be added to 1. The shaft angle can

also be defined differently than the helixangle and it will still require the sameincremental 2, but the tool front faceorientation and side relief angles have tobe calculated from the difference betweenhelix angle and the shaft angle. The side

view to the right (Fig. 1) shows a secondpossible tool inclination which is called

the tilt angle. This tool tilt angle canbe used to increase the effective reliefangles between the blades and the slots; itcan also be used to eliminate interferenc-es between the back-side of a long spurgear-style shaper cutter with minimumrelief angles (see section Skiving Tools).Within limits, it is also possible to utilizethe tilt angle for pressure angle correc-

tions.The three-dimensional side view (Fig.

2) shows an internal helical gear with ashaft anglebetween work and tool. Thegraphic shows the base angular veloci-ties of the work 1 and the formula forits calculation. Figure 2 also includesthe incremental angular velocity 2 and

Power Skiving of CylindricalGears on Different MachinePlatformsDr. H.J. Stadtfeld

Printed with permission of the copyright holder, the American Gear Manufacturers Association, 1001 N. Fairfax Street, Fifth Floor, Alexandria, VA 22314-1587. Statementspresented in this paper are those of the author(s) and may not represent the position or opinion of the American Gear Manufacturers Association

Figure 1 Basic geometry and kinematics of power skiving.

52 GEAR TECHNOLOGY | January/February 2014[www.geartechnology.com]

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the formula to calculate it from the helixangle and the axial feed motion (strokemotion). The cutting velocity is calcu-lated as the difference vector betweenthe circumferential velocity vectors ofwork and tool in the cutting zone. Figure3 shows a top view of the configurationbetween tool and work with the velocity

vectors.The reference profile of the tool is

determined from the reference profileof the work applying the procedure (Fig.4). The reference profile of the work withpressure angles 1and 2and point widthWp is drawn as a trapezoidal channel,and it is cut with a plane under the shaftangle (Fig. 4, top, right). The profile isdefined by the intersecting lines betweenthe plane and channel, and it representsthe reference profile of the tool. This tool

reference profile is used in order to gen-erate the involute in the tool cutting front(Fig. 4, bottom right).

The machine setting calculation isshown (Fig. 5, top) on the example of abevel gear cutting machine. The explana-tion of the formula symbols are:X, Y, ZMachine axis directions (Yis

perpendicular to the drawingplane)

Shaft angle between cutter andwork

CRT Cutter reference height

B Cutter swing angle PZ Pivot distance to spindle front in

Z direction if B = 0 PX Pivot distance to spindle center

line inX direction if B = 0 Z1, Z2Components in Z direction

Depending on the helix directions inwork and cutter, the cutting takes placebelow or above the work gear center linein order to keep the B axis angle below90. Should there be no corrections need-ed, the crossing point between the cutter

axis and the work axis lies in the cutterreference plane. The bottom section ofFigure 5 shows the cutting blade defini-tions as reference.

Chip Formation and Optimizationof Chip LoadAlthough the chip formation process ofskiving appears different when comparedto traditional gear cutting operations,understanding it is a fundamental task inrecognizing weaknesses or strength of the

skiving process. Power skiving has beencalled a combination of cold forming

Figure 2 Pitch cylinders of work and tool.

Figure 3 Calculation of cutting velocity.

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and cutting. But is not every metal remov-ing process such a combination? The taskof a successful process is an economicalcombination of speed, part quality, toollife (tool-cost-per-part), and of course theinvestment in the machine tool.

The plane in Figure 6 shows a segmentof an internal ring gear to be skived, and

it is defined along the face width at thepoint where the last generating occurs.The second cutting tooth from the lefthas just entered into a part of the slotwhich is already rolled out from the pre-vious cutting action. The third cuttingtooth is advanced towards the observerand just begins a generating cut (see topview of unrolled partial slots). The gen-erating cut continues to cut tooth num-ber six. The lowest scallop in the topview was generated between the second

and sixth cutting blade position. Cuttingblades seven and eight finish the form cutend section of the slot.

A photograph of the tooth sequencefrom Figure 6 is shown in Figure 7 as aclose-up. As one blade rotates throughthe cutting mesh, the orange-coloredscallop is generated and the green-col-ored section is form-cut. The entire

cutting action of one blade producesone chip, which includes the materialremoval from generating and form cut-ting. Beginning with its addendum, the

right side of the blade gradually engageswith the gear slot during the generatingmotion. It approaches the tip, and at thispoint it smoothly peels the chip up to thetop of the gear. As the generation worksits way from the right flank of the gearto the tip, and from this point up to theflank, every section that had at one pointchip removing contact with the work now

stays in contact to the end of the cut.Only the generating chip removal (withinthe scallop) converts quickly into form-cutting.

The form-cutting section might seemlike an interesting phenomenon but it canbe found in a similar form in all othergenerating cylindrical or bevel gear cut-ting methods. It is also common in allgenerating and form-cutting processes,that the tip region of the blades have thelongest exposure to chip removal actionwithin the green form-cutting region.

Figure 4 Procedure for the calculation of the tool reference profile.

Figure 5 Calculation of machine settings

(top) and cutting blade definitions(bottom).


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Since the front face of power skivingblades is a plane that connects the cuttingedges for both flanks, the side rake anglecannot be positive for both cutting edges.An acceptable compromise is a side rakeangle of zero degrees. In order to enhancethe cutting performance of the blade tip,a significant top rake angle can be intro-

duced. However, peripheral cutter headswith carbide blades and top rake anglesabove 4 seem to fail with blade chippingin the tip area (Fig. 5).

Power skiving chips with a 5 mag-nification are shown (Fig. 8, top). Thefirst chip (A) is a side chip from the firstroughing pass of a module 4.0 mm gearwith a 5 mm in-feed. The second chip(B) is U-shaped, which means, unlikethe first chip, the side chips and the bot-tom chip have not been separated. This

chip is from a second roughing pass with3 mm in-feed. The third chip (C) is froma finishing pass with 1 mm in-feed. Theresult of an unrolled and uncompressedchip that is just sheared off is a curvedchannel like that indicated in the draw-ing at the bottom left of Figure 8. The twoside walls, as well as the bottom sectionof the channel, are rolled up individuallyand mostly without breaking into sepa-rate pieces.

The microscope photo (Fig. 8, bottom

right) shows a cross-section through theleft wing of one chip with a magnificationof 100. At the beginning of cutting (cen-ter of the chip spiral), the chip thicknessis small and increases slightly during therather short generating section (orangescallop, Fig. 7). A proportional increaseof the chip thickness occurs from thebeginning to the end of the form-cuttingsection (Fig. 7, green area).

The right sides of the chips are thin-ner than the left sides, and a crack in the

middle of the rolled-up sidewall can beobserved. As the bottom left image indi-cates, the right channel wall has a morecomplex shape than the left side, and theskiving kinematic provides slightly dif-ferent cutting conditions on both flanks.This explains differences in chip thick-ness between the two sides and the addi-tional crack of the right side of the chip.

In order to avoid U-shaped chips,Gleason has developed an in-feed strat-egy. After each stroke an in-feed amount

and a work angle set-over is applied inorder to generate L-shaped chips (Fig. 9,

left); L-shaped chips reduce the wear onthe cutting blades.

It is possible to alternate the in-feedwork angle set-over direction from partto part in order to achieve even tool wear.Another possibility is to apply a posi-tive side rake (e.g., 2) to the left side ofthe blade (Fig. 8) that will enhance thecutting action on this side and gener-ate L-shaped chips. If the resulting feeddirection (Fig. 8) is not exactly parallelto the right flank, but about 3 steeper,then a perfect clean-up of the right flankis guaranteed and the surface finish of the

right flank will be equal or slightly betterthan the finish on the left flank.

HSS Cutters for Power Skivingand Surface Speed Calculation

Traditionally, power skiving is performedwith common shaper cutters. However, a

variety of different tools used for powerskiving is shown; the first cutter (Fig.10, left) is a shaft type that is slightlytapered without helix angle in the cut-ting teeth. This cutter can be used forgears with a helix angle. The shaft anglebetween cutter and work will be set to thehelix angle of the work. This also meansthat the helix angle of the work shouldbe above 10 in order to generate suffi-

cient cutting speed. Due to the straightnature of the cutting teeth, workpieces

Figure 6 Cutting sequence from engagement to exit.

Figure 7 Top view of unrolled partial real slots (top) and graphics (bottom).



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with small diameter and large face widthmight cause interference between the slotand the far end of the cutting blade. Theskiving cutter in the center (Fig. 10) is awafer cutter with only a few re-sharpen-ings. The cutting teeth are straight, whichmakes this cutter only suitable for work-pieces with a helix angle. The wafer cut-

ter has very short, relieved teeth, whichwill prevent interference problems in caseof helical slots that wind around a small-diameter workpiece.

The skiving cutter on the right (Fig. 10)has serrated blade front faces and teeththat are oriented under a helix angle; theblack coatings are AlCroNite and thegolden coating is TiN.

If the helix angle of the workpiece is15 and the tool helix angle is 20, thenthe shaft angle between skiving cutter

and work has to be set up to 5 (samehelix direction). If the helix directions areopposite, then a shaft angle of 35 mustbe used. An interesting situation presentsitself if the gear helix angle of the work isidentical to the cutter helix angle (sameamount and same hand). In this case theshaft angle between cutter and work iszero, and no skiving motion is generat-ed. The calculation of the cutting surfacespeed, depending on the helix angle ofthe work and the shaft angle , is shown

(Fig. 11). The upper graphic representsthe unrolled pitch cylinder with teeth andslots indicated (see also Fig. 11, right sidegraphic) for a spur gear. With = 0, theformula is simplified to the first specialcase. The lower graphic shows the for-mula simplification for the second specialcase, which occurs if the helix angle isequal to shaft angle. The cutting veloc-ity formula also considers next to thecircumferential velocity at the work gearpitch diameter the helix angle of the

work and the shaft anglebetween workand skiving cutter. The cutting veloc-ity vector is automatically directed in theflank lead direction if the formula (Fig.11) is applied. Although the formula indi-cates some interplay betweenand, themajor parameter for generation of suffi-cient cutting velocity is the shaft angle between the work and tool axes.

Figure 8 Analysis of chip formation.

Figure 9 In-feed strategy for optimized chip formation (Refs. 2, 3).

Figure 10 Solid HSS power skiving cutters coated with TiN and AlCroNite.


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High-Speed Carbide Cutter HeadSystem for Power SkivingA new type of cutter head PentacPS that uses stick blades has been devel-oped especially for power skiving (Fig.12). The blade material is carbide andthe blade profiles are 3-face-groundand all-around-coated. The blade pro-

file resembles an involute that is derivedfrom the tool reference profile (Fig. 4).The blades can either be ground as fullprofile blades just like the profiles ofthe standard skiving cutters shown inFigure 10 or as alternating left flank/right flank blades that allow it to real-ize sufficient side rake angles. This alter-nate blade arrangement offers very goodtool life and an exceptionally smooth cut-ting operation. However, the productiv-ity is slightly lower than using full-profile

blades.Due to the design of the PentacPS cut-

ter head, the blades have spaces betweenthem that are larger than the tooth thick-ness of the reference profile. PentacPS cut-ters are selected for a certain module, suchthat the blades in the cutter head representevery second, third or fourth slot of thereference profile. Regarding low work-piece run-out and high spacing quality, itis required to avoid a common denomi-nator between the theoretical number of

skiving cutter teeth and the number ofwork gear teeth. The same rule applies forsolid skiving cutters as well.

In order to establish a new cutterdesign, a procedure was developed thatallows a minimum of cutter head types.For example, external gears with a maxi-mal pitch diameter of 360 mm or internalring gears with a minimal pitch diam-eter of 450 mm and above can be skivedwith a 9-inch peripheral cutter head. Thespreadsheet in Figure 13 uses modules

from 2 to 7 mm, in 0.5 mm steps, to cal-culate a pitch diameter and the theoreti-cal number of teeth z2. The value for z2must be rounded up or down in order toreceive an integer number. This requiresa change in the pitch diameter of the tool.The developed stick blade system allowsadjustment of the blade stick out by somesmall amount to match the required pitchdiameter for the number of teeth selected.

However, the 9-inch-size cutter headsonly have blade numbers of 15, 17, 19,

21 and 23. In the next columns of thespreadsheet (Fig. 13), all existing inte-

Figure 11 Cutting velocity calculation.

Figure 12 Stick blade cutter PentacPS for power skiving with carbide blades.



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ger fractions between two and five aredetermined. The goal is to find the larg-est number of slots available in the 9-inchPentacPS line of cutters to assure themaximal productivity. In other words,the PentacPS cutter never represents thetheoretical tool tooth number with thenumber of slots rather, only a frac-

tion thereof. The theoretical number oftool teeth becomes the virtual tool toothnumber of which only a fraction is rep-resented on the cutter head. If a numberis selected and typed in the spreadsheetnext to the actual fraction of slot andtheoretical tooth number, the resultingnumber of cutter slots is shown in the lastcolumn. If this number does not matchan existing cutter head, then a second orthird number has to be chosen until amatching cutter is found.

Depending on the number of teeth ofthe work gear, the virtual number of toolteeth may be even, and never is a primenumber. This will not be of any disad-

vantage as long as a hunting-tooth rela-tionship between work and virtual cutterexists. In such cases the hunting-toothprinciple exists between work and realcutter. The peripheral stick blade cut-ter design will physically prevent a fit ofthe virtual number of blades next to eachother. The cutter drawing in Figure 14

represents each other tooth, as indicatedwith the dashed drawn (virtual) bladesbetween the real blades.

Power Skiving Machines andSoftwareDuring the last years dedicated powerskiving machines have been introduced,starting from very small gear sizes (below100 mm) up to 600 mm gear diameter(Fig. 15, left). A technology software wasdeveloped that calculates machine set-

tings from part geometry and chosen toolparameters; the software also determinesthe chip removal volume, depending onthe shaft angle between work and tool.The optimal in-feed strategy utilizingan involute roll simulation also featuresan interference check by comparing thetool path with the simulated slot surfaces(Ref. 4).

For the convenience of both gearengineer and machine setup person-nel, the power skiving technology soft-

ware resides on the control of the powerskiving machine. Coincidentally, dur-

Figure 13 Calculation scheme for cutter diameter and number of blades.

Figure 14 Virtual tool teeth.


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ing development of the power skivingprocess, it became apparent to Gleasonthat there was interest in applying thissuccessful process to bevel gear cut-ting machines as well. Manufacturerswho wanted fuller optimization oftheir Phoenix bevel cutting machinesbegan utilizing the power skiving pro-

cess for prototyping or manufacturingof small- and medium-batch sizes as a

value-added task for this rather versatilemachine. In order to address this inter-est, Gleason applied the power skivingdevelopments that had been conducteduntil 2012 and strictly on dedicatedmachines to all current Phoenix bevelgear cutting machines (Fig. 15, right);Figure 15 shows a power skiving setup ina Phoenix 600HC.

Along with this significant step, the

Gleason power skiving development teamwas expanded from only cylindrical gearexperts to a mix of cylindrical and bevelgear experts. The experience in bevel gearmanufacturing using carbide stick bladesthen led to development of the PentacPSperipheral skiving cutter system, which inturn was applied to the dedicated powerskiving machines as well.

As for power skiving, the Gleasonbevel gear cutting machines use the samesoftware as used on the PS machines.

Summary development, cycle optimi-zation, and corrections are conductedon the machine not on a remote desk-top as is common in bevel and hyp-oid gear manufacturing. Figure 16 showsthe main screens for gear data, processparameter and workholding entry.

The power skiving technology soft-ware can also be used as a standalonepackage on the gear engineers desktop.This allows the gear engineer to con-duct experiments and pre-optimizations

of future gear designs that will be soft-machined by power skiving. The desk-top software version is also more suitablefor the stick blade geometry calculation.This calculation delivers a blade-grindingsummary following the same standardsused for bevel gear cutting blades. Theblade-grinding machine accepts thosesummaries like summaries for regularbevel gear cutting blades.

The technology software for powerskiving on Phoenix machines allows the

input of tooth thickness, depth and helixangle corrections. Tooth thickness and

Figure 15 Different machines with power skiving setup.

Figure 16 Technology software process input screens (Ref. 4).



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depth are coupled corrections that fol-low a certain strategy. The correct tooththickness has the higher priority thanthe depth. In order to achieve the cor-rect thickness, the slots can be cut deeperwithin the limit the gear engineer allows.It is not recommended to cut the slotsshallow because of implications like rollinterferences in the operation of the gear-set. If the correct slot width cannot beachieved within the given possibilities,then the blades have to be corrected; or,

in case of an undersized slot, a side cut-ting in a second pass is possible, althoughit adds unwanted cutting time. If bothflanks have similar, small unidirectionalpressure angle errors (same sign), thena correction via the cutter tilt angle (Fig.1) is possible; larger pressure angle errorswith inverse signs must be executed bygrinding corrected blades.

Wet or Dry Power Skiving?A solid cutter from G50 (Rex76) mate-

rial with an AlCroNite coating is suit-able for a surface speed of 100 m/min

in a wet skiving environment. Carbidestick blades (H10F) with an ALCRONA-Pro coating allow about 300 m/min sur-face speed. However, regarding tool wearit has to be considered that in skiving

very high rpms are required in order toachieve the desired surface speed. Thisin turn creates a profile sliding whichis superimposed to the cutting speed.The profile sliding might have its highest

value at the blade tip, which has already along chip removing engagement path and

experiences due to the sliding and addi-tional side relief wear.

Cutting trials in Power Skiving haveshown it is possible to reduce the surfacespeed down to numbers between 150 and200 m/min (Under-Critical Speed, UCS)and increase the in-feed and feed rate inorder to keep the productivity high, andat the same time achieve a significantimprovement in tool life.

Chips from wet UCS skiving withAlcrona-Pro coated carbide blades and

172 m/min surface speed are shown inthe top row of Figure 17. The first rough-

ing pass used an in-feed setting of 5 mmand a feed rate of 0.045 mm per blade.The chips (Figure 17a) are large andonly slightly curved. Each chip repre-sents one flank and part of the slot bot-tom. The second pass used an in-feed set-ting of 3 mm and a feed rate of 0.28 mmper blade. This chip consists of the two

flank chips connected by the bottom chip(Figure 17b). The finishing pass usedan in-feed of 1.00 mm and a feed rate of0.015 mm per blade, and this chip has thetwo flank and the bottom chip connectedto a U-shaped appearance.

Chips d through f in Figure 17 havebeen created also with Alcrona-Pro coat-ed carbide blades and 172 m/min surfacespeed in a three-pass dry cutting processusing the same in-feed values and feedrates as applied in the wet cutting (Figure

17 a through c). The dry chips seem tohave the same appearance as the chipsfrom wet cutting except for the brownand blue color from the process heat.

The comparison between the wet anddry versions of power skiving with coatedcarbide blades shows a clear advantage ofthe dry process. The process heat helpsto plastically deform the chip during theshearing action. If the process param-eters and tool geometry are chosen tomove the process heat into the chips and

with the chips away from tool and workpiece, then a cool skiving process is theresult. Dry power skiving delivers a bettersurface finish and causes equal or evenlesser tool wear than the wet process

version. However, the chip surface onthe side adjacent to the sheared off side issmoother, and the machine power read-ing showed about 15 percent lower spin-dle power during dry skiving. The cur-rent skiving developments indicate thedry process version will deliver the bet-

ter tool life, which is expected to be moresignificant than in bevel gear cutting.

Dry high-speed UCS power skiv-ing with coated carbide blades result inthe optimal combination between lowtool wear and low skiving times. Theadditional advantage is, that machineswith medium-speed, high-torque spin-dles (e.g., 1,000 rpm max for machinesize 600 mm OD) can be applied with-out compromising the performance ofthe machine e.g. for bevel gears which

require low rpm and high torque. Thisargument is important if a manufacturer

Figure 17 Chips from wet/dry skiving and process temperature.


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applies power skiving to bevel gear cut-ting machines.

The bottom row in Figure 17 showsa dry UCS setup g, and it shows athermographic photo taken during theroughing pass at mid-face. The high-est temperatures of 107F (42C) occuraround the cutter and at the work gear

sections, which move away from the cut.These temperatures can also be mea-sured on part and cutter after the cycle.It can be concluded that the dry UCSprocess has an optimal heat transfer intothe chips and quickly reaches a rather lowand steady-state temperature of cutterand work holding.

A productivity comparison between thetraditional processes hobbing and shap-ing with three variations of the new powerskiving process is shown (Fig. 18). The

goal of this chart is to compare the pre-ferred embodiment of the different pro-cesses. In order to establish the same basisfor each process, an external ring gearwith the gear data shown in the diagramwas used for all processes. The objectivewas a finishing quality with scallop or gen-erating flat amplitudes at or below 5 m.The shaping process used an AlCroNite-coated shaper cutter from G50 materialwith 34 teeth and it was set up as a 3-cutfinishing cycle. The identical shaper cutter

was used for the wet power skiving wherethe cutting was done in four passes. Forthe hobbing process, a one-start hob with16 gashes, also from AlCroNite-coatedG50 material, was utilized in a 2-cut cycle.Dry power skiving with ALCRONA-Pro-coated H10F carbide blades is rep-resented in the diagram as UCS-skivingwith 172 m/min and as high-speed skiv-ing with 300 m/min both set up as athree-pass cycle. The dry power skiv-ing bars are based on a 24-blade and 9"

diameter PentacPS cutter head. The chipthickness in the case of UCS-skiving is 10percent-to-20-percent higher than in thecase of high-speed skiving, which reducesthe productivity difference between thetwo process variations, yet gives the UCS-skiving a tool life advantage. Figure 18indicates that power skiving has between6-to-12 times the productivity of shapingand between 1.6 and 3.3 times the produc-tivity of hobbing.

Measurement ResultsThis section discusses measurementresults from the newly developed UCSpower skiving with Pentac PS tools. Asmentioned earlier in this paper, correc-tions of the lead angle can be accom-plished with machine motions and cor-rections of tooth thickness and depth

are possible within limits using machinesettings. Unlimited tooth thickness and

depth corrections, as well as pressureangle corrections, are possible by re-grinding the stick blades. The measure-ment results (Fig. 19) show profile (top)and lead (bottom) measurement in theleft-side evaluation sheet. The measure-ment was taken after a pressure anglecorrection on the skiving blades. The lead

direction showed a perfect result after thefirst sample cutting. The waviness of the

Figure 18 Productivity comparison.

Figure 19 Measurement: profile, lead and spacing.



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lead graph is typical for power skivingand reflects the skiving scallops; however,their amplitudes are below 5 m.

Surface roughness and waviness mea-

surement results from a Zeiss surfacetracer are shown (Fig. 20). The profileroughness results in the two graphs ontop of Figure 20 delivered excellent valuesfor Raand Rz. The waviness in lead direc-tion is basically the result of the scallopamplitude of 5 m (theoretically). Due tothe different cutting condition on the twoflanks, the waviness on the right flankshows about 1.5 times the magnitude ofthe waviness of the left flank.

The right hand chart (Fig. 19) show

good results regarding fp and fu, consid-ered the skiving scallops are phase-shift-ed from tooth to tooth. Cumulative pitcherror Fpand run-out Frreflect the imper-fect temporary workholding (Fig. 17g).Improved gear quality can be achieved byusing production workholding or indi-vidual run-out truing in case of smallmanufacturing quantities. Single andadjacent tooth spacing numbers can beimproved by a lower feed rate, which willreduce the tooth-to-tooth variation due

to the moving scallops.

SummaryComplex solid skiving cutters lack someflexibility for lower quantities and forlarger parts. Next to the solid cutter disks,

Gleason developed a second solutionthat offers a high-speed dry power skiv-ing based on peripheral cutter designs.The new cutter system consists of threedifferent cutter sizes where each size isavailable with different blade numbers.Depending on the part size, this com-bination allows coverage of a rangebetween module two to module seven,with five different cutter bodies; and thestick blades can be ground on every mod-ern blade grinding machine.

The power skiving process with stickblade cutters is performed on 6-axis CNCbevel gear cutting machines. Feed andstroke motion are optimized in connec-tion with the particular stick blade geom-etry in order to create an optimized chipformation. All parameters for feed andstroke are calculated in advance in orderto assure high cutting performance, eventool wear and high tool life.

Lead correction, pressure angle bal-ance and anti-twist correction can be

achieved via delta value input direct-ly from the K- and lead-chart into thetechnology software screen on the skiv-ing machine. Although the perception in

the market is that power skiving seemsto compete only with shaping, and isparticularly suitable only for internalgears, it can also be applied to externalgears and is also equal and perhapsfaster than hobbing.

In the case of a power skiving processperformed next to bevel gear cutting on

a Phoenix 6-axis machine, the conflictof compromising the machines abilityfor bevel gear power cutting with a high-speed spindle, which suits the high-speeddry power skiving, was solved with thedevelopment of under-critical-speed(UCS) skiving. Power skiving with UCSonly requires 150 to 200 m/min effectivesurface speed, is highly productive, andhas excellent tool life.

References1. Pittler von, W. Verfahren zum Schneiden von

Zahnrdern mittels eines zahnrad-artigen, anden Stirnflchen der Zhne mit Schneidkantenversehen-en Schneidwerkzeuges, PatentApplication, Germany, March, 1910.

2. Kobialka, C. Contemporary Gear Pre-Machining Solutions, AGMA No. 12FTM11,October 2012, ISBN: 987-1-61481-042-1.

3. Stadtfeld, H.J. Optimal High-Speed Cutting ofBevel Gears, Gleason Company Publication,Rochester, New York, 2012.

4. Kreschel, J. Gleason Power Skiving: Technologyand Basics, Gleason Company Publication,Ludwigsburg, Germany, 2012.

Figure 20 Measurement: surface roughness and waviness.

Hermann Stadtfeldreceived in 1978 his B.S.and in 1982 his M.S. inmechanical engineeringat the Technical Universityin Aachen, Germany. Afterreceiving his Doctorate heworked as a scientist atthe Machine Tool Laboratory of the TechnicalUniversity of Aachen. In 1987 he acceptedthe position as head of engineering and R&Dof the Bevel Gear Machine Tool Division ofOerlikon Buehrle AG in Zurich, Switzerland.In 1992 Dr. Stadtfeld accepted a position asvisiting professor at the Rochester Instituteof Technology. Since 1994, he has worked forThe Gleason Works in Rochester, New York,first as director of R&D, and from 1996 as vicepresident R&D. After an absence from Gleasonbetween 2002 to 2005, when he established agear research company in Germany and taughtin parallel gear technology as a professorat the University of Ilmenau, he returned tothe Gleason Corporation where he holdstoday the position of vice president, bevelgear technology and R&D. Dr. Stadtfeld haspublished more than 200 technical papers and10 books on bevel gear technology. He holds

more than 50 international patents on geardesign, gear process and tools and machines.

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