1、05FTM07Spiral Bevel and Hypoid GearCutting Technology Updateby: T.J. Maiuri, The Gleason WorksTECHNICAL PAPERAmerican Gear Manufacturers AssociationSpiral Bevel and Hypoid Gear Cutting TechnologyUpdateT.J. Buzz Maiuri, The Gleason WorksThe statements and opinions contained herein are those of the au
2、thor and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractSpiral bevel and hypoid gear cutting technology has changed significantly over the years. The machines,tools, materials, coatings and processes have steadily advanced to the curren
3、t state of the art. This paper willcover the progression from mechanical machines with complex drive trains using the five cut method of cuttinggears with coolant, to machines with direct drive CNC technology dry cutting gears by the completing methodwith carbide and high speed steel tools. The late
4、st cutting tool materials and tool coatings will be discussed.Production examples from the automotive and truck industries will be provided, as well as examples from thegear jobbing industry.Copyright 2005American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22
5、314October, 2005ISBN: 1-55589-855-61Spiral Bevel and Hypoid Gear Cutting Technology UpdateT.J. Buzz Maiuri, The Gleason WorksIntroductionUp until the 19thcentury gear manufacturing was anart. Almost all gears were hand made and the gearswere cut with form cutters shaped to correspond tothe spaces be
6、tween the teeth.1The first known gearcutting by machine was developed by Juanelo To-rian (1501-1575). He was able to produce up tothree gears per day on his hand-powered machine,using cutting tools that were nothing more thanrotary files.2In 1910 a machine was invented forcutting spiral bevel teeth
7、with face hob cutters usingthe continuous index process. In 1913 a processand machine was introduced making it commercial-ly practical to produce spiral bevel gears using a cir-cular face mill cutter and an intermittent index of theblank. In 1927 a patent was granted for the first suc-cessful method
8、 of producing hypoid gears.3Thefirst machine capable of producing either face milledor face hobbed gears was introduced in 1988, andshortly thereafter full CNC control machines wereintroduced. Today, gears are made on high produc-tion automated machines with direct drives and pre-cision cutting tool
9、s.Face Mill (Single Index) and Face Hob(Continuous Index)There are two main methods of producing spiralbevel and hypoid gears in the production environ-ment today. There is the single indexing method re-ferred to as face milling Figure 1, and the continu-ous indexing method Figure 2 referred to as f
10、acehobbing.Differences in geometry exist between the gearsproduced by the two methods as can be seen by theaccompanying figures.Face Milled Geometry Single IndexTypically, gears produced by face milling have a ta-pered tooth depth the tooth is usually deeper at theheel, shallower at the toe and may
11、have a constantslot width Figure 3 and Figure 4. The tooth thick-ness is tapered, and the curvature along the facewidth is that of a circular arc Figure 7.Figure 1. Single IndexingFigure 2. Continuous IndexingFigure 3. Tapered Tooth Depth2Figure 4. Tapered Tooth DepthFace Hobbed Geometry ContinuousI
12、ndexGears produced by face hobbing have a constanttooth depth and a tapered slot width Figure 5 andFigure 6. As with face milled gears, the tooth thick-ness is tapered. The curvature along the face widthis that of an extended epicycloid Figure 7.Figure 5. Uniform Tooth DepthFace Hobbing or Face Mill
13、ingThere may be possible strength benefits in facehobbing due to what is known as the small cutter ef-fect. The small cutter effect is good for strength be-cause the tooth pattern is “pocketed” near the cen-ter of the tooth under load. Face hobbed gears arealso more conducive to the lapping process
14、due tothe direction of the generating flats on the tooth sur-face. Face hobbed gears can also be finished byskiving. Grinding is not recommended for facehobbed gears, as discussed later in the paper.Figure 6. Uniform Tooth DepthFace hob cycle times are often faster than face mill-ing due to the cont
15、inuous indexing method and facehobbing is always a completing process.In face milling one slot is cut at a time and the cuttermust withdraw and then index to the next slot. Facemilled gears can be lapped, skived or ground.Hard Finishing the Cut GearsThe differences in geometry from the design andmet
16、hod of production play a very important role inhow the gears may be finished. As mentionedabove, face milled gears can either be lapped,skived, or ground. Face hobbed gears should onlybe lapped or skived for the finishing operation.Although it is possible to grind a gear cut by the facehobbing metho
17、d, it is not recommended. The rea-son can be seen in Figures 7 and 8. The facehobbed gear will have an epicycloidal shape alongthe face width. The grinding operation would re-move the epicycloidal shape and leave a circulararc. This would result in a gear with an uneven casedepth after the grinding
18、process. In some cases, itmay turn out that all or most of the case depth wouldbe removed in some areas of the tooth and not eventouch (clean up) the tooth surface in other areas. Asimilar problem with uneven case depth will existbecause of the differences in tooth depth betweenface hobbed gears par
19、allel depth and face milledgears taper depth.3Face HobbingExtended EpicycloidFace MillingCircular ArcFigure 7.Face HobbingTapered SlotWidth TaperedTooth ThicknessFace MillingConstant SlotWidth TaperedTooth ThicknessFigure 8.Five Cut Process and CompletingProcessThe manufacturing of face milled spira
20、l and hypoidgear sets can be accomplished by using the “FiveCut Process” or by the “Completing Process”.Early production of face milled gears utilized theFive Cut Process, which consists of five indepen-dent operations two operations to finish the gear,and three operations to finish the pinion. The
21、gear isroughed out using an alternate blade roughing cut-ter, then finished in a second operation with an alter-nate blade finishing cutter. An alternate blade cutterhas an inside blade in one slot in the cutter head andan outside blade in the adjacent slot so both sides ofthe tooth slot are cut in
22、one operation. The first op-eration on the pinion is a roughing operation with analternate blade roughing cutter. The second andthird operations on the pinion involved cutting eachflank separately in different operations. The pinionconvex flank is finished with a cutter having insideblades only, and
23、 the pinion concave flank is finishedwith a cutter having only outside blades. Many com-panies are still utilizing the five cut process in pro-duction, however, most companies have switchedto the completing process.In the Completing Process both sides of the toothslot are finished with a single cutt
24、er in one operationfrom a solid blank. The cutters used for completinghave alternate blades inside and outside. Somecutter systems also use what is called a bottomblade in addition to the inside and outside blade.The completing process is applicable to either facemilling or face hobbing.In 1996 a si
25、gnificant improvement was introduced inthe production of spiral bevel and hypoid gears. Atthe IMTS Show in Chicago, POWERCUTTING wasintroduced. By definition, POWERCUTTING is theprocess of producing gears at high speeds with orwithout the use of coolants. This is achieved usingstick blades made out
26、of carbide material with a spe-cial tool coating. Since its introduction, almost allbevel cutting machines manufactured today are ar-ranged for high speed cutting with carbide bladeswithout the use of any coolant. The advantages ofhigh speed cutting with carbide are significant. Thecycle times are r
27、educed, the tool life is improved,the gear quality is better, and the elimination of thecoolant in the cutting process is environmentallyfriendly. See the production analysis example in theappendix.4Cutter SystemsThere are different cutter systems to choose from,depending on the method of producing
28、gears andthe supplier of the cutter system. In theearly days ofproducing spiral bevel gears by the single indexingmethod, cutters were available in three generaltypes integral blade, segmental or inserted blade.Integral blade cutters are also called solid body cut-ters with the blade solid with the
29、head. Segmentalcutters have groups of blades bolted to the cutterhead. Inserted blade cutters have individual bladesbolted to slotted heads as shown in figures 9through 11.The inserted blade circular face mill cutters can beused for single side cutting fixed setting by using allinside blades or all
30、outside blades in the cutter head.They can also be used for roughing and completingby using alternating inside and outside blades.Some cutter systems offer a third blade in the groupwith the inside and outside blade called a bottomblade. The blades have curved side relief and aresharpened in the cut
31、ter head by grinding the face ofthe blade only. The blades are bolted radially to thecircumference of the cutter body. Parallels and ta-pered shims between the blade and cutter body areused for mounting and truing the blades Figure 10.A stick blade cutter system for face milling wasintroduced in the
32、 1970s Figure 12. Stick bladesystems allow for more blades to be placed in thecutter head. The cutter heads cutter body haveprecision ground slots for exact radial and angularlocation of the blades. Stick blade systems for facemilling include the Gleason RSRand KlingelnbergARCON systems.4Klingelnber
33、g has a face millsystem called TWIN Blade that utilizes blades withzero degree rake angle and a blade width such thateach blade cuts both the convex and concave flanksof the work.5Stick blade systems for the face hobbing operationFigure 13 are always used in a completing processwhere the tooth slot
34、is completed in one cut. Thecutter head slot locations and orientation for facehobbing are more complex than for face milling.Early cutter systems utilized a three blade configu-ration in the blade grouping consisting of an insideblade, outside blade and a bottom blade. Currentcutter systems such as
35、 the Gleason TRI-ACsys-tem and Klingelnberg SPIRON system use onlyan inside blade and an outside blade for facehobbing.4Figure 9.Figure 10.Figure 11.5Figure 12.Figure 13.Figure 14.Figure 15.Stick blades cannot be sharpened in the cutterhead, but all relief surfaces are ground duringsharpening, which
36、 means blade pressure anglesand blade curvatures can be changed during thesharpening process. This is a significant advantageover the circular face mill cutters show in Figures 9through 11.In the late 1990s Gleason introduced a stick bladecutter system called PENTAC Figure 14 whichhas a positive 3-p
37、oint seating surface with a 60 /30 pentagon shaped stick cross section Figure15. The cutter head and blade design offers a morerigid system and allows for easier cutter buildingand truing. PENTAC style blades are availablefor either face milling or face hobbing. This cuttersystem offers improved eas
38、e of assembly andbladetruing over the other stick blade systems.Profile 2 Face and Profile Plus FrontFace 3 face sharpeningSome stick blade systems have pre-raked frontfaces. If new blades are coated, it is only necessaryto sharpen the top, pressure angle and clearanceangle of the blade, which is th
39、e traditional method ofsharpening. This method of sharpening preservesthe coating on the front face, and it is not necessaryto coat the blade after every sharpening.It has been demonstrated that with fully coated allaround coated blades, the tool life can be improvedby a minimum of 50%. When conside
40、ring re-coat-ing of blades after every sharpening, it is necessaryto consider the additional cost of stripping, recoat-6ing, and stocking additional blades. These costsmust be evaluated against the benefits of additionaltool life.One of the difficulties with using all-around coatedblades is the effe
41、ctive reclaiming of the surfaces forre-coating. Most chemical or mechanical means ofstripping blades often results in surface finish deteri-oration, and cobalt leaching in the case of carbideblades. It is possible to mask the substrate so thatthe coating is applied only to the sharpened profile.A re
42、liable method of reclaiming the surface is to addthe grinding of the front face during sharpening.This additional step will remove the coating off allsurfaces, and thus the blade is automaticallyreclaimed for all-around coating.Figure 16. 3 Face Sharpened BladeCutting Tool MaterialsEarly cutting too
43、l materials from the 1900s to1940s consisted of high speed steels designatedas 18-4-1, which consisted of 18% tungsten, 4%chromium and 1% vanadium.6Today we have manymaterials to choose from. Table 1 lists high speedsteel materials in use today, their chemical com-position and Rockwell C hardness.Wi
44、th the advent of cutting gears without coolant,carbide materials are the choice for bevel gear cut-ting operations today.Cemented carbides are a range of composite mate-rials that consist of hard carbide particles bonded to-gether by a metallic binder. The proportion of car-bide phase is generally b
45、etween 70-95% of the totalweight of the composite.From experience gained over many installations us-ing dry carbide cutting, the ISO “K” grade extra finegrain carbide is found to be the most appropriategrade for bevel gear cutting operations. ISO “K”grades of carbide are a simple two-phase composi-t
46、ion consisting of tungsten carbide (WC) and cobalt(Co). A typical composition of a “K” grade carbide is90% WC and 10% Co by weight. “K” grades havegood edge stability and abrasion resistance with agrain size range of 0.5mm0.9mm.Table 1.CCr WMoVCoHRCCPM M2 1.0 4.2 6.4 5.0 2.0 - 64ASP 2023 1.3 4.2 6.4
47、 5.0 3.1 - 64CPM M4 1.4 4.3 5.8 4.5 3.6 - 64CPM REX54 1.45 4.3 5.8 4.5 3.6 5.0 65CPM REX45 1.3 4.1 6.3 5.0 3.1 8.3 66ASP 2030 1.3 4.0 5.0 6.5 3.0 8.0 66CPM T15 1.6 4.0 12.3 - 5.0 5.0 66CPM REX76 1.5 3.8 10.0 5.3 3.1 9.0 67ASP 2060 2.3 4.0 6.5 7.0 6.5 10.5 68CPM REX121 3.3 3.8 10.0 5.3 9.0 9.0 707Whe
48、n initial trials for dry carbide cutting began, ex-periments were conducted on a variety of carbidegrades and range of 6% to 12% Cobalt. At that time,10% Cobalt was selected as the best compromisefor a “Standard” blade material. More recently, cut-ting high wear resistance steels has indicated anadv
49、antage using carbides with 6% Cobalt. Howev-er, the increase in brittleness can lead to edge chip-ping in production. Note that increasing the cobaltcontent increases the toughness of the material, butdecreases the wear resistance Figures 17 & 18.Other carbide specifications may be an advantagefor a particular application based on the materialcomposition, structure, and hardness.Figure 17. Fracture toughnessFigure 18. Wear resistanceThe following figures show some of the relative ma-terial properties of ca
