1、12FTM24AGMA Technical PaperRecent Inventions andInnovations in InductionHardening of Gearsand Gear-likeComponentsBy V. Rudnev, Inductoheat Inc.Recent Inventions and Innovations in Induction Hardening ofGears and Gear-like ComponentsDr. Valery Rudnev, Inductoheat Inc.The statements and opinions conta
2、ined herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractPresentation focuses on recent inventions and innovations (last 4-6 years) in induction hardening of gearsand gear-like components, including but not
3、 limited to:- “Know-how” in controlling distortion of induction hardened gears.- Simultaneous dual-frequency induction hardening.- Advanced induction hardening process recipes when hardening small and medium size gears.- Novel inductor designs to minimize a distortion when induction hardening of hyp
4、oid and spiral bevelgears.- IFP technology for induction gear hardening.- Induction tempering andstress relievingof gear-likecomponents withimprovedtemperatureuniformity.Presentationalsoprovidesareviewofbasicprinciplesandapplicationsdevotedtoinductionhardeningsmall,medium and large size gears using
5、tooth-by-tooth techniques and encircling method.Copyright 2012American Gear Manufacturers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-055-13 12FTM24Recent Inventions and Innovations in Induction Hardening of Gearsand Gear-like ComponentsDr. Val
6、ery Rudnev, Inductoheat Inc.Depending upon the gear size, required hardness pattern and tooth geometry, gears are induction hardenedbyencirclingthewholegearwithacoil(so-called“spinhardeningofgears”),orfor largergears, heatingthem“tooth-by-tooth” 1-6.“Tooth-by-tooth” hardeningTooth-by-toothmethodcomp
7、risestwoalternativetechniques:“tip-by-tip”or“gap-by-gap”hardening1-4.“Tip-by-tip” method can apply a single-shot heating mode or scanning mode. While “gap-by-gap” tech-niques exclusively applies the scanning mode. Inductor scanning rates are typically within 6 mm/sec to9 mm/sec. Both “tip-by-tip” an
8、d “gap-by-gap” techniques are typically not very suitable for small and finepitch gears (modules smaller than 6) 1,2.Accordingtothe“tip-by-tip”hardening,aninductorencirclesabodyofsingletooth. Presently,thistechniqueis not used, because the hardening patterns typically do not provide required fatigue
9、 and impact strength.“Gap-by-Gap”hardeningismuchmorepopulartechniquecomparedto“tip-by-tip”method. Thisisthereas-on why the term “tooth-by-tooth” hardening is often associated with the “gap-by-gap hardening method.“Gap-by-Gap” hardening requires the inductor to be symmetrically located between two fl
10、anks of adjacentteeth. Inductor geometry depends upon the shape of the teeth and the required hardness pattern. Speciallocators (probes) or electronic tracing systems are often used to ensure proper inductor positioning in thetooth space.Twoscanningtechniquesusedincludeonewheretheinductorisstationar
11、yandthegearismoveable,andtheother where the gear is stationary and the inductor is moveable. Later technique is more popular whenhardening large-sizegears. Inductors canbe designedto heatonly theroot and/orflank ofthe tooth,leavingthetipandtoothcoresoft,toughandductile(Figure 1). Thoughthisisoneofth
12、eoldesthardeningtechniques,recent innovations continue improving quality of gears heat-treated using this method.Figure 1. In tooth-by-tooth hardening, inductors can be designed to selectively harden specificareas of gear teeth where metallurgical changes are required 24 12FTM24Thermal expansion of
13、metal during the heating should be taken into consideration when determining andmaintaining the proper inductor-to-tooth air gap. After gear loading and initial inductor positioning, theprocess runs automatically based on an application recipe. Figure 2 shows examples of inductiontooth-by-tooth hard
14、ening machine.When developing tooth-by-tooth gear hardening process, particular attention should be paid toelectromagnetic end/edge effects and the ability to provide the required pattern in the gear end areas. Uponscanning gear tooth, the temperature is distributed within gear roots and flanks quit
15、e uniformly. At the sametime, since the eddy current makes a return path through the flank and, particularly through the tooth tip,proper care should be taken to prevent overheating the tooth tip regions, in particular at the beginning and atthe end of the scan hardening. Improved system design help
16、s to maintain required hardness uniformity.Specifics of gear geometry demand a particular process control algorithm. In the past, the process controlrecipe was limited to an available variation of power and scan rate vs. inductor position. Recent innovationsbringuniqueabilityofInductoheatsnovelinver
17、terstoindependentlycontrolbothpowerandfrequencyduringscanning operation, which optimizes electromagnetic and thermal conditions at initial, intermittent and finalstagesofscanning. Asanexample,Figure 3showstheSTATIPOWERIFPt(IndependentFrequencyandPower control) inverter. The ability to independently
18、change during scanning the frequency and power of aninductionsystem represents the long-awaiting dream of commercial inductionheat treaters,sincesuchtypeof setup would provide the greatest process flexibility. STATIPOWER IFPtis a novel IGBT-type powersupply specifically designed for hardening and te
19、mpering applications allowing independently adjustablefrequency via CNC-program in a 5-40kHz frequency range and power in the range of 10-360kW. Thisconcept substantially expands heat treat equipment capabilities for processing parts by programming powerand/or frequency changes on the fly, maximizin
20、g heating efficiency and temperature uniformity while heatingcomplex geometry componentsFigure 2. Induction gear hardening machine for a large bearing ring with teeth located onoutside (Courtesy of Inductoheat Inc.)5 12FTM24Figure 3. Inductoheats STATIPOWER IFPtis a novel IGBT-type power supply spec
21、ificallydesigned for induction hardening and tempering applications allowing independently adjustablefrequency via CNC-program in a 5-40kHz frequency range and power in the range of 10-360kWGear spin hardening (encircling inductors)Spinhardeningisthemostpopularapproachforinductionhardeninggearswithf
22、ine- andmedium-sizeteeth.Gearsarerotatedduringheatingtoensureanevendistributionofenergy. Single-turnormulti-turninductorsthat encircle the whole gear can be used 1,3-6. When applying encircling coils, it is possible to obtain sub-stantially different hardness patterns by varying process parameters.A
23、sarule,whenitisnecessarytohardenonlythetoothtips,ahigherfrequencyandhighpowerdensityshouldbe applied; to harden the tooth roots, use a lower frequency. A high power density in combination with therelatively short heat time generally results in a shallow pattern, while a low power density and extende
24、d heattime produces a deep pattern with wide transition zones.Quiteoften,topreventproblemssuchaspitting,spalling,toothfatigue,andenduranceandimpactlimitations,it is required to harden the contour of the gear, or to have gear-contour hardening (Figure 4). This often alsomaximizes beneficial compressi
25、ve stresses within the case depth and dramatically minimizes distortion ofas-hardened gears keeping it under 80-100 microns (0.003” 0.004”).Many times, obtaining a true contour hardened pattern can be a difficult task due to the difference in currentdensity (heat source) distribution and heat transf
26、er conditions within a gear tooth.Simultaneous dual frequency gear hardeningSome induction practitioners have heard about simultaneous dual frequency gear hardening, which utilizestwo appreciably different frequencies working on the same coil at the same time 6. Low frequency helps toaustenitize the
27、 roots of the teeth and high frequency helps to austenitize the teeth flanks and tips.However, it is not advantageous have two different frequencies working simultaneously all the time. Manytimes,dependinguponthegeargeometry,itispreferableapplyinglowerfrequencyatthebeginningofheatingcycleandafterach
28、ievingadesirablerootheating,thehigherfrequencycancomplementinitiallyappliedlowerfrequency completing a job by working together.6 12FTM24Figure 4. Contour hardened gears (Courtesy of Inductoheat Inc.)Figure 5 shows Inductoheats single-coil dual frequency system that comprises medium frequency (10kHz)
29、and high-frequency (120 to 400kHz) modules working simultaneously or in any sequence desirable tooptimizepropertiesoftheheat-treatedgears6. Totalpowerexceeds1,200kW. Asexpected,smallergearswill require less power.The Inductoheats simultaneous dual frequency induction gear hardening system (Figure 5)
30、 also has some“auto-match”itemstosimplifytuning. Itisruggedandcanbe usedfor high-volumesingle-shot hardeningofseveral powertrain components, dramatically minimizing distortion of heat-treated parts and providing asuperior hardness pattern with favorable distribution of residual stresses.Figure 5. In
31、ductoheats simultaneous dual frequency inverter for gear contour hardening(Courtesy of Inductoheat Inc.)7 12FTM24Novel development in induction gear hardening - TSH steelsThere was a belief that not all gears and pinions were well suited for induction hardening. Hypoid and bevelgears, spiral bevel a
32、utomotive pinions and noncircular gears used to be rarely induction hardened andtypically carburized. This situation has been changed. As an example, Figure 6a and Figure 6b show anexample of inductively case hardened components 7,8.TSH steels are low hardenability (LH) low-alloy steels characterize
33、d by limited hardenability and reducedtendency for grain growth during heating into the hardening temperature range. They can be substituted formore expensive standard steels typically used for conventional induction hardening or carburizing grades.TSHsteelshavesignificantlylessalloyingelementssucha
34、smanganese,molybdenum,chromiumandnickel,making them less expensive than majority of conventional low alloy steels. Their chemical composition issomewhere between micro-alloy steels and plain carbon steels, providing fine-grain martensite withextremely high compressive stresses at the tooth surface.W
35、ithTSHtechnologycomponentsareusuallythroughheatedatrelativelylowtemperaturessufficientforaus-tenization or partial heated (depth of heating needs to be 2-3x deeper than required harden depth) and thenare rapidly quenched. The hardened depth is mainly controlled by the steels chemical composition. Ev
36、enthough, components made from TSH steels are often heated through, their limited hardenability allowsobtaining crisp hardness case depth with well-controlled hardness pattern having minimum case hardnessdeviations even when hardening complex-shaped parts (Figure 7 and Figure 8).a) b)Figure 6. TSH T
37、echnology un-interrupted induction hardened pattern is obtained on a spiralbevel gear (Courtesy of ERS Engineering Corp.)Figure 7. Section of the induction hardened transmission gear(Courtesy of ERS Engineering Corp.)8 12FTM24Figure 8. Induction hardened automotive journal cross(Courtesy of ERS Engi
38、neering Corp.)In the past, it was practically impossible to induction harden components shown on Figure 6, Figure 7,Figure 8 and Figure 9). Now it ispossible toget thoseimpressive uninterruptedhardness patternsby usingasimple operation: through heating those parts using low frequency inverters and w
39、ater quenching. Noticed,thatspiralbevelpinion(Figure 6)wasinductionhardenedonOD,IDandteethregionusingasingleoperationhaving continuous hardness pattern. The carrier pin (Figure 9) was induction hardened on outside surface(1.25” diameter) and two inside diameters (longitudinal and transversal) using
40、a single operation that alsoproduced un-interrupted case hardness pattern. Inside diameter of longitudinal hole was 0.5“. Insidediameter of the transverse hole was 0.25” 7.ConclusionsInduction heat-treating being environmentally friendly, green and lean technology is increasingly popularchoice for i
41、nduction hardening of gears and gear-like components. Recently developed inverters andprocess know-how, further expands its capabilities.Figure 9. Carrier pin simultaneous OD and ID hardening (Courtesy of ERS Engineering Corp.)9 12FTM24References1 Rudnev, V. and Loveless, D., Handbook of Induction H
42、eating, Marcel Dekker, NY, 2003.2 Doyon, G., Brown, D., Rudnev, V., Andgea, F., Stilwala, C. and Almeida, E., Induction heating helps toput wind turbines in high gear, Heat Treating Progress, September, 2009, p.55-58.3 Rudnev, V., Spin Hardening of Gears Revisited, Heat Treating Progress, ASM Int.,
43、March/April, 2004,p.17-204 Rudnev, V., Induction hardening of gears and critical components, Part 1, Gear Technology, p 58-63,Sept./Oct. 20085 Rudnev, V., Induction hardening of gears and critical components, Part 2, Gear Technology, p 47-53,Nov./Dec. 20086 Rudnev, V., Single-coil dual frequency ind
44、uction hardening of gears, Heat Treating Progress, ASMInternational, October, 2009, p 9-117 Breakthrough contour hardening, ERS Engineering brochure, 20118 Brayman,S.,Kuznetsov,A.,Nikitin,S.,Binoniemi,B.andRudnev,V., Contourhardeningbevel,hypoid,and pinion gears, Gear Solutions, September, 2011, p. 30-35.
