1、12FTM22AGMA Technical PaperCrack Testing and HeatTreat Verification ofGears Using EddyCurrent TechnologyBy D. DeVries, Criterion NDTCrack Testing and Heat Treat Verification of Gears UsingEddy Current TechnologyDan DeVries, Criterion NDTThe statements and opinions contained herein are those of the a
2、uthor and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractWhile eddy current technology has long been used in the testing of bar, tube, and wire stock, advances inelectronics, automation, and coil design have paved the way for a new gene
3、ration of testers specificallydesigned for component testing applications. This includes the testing of gears and bearings which go intoautomotive and industrial applications. These testing systems easily integrate into production processesallowing forin-linetesting atproductionline speeds. Inadditi
4、on toenabling 100%of production componentstobeinspected,itcanhelpmonitorupstreamprocessesnotifyingoperatorsthatsomethingisnotfunctioningcorrectly. This greatly reduces scrap and warranty costs for gear and bearing manufacturers.Eddy current crack testing is performed by passing a small pair of coil
5、windings over a section of thecomponenttobetested. Thesecoilwindingsaresmallenoughtotestbetweengearteeth, andwithmulti-coilprobescantestverycomplexshapes. Mostcracktestapplicationsrequireonlyonetestfrequencysincemosttests require the detection of only surface flaws. Simultaneous testing with multipl
6、e frequencies allows fortesting of both surface and sub-surface defects when inspecting non-ferromagnetic parts.While not an absolute hardness test like a Rockwell test, eddy current heat treat verification can achievesortingresultsonparwithRockwelltesting. Thishasbeendemonstratedwithbothforgedandpo
7、wdermetalgears. Eddy current heat treat inspection coils come in both standard encircling coil configurations andmulti-coil custom configurations. The custom configurations allow for precise location testing verifying thatinduction heating parameters were correctly applied. Defects to be tested incl
8、ude misplaced case, shallowcase,shortquench,delayedquench,aircooled,non-heat-treat,andgroundoutconditions. Whenperformingheat-treatinspection,multipletestfrequenciesareusedtoreliablydetectthesevariousheat-treatanomalies.Eddy current testing offers fast, repeatable testing of gears and bearings. Test
9、ing data on each componentcan be stored electronically and re-analyzed off-line at a later date. Eddy current test instruments aredesignedtointegratewith PLC sinmaterialhandlingstationstosetupreal-timerejectioncapabilities. Theseare all features that complement modern QC requirements.Copyright 2012A
10、merican Gear Manufacturers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-053-73 12FTM22Crack Testing and Heat Treat Verification of GearsUsing Eddy Current TechnologyDan DeVries, Criterion NDTWhile eddy current technology was initially developed
11、for testing of bar, tube, and wire, advances inelectronics, automation and coildesign havepaved theway for a newgeneration of systems specifically de-signed to test components such as gears that go into automotive and industrial applications. These eddycurrentsystemsnotonlydetectcracksincomponents,b
12、utcanalsoverifyproperheat-treatconditions,properalloy composition, and the presence or absence of features such as splines or teeth.Eddycurrentsystemsarefast,clean,repeatableandeasytointegrateintoproductionprocesses allowingforin-linetestingatproductionlinespeeds. Inadditiontoenabling100%ofproductio
13、ncomponentstobeinspec-ted,eddycurrenttestinghelpmonitorupstream processesnotifyingoperatorsthat somethingis notfunction-ingcorrectly. This greatly reduces scrapandwarranty costsfor gearmanufacturers. Eliminatingorreducingoff-line chemical testing such as dye penetrant, magnetic particle or acid etch
14、 allows companies to reducewaste and go green.Eddy current 101Eddycurrenttestingworksbyinducinganelectromagneticfieldintoaconductivematerialandthenlookingforanomalies in that field. Figure 1 shows an energized coil that induces eddy currents to flow in the materialunder test. Changes in the material
15、 due to cracks or “structure” changes suchas heat treat variation, causetheeddycurrentsinthematerialtoflowdifferently. This differenceis detectedby aneddy currentinstrument.Figure 2shows ablock diagram of an eddy current test system. The eddy current instrument sends asinglefrequency or multiple fre
16、quencies out to a single coil or multiple coils. The real-time signal processing elec-tronics compares the returned signals with the sent signals and determines whether an alarm condition hasoccurred. If an alarm condition has occurred, a signal is sent to a PLC within a material handling station to
17、rejectthepartfrom theassembly line. Testingdatacanbesenttothefactory MESor QualitySystem totracktrends and store data. This data can be stored on-premise or in the cloud.Figure 1. Eddy current flows4 12FTM22Figure 2. Block diagram of an eddy current testing systemCrack testingEddy current crack test
18、ingis performedby passing apair of coil windings over asection of the component tobe tested. These coil windings can be made small enough to test between gear teeth, and with multi-coilprobes can test very complex shapes. Most crack test applications use one test frequency as they only re-quiredetec
19、tionofsurfaceflaws. Simultaneoustestingwithmultiplefrequenciesallowsfor testingof bothsur-face and sub-surface defects when inspecting non-ferromagnetic parts.Aneasytoseecracktestapplicationis showninFigure 3. Inthis case,thecarriergear experiencedcrackingupon assembly. The probe assembly shown in F
20、igure 4 was used to identify the flaws.Figure 3. Cracks in carrier gear assembly5 12FTM22Figure 4. Carrier gear assembly eddy current probe fixtureHeat treat verificationWhilenotanabsolutehardnesstestlikeaRockwelltest,eddycurrent heattreat verificationcanachievesort-ing results on par with Rockwell
21、testing. This has been demonstrated with both forged and powder metalgears. Eddy current heat treat inspection coils come in both standard encircling coil configurations andmulti-coil custom configurations. The custom configurations allow for precise location testing verifying thatinduction heating
22、parameters were correctly applied. Defects to be tested include misplaced case, shallowcase,shortquench,delayedquench,aircooled,non-heat-treatandgroundoutconditions. Whenperformingheat-treatinspection,multipletestfrequenciesareusedtoreliablydetectthesevariousheat-treatanomalies.Figure 5shows aheat t
23、reatedreactioninternalgear that neededto beheat treat tested intwo areas. Ontheleft hand side is the custom designed eddy current probe used to test the gear.Figure 6 shows a good example of a complex heat treat patternin acut-away bearingsample. The probeinFigure 7hasfourindividualcoilstoverifyprop
24、erplacementanddepthofheat treatat variouslocations onthepart. Thevisiblecoilwindingonthebottom inspects thebottom flangearea. Figure 8andFigure 9showthematerial handling station associated with this test.Figure 5. Eddy current probe and heat treated internal gear6 12FTM22Figure 6. Complex heat treat
25、 pattern on wheel spindle bearingFigure 7. Wheel spindle eddy current harness probeFigure 8. Heat treat test fixture7 12FTM22Figure 10 shows a set of powder metal gears that were tested just downstream of a heat treat furnace forproperhardness. Thetestwasdesignedtoinspect100%ofthecomponentsupto60par
26、ts/minute. Acorrela-tion between Rockwell hardness and eddy current hardness showed only about 13 HRB points variation.During a follow on production test, nearly 35,000 samples were tested with eddy current. The Rockwellhardness readings wereonly accurateto1.0HRB whiletheeddy current testingprovided
27、 moreconsistentresults. Figure 11 shows the correlation data.Figure 9. Heat treat testing station in production lineFigure 10. Powder metal gearsFigure 11. Correlation of eddy current and Rockwell hardness for powder metal gears8 12FTM22Figure 12shows aflangeareaof afulllengthaxleshaft withsplines o
28、ntheother end. Theapplicationwastoverify that proper heat treating was applied in the area indicated. Figure 13 shows the results of amulti-frequency test with grouping of the results from different conditions.Eddy current testing can also verify that proper materials were used in fabrication. Figur
29、e 14 shows a drivegearandeddycurrentprobes. Thistestwasputinplacetoverifythatasupplierwas deliveringgears withtheproper alloy.Figure 12. Axle flange heat treat areaFigure 13. Eddy current testing results for axle flange9 12FTM22Figure 14. Drive gear and eddy current probes used for alloy sortingAsse
30、mbly testingEddy current testingcanalsobeusedtoverify proper featuremanufacturing includingdetection of broachesand splines. It can also test for proper assembly of sub components. An eddy current test was designed toverify that all the needle bearings used in the assembly shown in Figure 15 were pr
31、esent.SummaryEddycurrenttestingoffersfast, repeatabletestingofgearsandothercriticalmetalcomponents. Testingdataon each component can be stored electronically and re-analyzed off-line at a later date. Eddy current testinstruments are designed to integrate with PLC s in material handling stations to set up real-time rejectioncapabilities. These are all features required in today s modern manufacturing environment.Figure 15. Gear assembly
