MULTI-FREQUENCY AXLE

SCAN HARDENING

Prof. Valentin Nemkov

Eng. Robert Goldstein

International Union for

Electricity Applications Association of the Polish

Electrical Engineers

Presented at the UIE Congress in Krakow, May 19-21, 2008

WWW.FLUXTROL.COM

Overview

• Background on Axle Hardening

• Current Coil Designs for Scan Hardening

• Axle Scan Hardening Design

– Traditional Hardening

– Optimized Single-frequency Hardening

– Optimized Multi-frequency Hardening

• Conclusions

Background on Axle Hardening

• Axles were one of the first parts hardened by induction

• Original process was scan hardening

• With improved power supplies and increased production demands, single shot method emerged. Both technologies used now, with scanning method as prevailing for long axles

Photo Courtesy of

AjaxTOCCO Magnethermic

• Typical light truck axles and car hubs

Background on Axle Hardening ctd.

Background on Axle Hardening ctd.

• Main difficulty is to achieve a combination of proper fillet hardening with high scanning speed and proper pattern in transient area

• Optimization of two-turn hardening coil at 1 and 3 kHz was presented at HES-07 Symposium in Padua

• Additional improvement due to frequency variation is the new topic in current presentation

Current Scan Hardening Inductors

• Two major inductor types

used for scan hardening:

– Single turn coils

• Machined MIQ

• Formed tubing (1)

– Two turn profiled coils (2)

• Single turn coils provide better

pattern control in fillet area

• Two turn coils provide higher

scanning speed

1 2

Geometry for Simulation:

2-turn Standard Coil

Box for motion • Deep case hardening –

10–14 mm

• Shaft diameter 48 mm

• Frequency used - 1 and 3 kHz

• Short term temperature surface Tmax = 1100 C

• Available power 100 kW per spindle

Standard 2-turn Coil: Temperature

Distribution at 1kHz Color Shade Results

Quantity : Temperature Deg. Celsius

Time (s.) : 23 Pos (mm): 138.999 Phase (Deg): 0

Scale / Color

20.10919 / 83.03406

83.03406 / 145.95891

145.95891 / 208.88379

208.88379 / 271.80862

271.80862 / 334.73349

334.73349 / 397.65836

397.65836 / 460.58319

460.58319 / 523.50806

523.50806 / 586.43292

586.43292 / 649.35779

649.35779 / 712.28265

712.28265 / 775.20752

775.20752 / 838.13239

838.13239 / 901.05725

901.05725 / 963.98212

963.98212 / 1.02691E3

After 10 sec dwell + “Jump”

+ 1sec scan at 20mm/sec

Color Shade ResultsQuantity : Temperature Deg. Celsius

Time (s.) : 11 Pos (mm): 25 Phase (Deg): 0

Scale / Color

20.00348 / 86.64462

86.64462 / 153.28577

153.28577 / 219.92691

219.92691 / 286.56805

286.56805 / 353.2092

353.2092 / 419.85034

419.85034 / 486.49149

486.49149 / 553.13269

553.13269 / 619.7738

619.7738 / 686.41492

686.41492 / 753.05603

753.05603 / 819.69727

819.69727 / 886.33838

886.33838 / 952.97949

952.97949 / 1.01962E3

1.01962E3 / 1.08626E3

9.5 mm/sec scan –

limited by power

Drawbacks of this coil:

• Marginal pattern control

• Difficult setup

• Low efficiency and scan speed

Steps to Improve the Inductor

• Change the profile of both turns

• Apply Fluxtrol A magnetic flux controller to

the lower turn to improve heating of the

fillet area

• Bring the upper turn closer to the part to

increase preheating and facilitate faster

scanning

Optimized 2-turn Coil: Temperature

Distribution at 1 kHz

After 8 sec dwell

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 22 Pos (mm): 152.4 Phase (Deg): 0Scale / Color20.1191 / 81.0046981.00469 / 141.88937141.88937 / 202.77408202.77408 / 263.65878263.65878 / 324.54346324.54346 / 385.42816385.42816 / 446.31287446.31287 / 507.19757507.19757 / 568.08228568.08228 / 628.96698628.96698 / 689.85162689.85162 / 750.73633750.73633 / 811.62103811.62103 / 872.50574872.50574 / 933.39044933.39044 / 994.27515

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 8 Pos (mm): 0 Phase (Deg): 0Scale / Color20.00113 / 80.8614780.86147 / 141.7218141.7218 / 202.58215202.58215 / 263.4425263.4425 / 324.30286324.30286 / 385.16318385.16318 / 446.02353446.02353 / 506.88385506.88385 / 567.7442567.7442 / 628.60455628.60455 / 689.4649689.4649 / 750.32526750.32526 / 811.18561811.18561 / 872.04596872.04596 / 932.90625932.90625 / 993.7666

11 mm/sec scan –

limited by power

1 kHz Summary

• At 1 kHz, available power was the factor that

limited the scan speed

• Dwell time required for the standard 2-turn coil

was longer in order to achieve sufficient depth in

the fillet without overheating the area above

• Special process start-up was required for the

standard 2-turn coil

• For the same inductor power, the new optimized

inductor could scan over 15% faster

Optimized 2-turn Coil: Temperature

Distributions at 3kHz

After 12 s dwell @ 3 kHz

Color Shade ResultsQuantity : Temperature Deg. Celsius

Time (s.) : 12 Pos (mm): 0.5 Phase (Deg): 0

Scale / Color

20.00098 / 82.64552

82.64552 / 145.29007

145.29007 / 207.9346

207.9346 / 270.57913

270.57913 / 333.22369

333.22369 / 395.86823

395.86823 / 458.51276

458.51276 / 521.15729

521.15729 / 583.80182

583.80182 / 646.44635

646.44635 / 709.09094

709.09094 / 771.73547

771.73547 / 834.3791

834.3791 / 897.02454

897.02454 / 959.66907

959.66907 / 1.02231E3

Color Shade ResultsQuantity : Temperature Deg. Celsius

Time (s.) : 22 Pos (mm): 90.499 Phase (Deg): 0

Scale / Color

20.00681 / 87.27763

87.27763 / 154.54846

154.54846 / 221.81929

221.81929 / 289.09015

289.09015 / 356.36096

356.36096 / 423.63177

423.63177 / 490.90265

490.90265 / 558.17346

558.17346 / 625.44427

625.44427 / 692.71509

692.71509 / 759.9859

759.9859 / 827.25677

827.25677 / 894.52759

894.52759 / 961.7984

961.7984 / 1.02907E3

1.02907E3 / 1.09634E3

9 mm/s scan – limited by

temperature (vs. 6.5

mm/s for standard coil)

New Approach

New machines with variable frequency may be built and we can:

• Use higher frequency (3 kHz) for initial heating (dwelling)

• Use lower frequency (1 kHz) for scanning

• Optimize power, speed and frequency switch time for transition from dwelling to regular scanning

• Design the coil for these conditions: – Reduce bottom face width

– Bring the upper turn closer to the axle and make it shorter to

increase preheating and scanning speed

User-guided computer simulation had been used for

optimal design (Flux 2D program)

New 2-turn Coil: Temperature

Distribution after Preheating at 3kHz

After 4.5 s dwell @ 3 kHz

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 4.5 Pos (mm): 0 Phase (Deg): 0Scale / Color20.00003 / 83.8028883.80288 / 147.60571147.60571 / 211.40857211.40857 / 275.21143275.21143 / 339.01428339.01428 / 402.81711402.81711 / 466.6191466.6191 / 530.42279530.42279 / 594.22565594.22565 / 658.0285658.0285 / 721.83136721.83136 / 785.63422785.63422 / 849.43707849.43707 / 913.23993913.23993 / 977.04272977.04272 / 1.04085E3

After dwell: 4.5 s @ 3 kHz + 3.5 s @ 1 kHz

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 8 Pos (mm): 0 Phase (Deg): 0Scale / Color20.00021 / 84.9569284.95692 / 149.91364149.91364 / 214.87035214.87035 / 279.82703279.82703 / 344.78375344.78375 / 409.74048409.74048 / 474.6972474.6972 / 539.65387539.65387 / 604.6106604.6106 / 669.56732669.56732 / 734.52399734.52399 / 799.48071799.48071 / 864.43744864.43744 / 929.39417929.39417 / 994.35089994.35089 / 1.05931E3

New 2-turn Coil: Temperature

Distribution after Dwell

New 2-turn Coil: Temperature

Distribution during Regular Scanning

11.6 mm/sec scan @ 1 kHz – limited by power supply

Video

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 20 Pos (mm): 134.499 Phase (Deg): 0Scale / Color20.04147 / 81.0405881.04058 / 142.03967142.03967 / 203.03879203.03879 / 264.0379264.0379 / 325.03702325.03702 / 386.0361386.0361 / 447.03522447.03522 / 508.03433508.03433 / 569.03345569.03345 / 630.03259630.03259 / 691.03168691.03168 / 752.03076752.03076 / 813.02991813.02991 / 874.02899874.02899 / 935.02814935.02814 / 996.02722

Comparison of Results

Freq-cy,

kHz

Coil Dwell

Time

sec

Scan

Start-up

Scan

Speed,

mm/sec

Coil

Current,

kA

1.0

Stand. 10 Special 9.5* 13.5

Optim. 8 Normal 11* 13.5

3.0

Stand. 12 Normal 6.5** 7.0

Optim. 12 Normal 9** 8.0

3.0+1.0 Optim. 8 Easy 11.6* 13.0

* Power limited ** Temperature limited

Conclusions • Significant improvements of axle scan hardening

are possible by optimization of coil design and frequency selection and combination

• Optimal coil design at 1 kHz gives the following improvements: – More reliable results for the fillet area hardening

– Higher scan speed due to better efficiency

– Lower current demand and therefore reduced losses in and size of the supplying circuitry

• Preheating at 3kHz makes possible to meet the most challenging specs for the fillet area treatment in combination with high scan speed

• Case-dependable optimal coil and process design may be made by user-guided computer simulation