100% Eddy Current Test for hardness testing and material mix Horsch Arnold Pálfi Géza Contents Why NDT test Random or 100% Test Basics of Eddy Current test Waht is PMFT with INSITE HT Expanded random test Dicussion 1
Why NDT test? Information about the quality All parts o.k. Idea of the spread in production 10 mm 2
Random test or 100% test SPC Random test 62 HRC SPC works??? 58 HRC Not at all!!! 3
SPC made processes safer But SPC can t guarantee to find individual wrong parts, that are to be expected as random events upon curing Typical heat treatment faults Austenitisation temperature Austenitisation time Quenching Tempering temperature Tempering time Wrong / mixed material To high To low To short To long To short To long Steam bubbles To high To low To short To long 1 2 3 5 4 6 7 8 9 10 11 12 4
Structure influences bei test Example 100 Cr 6 Carbides in tempered martensite, with 15 % retained austenite 61 HRC hardness structure o.k. Acicular martensite carbides largely resolved, with 25 30% retained austenite 60 HRC hardness structure n.o.k Surface area (picture) Martensite with troostite spots Surface hardness 600 HV10 Core (without picture) Carbides in tempered martensite, with 15 % retained austenite 61 HRC hardness structure o.k. Typical material mix Small numbers will be sorted with OES 5
Typical material mix Basics of eddy current test 6
Electric current is always accompanied by a magnetic field Alternating magnetic fields induce voltages in electrical conductors 7
The magnetic flux depends on the current (i) f i The induced voltage (u) dependent on the coupling Receiver i Transmitter u u 8
Signal acquisition i Test part u u The coupling is improved (through the Magnetic flux In the test sample) 2,5 B Magnetization curve 2 1,5 1 0,5 0 Magnetische Feldstärke [A/m] The magnetic flux depends on the magnetic field strength 0 1000 2000 3000 4000 H 9
Each structure, each alloy has his own Magnetizing CURVE The relationship between f field strength (H) and induction (B), is given by the Permeability (μ) 10
Permeability µ rel Permeability of diefferent alloys 600 500 400 300 200 C15 9S20 100Cr6 C45 St70-2 100 0 10 100 1000 10000 100000 Magnetic field strength [A/m] 11
Permeability Typical limited view of a single-frequency test 500 µ rel 400 300 i.o. Material 100Cr6 No difference beetwen o.k. material 100Cr6 and the unexpected C45 200 C45 100 St70-2 0 10 100 1000 10000 100000 Magnetische Feldstärke [A/m] 12
Single-frequency technology Amplitude Amplitude 50 Hz f [khz] 0,01 0,1 1 10 100 0,1 Zeitachse t [s] Typical single dimensional tolerances by a single-frequency system n.i.o i.o. n.i.o 13
Typical two-dimensional tolerances by a single-frequency system Preventive Multi-Frequency Test PMFT mit INSITE HT How does this work? Why is it so much better? - 28-15.06.2008 14
Preventive Multi-Frequency Test 500 µ rel 400 300 100Cr6 Only the broadband test with PMFT shows all the differences of permeability curves 200 C45 100 St70-2 0 10 100 1000 10000 100000 Magnetic field strength [A/m] Multi frequency technology Amplitude Amplitude 7,5 63 Hz 630 Hz 20 Hz 200 Hz 2 khz 6,3 khz 63 khz 20 khz 0,01 0,1 1 10 100 f [khz] 0,1 t [s] 0,15 No time restrictions in the multi-frequency technology. The Preventive Multi-Frequency Test is the solution 15
PRÄVENTIVE MEHR FREQUENZ PRÜFUNG 500 µ rel 400 300 100Cr6 Erst die Breitbandprüfung mit PMFP zeigt all die Unterschiede der Permeabilitätskurven 200 C45 100 St70-2 0 10 100 1000 10000 100000 Magnetische Feldstärke [A/m] Each alloy, material condition and structure have an individual magnetic fingerprint 16
Finger print Master Comparison Finger print 17
Signal acquisition 18
Two-dimensional impedance plane and 8 tolerances fields increase test reliability Im o.k part n.o.k part Re Calibrated with C15 Test part = C15 19
Calibrated with C15 Test part = 16Mn Cr5 Calibrated with C15 Test part = 9S Mn Pb28K 20
Calibrated with C15 Test part = C45K Calibrated with C15 Prüfling = X20 Cr13 21
What are the advantages of the user? Only o.k. parts needed for calibration No hassle of searching for the best separation frequencys highest test reliability Early warning of production errors PMFT is like an insurance policy What are the advantages of the users? Just 3 steps to verify: 1. CALIBRATION 2. Create TOLERANCE FIELDS 3. EXAMINATION 22
Application Application 100 % test Eccentric shaft Case hardened CHD 0,8mm Local inductive tempered 100% Überwachung Induktives anlassen CHD Prüfung Full automatic test station with 4 coils for individual test of different postions. Eccentric shaft Tempered area Two parts together Case hardened inductive tempered 23
Application Application bolt test Screw M6x130 ripped off during installation, suspected fault not correct tempered screws In the screening with a single frequency system only one wrong part were found Failure reason, wire fault the screws had partial soft spots The solution was a multi-frequency test on of two test posions Lot size 600000 pieces Faulty parts 287 piece Soft Spots 24
Application extended random test Application extended random test Scattering of CHD in the batch Scattering of the hardness in the batch Scattering of the tempering results in the batch 25
Application extended random test Application extended random test 26