100% Eddy Current Test for hardness testing and material · PDF file1 Arnold Horsch© Posted whole or in part only with permission 100% Eddy Current Test for hardness testing and material

1

Arnold Horsch© Posted whole or in part only with permission

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

2


Why NDT test?


• Information about the quality

• All parts o.K.

• Idea of the spread in production

10 mm

3


Random testor

100% test


SPC Random test

62 HRC

58 HRC

• SPC works ???

• Not at all !!!

4


• 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 temperatureTo high

To low

Austenitisation timeTo short

To long

QuenchingTo short

To long

Steam bubbles

Tempering temperatureTo high

To low

Tempering timeTo short

To long

Wrong / mixed material

1

2

3

5

4

6

8

9

10

11

7

12

5


Structure influences bei test

Example 100 Cr 6

Acicular martensite carbides

largely resolved, with

25 –30% retained austenite

60 HRC

hardness structure n.o.k

Carbides in tempered

martensite,

with 15 % retained austenite

61 HRC

hardness structure 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

6


Typical material mix


Basics of eddy

current test

7


Electric current is always

accompanied by a magnetic field


Alternating magnetic fields induce

voltages in electrical conductors

8


The magnetic flux depends on the current (i)

i

f


The induced voltage (u) dependent on the coupling

ui

u

Trans-

mitter

Receiver

9


The coupling is improved

(through the Magnetic flux

In the test sample)

Test part

i

u

u

Signal acquisition


Magnetization curve

Magnetische Feldstärke [A/m]

B

H

0

0,5

1

1,5

2

2,5

0 1000 2000 3000 4000

The magnetic flux

depends on the

magnetic field strength

10


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)

11


Permeability


Permeability of diefferent alloys

0

100

200

300

400

500

600

10 100 1000 10000 100000

C45

St70-2100Cr6

9S20

C15

Magnetic field strength [A/m]

µrel

12


Permeability


Typical „limited view” of a single-frequency test

0

100

200

300

400

500

10 100 1000 10000 100000

µrel

C45

St70-2

No difference

beetwen

o.k. material 100Cr6

and the unexpected C45i.O. Material

100Cr6


13


Single-frequency technology

f [kHz]

50 Hz

Amplitude

0,01 0,1 1 10 100

Amplitude

t [s]

Zeitachse

0,1


Typical single dimensional tolerances by

a single-frequency system

i.O.n.i.O n.i.O

14


Typical two-dimensional tolerances

by a single-frequency system


- 28 -

15.06.2008

Preventive Multi-Frequency Test

Why is it so much better?

PMFT mit

INSITE HT

How does this work?

15


Preventive Multi-Frequency Test

0

100

200

300

400

500

10 100 1000 10000 100000

µrel

C45

St70-2

100Cr6

Only the broadband test with

PMFT

shows all the differences of

permeability curves

Magnetic field strength [A/m]


No time restrictions in the multi-frequency

technology.

The Preventive Multi-Frequency Test is the

solution

0,1

t [s]

Amplitude

0,15

f [kHz]

0,01 0,1 1 10 100

Amplitude

20 Hz

63 Hz

200 Hz

630 Hz

2 kHz

6,3 kHz

20 kHz

63 kHz

7,5

Multi frequency technology

16


PRÄVENTIVE MEHR FREQUENZ PRÜFUNG

0

100

200

300

400

500

10 100 1000 10000 100000

µrel

C45

St70-2

100Cr6

Erst die Breitbandprüfung mit

PMFPzeigt all die Unterschiede der

Permeabilitätskurven



Each

alloy,

material condition

and structure

have an

individual magnetic fingerprint

17


Finger print

Master Comparison


Finger print

18


Signal acquisition


19


Two-dimensional impedance plane and

8 tolerances fields increase test reliability

Re

Im o.K part

n.o.k part


Calibrated with C15

Test part = C15

20


Calibrated with C15

Test part = 16Mn Cr5


Calibrated with C15

Test part = 9S Mn Pb28K

21


Calibrated with C15

Test part = C45K


Calibrated with C15

Prüfling = X20 Cr13

22


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

23


Application


Application 100 % test

• 100% Überwachung

• Induktives anlassen

• CHD Prüfung

Case hardened

inductive tempered

Eccentric shaft• Case hardened CHD 0,8mm

• Local inductive tempered

Full automatic test

station with 4 coils for

individual test of

different postions.

• Eccentric shaft

• Tempered area

• Two parts together

24


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

25


Application extended random test



• Scattering of the hardness in the batch

• Scattering of CHD in the batch

• Scattering of the tempering

results in the batch

26





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100% Eddy Current Test for hardness testing and material · PDF file1 Arnold Horsch© Posted whole or in part only with permission 100% Eddy Current Test for hardness testing and material