Inductive measurement of narrow gaps for high precision welding of square butt joints

65 Pages·2016·6.34 MB·English

E Licentiate Thesis
D
VA Production Technology
R
D 2016 No. 14
S
V
E
N
M
A
N
Inductive measurement of narrow gaps for
high precision welding of square butt joints
Inductive measurement of
IN
D
In laser beam welding without filler material, the gap between the parts to be joined must U
C narrow gaps for high precision
T
be narrow. Optical sensors are often used to measure the gap, but with precise machining, IV
E
it may become so narrow that it is difficult to detect, with the risk of welding in the wrong M
E
position. This thesis proposes the use of an inductive sensor with coils on either side of AS welding of square butt joints
U
R
the gap. Inducing currents into the metal, such a sensor can detect even gaps that are E
M
not visible. The new feature of the proposal is based on using the complex response of EN
T
each coil separately to measure the distance and height on both sides of the gap. This O
F
N
information allows measurement of gap width and misalignment as well as position. The A
R
properties of the new method have been examined experimentally, showing useful results RO Edvard Svenman
W
for gaps with up to 0.4 mm width and misalignment. G
A
P
S
F
O
R
H
IG
H
P
R
E
C
IS
IO
N
W
E
L
D
IN
G
O
F
S
Q
U
A
R
E
B
U
T
T
J
O
IN
T
S
2
0
1
ISBN 978-91-87531-45-3 (Printed) 6 N
O
ISBN 978-91-87531-44-6 (Electronic) .1
4

Tryck: Ineko AB, november 2016.
Licentiate Thesis
Production Technology
2016 No. 14
Inductive measurement of
narrow gaps for high precision
welding of square butt joints
Edvard Svenman
University West
SE-46186 Trollhättan
Sweden
[phone]
www.hv.se

© Edvard Svenman 2016
ISBN 978-91-87531-45-3 (print)
ISBN 978-91-87531-44-6 (electronic)
Acknowledgements
I am grateful to my supervisors for their patience, for their suggestions and for
rewarding discussions. At University West, Anna-Karin Christiansson and Anna
Runnemalm, and at GKN Per Henrikson.
I also gratefully acknowledge the financial support from the research school
SiCoMaP, funded by the Knowledge Foundation, and GKN Aerospace Engine
Systems.

Edvard Svenman
31st of October 2016

iii

Populärvetenskaplig Sammanfattning
Nyckelord: Automation, Virvelström; Spaltföljning; Mätteknik; Lasersvetsning

Lasersvetsning kräver smala spalter mellan de plåtar som skall fogas. Det kan
lätt hända att spalten blir så smal att den inte syns, och då fungerar inte de op-
tiska givare som ofta används. Riktas laserstrålen fel svetsas inte plåtarna ihop på
rätt sätt, och fogen håller inte lika bra. Med en induktiv sensor, som känner av
spalten med hjälp av magnetfält och virvelströmmar inne i metallplåten, kan
spalten upptäckas även om den inte syns.
Avhandlingen föreslår en ny metod med två induktiva sensorer, en på vardera
sidan av spalten. När svetshuvudet rör sig följer givaren med och mäter. Det nya
är att mäta med båda sensorerna separat, och att mäta hur ström och spänning
genom respektive sensor ändras med läget. Därigenom kan både avståndet till
spalten och höjden över plåten mätas för var och en av sensorerna. Det ger mer
information än om sensorerna är hopkopplade. Ett sådant givarsystem kan
monteras på svetshuvudet och kalibreras för en viss gapbredd och höjdskillnad
mellan plåtarna, men när dessa varierar kommer systemet att mäta lite fel. Detta
kan korrigeras med hjälp av en matematisk modell, som beskriver fel i gapbredd,
position och höjdskillnad. En sådan lösning fungerar bra, men är fortfarande
känslig för om spalten har både bredd och kantförskjutning samtidigt. Speciellt
gapbredd är svår att mäta. Båda sensorerna ska sitta relativt nära plåten, och de
mäter rätt även om de flyttas lite i höjd eller sidled. Arbetsområdet för det före-
slagna systemet är ganska litet, 1 mm avvikelse åt varje håll, men det är bättre än
tidigare publicerade induktiva sensorsystem som bara visat rätt om spalten var
rakt under givaren.
Metoden har kontrollerats genom experiment med en sensor, som mätt på en
sida i taget, varefter mätningarna kombinerats. Spalter upp till 0.40 mm bredd
har detekterats med goda resultat, liksom höjdskillnader upp till 0.40 mm.

v
Abstract
Title: Inductive measurement of narrow gaps for high precision weld-
ing of square butt joints
Keywords: Eddy current; Seam tracking; Measurement; Laser beam welding
ISBN: 978-91-87531-45-3 (print)
978-91-87531-44-6 (electronic)

A recent method in aero engine production is to fabricate components from
smaller pieces, rather than machining them from large castings. This has made
laser beam welding popular, offering high precision with low heat input and
distortion, but also high productivity. At the same time, the demand for automa-
tion of production has increased, to ensure high quality and consistent results.
In turn, the need for sensors to monitor and control the laser welding process is
increasing.
In laser beam welding without filler material, the gap between the parts to be
joined must be narrow. Optical sensors are often used to measure the gap, but
with precise machining, it may become so narrow that it is difficult to detect,
with the risk of welding in the wrong position. This kind of problems can cause
severe welding defects, where the parts are only partially joined without any
visible indication. This thesis proposes the use of an inductive sensor with coils
on either side of the gap. Inducing currents into the metal, such a sensor can
detect even gaps that are not visible. The new feature of the proposal is based
on using the complex response of each coil separately to measure the distance
and height on both sides of the gap, rather than an imbalance from the absolute
voltage of each coil related to gap position. This extra information allows meas-
urement of gap width and misalignment as well as position, and decreases the
influence from gap misalignment to the position measurement. The sensor
needs to be calibrated with a certain gap width and height alignment. In real use,
these will vary, causing the sensor to be less accurate. Using initial estimates of
the gap parameters from the basic sensor, a model of the response can be used
to estimate the measurement error of each coil, which in turn can be used for
compensation to improve the measurement of the gap properties.
The properties of the new method have been examined experimentally, using a
precise traverse mechanism to record single coil responses in a working range
around a variable dimension gap, and then using these responses to simulate a
vi