Study on system design and key technologies of case closure welding for ITER Correction Coil
Fang, Chao (2016-10-07)
Väitöskirja
Fang, Chao
07.10.2016
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-265-998-9
https://urn.fi/URN:ISBN:978-952-265-998-9
Tiivistelmä
International Thermonuclear Experimental Reactor (ITER) Correction Coil (CC) case,
made of ultra-low carbon austenitic stainless steel 316LN with 20 mm thickness, was
designed in the outmost layer of the CC, and was used to protect the internal
superconducting coil, resist the deformation effect caused by the powerful
electromagnetic force and thermal stress during the operation process. These cases have
characteristics of small cross-section, large dimension, and complex structure. They
were divided into two parts for the convenience of the internal superconducting coil
being inserted into the case, and they will be closure welded together after insertion.
Thus, weld seam is located the whole perimeter of the case, which will decide the large
quantity weld with the specific distribution caused by the geometric profile of the case.
The distribution requires a specific welding system, aim at the CC case closure welding
characteristic, should be developed to realize the field welding. The strict deformation
requirement, temperature control of internal coil and full penetration with high welding
quality brings the technology challenges to this closure welding. The welding system
must be constructed and these key technologies must be solved using this welding
tooling before the offcial production of CC.
A fibre laser robotic welding system was developed for the case closure welding based
on the research, scheme design and analysis in this thesis. The specific qualification
experiments were carried out on this laser welding system according to technology
challenges on the welding quality, temperature control and deformation.
Firstly, according to the distribution of weld seam, the preliminary scheme designs of
welding systems based on several different welding methods were carried out. It was
found that the laser welding is identified as the most suitable welding method. Based
on above, reasonable arrangement of robots and external rail, and simulation of robotic
welding motion process were carried out in order to further optimize design and
analysis. The simulation results show that there exist the dead zone where the robot arm
can not doing the effective welding and the robotic welding workspace should be increased. A slip plate module for the welding robot was added to assist travel, after that,
the robot was successful in covering all weld seams in all cases.
Secondly, to complete this welding system, the welding fixture should be developed to
support the welding platform, adjust the assembly tolerance and provide the rigid
constrain to control the welding deformation, and electric control should be developed
to integrate the welding system and increase its security and stability. A number of
ground supports match with the C-type clamps were designed and special distributed
aim at the geometric profile of case. The rotatable ground supports, which can provide
two types of welding platform, were developed to meet the two different welding
positions with arched and concave shape of SCC case. In order to provide the turn over
function for SCC case, a welding tilter with tilter framework, single central axis,
load-bearing jig was designed base on the good finite element analysis (FEA) result. In
addition, the design requirements of the control system of the CC case laser welding
were analyzed and the integrated control system was developed based on SIEMENS
PLC system S7-300. Thirdly, narrow gap multi-pass laser welding with hot wire was developed as the
welding process for the case closure welding. The welded jointed with defects-free and
good mechanical properties was achieved based on good optical system, reasonable
groove structure and optimized welding procedure. In order to protect the internal
superconducting coil, which is inside of the case, the backing strip was designed and
welded by laser welding behind the case in the actual welding structure of the CC case.
The temperature distribution of the welding process was simulated by FEA and
measured by the thermocouples on a short sample. The FEA temperature distribution
shows good agreement with the experimental measurement, the highest temperature of
the inner face of case was 255℃, and the highest temperature record of surface of the
internal coil was 59℃. The result shows the laser welding process will not harm the
superconducting coil, and the welding process, based on the laser welding system, can
meet the temperature control requirement. To study the welding deformation, a SCC
model case was designed, fabricated and welded by the laser welding system. The
principle of positioning welding before continuous welding, as well as segmented, skip,
symmetry and repeated turn over, was developed to keep uniform heating of the model
case. According to the detected results of welding deformation of the model case, the
overall welding deformation was controlled below ±2mm. Satisfactory results of the
welding deformation of the model case certify the reasonability of the welding structure,
system and process of the CC case closure welding, and also provide technical support
for the full scale CC case.
In conclusion, this thesis study to develop a special robotic laser welding system to
solve the CC case closure welding, and some key technologies were studied aim at the related engineering challenges.
made of ultra-low carbon austenitic stainless steel 316LN with 20 mm thickness, was
designed in the outmost layer of the CC, and was used to protect the internal
superconducting coil, resist the deformation effect caused by the powerful
electromagnetic force and thermal stress during the operation process. These cases have
characteristics of small cross-section, large dimension, and complex structure. They
were divided into two parts for the convenience of the internal superconducting coil
being inserted into the case, and they will be closure welded together after insertion.
Thus, weld seam is located the whole perimeter of the case, which will decide the large
quantity weld with the specific distribution caused by the geometric profile of the case.
The distribution requires a specific welding system, aim at the CC case closure welding
characteristic, should be developed to realize the field welding. The strict deformation
requirement, temperature control of internal coil and full penetration with high welding
quality brings the technology challenges to this closure welding. The welding system
must be constructed and these key technologies must be solved using this welding
tooling before the offcial production of CC.
A fibre laser robotic welding system was developed for the case closure welding based
on the research, scheme design and analysis in this thesis. The specific qualification
experiments were carried out on this laser welding system according to technology
challenges on the welding quality, temperature control and deformation.
Firstly, according to the distribution of weld seam, the preliminary scheme designs of
welding systems based on several different welding methods were carried out. It was
found that the laser welding is identified as the most suitable welding method. Based
on above, reasonable arrangement of robots and external rail, and simulation of robotic
welding motion process were carried out in order to further optimize design and
analysis. The simulation results show that there exist the dead zone where the robot arm
can not doing the effective welding and the robotic welding workspace should be increased. A slip plate module for the welding robot was added to assist travel, after that,
the robot was successful in covering all weld seams in all cases.
Secondly, to complete this welding system, the welding fixture should be developed to
support the welding platform, adjust the assembly tolerance and provide the rigid
constrain to control the welding deformation, and electric control should be developed
to integrate the welding system and increase its security and stability. A number of
ground supports match with the C-type clamps were designed and special distributed
aim at the geometric profile of case. The rotatable ground supports, which can provide
two types of welding platform, were developed to meet the two different welding
positions with arched and concave shape of SCC case. In order to provide the turn over
function for SCC case, a welding tilter with tilter framework, single central axis,
load-bearing jig was designed base on the good finite element analysis (FEA) result. In
addition, the design requirements of the control system of the CC case laser welding
were analyzed and the integrated control system was developed based on SIEMENS
PLC system S7-300. Thirdly, narrow gap multi-pass laser welding with hot wire was developed as the
welding process for the case closure welding. The welded jointed with defects-free and
good mechanical properties was achieved based on good optical system, reasonable
groove structure and optimized welding procedure. In order to protect the internal
superconducting coil, which is inside of the case, the backing strip was designed and
welded by laser welding behind the case in the actual welding structure of the CC case.
The temperature distribution of the welding process was simulated by FEA and
measured by the thermocouples on a short sample. The FEA temperature distribution
shows good agreement with the experimental measurement, the highest temperature of
the inner face of case was 255℃, and the highest temperature record of surface of the
internal coil was 59℃. The result shows the laser welding process will not harm the
superconducting coil, and the welding process, based on the laser welding system, can
meet the temperature control requirement. To study the welding deformation, a SCC
model case was designed, fabricated and welded by the laser welding system. The
principle of positioning welding before continuous welding, as well as segmented, skip,
symmetry and repeated turn over, was developed to keep uniform heating of the model
case. According to the detected results of welding deformation of the model case, the
overall welding deformation was controlled below ±2mm. Satisfactory results of the
welding deformation of the model case certify the reasonability of the welding structure,
system and process of the CC case closure welding, and also provide technical support
for the full scale CC case.
In conclusion, this thesis study to develop a special robotic laser welding system to
solve the CC case closure welding, and some key technologies were studied aim at the related engineering challenges.
Kokoelmat
- Väitöskirjat [1036]