98
3 Coupling Model and Numerical Computation Method of Keyhole and Weld Pool
numerical dissipation, while the result of the Particle Level Set method is almost the
same as the original shape.
The results of the above two calculation examples show that both Level Set and
Particle Level Set methods can achieve relatively good interface tracking effect,
but the Level Set method has larger numerical dissipation, while the Particle Level
Set method can better overcome the numerical dissipation indicated in the Level
Set method and achieve a more reasonable numerical interface tracking effect. The
realization of the above-mentioned high-precision Level Set and Particle Level Set
solutions provides an essential technology foundation for tracking the evolution of
transient pores in the laser welding process.
3.5.3 Solutions for Coupling Free Surface Flow and Heat
Transfer
The temperature field and the flow field in the motion weld pool affect each other. The
factors linking the flow field with the temperature field are the recoil pressure at the
free interface, the surface tension and the thermal capillary force, and the buoyancy
on the boundary and in the weld pool. It is difficult to solve the nonlinear, strongly
coupled free-interface flow and heat transfer model, such as deep penetration laser
welding.
The traditional solutions for coupling the flow field and the temperature field
mainly include SIMPLE method or SOLA method, and the explicit discrete method
is often adopted for solving the temperature field. It is generally believed that it’s
not efficient to use the pressure–velocity coupling correction methods such as SOLA
to calculate the flow field in the laser weld pool; it will be more efficient to use the
currently popular incompressible flow solving method—Projection. Therefore, the
Projection method is adopted for solving the flow field in this paper. In addition, in
the laser welding process, the physical dimensions of the pore and the weld pool are
very small. If an explicit method is used to discretely solve the temperature field, the
absolute time step will be 10
–12 –10
−14 s. In this case, at least 100 billion calculation
steps are required to calculate the actual laser welding process within 1 s. If one time
step is calculated per second (for current quad-core CPU, the actual calculation time
per step exceeds 1 s), it will take years to complete the calculation. Therefore, the
semi-implicit scheme with a relatively large time step available to be taken is adopted
for discretely solving the temperature field equation in this study.
3 Coupling Model and Numerical Computation Method of Keyhole and Weld Pool
numerical dissipation, while the result of the Particle Level Set method is almost the
same as the original shape.
The results of the above two calculation examples show that both Level Set and
Particle Level Set methods can achieve relatively good interface tracking effect,
but the Level Set method has larger numerical dissipation, while the Particle Level
Set method can better overcome the numerical dissipation indicated in the Level
Set method and achieve a more reasonable numerical interface tracking effect. The
realization of the above-mentioned high-precision Level Set and Particle Level Set
solutions provides an essential technology foundation for tracking the evolution of
transient pores in the laser welding process.
3.5.3 Solutions for Coupling Free Surface Flow and Heat
Transfer
The temperature field and the flow field in the motion weld pool affect each other. The
factors linking the flow field with the temperature field are the recoil pressure at the
free interface, the surface tension and the thermal capillary force, and the buoyancy
on the boundary and in the weld pool. It is difficult to solve the nonlinear, strongly
coupled free-interface flow and heat transfer model, such as deep penetration laser
welding.
The traditional solutions for coupling the flow field and the temperature field
mainly include SIMPLE method or SOLA method, and the explicit discrete method
is often adopted for solving the temperature field. It is generally believed that it’s
not efficient to use the pressure–velocity coupling correction methods such as SOLA
to calculate the flow field in the laser weld pool; it will be more efficient to use the
currently popular incompressible flow solving method—Projection. Therefore, the
Projection method is adopted for solving the flow field in this paper. In addition, in
the laser welding process, the physical dimensions of the pore and the weld pool are
very small. If an explicit method is used to discretely solve the temperature field, the
absolute time step will be 10
–12 –10
−14 s. In this case, at least 100 billion calculation
steps are required to calculate the actual laser welding process within 1 s. If one time
step is calculated per second (for current quad-core CPU, the actual calculation time
per step exceeds 1 s), it will take years to complete the calculation. Therefore, the
semi-implicit scheme with a relatively large time step available to be taken is adopted
for discretely solving the temperature field equation in this study.