Weld lines is not noticeable
A major cause of weld lines is the rapid decrease in flowability due to the cooling of the flow front by the mold. By using heat-and-cool molding, rapid cooling of the flow front can be avoided, and the mold surface is completely replicated due to the internal pressure of the mold, making the weld lines disappear.
In other words, after the materials merge, the internal pressure increases, allowing the mold cavity shape to be transferred, completely filling in the grooves at the weld points.