Meaning
Programmed control of the opening and closing of individual valve gates in a hot runner mold to govern the flow front of the polymer melt. In injection molding of large or complex plastic parts, valve gate sequencing prevents surface cosmetic defects by ensuring that the resin fills the cavity in a controlled, continuous manner. This technique is especially useful in automotive trim and large housing production.
The process relies on hydraulic or pneumatic actuators.
Injection Control
Sequential activation of the hot runner tips allows the polymer flow front to advance without interruption. During valve gate sequencing, the gate closest to the injection nozzle opens first to start filling the mold cavity. As the melt front passes subsequent gates, those nozzles are opened in a specific order to continue the flow.
This step-by-step fill pattern prevents the melt from cooling down and ensures a uniform packing density throughout the part.
Weld Line Elimination
Proper timing of the gate openings prevents the formation of weak joints where separate melt streams would otherwise meet. With valve gate sequencing, the polymer is fed from a single continuous flow front, avoiding the collision of cooled resin flows that creates visible lines. This approach is highly effective in producing large, high-gloss parts such as car bumpers where structural strength and surface finish are both required.
It reduces the need for secondary painting operations by eliminating surface blemishes. Molders can adjust the open trigger based on screw position or cavity pressure sensors to ensure the transition occurs at the exact millisecond required.
Pressure Management
Actuating the gates at precise intervals helps to balance the cavity pressure and reduce the total clamping force required. By utilizing valve gate sequencing, processors can avoid over-packing the area near the first gate while still ensuring the furthest extremities of the part are completely filled. This balanced distribution of pressure lowers the residual stress in the molded component, reducing the likelihood of post-mold warpage.
Consequently, the molded parts exhibit better dimensional stability.
