Rear Bumper Lower Guard Injection Mold

The engineering reality of this component

This rear bumper lower guard is a long, thin-wall exterior component with repetitive openings and non-uniform geometry.

Although not every surface is cosmetic, the final visual stability of the vehicle exterior depends on how the entire part behaves during molding. For components of this type, the key question is not whether the cavity can be filled, but whether the forming process itself remains predictable and stable.

Filling strategy as the first decisive judgment

In this project, mold design did not start from the question of “can it be filled,” but from how the melt should flow.

Given the overall length and structural rhythm of the part, a conventional synchronous filling approach would introduce multiple risks:

• unstable progression of the flow front,

• uncontrolled weld-line formation,

• uneven pressure transfer along the part length.

To address these risks at the source, the mold was designed with a hot runner system using multiple sequential valve gates. The intent was not to add complexity, but to establish early control — defining the filling sequence in a way that supports pressure stability and predictable shrinkage.

Venting as part of process control

For long parts with repetitive openings, venting plays a critical role in maintaining forming stability.

As the melt advances under sequential valve control, air evacuation becomes increasingly sensitive near flow-end and geometrically constrained regions. If venting is treated as a uniform or symbolic feature, trapped air can distort pressure transfer, weaken the effectiveness of the filling strategy, and introduce surface defects that are difficult to trace later.

In this mold, venting was treated as part of the forming system rather than a standalone detail. Cavity-side venting grooves were arranged along critical flow-end zones, while core-side clearances, ejector interfaces, and insert boundaries were deliberately utilized to support continuous air release during filling.

The goal was not aggressive venting, but controlled evacuation — ensuring that melt flow behavior defined by the gating strategy proceeds without interference from trapped air.

Predictability matters more than zero deformation

From an engineering standpoint, the objective is not to eliminate deformation entirely, but to make it predictable and manageable.

By coordinating filling, cooling, and venting strategies at the mold-design stage, shrinkage behavior can be anticipated rather than compensated through repeated mold modification. This approach reduces reliance on narrow processing windows and minimizes late-stage corrective work.

Engineering judgment before steel cutting

In this project, stability was not achieved through repeated post-machining adjustments. Instead, forming behavior was addressed early through integrated decisions on filling sequence, cooling balance, and venting strategy. As a result, key risks were resolved before steel cutting, rather than managed afterward.