Synchronized Collapsing Core and External Sliders in Polycarbonate Hatch Cover Mold

To release the part without stressing the rigid Polycarbonate material, the mold utilizes a multi-stage undercut release system split into internal and external mechanisms:

• Internal Collapsing Core Assembly: The central core section is segmented into 3 components (1 Central Main Core + 2 Inner Sliders). This mechanism is responsible for clearing the complex geometry around the central snap-fit latch.
• External Sliders (Top & Bottom): Two separate slider blocks are positioned at the top and bottom of the mold. Driven by robust angle pins (horn pins), these sliders handle the undercuts required for the acoustic foam.

Because both internal and external sliders operate in tight proximity, the mold’s opening sequence must be perfectly timed to avoid mechanical interference. The sequence is broken down into four critical phases:

When the injection molding machine initiates the opening cycle, mechanical locks keep the primary A/B plates strictly closed. During this delayed phase, an internal actuator pulls back the Central Main Core. Instantly, the 2 Inner Sliders collapse inward into the newly created central void, safely disengaging from the central snap-fit mechanism undercuts.

Once the internal collapse is verified, the external locks release. The primary A/B plates are forcefully separated. The molded PC cover remains retained on the moving half (B-plate) of the mold.

As the A/B plates separate, the Top and Bottom External Sliders are engaged by the stationary angle pins (mounted on the A-plate). The mechanical camming action drives these sliders outward, successfully clearing the deep top and bottom undercuts designed for the acoustic foam.

With all undercuts cleared, the machine's ejector system actuates. Standard ejector pins push the part uniformly off the B-plate. The hatch cover, along with the runner system, drops automatically for a fully hands-free production cycle.

Because the front of the hatch is a highly visible cosmetic surface, gating directly on the front was prohibited. The engineering team opted for an Edge Gate located on the back of the part.

A critical design challenge was routing the cold runner. The runner must pass over the top area of the mold where the top external slider is located.

• The Solution: The runner channel is designed to bridge over the top slider block. Crucially, no runner grooves were machined directly into the slider body itself.
• The Logic: Since the top slider actuates and pulls away during Phase 3 (before final ejection), having the runner physically inside the slider would cause the runner to snap or jam the mechanism. By keeping the runner path structurally independent from the sliding block, the runner remains securely attached to the part until the final ejection phase, where it falls away seamlessly.

When designing complex molds like this for Polycarbonate, engineers must account for several material-specific traits:

• Rigidity and Draft Angles: Unlike softer plastics (like PP or ABS), PC has virtually no "give." Even minor undercuts require dedicated sliding mechanisms. Furthermore, draft angles on core pins and ribs must be generous (typically 1 to 2 degrees minimum) to prevent part sticking and scuffing during Phase 4 ejection.
• Snap-Fit Design in PC: PC is prone to stress cracking under continuous strain. The snap-fit latch in this hatch cover must be designed with a well-radiused base (to distribute stress) and molded with minimal built-in internal stress, necessitating precise mold temperature control and optimized gate sizing to ensure a smooth melt flow.
• Venting: PC is injected at high temperatures and high injection speeds. Excellent mold venting along the parting line and slider tracks is mandatory to prevent diesel effect (burn marks) at the end-of-fill areas, particularly near the acoustic foam undercuts.