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Views: 0 Author: Site Editor Publish Time: 2025-10-23 Origin: Site
Sink marks are one of those subtle yet frustrating imperfections that can challenge even the most experienced moulding engineers. These tiny depressions—often found around thicker areas, ribs, or bosses—quietly remind us that in injection moulding, balance is everything. While they rarely threaten structural integrity, they can affect how a product feels in the hand, how it catches the light, and ultimately how it’s perceived. In this article, we explore the true nature of sink marks, how thoughtful design and precise control prevent them, and how Guangdian Technology approaches this challenge with craftsmanship and science in equal measure.
Sink marks form when molten plastic cools unevenly—when the outer surface freezes while the inner core continues to shrink. As the inner material contracts, the surface subtly pulls inward, leaving behind a shallow indentation.
In essence, a sink mark tells a story about timing, temperature, and pressure—each slightly out of sync. Understanding this delicate balance is the first step toward achieving flawless surfaces.
Where thickness varies, cooling times differ. Thicker areas hold heat longer, pulling the surface inward as they contract. A consistent wall thickness helps materials cool together and stay in harmony.
If pressure is released too soon, molten resin inside the cavity can’t refill the shrinking volume. The result is a subtle void beneath the surface.
An uneven cooling system creates temperature gradients that distort the solidification process. Well-designed cooling channels ensure the entire part cools in sync, preventing local shrinkage.
When the gate is too small or too far from thicker zones, melt flow and packing efficiency drop, leading to localized shrinkage.
Crystalline resins like PP, POM, or PA shrink more than amorphous resins such as ABS or PC. Material choice always influences how a mould behaves under cooling.
At Guangdian, design begins with empathy for how materials behave. Here are key design insights that help us prevent sink marks before steel is ever cut:
A smooth transition between thick and thin areas promotes even cooling and lowers stress accumulation.
Rib thickness ideally remains 50–70% of the base wall. It’s a small adjustment that yields visible improvements.
Modern conformal cooling and strategic baffle placement make temperature control more precise. Guangdian’s use of 5-axis CNC and thermal simulation ensures stable mould performance.
A well-placed gate supports consistent pressure across the cavity, helping the material settle evenly.
Sometimes, a subtle shift in resin selection—like opting for fiber-reinforced ABS—can eliminate recurring sink marks altogether.
→ Learn more about our mold design expertise.
Optimize Packing Pressure and Time. Consistent holding pressure allows material to fill micro-voids as the part cools, ensuring stable density throughout.
Balance Cooling Time. Cooling isn’t a race—it’s a rhythm. Allowing the part to fully stabilize before ejection prevents residual shrinkage.
Control Melt and Mould Temperature. A balanced temperature profile promotes smooth flow and dimensional stability without overstressing the surface.
Fine-Tune Injection Speed. A slightly slower fill rate can reduce internal stress, leading to cleaner, smoother finishes.
→ Discover our mold manufacturing precision process.
Two-Shot Moulding (2K Process). By layering two materials in a single cycle, two-shot molding creates more stable surfaces with fewer cosmetic flaws.
Gas-Assisted Injection Moulding. Gas injection redistributes internal pressure and evens out wall thickness naturally.
Mould Flow and Thermal Simulation. Before any machining begins, we analyze flow behavior and temperature distribution to anticipate potential imperfections.
High-Precision CNC and EDM Finishing. Our craftsmanship ensures mirror-like finishes, where even light reflection reveals precision.
→ Explore our auto lamp mold and automotive interior trim mold expertise.
In sectors where every surface speaks of quality, even the smallest imperfection tells a story. We work with:
Automotive lighting housings – demanding optical purity and consistency
Instrument panels and trims – balancing function and tactile beauty
Consumer electronics – where craftsmanship is perceived through smooth, flawless detail
Guangdian integrates rapid prototyping (3D printing) to visualize and refine every surface before production ever begins.
Decades of expertise in automotive lighting and two-shot moulding
A full-service engineering partner from design validation to manufacturing
5-axis precision machining, advanced EDM, and rigorous QC systems
A philosophy rooted in balance—between art, science, and precision
Our work isn’t about pushing a sale—it’s about creating confidence, one flawless surface at a time.
Sink marks may be small, but solving them reflects a deep respect for both design and material behavior. True quality lies not in perfection alone, but in understanding what causes imperfection—and mastering the process to prevent it.
At Guangdian Technology, every mould carries that understanding. Through design sensitivity, process control, and precise craftsmanship, we help ideas take shape—smoothly, beautifully, and without compromise.
→ Contact us when you’re ready to discuss your next project or simply to exchange insights on better moulding design.
