Turning "High Risk" into a "Stabilizer": Foray's Breakthrough in Thick-Walled Injection Molding

In the injection molding industry, thick-walled parts remain an unavoidable topic. They often serve critical functions such as load-bearing, sealing, or structural connections. However, due to their large wall thickness, slow cooling, and concentrated shrinkage, they are also highly prone to issues like sink marks, voids, and dimensional variation. For customers, the real pain point is not "whether a trial mold can succeed," but rather: can the product maintain consistent appearance and dimensional stability over long-term mass production? This is precisely the core challenge in thick-walled injection molding.

Sink marks in thick-walled parts may seem like a surface issue, but they actually reflect the capabilities of the entire system. In thick-walled molding, the material undergoes a prolonged and complex shrinking process within the mold cavity. If there is insufficient material packing, uneven cooling, or inadequate pressure transmission, shrinkage differences will directly manifest on the part surface. Often, the issue does not lie entirely in the process parameters themselves, but in whether the mold has "reserved sufficient process design space" for the thick-walled structure, and whether the equipment possesses the capability to consistently execute the process. This is why the same product design can yield completely different results with different molds and different machines.

Starting at the Mold Source: "Pre-Digesting" Shrinkage Risks for Thick-Walled Structures

In Foray, mold design philosophy, thick-walled parts are not handled with the traditional approach of simply "maintaining uniform wall thickness." Instead, we perform upfront planning and optimization for every potential high-risk area, based on perspectives of polymer rheology, solidification shrinkage behavior, and process window stability.

Firstly, during the product design stage, we conduct specialized analysis on thick sections based on key data such as material linear shrinkage rate, volumetric shrinkage curves, and thermal conductivity efficiency. Without compromising mechanical strength or functionality, we employ methods like local hollowing design, optimizing rib layouts, and incorporating functional transition features to reduce unnecessary solid volume. This fundamentally lowers the risk of volumetric shrinkage and sinking caused by uneven cooling.

Secondly, for the runner and gate system design, we prioritize "packing path priority." Thick-walled areas, due to slower cooling and greater shrinkage, rely more heavily on sustained packing. Therefore, we prioritize configuring more favorable gate types and runner layouts for these areas—such as extending the effective packing time at the flow front, employing efficient hot runner structures, and optimizing gate size and location—ensuring thick sections receive adequate and stable packing capability.

Simultaneously, in cooling system design, we use CAE thermal balance analysis to simulate the temperature distribution inside and outside the part, implementing targeted enhanced cooling for thick-walled areas. By utilizing multi-circuit cooling channels, local insert water wells, angular through-holes, or high-thermal-conductivity inserts, we work to align the cooling rates of thick and thin sections, reducing defects like internal stress, sink marks, and warpage caused by uneven cooling.

It is worth emphasizing that these specialized treatments do not make the product drawings appear "overly complex." However, during mass production, they significantly widen the process window, reducing the probability of sink marks, rejects, and rework. This ensures stable molding and surface quality for thick-walled parts from the source.

Stable Molding Outcomes Rely on "Controllable Machine Performance"

The demands of thick-walled injection molding on equipment go far beyond "whether the clamping force is sufficient." More critical are: whether pressure output is stable, whether transitions are precise, and whether packing is consistently effective. The injection molding solutions Foray provides place greater emphasis on the following for thick-walled part molding:
• Smooth transition between injection and packing phases.
• Fine control over multi-stage speed and pressure.
• Reliable parameter repeatability over long production runs.

Only when the injection molding machine can stably and accurately execute the set process can the process engineer's experience truly translate into product quality, moving away from "adjusting by feel."

In thick-walled part projects, Foray focuses more on the process window under mass production conditions, not just single-part results during trial molding. Through systematic matching of mold temperature, packing time, and cooling rhythm, we ensure the part's shrinkage process remains controllable, avoiding quality risks arising from environmental changes or machine fluctuations. For customers, this means: fewer appearance defects,more stable dimensional performance and more predictable delivery timelines.

This is also the key step in transitioning thick-walled injection molded parts from "difficult-to-make products" to "mature products."

Transforming Complex Challenges into Stable, Visible Results for Customers

Sink mark issues in thick-walled injection molded parts are never solved by a single trick. They test a company's comprehensive capabilities in mold design, injection equipment, process understanding, and mass production experience. Foray consistently adheres to a systematic, collaborative design approach—from product structure to mold manufacturing, to the injection molding solution—ensuring thick-walled structures cease to be a quality risk and instead become a value-add for product reliability. For customers, what truly matters is never how complex the process is, but whether the results are stable. And this is precisely the core value that Foray continues to invest in and refine.