Today's KNOWLEDGE Share : Shrinkage is one of the most fundamental factors in Injection molding process

Today's KNOWLEDGE Share

In injection molding, shrinkage is one of the most fundamental and misunderstood factors affecting final part dimensions.

Materials science tells us that shrinkage is volumetric, governed by pressure, cooling, and temperature.

But mold-making practice relies on a linear shrinkage value listed in the Technical Data Sheet (TDS), measured on a standardized test bar under controlled conditions.

This creates a challenge in how we approach accuracy, because the TDS value reflects the behavior of a controlled specimen, while your molded part experiences completely different conditions: geometry-dependent cooling, pressure profiles, crystallinity, flow orientation based on gate location and type, and wall-thickness variations.

👉 Shrinkage is not to be defeated — it is to be anticipated and managed.

This is why managing shrinkage becomes central to dimensional accuracy and repeatability. The methodology relies on understanding the actual conditions inside your part and preparing for the dimensional changes that occur after demolding.

👉 Simulation predicts what your part will do — not what the test bar did.

When I run a flow analysis, my goal is to predict the internal behavior that will ultimately drive dimensional outcomes after the part has cooled and stabilized.

This provides actionable insight at three levels:

Part design: Validate wall-thickness strategy, gate type and location, ribs and bosses, and identify areas sensitive to shrinkage or warpage.

Mold making: Support cavity scaling decisions, reduce uncertainty regarding dimensional deviation risks, and prepare the mold for dimension calibrations.

Injection settings: Show how holding pressure, cooling balance, and melt temperature influence final part dimensions and their stability over repeated cycles.

A useful way to view the workflow is:

TDS shrinkage = the rough map

Flow simulation = the GPS

Mold trials = the controlled production stage that provides real, measurable parts for dimensional evaluation

Steel-safe adjustments = applying these measurements to refine cavity dimensions and reach the target accuracy

A structured approach like this makes shrinkage predictable, supports dimensional accuracy, and strengthens the repeatability of every injected part.

🔥 Shrinkage happens — Precision is achieved through methodical work

source : Zachi Fizik