Frequently Asked Question

Fill, pack, cool, and eject

Injection molding is controlled as a sequence. Filling establishes flow fronts and weld lines; packing compensates for volumetric contraction; cooling develops stiffness; ejection can introduce stress and distortion. Wall thickness, gate location, venting, mold temperature, material moisture, and cooling-channel balance all affect the result.

Cooling time scales approximately with the square of wall thickness t, thermal diffusivity α, and a geometry-dependent coefficient C.

Worked example

If wall thickness increases by 20%, a first-order cooling-time ratio is 1.2² = 1.44. Expect approximately 44% more cooling time unless material, mold temperature, or process controls change. Confirm with part temperature, cycle data, and dimensional inspection.

Engineering check

For Injection Molding: Fill, Pack, Cool, and Eject, record the material condition, tool or fixture identity, process settings, measurement method, sampling plan, and reaction rule. Confirm that the measurement system is capable of resolving the requirement and that the process is stable before using capability or first-article data to justify release. Reconfirm the limits after a material, tool, or route change.

Engineering note

For Injection Molding: Fill, Pack, Cool, and Eject, state the intended use, input range, dominant mechanism, units, boundary conditions, acceptance criterion, and evidence owner. Use an independent balance, limiting case, repeat measurement, or sensitivity check to challenge the result. Document the configuration and uncertainty so another engineer can reproduce the reasoning and determine whether the result remains valid after a design, material, boundary, or process change.