Self-Demolding Geometry in Flexible Silicone Molds

Flexible silicone can temporarily deform during demolding, allowing some undercuts or return features to release without a mechanical side action.

Whether that is reliable depends on geometry, local mold section, tear strength, casting stiffness, release direction and how much deformation must be repeated over the mold’s service life.

The goal is not maximum stretch. It is a controlled release path.

A self-demolding feature can leave the flexible cavity through planned deformation of the mold.

The mold bends/peels; the casting should not be forced through an impossible rigid lock.

Review:

• where the operator starts peeling
• direction of travel
• how much silicone must invert
• whether the casting is supported
• whether another feature blocks the path

A shallow return may release through local peel.

A closed hole, deep hook or geometry trapped behind a wider feature may need:

• slit
• split
• plug
• core

Sharp returns concentrate stress.

Where the product allows, softer transitions can reduce:

• tear initiation
• casting chipping
• operator force

Do not apply one fixed radius to every mold.

Review:

• flexibility of the mold
• rigidity of the casting
• feature depth
• opening size
• local mold support
• production frequency

Choose a more controlled structure when:

• the casting is fragile
• the undercut is severe
• release needs repeated extreme stretch
• cosmetic damage occurs
• operators cannot demold consistently

Can I just choose a softer Shore A?

Hardness is one variable. Geometry, local thickness, tear properties and support still matter.

Can this be tested in one prototype?

Yes. A prototype is the right place to validate uncertain release behavior.

If the mold releases once, is the design proven?

Not necessarily. Repeatability and stress location also matter.

Before tooling:

• mark release direction
• mark undercuts
• define fragile casting features
• identify high-stress mold areas
• plan operator grip/peel
• define split/core fallback
• validate prototype

Is self-demolding the same as draft?

No. Draft can help release, but flexible deformation is a separate behavior.

Does LSR injection tooling use the same release logic?

No. Ejection from rigid metal tooling is a different DFM problem.