How Ejection Cracking are formed in the MIM Process? What are the solutions?

Date：2025-07-28   Views：1003

Possible Causes

• Excessive injection pressure

Causes the green part to adhere too tightly to the mold cavity, leading to excessive force during ejection.

• Insufficient hold time & premature demolding

Non-uniform part density and inadequate structural strength to withstand ejection forces.

• Inadequate draft angles

High mold adhesion force generates shear stress during ejection.

• Poor ejector system design

Insufficient or unevenly distributed ejector pins.

• Small contact area between pins and part

Localized stress concentration.

• Low binder strength

Brittle green parts prone to fracture (especially in complex geometries).

• Excessive wall-thickness variations

Thick sections cool slower → uneven shrinkage vs. thin walls → internal stress during ejection.

*Undercut structures: Parts trapped by mold protrusions → forced ejection causes cracking.

Selective Solutions

• Reduce parameters

Injection speed, molding pressure, hold pressure, mold temperature.
Effect: Lower mold adhesion & prevent over-compaction brittleness.

• Extend hold time

Ensures uniform density and enhances structural integrity.

• Increase draft angles

Standard: ≥1°

Complex features: 2°–3° 

Reduces adhesion force.

• Optimize ejector system

Add ejector pins & expand contact area.

Ensure even force distribution; avoid ejecting against thin/weak sections.

• Upgrade binder system

Use tougher binders to improve impact resistance.