TL;DR
Flash at the parting line means injection pressure exceeds clamp force, or the mold parting line has damage or contamination. Check clamp force first, then inspect the mold parting surfaces.
What you might see
- thin fin of material at parting line
- flash on side actions or vents
- clamp force monitor below target
- mold closing slowly or incompletely
Likely causes
Injection or pack pressure too high for the clamp tonnage in use
Clamp force below required tonnage due to machine wear or incorrect setup
Mold parting line damage, nicks, contamination, or uneven contact
Worn mold core or cavity allowing material to escape at the parting surface
Required tools
- Diamond file set (fine grit)
- Sharpening stone (fine)
- Mold release and solvent
- Lint-free cloths
- Clamp force measurement tool or controller readout
- Part weight scale
Safety first
- Never enter the mold area while the machine is in automatic or semi-automatic mode. The clamp closes at high force.
- Hot melt and hot mold surfaces cause burns. Wear heat-resistant gloves when touching mold surfaces during or after a run.
- Lock out the main disconnect and verify zero clamp pressure before placing hands or tools in the mold area for inspection.
Procedure
- 1
Record the current injection peak pressure, pack pressure, and clamp force from the Roboshot controller.
- 2
Verify the clamp force setpoint is at or above the value calculated for the projected part area and material pressure. Use the mold specification sheet.[1]
- 3
Reduce pack pressure in 5% increments while monitoring part weight and flash. If flash disappears with reduced pack, pressure was excessive.
- 4
Open the mold and inspect the parting line surface for nicks, raised burrs, or contamination. Any raised metal at the parting line will gap the mold under clamp force.
- 5
Polish out any raised burrs on the parting surface using a fine diamond file and stone. Work only on the non-sealing land area; do not remove stock from the sealing surface.[1]
- 6
Clean both parting surfaces with solvent and a lint-free cloth. Inspect for any material buildup in corners or runner areas.
- 7
If clamp force is within spec and parting line is clean but flash persists, suspect core or cavity wear. Contact the mold maker for a mold inspection.
- 8
Run a short first-stage fill study after any parameter change to confirm fill balance before adding pack pressure.
Sources
Milacron Roboshot All-Electric Injection Molding Machine Operator Manual, Milacron
Milacron Roboshot Injection Molding Machine Operation and Maintenance Manual, clamp force and mold setup procedures (general)
View source
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