Views: 0 Author: Site Editor Publish Time: 2025-11-13 Origin: Site
The Problem: The plastic doesn't completely fill the mold cavity, resulting in a missing section on the part.
Root Causes:
Low melt or nozzle temperature.
Insufficient injection pressure or speed.
The gate or runners are too small.
Poor venting, trapping air and creating an "air lock."
The Fix:
Soft: Increase melt temperature, injection pressure, and speed. Increase the cushion and use a higher back pressure for better plastication.
Hard: Enlarge the gates and runners. Add or enlarge vent channels at the end of the fill, especially in trapped air areas.
The Problem: Excess thin plastic appears along the parting line, ejector pins, or slider faces.
Root Causes:
Insufficient clamp force to keep the mold closed against injection pressure.
Excessive injection pressure, holding pressure, or shot size.
Melt temperature is too high, reducing viscosity.
Mold damage, wear, or poor alignment.
The Fix:
Soft: Increase clamp force. Decrease injection/holding pressure and shot size. Slightly lower the melt temperature.
Hard: Clean and polish the parting line. Repair damaged mold surfaces. Improve the fit of sliders and inserts.
The Problem: Small craters or depressions on the surface, often in thick sections like ribs or boss bases.
Root Causes:
Insufficient holding pressure or time (the #1 cause).
Inadequate cooling time.
Material shrinkage is too high.
Uneven wall thickness or poorly placed gates.
The Fix:
Soft: Increase holding pressure and time—this is the most critical step. Extend the cooling time.
Hard: Redesign the part for uniform wall thickness. Relocate or enlarge the gate to allow better pressure transmission to the thick area. Improve cooling around the sink zone.
The Problem: A visible line on the part where two flow fronts meet and fail to fuse properly.
Root Causes:
Low melt or mold temperature.
Slow injection speed.
Poor venting at the flow meeting point.
Too many gates or poor gate location.
The Fix:
Soft: Increase melt and mold temperatures. Increase injection speed to help the flows merge before they cool. Ensure good venting at weld line locations.
Hard: Change the gate location to move the weld line to a non-critical area. Add dedicated vents at the weld line.
The Problem: Silvery streaks or speckles on the surface, usually near the gate.
Root Causes:
Moisture in the material (a very common cause).
Material degradation from excessive barrel temperature.
Air trapped in the barrel due to high screw rotation speed or low back pressure.
The Fix:
Soft: Dry the material properly before processing! This is often the instant solution. Lower the barrel temperature, especially at the rear zones. Decrease screw speed and increase back pressure.
Hard: Improve mold venting in general.
The Problem: The part twists, bends, or bows out of its intended shape after ejection.
Root Causes:
Internal stress caused by uneven cooling or molecular orientation.
Non-uniform mold temperature.
Ejection system that pushes the part out unevenly.
Over-packing (too much holding pressure/time).
The Fix:
Soft: Lower the holding pressure and time. Balance the mold temperature on both halves. Reduce injection speed to minimize orientation.
Hard: Optimize the cooling channel layout for even heat removal. Add more ejector pins and ensure balanced ejection. Modify the gate to balance the flow.
Document Everything: Take photos, save the bad parts, and write down the exact machine settings for each shot.
Check the Basics: Is the material dry? Are the temperatures stable?
Adjust Parameters Methodically: Use the "one variable at a time" approach. Change only one setting (e.g., holding pressure) between shots to see its true effect.
Inspect the Mold: If process changes don't work, it's time to look at the "hard" stuff: vents, gates, cooling, and polish.
Decide on a Solution: Collaborate with your mold maker and designer to decide on the most effective and cost-efficient modification.
Remember, a successful mold trial isn't one where everything goes perfectly. It's one where you gather enough data to make the next iteration—whether a process setup or a mold revision—a resounding success.
Happy Molding!
