Views: 0 Author: Site Editor Publish Time: 2026-04-29 Origin: Site
If you work in injection molding, you know this truth: a great mold design means nothing without a disciplined trial process. A mold tryout isn’t just about making a few samples—it’s the bridge between design and stable mass production. Miss a step, and you’ll fight defects like flash, short shots, or warpage for months.
Here are the real-world key points for a successful mold trial.
Mold Inspection:
Check for clean parting lines, slides, ejector pins, and cooling channels. Any dirt or damage will ruin your process.
Manually verify smooth slide movement and ejector return (no interference).
Confirm water channel connectivity and flow.
Machine Matching:
Ensure mold thickness, locating ring, and ejector rod holes match the machine.
Check clamping force (rule of thumb: tonnage ≥ projected area × cavity pressure × safety factor).
Shot size should use 30–80% of the machine’s theoretical capacity.
Material:
Verify material grade, batch, and drying conditions (temperature/time). Wet material = sure failure.
Barrel temperature: Start in the material’s mid-to-low recommended range to avoid degradation.
Mold temperature: Use a mold temperature controller per material needs (e.g., PC needs high mold temp, PP can be lower).
Injection pressure: Start at 60–70% of max to avoid flash.
Injection speed: Start slow, especially the first stage through the gate (prevents jetting and air trapping).
Cushion: Keep 5–10 mm of cushion (prevents screw bottoming out).
Do a short shot series – gradually increase injection volume or speed to see the flow front.
Gas traps → show as burn marks or incomplete filling. Add vents on parting line or ejector pins.
Jetting → snake-like pattern past the gate. Fix by slowing first-stage speed or relocating gate.
Defect | Likely Causes | Quick Actions |
|---|---|---|
Flash (burrs) | Low clamp force, high injection pressure/speed | Reduce pressure/speed, check parting line debris |
Sink marks/voids | Insufficient pack/hold pressure, small gate | Increase hold pressure/time, raise mold/ melt temp |
Weld lines | Low melt/mold temp, poor venting | Raise temperatures, add venting, increase speed |
Burn marks (dieseling) | Trapped air compressing | Reduce last-stage speed, add vents |
Warpage | Uneven cooling, unbalanced packing | Optimize cooling circuit, use staged packing profile |
Check for balanced ejection – no white marks, cracks, or bending.
If ejection pins leave marks, add more pins, increase contact area, or use mild mold release (temporarily).
Confirm reliable return – broken return springs or missing forced return can crash the mold.
Data recording is non-negotiable. Record:
Complete process sheet (temperatures, pressures, speeds, positions, hold/cool times, cycle, cushion)
Product quality data (dimensions, weight, shrinkage, photos of defects)
Mold modification suggestions:
Propose specific changes: add venting, modify gate/runner, adjust cooling lines, increase ejector pins.
Measure real shrinkage – if it differs from design, adjust mold dimensions or process.
Run at least 30 consecutive good shots. Watch for parameter drift (e.g., temperature rising, oil heating up).
Short-term Cpk check – if below 1.33, your process window is too narrow. Revisit settings or mold design.
Use heat protection (hot runners, nozzle, mold heaters).
Depressurize before nozzle cleaning or mold removal – manually retract and purge.
Low-pressure mold protection must be active during clamp – the mold should open if it hits an obstacle.
Vent fumes from engineering plastics (PVC, POM, etc.).
A mold trial is not a test of luck. Start safe, observe the flow, fix defects through either process or mold modification, and always – always – write down what worked.
Once you validate stable production over 30 shots with documented settings, you’re ready for mass production. Skip any of these steps, and you’re just guessing.
