FA
Description
How to avoid the formation of bubbles in the production of thin-walled molds?
In the production of thin-walled molds, the formation of bubbles (cavities, air holes) is usually related to the retention of gases during the melt filling process, material degradation or water evaporation. Due to the extremely thin wall thickness of thin-walled parts (≤1mm), the melt flows at a high speed, and gases are difficult to be discharged quickly, making it very easy to form bubbles. The following are specific measures to avoid this, covering optimization from design, process to materials:
1. Mold design stage: Optimize exhaust and runner structure
1.1 Strengthen exhaust system design
Open exhaust channels:
Open shallow and wide exhaust channels in the areas where the melt fills last (such as the end of the cavity, the top of the rib), with a depth usually of 0.02 to 0.05mm (less than the overflow gap of the plastic melt), and a width of 5 to 10mm, to ensure that gases can be discharged smoothly without causing flash.
Example: For PP material, the depth of the exhaust channel should be ≤0.03mm; for PS material, the depth should be ≤0.05mm.
Utilize the gap between pins / inserts for exhaust:
Control the fit gap between pins and holes at 0.01 to 0.02mm to allow natural exhaust; for complex structures, design combined inserts and exhaust through the seams of the inserts.
Use porous steel (porous metal):
Embed porous steel in areas where it is difficult to open exhaust channels. Its internal micro-pore structure (pore diameter 10 to 20μm) can quickly exhaust gases while preventing melt leakage.
1.2 Optimize runner and gate design
Shorten runner length: Use hot runner systems or short straight main runners to reduce melt flow resistance and cooling, avoiding the entrapment of gases due to premature cooling of the melt.
Gate location and size:
Place the gate near the center of the thin-walled area to allow the melt to fill in a radial pattern, avoiding the entrapment of gases in corners due to one-sided filling.
The gate size should not be too small (such as a point gate diameter ≥1.5mm) to prevent the formation of turbulent flow due to high-speed injection of the melt and the entrainment of air.
Avoid melt "fountain flow": Use fan-shaped gates or submerged gates to allow the melt to expand smoothly along the cavity wall, reducing vortices and air entrainment.
