How do you prevent voids in injection molding?

Common ways to prevent voids include:

1. Raise the injection pressure to force out trapped air pockets.
2. Choose a grade of material with lower viscosity to limit the risk of air bubbles forming.
3. Place gates close to the thickest parts of the mold to prevent premature cooling where the material is most vulnerable to voids.

Where does the air go in injection Moulding?

Air actually flows through vents in both directions. While the more common scenario is for the air to exhaust out of the cavity during injection to prevent filling and burning issues, vents also allow air to enter the cavity during mold opening and ejection.

What are the defects in injection molding?

Top-10 Injection Molding Defects And How To Fix Them

• Flow Lines.
• Sink Marks.
• Vacuum Voids.
• Surface Delamination.
• Weld Lines.
• Short Shots.
• Warping.
• Burn Marks.

What is cushion in plastic injection molding?

The material remaining in the barrel, in front of the screw, after the mold filling and pack stages of the injection process is called the cushion. Having a cushion ensures that the screw does not bottom out against the front of the barrel, thereby preventing control of packing.

What causes splay in injection molding?

Splay is caused by tiny gas bubbles that are dragged across the surface of the part when the mold cavity is filled. Splay is usually caused by water that is absorbed within the plastic granules. As the mold fills, the steam migrates to the surface of molded part. It is these steam bubbles that you see as Splay.

What causes air bubbles in injection molding?

Gas bubbles may stem from flow-front issues, such as converging fronts, jetting, or mold/machine problems such as non-vented core pins, poor venting (try vacuum venting), too much decompression, or resin degradation due to overheating or long residence times.

Do injection molds need vents?

Air inside of the mold must be allowed to escape so that the plastic can fill the entire space. Without vents, the trapped air will compress as the plastic tries to force the air out of the mold and will cause burning. Generally, a vent should be as large as possible without allowing the plastic to escape.

What is proper mold venting?

Standard mold venting involves machining pathways between the mold’s mechanical elements through which air can escape. Typical vent locations may include, for example, between the parting lines, pins or ejector pins, or sliding elements such as sliders and cams.

What is switch over position in injection molding?

Solution: The V/P switch-over indicates the point – usually a percentage of the total volume – where the injection molding machine (IMM) will change the filling process from a velocity driven (fill) to a pressure driven control (pack).

What is cushion variation in injection molding?

Cushion is a critical concept and practice in injection molding, as it provides a necessary “buffer” to ensure that back pressure from the injection unit holds and packs the material in the injection cavity as needed. Cushion problems can be difficult to identify, and often can be time consuming to remedy.

How do you control white spots in injection molding?

Ⅲ. Countermeasures

1. Increase the amount of material feed.
2. Install a screw with a back-flow check valve.
3. Increase injection pressure.
4. Raise the cylinder temperature setting.
5. Make sure there are no severed lines to the heater.
6. Make sure the nozzle is not clogged.
7. Increase injection speed.