Glass-filled Plastic Parts – Why They’re So Popular & What Risks They Present

When discussing plastic resin injection molding, glass-filled plastic is commonly used to enhance part strength and rigidity.

Some of the most common glass-filled resins include:

While thermoplastics do have naturally-occurring mechanical properties that impart strength, durability, impact-resistance and other benefits within plastic molded parts, adding glass-filled plastic can help further reinforce the resin’s properties.

The one issue that can occur with glass-filled plastic parts is increased brittleness due to significant improvements in the part’s strength and rigidity.

However, if the glass-filled plastic part does not need to withstand high impact stress and deflection, but rather only support weight, then it can be an ideal plastic resin for injection molding.

In addition, glass fill percentages can range quite a bit (typically 13% to 45%), which will affect the final part’s properties accordingly.

If you’re considering using a glass-filled resin in the plastic molding process, it’s important to note that adding a glass-filled resin adds strength, but also poses risks as glass fibers can potentially cause internal stresses and warping, as well as fill rate, cooling rate and shrink rate issues.

Glass-filled resins do best when your mold has the following:

  • Uniform Wall Thickness
  • No Sharp, 90-degree Angles
  • Few Through Holes & Turns
  • Non-complex Geometries
  • Gate Location at the Long Axis of the Part

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