Measuring Polymer Radome Transmission Loss at Millimeter Wave Frequencies
Polymer radome transmission loss at mmWave frequencies depends on dielectric loss tangent and wall thickness precision to maintain regulatory EIRP compliance.
Injection Molding Shrinkage
Meaning
Volumetric changes in thermoplastic materials occur as the molten resin cools and solidifies within a steel cavity. This phenomenon called injection molding shrinkage leads to a final part that is smaller than the original mold dimensions. Designers must predict this behavior to maintain the tight tolerances required for interlocking electronic enclosures.
Thermal Contraction
Molecular alignment and cooling rates determine how much a specific polymer pulls away from the walls. Semi crystalline resins exhibit higher injection molding shrinkage than amorphous grades because the polymer chains pack more tightly during solidification. Cooling channels in the tool must provide uniform temperature distribution to prevent warping.
Uneven thermal gradients cause different areas of the part to contract at different rates.
Gate Geometry
The location where liquid plastic enters the cavity influences the direction of the material flow and the resulting fiber orientation. In glass filled plastics, injection molding shrinkage is lower along the flow path than across it. Choosing the correct gate position and material flow helps manage these dimensional variations.
Tooling Compensation
Engineers cut the steel cavity slightly larger than the nominal design to account for the expected reduction in size. Accurate data sheets for injection molding shrinkage allow for the creation of a mold that produces parts within the specified microns. Post molding moisture exposure can sometimes cause parts to expand slightly and offset some of the initial contraction.