Design of injection mold for fiber filler

When the glass fiber or carbon fiber and resin are mixed together, the elastic modulus and tensile strength of the plastic will be significantly increased, so that the plastic part becomes hard. This means that if a heavy load falls on the plastic part, the plastic part will not deform easily.
However, the impact strength will be lower and the plastic parts will become brittle. The shrinkage in the flow direction is smaller than that in the vertical flow direction.
In the design of injection mold, it is difficult to set shrinkage through the plastic flow direction of gate. CAD software only allows users to set shrinkage in X, y and Z directions. That is, if the part size is large and the tolerance is small, some dimensions may be out of tolerance.
The solution is to ensure safety by leaving more die steel than is required. It is easy to remove the excess die steel by CNC or EDM, but it is easy to remove the excess steel, and it is difficult to increase it. To achieve this, it is necessary to weld the injection mold. However, welding will lead to deformation of injection mold, which is unfavorable to the life of the mold and the quality of parts.

For further mold modifications, if the size of the plastic part exceeds the tolerance, it is necessary to remove or add some steel from the mold to change the shape or size of the injection mold. In order to avoid this step, opening experimental mold is one of the important methods to test whether the injection mold design is reasonable. The critical dimensions of plastic parts were compared with the printing results. If any key dimension is out of tolerance, the production mould needs to be changed accordingly. The purpose of the experimental mold is to determine which dimensions will exceed the tolerance and which key features meet the design requirements. Once the influence of different shrinkage in different flow directions on the size is clear, the adjustment can be made in the production of hard mold.

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