Design and considerations for injection mould casting systems

Basic principles for the design of injection mould casting systems

1. Consideration of CavityLayout

1) BalancesLayout should be used as far as possible.

2) The cavity layout and gate opening should be as symmetrical as possible to prevent uneven forces on the mould from generating bias loads and overflow problems.

3) The cavity arrangement should be as compact as possible to reduce the size of the mould.

2. Consideration of flow guidance

1) Smoothly guide the molten plastic to fill the mould cavity without creating eddy currents, and smoothly exhaust.

2) To avoid frontal impact of the molten plastic on small diameter cores and metal inserts to prevent core shifting or deformation.

3. Consideration of heat loss and pressure drop

1) The smaller the heat loss and pressure drop, the better.

2) The flow should be short.

3) The cross-sectional area of the flow channel should be large enough.

4) Avoid bends and sudden changes in flow direction (change of direction by rounding).

5) Low surface roughness when machining the runner.

6) Multi-point pouring can reduce the pressure drop and the required injection pressure, but there will be problems with the suture line.

4. Consideration of flow balance

1) When filling a mould with multiple cavities (Multi-Cavity), the flow path should be balanced so that the plastic fills each cavity at the same time to ensure consistency in the quality of the moulded products.

2) Use Naturally-BalancedLayout for the manifold as much as possible.

3) If natural balancing is not possible, use manual balancing to balance the runners.

5. Consideration of waste

To reduce the volume of the runner (length or cross-sectional area) to reduce the cost of runner waste generation and recovery, provided that the flow and pressure loss are not affected by a smooth filling.

6. Consideration of cold material

Design appropriate ColdSlugWell and overflow troughs in the runner system to make up for the colder plastic wave front at the initial stage of filling and to prevent cold material from entering the mould cavity directly and affecting the quality of filling.

7. Exhaust considerations

The plastic should be guided smoothly to fill the mould cavity and the air in the cavity should escape smoothly to avoid scorching of the seal.

8. Considerations for the quality of the moulded product

1) To avoid short shots, burrs, sealing, sutures, flow marks, spray, residual stresses, warpage and deflection of the die kernel.

2) Long runner systems or multiple gating should be avoided due to unbalanced flow, insufficient pressure retention or uneven shrinkage.

3) Good product appearance, easy gate removal and gate marks are not detrimental to the appearance and application of the part.

9. Consideration of production efficiency

To minimise the amount of post-processing required to shorten the moulding cycle and increase productivity.

10. Consideration of ejection points

The appropriate ejection point should be considered to avoid deformation of the moulded part.

11. Consideration of the plastic used

Avoid using long or small runners for plastics with high viscosity or relatively short L/t.