1. Insufficient plastic parts: mainly due to insufficient material supply, poor filling flow of melt materials, excessive inflation and poor exhaust, etc., leading to unsatisfactory filling of filling cavity, incomplete shape of plastic parts or unsatisfactory filling of individual cavity when multi-cavity.

2. Dimensional instability: It is mainly due to poor die strength, poor precision, instability of injection machine and unstable forming conditions, which makes the size of plastic parts unstable.

3. Bubble: Residual gas in plastic parts is caused by excessive inflation or poor exhaust in melting material, and presents as small volume or series of holes (attention should be paid to the difference between vacuum bubbles)

4. Collapse pits (dents) or vacuum bubbles: due to poor pressure-retaining filler, uneven cooling of plastic parts, uneven wall thickness and plastic shrinkage when large

5. Too large flying edge: due to poor die closure, too large gap, too good fluidity of plastics, too much filling, the plastic parts along the edge of the extrusion of excess sheets

6. Poor welding: Because of the low temperature of melt material and the incompatibility of resin and adhesives, the melt material will not be welded properly when confluence occurs, resulting in obvious fine seam lines along the surface or interior of plastic parts.

7. Surface ripple of plastic parts: Because melting material does not flow neatly along the surface of the die to fill the cavity, but flows in a semi-solidified wavy shape on the surface of the cavity or there is stagnation of melting material.

8. Poor demoulding: Due to the strong filling effect and poor demoulding performance of the mould, it is difficult to demould the plastic parts or the deformation and rupture of the plastic parts after demoulding, or the residual direction of the plastic parts does not meet the design requirements.

9. Mica flake delamination and peeling: Due to mixing of foreign material or low die temperature, the shearing effect of melting material flowing along the die surface is too large, which makes the material peel off in thin layers and reduces its physical properties.

10. Gate sticking die: due to mechanical resistance in the gate sleeve, insufficient cooling or failure of the pulling rod, the gate sticks to the gate sleeve

11. Poor transparency: Due to poor contact between melting material and die surface, there are small holes on the surface of plastic parts, which can cause irradiation of light or plastic decomposition, foreign matter impurities, or the surface of mould is not bright, so that the transparency of transparent plastics is poor or uneven.

12. Silver filament markings: due to excessive moisture or gas in the material, volatile matter, excessive shearing effect on the melt, poor bonding between the melt and the surface of the die, or rapid cooling or mixing with foreign materials or decomposition deterioration, the surface of the plastic parts appears silver-white needle-like stripes or mica sheet-like stripes along the direction of material flow.

13. Warpage and deformation: Internal stress caused by uneven residual stress, shear stress, cooling stress and shrinkage during forming; poor demoulding, insufficient cooling, insufficient strength of plastic parts and deformation of mould, etc. cause distortion of shape, uneven warping or hole deviation, uneven wall thickness of plastic parts.

14. Cracks: Due to excessive stress in plastic parts, poor demoulding, uneven cooling, poor plastic properties or poor design of plastic parts and other defects (such as deformation), cracks occur on the surface of plastic parts and near the inlet and outlet, or cracks occur or do not occur under the action of loads and solvents.

15. Black spots and black stripes: due to the decomposition of plastics or flammable volatiles in materials, air decomposes and combusts under high temperature and pressure, and the combustion materials are injected into the plastic cavity with the melting material, showing black spots, black stripes or charcoal burns along the surface of plastic parts.

16. Uneven color or discoloration: Due to poor distribution of pigments or fillers, the discoloration of plastics or pigments on the surface of plastic parts is uneven. The reasons for the uneven color are different. The uneven distribution of pigments near the inlet and outlet is the main reason. For example, the uneven color of the whole part is caused by the poor thermal stability of the plastics, and the uneven color of the fusion part is related to the nature of the pigments. These are the common problems in injection moulding.