The acceptance of injection parts consists of internal quality acceptance and external quality acceptance.
Under normal conditions of injection machine temperature, mold temperature, molding process, injection pressure, etc., the stable plastic parts produced by the mold should be used as the inspection samples.
Once a sample of the plastic part is obtained, an external quality inspection should be performed first. Check the overall shape for correctness, any deformations, and whether there are unacceptable molding defects. The basic shape should meet the product design requirements. Observe visible linear, rounded, and curved areas of the plastic part for continuity, consistency, smooth transition, and clarity. There should be no flashing at the parting line or fittings.
Check whether the surface roughness is too high or whether it meets the requirements specified in the design.
Next, inspect the basic dimensions of the plastic part. The fit dimensions refer to the dimensions that correspond between plastic parts or between plastic parts and related components, including local fit dimensions and overall relative position dimensions. Position dimensions are usually marked with tolerance requirements on the product drawings.
Conduct trial assembly inspection. When basic dimensions, external dimensions, and fit dimensions are checked and found to meet design requirements, trial assembly inspection can be carried out. This is a crucial method in plastic part inspection as it validates fit dimensions and assesses spatial curved surfaces. After the pre-assembly meets requirements, a comprehensive inspection of the appearance quality should be carried out to check if the surface smoothness and gloss meet the standards.
Verify that the wall thickness of the plastic part is uniform and that the weight is not excessive.
Surface texture processing inspection. Various patterns, such as textures, simulated leather patterns, and simulated fabric patterns processed in the cavity, have mature experience domestically. Their effects can closely resemble the original template. For texture cavities, pay special attention to the following aspects: ① The texture should be uniform and of consistent depth; ② The density of the texture should be consistent at corners and shape-changing areas; ③ The surface of the finished part should be bright and clean; ④ The width of the bright band between the texture and smooth surfaces should be uniform (generally 1-2 mm); ⑤ No bright, smooth areas should appear where textures are processed, and various spots caused by leakage should be absent.
Acceptance of the plastic part should occur at least 16 hours after molding or any required post-processing is completed. The standard environment for acceptance should be a temperature of (23±2)°C, relative humidity of (50±6)%, a dew point temperature of 12°C, atmospheric pressure of 89-104 kPa, and air velocity of ≤1 m/s. If the actual environment is not standard, both parties can negotiate conditions or adjust measured values according to the corresponding linear expansion coefficient.
Internal quality, also referred to as property quality, includes the internal structural morphology of the product (such as crystallization and orientation), the density of the product, its physical and mechanical properties, weld strength, and the dimensions and shape accuracy related to plastic shrinkage characteristics.
