Reasons for size discrepancies in injection molding products

Dimensional discrepancies in injection molded parts are a common problem and can be caused by a variety of factors. The following is a detailed analysis of the causes of dimensional discrepancies in injection molded parts:

1. Mold Factors
Mold Wear:
The surfaces of the cavity and core of molds used over time can wear due to the erosion of the plastic melt. For example, after repeated injection molding, the core edges may wear, causing the corresponding parts of the molded part to become larger.
Inadequate Mold Precision:
Improper tolerance control during mold manufacturing, such as deviations in cavity dimensions, can directly affect the dimensions of the molded part, resulting in non-compliant product dimensions.
Mold Deformation:
The mold is subjected to high pressure during the injection molding process. If the mold plate is not strong enough, it can deform. For example, if the mold plate is not thick enough, it may bend during injection, resulting in dimensional deviations in the molded part.
Improper Mold Structure:
Improper number or placement of gates, lack of a heating system or a failed heating system, or uneven cooling can also lead to dimensional discrepancies in the molded part. 2. Improper Process Parameter Control
Injection Pressure:
If the pressure is too high, the plastic melt will overfill the mold, resulting in oversized parts. If the pressure is too low, the melt will underfill, resulting in undersized parts.
Injection Temperature:
Plastic melt temperature affects its fluidity. If the temperature is too high, the melt viscosity decreases, making it more likely to overfill the mold and oversize the parts. If the temperature is too low, the melt will have poor fluidity, underfilling the mold and undersize the parts.
Dwell Time:
If the hold time is too long, the plastic will overfill within the mold, resulting in undersized parts. If the hold time is too short, underfilling the mold and oversize the parts.
Injection Speed:
Injection speed affects the filling and cooling of the melt, thus affecting part dimensions. Injection speeds that are too fast or too slow can result in dimensional discrepancies.
3. Material Factors
Material Shrinkage Variation:
Different plastics have different shrinkage rates. Even for the same plastic, shrinkage rates can vary between batches, leading to dimensional instability in the molded parts. Material Hygroscopic Properties:
Some plastics, such as nylon, are susceptible to moisture absorption. This affects the plastic's fluidity and shrinkage, thus affecting the dimensional accuracy of the molded part.
IV. Equipment Factors
Instability of the Injection Molding Machine's Hydraulic System:
Pressure fluctuations in the injection molding machine's hydraulic system can lead to unstable injection pressure, which in turn affects the dimensions of the molded part.
Inadequate Equipment Precision:
High-precision equipment ensures stability and precision during the injection molding process, thereby improving product dimensional accuracy. However, insufficient equipment precision can result in dimensional discrepancies in the molded part.
V. Human Factors
Inadequate operator skills or improper operation, such as improper settings of parameters like injection speed, pressure, and temperature, can also lead to dimensional discrepancies in the molded part.
Solutions
Improve Mold Precision:
By improving the machining accuracy of mold components and the quality of materials, the impact of the mold on product dimensions can be minimized.
Strictly Control Process Parameters:
Strictly control all parameters during the injection molding process, such as injection pressure, temperature, dwell time, and injection speed, to ensure they are within the appropriate range.
Select Appropriate Materials:
Select the appropriate plastic material based on product requirements and strictly control its shrinkage and moisture absorption properties. Regular Equipment Maintenance:
Perform regular maintenance and servicing on injection molding machines to ensure they are in good working condition.
Operator Training:
Train employees in the proper operation of injection molding equipment and molds, improving their skills and competence and minimizing the impact of human factors on product dimensions.
In summary, the causes of dimensional discrepancies in injection molded products involve multiple factors, including molds, process parameters, materials, equipment, and human factors. When addressing dimensional discrepancies in injection molded products, it's important to comprehensively consider these factors and implement appropriate improvement measures.