Under what circumstances do injection molded products warp?
Warpage in injection molded products is a common issue influenced by numerous factors, primarily including the following aspects:
1. Material Factors:
Differences in Material Shrinkage: Different materials have varying coefficients of linear expansion, leading to different cooling shrinkage rates. If the product wall thickness is uneven, the difference in shrinkage rates between different parts can cause warping.
Crystallinity of the Material: Materials with high crystallinity undergo significant volumetric shrinkage during cooling, making them prone to warping.
Water Absorption of the Material: Materials with high water absorption tend to absorb moisture and expand in humid environments, resulting in warping.
2. Mold Factors:
Mold Design Defects:
Improper Gate Location: The gate location directly affects the flow direction and cooling rate of the melt. An improper gate location can easily generate internal stress and cause warping.
Poor Cooling System Design: A poorly designed cooling system can lead to uneven temperature distribution in the mold, causing differences in shrinkage rates between different parts of the plastic part, thus causing warping.
Insufficient Dimensional Accuracy of the Mold Cavity: The dimensional accuracy of the mold cavity directly affects the dimensional accuracy of the plastic part. If it is insufficient, warping is likely to occur.
Mold Material: A significant difference in the coefficient of thermal expansion between the mold material and the plastic part material can also cause warping.
3. Processing Factors:
Excessive Injection Pressure: Excessive injection pressure can generate high shear stress in the melt within the cavity, increasing internal stress and leading to warping.
Excessive Injection Speed: An excessively high injection speed can prevent the melt from filling the cavity, resulting in cold welding, increasing internal stress, and causing warping.
Excessive or Insufficient Mold Temperature: Excessive mold temperature reduces the rigidity of the plastic part and makes it prone to warping; In contrast, insufficient mold temperature increases the internal stress of the plastic part, also making it prone to warping.
Excessive or Insufficient Holding Time: Excessive holding time increases the internal stress of the plastic part. In contrast, insufficient holding time can cause shrinkage of the plastic part, both of which can cause warping.
Excessive Mold Temperature: Excessive mold temperature reduces the rigidity of the plastic part and makes it prone to warping.
Improper Ejection Method: An improper ejection method can exert uneven stress on the plastic part, leading to warping.
4. Product Structure Factors:
Uneven Wall Thickness: Uneven wall thickness leads to different cooling rates in different parts, causing differences in shrinkage rates and warping.
Improper Design of Reinforcing Ribs: Improper design of reinforcing ribs can increase the internal stress of the plastic part and cause warping.
Complex Product Shape: Complex product shapes are prone to stress concentration, increasing the risk of warping.
Warpage in injection molded products is a complex phenomenon involving multiple factors such as materials, molds, processes, product structure, and environment. To effectively address warpage in injection molded products, it is necessary to comprehensively consider these factors and take appropriate measures.
