What Determines the Draft Angle in Injection-Molded Products?
The draft angle in injection-molded products refers to the inclined angle between the product surface and the mold core. Its design directly impacts demolding efficiency and surface quality.
1. Product Design and Geometry
Wall Thickness and Structural Complexity
Thicker walls or complex geometries increase the risk of uneven cooling and shrinkage deformation. A larger draft angle is typically required to prevent parts from sticking during demolding.
Sidewall Length and Depth
Deep-cavity or long-sidewall parts experience greater friction during demolding. Increasing the draft angle reduces contact friction between the sidewalls and the mold, ensuring smooth ejection.
2. Material Properties
Material Shrinkage Rate
Resins with higher shrinkage rates generate greater internal stress as they cool. A larger draft angle helps mitigate stress-induced defects like warping or surface scratches during demolding.
Material Flowability and Mold Adhesion
Materials with high adhesion to the mold surface (e.g., certain elastomers) often require steeper draft angles to overcome sticking and ensure reliable ejection.
3. Mold Design and Surface Treatment
Mold Surface Finish
Smoother mold surfaces reduce friction, allowing for smaller draft angles. Conversely, rough or textured surfaces may necessitate larger angles to compensate for increased resistance.
Ejection Mechanisms and Structure
Molds with advanced ejection systems (e.g., automated ejectors) or release coatings can reduce friction, enabling smaller draft angles. Simpler systems may require larger angles to ensure part integrity.
4. Process Parameters
Injection Machine Settings
Injection pressure, holding time, and cooling rate influence part stability and internal stress. Improper settings may amplify friction and stick during ejection, necessitating careful draft angle adjustments.
Cooling Uniformity
Uneven cooling due to poor mold temperature control can cause localized stress or premature solidification. Increasing the draft angle in affected areas improves overall demolding performance.
