Injection Points

The injection point is a key concept in the field of plastics processing, especially in injection molding processes. It refers to the exact location where the molten plastic enters the mold to form the desired part. While often invisible to the end customer, it plays a crucial role in the quality, aesthetics, and strength of the final product.

What is an injection point?

During injection molding, plastic is heated until it becomes liquid, then injected at high pressure into a closed mold. The injection point is the entry channel through which the material flows into the mold. Its placement varies depending on the part’s geometry, material distribution, visual finish, and other technical considerations.

Types of Gates in Plastic Injection Molding

		Gate Type	Description	Advantages	Disadvantages	Applications
1		Sprue Gate (Direct Injection)	Direct injection from the nozzle to the part.	– Simple design and manufacturing.  – Good mold filling.  – Ideal for large parts.	– High material waste due to large runner.  – Longer cooling time.  – Visible mark requiring post-processing.	Commonly used for barrel-shaped, large, and deep parts. Avoid using on shallow rubber parts due to warping risk. For cosmetic parts, the gate may be placed on the internal surface.
2		Fan Gate	Flared, fan-shaped entry.	– Uniform material distribution.  – Ideal for wide, thin parts.	– Bulky and harder to balance.  – Potential for flash.  – Requires more material.	Used for thin, wide plastic parts or transparent materials with poor flow properties like PC, PMMA, etc.
3		Tunnel Gate / Submarine Gate	Angled gate under the part that self-trims during ejection.	– Discreet, ideal for multi-cavity molds.  – No post-processing needed.  – Clean appearance.	– Complex machining.  – Can cause internal stress or weld lines.  – Not suitable for thick parts.	Perfect for parts requiring aesthetic finish, small to medium-sized parts. Balancing flow resistance is essential for optimal performance.
4		Cashew Gate / Banana Gate	Curved channel injecting from below.	– Invisible on aesthetic surfaces.  – Maintains flow.  – Reduces weld lines.	– Complex to machine, limited flow.  – Difficult to remove.  – May leave a residual mark.	Often used with ABS and HIPS. Not suitable for crystalline materials like POM, PBT, or rigid materials like PC, PMMA.
5		Pin Gate	Needle-like gate that mechanically seals the entry point.	– Suitable for precision parts.  – Nearly invisible gate mark.  – Minimal or no post-processing.	– Risk of blockage.  – Requires accurate temperature control.  – Must be highly precise.	Ideal for large flat surfaces or long barrel-shaped parts. Helps reduce flow path and improve weld line distribution.
6		Edge Gate	Side-entry gate at the edge of the part.	– Suitable for flat parts.  – Discreet and easy to trim.	– Visible edge mark.  – Can cause weld lines.  – Less effective for large parts.	Suitable for non-aesthetic parts and reinforced materials like fiberglass-filled plastics.
7		Tunnel Gate with Ejector	Tunnel gate combined with an ejector.	– Simplifies ejection.  – Enables automation.  – Precise and clean ejection.	– More complex design.  – Requires fine tuning.  – Costly setup and maintenance.	Used for small to medium-sized parts in mass production, common in automotive and electronics.
8		Overlap Gate	Slightly recessed gate.	– Good for thick walls.  – Reduces flow defects.  – Better surface finish.	– Higher material volume.  – Difficult demolding.  – Hard to balance in multi-cavity molds.	Best for flat parts with high surface quality requirements.
9		Diaphragm Gate	Circular injection around a central core.	– Even distribution.  – Precise centering.  – Reduces warping.	– Complex to implement.  – Gate mark inside the part.	Used for large or thick circular parts requiring centered, even filling. Ideal for high-precision applications.
10		Ring Gate	Annular gate for radial injection.	– Suitable for technical parts.  – Uniform material distribution.  – Prevents radial deformation.	– Complex mold design (requires core).  – Difficult to demold without visible separation.	Used for cylindrical or tubular parts like tubes, filters, or rings.
11		Hot Tip Gate	Heated tip injecting directly from a hot runner.	– No runner waste.  – Aesthetic finish.  – Controlled and smooth filling.	– High mold cost (heating system).  – Risk of overheating or material degradation.	Ideal for symmetrical parts, commonly used with hot runner systems for smooth filling and clean appearance.
12		Film Gate / Tab Gate	Thin, flat entry like a tab or film.	– Easy to machine post-molding.  – Reduces stress in part.  – Good flow control.	– Large gate area.  – Visible mark.  – Often requires manual trimming.	Lateral gate, used to reduce stress in sensitive areas. Best for wide or flat parts.