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 of plastic from the nozzle to the part.	– Easy to design and manufacture   – Good mold filling   – Ideal for large parts	– Visible marks on the part surface, post-processing required	Due to low pressure loss, it is suitable for barrel-shaped, large, and deep parts. For flat and shallow rubber parts, there is a risk of warping and deformation due to shrinkage and stress. For parts with visible surfaces, the gate can be placed on the inside.
2		Fan Gate	Flared, fan-shaped gate	– Uniform material distribution   – Ideal for wide, thin parts	– Bulky, harder to balance   – Can cause more flash   – Requires more material in the runner	Commonly used for wide thin-film plastic parts and transparent plastics with poor flow properties, such as PC, PMMA, etc.
3		Tunnel Gate / Submarine Gate	Angled gate under the part, self-trimming at ejection	– Discreet, ideal for multi-cavity molding   – Automatic injection, no trimming   – Clean appearance	– More complex machining   – Not suitable for very thick parts	Suitable for parts where visible gate marks must be avoided. Ideal for aesthetically demanding parts, used for small to medium-sized parts. Requires balanced flow resistance across cavities to prevent stagnation and ensure proper flow.
4		Cashew Gate / Banana Gate	Curved shape, suitable for injection in hidden areas	– Invisible, good for aesthetic parts   – Good flow maintenance	– Difficult mold machining   – Limited flow	Suitable for most plastic materials but not for PMMA or materials with high glass fiber content.
5		Pin Gate	Cold runner injection in a conventional three-plate mold	– Suitable for high-precision parts   – Gate can be positioned anywhere   – No post-processing needed	– Significant material loss	Often used for large flat parts, long barrel-type parts, precision components, and small parts. Allows for good venting and requires no post-processing.
6		Tunnel Gate with Ejector	Tunnel gate coupled with ejector	– Facilitates aesthetic control by hiding the gate	– Complex design and manufacturing   – Requires precise adjustments   – High cost, maintenance needed	Requires separate treatment for residual parts after molding. Suitable for parts injected from non-visible surfaces.
7		Overlap Gate	Injects slightly recessed from the surface	– Good for thick walls   – Better part appearance	– High material volume, hard to remove   – Hard to balance in multi-cavity mold   – Complex design	Suitable for flat-shaped plastic parts requiring good surface quality.
8		Diaphragm Gate	Circular injection around a central core	– Uniform distribution, precise centering   – Reduces deformation – Ideal for round or symmetrical parts	– High material loss   – Secondary machining requires jigs and is labor-intensive	High circularity requirements and weld line control on appearance.
9		Hot Tip Gate	Heated tip injecting directly from a hot nozzle into the part	– No cold runner waste   – Good appearance, suitable for various part sizes   – Good flow control   – Material saving	– High mold cost   – Complex mold machining	Commonly used for central injection in hot runner molds, such as for symmetrical small parts. Best suited for mass production.