What Are the Different Types of Gates for Injection Molding?

To manufacture plastic parts, the preferred method is to use injection molding. To ensure quality parts, you must have the best injection mold design first. Otherwise, if you don’t have the best mold, your plastic parts will not be of the best quality.

When designing a mold, you will have at least two face plates each with their own cavities for the plastic to flow into. Each plate will also have gates that allow the plastic to be injected into the mold.

If the gate is too big, trimming the plastic can be difficult and could damage the part. Conversely, if the gate is too small, insufficient plastic could be injected into the mold and result in a part that is incomplete, brittle, or easy to break.

For these reasons, you need to know about the different types of gates for injection molding. Gate placement in the molding design is critical, as it affects the quality of the parts being manufactured, as well as the ability to correctly inject the right amount of plastic into the mold.

You also need a skilled team of engineers to help create the molding design. Your team should be able to determine what type of gate is best for the desired part and how to minimize expenses and design the perfect mold to manufacturer the highest-quality parts.

What Is the Importance of Gates for Injection Molding?

Gates will directly influence the end results of the plastic injection molding process. We already mentioned what happens when the gates are too big or too small. The gate size is also directly related to timing.

You need to make sure the plastic can reach all areas of the mold before it starts to cool. If your timing is off, the plastic could start to harden in certain parts of the mold too soon. The finished part could end up with stress fractures or break more easily as a result.

To ensure you use the right gate size and that your timing is correct, you need to determine the most appropriate location for the gates on the mold. You want gates located in the thickest parts of the design and in locations that allow sufficient filling for the best flow rate.

The number of gates in the mold is another important factor you need to consider when developing your molding design. Small, basic designed parts may only require a single gate. On the other hand, as the design becomes more complex or the part larger, you will need to add more gates into the molding design.

Keep in mind, the more gates you add, the smaller they can be since each one is responsible for injecting plastic in a specific area of the part. Otherwise, there could be injection issues where too much plastic is being injected through each of the gates.

Common Gates Used with Manually Trimmed Plastic Injection Molding

Many of the most common gates used with plastic injection molding are referred to as manually trimmed gates. They are called this because a secondary finishing process must be used after the part has cooled and been removed from the mold to remove excess plastic and trim off the gates to create the finished part.

Manually trimmed gates are typically used when you have larger gates that automated processes cannot remove without damaging the part. They are also used when working with certain types of plastics that could be damaged because they could be damaged from high shear rates common with automated trimming.

There are other types of production processes and molding designs where manually trimming is better than automated trimming as well. Some common gate types used with plastic injection molding include:

• Edge Gate – An edge gate is located on the edge of the mold. It is frequently used when making square, rectangular, and other parts that have multiple cavities or are rather thick.
• Direct Sprue Gate – This type of plastic injection molding gate is used with parts molds that have a single cavity or are cylindrical.
• Diaphragm Gate – A disc is used for gating to manufacture round or cylindrical parts that must have an open end.
• Fan Gate – A fan gate is a variant of an edge gate used to manufacture large, flat parts, as well as those that have fragile sections that need to be uniformly filled.
• Film Gate – A film gate has a gate that runs along the edge of the width side of the mold from top to bottom of the mold. This gate is used when manufacturing thin parts.
• Overlap Gate – An overlap gate is a variant of an edge gate where the gate will overlap with the part on the top or bottom of the mold.
• Ring Gate – This is a variant of the diaphragm gate that is not used that often because it allows the plastic to flow freely into the mold, which could create issues as it trickles down the sides to the bottom of the mold.
• Spoke Gate – This type of gate is also called a cross gate. It typically has four injection gates to inject material into the mold. This configuration is used when making tube-type parts of different shapes.
• Tab Gate – This gate configuration uses an extended tab off the edge of the mold. A tab gate is often used when manufacturing parts that have low shear stress tolerances.

Common Gates Used with Automatically Trimmed Plastic Injection Molding

There are also automatically trimmed gates used with plastic injection molding, where the excess plastic on the mold is removed by a machine. Some of the more common gates for injection molding used with automated shearing include:

• Submarine Gate – Submarine gates are also called sub gates. This type of gate is used with two-plate molds and provides flexibility to the location of the gate on the mold design.
• Cashew Gate – Also called a banana gate, this is another type of gate used with automated shearing processes. The gate is placed below or behind the surface of the part directly below the parting line.
• Valve Gate – A valve gate is a type of hot runner gate that features a special pin or valve in the design. Valve gates are similar in function to thermal gates, apart from the valve. The valve allows the flow of plastic into the mold to be turned on and off as needed.
• Pin Gate – This type of gate is used for parts that have multiple cavities. The gates are typically located on top of the molding design. Pin gates can also be used with molds that have three plates.

Please keep in mind that there can be other types of manually trimmed and automatically trimmed gates for injection molding—or variants—that can be used based on the complexity and design of the part.

Why Does the Placement of Gates of Injection Molding Matter?

You want to make sure gates are placed in the right locations on the molding design. The gates are responsible for the flow and pressure of the plastic being injected into the mold. If the gate is not in the right place, all sorts of problems can occur, such as uneven thicknesses, fractures, weak spots, etc.

To help determine what injection mold design will work best for your parts production, you need to consider the finished design. Are there any potential weak spots, such as angles, corners, or bends? Are you making thick or thin parts? Are the parts small or large? Are the parts hollow or solid?

Asking yourself questions like these is the most appropriate way to decide which plastic injection molding gate to use. Don’t be afraid to get help from qualified injection mold design engineers when choosing the molding design with the right gates and correct gate placement.

For further information about plastic injection molding parts production, injection mold design assistance, or other plastic tooling process services, please feel free to contact Laszeray Technology, LLC at 440-582-8430 today!