What is Injection Molding Gate
The Injection molding gate is a small opening that allows molten plastic material to enter the mold cavities. Injection molding gate like our house’s door, we can through door enter into our house, melted plastic also can through the gate enter into the cavities. so injection gate is melted plastic enter into the cavities “door”.
Injection Molding Gate Trimming Methods
1)Manually Trimmed
The worker must separate the parts from the runners after every cycle. Usually, use scissor or knife trimmed them. The way disadvantage is increased cost and reduce parts yield, because worker maybe trimmed break parts. Common manually trimmed gates include: edge gate, fan gate, direct gate.
2)Automatically Trimmed Gates
No worker intervention is needed to separate parts from runners. When the tooling opens to eject the part, it is automatically sheared from the runner. Robots and other automation equipment used with automatic trimming can also reduce scratching and labor content. This also eliminates the need for manual separating as an additional operation and ensures that cycle times remain constant. this type tending advantage is improved parts quality, save cost. automatically trimmed gates including: tunnel/submarine gate, pin gate, cashew gate, hot runner gate.
Types of Injection Molding Gate
In injection molding, a successful gate design is determined by gate type, dimensions, location. Once injection molding gate design is wrong, there may be potential defects in the plastic parts. These Injection molding defects will affect the integrity of the component.
1）Edge Gate
Edge gates are widely used for their simplicity and effectiveness in the injection molding process. it is best suited for flat parts and is located on the edge of the part. Edge gates work well with medium and thick sections.
2）Tunnel Gate/Submarine Gate
Tunnel gates or sub gates, this injection molding gate design involves directing plastics to the cavity’s edge below the parting line.
A)One of the benefit it is the best is because a tunnel gate automatically separates or degates from the part when either the mold opens or when the parts and runner are ejected. Gate marks very small and not need Manually trimmed. so tunnel gate is widely used for automatically plastic products production.
B) Another advantageous feature is their ability to be machined at almost any angle, In common is 30-60ﾟ. The length of a tunnel gate can be very short or very long. Shorter tunnel gates can often be machined at shallow angles, whereas longer tunnel gates require larger angles for easier removal. Keep in mind, longer gates start out farther away from the cavity, which makes for a stronger mold. Gates that have a shallow angle have to be machined close to the cavity wall. Since the injection pressure at the gate is extremely high, it is often the first place to flash.
C)There are various types of tunnel gate designs. Different types main affect gate mark. you can according to parts request select the most appropriate type. Common types as following:
◆ l Full conical gate, which leaves an elliptical gate mark
◆ l Truncated cone or D-gate, which leaves a “D”-shaped gate mark
◆ l Spherical or ball-nosed gate, which leaves a perfectly round gate mark
◆ Chisel gate, also called a flare gate, which leaves a rectangular gate mark
3）Direct Gate/Sprue Gate
This gate must be manually trimmed gate is used to produce symmetrical filling of single cavity molds for large parts. Easy to design and with low maintenance costs, it produces parts that are typically lower stressed and high strength. This gate leaves a significant scar at the point of contact
4）Fan Gate
Fan gates are similar to edge gates. it have a shape like a fan, it permits mold flow enter into the cavity through a wide opening, it's used to create a stable flow into a wide parts, it had advantage to avoid deformation and maintain dimensional stability.
As our experience, for some transparent parts, thin wall parts of the product generally adopts fan gate. Like PC, strongly suggest us fan gate. fan gate processing is convenient, It is conducive to improving product quality. but can not automatically cut the water mouth, also need manual pruning.
5）Pin Gate
As our experience, this type of gate is great for conical or round shapes plastic parts that require uniform flow. And it is special suitable for servo automation production(not need trimmed gate mark). Typically located at the top of a part as opposed to the parting line, Pin gate is specially for 3 plates molds, the runner channel are located in a separate runner plate, mold flow is divided into several direction and lead into the cavity by several gate locations. The gate point is designed to be very small and it allowed to be trimmed off by the action of injection mold opening. This gate type has disadvantage of too much scraps rates as the runner is big. It leaves a small raised spot( gate mark) on the surface of the part
6）Cashew Gate
Cashew gates are a variation of tunnel gate, except that they can provide gating in regions that cannot be reached by the standard tunnel gate. This type gate will Automatic separation of the part and the gate is allowed,The gate area does not need processing in addition.
7) Hot Runner Gate
Hot runner feed systems offer many advantages over cold runner systems. Hot runner systems are designed so that the molding material is kept molten between the molding machine barrel and the part. But the most disadvantages for hot runner is cost too expensive, especially is valve gate. So hot runner gate is suitable for some parts which high quality, large quantity, parts color unique. Because hot runner mold change color cost very high, raw material waste too much.
A) Thermal hot runner gate
The thermal gate much like a normal pin gate. The advantage is not having the runner system leading up to the gate. Material is saved and slightly better process control is established. because there ia s temperature control system, control the molten material can keep ideal temperature, More conducive to injection molding.This gate design can leave gate vestige because the gate area is broken away from the hot runner tip during mold opening.
B) Valve hot runner gate
The valve gate adds a valve rod to the hot runner gate. The valve can be activated to close the gate just before the material near the gate freezes. This allows a larger gate diameter and smoothes over the gate scar. Since the valve rod controls the packing cycle, better control of the packing cycle is maintained with more consistent quality. This provides the ultimate control of a runner feed system, larger gate sizes, and less gate vestige.
Why is Injection Gate Type and location Important?
Gate placement determines the location at which material enters the mold cavities, and gate style can affect the force, angle, and temperature at which material can flow. Any one of them will affect the product molding.
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.
1) Jetting defect
If the gate size too small, A gate that is too small causes pressure to drop as the molten plastic enters the cavity. It will lead to a defect jetting. This defect is gate too small. This is the best manifestation of the defects caused by too small gate
2)Overheading defect
When the molten material form runner flow to small gate, at near the gate, will come into being Shear stress, add friction. Near gate material temperature is higher than other area. Once the gate size too small, will cause overhead. Overhead will lead to degrade the plastic. With that in mind, gate designs like tunnel gates have limitations to the maximum size of the gate, which may eliminate the gate design as a possibility for larger parts.
3)Gate freeze defect
When the gate is too small, the raw material cool, injection is insufficient. The most direct manifestation is short shot or shrinkage, As usually, gates need to be large enough to fill out the cavity properly but small enough to “seal” the cavity (gate freeze). according to our experience, for some small round part , the proper gate size is 0.8-1.5mm diameter, for flat gate, size 2-4mm length, 0.8-1.5mm thickness. Specific problems must be analyzed on a case-by-case basis.
Injection Molding Gate Design Critical Point
The gate is the link between the part and the runner system. The size, shape and location of the gate can significantly affect the ability to successfully mold a product. Mold gate design must be main considering the size, location, type. The gate type will be based on the structure, size and shape of the molding parts.
Now, we could know the appropriate injection molding gate and placement by mold flow analysis, according to the customer requirements. We suggest, if available, hope make the mold flow analysis, perhaps, will be help you and customer save lots of cost or time.
1) Injection Gate Size
The size of the gate depends on the product size, material properties and gate shape. The length, depth and width of the gate should be reduced as far as possible under the premise of ensuring the mechanical properties and forming efficiency of the product.
Once the gate is too small, product defects like insufficient filling, shrinkage, warpage and gate freeze will tend to occur.
2) Injection Gate Location
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
A) Typically ,Gates should be located at the thickest area of the part, thick place molten material flow performance better thin place. Pouring from the thickest part can provide better filling and pressure retaining effect. If the pressure is not enough, the thinner area will solidify more quickly than the thicker area, so as to avoid the occurrence of hysteresis or short shot.so that the part does not have defects,
B) Do not place the gate near pins, cores, or mold cavity obstructions very thin place. It maybe break the thin core or pin because of strong injection pressure.
C) Place gates in areas that will make them easy to remove, whether manually or automatically. It not only can save cost but also increased output, increased quality.
D) For a plastic products that only is long strip shaped. Gate place must be fit at the end of the part, because, if fit at the middle of this parts, shear stress too much will lead to warpage.
E) If part is round, advise using pin gate or hot runner, and gate place is at the center is the best solution.
For some high quality appearance request parts, advise mold flow analysis, sometimes, gate place maybe will affect welding line or flash, shrinkage, ect. defects. Once the customer couldn’t accept these defects. It will be waste much time to modify mold.
1) Injection gate quantity
Typically, Single gate is always preferred unless the molten material flow distance is too large for the injection pressure limit. Multiple gates are always unable to avoid the flow of the welding line of different gate. This welding line are not allowed sometimes specially when the injection molding parts have critical surface appearance requirement.
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Conclusion
Injection molding gates do more than affect fill rates. They also help drive tooling costs, cycle times, and part quality. Gate design is a critical component of the injection molding design process, also is a multifaceted engineering challenge. part appearance, cycle time and tooling constraints must be balanced against your design requirements and estimated annual usage (EAU). Accessing the variables like part/mold design, material selection, and production intentions are important considerations when deciding what gate design is right for the working.
