How Gate Design Affects Your Plastic Injection Molds
The Importance of Gate Location for Plastic Injection Molds
Considering the effect of finished product quality on gate location, we have to consider some general rules as below main points:
- It is crucial to locate gates away from the area on the finished part because of potential degradation of the plastic that is likely to occur in such areas.
- Thinned walled area must require additional gates to offer enough plastic volume in minimum cycle time.
- We will design the gate is away from internal obstructions, cores, and pins as this may cause mark lines because of flow of molten plastic around them, which cause reforms on the other side.
Gate Design Can Effect Part Quality (Jetting and Overheating)
- Jetting – this usually occurs with small gates, where instead of flowing smoothly, the resulting pressure sprays into the cavity, causing wavy falsifications known as worming. As a result, we need to enlarge the gate or decrease in force, or even both.
- Overheating – friction from the high injection speed causes this defect. Overheating causes decay of the resin that destroys molecular bonds. When the injection is slowed, other defects like poor mechanical strength are likely to occur. So the best way to minimize this defect is to divide the given volume of resin over several gate openings as this aids in dissipating pressure.
The Difference between Hot and Cold Runner Systems
For a hot runner system
- They use an electrically heated cylinder during plastic parts manufacturing into the fluid cavity.
- Using hot runner systems conserve resources, minimizes cycle times, and enables control of temperature precisely.
- Nevertheless, it is more expensive and complicated.
For a cold runner system
- Increases cycle times and costs
- Involves consumption of material because of longer runners.
- It is more cost effective.
Advantages of the Most Common Gate Types for Plastic Injection Molds
These are gates that fill the cavity from the side and are machined into the mold at the parting line.
- Easy to enlarge when needed
- Inexpensive to manufacture and design.
Cons: Where the witness mark locations is not good ideal and needs high injection pressure.
Direct, or Sprue Gate
These are gates that are built into the sprue directly.
- Easier to build
- Ideal where concentricity is crucial for cylindrical parts.
- Capable of injecting a high amount of plastic.
- Needs manual construction
- Causes a sink mark as a result of a significant witness mark formed on the opposite side.
these are gates formed only through two-plate mold construction.
- As the mold opens, it opens automatically
- The witness mark is located in a desirable location.
Cons: Expensive to build and time-consuming
This is another form of edge gate that has a consistent thickness that allows it to spread out to increase the volume.
- Minimizes pressure of injection for a specific volume
- Suitable for maximizing the flow volume for thinner parts.
Cons: Leaves a large witness mark that needs to be post-processed.
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