Injection moulding has become a highly popular manufacturing process, but understanding it isn’t quite easy. The reason behind this is the problems that one can face during this process. There are several problems that one might go through while injection moulding, of which short-shot injection moulding is crucial.
Short-shot injection moulding is a common issue that a manufacturer might face during the plastic injection moulding process. It usually occurs when the mould cavity isn’t entirely filled with molten plastic during the injection moulding process. The incomplete parts are often unusable, which results in significant quality issues.
In this blog, we will discover the reasons and causes behind injection moulding troubleshooting and will try to find the best solutions possible.
Before proceeding towards the causes and reasons behind this issue, you need to understand what actually is a short shot. As the name suggests, a short shot occurs when the mould cavity falls short of liquid plastic and isn’t entirely filled. This leaves thin areas and voids and creates a deficient product that is of no good use. If you are a professional worker or are planning to enter the manufacturing industry, you need to understand the shortcomings in depth.
A short shot typically occurs when there isn’t enough plastic to fill the melted spaces in the mold. These empty spaces are visible mostly on the edges where the plastic isn’t able to reach them. These empty spaces further cause issues with the product's overall performance, shape, and quality. The unfolded or empty space can be a weak spot where there is a high risk of breakage. This also affects the life span of the product.
To avoid injection moulding short shots, you need to understand the causes behind it and then find the best possible solutions to overcome this issue.
There are several reasons behind short shots, but the most common ones that one might face are:
Complex geometries of moulds can lead to short hots. The most important part of injection moulding is the design of your mould, on which the whole product is pendent. A badly designed or complex tool can cause quality control issues, and the short shot is no exception. Some of the mould issues that you might face while working include:
Due to variations in the thickness of the mould, the flow of the liquid either slows or pauses, causing a blockage.
The channels through which the plastic enters the mould can affect the flow, causing injection mould troubleshooting. The size and placement of the gates and runners can also affect this process.
The air that is created in the moulds should have some space to vent, or else it will create air traps.
The rate or speed at which the mould is filled during injection moulding is another cause of short OTS. If this problem occurs, then the speed and pressure of the injection need to be increased. The speed of injection is of crucial importance, as high speed will lead to permeating all the crannies and nooks of the mold. While slow injection speeds will lead to premature plastic solidification,.
If the pressure of the injection moulding machine is too low, it will not be able to fill the mood, completely leading to an injection moulding short shot. For this reason, you need to apply the pressure required to fill the mould cavity completely.
The flow of the liquid might be affected due to the inconsistencies in the properties of the materials that you are using. Make sure that the plastic that you are using doesn’t thicken instantly or is too runny.
When the mould doesn’t have proper ventilation, air will stick in the cavity of the mould, causing a short shot. It will stop the plastic from flowing in the mould equally in all parts, leading to an improper end product. The air in the mould has nowhere to go when the plastic is entering it, so the pressurised air will stop the flow of the liquid into the mould.
You need to make sure that the vents that are created in the mould are deep enough to allow the trapped air to pass out easily. The vents should be created in the moulds where the manufacturer thinks a short shot is occurring.
When the temperature of the mould is not high enough, the material will not be able to flow through the cavity. The material isn’t able to flow at the required speed, due to which injection moulding short shots can occur.
As a manufacturer, all you need to do at this point is increase the temperature. It will allow the plastic to flow and fill the cavity mould properly.
In short-shot injection moulding, what plays an important role is the viscosity of the material you are using. The more dense a liquid is, the more difficult it will be to flow and fill the cavity. A few plastics even get solidified before filling the mold. During the process, you need to take into account the viscosity of the liquid that you are using, or else it will cause a short-sighted defect.
There are several ways to get rid of the short-shot issue during injection moulding.
If the speed of the machine is slow, it will not allow the material to pass through quickly. By increasing the speed, you can fix the issue of short shots.
Sometimes liquids get solidified easily when the temperature is lower than the required one. Plastic gets hardened again, so you need to increase the temperature in order to fill the mould properly and solve the short-sighted issue.
A short shot can occur if the part’s walls are thin and liquid is unable to fill the mould cavity properly. To save yourself from injection moulding troubleshooting, you need to design the walls of your mould properly.
The frozen flow channels get blocked after some time, so they need to be cleared to maintain proper flow in the runner.
One can easily find a short-shot issue by looking at the moulded parts. There will be a sink mark where the mould wasn’t filled properly. When the plastic flows through the cold portions, there is a high chance that a short shot can occur due to several reasons. Identifying a short shot is easy, but finding the reason behind it can be tricky. So, a manufacturer should be knowledgeable enough to find the exact cause and resolve it.
The first step towards fixing your short-shot injection moulding problem is to look for the source. Once you have found the source, it will be easier to resolve the issue. There are several problems that one can face during injection moulding, but a crucial one is the short shot. It may occur due to several reasons, like low temperature, inadequate ventilation, variations in the material, filling rate, and many more. But fixing these simple problems can save you from major injection moulding troubleshooting.
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