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Several Principles Of Injection Mold Design
Jun 11, 2018

Core Tip: Several principles for the design of injection moulding systems for injection moulds I. Composition of gating systems II. Basic principles for gating system design

 One. The composition of the pouring system

The ordinary runner system (Runner System), also called the runner system, or the pouring system, is the necessary passage for the molten plastic to eject the nozzle from the nozzle to the mold cavity. The runner system includes a Primary Runner, a Sub-Runner, and a Gate.


1. Mainstream

Also referred to as a main sprue, sprue, or sprue, is the flow path from the portion where the jet nozzle comes into contact with the mold sprue bushing to the runner. This part is the part where the molten plastic first flows after entering the mold.

2. Shunt channel

Also known as a runner or runner. With the mold design, it can be divided into a first runner and a second runner. The runner is a transition zone from the main runner to the gate, which allows a smooth transition of the flow of the molten plastic. For a multi-cavity mold, it also has the function of evenly distributing the plastic to each cavity.

3. Gate

Also known as the feed port, it is a narrow passage between the runner and the mold cavity, and it is also the shortest part of the meat. Its role is to use the tight flow surface to accelerate the effect of plastic, high shear rate can make the plastic fluidity (because of the plastic thinning thinning properties); viscosity heating effect of temperature rise also has to increase the temperature, reduce viscosity effect.

After the molding is completed, the gate first solidifies the seal, preventing the plastic from flowing back, and avoiding the mold cavity pressure dropping too quickly, so that the molded product has a function of shrinkage and depression. After molding, it is easy to cut off to separate the runner system and plastic parts.

4. Cold material well

Also known as cold pit. The purpose is to store plastic wavefronts that are cold in the initial stage of complement filling to prevent the cold material from directly entering the mold cavity, affecting the filling quality or clogging the gate. Cold material wells are usually installed at the end of the main channel. When the length of the diversion channel is long, a cold material well should also be set at the end.

Two. The basic principles of gating system design

1. Cavity layout considerations


1) Use Balances Layout as much as possible;


2) The symmetry of the mold cavity arrangement and the gate opening are symmetrical to prevent the mold from uneven loading and the mold overflowing occurs.


3) The mold cavity arrangement is as compact as possible to reduce the size of the mold.


2. Flow guidance considerations


1) It can guide the molten plastic to fill the mold cavity smoothly, without eddy current, and can be smoothly exhausted;


2) Minimize the impact of small diameter cores and metal inserts on the front side of the plastic melt to avoid core shift or deformation.


3. Heat loss and pressure drop considerations


1) The smaller the heat loss and pressure drop, the better;


2) The process should be short;


3) The cross-sectional area of the flow path should be large enough;


4) Try to avoid bending the flow path and suddenly change the flow direction (change the direction with the arc angle);


5) The surface roughness of the runner is low;


6) Multi-point pouring can reduce pressure drop and required injection pressure, but there will be suture problems.


4. Consideration of flow balance


1) When Multi-Cavity is filled, the runners must be balanced. Plastics must be filled in at the same time to ensure the consistency of the quality of the molded parts.


2) Naturally-Balanced Layout is adopted for the runners as much as possible;


3) When it is impossible to balance naturally, the artificial balance method is used to balance the flow channel.


5. Waste considerations


Under the premise of smoothly filling without affecting the flow and pressure loss, the flow channel volume (length or cross-sectional area size) is reduced to reduce waste flow generation and recovery costs.


6. Consideration of cold material


Design suitable cold slug wells and overflow troughs on the runner system so as to fill the plastic wave fronts that are relatively cold in the initial stage to prevent the cold materials from directly entering the mold cavity and affecting the filling quality.


7. Exhaust considerations


The plastic should be successfully guided to fill the mold cavity and allow the air in the mold cavity to escape smoothly so as to avoid the problem of enveloping the scorch.


8. Consideration of the quality of molded products


1) Avoid short shots, burrs, wraps, sutures, flow marks, jets, residual stresses, warpage, mold deflection, and other issues;


2) When the flow system has a long flow or multiple gating, the warpage of the finished product due to unbalanced flow, insufficient pressure or uneven shrinkage should be prevented.


3) The appearance of the product is good, and it is easy to remove the trimming gate. The gate mark does not damage the appearance and application of the plastic part.


9. Consideration of production efficiency


Minimize the post-processing required to shorten the molding cycle and increase production efficiency.


10. Top-out considerations


Need to take into account the appropriate ejection position to avoid the mold release deformation.


11. Considerations for using plastics


Plastics with higher viscosity or shorter L/t, avoid use of flow channels that are too long or too small.