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Analysis of injection mold design process

2021-09-14

Analysis of injection mold design process

One: The mold design of this product can not be demoulded, how to do?

Two: demoulding Angle is not good, no matter how good the mold can not be taken off!

Three: the mold push block demoulding is really not difficult!

Four: mold slider (line) structure, understand the easy demoulding!

 

One.The Runner System, also known as the Nozzle System, or the pouring System, is the Nozzle of the molten plastic that goes to the Nozzle. Runner system includes Primary Runner, sub-runner and Gate, etc.

1. The main channel is also known as the main gate, injection channel (Sprue) or vertical gate. It refers to the flow channel from the part where the injection nozzle of the injection machine contacts with the bushing of the main channel of the mold to the shunting channel. This part is the first part that the molten plastic flows through after entering the mold.

2. The runner is also called a sprue or secondary runner. With mold design, it can be further divided into the First Runner and the second Runner. The shunting channel is the transition area between the main channel and the gate, which can make the flow direction of molten plastic smooth transformation; For multi-hole moulds, it also has the function of evenly distributing plastic to each hole.

3. The gate, also known as the feed port, is a narrow opening between the shunting channel and the die hole, and is also the shortest and thinnest part. Its function is to use the compressed flow surface to accelerate the effect of plastic, high shear rate can make plastic good liquidity (due to the shear thinning characteristics of plastic); The heating effect of viscous heating can also increase the material temperature and decrease the viscosity.

After molding, the gate is first solidified and sealed to prevent plastic backflow, and to avoid the mold pressure drop too fast, so that the molding products have the function of shrinkage depression. After molding, it is easy to cut off to separate the runner system and plastic parts.

4. Coolant well is also called coolant hole. The purpose is to store and collect the cold plastic wave front at the initial stage of filling and prevent cold materials from entering the cavity directly, affecting the filling quality or blocking the gate. The cold well is usually located at the end of the main passage. When the diverter passage is long, the cold well should also be opened at the end. 


Two. Basic principles of gating system design

1. Consideration of Cavity Layout

1) Balances Layout should be adopted as much as possible;

2) The layout of the die hole and the opening of the gate should be symmetrical, so as to prevent the uneven force of the die from biased load and overflow of the supporting die;

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

2. Consideration of flow guidance

1) can smoothly guide the molten plastic to fill the cavity, no eddy current, and can smoothly exhaust;

2) Try to avoid the impact of plastic melts on the Core and metal inserts with small diameter to prevent Core Shift or deformation.

3. Consideration of heat loss and pressure drop

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 channel should be large enough;

4) Try to avoid flow channel bending and sudden change of direction (change direction by arc Angle);

5) The surface roughness of the runner should be low;

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

4. Consideration of flow balance

1) In the case of multi-cavity filling, the flow channel should be balanced and plastic should be filled in each Cavity at the same time as possible to ensure the quality consistency of molded products in each Cavity;

2) Shunt channel as far as possible using Naturally Balanced Layout;

3) When the natural balance cannot be achieved, the manual balance method shall be adopted to balance the flow channel.

5. Waste considerations

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

6. Consideration of cold materials

Appropriate Cold Slug Well and overflow groove are designed on the flow passage system to collect the Cold plastic wave front at the initial stage of filling and prevent Cold material from entering the cavity directly and affecting the filling quality.

7. Exhaust considerations

The plastic should be successfully guided to fill the cavity, and the air in the cavity can be successfully escaped to avoid the problem of sealing and burning.

8. Consideration of forming product quality

1) Avoid short shot, burr, sealing, suture, flow mark, jet flow, residual stress, warping deformation, die offset and other problems;

2) Warpage deformation of finished products due to unbalanced flow, insufficient pressure holding, or uneven shrinkage should be prevented during long flow or Multiple pouring processes;

3) The product has good appearance and properties, it is convenient to remove and repair the Gate Mark, and the Gate Mark is not harmful to the appearance and application of the plastic parts.

9. Consideration of production efficiency

As far as possible to reduce the need for post-processing, so as to shorten the forming cycle, improve production efficiency.

10. Consideration of ejection points

Proper ejection position should be considered to avoid demoulding deformation.

11. Plastic considerations

Avoid using too long or too small runner for plastics with high viscosity or short L/ T.