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The Knowledg Of Plastic Mold Design

The Knowledg Of Plastic Mold Design
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The innovation of mold processing technology, the wide application of various new mold materials, and the standardization and specialization of mold parts have forced us to adapt to the development of mold faster and more.

The improvement of the degree requires that the design class be completed in about 3 days to the post class: the improvement of accuracy; it is required to consider the processing methods of each part in the design process, and try to use the high-precision and low-precision processing methods to process the cost. The increase in accuracy and speed is consistent. The increase in speed inevitably requires an increase in precision, and the increase in precision inevitably leads to an increase in speed.
The basic structure of plastic mold:
According to its overall functional structure, plastic molds can be divided into: guide system, support system, molding system, pouring system, cooling system, injection system and exhaust system.
Definition: The plastic flow path from the injection nozzle to the cavity in the mold. It consists of a main channel, a runner, a gate and a hole.

1. Mainstream:

Definition:
The main flow path refers to the cross section from the injection nozzle nozzle to the mold contact portion to the branch flow path.
2 Design considerations:

  • (1) The shape of the end surface of the main channel is usually round.
  • (2) In order to facilitate demoulding, the main road is generally made of slope, but if the main passage passes through multiple boards at the same time, you must pay attention to the slope of the hole and the size of each hole.
  • (3) The design of the mainstream flow channel size should be based on the flow characteristics of the plastic material.
  • (4) The design of mainstream roads is mostly conical. (As shown), note:
    a. Small head diameter d2 = d1 + (0.5 ~ 1mm)
    b. Small end ball radius r2 = r1 + (1 ~ 2mm)
    (Where d1 and r1 are the injection outlet diameter of the injection machine and the sphere radius of the injection head, respectively)

2. Sprue cover

The main channel should be in contact with and collide with the high-temperature plastic and the nozzle, so the main channel part of the plastic mold factory is usually designed as a removable replacement bushing, called a casting sleeve or gate bushing.

(1). Its main functions are:

a. When the mold is installed, it is easy to enter the positioning hole, the nozzle of the injection molding machine is well positioned on the injection molding machine, can withstand the back pressure of the plastic, and will not be extruded from the mold.
b. As the mainstream of the pouring system, the plastic in the barrel is transferred to the mold to ensure that the flow reaches the cavity forcefully and smoothly, and there should be no plastic overflow during the injection process. At the same time, it is convenient to prevent the main flow of aggregate .

(2) The structural form is integral split

Integral: the shoulder is combined with the main body of the main road
Split type: the shoulder is made separately from the main body
Japanese Industrial Standard: JIS
China Industrial Standard: SJB

3. Split flow channel:

Definition: a section between the main road and the gate. It is the transitional section of molten plastic flowing into the cavity from the main channel. By changing the cross-sectional area and plastic turning, the plasticity can be transformed smoothly, which is the transition section of the pouring system.
Sectional design

  • a. The overall design part is round
  • b. Generally speaking, u-shaped, v-shaped, trapezoidal and regular hexagonal shapes are designed from the perspective of convenient processing.
  • c. The cross-sectional shape and size of the runner should be determined according to the molding volume of the plastic part, the wall thickness of the plastic part, the shape of the plastic part, the process characteristics of the plastic used, the injection speed, and the length of the runner. And other factors. The layout of the runner is balanced feed and unbalanced feed. The balanced feed is to ensure that the feed port feeds at the same time. Unbalanced feeding means that the feeding ports cannot be fed at the same time, usually evaluated by the mold flow analysis method.

4. The gate

1 Definition: Gate is also called inlet or inner runner. It is the narrow part between the runner and the plastic part, also known as the shortest part of the pouring system;
2 Function: Accelerate the flow speed of molten plastic conveyed by the flow channel to form an ideal flow state and flow sequence.

Although the structure of the plastic mold may vary depending on the type and performance of the plastic, the shape and structure of the plastic product, and the type of injection machine, the basic structure is uniform. In actual work, due to the complexity of certain product structures, it is often necessary to design the inclined top of the slider and the complicated mechanical structure to achieve the product structure. Here are some molds collected from the Internet. Open mold animation, dedicated to friends engaged in the mold industry.

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