◆ Basic knowledge and technical application of plastic mold

1, the introduction

All kinds of tools and products used in our daily production and life, ranging from the base of machine tools, fuselage shell, to a blank head screw, buttons and the shell of various household appliances, are closely related to the mold. Mold shape determines the shape of these products, mold processing quality and precision also determines the quality of these products. Due to the different materials, appearance, specifications and USES of various products, the mold is divided into casting mold, forging mold, die-casting mold, stamping die and other non-plastic mold, and plastic mold.

In recent years, with the rapid development of plastic industry and general engineering plastics in the aspects of improving strength and precision, the application range of the plastic products are also constantly expanding, such as household appliances, instrumentation, construction equipment, automotive industry, daily hardware, and many other fields, proportion of plastics is rapidly increasing. One well-designed plastic piece can often replace multiple traditional metal pieces. Industrial products and daily products plastic trend is rising.

2. General definition of mold: in industrial production, metal or non-metal materials are produced into required parts or products by means of pressure with various presses and special tools mounted on the press. Such special tools are collectively called molds.

3, injection process description: the mold is a tool for the production of plastic products. It is composed of several parts, and the combination has a mold cavity. During injection molding, the mold is clamped on the injection molding machine, the molten plastic is injected into the mold cavity, and the cavity is cooled to finalize the design, and then the upper and lower molds are separated, the products are ejected from the mold cavity through the ejector system, and finally the mold is closed for the next injection, the entire injection process is cyclical.

4. General classification of molds: plastic molds and non-plastic molds:

(1) Non-plastic mold: casting mold, forging mold, stamping mold, die-casting mold, etc.

A. Casting mold -- faucet, pig iron platform

B. Forging die - car body

C. Stamping die -- computer panel

D. Die casting mold - super alloy, cylinder body

(2) Plastic molds can be divided into the following categories according to different production processes and products:

A. Injection molding mold -- TV housing, keyboard buttons (most commonly used)

B. Blow mold -- beverage bottle

C. Compression molding die - bakelwood switch, scientific porcelain dishes

D. Transfer moulding - integrated circuit products

E. Extrusion die - glue tube, plastic bag

F. Hot forming die - transparent shaped packaging shell

G. Rotary mold - soft glue doll toy

◆ Injection molding is the most commonly used method in plastic processing. This method is applicable to all thermoplastics and part of thermosetting plastics, plastic products made the great number of them is the other forming methods of dust, as the main tool of injection molding processing, one of the injection mould, the quality of precision, manufacturing cycle and injection molding production efficiency in the process of the level of high and low, directly affect the product quality, yield, cost and product updates, at the same time also determines the enterprise in the market competition ability and speed of reaction.

The injection mold is composed of several steel plates with various parts, which are basically divided into:

A Forming unit (die, punch)

B Positioning device (guide post, guide sleeve)

C Fixing device (I-plate, die pit)

D cooling system (water supply hole)

E Thermostatic system (heating tube, hot wire)

F runner system (jack hole, runner slot, runner hole)

G ejector system (ejector pin, ejector stick)

5. According to the pouring system, the molds can be divided into three categories:

(1) Large nozzle mold: the runner and gate are on the parting line, and the mold is released together with the product when the mold is opened. The design is the simplest, easy to process, and the cost is lower, so more people use the large nozzle system for operation.

(2) Fine nozzle mold: runner and gate are not on the mold dividing line, generally directly on the product. Therefore, it is necessary to design an additional set of nozzle dividing line, which is complicated in design and difficult to process. Generally, the fine nozzle system should be selected according to product requirements.

(3) the hot runner mold: this kind of mold is approximately the same structure and fine shuikou, the * * * * is the difference between flow into one or more of the temperature of heat flow but and heat pumping mouth, no cold feeding demoulding, runner and gate directly on the product, so the port don't need mold release, also known as no runner system, this system can save raw materials, applicable to the raw material is more expensive, high requirement of products, design and processing difficulties, mould cost is higher.

Hot runner system, also known as hot runner system, is mainly composed of hot runner cover, hot runner plate, temperature control electric box. Our common hot runner system has two forms: single hot runner and multi hot runner. Single point hot gate is used to shoot molten plastic directly into the mold cavity with a single hot gate sleeve. It is suitable for plastic mold with a single cavity and a single gate. The multi-point hot gate is used to branch the molten material into each hot gate sleeve through the hot gate plate and then into the mold cavity. It is suitable for single cavity multi-point feeding or multi-cavity mold.

◆ Advantages of hot runner system

(1) No nozzle, no post-processing is required, making the entire molding process fully automated, saving working time and improving working efficiency.

(2) Small pressure loss. The temperature of hot runner is equal to the nozzle temperature of injection molding machine, avoiding the surface condensation of raw materials in the runner and small injection pressure loss.

(3) The reuse of nozzle materials will degrade the plastic properties, while the use of hot runner system without nozzle materials can reduce the loss of raw materials, thus reducing the product cost. In the cavity temperature and pressure uniform, plastic parts stress is small, uniform density, under the smaller injection pressure, shorter molding time, injection molding system than the general better products. For transparent parts, thin parts, large plastic parts or high requirements of plastic parts can show its advantages, and can be smaller models to produce larger products.

(4) The hot nozzle adopts standardized and serialized design, equipped with a variety of optional nozzle heads, with good interchangeability. The electric heating ring with unique design and processing can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plate, temperature controller, etc., with exquisite design, various types, easy to use, stable and reliable quality.

◆ Shortcomings of hot runner system application

(1) The closing height of the overall mold is increased, and the overall height of the mold is increased due to the addition of hot runner plate.

(2) The heat radiation is difficult to control, the problem of hot runner **** is the heat loss of runner, is a major issue to be solved.

(3) There is thermal expansion, and thermal expansion and cold contraction is a problem to be considered in our design.

(4) The increase of mold manufacturing cost and the higher price of standard parts for hot runner system affect the popularity of hot runner mold.