Plastic mold development

All kinds of tools and products used in our daily production and life, ranging from the base and body shell of a machine tool to the shell of a germ head screw, button and various household appliances, are closely related to the mold. The shape of the mold determines the shape of these products, and the processing quality and precision of the mold also determine the quality of these products. Because the materials, appearances, specifications and uses of various products are different, molds are divided into casting molds, forging molds, die-casting molds, stamping molds and other non plastic molds, as well as plastic molds.

In recent years, with the rapid development of the plastic industry and the continuous improvement of the strength and precision of general and engineering plastics, the application scope of plastic products is also expanding. For example, in many fields such as household appliances, instrumentation, construction equipment, automobile industry, household hardware, the proportion of plastic products is increasing rapidly. A reasonably designed plastic part can often replace multiple traditional metal parts. The trend of plasticization of industrial products and daily products is on the rise.

meaning

General definition of mould: in industrial production, metal or non-metallic materials are made into parts or products of required shape by various presses and special tools installed on the press through pressure. This special tool is collectively called mould.

Injection molding process description: mold is a tool for producing plastic products. It is composed of several groups of parts, and the combination has a molding cavity. During injection molding, the mold is clamped on the injection molding machine, the molten plastic is injected into the molding mold cavity, cooled and shaped in the cavity, then the upper and lower molds are separated, the products are ejected from the mold cavity through the ejection system, and the mold is closed again for the next injection molding. The entire injection molding process is cyclical.

classification

A. Injection molding mold - TV shell, keyboard button, electronic products, plastic products around the computer, toys, household products (widely used)

B. Blowing mold - beverage bottle

C. Compression molding mould - bakelite switch, scientific porcelain bowl and dish

D. Transfer molding die - integrated circuit products

E. Extrusion mold - glue pipe, plastic bag

F. Thermoforming mould - transparent forming packaging shell

G. Rotary molding mould - soft rubber doll toy

The molds can be divided into three categories according to the different types of gating systems:

(1) Large spout mold: the runner and gate are on the parting line and demoulded together with the product when opening the mold, which is simple in design, easy to process and low in cost, so many people use the large spout system for operation.

(2) Fine nozzle mold: the runner and gate are not on the parting line, and are generally directly on the product. Therefore, a group of nozzle parting lines should be designed. The design is more complex, and processing is more difficult. Generally, the fine nozzle system should be selected according to the product requirements.

(3) Hot runner mould: the structure of this kind of mould is basically the same as that of the fine nozzle. The big difference is that the runner is located in one or more hot runner plates and hot pump mouths with constant temperature, and there is no cold material demoulding. The runner and gate are directly on the product, so the runner does not need demoulding. This system is also called a water free port system, which can save raw materials and is suitable for situations where raw materials are expensive and product requirements are high, It is difficult to design and process, and the mold cost is high.

Hot runner system, also known as hot runner system, is mainly composed of hot runner sleeve, hot runner plate and temperature control box. The common hot runner system includes single point hot runner system and multi-point hot runner system. Single point hot gate is used to directly inject molten plastic into the cavity with a single hot gate sleeve, which is suitable for plastic molds with a single cavity and single gate; The multi-point hot gate is used to branch the molten material into each sub hot gate bushing through the hot runner plate and then enter the cavity. It is suitable for single cavity multi-point feeding or multi cavity molds

◆ Advantages of hot runner system

(1) There is no need for post processing, so the whole forming process is fully automated, saving working time and improving work efficiency.

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

(3) Reuse of nozzle material will degrade the plastic performance, while the use of hot runner system without nozzle material can reduce the loss of raw materials, thus reducing the product cost. In the mold cavity, the temperature and pressure are uniform, the stress of the plastic part is small, and the density is uniform. Under the smaller injection pressure, the product can be injected into a better product than the general injection system in a shorter molding time. For transparent parts, thin parts, large plastic parts or plastic parts with high requirements, it can show its advantages and produce larger products with smaller models.

(4) The hot nozzle adopts standardized and serialized design, and is equipped with a variety of nozzle heads for selection, 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 plates, temperature controllers, etc., with exquisite design, various types, convenient 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 installation of hot runner plates.

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

(3) There is thermal expansion, and thermal expansion and cold contraction are problems we should consider when designing.

(4) The increase of mold manufacturing cost and the high price of standard accessories of hot runner system affect the popularity of hot runner molds.