Knowledge of plastic mold
All kinds of tools and products used in our daily production and life, from the base of machine tools and the fuselage shell to the shell of a embryo head screw, button and various household appliances, have a close relationship with the mold.
The shape of the mold determines the appearance of these products, and the processing quality and accuracy of the mold also determine the quality of these products. Because of the different materials, appearance, specifications and uses of various products, the die is divided into casting die, forging die, die casting die, stamping die and other non-plastic die, and plastic die.
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 reasonably designed plastic part can often replace many traditional metal parts.
General definition of die: in industrial production, with a variety of presses and special tools installed in the press, through the pressure of metal or non-metal materials to produce the required shape of the parts or products, this special tool collectively known as die.
Injection molding process description: Mold is a tool for the production of plastic products. It is composed of several groups of parts, the combination has a molding cavity.
When injection molding, the mold is clamped on the injection molding machine, molten plastic is injected into the molding mold cavity, and in the cavity cooling finalize the mold, and then separated from the upper and lower mold, through the ejection system will leave the mold from the mold cavity ejection, finally the mold is closed for the next injection, the entire injection process is cyclic.
General classification of mold: it can be divided into plastic mold and non-plastic mold:
Non plastic mold: casting die, forging die, stamping die, die casting die, etc.
- A. Casting mold — faucet, pig iron platform B. Forging mold — automobile body C. stamping mold — computer panel D. Die casting die – super alloy, cylinder body.
Plastic mold according to the production process and the production of different products are divided into: A. injection molding mold – television shell, keyboard button (the most commonly used) B. C. Compression molding mold — Bakelite switch, scientific porcelain bowl and dish D. Transfer molding die — integrated circuit products E. extrusion molding die — glue tube, plastic bag F. ◆ Injection molding is the most common method used in plastic processing. The method is suitable for all thermoplastics and some thermosetting plastics, the number of plastic products produced is far behind other molding methods, injection mold as one of the main tools of injection molding processing, in the quality of precision, manufacturing cycle and production efficiency in the process of injection molding level, It directly affects the quality, output, cost and renewal of products, and determines the reaction ability and speed of enterprises in the market competition.
Injection mold is composed of a number of steel plates with various parts, basically divided into: A forming device (concave die, punch) B positioning device (guide post, guide sleeve) C fixing device (I-plate, code pit) D cooling system (water hole) E constant temperature system (heating pipe, hot wire) F channel system (nozzle hole, channel groove, channel hole) G ejector system (thimble, ejector rod).
According to the different pouring system, the mold 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 low, so more people use the large nozzle system to work. (2) Fine water mouth mold: runner and gate are not on the parting line, generally directly on the product, so it is necessary to design a group of more water mouth parting line, the design is more complex, the processing is more difficult, generally according to the product requirements and choose the fine water mouth system.
Hot runner mold: Such mold structure to be about equal to the fine shuikou, the biggest difference is that the flow is in one or more have temperature and heat flow but 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, Mold cost is higher. The hot runner system, also known as the hot runner system, is mainly composed of the hot runner sleeve, hot runner plate and temperature control electric box.
The common hot runner system has two forms: single – point hot runner and multi – point hot runner. The single point hot gate is to use a single hot gate sleeve to directly shoot molten plastic into the cavity, it is suitable for single cavity single gate plastic mold; The multi-point hot gate is to branch the molten material into each sub-gate sleeve through the hot gate plate and then enter the mold cavity. It is suitable for single cavity multi-point feeding or multi-cavity mold.
In the injection mold design we need to pay attention to what matters
Injection mold metering and plasticization in the molding process, injection volume control (metering) and uniform plastic melting (plasticization) is performed by the plasticization mechanism of the injection machine.
1, heating cylinder temperature although the melting of plastic, about 60-85% is because of the heat generated by the rotation of the screw, but the melting state of plastic is still affected by the temperature of the heating cylinder, especially near the temperature of the nozzle front area – the temperature of the front area is too high when the drop and take out the wire phenomenon. 2, screw speed (1) plastic melting, is generally due to the heat generated by the rotation of the screw, so the screw speed is too fast, it has the following effects: ① thermal decomposition of plastic; (2) Glass fiber (fiber plastic) reduction; (3) the wear of screw or heating cylinder is accelerated.
(2) The setting of the speed can be measured by the size of the circle speed: circle speed =n (speed) *d (diameter) *π (PI). Generally, the circular speed of screw rotation can be set to about 1m/s for the plastic with good thermal stability of low viscosity, but the plastic with poor thermal stability should be as low as about 0.1. (3) In the practical application, we can try to lower the screw speed, so that the rotary feed can be completed before the die opening.