Injection molding is an important method in the plastic molding process and is applicable to almost all thermoplastic materials except for a few.
·Injection molding process
1, Preparation before molding
a, Raw material drying
The purpose of drying raw materials is to remove some of the excess water contained in plastic to prevent the formation of silver products appear, markings, bubbles and other defects.
b, Barrel cleaning
Injection machine in the new opening or encountered in the production of replacement of raw materials, and found that there is decomposition of the plastic phenomenon, must be the injection machine barrel cleaning.
2, Molding process
Injection molding is the granular or powdered plastic from the hopper of the injection machine into the heated cylinder, after heating and melting was flow-like, and then pushed by the plunger or screw, through the end of the nozzle injection temperature of the lower die , After cooling and curing, the mold was released after the products.
a, Plasticization process
Plasticizing process is the preparation process of injection molding, plastic melting in the barrel by heating to reach the state of flow, with good plasticity of the process.
b, Flow and cooling processes
Flow and cooling process is the use of plunger or screw drive, the melt into the mold, filling the cavity after a certain condition under the cold-formed, until the demolding process.
3, Process control factors
The injection molding speed, the injection speed, the molding time (injection time, holding time, cooling time), molding pressure (plasticizing pressure, injection pressure, holding pressure), molding temperature (barrel and nozzle temperature, mold temperature) , Injection volume, plasticization and so on.
a, Molding temperature
The temperature of the barrel of plastic molding process of plasticizing a great impact. Generally need to be adjusted before molding. There is also a close relationship between the cylinder temperature and the nozzle temperature. To prevent salivation, the nozzle temperature is usually slightly below the maximum cylinder temperature.
b, Molding pressure
Forming pressure, including plasticizing pressure, injection pressure and maintain pressure of three, it directly affects the plasticization of plastic and product quality.
c, Injection speed and injection rate
Injection speed is the plunger or screw moving speed at injection, the unit is cm / s. The injection rate is the theoretical capacity of the melt injected from the nozzle per unit time, expressed in cm3 / s.
d, Molding time
Molding time, also known as molding cycle or molding cycle, refers to the completion of an injection molding process required time. In the molding time, the injection time and cooling time is the most important, they have a decisive impact on the quality of products.
e, Injection volume
Injection volume refers to the injection machine in the empty injection (no mold) conditions, plunger or screw in a maximum injection stroke can produce the product quality and volume, that is, the maximum injection volume.
f, Plasticizing amount
Plasticization is the amount of plastic per hour to plastic injection temperature injection to KG / H said.
g, Cushion
In order to get a good product, in the molding process must be accurately control the feeding volume, and after each injection in the barrel left a certain amount of leftover material, play the role of the pressure transmission cushion.
4, Molding process conditions
According to the materials provided by the molding process conditions and then integrated into their own factors to be adjusted.
·Injection molding equipment
1, the classification of injection machines
There are many types of injection machine classification, such as according to the plastic can be divided into plunger, screw and screwless injection machine; according to the type of molding materials can be divided into thermoplastic, thermosetting and foam injection machine; The transmission of the machine can be divided into hydraulic and mechanical injection machines. The specific classification is as follows:
a, Classification by shape feature
Injection molding machine according to shape characteristics, can be divided into vertical, horizontal, angular and multi-mode and other types.
b, By processing capacity classification
Injection machine according to processing capacity classification, can be divided into ultra-small, small, medium, large and very large and other types. This is mainly based on injection molding machine injection force and the size of the size to determine.
c, Classified by purpose
Injection molding machine, injection molding machine, injection molding machine, injection molding machine, plastic injection molding machine, injection molding machine, injection molding machine, injection molding machine, injection molding machine, Thread products for injection machines, fiber-reinforced plastic injection machines and other types.
d, According to the operation mode
Injection machine by operating mode, can be divided into manual, semi-automatic and fully automatic injection machine. This is mainly classified by the degree of automation of the injection machine during operation.
e, By transmission mode classification
Injection machine classified by transmission, can be divided into manual mechanical, electric, hydraulic and pneumatic pressure type and other types.
f, Sort by the number of cartridges
Injection machine according to the number of heating cylinder classification, can be divided into single-cylinder injection machine and multi-barrel injection machine two types.
g, According to plasticized classification
Injection molding machine by plastic classification, can be divided into plunger - plunger injection machine, screw - plunger injection machine and reciprocating screw injection machine three types.
