Types of plastic injection process

Part or product design is the first step to produce a plastic product using a plastic injection machine. At this stage, there may be a sample of the desired part made by another manufacturer, in which case 3D modeling is done using CAD software from the witness sample. If the part or product in question has a unique design, the principles of design for production or DFM should be considered in its modeling.

Choosing the right plastic material is very vital to achieve the desired properties of the final product, and factors such as mechanical strength, chemical resistance, temperature resistance, and the cost of the product are directly affected by the raw material. . Thermoplastic polymers are the most common raw materials used in the plastic injection process, but despite this, the vast advances of this technology have made some types of thermoset plastics to be used in this process as well.

Preparing the mold is the most key step in the production of a plastic part by the plastic injection method. The injection mold is custom-made based on the desired part, so a separate mold is needed to produce each part. Designing and making molds is a complex job, and gaining expertise in it requires years of experience, extensive knowledge, and advanced machine tools, so it is recommended to leave mold design and manufacturing to experienced mold makers.

To produce a plastic part, in addition to the mold, a plastic injection machine is also needed. If the volume of part production is high, buying a plastic injection machine is economically justified, otherwise, part production can be outsourced.

The plastic injection process includes a wide range of techniques and methods, each of which responds to different needs of product design and complexity. Understanding these processes helps manufacturers choose the most appropriate approach to meet their specific needs.

This process is the most common type of plastic injection, suitable for producing a wide range of thermoplastic plastic parts from small and simple to large and complex. The device used in this process is usually a three-plate type with a hydraulic system, which has an affordable price.

This process involves placing prefabricated parts, such as metal inserts or other plastic parts, into a mold before injecting the material into it. This technique increases the strength of the final product, reduces the assembly steps and provides a wide range of capabilities to the product. The best machine for injecting plastic inserts is a vertical plastic injection machine, in which metal and non-metal inserts easily remain in the fixed mold due to the movement axis of the clamp.

In plastic injection, several shots or several components of raw materials with different materials or colors are injected into the mold, resulting in complex parts with multiple colors. Or a different gender is produced. This process eliminates the need for assembly after injection and provides the possibility of producing parts with beautiful appearance and special efficiency. Special injection machines equipped with more than one injection unit are used to inject multi-colored or multi-component parts.

In the gas injection process, a controlled amount of gas (usually nitrogen or carbon dioxide) is injected into the mold cavity, which causes the formation of parts It becomes hollow inside the piece. In this technique, hollow forms are created inside the piece, which reduces the consumption of raw materials, improves the strength of the product, and eliminates surface indentation or sink marks.

The microinjection process is used in the production of miniature and very precise plastic parts with complex geometric and dimensional features. Such parts are used in industries such as electronics, medical equipment and optics, and their production requires a special plastic injection machine.

The choice of raw materials is critical to achieve the desired performance, durability and appearance of the final product. In the selection of materials, considerations such as mechanical properties, chemical resistance, temperature resistance, cost-effectiveness, and compliance with regulations and standards related to product use should be considered. In the process of plastic injection, various plastic materials are used, each of which has its own characteristics and applications.

Polyethylene (PE) is the most widely used raw material in plastic injection, which is usually classified into two general groups: HDPE and LDPE, or heavy polyethylene and light polyethylene. And it is offered. Polyethylene has very high flexibility and chemical resistance, and in terms of price, it is one of the cheapest raw materials for injection. Polyethylene is used in making bottle caps, shampoo bottles, dishwashing liquid, plastic pots and gallons, plastic buckets and household appliances.

Polypropylene (PP) is the most used polymer in the production of injection parts after polyethylene. High chemical resistance, unique flexibility, proper strength, toughness, and excellent impact resistance of polypropylene, along with its transparency and reasonable price, have led to the production of various products such as household appliances, plastic chairs, buckets, basins, plastic baskets, pallets, and hospital trash cans. , microwave plastic containers, syringes and medical equipment parts should be made of polypropylene.

Nylon or Polyamide (PA) is one of the most widely used polymers in plastic injection and is a family of engineering plastics that is used to make many spare and original parts. Automobiles and motor vehicles such as gear wheels, idler bearings, air manifolds, radiator impellers and map sensor frames are used. Different grades of polyamide with or without fibers have unique advantages and characteristics such as impact resistance, extreme strength, low friction coefficient, high temperature tolerance and excellent chemical resistance. Polyamide types such as Nylon 6 and Nylon 6-6 are vulnerable to moisture absorption and their mechanical properties are damaged by exposure to moisture.

Polycarbonate (PC) is one of the transparent thermoplastics with excellent impact resistance, which is used in the manufacture of rear lights and Car front, LED bulb, safety glasses and plastic lens are widely used. Polycarbonate injection requires the use of a special cylinder and mortar and a plastic gasifier or dryer.

Crystal or polystyrene (PS) is a transparent but somewhat fragile polymer that is widely used in manufacturing due to its low price and affordability. It has disposable cups, disposable spoons and forks, medical equipment and laboratory consumables.

Polyoxymethylene (POM), which is better known in the Iranian market as Hostaform, Acetal or Polysteel, is a thermoplastic with very high toughness and strength that even It maintains its shock resistance even at low temperatures. Unlike polyamide, polyester is not sensitive to moisture and due to its dimensional stability and high wear resistance, it is used to produce all kinds of plastic gears.