Polymer injection molding is an efficient and precise molding process widely used in the production of plastic products. Polymers, also known as polymer compounds, are large chains of molecules consisting of a large number of repeating units (monomers) connected by covalent bonds. During the injection molding process, these polymer materials are heated to a molten state and subsequently injected into the mold under high pressure, and then cooled and solidified to form the desired shape of the product.
1. Principle of Polymer Injection Molding Technology
Polymer injection molding is based on the thermoplasticity and fluidity of the plastic material. First, the polymer particles are fed into the hopper of the injection molding machine and are heated and melted by the rotating and shearing action of the screw. The molten plastic is injected into the cavity of the mold through a nozzle driven by the screw. The mold usually consists of two or more parts which, when closed, form the shape of the product. Inside the mold, the molten plastic cools and solidifies, after which the mold is opened and the molded product is removed. The injection molding process ensures the quality and dimensional accuracy of the product by precisely controlling parameters such as temperature, pressure and injection speed.
2. Customization of polymer injection molded products
Polymer injection molding technology is popular for its high degree of flexibility and customizability. By changing different molds, plastic products of various shapes, sizes and functions can be produced. Product customization usually includes steps such as designing the mold, selecting materials, setting injection parameters and performing subsequent processing. Injection molding manufacturers provide one-stop service from product design to finished product delivery according to customer needs.
3. Polymer injection molding material selection and properties
The selection of polymer injection molding materials depends on the application environment and performance requirements of the product. The following are several common injection molding materials and their characteristics:
3.1 Polyethylene (PE): soft, non-toxic, inexpensive, easy to process, good chemical resistance, not easy to corrode. Divided into low-density polyethylene (LDPE), high-density polyethylene (HDPE) and very low-density polyethylene (LLDPE) and so on.
3.2 Polypropylene (PP): excellent heat resistance, chemical resistance and mechanical strength, widely used in food packaging, medical equipment, auto parts and other fields.
3.3 Polystyrene (PS): amorphous polymer, good fluidity, low water absorption, easy molding and processing, high transparency, strong coloring power, high hardness.
3.4 Acrylonitrile-butadiene-styrene copolymer (ABS): non-crystalline material with high mechanical strength and good overall performance, widely used in automotive, electronics, home appliances and other fields.
3.5 Polycarbonate (PC): excellent transparency, heat resistance, impact resistance and mechanical strength, commonly used in the production of highly demanding transparent products, such as eyeglass lenses, safety helmets.
3.6 Nylon (PA): wear-resistant, oil-resistant, chemical-resistant, with high mechanical strength and toughness, commonly used in the production of gears, bearings and other mechanical parts.
These materials have different physical and chemical properties, such as hardness, density, compressive strength, tensile strength, etc., for different product applications.
4. Polymer injection molding product characteristics test data
The following is a list of several materials injection molded product characteristics test data:
4.1 ABS injection molded products (electronic product shell):
Hardness (Shore D): 80-90
Density (g/cm³): 1.03-1.07
Compressive strength (MPa): 50-70
Tensile strength (MPa): 35-55
4.2 PC injection molding products (eyeglass lenses)
Transparency: up to 90% or more
Heat distortion temperature (℃): 130-140
Impact strength (kJ/m²): high
Refractive index: about 1.58
4.3 PP injection molding products (food packaging box):
Density (g/cm³): 0.90-0.91
Heat resistance: can withstand boiling water temperature
Chemical resistance: excellent, stable to a variety of food acids, alkalis, oils and fats, etc.
Tensile strength (MPa): 20-30
4.4 PE injection molded products (water pipe)
Density (g/cm³): HDPE about 0.94-0.96, LDPE about 0.91-0.93
Compressive strength (MPa): varies according to wall thickness and grade, generally higher
Chemical resistance: stable to many chemicals
Flexibility: good, easy to bend and install
These test data demonstrate the characteristics of injection-molded products made from different materials and provide a scientific basis for choosing the right material.
Polymer Injection Molding FAQ
Q: What is the dimensional accuracy of polymer injection molded products?
A: The dimensional accuracy of polymer injection molded products mainly depends on the precision of the mold and the control of the injection molding process. Modern injection molding technology can achieve high precision product dimensional control to meet the needs of precision manufacturing.
Q: How to choose suitable injection molding materials?
A: Choosing the right injection molding material requires consideration of the product’s application environment, performance requirements, cost and other factors. Common selection criteria include hardness, density, compressive strength, tensile strength, chemical resistance, heat resistance, and so on.
Q: How can I avoid product defects during polymer injection molding?
A: The key to avoiding defects in polymer injection molding products lies in the strict control of injection process parameters, such as temperature, pressure, injection speed and time. At the same time, the quality of mold design and manufacturing is also critical. By optimizing the process parameters and mold design, the product defect rate can be significantly reduced.
