Plastic Injection Molding
Plastic injection molding is suitable for mass production and molding of complex shaped products, and its highly automated advantages can meet the needs and standards of different industries.
Plastic Injection Molding Services | Forming Process
Plastic injection molding companies not only provide product production services, but also offer services such as design, development or improvement, product labeling, and assembly packaging. The molding process of plastic injection molding is also very complex. The selection of plastic molding methods and processes mainly depends on whether the properties of the plastic are thermosetting or thermoplastic, the initial form of the plastic, and the shape of the final product. The main methods for processing thermoplastic materials include extrusion, injection molding, extrusion, blow molding, and hot forming; The processing of thermosetting plastics generally involves transfer molding, compression molding, and injection molding. There are many methods and processes for molding, so plastic custom injection molding companies should choose carefully and correctly when providing services.
Common Plastic Injection Molding Materials
Before starting plastic injection molding services, it is necessary to carefully choose which materials to use for processing. Appropriate processing materials can bring higher efficiency and more practical products to later product production.
Polyethylene (PE): Polyethylene is a white solid in powder or granular form, with excellent water resistance and extremely low water absorption, as well as breathability and electrical insulation. After being heated and plasticized during the injection molding process, its viscosity is lower and its fluidity is better, so the required molding pressure is also lower. But its strength is weak, it is prone to deformation at high temperatures, and it is also extremely prone to oxidation when in contact with oxygen during heating. It is also easy to produce warping deformation when the temperature is uneven, therefore, PE materials require extremely high-temperature stability. The hardness of the molded parts made of polyethylene is relatively low, so sufficient cooling is required, and there is a high requirement for the cooling system. Polyethylene is mainly used in the manufacturing of coolers, oil tanks, and industrial drums.
Polypropylene (PP): Polypropylene is a colorless, odorless, and non-toxic semi-transparent solid. It is a thermoplastic with good heat resistance, chemical resistance, and insulation properties. It has low density, high strength, and low water absorption, so it does not need to be dried before use. Polypropylene can be dyed into various colors with pigments, and the formed parts are also quite diverse. However its aging resistance is poor, and it is easy to become brittle and fracture after long-term use. Polypropylene is widely used in the automotive, construction, prevention, packaging, and food industries.
Polyvinyl chloride (PVC): PVC is a white powder with an amorphous (amorphous) structure. In practical use, it is divided into soft polyvinyl chloride and hard polyvinyl chloride according to the amount of plasticizer added. Due to the poor heat resistance of polyvinyl chloride, it is usually necessary to add heat stabilizers and other additives during processing, which gives it a certain degree of toxicity. PVC is lightweight and suitable for lightweight design products; It has low water absorption and usually does not require drying treatment before use. Polyvinyl chloride has good adaptability to climate change and has good chemical resistance, but still cannot resist strong acids and alkalis. The flow resistance of polyvinyl chloride is strong, but when the temperature is not appropriate, this characteristic will weaken, leading to quality problems in processed products. The main applications of PVC include floor leather, floor tiles, water supply pipelines, electronic products, packaging of medical devices, and wires and cables.
Polystyrene (PS): Polystyrene is a colorless, odorless, and glossy transparent amorphous solid. Compared to other materials, polystyrene has good optical properties and lower water absorption, which can maintain dryness in specific scenarios. However, polystyrene is brittle and prone to cracking, with weak impact resistance and flammability. Mainly used for product packaging, household items (tableware, trays, etc.), electrical (transparent containers, light scattering devices, insulating films, etc.), and children’s toys.
ABS: ABS is usually a light yellow or milky white granular amorphous resin, which is one of the most commonly used engineering plastics. It can provide outstanding plastic injection molding services with advantages. It has high strength, excellent toughness, and low creep, making it easy to process and shape. Mainly used in: automobiles (dashboard, tool compartment doors, wheel covers, reflector boxes, etc.), refrigerators, high-strength tools (hair dryers, mixers, food processing machines, lawn mowers, etc.), telephone casings, typewriter keyboards, entertainment vehicles such as golf carts and jet sleds.
Plastic Injection Molding Process
The main equipment for plastic injection molding services is the mold and injection machine, which work together to manufacture products with determined shape and dimensional accuracy.
Step 1: First, dry the plastic that has good water absorption and needs to be dried. After reaching the appropriate moisture content, mix the plastic with the color masterbatch to obtain the desired color of the product.
Step 2: Pour the plastic raw materials into the barrel and heat them. Under the rotation of the screw, plastic melts while moving forward, becoming liquid and then injected into the mold.
Step 3: The mold automatically closes, and the molten plastic is given a shape in the mold.
Step 4: After the mold is formed, it is cooled and the internal parts solidify into finished products.
Step 5: After the product cools down, open the mold and take it out, then immediately start the next production.
Product Issues in Injection Molding
When manufacturers provide plastic injection molding services, the products they produce may encounter various problems due to various reasons, which are extremely detrimental to product production.
- Uneven or Discolored Color
The uneven color of plastics or pigments on the surface of plastic parts may be caused by uneven distribution of pigments or fillers. The reasons for uneven color are different, and the phenomena presented are also different. If the color of the entire part is uneven, it is caused by poor plastic thermal stability, and if the color of the fusion joint is uneven, it is related to the properties of the pigment. Especially in small-scale production, due to the combination of color powder and masterbatch, the color is uneven, resulting in severe scrapping.
- Unstable Size
The instability of dimensions is mainly caused by insufficient mold accuracy, weak strength, unstable operation of injection machines, and unstable forming conditions. The main reason for manual picking is that the molding cycle of each mold is not fixed, resulting in unstable product dimensions.
- Bubbles
Due to excessive inflation or poor exhaust in the melt material, residual gas is left in the plastic part, forming a small series of depressions. Mainly in intermittent production, due to the blockage of the exhaust groove by powdered plastic, insufficient exhaust is caused, and bubbles or burning may occur inside or locally in the product.
- Excessive Flying Edge
Poor opening and closing of the mold, large gaps, strong plastic fluidity, and excessive feeding cause excess thin sheets to be extruded along the edges of the plastic parts, resulting in excessive trimming and greatly increasing the workload of edge trimming.
- Poor Fusion Welding
Due to the low temperature of the material during the separation and convergence of the molten material, as well as the incompatibility between the resin and the attachment, poor fusion occurs during the convergence of the molten material, resulting in obvious fine seam lines along the surface or inside of the plastic part.
- Surface Ripple of Plastic Parts
Due to inadequate temperature control, the flow rate of the molten material varies, making it impossible to flow neatly along the surface of the mold and fill the cavity, resulting in surface ripple defects.
- Poor Demolding
Due to improper feeding parameters, excessive plastic filling, and poor demolding performance of the mold, it is difficult to de-mold the plastic part or the plastic part undergoes deformation and cracking after demolding, or the final molding of the plastic part does not meet the design requirements.
- Gate Sticking Mold
Due to the high frictional force inside the sprue sleeve, insufficient cooling or time, or high sprue tension, the sprue adheres to the sprue sleeve. This is very unfavorable for the provision of plastic injection molding services in the future.
- Poor Transparency
Due to insufficient contact between the melted material and the surface of the mold, there are small indentations on the surface of the plastic parts, which can cause radiation problems or plastic decomposition, foreign objects, and impurities, or the surface of the mold is not bright, resulting in poor or uneven transparency of transparent plastic.
- Silver Streaks
Due to excessive moisture, air, and volatile substances in the material, the melted material is subjected to excessive shear and does not fit well with the surface of the mold. Excessive cooling speed or mixing of different materials can cause decomposition and deterioration, resulting in silver-white glossy needle-like stripes or mica flake-like spots on the surface of the plastic parts along the direction of material flow.
- Warping Deformation
Internal stress caused by residual stress, shear stress, cooling stress, and uneven shrinkage during forming; Poor demolding, insufficient cooling, insufficient strength of the plastic parts, mold deformation, and other reasons can cause shape distortion, uneven warping or hole deviation, and uneven wall thickness of the plastic parts.
To provide better and better plastic injection molding services, manufacturers are constantly developing new technologies and processes.
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